A review of the recent advances in the heat transfer physics in latent heat storage systems

Abstract

Overwhelming research interest in developing green and renewable energy systems has fostered the innovation of novel latent heat storage systems. Transport phenomena during phase transitions significantly influence the thermal energy transfer rates and the efficiency of charging and discharging such systems. Hence, a comprehensive elucidation of heat transfer physics is essential for researchers to develop the insight, model, experiment, and analyze a thermal system. This paper reviews the heat transfer mechanisms involved in phase-changing processes in various latent heat storage system configurations. At the outset, though the phase-changing process in latent heat storage systems appears simple, a critical observation unveils the complex evolution of various coupled fluid-thermal transfer processes. An astute examination of such phenomena is essential to effectively figure out the role of geometry, orientation, process variables and their dimensionless groups, boundary conditions, material property, etc., in developing accurate models and correlations. The presence of vortical flow structures and gradients of velocity and temperature lead to local variations in heat transfer coefficients in boundaries separating the heat transfer fluid (HTF) passages and phase-changing material (PCM). Gravity influences the Rayleigh–Bénard convection phase-changing process, which offers a higher energy transfer rate than heat diffusion-dominated melting/solidification. A wide variety of test cases are surveyed and conclusively figured out the role of geometry and orientation-dependent convection in the phase-changing process. The present overview of heat transfer physics shall provide a guideline for the system designers to fine-tune HTF flow path geometrical aspects and PCM confinement for improved heat transfer response and system performance.