Numerical modeling and simulation of thermal energy storage for solar cooking using Comsol multiphysics software

Abstract

When there is a mismatch between time of energy generation and utilization latent heat energy storage systems (LHESS) are potential technology that can be used as a back-up. This paper presents a numerical study of a shell and tube type of thermal energy storage (TES) unit for solar cooking using a binary salt group phase change material (PCM) type known as potassium sodium nitrate salts (KNO3−NaNO3). The melting point temperature of the selected PCM is 222°C. The internal diameter and length of theTES is 240 mm and 960mm respectively. Using optimization method 19 heat transfer fluid (HTF) tubes are selected with external and internal diameter of 18 mm and 15.6 mm respectively. To improve heat transferring rate of the PCM storage each tube will be integrated with four longitudinal fins.COMSOL Multiphysics has been selected to model LHESS that enables testing of a multiple of configurations and optimization of the geometry used. Effective heat capacity method is employed to incorporate sensible and latent heat required for melting the PCM. To integrate the buoyancy effect of the molten layer of PCM, Boussinesq approximation has been included in the model and the governing equations taken in account the model are solved using the COMSOL Multiphysics software. And the circular configuration of tubes and fins embedded with PCM has been found best option. To evaluate the performance of energy storage unit three parameters have been selected: melt fraction, charging time and Energy stored. A finer mesh with 55428 elementssize is considered for the entire simulation of the LHS models. The inlet temperature of the HTF is set to be 235°C and the outside walls are thermally insulated. At time of 60 minutes the PCM becomes fully charged, at this moment the amount of stored latent, sensible and total energy during charging process in the LHS system is 5.88 MJ, 4.29 MJ, and 10.17 MJ respectively.