Radiation absorption is investigated in a particle curtain formed in a solar free-falling particle receiver. An Eulerian–Eulerian granular two-phase model is used to solve the two-dimensional mass and momentum equations by employing computational fluid dynamics (CFD) to find particle distribution in the curtain. The radiative transfer equation (RTE) is subsequently solved by the Monte Carlo (MC) ray-tracing technique to obtain the radiation intensity distribution in the particle curtain. The predicted opacity is validated with the experimental results reported in the literature for 280 and 697 μm sintered bauxite particles. The particle curtain is found to absorb the solar radiation most efficiently at flowrates upper-bounded at approximately 20 kg s−1 m−1. In comparison, 280 μm particles have higher average absorptance than 697 μm particles (due to higher radiation extinction characteristics) at similar particle flowrates. However, as the absorption of solar radiation becomes more efficient, nonuniform radiation absorption across the particle curtain and hydrodynamic instability in the receiver are more probable.
