(567e) Performance Study of High Temperature Microencapsulated Phase Change Material for Thermal Energy Storage through Mathematical Modeling

Heat produced during industrial processes can be captured and reused to minimize the amount of heat loss. Latent heat storage using phase change material (PCM) is a promising technique to capture and recycle industrial waste heat. PCM can be used to capture different grades of waste heat. Use of PCM to capture high temperature (> 400 ºC) waste heat is under development. A mathematical simulation can help understand the heat transfer behavior and efficiency to optimize the heat storage system design and operation. Microencapsulated phase change materials (MEPCMs) consisting of phase change materials packed inside a resilient shell (e.g., polymer, alumina, sodium silicate, or steel) have advantages of isolation from the external environment and preventing materials loss by liquid leakage. Additionally, MECPCM can easily be transported from the charging site (industrial facility) to the service site. This work studies the heat transfer and phase change behaviors of high temperature MEPCM during charging (heating) and discharging (cooling) processes.

A finite element analysis model of heat transfer and solid-liquid phase change in a phase change material has been developed using COMSOL Multiphysics®. In this model, temperatures at different time, location, and PCM phase (solid or liquid) inside the MEPCM of a shell have been calculated. Different materials have been used as PCMs to study their individual phase change behavior and heat storage capacity. Alumina was used as the outer shell material of the MEPCM. Temperatures of MEPCM at solid and liquid phases were calculated using Fourier’s law of heat conduction integrated with heat convection between the MEPCM and surroundings. Temperature during solid/liquid phase transition was calculated numerically using the general concept of first order phase transition by absorbing/releasing a fixed amount of heat at a constant temperature. Temperature and composition dependent thermophysical and thermodynamic properties of the PCMs and alumina from literature were used in this model. Three different heating/cooling conditions were studied in this work: 1) the outermost surface of the MEPCM is maintained at a constant temperature; 2) a constant heat flux is applied on the MEPCM shell surface and 3) a convection heat transfer condition is used for heat exchange between environment and MEPCMs. Different environments have been used for convection heat transfer conditions, including air, water, and oil. The calculated results were analyzed to study the phase change phenomena of different MEPCMs in different conditions and environments, which reflect comparative understanding about the overall performance of MEPCM heat storage capacity and heat transfer rate during the charging and discharging processes.