# Homework Help: Particles in fluid

1. Mar 29, 2017

### nabilah

1. The problem statement, all variables and given/known data
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.

2. Relevant
equations

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

3. 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.

Last edited: Mar 29, 2017
2. Mar 29, 2017

### Nidum

Last edited by a moderator: May 8, 2017
3. Mar 29, 2017

### Nidum

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 .