Abstract
An experimental investigation was carried out to study the impact of two retrofitting techniques on the flow pattern and rate of discharging solids from a conical screen hopper at the bottom of an ion-exchange column. The two retrofits were a double-pyramid insert and a throttling vertical tube attached to the outlet orifice. Part 1 [1] discussed the impact of the double-pyramid insert on converting the flow pattern in the conical screen hopper from funnel to mass flow. Part 2 shows that developing severe and sudden constriction at the outlet orifice, by utilizing throttling vertical tube, will raise the shear rate and magnify the interstitial drag effects. This will induce the solid particles to dilate in order to accommodate the shear thereby causing transition from packed bed to suspension flow regime. The dynamics of the flow transition may include a sudden collapse of the interface between the two flow regimes resulting in a significant increase in the mass flowrate. Cavitation is believed to occur under these circumstances resulting in an intensified transition. Furthermore, experimental results support the hypothesis that as the constriction increases, the flow switches to a regime with density waves (plugs) of constant velocity down the throttling vertical tube.
