The behaviour of silica sand particles with mean sizes 0.3, 0.45 and 0.6 mmfluidised by air under pressures from 0.1 to 0.8 MPawas observed in a transparent two-dimensional bed. Minimumfluidisation velocity, bed expansion and bed height fluctuation were measured by the usual methods, bubble characteristics such as the size, rising velocity and frequency by cine-photography.The minimumfluidisation velocity decreased with pressure, explainable by considering the increase of the turbulent flow contribution to bed pressure drop, and fairly well described by the Wenand Yucorrelation. No virtual effect of pressure on bubble size was observed but bubble shape became flattened, which in turn accompanied a decrease in the bubble rise velocity. Based on these results, the increased bed expansion and the unchanged bed fluctuation could be consistently explained.

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