Analyses of entropy generation for a solar minichannel flat plate collector system using different types of nanofluids

The working fluid plays a major role in improving the efficiency of the energy system, so the method and criteria of choice are extremely important. Nevertheless, these methods are usually based on the First Law of Thermodynamics (FLT), while the concepts of entropy and irreversibility on which the Second Law of Thermodynamics (SLT) is based are often ignored in the choice of the fluid. In this paper, a new approach is proposed to select a fluid among a group of fluids in order to use it as a working fluid in a Minichannel Flat Plate Solar Collector (MFPSC). For this, a numerical simulation was performed on a fluid in laminar flow in a small rectangular channel subjected to a uniform heat flux of (1000 W/m2). The use of Computational Fluid Dynamics (CFD) based on the finite volume method was implemented to solve the governing equations. The essential parameters on which the selection is based are the entropy generation (Sgen), the irreversibility of entropy generation number (Ns), the Bejan number (Be), and the Energy Performance Criterion (EPC). The analyses were performed on a group of five fluids two conventional (water and methanol), the rest are nanofluids (Al2O3-H2O, CuO-H2O, and Fe3O4 -H2O). Multiple parallel-computation phases are defined by user-defined functions (UDFs) for all fluids. It is found that nanofluids offer higher heat transfer ability than conventional fluids, and the behavior of the nanofluid (CuO-H2O) shows on average a minimum total entropy generation (minimum irreversibility) compared to other fluids (conventional and nanofluids), which reduces the energy degradation and improves the heat transfer. Therefore, it is chosen as the working fluid for the MFPSC.