Modeling Thermal Storage in Wax-Impregnated Foams with a Pore-Scale Submodel

Calculations of heat transfer through porous foams filled with phase-change materials are often performed using either an effective medium approach or a coupled two-temperature model. These models are generally applied to simulate heating processes that occur over a few hours, thus allowing for an assumption of effective melting front in which both liquid and solid phases are present or clear delineation of liquid and solid phases. However, in the instance of a rapidly changing heating process, a melting front cannot be assumed due to the possibility that layers of phases exist. A model has been developed to allow for variable phase sections within the foam without requiring an assumption of local thermal equilibrium, in which the temperature of the foam and phase-change materials are equal to each other at a set point. By assuming spherical pores with microscopic temperature variations therein, the model allows for the existence of multiple phases within a single foam pore while also integrating an effective medium model of the overall foam/wax system. The overall model is compared and validated with experimental results and models from literature. Following validation, cases are assessed under various time scales to demonstrate the model's versatility.