An experimental and numerical study of granular flows through a perforated square lattice for central solar receiver applications

Abstract

A proposed design for a concentrating solar power (CSP) receiver uses a granular material - such as sand - as the heat transfer and energy storage medium. Early designs of particle heating receivers (PHR) utilize a falling curtain of particles which directly absorbs the concentrated solar radiation. However, falling curtain receivers have several disadvantages, including significant heat and particle losses, and a short residence time within the irradiation zone. One design proposal which overcomes these challenges is the so called “impeded flow PHR design”, in which the particles flow over, around, or through a series of obstacles in the flow path. This reduces the average velocity of the particles, thereby increasing residence time in the irradiation zone of the receiver. It also reduces heat and particle losses from the receiver. However, granular flows through complex structures are not well understood, rendering a priori design of impeded flow PHR geometries difficult. To better understand these flows, lab scale models of a PHR design variant using a perforated square lattice at an oblique angle have been constructed, allowing granular flows through the receiver geometry to be experimentally analyzed. In addition, two different numerical modeling approaches - the discrete element method (DEM) model, and a two-fluid computational fluid dynamics (CFD) model - have been developed to model the flow of particles through the specified receiver geometry. The results of the DEM model are in reasonable agreement with the experimental data with respect to mass flux, and better matches the experimental data than the CFD model.