Abstract

We carried out synthesis of single-walled carbon nanotubes (SWCNTs) in the hot-wall reactor by alcohol catalytic chemical vapor deposition using an Ir as a catalyst. By optimizing the ethanol flow rate, SWCNTs were grown at the growth temperature between 700 °C and 900 °C. Raman results using the four excitation wavelengths of 488, 532, 671 and 785 nm showed that the diameters of most SWCNTs grown from an Ir catalyst were less than 1.0 nm at 700 °C and 800 °C. When the growth temperature was above 800 °C, vertically-aligned SWCNTs were grown, and the thickness reached 1.8 μm after the growth at 900 °C for 60 min under an ethanol flow rate of 500 sccm. However, at 900 °C, the diameters of SWCNTs were enlarged and most of them were distributed above 1 nm. Our result demonstrates that an Ir catalyst is useful to obtain small-diameter SWCNTs on a large scale.

In this study, we have developed a heat storage system, which is able to store waste heat and release it to an appropriate heating equipment elsewhere, in order to improve utility of waste heat and thus reduce environmental pollutants. The heat of solution of a solid-liquid reaction was adopted for the heat storage system. In this system, the reactant was also used as heat transfer medium and being sent to heating parts. Therefore, the evaporator that has been used in conventional chemical heat storage can be omitted to reduce the device size and for motive use. The heat value, heat release rate and cyclic performance of CaCl₂/H₂O system were measured. The results indicated that the heat of solution was proportional to the mass concentration as far as the reaction reached its saturation solubility under ambient temperature. In addition, the heat value per unit mass was higher at lower concentration than that at higher concentration. During the first 1 minute, the heat output of 5.06kW/L- H₂O was obtained for CaCl₂ (s) /H₂O (l) when the reaction reached its saturated solubility. It was found no degradation in chemical composition after 50 times of cyclic operation.

A heat storage system without an evaporator promises high-density heat storage and a high rate of heat output since the solid-liquid product that is formed will itself be transferred as a heat medium to an object that requires heat. In this study, we compared the characteristics of this system using solid CaCl₂, CaBr₂, or LiBr with liquid H₂O as reactants for the storage system. The exothermic heat produced for each reaction was measured and a relationship between the equivalence ratio and the reaction heat was observed. Heat values of 622, 534, and 481 kJ/L were obtained for CaBr₂/H₂O, LiBr₂/H₂O, and CaCl₂/H₂O, respectively. CaBr₂ has the highest solubility and heat storage density of the three materials, as well as the highest heat value. The rate of heat output using CaBr₂/H₂O reached 10 kW/L 10 s after the reaction was initiated, and thus CaBr₂ is considered the most effective material for this system.