Computational study of heat transfer in solar collectors with different radiative flux models

Abstract

Two-dimensional steady incompressible laminar Newtonian viscous convection-radiative heat transfer in a rectangular solar collector geometry is considered. The ANSYS FLUENT finite volume code (version 17.2) is used to simulate the thermo-fluid characteristics. Extensive details of computational methodology are given to provide engineers with a framework for simulating radiative-convection in enclosures. Mesh-independence tests and validation are conducted. The influence of aspect ratio, Prandtl number (Pr), Rayleigh number (Ra) and radiative flux model on temperature, isotherms, velocity, and pressure is evaluated and visualized in colour plots. In addition, local convective heat flux is computed, and solutions are compared with the MAC solver for various buoyancy effects achieving excellent agreement. The P1 model is shown to better predict the actual influence of solar radiative flux on thermal fluid behaviour compared with the limited Rosseland model. With increasing Ra, the hot zone emanating from the base of the collector is found to penetrate deeper into the collector and rises symmetrically dividing into two vortex regions with very high buoyancy effect. With increasing Pr there is a progressive incursion of the hot zone at the solar collector base higher into the solar collector space and simultaneously a greater asymmetric behaviour of the dual isothermal zones.