Measurements of solid volume fraction and granular temperature at granular avalanches in a drum

Abstract

A granular flow in the drum has high heat exchange efficiency and mixing efficiency, and is widely used in industrial productions. Accurately describing the flow properties is extremely important for industrial production. In this work, an image measuring device based on area array CCD camera and a Speckle Visibility Spectroscopy (SVS) measuring device based on linear array CCD camera were established. Spherical particles having a mean particle diameter of 0.5 mm and irregular particles having an equivalent particle diameter of 0.5 mm were used. By measuring the profile of the side surface of the granular system in the drum, the volume fractions before and after the avalanche of the granular system were calculated. It was found that both the spherical particle system and the irregular particle system expanded during the avalanche process; before the avalanche, the irregular particle system was compacted, while the spherical particle system did not compact. Furthermore, granular temperature at different locations on the free surface of the granular flow was measured. It was found that the avalanche of the spherical particles and the irregular particles occurred at the same position; the compaction of the irregular particle system first occurred in the upper half of the system, and the compaction phenomenon occurred only once during one avalanche cycle time. Finally, based on the side surface profile and granular temperature, the angle of repose and characteristic time parameters were measured. It was found that the relationship between the angle of repose of the spherical particle system and the avalanche time was consistent with the model proposed by Davidson, and the compaction of the irregular particle system before avalanche would shorten the avalanche time of the particles. The experimental results obtained in this work provide reference data for improving the precise control technology of the flow and heat transfer of the granular materials in industrial productions.