Development of a model for heat storage system using phase change materials in cogeneration units.

This study deals with the modelling of a packed bed latent heat thermal energy storage (TES) unit, integrating a reciprocating engine as cogeneration system. The TES unit contains phase change materials (PCMs) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. Water is used as heat transfer fluid (HTF) to transfer heat from the tank to the final uses, and exhausts from the engine are used as thermal source. PCMs are considered especially for their large heat storage capacity and their isothermal behaviour during the phase change processes. Despite this, most of them have a low thermal conductivity, hence PCMs encapsulation technique is adopted in order to improve heat transfer. The model permits to choose the electrical load of the engine, the dimensions of the tank and the spheres, thickness and diameter of the heat exchanger and the nature of phase change materials. According to the energy loads of the farm, a daily thermal energy balance is obtained and charging and discharging cycles during the day are showed as solid/liquid percentages of PCMs. Different types of PCMs were investigated for this application and TES unit dimensions were consequently changed in order to achieve optimal operating conditions.