Updated on 2025/06/23

写真a

 
SAITO, Kiyoshi
 
Affiliation
Faculty of Science and Engineering, School of Fundamental Science and Engineering
Job title
Professor
Degree
Dr. Engineering ( Waseda University )

Research Experience

  • 2023.05
    -
    Now

    日本冷凍空調学会 会長

  • 2022.04
    -
    Now

    Waseda University

  • 2019.04
    -
    Now

    Waseda University

  • 2008.04
    -
    Now

    Present Professor

  • 2014
    -
     

    Adjunct professor, University of Indonesia

  • 2011
    -
     

    Visiting professor, University of the philippines

  • 2002
    -
     

    Associate professor, Waseda University

  • 2000
    -
     

    National Institute for Resources and Environment

  • 1999
    -
    2000

    Domestic research fellow,

  • 1996
    -
    1998

    Research associate, Waseda University

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Education Background

  •  
    -
    1997

    Waseda University   Graduate School, Division of Science and Engineering   Mechanical engineering  

  •  
    -
    1992

    Waseda University   Faculty of Science and Engineering   mechanical engineering  

Committee Memberships

  • 2025.05
    -
    Now

    経済産業省 資源エネルギー庁  基本政策分科会 委員

  • 2025.05
    -
    Now

    経済産業省 資源エネルギー庁  省エネルギー小委員会 委員長

  • 2025.04
    -
    Now

    経済産業省  省エネルギー・新エネルギー分科会 分科会長

  • 2025.02
    -
    Now

    経済産業省 資源エネルギー庁  家庭用温水機器判断基準ワーキング 座長

  • 2023.05
    -
    Now

    Japan society of refrigerating, air-conditioning engineers  President

  • 2021.04
    -
    Now

    経済産業省  産業構造審議会 フロン類等対策ワーキング 座長

  •  
    -
    Now

    新エネルギー・産業技術総開発機構(NEDO)技術委員  技術委員

  •  
    -
    Now

    環境省  中央環境審議会 委員

  •  
    -
    Now

    国際冷凍学会  E2(ヒートポンプ)部門 副部門長

  • 2018.05
    -
    2024.04

    日本冷凍空調研究所  理事長

  • 2020.04
    -
    2024.03

    日本冷凍空調学会  自然冷媒空調技術委員会 委員長

  • 2017.04
    -
    2018.03

    日本機械学会  環境工学部門 部門長

  • 2017.09
    -
     

    国際吸収ヒートポンプ会議 実行委員会委員長

  • 2017.06
    -
     

    日本機械学会  環境工学総合シンポジウム実行委員会 委員長

  •  
     
     

    経済産業省  給湯機器の測定方法等事業検討委員会 委員長

  •  
     
     

    日本冷凍空調学会  常務理事

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Professional Memberships

  •  
     
     

    日本エネルギー学会

  •  
     
     

    ASHRAE

  •  
     
     

    IIR

  •  
     
     

    日本冷凍空調学会

  •  
     
     

    日本機械学会

Research Areas

  • Earth resource engineering, Energy sciences / Control and system engineering / Thermal engineering / Robotics and intelligent system

Research Interests

  • 熱工学

  • 環境工学

  • 非化石転換

  • 脱炭素

  • Energy saving

Awards

  • 論文賞

    2023.04   日本冷凍空調学会  

  • 文部科学大臣表彰 (科学技術賞 研究部門)

    2022.04   文部科学省  

  • 早稲田リサーチアワード

    2022.02   早稲田大学  

  • 早稲田リサーチアワード

    2021.02   早稲田大学  

  • 早稲田リサーチアワード

    2020.04   早稲田大学  

  • 日本機械学会賞

    2013  

  • 日本冷凍空調学会学術賞

    2012  

  • ERDT Best paper award

    2010  

  • SAREK Best paper award

    2010  

  • 日本冷凍空調学会学術賞

    2010  

  • 日本機械学会奨励賞

    2001  

▼display all

 

Papers

  • Characteristics of heat and mass transfer in moist air-ionic liquid desiccant bubbly systems: Parametric assessment of regeneration performance

    Bowen Cao, Yonggao Yin, Moojoong Kim, Kiyoshi Saito, Christos N. Markides, Xinming Wang

    Applied Thermal Engineering   257   124487 - 124487  2024.12

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Measurement of void fraction of zeotropic refrigerant R454C using capacitance-based sensor in horizontal flow configuration

    Moojoong Kim, Tetsuya Sato, Kiyoshi Saito

    Applied Thermal Engineering   252   123625 - 123625  2024.09

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Prediction of Boiling Heat Transfer Coefficient for Micro-Fin Using Mini-Channel

    Tomihiro Kinjo, Yuichi Sei, Niccolo Giannetti, Kiyoshi Saito, Koji Enoki

    Applied Sciences   14 ( 15 ) 6777 - 6777  2024.08

     View Summary

    The prediction of the heat transfer coefficient commonly relies on the development of new empirical prediction equations when operating conditions and refrigerants change from the existing equations. Creating new prediction equations is expensive and time-consuming; therefore, recent attention has been given to machine learning approaches. However, machine learning requires a large amount of data, and insufficient data can result in inadequate accuracy and applicability. This study showed that using mini-channel data as highly relevant data for the micro-fin heat transfer coefficient yields high prediction accuracy, even when the experimental dataset of interest is limited. In the proposed method, we added dimensionless numbers assumed to significantly influence heat transfer coefficients calculated from experimental data to the training dataset. This allowed efficient learning of the characteristics of thin liquid films present in mini-channels and micro-fins. By combining distinctive physical mechanisms related to heat transfer coefficients with DNN/GPR/Fine-tuning, the proposed method can predict 96.7% of the data points within ±30% deviation. In addition, it has been confirmed that the dryout quality and post-dryout heat transfer coefficients were predicted with high accuracy. Additionally, we utilized visualization techniques to investigate the contents of the black-box machine learning models.

    DOI

    Scopus

  • Feed-Forward Compensation for Emulator-Type Testing Facilities

    N. Giannetti, Sholahudin, A. Mizuno, Y. Miyaoka, Y. Sei, K. Enoki, K. Saito, José Ricardo Ferreira Oliveira

    International Journal of Refrigeration    2024.07

    DOI

    Scopus

  • Experimental study of the two-phase flow distribution in helical-structured vertical headers

    Moojoong Kim, Jongsoo Jeong, Kiyoshi Saito, Sangmu Lee, Hyunyoung Kim

    Heliyon   10 ( 12 ) e32608 - e32608  2024.06

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Thermodynamic optimization of heat exchanger circuitry via genetic programming

    Niccolo Giannetti, Adriano Milazzo, John Carlo S. Garcia, Cheol Hwan Kim, Yuichi Sei, Koji Enoki, Kiyoshi Saito

    Applied Thermal Engineering     123623 - 123623  2024.06

    DOI

    Scopus

  • Implementation of scalable performance monitoring method for air conditioners

    Sholahudin, Niccolo Giannetti, Yoichi Miyaoka, Katsuhiko Tanaka, Wataru Kowa, Kiyoshi Saito

    Applied Thermal Engineering   245   122820 - 122820  2024.05

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Experimental investigation of the void fractions of refrigerants R32 and R1234yf in a 1 mm diameter horizontal channel using a capacitance-based method

    Moojoong Kim, Yuya Uemura, Tetsuya Sato, Kiyoshi Saito

    Applied Thermal Engineering   238  2024.02

     View Summary

    The void fraction of two-phase flow in the 1 mm of channel is investigated in this study. The small channels, including micro to mini-channel, are widely used for developing miniaturized air conditioning systems. In terms of carbon emission reduction, optimizing the refrigerant charging amount based on sufficient information and understanding of the characteristics of the two-phase flow is a noteworthy challenge. The void fraction is a parameter of the two-phase flow that is essential for determining the heat transfer coefficient, modeling the pressure drop, and predicting the refrigerant charging amount. Therefore, the precise measurement and prediction of void fraction in small channels for various refrigerants are required. However, thus far, the void fraction characteristics of small channels have not been actively investigated because of the limited volume inside a single small channel and the relatively high error of the quick-closing valve (QCV) method for small channels. This study proposes a capacitance-based sensor as an alternative method for void fraction measurement of small channels. The newly designed void fraction sensor was fabricated with 7.8 % uncertainty under compensation for manufacturing limitations. The void fractions of refrigerants R32 and R1234yf flowing through smooth small horizontal channels under adiabatic conditions (inner diameter: 1 mm, mass flux: 300–600 kg m−2 s−1, saturation temperature: 20–30 °C, vapor quality: 0.025–0.900) were measured. The measurement results were compared with ten existing prediction correlations of five classifications, and the correlations that optimally predicted the void fractions of R32 and R1234yf in the small horizontal channel were presented.

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Experimental investigation of the void fractions of refrigerants R32 and R1234yf in a 1 mm diameter horizontal channel using a capacitance-based method

    Moojoong Kim, Yuya Uemura, Tetsuya Sato, Kiyoshi Saito

    Applied Thermal Engineering   238   122113 - 122113  2024.02

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • EXPERIMENTAL AND THEORETICAL CHARACTERIZATION OF TWO-PHASE FLOW DISTRIBUTION IN UNBALANCED FLOW NETWORKS

    Cheol-Hwan Kim, Niccolo Giannetti, Nae-Hyun Kim, Kiyoshi Saito

    Journal of Enhanced Heat Transfer    2024

    DOI

  • Circuitry optimization using genetic programming for the advancement of next generation refrigerants

    N. Giannetti, J. C.S. Garcia, C. Kim, Y. Sei, K. Enoki, K. Saito

    International Journal of Heat and Mass Transfer   217  2023.12

     View Summary

    In this study, a new evolutionary method, which can handle the implementation of genetic operators with unrestrained number and locations of splitting and merging nodes for the optimization of heat exchanger circuitries, is developed. Accordingly, this technique expands the search space of previous optimization studies. To this end, a finned-tube heat exchanger simulator is structured around a bijective mathematical representation of a refrigerant circuitry (the tube–tube adjacency matrix), which is used in combination with traversing algorithms from graph theory to recognize infeasible circuitries and constrain the evolutionary search to coherent and feasible offspring. The performance of three refrigerants, namely R32, R410A, and R454C, commonly used in air-conditioning applications was assessed for the optimized circuitries of a 36-tube evaporator while converging to a given cooling capacity, degree of superheating, and heat source boundary conditions. At a given output capacity and air outlet temperature, larger coefficient-of-performance improvements (up to 9.99% with reference to a common serpentine configuration) were realized for zeotropic refrigerant mixtures, such as R454C, where appropriate matching of the temperature glide with the temperature variation of the air yielded the possibility of further reducing the required compression ratio under the corresponding operating conditions. Hence, it was demonstrated that low-GWP zeotropic mixtures with temperature glide can realize a performance comparable to that of R32 and higher than that of R410A by approaching the Lorenz cycle operation.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Experimental verification of artificial neural network scalability for performance monitoring of multi-split type air conditioners

    Sholahudin, Niccolo Giannetti, Yoichi Miyaoka, Kiyoshi Saito, Katsuhiko Tanaka, Hiroto Ogami

    Journal of Building Engineering   76   107427 - 107427  2023.10

    DOI

    Scopus

    3
    Citation
    (Scopus)
  • 膨張弁狭隘流路の流量評価法

    Akihiko MINATO, Seiichi YAMAGUCHI, Koji ENOKI, Kiyoshi SAITO

    JAPANESE JOURNAL OF MULTIPHASE FLOW    2023.05  [Refereed]

    DOI

  • Dynamic analysis of single–double-effect absorption chiller with variable thermal conductance during partial-load operation

    Arnas Lubis, Niccolo Giannetti, Muhammad I. Alhamid, Kiyoshi Saito, Hajime Yabase

    Applied Thermal Engineering   218  2023.01

     View Summary

    A numerical model for the dynamic analysis and control of a solar-assisted single–double-effect absorption chiller is presented. The mathematical model relies on energy and mass balances, which consider the heat and mass storage in each component. The resistance ratio method is introduced to capture the variation in the thermal conductance representing system disturbances and load variations according to the internal and external flow rates. The model was validated with reference to the outlet temperatures of hot, cooling, and chilled water from field test data for a given gas flow rate and corresponding inlet temperatures. The agreement between the field test and simulation results demonstrates the reliability of the model. Deviations between simulated and experimental temperatures mostly stays below 0.5 °C. The model was used to establish an effective operating strategy capable of minimizing the primary energy consumption without affecting the stability of the cooling output capacity and to verify the corresponding beneficial effect. The proposed operational approach increases the coefficient of performance by as much as 32 % compared with the previously implemented operation strategy, reaching up to a maximum value of 10.7 at 60 % cooling capacity.

