Experimental study of storage system of a solar water heater equipped with an innovative absorber spherical double-walled tank immersed in a phase change material

Abstract

In commercial active solar water heaters, during the thermal charge process, water is continuously circulated between the collector and the tank. The water is heated in the collector and then stored in a tank whose surface is insulated. The shape of the collector and tank is an important factor in the development of solar thermal storage systems. In this study, the collector and tank are made spherical, fixed, symmetrical and capable of tracking the sun regardless of the placement angle. Also, in an innovative idea, the solar thermal storage tank is designed as a double-walled spherical tank. The water heated by the collector is stored in the inner chamber of the double-walled tank, and this chamber is surrounded by a Phase Change Material (PCM) by embedding the PCM in the outer chamber of the tank. Therefore, the PCM has the two roles of thermal insulation and thermal storage. As well as removing the thermal insulation, it is also possible to absorb solar energy on the external surface of the tank. To reduce heat losses, the tank is surrounded by a transparent glass cover in a greenhouse space. The maximum storage temperature and the maximum thermal efficiency in the thermal charge process are 80.3 °C and 74 %, respectively, which occur at a flow rate of 1.75 l/min. In this situation, the warm water needed by 8.43 people is produced. The greatest thermal stratification occurs at a flow rate of 1.25 l/min, and it weakens by raising the flow rate.