Thermal performance analysis of phase change material based systems with volumetric expansion and shrinkage

Abstract

Present thesis reports the theoretical investigations pertaining to the heat transfer characteristics of phase change materials (PCMs) during melting/solidification incorporating volumetric expansion and shrinkage void in the thermal energy system. The objective of the present study is to investigate the thermal performance of PCM based systems for numerous applications including thermal management of electronic devices and thermal energy storage systems. Initially, a one dimensional analytical model is proposed to analyze the solidification/melting of phase change materials (PCMs) incorporating the shrinkage/expansion void in an annulus. An air-PCM system is considered in the analysis; paraffin wax is considered as PCM and filled inside the annulus, while air is considered inside the void. Separation of variable method involving Bessel’s function is employed to obtain temperature distribution for air, solid and liquid domains and to locate interface positions. Stefan condition and mass conservation equation are used at the interfaces. Effect of various parameters such as density ratio, end wall temperature, and radius ratio on the solidification/melting of PCM have been investigated. Results obtained from the analytical model are found to be in good agreement with the existing test results. Next, the analysis is extended to investigate the thermal performance of PCM/PCM-metal foam (MF) composite based rectangular energy storage system incorporating the volumetric change and void in PCM with steady and transient heat loads. Separation of variable method with Bessel function has been employed to solve the conduction equation associated with different thermal boundary conditions; Stefan condition and mass balance equation are used to locate the interface position. Paraffin wax and copper is considered as PCM and MF material, respectively. Solutions are obtained for temperature distribution and interface position for different domains namely, air, solid, and liquid. Effect of various parameters such as density ratio, wall heat flux, convective heat transfer coefficient, and porosity on the melting/solidification of PCM are investigated. Also, the energy stored/extracted in PCM-MF composite is greater compared to pure PCM. The theoretical prediction exhibits good agreement with existing test data. Keywords: Phase change material (PCM), Shrinkage/expansion, Void, Metal foam (MF), Melting/solidification