A capacitive system for three-dimensional imaging of fluidized beds

Abstract

A novel capacitance imaging system (CIS) has been developed which has unique capabilities for providing real-time, three-dimensional monitoring of fluidized-bed density. While the system was developed primarily to serve as a high-speed, density-imaging tool in fluidization research and development, it could also be used in other applications, such as pipeline transfer of solids, where multiphase dielectric material density changes are to be monitored. The CIS uses 16 evenly spaced, circumferentially located electrodes at each of four levels evenly spaced along the axis of a 6-in. diam fluidized bed as the density-sensing elements. The electronic system utilizes interelectrode displacement current values to obtain bed density estimates at each of the 49 pixels defined at each of the four levels. The system provides a real-time display of each of the four density maps at a rate of 30 maps per second at each level. The system also stores displacement current data, updated 100 times per second, for post-run analysis of bed behavior. The CIS capabilities are demonstrated for a plastic bead bed material. Density maps show the progression of a low-density region upward through a fluidized bed. Experimental use of the system by others produced values of bubble dimension and velocity that are consistent with values predicted by accepted theory.