Investigation of the influence of heat source orientation on the transient flow behavior during PCM melting using particle image velocimetry

The present study reports the characterization of transient flow and thermal behavior of phase change material (PCM) during solid-liquid phase change (melting) through experimental investigation. Two specific aspects of the current work, both important in the field of latent heat thermal energy storage, are to investigate the influence of the flow behavior within liquid PCM on the melting and heat transfer processes, and the impact of heat source orientation on the underlying melting and heat transfer processes. Particle image velocimetry (PIV) was used to measure the velocity fields in the liquid PCM, while thermocouples were used to measure the temperature fields. During PCM melting, three distinct phases of heat transfer were found: strong conduction, strong natural convection and weakening natural convection. The transient Nusselt number characterized the underlying physical behavior observed through transient flow and temperature fields. The findings show that the fluid velocity plays a critical role in the transportation of heat within the liquid domain, which in turn regulates the melting trend and hence, the overall heat transfer. These results further extended the understanding of phase change and the associated heat transfer processes in the PCM and provide comprehensive benchmark data for the improvement of numerical models simulating the solid-liquid phase change process.