Quantitative Measurement of Hydrodynamics in a Binary Fluidized Bed by Capacitance Probes

The hydrodynamics of binary particle mixing in a gas-solid fluidized bed were measured by using the capacitance probe method. A novel output voltage signal processing method based on a double threshold was proposed. Originally employed for voidage measurement in monodisperse systems, the capacitance probe method has been successfully extended to assess bubble and mixing characteristics in binary systems by establishing bubble and emulsion phase search algorithms. Through direct comparison with digital image analysis (DIA), quantiles of 0.15 and 0.45 were determined as thresholds for identifying emulsion and bubble phase, respectively. Experimental results demonstrated that under steady-state conditions, the volume ratio of jetsam decreased with increasing bed height, while higher gas velocities enhanced longitudinal and transverse mixing. Average bubble size and rising velocity increased with both the probe height and gas velocity. An improved empirical correlation for bubble diameter was proposed based on variations in local bed mixing degree, yielding a relative error below 20%. The average bubble rising velocity exhibited a direct relationship with the bubble diameter. Relative errors of measured velocities obtained through the capacitance probe method, DIA method, and empirical relation all remained below 15% across each operating condition.