Multibubble Behavior and Solid Circulation Rate in a Gas–Liquid–Solid Circulating Microfluidized Bed

Comprehensively understanding the hydrodynamics of microfluidized beds is advantageous for guiding their application in chemical and related process industries. This paper investigated the flow regime transition, multibubble behavior, and solid circulation rate of a three-phase circulating microfluidized bed with an inner diameter of 0.8 mm. Experimental results showed that increasing the gas velocity significantly facilitated the transition to the circulating fluidization regime. Transitions between different flow regimes could be delayed by enhanced wall effects. The bubble diameter ranged from 0.1 to 0.5 mm and followed a log-normal distribution. The bubble velocity could be affected by wall effects, particles, bubble coalescence, and bubble spacing. The average bubble velocity was related to the flow regime and decreased in the axial direction. The solid circulation rate, expressed in terms of mass flow rate, was determined using the image mean gray value method in combination with the PIVlab, with a deviation from measurements obtained using traditional methods of less than 10%.