Energy storage with PCM in fluidized beds: Modeling and experiments

Abstract

In recent years, the development of phase change materials (PCMs) has introduced new ways to increase the energy storage capacity of a system due to the high latent heat and high storage density of these materials. The aim of this work is to model the charging process of a fluidized bed with PCMs operating as an energy storage device. The temperature in the bed during the charging process of the fluidized bed has been modeled using the two phase theory of fluidization. The dense phase is taken to be perfectly mixed, and the bubble phase is taken to be in plug flow. The numerical model presented takes into account the fact that the phase change process of the bed material occurs over a temperature range and also estimates the energy stored in the wall of the bed and in the distributor plate. The energy equation of the dense phase is numerically solved in enthalpy form, considering the dependence of enthalpy on temperature for phase changes occurring over a range of temperatures. The model’s validity is verified against experimental data for two granular materials: sand, a typical material used in fluidized beds, and a granular PCM with a mean particle diameter of 0.54mm and a phase change temperature of approximately 50°C. For the sand, the temperature profiles obtained numerically perfectly agree with the values measured experimentally. In the case of the granular PCM, the fitting of the curves is improved when slow and similar heating rates are selected for the experiments and for the DSC measurements used to determine the PCM enthalpy–temperature curve.