Interfacial and capillary pressure effects on the thermal performance of wax/foam composites

A numerical investigation study was performed to study the phase change behavior of wax/foam composite encapsulated in an aluminum casing. Two types of foam materials, namely, aluminum and carbon, were infiltrated with paraffin wax. The progress of melt interface and temperature distribution within the encapsulated composite was analyzed using computational fluid dynamics software (CFD). A two-energy equation model was implemented in the CFD software through the use of user defined function (UDF). Interfacial effects influencing the heat transfer process at the casing-composite junction and between the wax-foam surfaces within the composite were addressed through the use of separate UDF. In addition, the effect of capillary pressure developed within the foam matrix was incorporated using an area ratio parameter. The contact resistance at the foam-casing interface and the capillary pressure had a major influence on the thermal behavior of the system. These two factors lowered down the heat transfer rate considerably and the melting area was reduced by more than 30%. The temperature profiles for the foam material showed a different pattern as compared to the temperature within the wax, which was due to the effect of thermal nonequilibrium.