Blockage in vertical slots: Experimental measurement of minimum slot width for a variety of granular materials
The design of some processing equipment requires knowledge of the safe minimum dimensions of slots, channels or conduits for flowing granular materials. This work was prompted by the need to ensure that when narrow slots were used in a slot flow meter, they were capable of providing a continuous and uninterrupted flow. There are some data in the literature for blockage of openings in the horizontal plane, but there is very little published information of any sort on vertical slots. The materials tested in this investigation included agricultural seeds (amaranth, panicum, millet, rape, wheat, barley), various plastic granules used in extrusion processes (polyethylene pellets, high impact plastic in the form of cut rod), and a sample of urea. The characteristic diameter of these materials which all had narrow size distributions, ranged from about 1 mm to about 8 mm, and the bulk densities were in the range 600 to 800 Kg/m3. Widths at blockage were obtained for vertical slots, and some experiments were also performed with horizontal slots and orifices. At blockage, the critical ratio of vertical slot width to particle diameter, ranged from ~1.4 to ~2. These results are qualitatively consistent, with those of Langmaid and Rose, Jnl. Inst. Fuel, April, 1957, pp 166-172, who worked with mineral materials and metal punchings, for openings in the horizontal plane, though the critical ratios for slots are smaller than those for orifices.