On the effect of storage tank type on the performance of evacuated tube solar collectors: Solar radiation prediction analysis and case study

The effect of variation of longitude and latitude on the amount of solar radiation is investigated in this work in the Iranian climate context on different solar collectors and storage tank geometries. An equation for prediction of solar radiation intensity is presented through regression analysis (R² = 0.9976). The effects of different types of storage tanks, change of Grashof number, and change of time of experiments on the thermal characteristics of the evacuated tube solar collectors are numerically investigated. Solar irradiance on the collector surface was simulated via P-1 method. Results demonstrated that changing longitude does not influence the amount of solar radiation, whereas change of latitude affects such amount, and regions with higher latitudes (northern areas) receive more beam radiation around solar noon. In addition, the tank with longer height absorbs more heat, and presents a better efficiency. Also, the tank geometry affects its performance; the useful heat gain of a collector possessing a vertical square tank is about 10% more than that of a collector with a cylindrical tank without consideration of heat loss from the tank. Nonetheless, considering such heat loss, the collector with cylindrical tank presents the highest performance due to minor heat loss area of the tank.