Thermal–hydraulic performance enhancement of graded double–layered volumetric solar air receiver under parallel and counter flow schemes

This study numerically investigates the thermal and hydraulic performances of a novel double–layered volumetric solar receiver (VSR) using silicon carbide (SiC) foam. In contrast to prior studies that mainly investigated the ceramic foam without preserving a constant total solid volume in double–layered configuration, the present work proposes a constrained optimization approach in which the solid volume of a uniform single layer foam is optimally redistributed into a double–layered configuration while maintaining the total solid volume constant. This approach ensures a fair comparison among different receiver configurations and systematically explores both parallel and counter flow schemes relative to the incident concentrated solar radiation direction which have not been addressed in the literature. Using the volume–averaged approach, P1 approximation and local thermal non–equilibrium (LTNE) models, the temperature distributions within the solid and fluid phases were simulated. The results reveals that the double–layered configuration can significantly boost overall efficiency from approximately 56 % to over 84 %. The optimal design with a graded porosity configuration of ( ϕ ₁ = 0.90, ϕ ₂ = 0.70) under the counter flow scheme achieved a peak efficiency of 84.86 % with a maximum outflow temperature of 833.1 K, demonstrating a substantial enhancement in thermal performance.