I'm trying to calculate the settling velocity of particles traveling through a horizontal section of pipe. I've not been able to find information about settling velocities in moving fluids, only still fluids.

  1. Assuming laminar flow, is the settling rate of a given particle the same in a moving fluid as it is in a still fluid?
  2. Am I able to apply Stokes' law?
  3. Are there other/better laws or research which I can use to calculate settling velocities in this circumstance?

The context is that I'm trying to build a device which accept sediments of a roughly uniform size and removes materials of a low density (for instance, if I have a mixture of quartz and platinum, I'd like to remove the quartz and keep the platinum). This is accomplished by allowing the material to settle in a horizontal section of pipe. The length and width of the pipe are constant, and the flow rate is adjusted according to the composition of our material.

I know that someone else has built such a device, and they calculated that at a rate of 10 gallons/minute through a 2" pipe, gold would settle within 9". I believe this was using a 200 mesh (.075 mm diameter) particle with a Corey's Shape Factor of .25, but I'm not certain. I'd like to be able to verify this work & calculate it for other circumstances.


  • $\begingroup$ would this be better suited for engineering? $\endgroup$ – ZeroTheHero Aug 14 '17 at 1:39
  • $\begingroup$ In my judgment, Stokes law would be adequate for making these predictions, assuming that the settling Reynolds number is low. Don't forget to include buoyancy. $\endgroup$ – Chet Miller Aug 14 '17 at 12:47

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