Two-phase heat and mass transfer of phase change materials in thermal management systems

Abstract

This paper experimentally and numerically studies the solid–liquid heat transfer mechanism of octadecane which is a phase change material (PCM) with the melting temperature of 28°C in thermal management systems. This study finds that the convective heat transfer driven by the buoyancy force could be dominant during the melting of pure PCM: the time to melt 30mm of PCM decreases from 453min to 13min when the heating direction changes from downwards to upwards. The use of porous materials such as metal foams (made from Cu, Al or C) with various porosities and pore sizes in the thermal management system significantly increases the overall heat transfer rate due to the increase of effective conductivity. The amount of heat absorption within 60min significantly increases from 105.6kJ to 248.9kJ after using the Al foam with 0.97 porosity. Further decreasing the porosity to 0.925 and 0.88, however, will decrease the amount of absorbed heat to 230.7kJ and 179.7kJ because of the decrease of natural convection and the decrease of overall heat capacity. Considering the increase of weight and cost of the thermal management system by using porous materials, the Al foam (compared with C and Cu foams) with the porosity of 0.97 (compared with 0.88 and 0.925) and the pore size of 5.08mm (compared with 0.64mm, 1.27mm, 2.54mm) is preferred within the porous materials investigated by this study.