Pickup Velocity of Solids for Ventilation

[RJB32482]

I am looking at ventilating a bulk bag dropping method. I want to make sure that the ventilation velocity is not too high and will pick up the particles into the ventilation syste. What correlation (Stoke's Law)??

Thanks.

 

[m777182]

I am not sure if I understand your question correctly: if you want to remove particles then the fluid flow velocity should be higher then settling velocity of your dust. There are numerous empirical relations how to calculate it (Google on "fluidization").It dependes on particles diameter and shape, denstiy difference (d_particles-d_fluid)and viscosity of the fluid (probably air). By a cyclon calculation or by fluid transport calculation the same approach is used and you may further come across a term called saltation velocity. Particles in a swarm behave slightly differently if their proportion to the fluid phase is high compared to a single particle, which is howevever a starting point for the calculations.If you do not want to pick up particles then the velocity of the fluid should be less then the settling velocity but keep in mind that there will always be particles small enough to be entrained.
m777182

 

[Compositepro]

You might look at premade bag dump stations. These have self contained air filters that self-clean and drop what is collected on the filters back into the hopper. I've seen a lot of poorly designed home made solutions. Usually the dust pick-up is placed very close to the powder handling operation to protect operators from exposure but this actually raises the dust, as you've noted. The operator is often not well protected because of air turbulence and a lot of product is lost.