(392e) Mathematical Model of Energy Storage By High Temperature Microencapsulated Phase Change Material

Enormous amount of heat released by industrial processes can be reused to improve energy efficiency as well as to reduce heat pollution for a sustainable and greener environment. Latent heat storage using phase change material (PCM) is a promising technique to capture and recycle industrial waste heat. Use of high temperature (m.p. >300ºC) PCM in a large scale is still under development. A mathematical simulation can help understand the heat transfer behavior and energy storage 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, increasing the heat exchange area and preventing leakage. In addition, MEPCMs can be transported between remote site and heat source safely and economically. This work studies the heat transfer behavior of high temperature MEPCMs during charging (heating) and discharging (cooling) processes.

A finite element analysis model of heat transfer in a phase change material pushing towards phase transition has been developed using COMSOL Multiphysics®. In this model, temperatures at different time, location, and PCM phase (solid or liquid) inside the MEPCM of an alumina shell have been calculated. Temperatures of MEPCM at solid and liquid phases were calculated using Fourier’s law of heat conduction. Temperature during solid/liquid phase transition (melting point) was calculated numerically using the general concept of first order phase transition by absorbing/releasing fixed amount of heat at a constant temperature. Temperature and composition dependent thermophysical and thermodynamic properties of the PCM and alumina reported in literatures were used in this model. Three different heating/cooling conditions were investigated in this work: i) the outermost surface of the MEPCM is maintained at a constant temperature; ii) a constant heat flux is applied on the MEPCM shell surface, and iii) a convection heat transfer condition is used for heat exchange between environment and MEPCMs. The calculated results are analyzed to study the phase change phenomenon of MEPCM which reflects the overall performance of MEPCM heat storage during charging and discharging process.