INVESTIGATIONS OF PHASE CHANGE MATERIALS USED IN SOLAR ENERGY SYSTEMS AS THERMAL ENERGY STORAGE

Abstract

This study address to numerically investigate the performance and behavior of the phase change material (PCM)during melting and solidification process inside the annulus between two concentric pipes. Local paraffin wax has selected as PCM, which has a melting temperature of 334K. Water is chosen as the heat transfer fluid flows through the inner pipe (hot water for charging and cold water for discharging). The thermal conditions of the outer pipe was selected to be insulated (adiabatic) and the inner pipe was kept at constant temperature (isothermal). Finite volume method (FVM) is used to solve the governing equations of transient fully developed laminar flow. The fluid flow in the mushy zone was accounted for using the Darcy drag source term in momentum equation, and the liquid percentage in each cell was updated using the enthalpy-porosity method. The outcomes of the simulation are represented as contours of average temperature and liquid fraction distribution in the flow domain. The simulation findings indicate that convective heat transmission has considerable impact on the melting of the upper zone of the (PCM) but has less impact on the melting of the lower zone. It is obvious that the melting process ends up with a relatively short period of time in the top region, followed by the middle region, and finally the bottom region of the annulus. During the solidification process, natural convection plays a role only during the early periods of solidification and then thermal conduction remains the dominant heat transfer mode for the entire process. The predicted result shows the capturing phenomenon: primary heat conduction in all regions and then heat convection and conduction become dominant in the top and bottom regions, respectively. The maximum and minimum temperature changes near the outer pipe surface during the 16 hours are 56.25 % and 42.5 %, respectively.