Mathematical model and numerical analysis of uniform and axially graded volumetric solar receivers with radiation boundary condition

Resumo

© 2026 Elsevier LtdConcentrated Solar Power (CSP) plants generate electricity by concentrating solar radiation onto a receiver, where a heat transfer fluid absorbs and transports thermal energy to a power cycle. Volumetric solar receivers (VSRs) have attracted attention due to their enhanced heat transfer characteristics and high-temperature capability, which contribute to improved overall system efficiency. Here, the performance of different VSR configurations is investigated numerically, focusing on both uniform and axially graded particle size distributions. Four configurations are analyzed: two with constant particle diameters of 1 mm and 3 mm, and two graded configurations in which the particle diameter varies linearly between these values along the flow direction, either increasing or decreasing. The numerical model employs the thermal non-equilibrium assumption and the Rosseland approximation to simulate radiative heat transfer within the porous medium. A radiation boundary condition was applied at the inlet to model the heat transfer, and verification against analytical solutions showed negligible discrepancies. The study analyzed the effects of different inlet velocities and porosities on these receivers. Results show that lower mass flow rates and porosities increase receiver temperatures. Configurations with the same inlet particle size display similar temperature profiles, with larger particles causing more pronounced differences. For smaller inlet particle sizes, graded configurations with increasing diameter achieve similar temperatures as the uniform case but with lower pressure drops. Moreover, decreasing particle sizes along the flow direction led to faster thermal equilibrium for higher porosities, allowing for more compact receiver designs. These findings provide insights for optimizing solar volumetric absorbers to enhance thermal efficiency in CSP applications.

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