INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER

Evacuated tube solar collectors (ETSC) constitute an important place among water heating systems. The use of solar energy systems will reduce CO2 and SO2 emissions for green nature. In this context, geometric and technical values of the open-ended ETSC systems were optimized by considering different parameters. In the optimization study, the solar tube collector with vacuum tube which gives the most appropriate results was discussed and its effects on heat transfer according to the presence of different work fluids were investigated. For this study, a numerical study was carried out by applying the finite volume method, one of the computational fluid dynamics methods. We confirmed our numerical study with both experimental and numerical studies. In our study, water and water-based nano-fluids are used as heat transfer fluid in 24 heat tubes with 300 inclination and the related tank that connected to it. The water-based nano-fluids we used are water as the basic fluid and MWCNT, TiO2, SiO2 and Cu as the nanoparticles. We modeled nanofluids homogeneously by handling them for different volumetric ratios. The thermal and hydrodynamic conditions of the collector were investigated using the Boussinesq Approach and the tank exit temperatures were determined. As a result of this study, it was seen that the use of nano-fluids improved the heat transfer in the ETSCs and the best thermal recovery among the nano-fluids we used in our study was realized in Cu-Water nano-fluid. Improving the thermal performance of the ETSC is important for better energy conversion. For this reason, the effects of nano-fluid usage on thermal performance in solar energy systems of pollution-free energy are promising. (C) 2020 Elsevier Ltd. All rights reserved