Experimental investigation of a hemispherical solar collector performance with helical risers by using Ag–CuO/water hybrid nanofluid

A stationary, symmetrical hemispherical solar collector with helical risers is experimentally investigated. Pure water and Ag-CuO/water hybrid nanofluid are used as the working fluid. The nanoparticle's volume fractions are 0.1 and 0.3%, and the flow rates of the working fluid are 1, 1.5, and 2 Lmin⁻¹. A total of 9 tests have been conducted in 9 consecutive days during August 2022. All tests were performed according to ASHRAE standards. The main novelty of this study is the practical use of hybrid nanofluid and helical risers in a solar collector with hemispherical geometry. According to the results, a hemispherical solar collector exhibits hopeful and favorable thermal efficiency due to its particular shape and the unique arrangement of its helical risers. The results show that with the increase in flow rate, the temperature difference between the inlet and outlet of the hemispherical solar collector and the heat exchanger inside storage tank decreases, while the thermal performance of the solar collector increases. Also, when the concentration of nanoparticles increases, the temperature difference between the inlet and outlet of the collector, and the thermal efficiency, increases. The results show that the maximum thermal efficiency of the solar collector is 86.8% and the maximum average temperature of the fluid around the heat exchanger in the storage tank is 79.8 °C, and these results are related to the hybrid nanofluid with a volume fraction of 0.3% and a flow rate of 2 Lmin⁻¹.