Numerical and Experimental Approaches for the Characterization of Heat Transfer Mechanisms in Compound Parabolic Concentrators

Several physical mechanisms including conduction, convection, diffusion and radiation are involved when modelling heat transfer in a solar collector. A lab scale compound parabolic concentrator collector model was first analysed by particle image velocimetry (PIV) and local temperature probes for various tilt angles of the setup and different absorber tube temperatures to provide a base for comparison to computational fluid dynamics (CFD) results. To be able to separate the occurring effects no incoming radiation was used for the measurements: To drive the convective flow inside the CPC, the absorber temperature was fixed to a constant temperature instead. The Navier Stokes equations have been solved on 2D and 3D meshes using steady and transient solutions: for a detailed reproduction of the experimentally observed natural convection currents transient 3D approaches are required - if only overall temperatures, approximate velocity ranges and heat fluxes are of primary interest, computationally cheap two dimensional steady approaches can be facilitated. These simulations can also be used for a fast assessment of efficiency curves in various scenarios. Ray-tracing is utilized to describe the solar radiation patterns and investigate the influence of distributed energy sources on tube and mirror.