    DOI

    Scopus

    7
    Citation
    (Scopus)
  • Experimental Investigation of Two-Phase Flow Distribution with Different Vertical Header Configurations

    Moojong Kim, Mark Anthony Redo, Jongsoo Jeong, Kiyoshi Saito, Sangmu Lee, Hyunyoung Kim

    ENERGIES   15 ( 21 )  2022.11

     View Summary

    In this study, we investigated the behavior of two-phase flow distribution inside a vertical header of a microchannel heat exchanger (MCHX) that functions as an evaporator of a heat pump system. In general, the two-phase flow distribution behavior of the refrigerant differs depending on the target application, which ranges from small-scale automobile air-conditioners to large-scale building heat pump systems. Particularly, it is reported that the distribution characteristics in the vertical header of the MCHX vary extensively according to the inlet flow conditions of the refrigerant and the physical profile of the header. In this study, the physical configurations (header height, branch tube diameter) of four types of vertical headers were considered. Thereafter, the operating conditions in an experimental device that simulates an MCHX with a vertical header were selected. The experiment was performed under R410A as the working fluid, with a saturation temperature of 15 degrees C, inlet mass flow rate of 50-150 kg h(-1) (mass flux of 908-2723 kg m(-2) s(-1)), and an inlet vapor quality of 0.1-0.2. The liquid and vapor flow ratios and the relative standard deviation were adopted as metrics to characterize the uniformity of flow distribution. The distribution characteristics were subsequently described according to Reynolds and Froude numbers. The larger the Reynolds number and the smaller the Froude number, the more uniform the two-phase flow distribution becomes. A correlation was proposed as a function of the Reynolds and Froude numbers to predict the flow distribution characteristics for the considered vertical headers.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Experimental Investigation of Two-Phase Flow Distribution with Different Vertical Header Configurations

    Moojong Kim, Mark Anthony Redo, Jongsoo Jeong, Kiyoshi Saito, Sangmu Lee, Hyunyoung Kim

    Energies   15 ( 21 )  2022.11

     View Summary

    In this study, we investigated the behavior of two-phase flow distribution inside a vertical header of a microchannel heat exchanger (MCHX) that functions as an evaporator of a heat pump system. In general, the two-phase flow distribution behavior of the refrigerant differs depending on the target application, which ranges from small-scale automobile air-conditioners to large-scale building heat pump systems. Particularly, it is reported that the distribution characteristics in the vertical header of the MCHX vary extensively according to the inlet flow conditions of the refrigerant and the physical profile of the header. In this study, the physical configurations (header height, branch tube diameter) of four types of vertical headers were considered. Thereafter, the operating conditions in an experimental device that simulates an MCHX with a vertical header were selected. The experiment was performed under R410A as the working fluid, with a saturation temperature of 15 °C, inlet mass flow rate of 50–150 kg h−1 (mass flux of 908–2723 kg m−2 s−1), and an inlet vapor quality of 0.1–0.2. The liquid and vapor flow ratios and the relative standard deviation were adopted as metrics to characterize the uniformity of flow distribution. The distribution characteristics were subsequently described according to Reynolds and Froude numbers. The larger the Reynolds number and the smaller the Froude number, the more uniform the two-phase flow distribution becomes. A correlation was proposed as a function of the Reynolds and Froude numbers to predict the flow distribution characteristics for the considered vertical headers.

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Development and validation of a variational formulation of Two-Phase flow distribution

    Mark Anthony Redo, Niccolo Giannetti, Hiroaki Yoshimura, Kiyoshi Saito, Manabu Watanabe

    International Journal of Multiphase Flow   155   104190 - 104190  2022.10

    DOI

    Scopus

    1
    Citation
    (Scopus)
  • Emulator-type load-based tests for dynamic performance characterization of air conditioners

    Niccolo Giannetti, Shun Matsui, Ryohei Mori, Jongsoo Jeong, Hifni Mukhtar Ariyadi, Yoichi Miyaoka, Eisuke Togashi, Kiyoshi Saito

    Energy and Buildings   273   112411 - 112411  2022.10

    DOI

    Scopus

    9
    Citation
    (Scopus)
  • Performance assessment of integrated liquid desiccant dehumidification with vapor-compression system for energy-efficient air conditioning applications

    Mrinal Bhowmik, Siddharth Rath, Richard Jayson Varela, P. Muthukumar, R. Anandalakshmi, Kiyoshi Saito

    Applied Thermal Engineering     119118 - 119118  2022.08

    DOI

    Scopus

    16
    Citation
    (Scopus)
  • Experimental performance of a three-fluid desiccant contactor using a novel ionic liquid

    Richard Jayson Varela, Niccolo Giannetti, Kiyoshi Saito, Xinming Wang, Hiroshi Nakayama

    Applied Thermal Engineering   210   118343 - 118343  2022.06

    DOI

    Scopus

    31
    Citation
    (Scopus)
  • Optimizing Calibration for a Capacitance-Based Void Fraction Sensor with Asymmetric Electrodes under Horizontal Flow in a Smoothed Circular Macro-Tube

    Moojoong Kim, Kanta Komeda, Jongsoo Jeong, Mizuki Oinuma, Tetsuya Sato, Kiyoshi Saito

    SENSORS   22 ( 9 )  2022.05

     View Summary

    In this study, a technique that uses a capacitance sensor with an asymmetric electrode to measure the void fraction of a refrigerant was developed. It is known that the void fraction and flow pattern affect the measured capacitance. Therefore, the relationship between the void fraction and capacitance is not linear; hence, a calibration method for obtaining accurate measurements is necessary. A calibration method was designed in this study based on repeated capacitance measurements and the bimodal temporal distribution to calibrate the atypical and repetitive flow patterns of slug flow and its transition to the intermittent flow regime. The calibration method also considers the weighted-average relation for the gradual transition of the intermittent to annular flow pattern according to the change from low to high quality. The proposed method was experimentally analyzed under the conditions of R32 refrigerant, a tube inner diameter of 7.1 mm, saturation temperature of 25 degrees C, mass flux of 100-400 kg m(-2) s(-1), and vapor quality of 0.025-0.900, and it was validated using a quick-closing valve (QCV) system under identical conditions. A relative error of 2.99% was obtained for the entire system, indicating good agreement between the proposed and QCV-based methods.

    DOI

    Scopus

    9
    Citation
    (Scopus)
  • Prediction of Boiling Heat Transfer Coefficients for Mini-Channels

    Yuichi Sei, Koji Enoki, Seiichi Yamaguchi, Kiyoshi Saito

    Multiphase Science and Technology   34 ( 2 ) 43 - 65  2022.05  [Refereed]

     View Summary

    Artificial intelligence (AI) techniques have been widely used across many fields. However, few studies have focused on the use of AI techniques for predicting heat transfer coefficients regardless of single-phase or two-phase flows. The applicability of deep neural networks [(DNNs), also known as deep learning], one of the most promising AI techniques, to horizontal-flow boiling heat transfer in mini-channels is being actively researched. The effect of surface tension in mini-channels is significant in comparison to that in conventional large tubes, and the heat transfer mechanism in the mini-channels is complicated. Thus, the accuracy of the prediction results based on existing studies is not satisfactory. Moreover, we cannot determine the uncertainty of the predicted heat transfer coefficients by using existing approaches. In this study, we propose a novel prediction mechanism, based on the combination of a DNN and Gaussian process regression, that can predict not only heat transfer coefficients with high accuracy but also the uncertainties of the predicted heat transfer coefficients. We refer to this new research field, which integrates thermal engineering and informatics, as thermoinformatics, and consider the scope of its future development.

    DOI

  • Multiobjective Geometry Optimization of Microchannel Heat Exchanger Using Real-Coded Genetic Algorithm

    John Carlo Solomon Garcia, Niccolo Giannetti, Yuichi Sei, Kiyoshi Saito, Mamoru Houfuku, Ryoichi Takafuji

    Applied Thermal Engineering   202 ( 117821 ) 1 - 13  2022.02  [Refereed]

    DOI

    Scopus

    34
    Citation
    (Scopus)
  • Performance assessment of an R32 commercial heat pump water heater in different climates

    Muhamad Yulianto, Takaoki Suzuki, Zheng Ge, Takashi Tsuchino, Masakazu Urakawa, Shigeru Taira, Yoichi Miyaoka, Niccolo Giannetti, Liang Li, Kiyoshi Saito

    Sustainable Energy Technologies and Assessments   49   101679 - 101679  2022.02

    DOI

    Scopus

    12
    Citation
    (Scopus)
  • Variational formulation of non-equilibrium void fraction

    Niccolo Giannetti, Moojoong Kim, Hiroaki Yoshimura, Kiyoshi Saito

    International Journal of Heat and Mass Transfer   183   122119 - 122119  2022.02

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Thermodynamic investigation of asynchronous inverse air cycle integrated with compressed-air energy storage

    Niccolò Giannetti, Adriano Milazzo, Kiyoshi Saito

    Journal of Energy Storage   45   103750 - 103750  2022.01

    DOI

    Scopus

    10
    Citation
    (Scopus)
  • Intelligent performance prediction of air conditioning systems based on refrigerant temperatures

    Sholahudin, Niccolo Giannetti, Yoichi Miyaoka, Kiyoshi Saito

    Thermal Science and Engineering Progress   27   101150 - 101150  2022.01

    DOI

    Scopus

    5
    Citation
    (Scopus)
  • Design of a Numerical Simulator for Finned-Tube Heat Exchangers with Arbitrary Circuitry

    John Carlo S. Garcia, Niccolo Giannetti, Daryl Anne B. Varela, Richard Jayson Varela, Seiichi Yamaguchi, Kiyoshi Saito, Menandro S. Berana

    Heat Transfer Engineering     1 - 19  2021.11

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Numerically Trained Artificial Neural Network for Experimental Performance Prediction of Air Conditioning Systems

    Sholahudin, Niccolo Giannetti, Yoichi Miyaoka, Jeongsoo Jeong, Kiyoshi Saito

    2021 60th Annual Conference of the Society of Instrument and Control Engineers of Japan, SICE 2021     1432 - 1436  2021.09

     View Summary

    This paper presents the development of a method for predicting the performance of air conditioning systems using few accessible and inexpensive input parameters. The cooling capacity is predicted using artificial neural network with four selected refrigerant temperatures measured from the outdoor unit as the inputs. Input output prediction data are obtained numerically and experimentally from two representative variable refrigerant flow (VRF) systems. The two systems have different characteristics and nominal capacity. The training of the ANN model is conducted with the data obtained from numerical simulations. Consequently, the ANN is tested for the prediction of the experimental cooling capacity in a quasi-certified testing equipment. The results indicate that the proposed performance prediction method demonstrates a relative error lower than 10%.

  • Variational formulation of stationary two-phase flow distribution

    Niccolo Giannetti, Mark Anthony Redo, Kiyoshi Saito, Hiroaki Yoshimura

    Case Studies in Thermal Engineering   26   101082 - 101082  2021.08

    DOI

    Scopus

    4
    Citation
    (Scopus)
  • Absorption heat transformer - state-of-the-art of industrial applications

    Falk Cudok, Niccolò Giannetti, José L. Corrales Ciganda, Jun Aoyama, P. Babu, Alberto Coronas, Tatsuo Fujii, Naoyuki Inoue, Kiyoshi Saito, Seiichi Yamaguchi, Felix Ziegler

    Renewable and Sustainable Energy Reviews   141   110757 - 110757  2021.05

    DOI

    Scopus

    67
    Citation
    (Scopus)
  • Modeling of Flow Distribution in Multi-Branch Channels using the Second Law of Thermodynamics

    Mark Anthony Redo, Niccolo Giannetti, Hiroaki Yoshimura, Kiyoshi Saito, Manabu Watanabe

    6TH IIR CONFERENCE ON THERMOPHYSICAL PROPERTIES AND TRANSFER PROCESSES OF REFRIGERANTS (TPTPR2021)     135 - 142  2021

     View Summary

    Flow maldistribution has been an on-going issue that limits the full potential attainment of microchannel heat exchangers (MCHX). The underlying cause is the lack of theoretical understanding due to many complex interdependent factors at play. This results to high variability leading to a mathematical challenge of representing and solving the physical system. Hence, the available studies in the literature are limited to experimental investigations or CFD models that are case specific. This paper reports the method of incorporating a pressure drop model and integrating a variational formulation by extremizing the entropy generation rate. The extremum principle points at the maximum entropy production rate toward a stationary state, hence providing a general representation of the phenomenon which is unrestrained from limitations to a specific working fluid and structural geometry of the MCHX. Distribution results are investigated for different inlet conditions. A first comparison to experimental data shows a fair prediction accuracy.

    DOI

  • Non-Equilibrium Formulation of Void Fraction in Two-Phase Flows

    Niccolo Giannetti, Moojoong Kim, Hiroaki Yoshimura, Kiyoshi Saito

    6TH IIR CONFERENCE ON THERMOPHYSICAL PROPERTIES AND TRANSFER PROCESSES OF REFRIGERANTS (TPTPR2021)     127 - 134  2021

     View Summary

    A general variational formulation of the void fraction in dissipative two-phase flows is developed. In particular, the steady-state void fraction is extracted by the extremization of the entropy generation rate, based on a comprehensive non-equilibrium expression that introduces interfacial contributions due to surface tension between different phases and fluxes due to heat and mass transfer.Such formulation opens up to the possibility of obtaining different theoretical formulas by the direct application of Prigogine's theorom of minimum entropy production and it is investigated in terms of different assumptions for showing the effect of different flow conditions, flow pattern interfacial geometry, entrainment ratio, heat flux from the external environment, and thermophysical properties of the refrigerant. Consequently, the widely-accepted Zivi's expression of void fraction is obtained as a particular case of this general formulation.

