Heat transfer in a directly irradiated ceria particle bed under vacuum conditions

Vacuum particle receivers have been proposed recently for the reduction of redox material in solar thermochemical redox cycles. To assess the performance of these receivers, it is essential to describe the heat transfer in particle beds correctly. A widely used model for effective thermal bed conductivity is the one developed by Zehner, Bauer and Schlünder, which was derived for the steady state case without interstitial gas flow. In this study it was investigated if the model is also applicable for suddenly irradiated ceria particle beds in a typical solar vacuum receiver environment. Therefore a particle bed of ceria was irradiated with a solar simulator under vacuum conditions to peak temperatures above 1300°C. Within the bed, temperatures were measured at different locations for various pressures between 25 Pa and ambient conditions. The experimental results were compared to heat transfer simulations in ANSYS Workbench incorporating the aforementioned bed conductivity model. A good agreement between experiment and simulation was found and the model was considered applicable.