Experimental study of an absorber coil in spherical solar collector with practical dimensions at different flow rates

The solar collectors’ shape is an essential parameter in the thermal performance of solar water heaters, and absorption of maximum radiation at different hours, regardless of the angle of the collector, is an important issue. A spherical solar water heater is experimentally investigated in practical dimensions. This solar water heater is a fixed, symmetrical collector with the ability to track the sun independent of the optimal placement angle. The heat transfer surface is also increased by designing the fluid passage bed as a spherical absorber coil. When the flow rate intensifies, the temperature difference between the input and output currents reduces. The maximum instantaneous and average daily thermal efficiencies are 87% and 69.7%, respectively, for a flow rate of 1.6 lit/min. In this case, the hot water required by 6.35 people is provided, then at higher flow rates, the thermal efficiency is reduced. At solar noon, the upper and lower semi-spheres absorb the maximum and minimum radiations, respectively. In general, the trend of changes in the absorption of the solar radiation has no absolute extremes, meaning proper tracking of the sun and stable performance during the day. This solar heater can be easily used in the facade of buildings.