Coupled conjugate heat transfer model for melting of PCM in cylindrical capsules

Abstract

Phase change processes in latent heat thermal energy storage (LHTES) units are relevant, due to their ability in storing surplus power generated from renewable and conventional power plants. Macroencapsulation of phase change material (PCM) is one of several approaches to increase the mean discharging and charging power of such storage units. Numerical modelling and simulation in this context is a necessary alternative to rapid-prototyping to study solid-liquid phase change in latent heat thermal energy storage units. In this work, a numerical model is developed to represent the detailed thermal coupling between the heat transfer fluid (HTF) and phase change material capsules in a storage unit. An optimized iterative approach to represent the non-linear enthalpy-temperature and variable viscosity method for fixing and settling of solid phase in the capsule are employed in this work. Different computational domains for phase change material (PCM), heat transfer fluid (HTF) and capsule wall are employed, whose conjugated heat transfer is modelled in this work. A small representative latent heat thermal energy storage container is conceptualized to validate the developed conjugated heat transfer model. The melt front of phase change material is captured using photographic measurement in experiments over the complete melting time. The developed computational fluid dynamics (CFD) based conjugated heat transfer model has shown a very good agreement with experiments to estimate the heat transfer and melting of phase change material in the cylindrical capsule of a small scale latent heat thermal energy storage unit.