Thermo-hydrodynamical optimization of direct absorption solar collector from Stokes to low Reynolds numbers regimes of nanofluid flow

Abstract

It has been proven that optical properties of base working fluids are significantly enhanced, where very small amount of nanoparticles are exploited. In the current study, numerical investigation of microchannel-based direct absorption flat solar collector (DAFSC) filled with graphite water based nanofluids at various volume fractions in an independent-scattering regime map of nanofluids were taken into account to evaluate thermo-hydrodynamical performance of DAFSC. Furthermore, multi-response optimization of DAFSC including thermodynamics second law efficiency (ηII), thermal efficiency (η(th)), heat loss rate (Q̇(out)), dimensionless temperature difference (θ), pressure drop (Δp), and also cost function (Cost) was carried out by response surface methodology. Fifty four numerical designs proposed by face-centred central composite designs (FCCD) have been used to provide sufficient data to obtain mathematical regression models of response functions in which the significant model's terms were evaluated by analysis of variance. Furthermore, composite desirability function approach was taken into account for multi-response optimization of direct absorption solar collector to maximize ηII, η(th), θ, and to minimize Q̇(out),Δp and Cost functions. Strikingly, the CFD results unveiled that maximum thermal efficiency of DAFSC with black back absorber surface, which was enhanced up to 18% compare to base case, is mainly shape-dependent rather than to that of nanoparticles volume fractions, which can be justified by presence of different dominant heat absorption mechanisms transforming from volumetric absorption for nanofluids to surface one for pure water.