Effect of pipe orientation on dense-phase transport in inclined upward and downward flows

A physical model is presented to describe the flow characteristics of cocurrent two-layer upflow and downflow through inclined tubes. The influence of inclination angle on these two kinds of flow patterns has been investigated. For inclined upflow, the solids/gas velocity ratio is less than unity and decreases slightly with the increase of inclination angle, whereas for inclined downflow, this velocity ratio is, in general, greater than unity and increases with the inclination angle. The average voidage increases as the inclination angle decreases for inclined upflow while an opposite trend exists for inclined downflow. The pressure gradient is invariably negative for inclined upflow at various inclination angles and for inclined downflow of low inclination; however, the gradient becomes positive for inclined downflow at higher inclination angles. A flow regime map has also been presented. The present predictions agree well with the existing published experimental results.