Study of the optimum discrete structure configuration in obstructed flow particle heating receivers

Abstract

Particle heating receivers (PHR) are a new class of receivers that use particulate materials as the heat absorption and storage medium. One variation of PHRs is the obstructed flow receiver, where particles are released from a slender slot in the form of a curtain and then forced to go through and around discrete obstructions (called chevrons) to limit their acceleration and increase their residence time, thereby increasing receiver efficiency. This design was successfully tested at the proof-of-concept scale. However, two of the potential issues with this design are dense packing of chevrons which can make the installation process cumbersome and potentially expensive, and that the velocities can be too low to the point that overheating of the chevrons can occur. This study addresses these issues by looking at the particle flow characteristics of less dense chevron configurations. For this purpose, a full-scale 2.5-m mock-up obstructed flow PHR was constructed, with a particle feeding hopper and a receiving tank. The feeding hopper is fitted with a slot at the bottom to allow a predetermined mass flow rate to go through it. Two characterization tools were used: a high-speed camera with particle image velocimetry analysis to measure the particle velocity profile, and a light source/lightmeter arrangement to measure curtain opacity. Two chevron spacing cases were considered: a spacing of 30 mm and a spacing of 60 mm. The tilt angle was also varied from 3 degrees to 10 degrees. Results show that a considerable tilt angle (10 degrees) is needed to retain a majority of particles within the PHR. It was also found that the obstructed flow PHR design effectively and consistently limited particle velocity, with the highest recorded velocities being 0.7 m/s and 0.95 m/s for chevrons spacings of 30 mm and 60 mm, respectively. Furthermore, particle curtain opacity was found to be high (approximately 71%) at a chevron spacing of 60 mm, despite the low mass flow rate at which testing took place (1.53 kg/s.m).