Numerical analysis of radiation propagation in a multi-layer volumetric solar absorber composed of a stack of square grids

• We present an original and simple geometric concept of volumetric absorber.
• Radiation propagation is detailed analyzed using Monte Carlo ray-tracing technique.
• Absorption performance in terms of geometrical characteristics of the absorber are provided.
• We propose a modified Beer–Lambert Law to describe the radiation absorption along the absorber.

In volumetric receivers of solar tower power plants, the absorber operates as a convective heat exchanger, absorbing concentrated solar radiation and transferring thermal energy to a heat transfer fluid flowing through it. A high-performance volumetric absorber must minimize the power losses by reflection and re-emission on its frontal face, promote radiation propagation and encourage a high heat transfer to the fluid. This paper analyses the radiation propagation in an original volumetric absorber, applying the Monte Carlo ray-tracing method. The proposed absorber consists of a stack of thick square grids in which the relative position between consecutive grids is shifted in the transversal direction. This study analyses the influence of the grid length, the gap between consecutive grids and the wall thickness, the significance of the absorber reflectivity, and the effect of the direction of the incident radiation. A general expression that describes the absorption capacity of the absorber and its extinction length is obtained.