CFD modeling of heat charging process in a direct-contact container for mobilized thermal energy storage

Abstract: Thermal energy storage and phase change materials become increasingly important topics during the last 20 years for heating and cooling purpose in buildings. When there is time delay or mismatch between producing energy and energy demand, thermal energy storage provides a great solution. Furthermore, in the case of space differences between supplier and end user, the mobilized thermal energy storage can be introduced. In this solution the waste and excess heat, which is released from a factory, is recycled by storing in the PCM through heat transfer fluid and transported by a mobilized container to a consumer. In charging process the PCM is initially solid; it becomes melt while the heat transfer fluid flows inside the container. In order to achieve the highest efficiency of transferring energy in charging and discharging process, the melting and solidification times should be considered. In this paper the heat transfer behavior of the phase change material during the charging process has been simulated by CFD modeling of the previous work on Mobilized Thermal Energy Storage. Transient two dimensional heat transfer problems are solved by simulating in the Fluent software while heat is stored in PCM. In order to simulate the phase change in PCM, the Volume-Of-Fluid (VOF) method is extended by the energy conservation to solve for the temperature in the material. The validation of the computational model has been conducted by comparison between experimental data and CFD results; the agreements between the results are convincing. The liquid fraction as functions of time is achieved and the total melting time is estimated. Presented results in this paper lay the groundwork for a future investigation to get more accurate prediction of thermal performance of mobilized thermal energy storage system.