Distribution of lift forces on a cubic particle exhibiting sporadic movement during hydraulic conveying

The sporadic motion of a single cubic particle hydraulically conveyed up an inclined pipe has been investigated. The distribution of lift forces acting on the particle was inferred by assuming the sporadic motion conformed to simple binomial statistics. Experimental data were found to support the hypothesis, with the frequency decreasing exponentially with increasing rest time. By combining the binomial probability value with the critical lift force required for motion to occur, the full distribution of lift forces was determined. Interestingly, these forces were rarely sufficient to produce movement, exhibiting negative values most of the time. We suspect the negative lift-forces are, in part, a consequence of the cubic particle geometry. Boundary layer separation at the leading edge of the particle may give rise to a downward pressure force on the particle. Indeed, with a vertical pipe configuration, the particles were observed to be forced against the wall for brief intervals of time.