For two particle sizes (say 200 and 600 microns) how will the free falling particle curtain width vary with dropping height? I am trying to simulate free falling particles in a cavity and want to understand how does the spread of particles depends on the particle size. As per my understanding, small particle size will have larger spread due to higher entrainment of air. Am I right? Would be grateful for more insights into the physics behind particle spread and its dependence on particle size.
I am looking for data (or an empirical model) on falling water drops of similar size, but only found various numerical studies. The spread also depends on the number of particles. Your flow problem could be similar to a bubble curtain (air bubbles rising in a initially stagnant reservoir of water).
The variation of width over height... For bubble plumes, you have an Initial starting zone, often accounted by a virtual source. Then you have a linear development of the width of the plume, assuming a constant entrainment coefficient. Close to the surface (or the bottom of your cavity), the flow regime changes again as the fluid flow is deflected.
The width of the curtain can be affected by fluid recirculation in case the spatial dimension of your cavity is too small.
Article Recirculating Flow Generated by Line-Source Bubble Plumes
200 and 600 micron particles are large and easily simulated with Stokes' law calculations. For small material (typically < 2 microns or so) there'll be competing Brownian motion and (great) susceptibility to any convection or air currents In the old days a device existed for measurement of particle size by air settling. I think an instrument is shown and described in John DallaValle's book 'Micromeritics, The technology of fine particles' (1948)
Thanks Alan and Ingo for your answers. Very much helpful!
I did a bit of digging in literature myself and found the attached paper. As per the results, the inter-particle collisions dominate the spread of the curtain. The experiments with glass ballotini particles for different particle size showed an increase in curtain width.
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