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I Stoke's equation -- particle size

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  1. Jun 29, 2017 #1
    I want to solve stokes eq. for particle diameter in um size. Do i have to change the units to make them uniform. please help in solving the eq. by plugging these numbers.
    velocity= 50 mm/h
    Particle density= 2650 kg/m^3
    Medium density= 1000 kg/m^3
    viscosity = 1.002 mPa
    Gravity= 9.8 m/s^2
     
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  3. Jun 29, 2017 #2

    mfb

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    As long as you work with units consistently, you cannot make anything wrong.
    Some unit conversions can be necessary to get a nice unit for the result.
     
  4. Jun 30, 2017 #3

    Andy Resnick

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    Your units of viscosity are incorrect, could/should be mPa*s.
     
  5. Jul 1, 2017 #4
    Thanks for advise. Also, I want to solve the following equation for particle size (d) using stokes eq
    V= g (Ps – Pw) d2/18 µ

    for unknown variable (d) i rearranged the eq. as follow and took the square root of my answer. Is this the correct way to rearrange and solve this eq for particle size determination. Please, advise.

    d= 18 µ V/ g (Ps – Pw)
     
  6. Jul 1, 2017 #5

    mfb

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    Something went wrong with the formatting. I guess you mean this:$$V= \frac {g(P_s-P_w)d^2}{18 \mu}$$
    Solved for d:$$d= \sqrt \frac{18 \mu V} {g(P_s-P_w)}$$
    Sure.
     
  7. Jul 3, 2017 #6
    I would recommend that you use dimensionless variables. It will greatly simplify your calculations if you are planning to find the flow profile.
     
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