Evaluating the Thermal Performance of Solar Water Heating System Used Polypropylene Glycol with Al2O3 Nanoparticles in Different Concentrations as a Thermal Medium

In this study, three laboratory samples of a nanofluid consisting of alumina in a propylene glycol solution were prepared for three different concentrations in weight ratios (0.2, 0.4, and 0.6%). The thermal conductivity and dynamic viscosity of the three concentrations were measured at different temperatures (20, 60, 100, 140, and 180) °C. The results showed that the concentration of 0.6% is the highest value for thermal conductivity, and it was chosen as a working fluid in the experimental device. The nanofluid was placed in copper tubes to act as a heat transfer fluid. Sunflower oil was used as a medium to store the heat acquired from solar radiation. The oil was placed inside the evacuated tube, and the spiral annular copper tube was immersed in the vegetable oil and the second copper tube inside the water tank. They were connected to each other with copper connectors and copper ball valves. The experimental device was operated on March 2, 2024, and the highest temperature of vegetable oil was recorded at 134.9 °C, nanofluid coming out of the water tank at 35.6 °C, nanofluid entering the water tank at 80 °C, and water temperature at 42 °C at 6 pm. The experimental device continued to operate, and on April 2, 2024, the highest temperatures of oil, outgoing liquid, incoming liquid, and water were recorded at (164.1, 62.9, 103, and 70.8) °C, respectively, at 6 pm. With the continued operation of the experimental device, there was a noticeable increase in temperatures, and the highest temperatures were recorded on May 15, 2024, for oil, outgoing liquid, incoming liquid, and water at (174.1, 69.4, 115.9, and 80) °C, respectively. At the same time, the intensity of solar radiation falling on the evacuated tube was calculated during the daytime hours from 8 am to 6 pm. The average solar radiation for one day was recorded and the amount of heat stored in sunflower oil and the amount of heat stored in water were calculated and the efficiency of the evacuated tube was calculated. The efficiency of the evacuated tube was (66%,54%,52%) For the days mentioned above.