Exergetic performance of medium temperature metallic solder based cascaded PCM thermal energy storage systems during charging
Abstract
Metallic phase change materials are attractive candidates for use in thermal energy storage systems, but their high cost per unit volume may prohibit their usage. To reduce the cost, some volume of metallic phase change materials may be replaced with other cheaper phase change materials. Three packed bed cascaded latent heat thermal energy storage (LHTES) systems for medium temperature applications are experimentally evaluated and compared to a single phase change material (PCM) packed bed LHTES of eutectic solder capsules from a charging exergetic rate perspective. Cascaded system 1 comprises of eutectic solder PCM capsules at the top, and erythritol PCM capsules at the bottom in equal storage volumes. Cascaded system 2 consists of eutectic solder PCM capsules at the top and adipic acid PCM capsules at the bottom in equal storage volumes. Cascaded system 3 consists of three PCM capsule layers of eutectic solder at the top, adipic acid in the middle, and erythritol at the bottom in equal storage volumes. Cascaded system 3, the 3 PCM cascaded system shows higher exergy charging rates because of the release of latent heat in 3 phase change transitions. Its thermal performance is, however, comparable to cascaded system 2 with adipic acid at the bottom of the storage tank. The charging times for cascaded system 2 and cascaded system 3 are also shorter as compared to the other storage systems suggesting a better charging performance. The single PCM shows the lowest exergy charging rate at the lowest flowrate but its performance improved to be better than that of cascaded system 1 with an increase in the flowrate.