Observations of a fluidized bed using capacitance imaging

Abstract

The Morgantown Energy Technology Center has developed a unique method for imaging voidage distributions within fluidized beds. This system allow high-speed three-dimensional imaging of the voidage distribution in a bed to be recorded. From these imaging data a variety of visualizations can be constructed and quantitative information extracted. Five materials with differing particles shapes and sizes were fluidized and imaged in a 15.24 cm diameter bed over a range of superficial velocities. The imaging revealed a variety of bubble sizes and shapes depending on the material and velocity. Bubble properties including a frontal diameter, length, velocity and spacing were determined. A correlation of bubble rise velocity developed from an earlier study was modified to include the bubble length as the primary dimension defining the bubble. The imaging also revealed detailed voidage distributions around bubbles and slugs. These images show round-nose bubbles and slugs for the fine materials examined. With the coarser materials, a very blunt slug was common. The technique has the potential to substantially improve design and scale-up of fluidized beds and other gas-solid systems by providing a detailed understanding of voidage distributions in these systems.