Radiative Transfer Within a Cylindrical Cavity With Diffusely/Specularly Reflecting Inner Walls Containing an Array of Tubular Absorbers

Abstract

Monte Carlo radiative transfer analysis is applied to a cylindrical cavity-receiver containing an array of high-temperature tubular absorbers directly exposed to concentrated solar power entering through a spectrally selective window. The cavity walls are assumed either diffusely or specularly reflective. The relative dimensions, the number of tubes, and their position are optimized for maximum energy transfer efficiency or maximum absorber temperature. A single-tube absorber operating at 2000K performs best when located at 60% relative distance to the cavity’s aperture. Higher absorber temperatures are attained for a specularly reflective cavity that serves as internal infrared mirror but at the expense of lower energy transfer efficiencies. In contrast, diffuse reflecting cavity walls promote a more uniform temperature distribution around the tubular absorber. Decreasing the window-to-cavity areas ratio further results in an increase of the absorber temperature, which peaks for an optimum absorber-to-cavity radii ratio. This optimum ratio shifts to lower values for multiple-tube absorbers. However, the average absorber temperature is not significantly affected by using multiple-tube absorbers of constant total cross sectional area.