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Fluid through two cylinders

  1. Oct 7, 2004 #1
    I am trying to solve a problem concering roll coating. This is 2 rotating cylinders whith different speeds. The two cylinders are in the same horizontal plane. They don't touch eachother, but are close together. On one cylinder there is a fluid. When the fluid goes through the gap, the point where the cylinders are closest to eachother, both cylinders take some of the fluid. Is it possible to calculate how thick the film is on each cylinder??

    I have looked a month at this problem now. I think it can be done with the Navier-Stokes formulas, but they could be too difficult to calculate manualy. I know it abolutely has something to do with the speed of the cylinders, and probably the gap between them.
  2. jcsd
  3. Oct 7, 2004 #2


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    Sorry but I cannot imagine your problem. Do you mind posting a picture of it?. It can be done in .bmp and clicking below in Manage Attachments. I don't know if the cylinders are concentric, parallel, and I don't understand what you mean with the closest point and "both cylinders take some of the fluid".
  4. Oct 7, 2004 #3
    The problem

    At the top you see how the cylinders are located to eachother. In the close up, the red is the fluid. One cylinder has all the fluid first, then it is divided between the two cylinders. I want to "know"/calculate the thickness one cylinder 1. Between the two blue arrows.
    Hope it is clearer now. Sorry about the description, it is a bit difficult to describe.
  5. Oct 7, 2004 #4


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    :surprised :surprised Wow!!

    I'm sorry. To be honest, I think your problem is very difficult to be solved in a classical way. I will explain that:

    Making your own numerical simulation with the N-S equations will be a serious challenge. It's a viscous free surface flow. The free surfaces flow are heavier to simulate, because you need a boundary condition between the fluid and the air.

    My advice, if you want to listen it, is to use a commercial simulation software of Computational Fluid Dynamics. Surely Fluent 6.0 can solve your problem.

    Your question is not trivial at all. :bugeye:

    Another posibility would be to measure experimentally some fluid variables and to obtain the thickness by means of integral conservation laws.
  6. Oct 7, 2004 #5
    Thanks, that is what I thought. I had to verify.
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