A 3D pore-scale model for macro-encapsulated phase change material-metal foam hybrid energy storage system

Abstract

A 3D pore-scale model is presented to predict the energy storage characteristics of a macro-encapsulated phase change material (PCM)-metal foam hybrid energy storage system. A single capsule with metallic shell filled with PCM-metal foam composite is considered. The energy transfer from a heat transfer fluid (HTF) flowing over the capsule, the evolution of temperature, and the melting of PCM in the metal foam pores within the capsule are simulated using the model. The model resolves the geometry of the individual pores in the metal foam and thus captures the local heat transfer between the metal foam and PCM, and the movement of PCM solid-liquid interface during melting inside each pore. Heat transfer from the HTF to the metal shell, metal foam, and PCM, and the resulting melting and energy storage characteristics are predicted by using the model. The effects of important geometrical parameters such as capsule size, capsule shell thickness, pore size distribution and porosity of the foam are studied. As a significant fraction of energy storage is in the form of sensible energy, the total energy storage with the variation of these parameters are quantitatively compared. For the range of parameters considered in the study, it is found that the increase in foam porosity from 50 % to 70 % increases the total energy storage by 5.41 % while increasing the average pore radius from 0.5 mm to 0.9 mm keeping the porosity 60 %, increases the total energy storage by only 1.54 %. Change in capsule inner diameter from 7 to 11 mm increases the total energy storage by 211.99 % although the energy stored per unit volume is reduced by 7.55 %. Similar effect is also observed for increase in shell thickness from 0.5 to 1.5 mm.