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

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SUMMARY

The discussion focuses on using Stoke's Law to estimate the sedimentation of starch particles in water, specifically addressing the challenge of calculating the distance that 90% of 10 µm starch particles travel to reach the bottom of a cylinder. The user initially attempts to apply Stoke's Law but realizes it is insufficient for estimating the distance traveled by the particles. Alternative equations, such as the kinematic equation d=Vi(t)+(0.5*a*t²), are considered but deemed irrelevant. The conversation highlights the need for a model that accounts for terminal velocity and particle interactions.

PREREQUISITES
  • Understanding of Stoke's Law and its application in sedimentation.
  • Familiarity with kinematic equations and their relevance in motion analysis.
  • Basic knowledge of fluid dynamics and particle behavior in fluids.
  • Experience with experimental design involving particle separation techniques.
NEXT STEPS
  • Research the concept of terminal velocity in sedimentation processes.
  • Explore the use of computational fluid dynamics (CFD) tools for modeling particle behavior.
  • Investigate alternative equations for sedimentation beyond Stoke's Law.
  • Learn about the effects of particle size distribution on sedimentation rates.
USEFUL FOR

This discussion is beneficial for students and researchers in the fields of chemistry and engineering, particularly those involved in fluid mechanics, sedimentation processes, and experimental design for particle separation.

nabilah
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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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Last edited:
Physics news on Phys.org
https://en.wikipedia.org/wiki/Sedimentation

http://www.nzifst.org.nz/unitoperations/mechseparation3.htm

https://www.researchgate.net/publication/229128063_PH-Postharvest_Technology_Kinetics_of_Gravity_Settling_of_Cassava_Starch_in_its_Aqueous_Suspension
 
Last edited by a moderator:
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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