Parametric study of volumetric absorber performance

This study investigates the possible performance of volumetric absorbers as a function of geometric and material properties, aiming to identify the best absorber design parameters and the highest efficiency that may be expected. A simplified model is used with non-equilibrium heat transfer correlations and the two-flux approximation of one-dimensional radiative transfer. The radiative flux model has been validated against a detailed Monte-Carlo simulation. This model is simple enough for fast computation and parametric study. The results show that considerable gains in volumetric absorber efficiency can be achieved by careful selection of the absorber properties. In addition to porosity and pore size, two additional overlooked properties are also significant: the thermal conductivity of the absorber material, and the optical selectivity of the absorber surface. Under certain conditions, reducing the thermal conductivity leads to a significant decrease in emission loss, almost reaching the ideal volumetric absorber at local thermal equilibrium. This implies that the common preference for absorber materials such as SiC should be reconsidered. Spectral selectivity of the absorber material can also produce a significant increase in efficiency, but this is valid only when the selectivity is close to ideal.