Effect of Dimensionless Heat Transfer Parameters on Charging in a Latent Heat Thermal Energy Storage System Using Spherical Phase Change Material Balls

ABSTRACT Latent heat thermal energy storage (LHTES) systems are implemented to mitigate temporal mismatches between energy generation and demand, and accurate characterization of the governing dimensionless parameters is essential for predicting charging behavior in packed configurations of spherical PCM balls under forced convection. This study presents an experimental investigation of a packed‐bed LHTES module containing spherical PCM balls encapsulating myristic acid, with water as the heat transfer fluid (HTF). Experiments were conducted at HTF inlet temperatures of 70°C and 75°C and volumetric flow rates of 200, 300, and 400 LPH. The transient evolution of Stefan, Reynolds, Rayleigh, Nusselt, Stanton, and Biot numbers was evaluated and correlated with melting progression, charging duration, and average thermal power. Increasing the inlet temperature from 70°C to 75°C decreased charging time by 31.03%, 36.00%, and 36.84% at 200, 300, and 400 LPH, respectively, indicating intensified sensible‐to‐latent heat transfer. Higher Reynolds numbers enhanced convective transport, increased interfacial heat flux, and accelerated phase front propagation within the spherical PCM balls. Biot numbers below 0.1 signified predominant external thermal resistance and nearly uniform internal temperature distribution, facilitating effective radial heat diffusion. The coupled behavior of Rayleigh and Nusselt numbers clarified the interaction between buoyancy‐induced effects and external convection during melting. The results establish a dimensionless thermo‐fluidic framework for describing charging characteristics in packed beds of spherical PCM balls and provide experimentally substantiated guidance for performance‐oriented design and optimization of PCM‐based thermal energy storage systems for renewable and industrial applications.