The Effect of Freezing and Melting on the Efficiency of Latent Heat Storage Systems

This paper presents a thermodynamic analysis of latent heat storage systems (LHSSs). The study is based on a model that, although simplified, takes full account of the physics of the phase-change process that takes place in the LHSS during charge and discharge. The model characterizes an LHSS with only two parameters and four operating temperatures. This simplicity allows a detailed study of the unit. Two different situations are analyzed. The first is an LHSS in which the phase-change material (PCM) is stored in a single container. The second is an LHSS with many small cells containing the phase-change material. The simplified model presented in this paper is successful in describing the effects of the physics of the phase-change process on the performance of LHSSs. Optimum efficiencies and phase change temperatures in the LHSSs related to the inlet temperature of the charge fluid are obtained based on exergy analysis. The results also indicate that the insulating effect of the solid layer during the discharge process reduces both the exergetic efficiency and the storage capacity of the unit. On the other hand, the study points to enhanced heat transfer inside the unit as very important for improving LHSSs performance.