Effect of Concentration Ratio on Flow Pattern in Solar CPC Cavity

A two-dimensional numerical model of the compound parabolic collector (CPC) with a tubular receiver has been developed to study the effect of the concentration ratio of the collector on the flow profile in a horizontally held cavity and heat losses by the collector. Six concentration ratio (CR) values have been analyzed for three diameters. As per the literature, very few studies have investigated this effect for a horizontal CPC cavity. The convective and radiative heat losses have been modeled using the k-epsilon turbulence and surface-to-surface (S2S) radiation models. The heat conduction in walls is considered by giving suitable wall thickness. Different cases have been simulated to obtain total heat losses, Rayleigh number, velocity vectors, and temperature contours. The results showed total heat losses, and the Rayleigh number increased with the concentration ratio. A symmetric bicellular flow pattern was obtained in the CPC cavity for four CR values (1.1, 1.4, 2.9, and 3.9). However, CR values of 2.0 and 2.5 showed a deviation from this behavior by showing an asymmetric behavior for the flow pattern for the same boundary conditions.