Non-uniform and volumetric effect on the hydrodynamic and thermal characteristic in a unit solar absorber

Experimental and numerical analyses on the thermal and hydrodynamic performance of volumetric solar receivers were conducted. Silicon carbide (SiC) absorbers with various pore structures were systematically investigated on a laboratory-scale test platform. A three-dimensional theoretical model coupling the fluid flow with internal heat transfer was presented. The major characteristics of the thermal and hydrodynamic behavior combining radiation, thermal conduction, and interphase convection in the absorber were presented. In addition, the key design parameters were systematically analyzed. The experimental results revealed that a small pore diameter significantly enhances the volumetric heat-transfer coefficient, which in turn increases the fluid temperature and subsequently leads to a high thermal efficiency. Under high local thermal non-equilibrium state, the non-uniform hydrodynamic characteristic significantly influenced due to the increase in the fluid viscosity at the hot spot, especially in the case of a small-pore-sized absorber, thereby increasing the risk of overheating. For absorbers with similar porosities (ϕ ∼ 0.85), dp decreased from 5.83 mm to 2.22 mm, and the thermal efficiency η increased by nearly 3%. Moreover, the simulation results revealed that the absorber unit with dp of 2.22 mm and ϕ of 0.95 exhibits the maximum thermal efficiency of 72.48%.