Atsushi Kanzawa

Thermal Performance of a Heat Storage Module Using PCM’s With Different Melting Temperatures: Mathematical Modeling

In the present study, the performance of a heat storage unit consisting of number of vertical cylindrical capsules filled with phase change materials, with air flowing across them for heat exchange has been analyzed. Earlier theoretical models did not consider temperature distribution in the radial direction within the capsules, an assumption that limits their applications for small diameter capsules. The mathematical model developed in this work is based on solving the heat conduction equation in both melt and solid phases in cylindrical coordinates, taking into account the radial temperature distribution in both phases. Heat flux was then evaluated at the surface of the first row of the capsules to determine the temperature of the air leaving that row by a simple heat balance. It was found that such computation may be carried out for every few rows rather than for a single row to minimize computer time. The simulation study showed a significant improvement in the rate of heat transfer during heat charge and discharge when phase change materials with different melting temperatures were used. Air must flow in the direction of decreasing melting temperature during heat charge, while it must be reversed during heat discharge.

Enhancement of charging and discharging rates in a latent heat storage system by use of PCM with different melting temperatures

Abstract A latent heat storage module with rapid charging and discharging rates has been developed. The heat storage module consisted of horizontal cylindrical capsules filled with three types of PCM with different melting temperatures. A numerical model has been developed to predict the transient behavior of the heat storage module. Both the experimental and numerical results showed some improvements in charging and discharging rates by use of a “three-type” PCM

Deformation and solidification of a droplet on a cold substrate

The numerical simulation of a droplet deformation and solidification on a cold substrate was performed with SMAC algorithm. The substrate temperature histories and the degree of deformation were measured by use of a droplet of n-eicosane and n-cetane. The numerical results showed good agreement with the measured ones. The solidification of a droplet on a substrate occurs immediately after the deformation. A simple model to estimate the deformation and the solidification time was also proposed. Both the normalized deformation and solidification time are proportional to the 0.2 power of the Reynolds number. The solidification time is two orders of magnitude higher than the deformation time.

Second law optimization of a latent heat storage system with PCMS having different melting points

Abstract The exergy efficiency, as well as the charging and discharging rates, in a latent heat storage system can be improved by use of the PCMs having different melting points. The melting point distribution of the PCMs has substantial effects on the exergy efficiency. The optimum melting point distribution of the PCMs has been estimated from numerical simulations and also from simple equations. The fast charging or discharging rate leads to high exergy efficiency.

Thermal energy storage by the chemical reaction augmentation of heat transfer and thermal decomposition in the CaOCa(OH)2 powder

Abstract The present paper is concerned with the utilization of a thermal decomposition reaction, Ca(OH) 2 ⇄CaO + H 2 O, for energy storage. One of the important problems in this case is how to heat up and decompose the powder of Ca(OH) 2 effectively, where the thermal conduction is poor. In this study, the effect of copper plates, which are placed in the powder of Ca(OH) 2 as heat-transfer fins, is investigated experimentally and numerically. The results show that the Cu-plates are very effective for heat transfer and the thermal decomposition, and that the optimum configuration of the Cu-plate is 5–10 cm in height and 0.5–1 cm in interval for the condition of this study.

Thermal plasma treatment of titanium carbide powders: Part II. In-flight formation of carbon-site vacancies and subsequent nitridation in titanium carbide powders during induction plasma treatment

The in-flight modification of titanium carbide powders was carried out in radio-frequency (rf) inductively coupled plasmas. The powders were partially melted and evaporated, and then subjected to modifications in morphology, size, and chemical composition. Both the Ar–H 2 and Ar–N 2 plasma treatments induced the formation of carbon-site vacancies in titanium carbide. The mixing of NH 3 to Ar–H 2 plasma at the plasma tail, and the Ar–N 2 plasma treatment resulted in the partial substitution of carbon by nitrogen. The variation in physical and chemical modification was discussed compared with the predictions by the thermochemical analysis, and the numerically obtained heat transfer of our preceding paper.

Thermal plasma decomposition of chlorofluorocarbons

Dichlorodifluoromethane was decomposed by a thermal argon plasma generated by a DC are discharge. The experiments and the kinetic calculations showed that the complete decomposition of the chlorofluorocarbon proceeded with the simultaneous additions of hydrogen and oxygen. Both the expertimental and calculated results confirmed that it is favorable, for the decomposition, not to quench the products but to add an excess of hydrogen over the stoichiometric amount, which leads to a reduction in chlorine formation.

Proposal of a chemical heat pump with paraldehyde depolymerization for cooling system

A chemical heat pump system with paraldehyde/acetaldehyde (Pa/A) is proposed for a cooling system. This chemical heat pump is similar to the vapor-compression heat pump. The coefficient of performance (COP) was estimated from equilibrium data. The coefficient of performance (COP) was estimated from equilibrium data. The pressure and the concentration at the reaction equilibrium state were measured for estimation of the performance of the CHP. The COP of the Pa/A system is same as the COP of a vapor-compression heat pump with CFCs.

A solar-powered adsorption cooling system using a silica gel–water mixture

Solar-powered adsorption cooling is an attractive solar energy application. Metallic solar collectors with fins have been used to increase the thermal conductivity in solar collectors. This approach has a negative effect due to solar energy loss by reflection and heat loss resulting from the sensible heat of the metal. For these reasons, a direct-radiation absorption collector is proposed here. The effects of the wavelength of the absorbed light, types of silica gel used and additives to improve the absorptivity have been investigated. We have verified that blue silica gel has a better absorptivity in the near-infrared region than white silica gel. The addition of activated carbon to the silica gel improves the desorption rate and regeneration temperature of the packed bed.

Enhancement of the deposition rate of TiO2 film in radio frequency reactive sputtering

Titanium oxide thin films were prepared using rf reactive sputtering in which a titanium target was sputtered in a mixture of Ar and reactive O2 gas. The flow modulation of reactive gas was proposed to enhance the deposition rate of the film which is generally low in continuous flow reactive sputtering. The experimental results indicated that the deposition rate could be enhanced maintaining the film stoichiometric ratio of TiO2. The enhancement occurred because the modulated flow appeared to reduce the formation of compounds on the target surface which inhibit sputtering under continuous flow conditions. The effects of the flow modulation were understood by adapting a reactive sputtering theoretical model.