High-Temperature Performance of Porous Volumetric Solar Absorbers Under Axial and Radial Inlet Flow Configurations

This work presents a parametric numerical study of porous volumetric solar absorbers under high-temperature operation, focusing on the coupled effects of inlet feeding pattern (axial vs. radial), target outlet fluid temperature (T_f,out = 1000 K and 1300 K), and incident-flux nonuniformity quantified by I_peak/I_avg. For each condition, the inlet velocity was iteratively adjusted until the computed outlet fluid temperature matched the target value, and the corresponding mass flow rate was obtained from the converged solution, enabling consistent comparisons across configurations and irradiation levels. The results show a marked efficiency reduction at 1300 K, mainly driven by increased reradiation losses that scale strongly with temperature. Increasing I_peak/I_avg further decreases efficiency in both inlet patterns, consistent with hotspot-dominated heating under peaked irradiation. Under the present modeling assumptions, the axial inlet predicts systematically higher efficiency than the radial inlet, with the axial–radial separation becoming more relevant at 1300 K, indicating that inlet specification can affect predictions under high-temperature conditions. Temperature contours, foam-surface temperature profiles, and inlet-plane velocity components reveal that radial feeding sustains a hotter porous matrix—particularly near the wall—associated with inlet-driven flow redistribution and weaker local convective extraction. These findings link flux nonuniformity to hotspot formation and radiative losses, and provide guidance on inlet-modeling assumptions for high-temperature porous receivers.