Generation of a radiation absorbing medium for a solar receiver by elutriation of fine particles from a spouted bed

In high-temperature solar-thermal systems the conversion of solar to thermal energy requires a radiation absorbing sur ace to transfer the radiative solar energy to the working fluid. The present study focuses on the generation of a moving radiation absorber using particles suspended in the working fluid. Three methods of particle entrainment in a gas were investigated. Elutriating fine particles from a spouted bed was found to be the preferred method. The diameter range of the entrained carbon black particles was 0.030-25 mu m, with 99.7% of the particles having an equivalent diameter less than 1 mu m, and 48% of the projected surface area was due to agglomerated particles with average equivalent diameter >5 mu m. The moving radiation absorber was tested in a solar receiver using nitrogen as a working fluid. The inner, wall temperatures in the receiver cavity were below the gas exit temperature, which shows that the bulk heat transfer from the incoming solar radiation to the gas takes place via the moving radiation absorbing particles.