    DOI

  • Semitheoretical formulation of annular flow void fraction using the principle of minimum entropy production

    Niccolò Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Hiroaki Yoshimura

    International Journal of Thermal Sciences   158  2020.12

     View Summary

    © 2020 Elsevier Masson SAS The two-phase flow void fraction is a critical parameter for characterising the pressure drop as well as heat and mass transfer capability of the working fluid within thermal systems, the accurate estimation of which drives heat exchanger design and control optimisation. A semitheoretical expression for the void fraction of two-phase flows, also applicable to small-sized channels, is obtained from an analytical study based on the principle of minimum entropy production and the introduction of empirical coefficients to be fitted to experimental data available in the open literature. These coefficients embody the importance of the simplified physical terms of this formulation while recovering the accuracy loss owing to nonlinear phenomena, heat and mass transfer, and three-dimensional effects. By accounting for surface tension, this model generalises previous theories and describes the influence of smaller-sized channels in terms of the stable void fraction. This mathematical framework can be used to summarise data covering different refrigerants, channel diameters, and operating conditions.

    DOI

    Scopus

    8
    Citation
    (Scopus)
  • A cost effective and non-intrusive method for performance prediction of air conditioners under fouling and leakage effect

    Sholahudin, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Katsuhiko Tanaka, Hiroto Ogami

    SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS   42  2020.12

     View Summary

    Realistic performance predictions are required for efficient operation strategy of air conditioners. In this study, the application of a cost effective and non-intrusive black box model utilizing artificial neural networks (ANN) to predict the cooling capacity of air conditioning systems is investigated, while considering the effect of fouling and leakage that may occur after prolonged operation. The effect of various leakage and fouling combinations on the output cooling capacity were numerically simulated. The training data set is first generated for a system that is ideally operating without any fouling or leakage. The developed ANN model is tested to predict cooling capacity in "faulty" systems. The results indicated that, as long as leakage and fouling are limited below 10% and 4% respectively, the ANN model trained by the data generated with the ideal system, can predict cooling capacity with a relative averaged cooling capacity difference (Delta(Q) over bar (e,rel)) of approximately 13%. Moreover, the inclusion of data with different leakage and fouling combinations in the training set enables accurate predictions of the cooling capacity of the air conditioning system during the entire timespan of its operation. It suggests that cooling capacity under the fouling and leakage phenomena can be predicted using limited input information.

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    8
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  • Experimental implementation of artificial neural network for cost effective and non-intrusive performance estimation of air conditioning systems

    Sholahudin, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Yoichi Miyaoka, Katsuhiko Tanaka, Hiroto Ogami

    APPLIED THERMAL ENGINEERING   181  2020.11

     View Summary

    Owing to the high variability of operating conditions and the complexity of dynamic phenomena occurring within air conditioning cycles, the realistic performance estimation of these systems remains an open question in this field. This paper demonstrates the applicability of a cost-effective estimation method based on an artificial neural network exclusively using four refrigerant temperatures as the network input. The experimental datasets are collected from a reference experimental facility. The system is operated with variable cooling load, outdoor temperature, and indoor temperature settings, as representative of the actual operation. The artificial neural network structure was optimized by considering the effect of previous time step inputs, number of neurons, sampling time, and number of training data. The results reveal that the developed model can successfully estimate the cooling capacity of an air conditioning system during on-off, continuous unsteady, and steady operation, using four temperature inputs with relative averaged error below 5%.

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    13
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  • Characterization and improvement of flow distribution in a vertical dual-compartment header of a microchannel heat exchanger

    Mark Anthony Redo, Jongsoo Jeong, Seiichi Yamaguchi, Kiyoshi Saito, Hyunyoung Kim

    International Journal of Refrigeration   116   36 - 48  2020.08

     View Summary

    Poor distribution of two-phase flow in a microchannel heat exchanger header requires a solution to maximize its potential advantage of compactness while offering a high heat-transfer rate. While previous works have attempted to improve two-phase flow distribution, most have focused on horizontal headers, which commonly appear in indoor units. However, there are a few studies on vertical headers that function as an evaporator in heat pump mode that are typical in outdoor units. This study describes the development of a modified vertical header with a dual-compartment structure aimed at improving the flow distribution. Experiments and visualizations were conducted using R410A in a test section that represented the size and capacity of an actual heat exchanger. The inlet mass flux was 309–1235 kg·m−2s−1 (50–200 kg·h−1), vapor quality was 0.1–0.2, and the evaporating temperature was maintained at 15 °C. The results were compared to the conventional header previously evaluated by our research group. Results showed that the dual-compartment header was able to enhance the liquid flow distribution at low inlet mass flux from approximately 30% to 80% based on relative standard deviation (RSD), with a generally higher liquid Reynolds number when compared to the conventional header.

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    18
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  • Prediction of two-phase flow distribution in microchannel heat exchangers using artificial neural network

    Niccolo Giannetti, Mark Anthony Redo, Sholahudin, Jongsoo Jeong, Seiichi Yamaguchi, Kiyoshi Saito, Hyunyoung Kim

    International Journal of Refrigeration   111   53 - 62  2020.03

     View Summary

    © 2019 Due to the intrinsic complexity of two-phase flow distribution and the limited mathematical flexibility of conventional formulations of the phenomenon, previous attempts generally fall short in the accuracy and applicability of their prediction. To address these issues, this study focuses on methods with higher mathematical flexibility. Specifically, the construction and training of Artificial Neural Network (ANN) is presented for the identification of this complex phenomenon. The interaction of the numerous physical phenomena, occurring at different scales, is thus represented by the network structure, offering a formulation capable of achieving higher accuracy. Experimental data from a full-scale heat exchanger of an air-conditioning system operating over a wide range of conditions are used to train and test the ANN. The network optimisation with Bayesian regularisation against experimental data leads to a structure featuring 4 inputs, 3 hidden layers, and 3 neurons for each layer, which demonstrates deviations on the single output mostly lower than ± 10% and a correlation index higher than 98%, when the whole data set is used for training the ANN. The analysis of the network optimisation for different shares of data used for the network testing, shows higher training and testing accuracy as the number of training data increases, along with no apparent overfitting.

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    36
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  • Numerical investigation of CO2 heat pump water heater performance

    Muhamad Yulianto, Takaoki Suzuki, Yoichi Miyaoka, Keisuke Ohno, Niccolo Giannetti, Kiyoshi Saito, Seiichi Yamaguchi

    Refrigeration Science and Technology   2020-   61 - 66  2020

     View Summary

    This study presents a preliminary investigation of the performance of a Heat Pump Water Heater (HPWH) that uses CO2 as refrigerant. The global market of this technology is led by Japan and several units are being installed all around the world under different climates. The main challenge for an efficient spreading of this technology is to maintain the excellent performance of CO2 HPWH under a broad variety of weather conditions. A numerical model was developed to flexibly investigate the performance of the CO2 HPWH under various distributions of inlet air temperature at the evaporator and inlet water temperature_in gas cooler. The simulation results are firstly compared with those from a general pinch point analysis. The Result show that the highest water temperature inlet and lowest air temperature inlet will produce lowest COP and Highest LCCP Contribution

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  • Experimental performance analysis and simulation of an internally cooled liquid desiccant air conditioning system using a novel ionic liquid

    Richard Jayson Varela, Seiichi Yamaguchi, Niccolo Giannetti, Kiyoshi Saito, Xin-Ming Wang, Hiroshi Nakayama

    Refrigeration Science and Technology   2020-   304 - 309  2020

     View Summary

    The search for new and more energy-efficient solutions with natural fluids has become a clear countermeasure for mitigating the carbon footprint of air conditioning and refrigerating systems. In the absorption field, specifically in liquid desiccant air conditioning systems, the application of internal cooling in gas-liquid contactors is limited due to the corrosion property of commonly used liquid desiccants. Internally cooled/heated liquid desiccant systems have better heat and mass transfer performance compared to adiabatic systems but mathematical modeling becomes more complicated. In this study, experiments and simulations were carried out to evaluate the performance of an internally cooled/heated liquid desiccant air conditioning system using a novel ionic liquid. This innovative solution became possible due to the compatibility, in terms of corrosion, of the newly developed ionic liquid with aluminum. The validated mathematical model can be used to conduct parametric and optimization studies for the internally cooled/heated liquid desiccant air conditioning system.

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    2
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  • Thermodynamic investigation of asynchronous open inverse air cycle integrated with compressed air energy storage

    Adriano Milazzo, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    Refrigeration Science and Technology   2020-   129 - 134  2020

     View Summary

    An integrated system for heating, cooling and compressed air energy storage (CAES) is analyzed from a thermodynamic point of view. The system is based on asynchronous air compression and expansion, in order to take advantage from the daily ambient temperature oscillations and energy cost variations. The analysis is intentionally kept on a fundamental level, without explicit reference to specific components, in order to enlarge the choice of potential applications. Effects of losses in compressor, expander and heat exchangers, as well as heat transfer in the CAES, are included. The proposed system, once optimized and experimentally validated, could become viable options in the wide arena of demand-side energy management.

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    1
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  • Assessment of surfactant-induced Marangoni convection within high-temperature aqueous Lithium-Bromide solution

    Niccolo Giannetti, Luca Rametta, Ryota Fukui, Masayoshi Hirasawa, Noriyuki Nishiyama, Seiichi Yamaguchi, Kiyoshi Saito

    Refrigeration Science and Technology   2020-   97 - 102  2020

     View Summary

    A common technical practice to boost the transfer performance of falling film absorbers within absorption cycles relies on surfactant additives for triggering the interfacial turbulence known as Marangoni convection. Given the phenomenon complexity and the interdependencies with other phenomena, such as surface wetting, the assessment of the related enhancement is unresolved yet, and data from previous literature are limited to the operative conditions of single effect refrigerators. This work combines numerical simulations and experiments for evaluating the transfer performance enhancement due to Marangoni convection in a wide operative range encompassing refrigeration and heat pump cycles. Falling film transfer coefficients are measured, with and without n-octanol, with LiBr solution temperature between 50 and 120oC, and specific mass flow rate between 0.011 and 0.11Kg·m-1s-1. Consequently, a semi-empirical model estimates the contribution of improved wettability and consequently indicates the portion of the transfer enhancement related to the Marangoni convection.

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  • Flow characteristics and noise diagnosis of hydrogen charging solenoid valve in hydrogen- fueled automobile

    Hifni M. Ariyadi, Niccolò Giannetti, Jongsoo Jeong, Seiichi Yamaguchi, Kiyoshi Saito, Changhoon Lee, Jungtae Kim, Seungbeom Lee, Jiyong Lee, Kwangyeol Jeong

    ECOS 2020 - Proceedings of the 33rd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems     104 - 111  2020

     View Summary

    There is a growing interest in green vehicles, such as hydrogen powered fuel cell cars, along with the increase in public awareness towards the environmental issues. However, with compressed systems applied for fuel storage purpose, refueling of hydrogen causes an issue, during which high-pressure hydrogen from the station storage tank passes through filling components before entering the empty tank in the vehicle. In this state, as the pressure difference between the station tank and the vehicle tank can be very high, the complexity of solenoid valve geometry creates complex flow characteristics (turbulence and interaction of gas and wall) that could generate intense pressure fluctuation and excessive noise. This paper presents the results of a three-dimensional simulation for characterizing the complex flow inside the solenoid valve and for diagnosing flow-induced noise generated during the charging process at different valve openings and pressures. Simulation is carried out using computational fluid dynamics (CFD) by implementing appropriate turbulence and viscous models. Firstly, the simulation is conducted in a steady state condition to investigate the acoustic power and to localize the regions that are most likely to be affected. In addition, transient simulations are performed to obtain the frequency of the pressure fluctuation inside the solenoid valve. The results provide accurate and useful data about flow pattern inside the solenoid valve and additionally, furnish information to determine the sources, locations, and characteristics of flow-induced noise generated within the solenoid valve. This investigation can be applied to reduce the undesirable noise and to analyze the possibility of system failure due to flow-induced vibrations.

  • Formulation of steady-state void fraction through the principle of minimum entropy production

    Niccolo GIANNETTI, Kiyoshi SAITO, Hiroaki YOSHIMURA

    Journal of Thermal Science and Technology   15 ( 3 ) JTST0025 - JTST0025  2020

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    2
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  • Seasonal performance evaluation of CO2 open refrigerated display cabinets

    Mark Anthony Redo, Keisuke Ohno, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    Applied Thermal Engineering   163  2019.12

     View Summary

    An increasing number of supermarkets and convenience stores has led to a proportionally higher demand for open refrigerated display cabinets (ORDCs). Ease of access to refrigerated products is the main advantage of ORDCs
    however, they also exhibit high cumulative energy consumption as well as direct and indirect CO2 emissions. This work aims to formulate, establish, and apply a seasonal performance evaluation method for ORDCs and “walk-in” type refrigerated device driven by CO2 chillers. First, a thermodynamic modeling approach is used and fitted to experimental data. The relative error between the predicted and actual heat load is within ±10%, whereas it is within ±20% for the normalized compressor electric input. Then, an evaluation tool is constructed using the seasonal energy consumption of ORDCs commonly used in Japan and driven by a transcritical CO2-compression chiller within Japanese climatic conditions. This tool can be used to predict the annual energy demand for given ambient conditions as well as the reduced environmental impact of multiple combinations of refrigerated display cabinets compared to conventional HFC/HCFC-based systems. According to the annual temperature distribution in chosen regions, the annual thermal load, annual electricity consumption, and annual coefficient of performance are calculated and analyzed. Simulation results quantitatively evaluate the beneficial effect of Te as being translated to a better COP, and lower energy consumption and CO2 emissions. Considering the geographic location of the store, the quantitative results show how a hotter climatic condition leads to higher energy consumption and CO2 emissions, and lower COP. The proposed evaluation method is generally applicable to any regional setting and any chiller-ORDC combination.

