Thermal performance analysis of multi-stage cold storage packed bed with modified phase change material based on Na2SO4·10H2O

Abstract

Packed bed cold storage integrates a large number of phase change materials (PCMs) in a low-cost way, improves heat transfer performance by providing a larger heat transfer surface, and is considered a promising energy storage method in the field of air conditioning. However, PCM based on eutectic salt is often used for single-stage cold storage packed bed, which has poor cold storage performance and inferior stability. In this paper, the modified PCMs based on Na2SO4·10H2O with solidification temperatures of 5.11 °C, 7.06 °C, and 12.89 °C were proposed for multi-stage packed bed cold storage, and the formula of the material was modified and tested to improve the stability. The test showed that preheating before utilization can further reduce the subcooling degree caused by the freeze–thaw cycle. Through the CFD simulation of the established multi-stage packed bed model containing cylindrical encapsulated capsules, the cold storage capacity of a multi-stage packed bed with different PCMs filling ratios was compared. Results show that the cold storage density of the multi-stage packed bed with the filling ratio of 4:2:4 (PCM1:PCM2:PCM3) is 7.3 % higher than that of the single-stage packed bed, and the cold storage capacity can meet the emergency cooling demand of the air conditioner for at least one hour. This study provides a theoretical basis for the feasibility of the proposed modified eutectic salt PCM applied to multi-stage packed bed cold storage for air conditioning conditions.