Solving Distance of Starch Particles in Fluid w/Stoke's Law

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1. Homework Statement
I did an experiment to separate different sizes of starch particles (range of size 1 µm to 10 µm). I mixed the starch powder with water in a long cylinder. I have to create model by using long cylinder to separate those starch particles according to their size (<1µm, <5µm.,<10 µm) with fluid outlet for each sizes.

I use the Stoke's law to estimate the time of starch particle (for example for size 5 µm) left on top of the solution. but I have a problem on how to calculate/estimate the distance of 90% of 10µm starch particles in fluid (water) reach to the bottom of cylinder? and estimation of time for it to fall at the bottom. I figured out that I can use a Stoke's law but this equation could not use to estimate for how distance for 90% of 10 micrometer of starch particles reached the bottom of the cylinder.
stokes_law_terminal_velocity.png
2. Relevant
equations

By using the stoke's law I can estimate the time for <5 µm of starch particle left on the top.
stokes_law_terminal_velocity.png




The Attempt at a Solution



Can I use the other relevant equation other than Stle's law to measure the distance of 90% 10µm starch travel until reach the bottom of cylinder?
I tried to use the equation

d=Vi(t)+(0.5*a*t2)
but I think this equation is not relevant to my case.
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You could start with a very simple model which assumes that the particles all fall separately from each other and that the particles reach terminal velocity almost immediately on entering the water .
 
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