Design, development and performance investigations of a latent heat storage with PCM encapsulation

Encapsulation of phase change material (PCM) in cylindrical capsules has been proven to be one of the promising techniques for improving the heat transfer characteristics in latent heat storage (LHS) systems. The distribution of the capsules has a great impact on the thermal performance of these LHS systems. Therefore, in the present study, an LHS unit with cylindrical PCM encapsulation is developed numerically using COMSOL Multiphysics software. Various models (Model A, Model B, Model C, and Model D) with varying spacing between the capsules are modeled to optimize the capsule distribution inside a cylindrical shell. For this high-temperature investigation, Sodium nitrate with a phase transition temperature of 305 degrees C is selected as PCM, and ambient air is used as the heat transfer fluid (HTF). The performance of these models is assessed by comparing temporal variation of temperature, phase fraction in the PCM and HTF velocity in the outer shell. It is observed that the distribution of capsules greatly influences the flow dynamics of HTF which crucially altered the thermal performance of the LHS models. Model C is found to be an optimum configuration with a minimum charging/discharging time of 364/ 337 min. LHS module with an optimum distribution of capsules was fabricated and its charging and discharging performances were investigated in the temperature range of 270-330 degrees C. The heat transfer behaviour in the PCM is studied by plotting the temperature evolution at different locations in the capsules. It was observed that the LHS module with approximately 14 kg of PCM mass, stored/discharged a total heat of 3.97/3.94 MJ in the given temperature range.