Numerical Investigation of Natural Convection Loss in Cavity-Type Solar Receivers

In solar thermal systems, especially for high concentration applications, natural convection contributes a significant fraction of energy loss. Its characteristics hence need to be understood so that it can be effectively minimized in order to improve system efficiency. The present study numerically investigates the influence of cavity geometry and inclination on the convective loss through the aperture. The Computational Fluid Dynamics package “Fluent 6.0” has been used to investigate three cases of geometrically different receivers. The calculated heat loss results shows a nonlinear dependence on the inclination angle and shows qualitatively good agreement with those calculated by various previously proposed empirical models. The Clausing model (1981) shows the closest prediction to both numerical and experimental results despite its original use for larger-scale central receiver systems.