Heat transfer enhancement in latent heat thermal energy storage using copper foams with varying porosity.

• Metal foam reduces full melting time by 73.7% compared with pure paraffin. • Dividing metal foam into two parts (upper and lower) improves heat transfer. • Metal foam with increased porosity in positive y-direction enhances heat transfer. • Full melting time was reduced by 75.5% by using metal foam with two parts. Latent Heat Thermal Energy Storage (LHTES) is a promising solution to alleviate the supply-demand mismatch in the field of energy utilization. LHTES relies on high-quality phase change materials (PCMs) for high thermal capacity and narrow temperature variation. As an important class of PCMs, paraffin shows advantages of safe, non-corrosive, low-cost, but has limited applications because of relatively low thermal conductivity. The heat transfer performance of LHTES could be remarkably improved by embedding metal foams into PCMs. In the present work, water, paraffin (RT54HC) and copper foam were used to study the heat transfer enhancement, which acted as heat transfer fluid (HTF), PCM and heat transfer enhancer, respectively. The non-thermal-equilibrium energy model was applied in the numerical investigation. The liquid fraction profile was compared between pure PCM and composite PCM. The melting process, interface evolution and the average heat flux density under copper foams with different porosity changing modes were investigated. Results indicated that the incorporation of copper foams into PCM significantly increased the heat transfer performance of LHTES. The full melting time was reduced by 73.7% compared to that of pure PCM. The average heat flux density was improved from 96.38 W to 330.16 W. The optimal method was that dividing the copper foam into upper and lower parts, where the porosity increased separately along with the positive x-direction and positive y-direction. Compared with fixed porosity, the full melting time and average heat flux density were reduced by 6.78% and increased by 4.26%, respectively. [ABSTRACT FROM AUTHOR]