On dense phase voidage and bubble size in high pressure fluidized beds of fine powders

Dense phase voidage, ε D , dense phase superficial gas velocity, u Do , and absolute bubble rise velocity, u B , were measured at pressures up to 8300 kPa in a pilot‐scale, fluidized bed of Group A and boundary Group A/B powders. The mean equivalent bubble diameter, d b , near the top of the bed was inferred from u B , and known bed operating conditions. Increased pressure at fixed superficial gas velocity, u o , increased ε D and u Do and decreased d b for Group A powders. The marked decrease in inferred maximum bubble size, d   b   max'with increased pressure could not be explained by a decrease in gas contributing to bubble flow, u Bo , but rather appeared to be the result of a bubble instability phenomenon limiting bubble growth.