Simulation research on PCM freezing process to recover and store the cold energy of cryogenic gas

This paper is concerned with the Phase Change Material (PCM) freezing process that is used for recovery and storage of the cryogenic gas cold energy. Water has been employed as the PCM to investigate the solidification phenomenon outside a tube in which cryogenic nitrogen gas flowed, and numerical study has been conducted on this two-dimensional transient freezing problem by using the Solidification and Melting model in the Computational Fluid Dynamics (CFD) code FLUENT. The calculation results, verified by experimentally measured data, showed that the dimensionless numbers, such as Biot number and Stefan number of PCM, and the Stanton number of the coolant flowing in the tube, have remarkable effects on the characteristics of the two-dimensional freezing problem. Larger Biot number is beneficial to the heat transfer between PCM and the coolant, and can promote higher freezing rate. Higher Stefan number appears to result in larger freezing rate in a fixed axial position. Moreover, the frozen layer slope along the tube is steeper at larger Stanton numbers.