Investigation of thermal characteristics and entropy generation in a solar collector including Fly Ash-Cu hybrid nanofluids: Numerical approach using mixture model

Heat transfer enhancement is one of the substantial challenges in solar energy conversion systems. By using two different working fluids, namely water and Fly Ash-Cu/water hybrid nanofluids (80:20 Vol.%), this numerical research aims to improve heat transfer by modeling the flat plate solar collector's (FPSC) tube in a zigzag shape instead of a common straight pipe. The innovation of the present study is to evaluate the second law of thermodynamics in a proposed solar collector including Fly Ash-Cu/water hybrid nanofluids and compare the second law of thermodynamics' results with the Mixture model. Also, various thermal characteristics, such as the Nusselt number, convection heat transfer coefficient (HTC), friction factor, and outlet temperature, are examined at different nanoparticle concentrations, two inlet temperatures, and different mass flow rates. The system works under conjugated laminar mixed convection and constant solar irradiation, 800 W m-2. Results reveal that working fluid pumps with a higher flow rate increase Nusselt number, convection heat transfer coefficient, and friction entropy generation, about 33.33%, 41%, and 88%, respectively, while outlet temperature, friction factor, and thermal entropy generation decrease with increasing mass flow rate. Furthermore, using nanoparticles with a higher concentration considerably increase friction and thermal entropy generation.