Melting process of various phase change materials in presence of auxiliary fluid with sinusoidal wall temperature

This paper presents a numerical simulation approach to investigate the water effect as an auxiliary fluid in direct contact with various phase change materials (PCMs). The technique is defined as a hybrid method due to the using of an external intermediary for melting process improvement. Oleic acid (OA), coconut oil (CO), hexadecane, and heptadecane are selected as PCMs due to immiscibility in water and differences in density, melting point, and enthalpy of fusion. An auxiliary fluid is embedded above PCM in an enclosure subjected to sinusoidal wall temperature for melting rate increase through density differences improving heat transfer rate due to materials displacement during process. Based on water accessibility and price, this approach would be preferable to costly enhancement methods such as nanoparticles addition or utilizing extending heat transfer surfaces. Each PCM melting process in the hybrid system with a volume ratio of 50% PCM - 50% water is simulated and compared with a pure (100% PCM) reference melting process. A 23%, 30%, 62%, and 98% increase in energy storage capacity can be attributed to hybrid systems with OA, CO, hexadecane, and heptadecane, respectively. Also, stored heat rate computation shows that using water increases 177% stored heat rate per PCM kg in the system. Meanwhile, it accelerates PCM melting process. Higher density differences cause a dynamic flow field and faster melting process, increasing stored heat rate about twice, which is a significant result for system design and optimization.