Experimental investigation of wet particle flow characteristics in a pseudo two-dimensional fluidized bed

Abstract

The flow characteristics of wet particles in a fluidized bed are extremely complicated due to the presence of moisture. It is essential to understand the complex behavior and flow characteristics of wet particles in the drying, coating and granulation process for optimizing the process efficiency and product quality. Thus, the flow characteristics of wet particles, such as pressure fluctuation, bubble size and bubble fraction, in a pseudo two-dimensional fluidized bed were investigated through the multi-resolution time-frequency analysis of the pressure signal combined with the high-speed camera images. Results show that the critical fluidization velocity increases after the particles are wetted, and it shows a slight increase with higher moisture content levels. Besides, there are two main characteristic frequencies, which correspond to the gas-solid flow state of the gas channel and the large bubble in the bed, respectively. Notably, higher gas velocities promote the dominance of large bubbles. And increasing particle moisture inhibits bubble expansion and reduces bubble size, while dense particle areas expand vertically due to enhanced bonding. The bed height increases with the increase of moisture, and the fluctuation of bubble fraction decreases. In the drying experiment, two characteristic frequencies also appear and the pressure drop reduce slightly due to the reduction of water. During the drying process, both the average bubble fraction and fluctuation intensity increase.