Computational fluid dynamic simulation of a solar enclosure with radiative flux and different metallic nano-particles

Nanofluids are currently being explored extensively in solar energy engineering to achieve improved performance in direct thermal absorber systems. Nanofluids achieve significant enhancement in the heat transfer performance i.e. thermal efficiency. Motivated by these developments in nano-technology, in this poster we present recent simulations of steady-state nanofluid natural convection in a solar collector enclosure. Two-dimensional, steady-state, incompressible laminar Newtonian viscous convection-radiative heat transfer in a rectangular solar collector enclosure geometry is modelled with ANSYS FLUENT finite volume code (version 18.1). The enclosure has two adiabatic walls, one hot (solar receiving) and one colder wall. The TiwariDas volume fraction nanofluid model is used and three different nanoparticles are studied (Copper (Cu), Silver (Ag) and Titanium Oxide (TiO2)) and water base fluid. The solar radiative heat transfer is simulated in the ANSYS workbench, with the elegant P1 flux model and the Rosseland model. The influence of geometrical aspect ratio (AR) and solid volume fraction for nanofluids is also studied and a wider range is considered than in other studies. These constitute novel contributions in the area of solar nanofluid collectors since these aspects are considered collectively. Mesh-independence tests are conducted. Validation with published studies from the literature is included for the copper-water nanofluid case. The P1 model is shown to more accurately predict the actual influence of solar radiative flux on thermal fluid behaviour compared with Rosseland radiative model. With increasing Rayleigh number (natural convection i.e. buoyancy effect), significant modification in the thermal flow characteristics is induced with emergence of different vortex regions. With increasing aspect ratio (wider base relative to height of the solar collector geometry) there is a greater thermal convection pattern around the whole geometry, higher temperatures and the elimination of the cold upper zone associated with lower aspect ratio. Titanium Oxide nano-particles achieve higher temperatures and a greater local heat flux at the hot wall. Thermal performance can be optimized with careful selection of aspect ratio and nano-particles and this is very beneficial to solar collector designers. The modelling approach can be extended in future to consider fully three-dimensional simulations and unsteady effects.