Melting and energy storage characteristics of macro-encapsulated PCM-metal foam system

Abstract

In this study a novel encapsulated phase change material (PCM)-metal foam hybrid system is proposed for energy storage applications. The idea is to improve the melting rate of PCM in encapsulated PCM systems with the introduction of metal foam structures inside the capsules. The main objective of the work is to develop a numerical model which can simulate the melting of PCM in this hybrid system due to the flow of heat transfer fluid (HTF) around the capsule with the resolution of the metal foam geometry at the pore-scale level. The developed model couples geometry creation, phase change and fluid flow models. The foam geometry is created using overlapping circular pores with random location, radii, and overlap. The phase change model is developed by modifying the enthalpy method to incorporate the presence of four phases – HTF, metal, solid PCM, and liquid PCM. This is coupled with an implicit flow solver within a finite volume framework. An in-depth analysis of a base case is conducted by fixing different geometrical parameters such as capsule size, porosity, pore size distribution and shell thickness. The results of the base case are then compared in subsequent parametric studies, by varying one geometrical parameter at a time. The parametric studies reveal that the structure of the metal foam plays an important role in determining the melting pattern and the energy storage characteristics because of its net-like large inner surface area. It is found that the melting time is reduced for lower capsule size, lower porosity, and higher shell thickness. The average pore size and range are crucial in determining the rate of melting.