Numerical simulation and experimental verification of constrained melting of phase change material in cylindrical enclosure subjected to a constant heat flux

Abstract

The transient melting process of the phase change material (PCM) is controlled by heat conduction and natural convection. Several experimental investigations are essential to understand the heat transfer mechanisms and performance for different designs of PCM thermal storage systems. Therefore, the present study experimentally investigated paraffin wax's melting process in a vertical cylindrical enclosure. The PCM, initially at 30 °C, was heated using an electric heater located at the center of the enclosure. The heat flux density varied to 1300, 1000, and 700 W/m2. Local temperatures of the PCM were measured, and the solid-liquid interface was tracked. A CFD (computational fluid dynamic) model was developed to numerically investigate the melting process with and without considering the convection effect. The CFD model was validated with the current experiments and with data from the literature. A very good agreement was obtained. The results showed that; the melting was initially dominated by conduction at an early stage, and this period increased with a decrease in heat flux. Natural convection was promoted, at a later time, leading to a curved shape of the solid-liquid interface. Numerical results indicated a robust thermal stratification of the molten liquid in the upper half of the storage unit. It was observed that increasing the input power from 700 W/m2 to 1000 W/m2 and 1300 W/m2 decreased the total melting time by 24.82% and 43.58%, respectively. It is recommended for the future modeling of the PCM melting process to consider the convection effect.