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    10
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  • Film rupture and partial wetting over flat surfaces with variable distributor width

    Niccolo Giannetti, Piyatida Trinuruk, Seiichi Yamaguchi, Kiyoshi Saito

    Science and Technology for the Built Environment   25 ( 10 ) 1313 - 1324  2019.11

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    2
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  • Optimization of HVAC system energy consumption in a building using artificial neural network and multi-objective genetic algorithm

    Nasruddin, Sholahudin, Pujo Satrio, Teuku Meurah Indra Mahlia, Niccolo Giannetti, Kiyoshi Saito

    Sustainable Energy Technologies and Assessments   35   48 - 57  2019.10

     View Summary

    The optimization of heating, ventilating and air conditioning (HVAC) system operations and other building parameters intended to minimize annual energy consumption and maximize the thermal comfort is presented in this paper. The combination of artificial neural network (ANN) and multi-objective genetic algorithm (MOGA) is applied to optimize the two-chiller system operation in a building. The HVAC system installed in the building integrates radiant cooling system, variable air volume (VAV) chiller system, and dedicated outdoor air system (DOAS). Several parameters including thermostat setting, passive solar design, and chiller operation control are considered as decision variables. Subsequently, the percentage of people dissatisfied (PPD) and annual building energy consumption is chosen as objective functions. Multi-objective optimization is employed to optimize the system with two objective functions. As the result, ANN performed a good correlation between decision variables and the objective function. Moreover, MOGA successfully provides several alternative possible design variables to achieve optimum system in terms of thermal comfort and annual energy consumption. In conclusion, the optimization that considers two objectives shows the best result regarding thermal comfort and energy consumption compared to base case design.

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    237
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  • Characterization of two-phase flow distribution in microchannel heat exchanger header for air-conditioning system

    Mark Anthony Redo, Jongsoo Jeong, Niccolo Giannetti, Koji Enoki, Seiichi Yamaguchi, Kiyoshi Saito, Hyunyoung Kim

    Experimental Thermal and Fluid Science   106   183 - 193  2019.09

     View Summary

    The two-phase flow distribution behavior of R410A within the vertical header of a microchannel heat exchanger with multiple horizontally oriented microchannel flat tubes was investigated and is reported in this paper. Unlike most previous studies, which examined the distribution at lower flowrates applicable mostly to automobile applications, this work evaluated higher flowrates relevant to actual air conditioning evaporator applications with larger size headers. The following operating conditions, were utilized: an inlet mass flowrate that varied from 40 to 200 kg h−1 (mass flux of 27–250 kg m−2 s−1 in the header), vapor qualities of 0.1, 0.2, and 0.6, and evaporating temperatures of 10 and 15 °C. The tube protrusion depth into the header was set at 0 and 50%. Flow distribution profiles derived from the experiment measurements and clear visualization images captured by a high speed camera showed that the distribution improves for increased inlet mass flux at low vapor quality, while a 5 °C difference in evaporating temperature does not yield a substantial distribution change. A 50% protrusion produces higher inertial forces pushing the liquid level towards the top section. A correlation was developed to predict the liquid distribution by relating the portion of liquid exiting the branch tube to the liquid at the immediate header as a function of the liquid Froude number.

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    47
    Citation
    (Scopus)
  • Characterization of two-phase flow distribution in microchannel heat exchanger header for air-conditioning system

    Mark Anthony Redo, Jongsoo Jeong, Niccolo Giannetti, Koji Enoki, Seiichi Yamaguchi, Kiyoshi Saito, Hyunyoung Kim

    EXPERIMENTAL THERMAL AND FLUID SCIENCE   106   183 - 193  2019.09

     View Summary

    The two-phase flow distribution behavior of R410A within the vertical header of a microchannel heat exchanger with multiple horizontally oriented microchannel flat tubes was investigated and is reported in this paper. Unlike most previous studies, which examined the distribution at lower flowrates applicable mostly to automobile applications, this work evaluated higher flowrates relevant to actual air conditioning evaporator applications with larger size headers. The following operating conditions, were utilized: an inlet mass flowrate that varied from 40 to 200 kg h(-1) (mass flux of 27-250 kg m(-2) s(-1) in the header), vapor qualities of 0.1, 0.2, and 0.6, and evaporating temperatures of 10 and 15 degrees C. The tube protrusion depth into the header was set at 0 and 50%. Flow distribution profiles derived from the experiment measurements and clear visualization images captured by a high speed camera showed that the distribution improves for increased inlet mass flux at low vapor quality, while a 5 degrees C difference in evaporating temperature does not yield a substantial distribution change. A 50% protrusion produces higher inertial forces pushing the liquid level towards the top section. A correlation was developed to predict the liquid distribution by relating the portion of liquid exiting the branch tube to the liquid at the immediate header as a function of the liquid Froude number.

    DOI

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    47
    Citation
    (Scopus)
  • A practical heat and mass transfer model between air and ionic liquid solution in an internally cooled dehumidifier with partial wetting.

    Richard J. VARELA, Niccolo GIANNETTI, Hifni M. ARIYADI, Seiichi YAMAGUCHI, Kiyoshi SAITO, Xin-Ming WANG, Hiroshi NAKAYAMA

    Proceedings of the 25th IIR International Congress of Refrigeration: Montréal , Canada, August 24-30, 2019.    2019.08  [Refereed]

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    2
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  • Comparative analysis of ionic liquids as sorptive media for absorption cooling systems.

    Hifni M. ARIYADI, Niccolo GIANNETTI, Seiichi YAMAGUCHI, Kiyoshi SAITO

    Proceedings of the 25th IIR International Congress of Refrigeration: Montréal , Canada, August 24-30, 2019.    2019.08  [Refereed]

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    6
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  • Dynamic modeling of room temperature and thermodynamic efficiency for direct expansion air conditioning systems using Bayesian neural network

    Sholahudin, Keisuke Ohno, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    APPLIED THERMAL ENGINEERING   158  2019.07

     View Summary

    In this paper, dynamic performance identification for a direct expansion (DX) air conditioning (AC) system is proposed using Bayesian artificial neural network (ANN). The input and output datasets are generated by a dedicated AC simulator by varying the compressor speed in various signal amplitudes and including dynamic cooling load and ambient temperature. The exergy destruction, which represents the work potential losses in the system and room temperature indicating the thermal comfort are selected as the output variables. The key parameters of an ANN model, including the number of neurons and tapped delay lines, are optimized to improve the prediction accuracy. The results show that the dynamic response of the exergy destruction and room temperature can be predicted accurately by the optimized ANN model using three neurons, a Bayesian regularization algorithm, five delayed inputs for the compressor speed and room temperature, and six delayed inputs for the cooling load and ambient temperature. The validation of the multi-step-ahead prediction showed satisfying results with respect to the root mean squared errors (RMSEs) and coefficient of variations (CVs) of the room temperature (RMSE: 0.18 degrees C and CV: 0.85%) and exergy destruction (RMSE: 1.79 W and CV: 0.4%). Accordingly, the identification of the AC system behavior presented in this paper could be further implemented to control the DX AC system operation to achieve a desired thermal comfort with low exergy destruction.

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    21
    Citation
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  • Numerical analysis of control characteristics of variable refrigerant flow heat-pump systems focusing on the effect of expansion valve and indoor fan

    Kuniyasu Matsumoto, Keisuke Ohno, Seiichi Yamaguchi, Kiyoshi Saito

    International Journal of Refrigeration   99   440 - 452  2019.03

     View Summary

    In commercial and office buildings, it has recently become popular to install variable refrigerant flow (VRF) compression-type heat pump systems. In particular, VRF systems with multiple indoor units are being installed in large buildings because such systems have large adjustment capacity. On the other hand, because users of VRF systems can freely choose the number of indoor units to install and can turn indoor units on and off independently, operating conditions are not predictable and it is difficult to find adequate control parameters under wide changes in load. With this background, we are developing a new numerical simulation model based on the laws of physics. Because this model can easily add and delete system elements, we believe that it will be useful for VRF system analysis. In this study, we utilize a numerical simulation model to evaluate both steady and unsteady conditions in VRF systems. In this paper, we focus on the connection between manipulated variables (the expansion valve's open pulse and fan rotational speed) and controlled variables (supply air temperature and the degree of superheating at the evaporator outlet). Moreover, we compare the difference between the performance of a single indoor unit and that of multiple indoor units operating simultaneously. As a result, we can evaluate the dynamic characteristics of manipulated variables and the effect of changing the number of active indoor units, each of which has their own VRF characteristics.

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    10
    Citation
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  • Two-phase flow distribution in dual-compartment microchannel heat exchanger header

    Mark Anthony Redo, Jongsoo Jeong, Seiichi Yamaguchi, Kiyoshi Saito, Hyunyoung Kim

    Refrigeration Science and Technology   2019-   1515 - 1522  2019

     View Summary

    With the inherent flow maldistribution problem within the microchannel heat exchanger header, which degrades the heat transfer performance, new microchannel heat exchanger header was designed and tested to improve this flow distribution performance, specifically for R410A. It features dual-compartment made of multiple layers consisting of the main section, baffle and hole seat, and rear section. Twenty flat tubes containing microchannels were inserted at 50% protrusion. Experiments and visualizations were conducted at 50, 100, and 200 kg·h-1 of mass flow rate (equivalent mass flux of 220.5, 441, and 882 kg·m-2s-1), which were at partial to full loading capacity. Inlet vapor quality was fixed at 0.2 and evaporating temperature at 15 ºC, for evaporator application of air-conditioning system. Considering the same microchannel element, flow distribution enhancement was achieved when compared to the conventional header data. Liquid flow distribution was improved by around 65% at part-load conditions based on the relative standard deviation.

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    1
    Citation
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  • Control analysis of VRF air-conditioners for the evaluation of demand response

    Kuniyasu Matsumoto, Kiyoshi Saito, Seiichi Yamaguchi, Keisuke Ohno

    Refrigeration Science and Technology   2019-   3957 - 3964  2019

     View Summary

    The number of renewable power plants has recently been increasing
    hence, it is essential to maintain a balance between the supply and demand of electric power. We employ the technique of demand response (DR) through the manipulation of air conditioners. In summer, the electric demand for air conditioning consumes the majority of the available total electric power
    therefore, regulating this demand compliments the requirements of peak-cut and load leveling. However, the manipulation of air conditioning impacts the user comfort and the stability of the machine. Moreover, the energy consumption of air-conditioners is uncertain owing to the operation conditions. Consequently, it is difficult to estimate the performance of the DR method. In this study, we focus on the variable refrigerant flow system, which is a popular air-conditioning system in Japan. We evaluate the performance of the demand response method using a simulation analysis and ensure that the amount of DR to regulate the air-conditioner is controlled quantitatively.

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  • Identification of vapour compression air conditioning system behaviour using Bayesian regularization neural network

    Sholahudin, Keisuke Ohno, Seiichi Yamaguchi, Kiyoshi Saito

    Refrigeration Science and Technology   2019-   4061 - 4068  2019

     View Summary

    Identification for system dynamic behaviour is necessary to develop control strategy. In this paper, the dynamic performance of air conditioning (AC) system is predicted using artificial neural network (ANN) approach. The ANN is developed to predict exergy efficiency, coefficient of performance (COP), and cooling capacity. The controllable parameters including compressor speed and evaporator and condenser fan speed are considered as the input. The datasets for prediction are generated by AC system simulator. The system was simulated by randomly varying compressor speed and evaporator and condenser fan speed with N-sample signal input. The dynamic ANN configuration with Bayesian regularization is proposed to predict one-step ahead of system performance behaviour. The results show that the developed ANN in present study yields good prediction accuracy for all outputs. Accordingly, ANN can be further applied for predictive control application in AC system to control cooling capacity while maintaining system efficiency.

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  • Semi-theoretical model of the wetting characteristics of aqueous ionic liquid on an aluminium finned-tube desiccant contactor

    Niccolo Giannetti, Richard Jayson Varela, Hifni Ariyadi, Seiichi Yamaguchi, Kiyoshi Saito, Xin Ming Wang, Hiroshi Nakayama

    Refrigeration Science and Technology   2019-August   4616 - 4623  2019

     View Summary

    © 2019 International Institute of Refrigeration. All rights reserved. A new design of an internally cooled desiccant contactor which uses a new ionic liquid (IL) solution as sorptive medium is targeted. To optimise its operative performance, a semi-theoretical model based on a variational thermodynamic principle is developed to predict the film rupture and wetting ability of the IL solution for different values of the IL mass fraction over a comprehensive range of liquid spray density. The minimum Reynolds number Reb allowing the film-like flow configuration and, below this value, the wetted fraction of the solid substrate are firstly formulated on an analytical basis. Successively, the theoretical formulation is used as a reference to minimise deviations between predicted results and measured data by calibrating dedicated characteristic coefficients. Predicted film rupture, wetting ability and wetting hysteresis behaviour are strongly affected by the IL mass fraction and found in good agreement with the measurements.

