Robust Heat Transfer Enhancement During Melting and Solidification of a Phase Change Material Using a Combined Heat Pipe Metal Foam or Foil Configuration

Abstract

Experiments are performed to analyze melting and solidification of a phase change material (PCM) enclosed in a vertical cylinder by a concentrically located heat pipe (HP) surrounded by either aluminum foam or radial aluminum foils. The PCM liquid fraction, temperature distribution, melting (solidification) rates, and effectiveness are reported to quantify the improvement in thermal performance relative to a base case, a RodPCM configuration. Parameters of interest include the porosity of the PCMmetal composite, the foil thickness, the number of foils, and the foam pore density. The main contributor to enhanced performance is shown to be the porosity for both the HPFoilPCM and HPFoamPCM configurations. Both of these configurations improve heat transfer rates relative to either the HPPCM or the RodPCM configuration. However, the HPFoilPCM configuration with onethird of the metal (foil) mass is shown to have approximately the same performance as the HPFoamPCM configuration, for the range of porosities studied here (0.870–0.987). This may be attributed to the metal morphology and resulting contact area between the metal enhancer and the HP. The HPFoilPCM configuration, with a porosity of 0.957 using 162 foils of thickness 0.024 mm, attained an overall rate of phase change that is about 15 times greater than that of the RodPCM configuration and about 10 times greater than that of the HPPCM configuration. The greatest degree of enhancement was achieved with the HPFoilPCM configuration (with porosity 0.957) yielding an average effectiveness during melting (solidification) of 14.7 (8.4), which is an extraordinary improvement over the base case.