Numerical Investigation on Melting Behavior in Encapsulated Paraffin Wax for Thermal Energy Storage

Abstract

Thermal energy storage (TES) is crucial for increasing the effectiveness and consistency of renewable energy sources. Among TES methods, using phase change materials (PCMs) for latent heat storage offers significant energy storage capabilities and maintains a nearly constant temperature throughout phase transitions. However, direct application of PCMs suffers from drawbacks including leakage, poor thermal conductivity, and structural instability. Encapsulation techniques have been developed to address these limitations by improving thermal performance and preventing PCM leakage. This study numerically examines melting characteristics of paraffin wax as a PCM utilizing an enthalpy-porosity approach. The analysis focuses on liquid fraction evolution and temperature distribution over time to understand the heat transfer mechanism. Melting of the PCM begins at its outer surface, primarily driven by conduction in the initial stages. This conductive heat transfer creates a steep temperature gradient at the solid-liquid interface. As melting progresses, the increasing thickness of the molten layer enhances natural convection effects throughout the liquid PCM, which subsequently accelerates the melting rate and reduces temperature gradients. The total melting duration is approximately 188 minutes, with a nonlinear melting rate due to increased thermal resistance as the remaining solid fraction decreases. Additionally, the enthalpy variation over time highlights the combined effect of sensible and latent heat absorption, requiring approximately 221 kJ/kg of energy for nearly complete melting.