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    2
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  • Performance and Application of Combined System of Liquid Desiccant and R718 Centrifugal Heat Pump

    Hajime Yabase, Seiichi Yamaguchi, Kiyoshi Saito, Hiroshi Hasuike, Hayato Sakamoto, Satoru Matsumoto, Masatoshi Harada

    10TH INTERNATIONAL MEETING OF ADVANCES IN THERMOFLUIDS (IMAT 2018): SMART CITY: ADVANCES IN THERMOFLUID TECHNOLOGY IN TROPICAL URBAN DEVELOPMENT   2062  2019

     View Summary

    The air-conditioning system for buildings and facilities is required that the room temperature and the humidity are kept in a predetermined range for comfortable air-conditioning. For achieving the above only by a heat pump, the room condition should be heated till the preset temperature after cooling till the temperature from which the request humidity is obtained, and this operation is inefficient.To overcome such inefficiency, separation of latent heat and sensible heat has been proposed. This is a two-step process in which temperature and humidity are adjusted separately in two steps by combining desiccant dehumidifier and heat pump. Theoretically, the system is known to be effective in reducing energy consumption, but in practical application, this technology can be further improved.In this research, we combined the liquid desiccant equipment which can perform low temperature regeneration and R718 centrifugal heat pump suitable for high efficiency for this application. Based on this concept, we have developed a highly efficient air-conditioning system by improving element equipment and optimizing operating conditions. The performance of this system is reported here.

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  • Assessment of thermal and transport properties of ionic liquids as suitable absorbent for absorption cooling applications

    H. M. Ariyadi, S. Yamaguchi, K. Saito

    IOP Conference Series: Materials Science and Engineering   539  2019.01

     View Summary

    © Published under licence by IOP Publishing Ltd. Ionic liquids, salts which have liquid phase at temperature below 100°C, have been widely introduced in engineering applications, including absorption cooling systems. The application of ionic liquids in absorption cooling systems is intended to remove the disadvantages of conventional working fluids such as corrosion and crystallization. In terms of thermodynamic performances, theoretical investigation based on solubility behavior of ionic liquids in natural refrigerants show a competitive performance in comparison with conventional working fluid. Nevertheless, heat transfer performance, which is also an important key in absorption cooling systems, particularly in terms of system design and size, needs to be deeply explored and investigated. This study aims to assess the thermal and transport properties of ionic liquids as absorbent in relation to the heat and mass transfer characteristics of these working fluids. The thermal and transport properties of ionic liquids proposed as absorbent for absorption cooling systems are collected, and heat and mass transfer characteristic of these ionic liquids based on their thermal and transport properties are investigated and analyzed. Finally, the most suitable ionic liquids for absorption machines, both in terms of thermodynamics and heat and mass transfer performances can be proposed.

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    7
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  • Semitheoretical Prediction of the Wetting Characteristics of Aqueous Ionic Liquid Solution on an Aluminum Finned-Tube Desiccant Contactor

    Niccolo Giannetti, Richard Jayson Varela, Hifni Ariyadi, Seiichi Yamaguchi, Kiyoshi Saito, Xin-Ming Wang, Hiroshi Nakayama

    Journal of Fluids Engineering   140 ( 12 )  2018.12

     View Summary

    This study involves exploring a new design of an internally cooled/heated desiccant contactor by using a new ionic liquid (IL) solution as the sorptive solution. In order to optimize its operative performance, a semitheoretical model based on the principle of minimum energy is developed to predict the film rupture and wetting ability of the IL solution over a comprehensive range of IL mass fraction and flow rates. A first experimental validation of the fundamental equations of the theoretical model is presented and used as a reference to minimize deviations between predicted results and measured data by calibrating dedicated characteristic coefficients. The noteworthy quantitative and qualitative agreement in the whole range of IL mass fractions and flow rates is promising for contributing to the design of optimized system configurations and control strategies.

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    15
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  • Development and validation of an analytical formulation of the Nusselt and Sherwood numbers on a partially wetted absorber tube

    Niccolo Giannetti, Ryosuke Moriwaki, Seiichi Yamaguchi, Kiyoshi Saito

    Science and Technology for the Built Environment   24 ( 8 ) 850 - 860  2018.09

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    3
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  • Numerical simulation of Marangoni convection within absorptive aqueous Li-Br

    Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    International Journal of Refrigeration   92   176  2018.08  [Refereed]

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    7
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  • Simplified expressions of the transfer coefficients on a partially wet absorber tube

    Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    International Journal of Refrigeration    2018.07  [Refereed]

    DOI

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    9
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  • Operation performance enhancement of single-double-effect absorption chiller

    Arnas Lubis, Jongsoo Jeong, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Hajime Yabase, Muhammad I. Alhamid, Nasruddin

    Applied Energy   219   299 - 311  2018.06  [Refereed]

     View Summary

    Absorption chillers constitute a valuable option for utilising solar energy. Specifically, when installed in tropical regions, this technology ideally matches the needs for refrigeration and air-conditioning because of the abundance of solar energy throughout the year. A single-double-effect absorption chiller combines the single and double-effect configurations to compensate for the unpredictable instantaneous availability of solar radiation and cooling load fluctuations. The operative performance of this system is strongly affected by internal parameters such as the absorber outlet solution flow rate and the solution distribution ratio, which connect the operability of the single and double-effect configurations. Therefore, these important parameters are currently used to maximise system performance while assuring its stability. This study discusses how the COP of a single-double-effect absorption chiller, for solar cooling applications in tropical areas, can be maximised (1.55 at full load, and up to 2.42 at 60% partial load) by manipulating those internal parameters. The simulation results were compared with the experimental data (field test data) and, by adopting the appropriate control method, showed an improvement of the system performance between 12 and 60% when compared to a corresponding double-effect configuration.

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    48
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  • General correlations for the heat and mass transfer coefficients in an air-solution contactor of a liquid desiccant system and an experimental case application

    Richard Jayson Varela, Seiichi Yamaguchi, Niccolo Giannetti, Kiyoshi Saito, Masatoshi Harada, Hikoo Miyauchi

    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER   120   851 - 860  2018.05

     View Summary

    This paper presents general types of correlation for the heat and mass transfer coefficients inside an air solution contactor as expressions of Reynolds-Prandtl numbers and Reynolds-Schmidt numbers, respectively. These general equations summarize the physical and thermophysical properties of the air, the solution, and the contactor, which make them capable to be used for parametric studies provided they are fitted in a wide range of experimental data that include all the properties involved. In this work, a liquid desiccant system with an adiabatic structured packed bed as contactor and an aqueous lithium chloride as solution was constructed. The experimental data taken at various air superficial velocities and solution flow rates were fitted to the general correlations, and comparisons between the predicted and experimental results for both coefficients are within +/- 10%, for both dehumidification and regeneration processes. In addition, the calculated values of the outlet air humidity ratio and temperature agree well with the experimental data for both processes. The particular equations for the heat and mass transfer coefficients can be used to perform parametric studies at different air superficial velocities and solution flow rates with very good accuracy. Results from this study can help improve the system design and operation methods of air-solution contactors. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI

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    27
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  • Heat and mass transfer coefficients of falling-film absorption on a partially wetted horizontal tube

    Niccolò Giannetti, Andrea Rocchetti, Seiichi Yamaguchi, Kiyoshi Saito

    International Journal of Thermal Sciences   126   56 - 66  2018.04  [Refereed]

     View Summary

    Detailed, reliable, and time-saving methods to predict the transfer characteristics of horizontal-tube falling-film absorbers are critical to control system operability, such that it is closer to its technical limitations, and to optimise increasingly complex configurations. In this context, analytical approaches continue to hold their fundamental importance. This study presents an analytical solution of the governing transport equations of film absorption around a partially wetted tube. A film stability criterion and a wettability model extend the validity range of the resulting solution and increase its accuracy. Temperature and mass fraction fields are analytically expressed as functions of Prandtl, Schmidt, and Reynolds numbers as well as tube dimensionless diameter and wetting ratio of the exchange surface. Inlet conditions are arbitrary. The Lewis number and a dimensionless heat of absorption affect the characteristic equation and the corresponding eigenvalues. Consequently, local and average transfer coefficients are estimated and discussed with reference to the main geometrical and operative parameters. Finally, a first comparison with the numerical solution of the problem and experimental data from previous literature is presented to support the simplifying assumptions, which are introduced and as a first model validation.

    DOI

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    38
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  • Experimental investigation of the wetting characteristics of an aqueous ionic liquid solution on an aluminum fin-tube substrate

    Richard Jayson Varela, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Xin-Ming Wang, Hiroshi Nakayama

    INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID   88   472 - 482  2018.04  [Refereed]

     View Summary

    In falling film liquid desiccant systems, finding a suitable pair of liquid desiccant and contact surface is of primary engineering interest. This requires knowledge on the wetting characteristics of the liquid on the solid substrate, which consequently requires intensive experimental investigation. In this study, the wetting characteristics of a new ionic liquid aqueous solution in an aluminum fin-tube substrate were experimentally investigated. Then, a simple method for estimating the wetted area on the substrate through image processing was developed. Visual analysis of the surface wetting was also conducted, and three types of wetting patterns are discussed. Experimental results on the static contact angle and contact angle hysteresis suggest that the ionic liquid solution is mostly wetting, and the aluminum surface is slightly to moderately rough. It was found that the wettability of the ionic liquid solution increases as the ionic liquid mass fraction increases. The wetting hysteresis phenomenon and the factors contributing to its occurrence were also clarified. The results from this study would be useful for the development of a new model or improvement of existing wetting models, which can help improve the prediction and control of the heat and mass transfer performance in internally cooled/heated fin-tube contactors. (C) 2018 Elsevier Ltd and IIR. All rights reserved.

    DOI

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    26
    Citation
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  • Evaluation of control method of VRF (variable refrigerant flow) system by experimental study and simulation analysis

    Kuniyasu Matsumoto, Keisuke Ohno, Seiichi Yamaguchi, Kiyoshi Saito

    ACRA 2018 - 9th Asian Conference on Refrigeration and Air-Conditioning    2018

     View Summary

    Recently in Japan, it has been popular to install VRF (Variable Refrigerant Flow) heat pump system to office buildings regardless of size and shape, because many Japanese regard it as the virtue to turn off the air conditioner frequently for energy saving if it is not necessary. This system consists of packaged outdoor unit and multi indoor units connected by refrigerant pipe, and there are some merits for users and owners. For example, it is easy to design for planning building system because of standardized system. Moreover, this system contributes to saving energy and to increasing comfort for users, because it can be operated adequate indoor unit as necessary. On the other hand, because refrigerant flow rate changes dynamically depend on load condition, this system needs complicated control system for keeping stable operation under many manipulating elements. For that reason, it is too difficult to find adequate each elements' condition by only experimental study. In order to evaluate VRF system by easy way, we build the numerical simulation model based on law of physics and we research adequate control condition under various sorts of cooling condition. It is said that conventional control method occurs uns table manipulating condition in case of changing load condition. In this report, we reproduce unstable condition of expansion valve by simulation study.

  • Start-up behaviour of a combined air-conditioning system in cooling and heating operating modes

    Jongsoo Jeong, Arnas Lubis, Kiyoshi Saito, Sarngwoo Karng, Seoyoung Kim, Kwangho Kim

    Energy and Buildings   158   1346 - 1357  2018.01

     View Summary

    The energy demand of the commercial building sector is largely for cooling and heating and will eventually result in energy and environmental crises
    therefore, enhancing the performance of the cooling and heating systems used in buildings is paramount. In response to this need, focus was set on the gas engine-driven heat pump-combined system (GHPC)—consisting of a gas engine, single-stage vapour compression system, and single-effect absorption system— that saves more energy as compared to a conventional gas engine-driven heat pump. However, so far, only the performance and transient characteristics of a fabricated GHPC have been investigated. Therefore, to ascertain the characteristics of the GHPC start-up dynamics under unsteady state operations so as to achieve efficient and stable start-up operation, experiments and simulations were attempted in this study. The transient behaviour from the start-up of this combined system in cooling and heating operating modes was also scrutinized. Accordingly, it was found that simulation results agreed well with experimental data. It was concluded that there were no large delayed responses in the absorption system during start-up operation when start-up of the absorption system is considered based on the system cooling capacity response after the solution pump starts.

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    5
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  • Thermodynamic analysis of irreversible desiccant systems

    Giannetti N, Yamaguchi S, Rocchetti A, Saito K

    Entropy   20 ( 8 )  2018  [Refereed]

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    5
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  • Performance evaluation method of heat pump driven refrigerated display cabinets

    Keisuke Ohno, Mark Anthony Redo, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    Refrigeration Science and Technology   2018-   294 - 301  2018  [Refereed]

     View Summary

    Annual heat load, energy consumption and COP of open refrigerated display cabinets (ORDC) driven by heat pump in supermarkets are assessed by means of a dedicated performance evaluation method. The system modelling approach is firstly presented, and subsequently fitted to experimental data measured within actual equipment working in a comprehensive range of operative conditions. The obtained characteristic equations for estimating the heat load of the ORDC and energy consumption of the condensing unit are employed for a first screening of the results with reference to the effect of the display cabinet set temperature, refrigerant evaporating temperature and supermarket room temperature. Seasonal temperature distributions of three representative locations are applied for the performance calculation of a selected arrangement of 5 different models of ORDCs in a store. This methodology is integrated in a dedicated software, with a user friendly interface, which is generally capable of predicting the annual performance of various combinations of different ORDCs and can therefore be used for benchmarking and identifying energy conservation opportunities.

