CFD simulation of air layer effects on RT42 PCM melting in a square cell

Latent heat storage technology has been receiving significant attention from scientists, researchers, and engineers working in solar heating and cooling, waste heat recovery, as well as building energy management. Phase change materials (PCMs) have been extensively utilized for this purpose due to their high energy storage capacity and cost-effectiveness. In this study, a numerical investigation was conducted to evaluate heat transfer in paraffin wax RT42 during its complete phase transition from solid to liquid within a square cell, both with and without an air layer on the left hot wall, with the rest of the walls thermally insulated. The enthalpy-porosity approach was quantitatively analysed using the ANSYS/FLUENT 16 program. The results indicate that the presence of a 1 mm thick air layer doubled the complete melting time, and a 2 mm thick air layer tripled the melting time compared to scenarios without an air layer. Additionally, it was shown that thermal conduction drives early melting, while density differences influence free convection in later stages. This study underscores the significant impact of air layers in delaying the melting process of PCMs paraffin wax in square latent heat storage units. Furthermore, guidelines for future investigation were provided, including examining the effects of adding air layers and providing a heat flow from the top or bottom of the square cell. This further research might assist in revealing more specifics of the interactions among the environment, phase change mechanisms, and heat transport in thermal energy storage systems.