Opacity Measurement of Particle Curtain of Obstructed Flow Particle Heating Receivers

Understanding particles flow behavior is of paramount importance in designing obstructed flow particle heating receivers (OF-PHR), and one of the important metrics is opacity of the particle curtain. In this work, the opacity is defined geometrically, i.e., ratio of area covered by the particles to the total area of the curtain. Particle curtain opacity of an OF-PHR having a single row obstruction was measured. The obstructions tested were perforated plates with two different holes-arrangements, i.e., parallel and staggered. Plate thickness, hole diameter, and pitch were measured to be 1.38, 2.84, and 4.29 mm, respectively, with angles of 60° between three adjacent holes. Two different fall distances (release point) above the obstruction were tested: 30 mm and 60 mm. The tilt angle and mass flow rate used were fixed, i.e., 0° and 1.91 kg/(s∙m), respectively. The opacity was measured across a region for every 20 mm below the obstruction (0-20, 20-40, 40-60, and 60-80 mm); the opacity encompassing the whole region (0-80 mm; overall opacity) was also measured. It was found that the fall distance affects the opacity a little, i.e., doubling the distance from 30 to 60 mm only increased the opacity by 14.4% (relative change) at most. Parallel and staggered hole arrangement resulted in very close values of particle curtain opacity. Finally, it is concluded that to ensure opacity values to remain equal or greater than 85% throughout PHRs with multiple rows downstream, spacing between the perforate plate should be no greater than 40 mm.