عنوان مقاله [English]
Regarding the variability nature of the solar ray in a day, application of a thermal storage system seems necessary to accompany the solar system. Latent heat energy storage in a solar water heater can occur in a phase-change material. These materials are generally encapsulated in a container and positioned in the water container. Shape, material type, and size of the encapsulating container have direct effect on the efficiency of the storage system. In this paper, effort has been made to investigate experimentally the encapsulation diameter effect on the storage system efficiency. Industrial paraffin with 5-7\% fat was used as a phase-change material. They were encapsulated in aluminum tubes of 6, 10, and 12 mm diameter. The thicknesses of the capsules in all diameters are 1mm. For each tube size, a set of tests was carried out. For each test, 88 capsules with 280 mm height containing the paraffin were used. As a result, for capsules with 6, 10, and 12mm diameter, 281.6gr, 1126.4gr, and 1760gr of paraffin were used, respectively. The results show that the rate of energy storage using aluminum tubes of 6, 10, and 12 mm with phase-change material in comparison to when using no phase-change material, improved energy storage efficiency by 4.4, 15.3, and 11.2\%, respectively. With regard to the fact that by reduction of capsule diameter, the rate of surface area to the volume increases; hence, heat transferring surface area increases. Therefore, it is expected that by reducing the capsule diameter, density of energy storage will increase. Consequently, by reducing the capsule diameter, total paraffin mass will decrease. Hence, by considering these two factors, maximum rate of energy storage occurs when the capsule diameter is 10mm.