Iwane Fujii

An analysis of isothermal phase change of phase change material within rectangular and cylindrical containers

Abstract In this paper, a simple computational model for isothermal phase change of phase change material (PCM) encapsulated in a single container is presented. The mathematical model was based on an enthalpy formulation with equations cast in such a form that the only unknown variable is the PCM’s temperature. The theoretical model was verified with a test problem and an experiment performed in order to assess the validity of the assumptions of the mathematical model. With very good agreement between experimental and computational data, it can be concluded that conduction within the PCM in the direction of heat transfer fluid flow, thermal resistance of the container’s wall, and the effects of natural convection within the melt can be ignored for the conditions investigated in this study. The numerical analysis of the melting time for rectangular and cylindrical containers was then performed using the computational model presented in this paper. Results show that the rectangular container requires nearly half of the melting time as for the cylindrical container of the same volume and heat transfer area.

Studies of an energy storage system by use of the reversible chemical reaction: CaO + H2O ⇌ Ca(OH)2

Abstract Due to no heat losses under the heat storage period, thermochemical energy storage is remarked as one of promising means particularly for long-term heat storage. Under such circumstances, some heat storage tests were carried out using an improved storage system built for heat recovery utilizing solid-gas reaction: CaO + H 2 O ⇌ Ca(OH) 2 . Besides descriptions on the system outline, several experimental results on heat charging and discharging are shown here together with a new method applied for detecting the completion of Ca(OH) 2 dehydration. The results obtained here will also supply useful information in designing a storage system for solar energy.

Behavior of Ca(OH)2/CaO pellet under dehydration and hydration

With construction of a thermochemical energy conversion prototype system to store solar heat, thermal dissociation of pellets of Ca(OH)2 and hydration of CaO have been investigated in some detail for its application to the system. The inorganic substance is very attractive as a material for long term heat storage, but molar density changes associated with the reaction are fairly large. Therefore, this factor has been taken into account in the kinetic equation. The importance of additives and pellet size has been discussed considering reactivity and strength of pellets. An analysis has been attempted when chemical reaction is important. The deformation of pellets was observed during hydration.

A Theoretical Analysis and an Analogue Test of Two-Dimensional Thermal Stress : The Case When the Temperature of Boundaries for a Rectangular Cross Sectional Solid is Suddenly Changed

Though there are many papers about thermal stress, it is generally fairly difficult to solve two-dimensional thermal stress problems exactly by means of theoretical analysis except in some special cases. So most of interesting problems from an engineering view point are frequently treated by approximate calculations such as the finite-difference methods, or by experimental approaches as photoelasticity method. Under these circumstances, we performed an analogue test of two dimensional thermal stress taking place in a rectangular block where boundary temperature is suddenly changed, using characteristics of laminar viscous flow and pressure expansion. On the other hand, we analyzed theoretically the thermal stress described above and compared the numerical calculations with the experimental results. By calculation and experiment, the general tendency in such a thermal stress can be made clear and this physical analogue technique is also applicable for two-dimensional problems.