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Flow rate of water from thin tubes under high g-force

  1. Jan 17, 2016 #1
    Hi guys,

    I was wondering if you could help me with something. I work in the paper industry with what is called a suction roll. The roll has a rotating perforated steel cylinder with a stationary vacuum box on the inside and as the wet paper web travels over the surface of the roll, the vacuum pulls water into the holes. The vacuum box is approx. 45 degrees wide, so the holes fill up when over the suction zone, but right after the zone centrifugal force causes the water to be thrown out of the holes (and away from the process). I am interested in the drainage rate/speed of the water coming out of the holes are no longer under vacuum. This process is very fast, with average surface speeds of approx. 50 mph, and g-forces acting on the holes typically around 50 g. So you basically have water being pulled into the holes, and then thrown out again, within milliseconds. Assuming the typical hole has a diameter of 5 mm and it gets filled to a depth of 30 mm, how long will it take to drain the hole the moment the vacuum stops, centrifugal force takes over, and atmospheric air is allowed to stream in from the bottom side?

    Thanks in advance!

  2. jcsd
  3. Jan 17, 2016 #2
    Have a look at the water flying out of the suction roll (breast roll) into the downcomer. The direction of travel will be tangent to the breast roll surface at the trailing suction box edge. Once the water passes over the trailing lip of the vacuum box, the water will travel in a straight line as the breast roll curves down and away.
  4. Jan 18, 2016 #3


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    If you just want an order of magnitude estimate try....

    S = ut + 0.5at^2

    Solve for t
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