Numerical investigation of different PCM volume on cold thermal energy storage system

Abstract

In general, one of the promising methods to reduce energy consumption and off peak load is the employment of cold thermal energy storage (CTES) in energy systems. In this paper, a numerical investigation is conducted on a CTES system mounted in a freezer to find out the effective phase change material (PCM) volume. A large amount of the cold thermal energy is stored as latent heat during solidification of eutectic solution NaCl-H2O as PCM with −21 °C melting temperature. This latent cold thermal energy is then released into the freezer compartment when the compressor of the refrigeration cycle is off. Because of the space limitation in freezer cabin, CTES system should be designed as much as compact and efficient. Thereby, PCM boxes with the maximum exposed area and different PCM thicknesses of 0.5, 1, 2, 3, 4, 5 and 6 cm are simulated using computational fluid dynamics (CFD) method. The total discharged cold thermal energy, as well as its period, was obtained for all 7 PCM thicknesses. Discharging time per unit of PCM mass (τdisch) is introduced as the ratio of the discharging time of PCM (time of off-compressor) to the total PCM mass to comparison the effectiveness of CTES system. It is revealed that the τdisch does not rise with the PCM volume, proportionally. Just when the PCM thickness is raised from 2 cm to 3 cm, the τdisch improved significantly for 45% and weakly increased afterward. It means that container with 3 cm thickness would be the best one for this type of storage system.