The effect of nanoparticle morphology on heat transfer and entropy generation of supported nanofluids in a heat sink solar collector

Abstract

The thermal conductivity enhancement of nanofluids can be attributed to several factors such as volume fraction, temperature, material type, size and shape. In this study the effects of different morphology of supported nanoparticles, including copper (Cu), silver (Ag), aluminum dioxide (Al2O3), boehmite alumina (γ-AlOOH), molybdenum disulfide (MoS2) and silicon dioxide (SiO2), on heat transfer and entropy generation have been investigated in compression with each other in case of a water-based heat-sink solar collector located in Isfahan city, Iran. The control volume approach was used to solve the system of classical single phase three-dimensional governing equations by using the finite volume method (FVM). The standard k–ε turbulence model with enhanced wall function was selected. Furthermore, the spectral radiative transfer equation (RTE) was used to consider radiative heat transfer effects. Based on obtained results, the maximum value of averaged Nusselt number is achieved for MoS2 nanoparticles with sphere shape in φ = 4%, and it is followed by Ag with sphere shape in φ = 0.15%, Cu with sphere shape in φ = 0.20%, γ-AlOOH with sphere shape in φ = 4%, Al2O3 with sphere shape in φ = 4% and SiO2 with sphere shape in φ = 4%. The maximum value of outlet temperature is achieved for Ag nanoparticles with sphere shape in φ = 0.15%, and it is followed by Cu with sphere shape in φ = 0.20%, MoS2 with sphere shape in φ = 4%, Al2O3 with sphere shape in φ = 4%, SiO2 with sphere shape in φ = 4% and γ-AlOOH with sphere shape in φ = 4%. The minimum value of entropy generation is achieved for γ-AlOOH nanoparticles with bricks shape in φ = 2%, and it is followed by SiO2 with bricks shape in φ = 1%, MoS2 with bricks shape in φ = 1%, Ag with sphere shape in φ = 0.05%, Cu with sphere shape in φ = 0.05% and Al2O3 with bricks shape in φ = 1%. In case of heat transfer for all studied nanoparticles (metal and nonmetal nanoparticles), sphere shape is the best morphology for each nanoparticle material. For metal nanoparticles the minimum value of entropy generation is achieved by sphere shape. But for nonmetal nanoparticles the minimum value of entropy generation is reached by bricks shape morphology. Due to fulfill a heat exchanger with more energy efficiency (1st law view point), usage of sphere nanoparticles with optimum size and volume fraction is suggested. In order to achieve a heat exchanger with less entropy generation (2nd law view point), usage of bricks shape nonmetal nanoparticles with optimum size and volume fraction and sphere shape metal nanoparticles with optimum size and volume fraction is suggested.