    DOI

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    1
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  • DEVELOPMENT OF HIGH PERFORMANCE AIR-CONDITIONING SYSTEM COMBINED LIQUID DESICCANT AND R718 CENTRIFUGAL HEAT PUMP

    Hajime Yabase, Seiichi Yamaguchi, Kiyoshi Saito, Hiroshi Hasuike, Hayato Sakamoto, Satoru Matsumoto, Masatoshi Harada

    13TH IIR GUSTAV LORENTZEN CONFERENCE ON NATURAL REFRIGERANTS     1345 - 1352  2018

     View Summary

    General implementation of air conditioning in buildings and facilities is such that in order to keep room temperature and humidity within predetermined range, heat pump is used to lower the air temperature to achieve desired humidity and then the air is heated to the specified temperature. From energy-saving perspective, this process is inefficient.To overcome such inefficiency, separation of latent heat and sensible heat has been proposed. This is a two-step process in which temperature and humidity are adjusted separately in two steps by combining desiccant dehumidifier and heat pump. Theoretically, the system is known to be effective in reducing energy consumption, but in practical application, this technology can be further improved.For this research, we have chosen liquid desiccant dehumidifier as the desiccant can be regenerated at low temperature. For heat pump system, we have chosen R718 centrifugal as it is suited for increasing efficiency for such combination of desiccant and heat pump. By improving each element of the system and seeking optimization of operating conditions, we aim to develop a high efficiency air-conditioning system. The result is reported here.

    DOI

    Scopus

  • Annular flow stability within small-sized channels

    Niccolo Giannetti, Daisuke Kunita, Seiichi Yamaguchi, Kiyoshi Saito

    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER   116   1153 - 1162  2018.01  [Refereed]

     View Summary

    An analytical study based on a variational thermodynamic principle is presented to evaluate the influence of surface tension on the stability of annular flow within small-sized channels. The model introduces phenomenological assumptions in the interfacial structure of the flow regime and theoretically draws the equilibrium transition line from an annular regime to the initiation of the partial wetting condition on the inner surface. By including surface tension, this model expands previous theories and identifies the stable flow configuration in terms of void fraction and interfacial extension. The significant influence of a higher surface tension and smaller diameter (i.e. lower Weber number) are responsible for a lower stable void fraction and higher slip ratio. A complete screening of the main influential parameters is conducted to explore the descriptive ability of the model. This analysis aims at contributing to the understanding of the stability of two-phase flow regimes and can be extended to the transition between other neighbouring regimes, including wall friction as well as liquid entrainment phenomena. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI

  • MODELLING OF WATER VAPOR ABSORPTION BY AQUEOUS IONIC LIQUID FLUIDS IN A VERTICAL-TUBE FALLING FILM ABSORBER

    Ariyadi Hifni Mukhtar, Giannetti Niccolò, Yamaguchi Seiichi, Saito Kiyoshi

    Grand Renewable Energy proceedings   1 ( 0 )  2018

     View Summary

    Due to their unique characteristics, recently ionic liquids have been proposed as a novel absorbent for absorption systems to eliminate the drawbacks of conventional water/LiBr working fluids, particularly crystallization and corrosion. Studies on the cycle performance of absorption cooling systems using water/ionic liquid working pairs have been published in many literatures. However, specific studies on the absorption characteristics of these new working pairs still remains open. Present study theoretically analyses the absorption characteristics of water vapor by aqueous ionic liquid solutions in a vertical tube falling film absorber. The model is developed by employing three ordinary differential equations describing the absorption process and is validated. The results are analyzed and the performances of water/ionic liquid are compared with those of conventional water/LiBr working fluid.

    CiNii

  • Cascade refrigeration system with inverse Brayton cycle on the cold side

    Niccolo Giannetti, Adriano Milazzo, Andrea Rocchetti, Kiyoshi Saito

    APPLIED THERMAL ENGINEERING   127   986 - 995  2017.12  [Refereed]

     View Summary

    temperature refrigeration of cold stores poses some specific issues: single stage, vapour compression cycles have modest COP at low evaporation temperature; cold evaporator surfaces require de-frosting and a fan for air circulation; a part of the refrigeration load may be delivered at intermediate temperature levels, e.g. for the cold store loading dock. Cascade system may improve the COP and add flexibility on the temperature levels and working fluids, but the problems related to the cold evaporator surface remain unsolved.
    The refrigeration system presented herein features a cascade configuration combining a vapour compression cycle and an inverse Brayton cycle. Both cycles use "natural" fluids, complying with strictest regulations. The top cycle uses Ammonia in order to increase efficiency, while the bottom cycle uses air, which directly circulates in the cold space and hence eliminates the cold heat exchanger. A detailed thermodynamic analysis allows a complete screening of the relevant design parameters for an overall system optimization.
    The results show that, notwithstanding the intrinsic gap of efficiency suffered by the Brayton cycle, the proposed system features an acceptable global performance and widens the implementation field of this technology. This system configuration shows a COP 50% higher than the corresponding simple Brayton cycle at temperatures of the refrigerated storage of -50 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI

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    28
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  • Experimental performance of a double-lift absorption heat transformer for manufacturing-process steam generation

    Arnas Lubis, Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito, Naoyuki Inoue

    ENERGY CONVERSION AND MANAGEMENT   148   267 - 278  2017.09  [Refereed]

     View Summary

    As widely known, some industrial processes produce a large amount of waste heat while others require a large amount of steam to heat the process flow. The main difference involves the temperature level of these heat quantities. Absorption heat transformers play a strategic role in waste heat recovery and heat supply to manufacturing processes due to their ability to utilize heat at a certain temperature level and release the enthalpy of mixing of the refrigerant at a different temperature level with a negligible amount of mechanical work input. However, given the lack of examples that find application as operative plants, the feasibility of the technology is questioned in academic and technical domains. In this study, the operability of a double-lift absorption heat transformer that generates pressurized steam at 170 degrees C is studied across a full range of operative conditions. The results demonstrate and clarify the manner in which the system can operate steadily and efficiently when driven by hot water temperature at approximately 80 degrees C while safely generating steam at a temperature exceeding 170 degrees C. The conditions yielding maximum system efficiency and capacity are identified, and the obtained experimental results are used to define an optimal control strategy. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI

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    26
    Citation
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  • Analytical solution of film mass-transfer on a partially wetted absorber tube

    Niccolo Giannetti, Andrea Rocchetti, Seiichi Yamaguchi, Kiyoshi Saito

    INTERNATIONAL JOURNAL OF THERMAL SCIENCES   118   176 - 186  2017.08  [Refereed]

     View Summary

    This work presents a two-dimensional analytical solution of the governing differential equation for falling film vapour-absorption around a plain horizontal tube. The solution of the species transport equation gives the LiBr mass fraction distribution within the liquid absorptive film flowing along the tube surface and can be used to characterize the mass transfer performance of falling film absorbers or generators. By means of the inclusion of partial wetting effects at reduced solution mass flowrates, this study obtains an analytical expression of the mass transfer coefficient of these devices applicable over an extended range of operative conditions. The hypotheses of small penetration for physical absorption and constant heat flux condition are applied at the film interface to reach a closed-form solution. Fourier method is used to solve the problem and the eigenvalues obtained from the characteristic equation depend on Lewis number, Biot number and the dimensionless heat of absorption. Given the boundary condition at the wall, the two-dimensional mass fraction field of the laminar film can be expressed analytically as a function of Schmidt, Reynolds numbers, the tube dimensionless diameter and the ratio of the wetted area to the total exchange surface. Finally, mass transfer coefficient and absorbed mass flux are locally and globally investigated as functions of the influent dimensionless groups to clarify their effects on the physical process and screen the potentiality of the model. Results show notable qualitative and quantitative agreement with previous numerical solutions and experimental results from previous literature. This model constitutes a widely applicable and time-saving tool for actual system simulations, design and control. (C) 2017 Elsevier Masson SAS. All rights reserved.

    DOI

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    16
    Citation
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  • Derivation and validation of dimensionless models for the heat and mass transfer coefficients of a structured packed bed dehumidifier

    Richard Jayson Varela, Seiichi Yamaguchi, Niccolo Giannetti, Kiyoshi Saito, Masatoshi Harada, Hikoo Miyauchi

    2nd International Conference on Energy and Indoor Environment for Hot Climates - ASHRAE, HotClimates 2017     247 - 254  2017

     View Summary

    This study presents the derivation of two general types of correlation for the heat and the mass transfer coefficients (inside an adiabatic structured packed bed of a liquid desiccant system, which uses aqueous lithium chloride as a solution) as expressions of Nusselt and Sherwood numbers, respectively. These general equations summarize the physical and thermophysical properties of the air, the solution, and the contactor, which make them capable to be used for any parametric study provided they are fitted in a wide range of experimental data that include all the properties involved. Specifically, in this study, the experimental data taken at various air superficial velocities and solution flow rates were fitted to the said correlations. Comparison between the predicted and experimental values shows very good agreement with deviations for both coefficients within ±10% and average errors of 4.58 and 2.79% for the heat and the mass transfer coefficients, respectively. In addition, the calculated outlet air humidity ratios and temperatures match closely the experimental data. The fitted correlations for the heat and the mass transfer coefficients can be used to perform parametric studies at different air superficial velocities and solution flow rates with very good accuracy.

  • Prediction for Flow Boiling Heat Transfer in Small Diameter Tube Using Deep Learning

    ENOKI Koji, SEI Yuichi, OKAWA Tomio, SAITO Kiyoshi

    JAPANESE JOURNAL OF MULTIPHASE FLOW   31 ( 4 ) 412 - 421  2017

     View Summary

    The applications of Artificial Intelligence ie AI show diversity in any fields. On the other hand, research of the predicting heat transfer regardless of single-phase or two-phase flow is still untouched. Therefore, we have confirmed usefulness using AI’s deep learning function on horizontal flow boiling heat transfer in flowing mini-channel that is actively researched. The effect of the surface tension in the mini-channel is large compared with conventional large tubes, and then the heat transfer mechanism is very complicated. For this reason, the numerical correlations of many existing researchers the prediction result is not good. However, the mechanistic correlation based on the visualization experiment, which the authors' research group published several years ago has very high precision. Therefore, in this research paper, we confirmed the effectiveness of using deep learning for predicting of the boiling heat transfer in mini-channel while comparing our correlation.

    DOI DOI2 CiNii

  • Two-phase flow distribution of R410A within the vertical header of a microchannel heat exchanger

    REDO Mark Anthony, GIANNETTI Niccolo, JEONG Jongsoo, ENOKI Koji, OTA Ikuhide, SAITO Kiyoshi, KIM Hyunyoung

    The Proceedings of the Symposium on Environmental Engineering   2017.27   427  2017

     View Summary

    With an ultimate goal of enhancing the flow distribution within a microchannel heat exchanger, an experimental apparatus was designed and constructed. This study presented an initial evaluation and investigation of R410A distribution with mass flowrate of 40, 60, 80 kg/h or mass flux of 120, 180, 240 kg/m2s. The inlet vapor quality before the header was varied at 0.1, 0.2 and 0.6. The inlet flow entered at the bottom with a normal location towards the vertical header. 20 horizontal parallel flat tubes having microchannel holes were protruded half-width of the header where the flow was distributed. Individual pressure drop and flowrate were measured. Corresponding inlet vapor quality for each was calculated. Visualization was conducted for the observation of the flow behavior at the vertical header. Increase on the liquid level at higher mass flux and more homogeneous two-phase flow at lower quality were observed within the header, which yielded better distribution.

    DOI CiNii

  • EXPERIMENT AND VISUALIZATION OF R410A FLOW DISTRIBUTION WITHIN THE VERTICAL HEADER OF MICROCHANNEL HEAT EXCHANGER

    Mark Anthony Redo, Niccolo Giannetti, Jongsoo Jeong, Koji Enoki, Ikuhide Ota, Kiyoshi Saito, Hyunyoung Kim

    5TH IIR INTERNATIONAL CONFERENCE ON THERMOPHYSICAL PROPERTIES AND TRANSFER PROCESSES OF REFRIGERANTS (TPTPR)     236 - 243  2017

     View Summary

    This paper reports an initial step to obtain an equally distributed fluid flow in an evaporator heat exchanger and eventually increase its performance. Experiments are carried out for R410A, using a vertical header where 20 horizontal parallel flat tubes are connected and the protrusion depth is half of the header width. The flow enters the header from a bottom inlet port and there is no heat load applied on the flat tubes. Inlet vapor quality before the header is varied for a fixed total mass flow rate of 60 kg/h. For each set of conditions, the mass flow rate and quality at different vertical positions of the header are singularly measured. Visualization data and experimental results have shown that 0.6 vapor quality before the header produces a more even distribution having a more homogeneous two-phase flow compared to 0.2 where phases are distinctly separated yielding dryouts on the top channels.

    DOI

  • EXPERIMENT AND VISUALIZATION OF R410A FLOW DISTRIBUTION WITHIN THE VERTICAL HEADER OF MICROCHANNEL HEAT EXCHANGER

    Mark Anthony Redo, Niccolo Giannetti, Jongsoo Jeong, Koji Enoki, Ikuhide Ota, Kiyoshi Saito, Hyunyoung Kim

    5TH IIR INTERNATIONAL CONFERENCE ON THERMOPHYSICAL PROPERTIES AND TRANSFER PROCESSES OF REFRIGERANTS (TPTPR)     891 - 898  2017

     View Summary

    This paper reports an initial step to obtain an equally distributed fluid flow in an evaporator heat exchanger and eventually increase its performance. Experiments are carried out for R410A, using a vertical header where 20 horizontal parallel flat tubes are connected and the protrusion depth is half of the header width. The flow enters the header from a bottom inlet port and there is no heat load applied on the flat tubes. Inlet vapor quality before the header is varied for a fixed total mass flow rate of 60 kg/h. For each set of conditions, the mass flow rate and quality at different vertical positions of the header are singularly measured. Visualization data and experimental results have shown that 0.6 vapor quality before the header produces a more even distribution having a more homogeneous two-phase flow compared to 0.2 where phases are distinctly separated yielding dryouts on the top channels.

