(723d) Experimental Investigation of Residence Time Distribution of Free-Flowing Particles in a Lab-Scale Cylindrical Silo

The effect of hopper half-angle and wall condition on residence time distribution (RTD) of 2 mm free flowing particles (mustard seed) in an 80 mm cylindrical silo has been investigated. Two wall conditions, rough and smooth, and hopper half-angles of 20, 24, 30, 45, 60; and 90° (flat bottom) were used; the discharge opening diameter was 14 mm in all experiments. Tracer experiments were carried out using samples of the test material dyed to be optically distinct; red and blue dyes were used as these had negligible impact of the flow properties of the particles. In each experiment, material exiting the silo was collected in the compartments of a rotary table sampler turning at a constant rate. In all experiments the relative proportions, concentrations, of red and blue particles were determined from photographs of all the particles in each sample. Classical analysis of the response to a step change, here a change in the colour of the test material in the silo, was then used to extract RTD from the relative proportions of red and blue particles in the silo discharge; the timeline was established from the angular speed of the rotary sampler. The effect of increased wall friction was significant for hoppers with a small half-angle; for the larger half-angles residence time distribution changed only minimally when the silo walls were roughened.