Using TİO₂/water nanofluid in a series connected U-pipe evacuated tube solar collector

Increasing energy demand due to reasons such as population growth in the world, industrial and technological developments, limited fossil fuels reveal the importance of renewable energy sources. Solar energy is one of the renewable energy sources. One of the most common uses of solar energy, which is used in many different applications, is water heating systems. Efforts to increase the efficiency of solar thermal systems continue. In this study, the effect of nanofluid use on collector efficiency in U-tube solar collectors with vacuum tubes was experimentally investigated. TiO₂/water nanofluid was used as the heat transfer fluid in the measurements performed with a solar simulator under indoor conditions. As a result of the measurements carried out with nanofluids prepared at 0.5%, 1%, 1.5% and 2% ratios, it was determined that the collector efficiency had an effect of approximately 5%, 7%, 8% and 10%, respectively. It was observed that the collector efficiency increased as the TiO₂ ratio added to the water increased. In addition, when water is used as the fluid, the average fluid temperature in the collector is 38 ℃, while the pressure drop is approximately 62 kPa. In the system tests using nanofluid, the fluid temperature is 39.5 ℃ on average and the pressure drop is about 53 kPa.