The Effect of Using Hot and Cold Water Separator Plates in Evacuated Tubes of a Solar Water Heaters

Abstract

So far, different methods have been proposed to increase the efficiency and the temperature of hot water from evacuated tube solar collectors. In this article, the impact of a separator plate between the hot and cold fluids in the evacuated tube water heater on the temperature changes and the efficiency of hot water produced by the evacuated tube solar water heater is investigated. Experiments were conducted on a thermosyphon evacuated tube solar water heater (Solar Polar, E180) with eighteen evacuated glass tubes with a length of 1800 mm and a diameter of 58 mm with a 180-liter tank made of isolated stainless steel (SUS304). The experiments were performed in four different modes: in the absence of separator plates and with separator plates with a length of 1.2 m, 1.4 m and 1.6 m. To validate the results, the experiments were repeated three times. The solar water heater in the absence of the separator plates was modeled and simulated with the help of energy relations. The simulation results were consistent with experimental results. After validation of the results, the other cases were investigated experimentally. The use of separator plates in the evacuated tube solar water heater distinguishes this article from previous studies. According to the results, the length of stagnation region at the end of the evacuated tube is about 0.6 m. By placing a separator plate between the hot and cold fluids, the length of stagnation region can be reduced and consequently the efficiency can be increased. According to the results, the use of 1.6 m separator plates led to 5% increase in the overall thermal efficiency.