Thermal Effect on Natural Circulation Flow using Water and Al2O3 Nanofluids Inside Rectangular Loop in Vertical Position

Abstract Passive cooling technology in closed circuits without the use of pumps works based on the principle of natural circulation, where the variable geometry and working fluid used will affect the amount of flow rate that occurs. The impact of changes in the working fluid and thermal effects on the natural circulation flow rate needs to be studied for their effectiveness. This research aims to investigate the characterization of thermal effects on natural circulation flow using water fluid and Al2O3 Nanofluid in a rectangular loop in a vertical position. The research method was carried out experimentally by varying the heating water temperature from 50°C, 60°C, and 70°C with the cooling water temperature set at 10°C. The analysis was carried out for steady conditions. The experimental results show that the highest temperature difference occurs in the heating water temperature variation of 70°C and 10°C cooling water with an average temperature difference of 6.5°C at steady state. In contrast, the lowest temperature difference occurs at 50°C heating water temperature of 4.8°C. So, the highest mass flow rate in water fluid is 0.01728 kg/s at a temperature of 70°C, and the lowest is 0.01167 kg/s at 50°C. As for the results of the correlation comparison between the mass flow rate of water fluid and nanofluids, the highest value was obtained for Al2O3 nanofluids of 0.01736 kg/s, and the lowest was 0.01173 kg/s.