Assessments of thermal performance of hybrid and mono nanofluid U-tube solar collector system

Abstract

Solar energy systems are of great importance for water heating, where we spend most of the energy. U-tube solar collectors have a very important place in water heating among solar energy systems. Compensation of the intense energy used for water heating by this type of environmentally friendly solar energy system, will reduce CO2 and SO2 emissions for a cleaner nature. Therefore; the thermal performance of a U-tube complete system from evacuated tube solar collector (ETSC) systems was assessed. The heat transfer capability of the system, which contains 10 U-tubes, has been examined by considering the fact that it has different work fluids and different heat fluxes and flow rates. The finite volume method is used for this analysis. The model has been verified by many experimental and numerical studies. In the system under consideration has been used 10 vacuum U-tubes inclined at 30°, and water and nanofluid (SiO2 - Cu) which were used as working fluid in the manifolds connected to these tubes. Nanoparticles modeled in the work fluid are considered as hybrid and mono at different volume fractions. The thermal and hydrodynamic behaviors of the system have been examined by taking into account the Boussinesq approach, and the system outlet temperatures have been calculated. As a result of analyzes and comparisons made, it has been seen that the use of nanofluid improves the thermal capability of the system under consideration. It has been determined that this improvement reaches up to 15% compared to water. The thermal effects of using SiO2 nanoparticles, which are lighter than Cu nanoparticles, were observed in terms of the precipitation problem encountered in many systems when using hybrid nanofluids. Thus, instead of using more Cu nanoparticles in volume, using smaller amounts together with SiO2 nanoparticles as a hybrid both eliminates the problem of precipitation and improves the heat capability of the work fluid.