Performance analysis of a minichannel-based solar collector using different nanofluids

In this paper, an analytical analysis has been performed to evaluate the performance of a minichannel-based solar collector using four different nanofluids including Cu/water, Al₂O₃/water, TiO₂/water, and SiO₂/water. The analysis of first and second laws is conducted for turbulent flow by considering the constant mass flow rate of nanofluid. The results are presented for volume fractions up to 4% and nanoparticle size of 25 nm where the inner diameter of the risers of flat plate collector is assumed to be 2 mm. Analysis of the first law of thermodynamics reveals that Al₂O₃/water nanofluids show the highest heat transfer coefficient in the tubes while the lowest value belongs to SiO₂/water nanofluids. The highest outlet temperature is provided by Cu/water nanofluids, and after that TiO₂/water, Al₂O₃/water, and SiO₂/water nanofluids are in ranks of second to fourth. The results of second law analysis elucidate that Cu/water nanofluid produces the lowest entropy generation among the nanofluids. It is found that although the effective thermal conductivity of TiO₂/water nanofluids is less than Al₂O₃/water nanofluids, but the entropy generation of TiO₂/water is lower than Al₂O₃/water. Finally, some recommendations are given for future studies on the applications of nanofluids in solar collectors.