  • Transient operation characteristics and control method in combined air-conditioning systems

    Jongsoo Jeong, Kiyoshi Saito, Sarngwoo Karng, Seoyoung Kim, Kwangho Kim

    SCIENCE AND TECHNOLOGY FOR THE BUILT ENVIRONMENT   23 ( 4 ) 567 - 581  2017  [Refereed]

     View Summary

    This study examines, using actual driving and simulations, transient operation characteristics and control methods for a combined system. It consists of both single-stage compression-type and single-effect absorption-type refrigerators and is driven by the shaft power and waste heat from a gas engine. Given the complicated nature of the system, determining the unsteady-state performance and control characteristics of the entire system is difficult. Hence, it must be equipped with an adequate control system to maintain acceptable system performance. Our results reveal that this system is controlled, as predicted, under unsteady-state conditions by using a novel control method. The unsteady-state simulation model is validated by comparing the driving results with the simulated results. Thus, gas-engine-driven combined air-conditioning systems possess a response time similar to absorption-type refrigerators. This indicates that the transient response of the entire system is governed by the absorption-type refrigerator, although the cooling capacity of the absorption-type refrigerator is only 13% of the entire cooling capacity. Therefore, when designing the control system of the combined system, the fact that the entire combined system is mainly governed by the absorption-type refrigerator should be considered despite its low cooling capacity.

    DOI

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    2
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  • Solar-assisted single-double-effect absorption chiller for use in Asian tropical climates

    Arnas Lubis, Jongsoo Jeong, Kiyoshi Saito, Niccolo Giannetti, Hajime Yabase, Muhammad Idrus Alhamid, Nasruddin

    RENEWABLE ENERGY   99   825 - 835  2016.12  [Refereed]

     View Summary

    Solar energy is accessible throughout the year in tropical regions. The latest development of absorption chillers has demonstrated that these systems are suitable for effective use of solar energy. The utilisation of solar energy for heat-driven cooling systems has significant advantages. Without a doubt, solar energy represents a clean energy source that is available without any additional fuel cost, and that can be proportionally accessible when the cooling load increases during the middle hours of the day. This study focuses on a single-double-effect absorption chiller machine that was installed in Indonesia. The system is driven by a dual-heat source that combines gas and solar energy. This system is characterised by simulating its performance in various conditions in terms of the cooling water (28-34 degrees C) and the hot water (75-90 degrees C) inlet temperatures. The reference operating condition of this system is 239 kW of cooling capacity. The mathematical model is validated and shows a good agreement with experimental data. In the operative range considered, simulation results yield a coefficient of performance between 1.4 and 3.3, and a gas reduction ratio from 7 to 58% when compared to a double-effect absorption chiller driven by gas. Based on the simulation results, this system is expected to have a good potential for widespread use in tropical Asia regions. (C) 2016 Elsevier Ltd. All rights reserved.

    DOI

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    65
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  • Wetting behavior of a liquid film on an internally-cooled desiccant contactor

    Niccolo Giannetti, Seiichi Yamaguchi, Kiyoshi Saito

    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER   101   958 - 969  2016.10  [Refereed]

     View Summary

    Heat and mass transfer processes performed by using thin liquid films are recurrent in a series of technical applications. The circumstances under which dry spots appear on the exchange surface for the film breakage, as well as the extent of the wetted part of the surface and the liquid vapor interface, are critical to predict and control the performances of these devices. To characterize the wetting behavior of liquid films on internally-cooled desiccant contactors, this paper originates from an experimental study and, adopting a standpoint useful for a practical interpretation of wettability measurements, introduces a corresponding theoretical model based on the principle of minimum energy. Both the estimation of the wetted area by image processing of the test section and the theoretical model highlight a hysteresis phenomenon of the film wetting behavior for gradually increasing and decreasing liquid flowrates. The modeling approach, experimental results and a first comparison are hereby presented and discussed. Quantitative and qualitative agreement appears promising for a further employment of the model in actual system design and control. (C) 2016 Elsevier Ltd. All rights reserved.

    DOI

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    29
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  • Heat and mass transfer characteristics of a dehumidifier using an ionic liquid for a liquid desiccant system

    Tadashi Usuzaka, Yuto Kobayashi, Seiichi Yamaguchi, Kiyoshi Saito, Hiroshi Nakayama, Youichi Miyaoka, Xinming Wang

    ACRA 2016 - 8th Asian Conference on Refrigeration and Air-Conditioning    2016

     View Summary

    We studied an air-liquid contactor that uses an ionic liquid as the absorptive solution, in the context of employing liquid desiccant systems for air humidity control. Most liquid desiccant systems use a packed column air-liquid contactor with lithium chloride as the absorptive solution. One of the advantages of using ionic liquids is that some of them are not corrosive towards aluminum or copper. Provided that an air-liquid contactor with ionic liquid can achieve the same or higher performance than a packed column air-liquid contactor, this component can be constructed from metal which allows it to be redesigned to improve the system performance. Therefore, the ultimate purpose of this study is to evaluate the potential of an aluminum-fabricated air-liquid contactor which uses an ionic liquid as the working fluid, and to design a system that can both dehumidify and regenerate the absorptive solution more effectively. In addition, the associated heat, mass and momentum transfer phenomena, were studied to clarify the performance of the air-liquid contactor. An experimental air-liquid contactor apparatus using an ionic liquid was used to measure temperature, concentration, mass flow rate, pressure, and humidity. By adjusting temperature, humidity, and air flow velocity, it was found that the air-liquid contactor using an ionic liquid showed comparable dehumidification performance as the lithium chloride system. This suggests the feasibility of an air-liquid contactor made of metal
    such a contactor can be redesigned to further improve its performance.

  • Experimental study on heat and mass transfer performance of a falling film absorber

    Motohiro Takigiri, Shouta Hatada, Seiichi Yamaguchi, Kiyoshi Saito, Yonezou Ikumi

    ACRA 2016 - 8th Asian Conference on Refrigeration and Air-Conditioning    2016

     View Summary

    The objective of this study is to evaluate the performance of a falling film absorber for absorption refrigeration machines. Experiments with smooth and enhanced tubes were conducted to measure the heat transfer coefficient of this component in a wide range of mass flow rates, at temperature levels corresponding to an absorption chiller application case. The aim of this study is to experimentally clarify the absorption phenomenon of smooth and enhanced tubes in a wide range of mass flow rates, which would then be useful in designing absorption systems. Regarding the working medium, LiBr-H2O solution was used as the absorbent and water as the refrigerant. Additionally, 1-ocatanol was added as a surfactant. The experimental apparatus consists of 10 horizontal tubes, a distributer, and a desorber. A falling film absorber is that absorption falls from the distributer to the horizontal tubes, which are surrounded by water vapor. The flowing behavior of the absorptive solution on horizontal tubes influences heat and mass transfer coefficient. The mass flow rate and shape of the tube has influence on the flowing behavior. Hence, the experiment was conducted in a wide range of mass flow rate and using different tubes with smooth or enhanced surfaces. The heat transfer coefficient was calculated from the heat transfer rate. As a result, the differences in the heat transfer performance of the absorber for each kind of tube were clarified. It was concluded that the shape of the tube significantly influences the heat transfer coefficient.

  • Analytical description of falling film absorption

    Giannetti N, Rocchetti A, Saito K, Yamaguchi S

    ACRA 2016 - 8th Asian Conference on Refrigeration and Air-Conditioning    2016  [Refereed]

  • Effect of Gas-Liquid Contactor Structure on the Dehumidification Performance of a Liquid Desiccant System

    Richard Jayson VARELA, Seiichi YAMAGUCHI, Kiyoshi SAITO, Masatoshi HARADA, Hikoo MIYAUCHI

    The Proceedings of the Symposium on Environmental Engineering   2016.26   402 - 402  2016

    DOI

  • High Efficiency Air Conditioning System for Data Centers Part 1 : Characteristic Analysis of the Pump cycle

    Techinical Papers of Annual Meeting the Society of Heating,Air-conditioning and Sanitary Engineers of Japan   2014   21 - 24  2016

    DOI CiNii

  • High Efficiency Air Conditioning System for Data Centers Part 2 : Control of the Pump cycle

    Techinical Papers of Annual Meeting the Society of Heating,Air-conditioning and Sanitary Engineers of Japan   2014   25 - 28  2016

    DOI CiNii

  • Entropy parameters for falling film absorber optimization

    Niccolo Giannetti, Andrea Rocchetti, Arnas Lubis, Kiyoshi Saito, Seiichi Yamaguchi

    APPLIED THERMAL ENGINEERING   93   750 - 762  2016.01

     View Summary

    A local entropy generation analysis, for water vapor absorption in LiBr-H2O solution, is performed referring to velocity, temperature and concentration fields obtained from the numerical solution of mass and energy transport equations. The hydrodynamic description is based on Nusselt boundary layer assumption and the actual amount of irreversibility introduced is determined for an absorptive falling film over a cooled horizontal tube inside the absorber. Results are explored in different operative conditions in order to examine the impact of the various irreversibility sources in a wide operative range. A least irreversible solution mass flow-rate can always be identified. Furthermore, a simple and general thermodynamic analysis, carried out regarding a refrigerating and a heat boosting applications, makes evidence of a dimensionless group "Q/sigma T" that separates the weight of the irreversibilities and gives the way to an optimization criterion applied to the absorber in order to improve the whole system efficiency. Both thermodynamic equilibrium and sub-cooling conditions of the solution at the inlet are considered for typical temperature and concentration of refrigerators' absorbers and heat transformers' absorbers. Results suggest the importance to work at reduced mass flow-rates with a thin uniform film. In practice, tension-active additives are required to realize this condition. Also, it is highlighted that the two parameters defined with reference to the dimensionless group "Q/sigma T" can be maximized by specific values of the tube radius, operative Reynolds number, solution sub-cooling and temperature difference between the wall and the inlet solution. (C) 2015 Elsevier Ltd. All rights reserved.

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  • SOLAR AIR-CONDITIONING SYSTEM AT THE UNIVERSITY OF INDONESIA

    Hajime Yabase, Kiyoshi Saito, Arnas Lubis, Idrus Alhamid, Nasruddin

    INTERNATIONAL JOURNAL OF TECHNOLOGY   7 ( 2 ) 212 - 218  2016

     View Summary

    Indonesia's economic growth has continued at a steady rate of approximately 5% to 6% annually, and energy consumption in the entire country has been increasing year by year. Demand for air conditioning in buildings is expanding. In line with this expansion, a 239 kW solar air-conditioning system using a single-double effect combined absorption chiller was installed in a building at the University of Indonesia's Faculty of Engineering located in Depok city, near Jakarta, with the aim of reducing greenhouse gas emissions. We collected and analyzed data from this air-conditioning system to better comprehend its performance. We report the outline and the performance of the chiller and the air-conditioning system.

    DOI

    Scopus

    3
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  • Thermodynamic optimization of three-thermal irreversible systems

    Niccolo Giannetti, Andrea Rocchetti, Kiyoshi Saito

    International Journal of Heat and Technology   34   S83 - S90  2016.01

     View Summary

    Multi-temperature-level systems enlarge the prospects and degrees of freedom for an effective design and an environment-friendly use of energy. Based on a general thermodynamic model of three-thermal cycles and finite thermal capacity of the heat sources, this paper aims at the analysis and the performance optimization of these systems by considering the influence of irreversibility. Suitable dimensionless parameters for an overall optimization are introduced and their influence on the cycle efficiency is investigated. This approach identifies the limitations imposed to the physical processes by accounting for the inevitable dissipation due to their constrained duration and intensity, and constitutes a general thermodynamic criterion for the optimization of three-thermal irreversible systems. Dependence on the main factors is highlighted in a way that shows how to change them in order to improve the overall efficiency. Under this point of view, the analysis evaluates COP improvements and can be used to perform plant diagnostics, besides predicting the system performance. The use of this criterion is exemplified for the absorption chiller application case.

