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. Meshindependence 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.ANSYS FLUENT, aspect ratio, inite volume, MAC computational algorithm, radiative heat transfer, solar collector enclosure, thermal convection 1 | INTRODUCTION The interest in sustainable and renewable energy systems has witnessed significant expansion in the 21st century. Both land-based (terrestrial) and space-based (astronautical) types of solar collector have attracted considerable attention. Solar thermal collectors utilize the incoming radiation by converting it directly into heat whereas photovoltaics convert the radiation into electricity. Solar thermal systems therefore offer many desirable characteristics for propulsion, water and space heating.Space solar power collectors have multiple advantages over earth-based solar power plants. They receive more sun light, are unaffected by weather, free from the day-night cycle, and expensive storage can be avoided. 1,2 The types of geometric designs, which have been developed for spacecraft solar collectors, are generally similar to those of terrestrial systems. They invariably feature an enclosure (cavity) in which the solar radiation initiates and sustains a circulation flow field. The thermo-physics inevitably involves all three modes of heat transfer (conduction, convection, and radiation) although the individual contributions may vary with the particular design adopted, as elaborated by Kreith. 3 Several studies have confined attention to thermal conduction and radiation in spacecraft solar collectors, including Yang et al, 4 who studied three-dimensional anisotropic conduction and a simple radiation network model for collectors in deep cold space. The key mechanism in fluid-based solar collec...

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“…This is a simple but acceptable approach in engineering simulation; however, alternative radiative flux models are being considered for future investigations to provide more refinement to the optical properties of the nanofluid. 39 Figures 16 and 17 illustrate the influence of the Brownian motion parameter Nb on temperature (θ) and nanoparticle volume fraction concentration (ϕ). A slight increase in temperature profiles is observed with an increase in Nb values.…”

Dissipative-Radiative Micropolar Fluid Transport in a Non-Darcy Porous Medium with Cross-Diffusion Effects

“…These phenomena are of the same order of magnitude for the special case when Pr 1  . For Pr 1  physically corresponds that heat will transfer at an exceptionally faster rate than the momentum [52]. For Pr 1  , physically corresponds that momentum will diffuse faster than the heat through the regime.…”

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