An investigation of serial connected U-pipe evacuated tube solar collector performance using TiO2/Water nanofluid

U-pipe evacuated solar collector is one of the efficient ways to convert solar energy to heat. In this study, different from the literature, thermal efficiency and pressure drop of a solar collector established with serial connected U-pipe evacuated tubes are investigated. However, a nanofluid has been used in the experimental studies with different concentration ratios. The experimental studies have been performed with water and TiO2/water nanofluid. Thermal efficiency and pressure drop of the collector have been experimentally investigated with different working concentration ratios of the fluid at constant solar radiation rate. Efficiency increased by 14.3% to 22.1% compared to water when using a 2% concentration fluid with decreasing reduced temperature. The highest collector efficiency was 80% approximately with using 2% TiO2 concentrated nanofluid. At the same time, the lowest value was almost 60% with water at 0.033 reduced temperature conditions. Pressure drop of working fluid increased 17.7% with using 2% concentration ratio than water at 40 celcius average collector temperature. With increasing average collector temperature, pressure drop of working fluid decreased. Similarly, the maximum pumping power was obtained with a 2% concentrated fluid of about 52 W. The results of this study are expected to contribute to filling this deficiency in the literature.