Melting enhancement of nano-phase change material in cylindrical enclosure using convex/concave dimples: Numerical simulation with experimental validation

Abstract

Several experimental studies are required to recognize the thermal performance for different designs of phase change material (PCM) storage systems. In this study, the melting process of paraffin wax was experimentally and numerically studied in a double tube vertical unit. Initially, the storage unit was at 30 ºC and an electric heater in the enclosure's center was used to heat the PCM. The heat flux density ranged from 1000 to 1400 W/m2. The solid-liquid interface was tracked and the PCM local temperatures were measured. The numerical model was established to study the influences of convex/concave dimples, nanoparticles, and heat flux densities on the PCM melting process. The numerical model was validated using data from the literature as well as the present experiments, resulting in an excellent agreement. The convex/concave surface decreases the melting time compared to the smooth surface. The minimum melting time occurred at six dimples with a percentage decrease of 15.56% compared to the smooth wall. The melting time reduced by 19%, 16.61%, and 15.82% at 1200 W/m2 in the case of 5 w.t% of SiO2, Al2O3, and CuO nanoparticles, respectively referred to the smooth wall. The charging time was decreased by 11.02% and 21.73% when the input power was increased from 1000 W/m2 to 1200 W/m2 and 1400 W/m2, respectively, in the case of dimples with nanoparticles. The dimples with nanoparticles are suggested for future modeling of the PCM melting process with small and high heat flux.