Heat transfer mechanisms in a compound parabolic concentrator: Comparison of computational fluid dynamics simulations to particle image velocimetry and local temperature measurements

Abstract

Particle image velocimetry (PIV) and local temperature measurements have been carried out on a lab-scale compound parabolic concentrator (CPC) collector model for various absorber temperatures and tilt angles. The results of these experiments are compared to computational fluid dynamics (CFD) calculations of the velocity field and temperature distribution. We found that transient simulations in 3D are required for a detailed reproduction of the natural convection currents obtained by PIV. Steady calculations in 2D, which are computationally much cheaper, lead to a reasonable overall agreement of the velocity field. The temperatures recorded at the mirror and the glass cover are well matched by the simulations, provided that the resolution of the mesh is fine enough to allow heat conduction along the thin features of the geometry (mirror and tube). With this knowledge we studied several scenarios, which are important for applications (reduced air pressure, inert gas fillings, temperature dependent material parameters) or physically interesting (effects of radiation and gravity). Finally, we demonstrate the level of detail, which can be obtained with these simulations: it is possible to separate the individual heat transfer mechanisms (conduction, convection and radiation) and to quantify their contributions to the heat loss of the collector.