Experimental study of flow regimes and dust emission in a free falling particle stream

• Three flow regimes of free falling particle stream are quantitatively identified.
• ηr decreases with the drop height in the transitive regime and increases in the dispersive regime.
• The second fugitive dust cannot be eliminated by the water surface.

The flow regimes in a free falling particle stream and the dust emission rate are experimentally explored in this paper. The results show that the particle stream could be divided successively into the stable regime, the transitive regime and the dispersive regime. The length of each regime is quantitatively identified. In our testing range, the dust emission rate (ηr) increases monotonically with Z and the gratitude gradually increases when the particle stream impacts onto the rigid surface in the transitive regime. The dust generation rate shows linear to the dimensionless drop height. However, the rate decreases slightly monotonically with the drop height (Z) when the particle stream impacts onto the surface in the dispersive regime. The dust generation rate presents an exponent relation with the dimensionless drop height. The empirical equation about ηr is derived. It is found that the second fugitive dust still emits under the condition that the particle stream impacts into the water surface when the hopper outlet diameter is from 1 to 8 mm. Reducing the expanding level and the impaction intensity of the particle flow is considerably important when the contact surface is in the transitive regime and the dispersive regime, respectively.

ηr decreases with the drop height in the transitive regime and increases in the dispersive regime.Figure optionsDownload as PowerPoint slide