Numerical evaluation of the extinction coefficient of honeycomb solar receivers

Abstract

Open volumetric receivers are porous media used in absorbing concentrated solar radiation reflected from a heliostat field with the objective to gain heat for an electricity generating thermal engine. Air is sucked through the hot, open porous material and heats up to high temperatures before it enters the steam generator of a turbine. In order to optimize these components in terms of pore geometry, a numerical prediction of the heat transfer and flow properties is useful. Due to the high complexity of the porous media’s microstructure, effective parameters are used to describe the physical phenomena occurring in such structures on a macro-scale level. This study evaluates numerically one of the necessary parameters: the effective extinction coefficient. It describes how the concentrated radiation is absorbed in the volume of the receiver. For this purpose, a self-developed numerical tool in ANSYS environment has been used. The developed tool calculates the effective extinction coefficient of the solar radiation striking the receiver’s inlet at any angle of incidence. Afterwards the tool can be applied for various honeycomb geometries and the generated coefficients may be used to predict the complete thermal behaviour of the receiver with the purpose to find a new geometry with a higher solar-to-thermal efficiency.