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Fluid Mechanics of a French press

  1. Oct 15, 2012 #1
    I'm interested in making a larger-scale French Press (VIDEO, go to :30) It has a mesh-screening filter that keeps the coffee grounds contained when you push down.


    I'm theoretically using a large bucket, like those 5gal buckets at Home Depot, with the dimensions shown below. And theoretically this bucket will have a constant diameter all the way down.

    8091805884_dcb804b33a_z.jpg

    Neglecting the weight of the filtering mechanism/screening, the force needed to move the filter-screening down through the water is equal to the drag force of the water acting on the screen.

    8091862791_55d72200d2_z.jpg

    I'm not sure what to do now when it comes to calculating the drag force acting on filter-screening.
    It will be a stainless-steel 5micron mesh, very small. Something similar to this:

    ruishen$104825314%28s%29.jpg

    FD = ρV2ACD In the drag force equation, V will be the velocity of the screen moving through the water. I'm assuming the A is going to be the total surface area of all the little strands of wire that make up the screen...right?

    Am I starting this off right?
     
  2. jcsd
  3. Oct 17, 2012 #2
    bump...
     
  4. Oct 18, 2012 #3
    Flow through mesh screens is much different than flow over bluff bodies. You'll never find a suitable Cd because of this, and also because the flow is not going around the body, but through it.

    Generally the way a fluid will react when it contacts the screen will have to be determined experimentally. I'd contact the manufacturer and see if they have any information. You might have to spend some time trying to find the right person to answer your questions, though.
     
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