STUDY OF HEAT TRANSFER DURING SOLIDIFICATION OF PHASE CHANGE MATERIAL INSIDE CAPSULES

摘要

In many countries cool storage systems for air conditioning are largely used for two reasons in order to limit the use of greenhouse gases used in conventional systems in a hand and to decrease peak electrical charge in other hand. These systems include phase change materials (PCM) contained in small capsules. This paper is mainly aimed to extend the conduction model of Bilir and Ilken (2005) describing inward solidification of a phase change material inside capsules of spherical/cylindrical geometries to be applicable even for rectangular capsules. The physical model is based on general thermal conduction equation taking account of the capsule geometry and coupled to convective boundary condition. The numerical solution is realised using enthalpy method with control volume approach. The model is validated by comparison with results available in literature for the three kinds of capsules: spherical, cylindrical and rectangular. Then the model is used for a study of solidification of a PCM inside these capsules. Variation of the dimensionless temperature and enthalpy at the centre of the three capsules is presented. Furthermore, the present model is used to study inward solidification process for a typical capsule (spherical Φ77 mm) as practical case where operational parameters: coolant fluid temperature, initial PCM temperature and convective heat transfer coefficient at the surface of the capsule and their effect on total time for solidification of the capsule are investigated.