    DOI

    Scopus

    15
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  • Irreversibility analysis of falling film absorption over a cooled horizontal tube

    Niccolo Giannetti, Andrea Rocchetti, Kiyoshi Saito, Seiichi Yamaguchi

    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER   88   755 - 765  2015.09

     View Summary

    Based on a numerical study of the water vapour absorption process in LiBr-H2O solution, for a laminar, gravity driven, viscous, incompressible liquid film, flowing over a horizontal cooled tube, irreversibilities related to fluid friction, heat transfer, mass transfer and their coupling effects have been locally and globally examined. The hydrodynamic description is based on Nusselt boundary layer assumptions. The tangential and normal velocity components, respectively obtained from momentum and continuity equations, have been used for the numerical solution of mass and energy transport equations in the two-dimensional domain defined by the film thickness and the position along the tube surface. Local entropy generation calculation can be performed referring to the calculated velocity, temperature and concentration fields. Results have been explored in different operative conditions, in order to examine comprehensively the impact of the various irreversibility sources and to identify the least irreversible solution mass flow-rate for the absorber. As a parallel, a refined understanding of the absorption process can be obtained. Considering absorption at the film interface and cooling effect at the tube wall, the analysis thermodynamically characterises the absorption process which occurs inside actual falling film heat exchangers and establishes a criterion for their thermodynamic optimisation. Results suggest the importance to operate at reduced mass flow rates with a thin uniform film. Meanwhile, tension-active additives are required to realise this condition. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI

    Scopus

    16
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  • Thermodynamic Analysis of Irreversible Heat-transformers

    Niccolo Giannetti, Arnas, Andrea Rocchetti, Kiyoshi Saito

    MAKARA JOURNAL OF TECHNOLOGY   19 ( 2 ) 90 - 96  2015.08

     View Summary

    Absorption heat transformers extend the possibilities for efficient and environment-friendly energy conversion processes. Based on a general thermodynamic model of three-thermal cycles with finite thermal capacity of the heat sources, this paper is intent upon analyzing and optimizing the performance of absorption heat transformers, by including the influence of irreversibility in the analytical expression of the system efficiency. Dimensionless parameters for an overall optimization are defined and a first screening is performed to clarify their influence. Dependence on the main factors is highlighted to suggest how to change them in order to enhance the whole system performance. Under this point of view, the analysis evaluates coefficient of performance (COP) improvements and can be used to perform existing plant diagnostics, besides predicting the system performance. The use of this criterion is exemplified for specific heat transformers data from literature. This approach identifies the limitations imposed to the physical processes by accounting for the inevitable dissipation due to their constrained duration and intensity, and constitutes a general thermodynamic criterion for the optimization of three-thermal irreversible systems.

    DOI

  • Local entropy generation analysis of water vapour absorption in a LiBr-H2O solution film, over a horizontal cooled tube

    Niccolò Giannetti, Andrea Rocchetti, Kiyoshi Saito, Seiichi Yamaguchi

    Refrigeration Science and Technology     786 - 793  2015  [Refereed]

     View Summary

    This study is based on a numerical analysis of water vapour absorption in a laminar, gravity driven, viscous, incompressible liquid film of LiBr-H2O solution, flowing over a horizontal cooled tube. The hydrodynamic description is based on Nusselt boundary layer assumptions. A local entropy generation calculation can be performed referring to velocity, temperature and concentration fields. From a general form of volumetric entropy generation, a suitable expression for the absorption process has been obtained and different irreversibility sources have been highlighted. The impact of each term (fluid friction, heat transfer, mass transfer and their coupling effects) has been locally examined. Results have been explored for different tube radii, wall temperatures and operative conditions (representing both chiller and heat transformer configurations), in order to characterise the process from a second law point of view and establish a criterion for the optimisation of the absorber.

    DOI

    Scopus

  • Study on Control of Desiccant Air-Conditioning System for Low-Humidity Environment : Part1-Basic Characteristics of Controlled System

    ITO Suguru, OMAGARI Yasuhito, YAMAGUCHI Seiichi, SAITO Kiyoshi

    Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan   40 ( 224 ) 9 - 17  2015

     View Summary

    The purpose of this study is to develop a supply air dew point temperature control of a desiccant air-conditioning system for low-humidity environments. To develop the control, we need to know the basic characteristics of the desiccant air conditioning system, which is a controlled system. In this paper, we construct a mathematical model and analyze systematically the basic characteristics of the controlled system. Specifically, we investigate the static and dynamic characteristics of the controlled system with respect to manipulated variables such as desiccant-wheel rotary speed and regeneration outside air flow rate. For static characteristics, we investigate the relation between controlled and manipulated variables and examine the influence of manipulated variables on controlled variables. For dynamic characteristics, we investigate the step response of controlled variables and examine the responsivity or overshoot of controlled variables.

    DOI CiNii

  • Evaluate VRF Compression Heat-pump System under Steady-State Analysis:-1st Report: Analysis of Numerical Simulation and Experimental Study Focusing on Changing the Number of Active Indoor Units-

    MATSUMOTO Kuniyasu, OHNO Keisuke, SAITO Kiyoshi, KISHIMOTO Tetsuro

    Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers   32 ( 2 ) 95 - 107  2015

     View Summary

    Recently at commercial buildings and office buildings it is popular to install variable refrigerant flow compression type heat pump system. Those systems have many merits for users and constructors. At first, Cooling capacity's range are wide for choosing adequate capacity, secondly the facilities were downsizing and separable to small units for easy transportation, thirdly multi indoor units can be controlled independently and so on. On the other hand, because driving conditions are changing dynamic for meeting user's needs, it is complicated to adequate driving conditions to save energy consumption. We constructed simulation model by mathematical methods and we tested VRF compression heat-pump system at test room which can adjust temperature conditions freely. We evaluated the system changing the number of active indoor units on partial lord and we showed the effect of COP on this conditions.

    DOI CiNii

  • Entropy parameters for desiccant wheel design

    Niccolo Giannetti, Andrea Rocchetti, Kiyoshi Saito, Seiichi Yamaguchi

    APPLIED THERMAL ENGINEERING   75   826 - 838  2015.01  [Refereed]

     View Summary

    In this work a thermodynamic analysis of a desiccant wheel is proposed to investigate and identify the optimum size and operating regime of this device. A steady state entropy generation expression, based on effectiveness parameters suitable for desiccant wheels operability, is obtained applying a control volume approach and assuming perfect gas behaviour of the binary air-vapour mixture. A new entropy generation number N-L, is defined using a minimum indicative value of the entropy generation S-L,S-min and investigated in order to obtain useful criteria for desiccant wheels optimization. The effectiveness-NTU design method is employed by combining solution of thermal exchange efficiency for rotary heat exchanger with the characteristic potential method, under the conditions of heat and mass transfer analogy. The analysis is applied to a specific desiccant wheel and N-L, variation with NTU is explored under various operative conditions and wheels characteristics in terms of dimensionless velocity and flow unbalance ratio. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI

    Scopus

    17
    Citation
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  • Comparison of heat transfer coefficient during evaporation of natural refrigerants and R-1234yf in horizontal small tube

    Kwang-Il Choi, Jong-Taek Oh, Kiyoshi Saito, Jong Soo Jeong

    INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID   41   210 - 218  2014.05  [Refereed]

     View Summary

    An experimental data comparison of evaporation heat transfer coefficient of R-744(CO2), R717(NH3), R-290(C3H8) and R-1234yf in horizontal small tubes was conducted under some various flow conditions. The experimental data were obtained over a heat flux range of 5 -60 kW m(-2), mass fluxes from 50 to 600 kg m(-2) S-1, saturation temperatures from 0 to 10 degrees C, and quality up to 1.0. The test section made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 1000 and 2000 mm, respectively, was heated uniformly by applying an electric power to the tubes directly. Effects of mass flux, heat flux, saturation temperature and inner tube diameter on heat transfer coefficient are reported in the present study. Among the present working refrigerants, R-744 has a highest heat transfer coefficient. Laminar flow was observed in the evaporative small tubes and considered in the modification of evaporation heat transfer coefficient correlations. (C) 2013 Elsevier Ltd and IIR. All rights reserved.

    DOI

    Scopus

    46
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  • Study on Free Cooling Combination Type Air Conditioning System for Data Centers:-1st Report: Mathematical Modeling and Static Characteristic Analysis

    UDAGAWA Yosuke, SEKIGUCHI Keisuke, YANAGI Masahide, SAITO Kiyoshi, OHNO Keisuke

    Trans.JSRAE   31 ( 2 ) 157 - 168  2014

     View Summary

    In the data center, air conditioning has been carried out throughout the year to remove waste heat of servers. In order to realize efficient cooling, it is important to use cold outdoor air in winter. Therefore we study the performance of the air conditioning system that uses outside air in winter. In the proposed system, it is possible to switch compression cycle and free cooling cycle. In this report, we construct the static mathematical models of this system and verify the validity of this mathematical model by experiment. Validity of the mathematical model has been confirmed as a result. And we elucidated the static characteristics of this system in regard to outdoor temperatures and Indoor temperatures.

    DOI CiNii

  • :Design Method for Solar Single-Double Effect Combined Absorption Chiller

    YABASE Hajime, SAITO Kiyoshi, JEONG Jongsoo

    Trans.JSRAE     431 - 437  2014

     View Summary

    Solar single-double effect combined absorption chiller has come into wide use compared with other types of solar absorption system because it is equipped with high-efficient double effect apparatus of helping solar heat. This paper reports the machine design to enhance the performance by solar heat. So far, thermal conductance KAs of elements composed in absorption chillae have been often limited in machine design because the change of KAs means remanufacture of the test machine. Hence, easily to realize the machine design with the most efficient performance COP in the objected system, we evaluated the performance with KAs designed by simulation, which is a good way to evaluate system performance easily without empirical method and leads to design to save time. Each KA needs to be concluded under the conditions of common parameter, for example, evaporator temperature, condensation temperature, pinch temperatures of heat exchangers, etc. In the simulation result, it is clarified that the reverse flow type can be the highest performance among several types of single-double effect absorption cycle suggested.

    DOI CiNii

  • Intermittent Driving Simulation of Compression type Heat Pump : 1st Report : Mathematical model and simulation of single-stage vapor compression type heat pump

    OHNO Keisuke, SAITO Kiyoshi, YAMAGUCH Seiichi, KISHIMOTO Tetsuro, MATSUMOTO Kuniyasu

    Trans.JSRAE   30 ( 2 ) 107 - 122  2013.06

     View Summary

    Compression-type heat pumps have been employed in many fields of refrigeration and air conditioning for achieving energy savings. In addition, the system operates at high efficiency under a variety of operating conditions throughout the year through various innovative components, such as the inverter, and the annual performance improvement. However, the running time of the system over the year under low load conditions is very long, and under such conditions, the system operates intermittently because of the difficulty in the continuous running of the compressor. Of course, because intermittent driving is made under such an operating condition, the performance can estimate that it decreases greatly easily, but it is the present conditions that field operation performance does not become clear almost. Therefore, the key goals of this study were to clarify the intermittent driving performance of the compression-type heat pump and to devise a way to improve its performance and develop an optimum operation method. As the first step, we constructed a mathematical model that can predict intermittent driving characteristics at the time of low load of the pump, which are crucial to investigation of the performance. The constructed model was validated experimentally. In summary, a mathematical model of the compression-type heat pump was constructed, and its validity was demonstrated via comparison of its results with those obtained experimentally.

    DOI CiNii

  • Numerical and experimental performance analysis of rotary desiccant wheels

    Seiichi Yamaguchi, Kiyoshi Saito

    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER   60   51 - 60  2013.05  [Refereed]

     View Summary

    In air-conditioning field, a dehumidification has become increasingly important for human health and comfort especially in hot and humid climates. However, a conventional mechanical dehumidification with a vapor compression refrigerator has some problems. Therefore, much attention has been paid recently to a desiccant air-conditioning system as an alternative to the conventional system. In this paper, we focus on a rotary desiccant wheel which is the main component of the desiccant air-conditioning system and develop and validate the mathematical model by comparison with experimental results. The validation is conducted under various operating conditions. The mathematical model discussed in this paper includes, for example, the entrance region effect in air channel, detailed diffusion phenomenon in porous solid. In experiments, effects of the regeneration air temperature, air superficial velocity, wheel thickness and wheel rotational speed on the desiccant wheel performance are investigated. In addition, the temperature and humidity distribution at the outlet of the desiccant wheel are measured. As a result, an average relative error between the predicted and the measured humidity ratio difference distribution is 3.3% and temperature difference distribution 10.8%. Moreover, the effect of the regeneration air inlet temperature, the air superficial velocity, wheel thickness and wheel rotational speed on the desiccant wheel performance are clarified and the predicted results are totally in good agreement with the measured results. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

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    110
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  • Thermodynamic performance of a hybrid air cycle refrigeration system using a desiccant rotor

    Kyudae Hwang, Chan Ho Song, Sung Ki Kim, Kiyoshi Saito, Sunao Kawai

    HEAT AND MASS TRANSFER   49 ( 3 ) 359 - 367  2013.03  [Refereed]

     View Summary

    Due to the concern on global warming, the demand for a system using natural refrigerant is increasing and many researches have been devoted to develop systems with natural refrigerants. Among natural refrigerant systems, an air cycle system has emerged as one of alternatives of Freon gas system due to environmentally friendly feature in spite of the inherent low efficiency. To overcome the technical barrier, this study proposed combination of multiple systems as a hybrid cycle to achieve higher efficiency of an air cycle system. The hybrid air cycle adopts a humidity control units such as an adsorber and a desorber to obtain the cooling effect from latent heat as well as sensible heat. To investigate the efficacy of the hybrid air cycle, the cooling performance of a hybrid air cycle is investigated analytically and experimentally. From the simulation result, it is found that COP of the hybrid air cycle is two times higher than that of the conventional air cycle. The experiments are conducted on the performance of the desiccant system according to the rotation speed in the system and displayed the feasibility of the key element in the hybrid air cycle system. From the results, it is shown that the system efficiency can be enhanced by utilization of the exhausted heat through the ambient heat exchanger with advantage of controlling the humidity by the desiccant rotor.

    DOI

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    9
    Citation
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