Design optimization of a latent heat storage using sodium acetate trihydrate

This paper presents numerical investigations on a heat storage utilizing sodium acetate trihydrate (SAT) as phase change material (PCM). The heat storage can be used both in short-term and in long-term by utilizing stable supercooling of SAT. The store contains 137.8 kg PCM and 75 L water. Based on a validated CFD model, the flow conditions of the heat storage was analyzed. Uneven flow distribution inside the heat storage was revealed. Three design optimization methods were investigated to eliminate the uneven flow distribution. The results were analyzed using key performance indicators inclusive charging time, charged heat, degree of thermal stratification and the mixing of the heat storage. The influence of flow direction, inlet size and addition of a porous plate on the thermal performance of the heat storage were elucidated. Concerning flow direction, after moving the inlet from the bottom to the top of the storage, the time needed to completely melt the PCM was shortened by 50%. The best storage design was identified: For charge of the storage, the top inlet should be used, while for discharge, the bottom inlet should be used. Concerning the size of inlet opening, the charging time of the heat storage was reduced from 75 min to 51 min by using 3.0 mm radius instead of a 11.2 mm inlet. The small inlet size (3.0-8.0 mm) was suggested to make a uniform temperature distribution inside the heat storage. Short circuit was completely eliminated by adding a porous plate with 10% porosity. The charging time of the heat storage was shortened 28% by adding the porous plate. Finally, recommendations were proposed for different applications of the heat storage. The findings of the paper serve as a good basis for designers and manufacturers of PCM heat storages.