Effect of inclination angle during melting and solidification of a phase change material using a combined heat pipe-metal foam or foil configuration

Experiments are performed to analyze the impact of system inclination (ranging from 0° to 90°) on the melting and solidification of a phase change material (PCM) in a cylindrical enclosure. Heat transfer occurs through a concentrically located heat pipe (HP) or solid copper rod and an underlying copper disc. The HP may also be combined with aluminum foils and foam. Six configurations are investigated: HP-Foil-PCM, HP-Foam-PCM, HP-PCM, Rod-PCM, Foam-PCM and non-enhanced PCM. The PCM liquid fraction histories, temperature distributions and photographs provide insight into the influence of the inclination angle, as well as the three-dimensional melting phenomena. Experimental measurements indicate that the system orientation has a minimal effect on the solidification rates for nearly all case studies due to conduction-dominated heat transfer. However, during melting, the presence of natural convection may significantly alter the liquid fraction histories for systems without foam or foils. For the HP-PCM and Rod-PCM configurations with a horizontal orientation, the liquid fraction may be increased by up to 0.09 and 0.20 compared to a vertical orientation for a system with and without heat transfer through the base, respectively. For the HP-Foil-PCM and HP-Foam-PCM configurations, a vertical orientation achieved a slightly higher liquid fraction by approximately 0.03 and 0.05, respectively, relative to horizontal orientation. This may be attributed to the flow of the HP's internal working fluid, in which gravity assists the return of the liquid working fluid to the HP evaporator in a vertical orientation. The time for complete melting and solidification for the HP-Foil-PCM configuration was reduced to 11% and 3% of that for a non-enhanced system, respectively, regardless of orientation. Overall, the combination of a HP with foils or foam may achieve much higher melting and solidification rates with respect to a non-enhanced system.