Cold-state experimental study on discharge characteristics of solid particles in a gravity driven moving bed solar receiver

Abstract

A small-scale multi-tube experimental system was established to pretest the workability of a gravity driven moving bed solar receiver with its absorbing section containing an insert in each tube. Discharge characteristics of solid particles with various particle sizes range from 149 μm to 1359 μm in mean diameter are studied at ambient temperature. In multi-tube experiments, the discharge rate in each tube is almost uniform. In single-tube experiments, the packed height in the particle dispenser exhibits negligible influence on the mass flow rate. Three models have been set up to predict the mass flow rate in the without-insert case of particle flow experiments. Among them, Model-3 is shown to obtain the minimum mean error of 1.54% compared with the experimental results, and proved that the influence of particle size and orifice diameter on the gas-solid slip velocity should be considered. Effect of the insert on particle flow characteristics was also investigated. The added insert in the tubes is proved to increase the mass flow rate of the finest particles. However, for particles coarser than 642 μm in mean diameter, this effect is insignificant and the mass flow rate in with-insert case is consistent with predicted results by Beveloo equation and Model-3. Besides, the experimental results of particles finer than 297 μm in with-insert case are larger than predicted results by Model-3 and less than that by Beveloo equation. It is noteworthy that two types of flow instability are observed with specific experimental variables, indicates that particle layer thickness, particle size and orifice diameter are relevant parameters to affect the granular flow state. Hence, optimizing structural parameters and selecting suitable size of particles are necessary to avoid flow instability in this type of solid particle solar receiver.