Comparison of Experimental and Numerical Air Temperature Distributions Behind a Cylindrical Volumetric Solar Absorber Module

The current trend in volumetric solar receiver technology is to build modular receivers cooled by air (Hitrec I and II, Solair $200kW$ and $3MW$⁠) in order to facilitate the replacement of broken absorber modules (cups) and to simplify the upscaling of the receiver. In addition, the modular designs include an air return circuit to cool down the structure supporting the cups. Usually, the air outlet temperature from each module is characterized by measurements taken from a single thermocouple. However, the air temperature distribution behind the volumetric absorber module is not homogeneous, as it can be seen in some specific tests where several thermocouples were added behind different absorber modules. The radial distribution of outlet air temperatures shows very high temperature gradients. The goal of this work is to explain the inhomogeneous thermal maps behind the metallic absorbers by comparing some experimental results with numerical simulations performed using the computational fluid dynamics FLUENT code. The results show the wind influence over the air recirculation flow and its effects on the outlet air temperature radial distribution. Thus, the simulations suggest different ways to reduce the temperature gradients behind each cup.