Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.
The paper describes the Computational Fluid Dynamics (CFD) analysis of a parabolic dish tubular cavity receiver. The analysis uses the geometry of an experimental setup and considers experimental conditions as well as ideal conditions linked to a Brayton cycle microturbine implementation. The CFD analysis comprises of two parts. First, the Radiative Transfer Equation (RTE) is solved with a Finite Volume (FV) method using the Discrete Ordinates (DO) method for the optical performance of the dish and receiver to obtain the absorbed radiation on the receiver tube. In this method both an axi-symmetric model with a ring-like receiver is considered utilizing a 2-D mesh as well as a 3-D model with the spiraling tubular receiver. The former is much less computationally intensive because of the extra dimension but simplifies the receiver shape. The result of this FV simulation is an absorbed radiation distribution that is patched as volumetric heat source in the second CFD simulation. This simulation is a conjugate heat transfer model that evaluates the heat transfer to the heat transfer fluid as well as the losses from the cavity insulation and due to thermal re-radiation. The method is evaluated for an ambient lower pressure experimental test at the University of Pretoria as well as a theoretical implementation at Brayton cycle conditions.