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Fluid Pressure and Flow

  1. May 25, 2013 #1
    If anyone can help it will be greatly appreciated.

    Im trying to figure out what type of pressure valves to use in an underwater flow widget. The widget is a cylinder with 1 inflow valve and 1 outflow valve. The cylinder is filled with colored water. As the cylinder moves through water I want water to run through the widget and release the colored fluid thats inside drop by drop.

    Also, the cylinder is actually a series of 3 cylinders connected together.
    This is what i can tell you about the cylinder:

    Point A: At 1.5 meters in depth, water will be pushing onto valve A at 148 (mbar) and into a cylinder thats 12 mm long and 7mm in diameter.

    Point B: It then will enter another cylinder that is 40 mm long 10 mm in diameter.

    Point C: At this point it will enter another cylinder 5mm long and 7mm in diameter and out another valve, valve C.

    Im trying to figure out what the pressure will be at Point A and Point C so that I can choose the correct umbrella valves to use so that water flows out of the chamber drop by drop. Maybe 1 drop or .1 ml per 1 meters
  2. jcsd
  3. May 25, 2013 #2

    Simon Bridge

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    You want Bournoulli's equation to relate the pressures at each end of the tube.

    Note: 0.1ml per meter is not a rate of flow ... you need ml per second.
    You want the drops to exit the tube and then fall so that each of them fall 1m before the next one comes out?
  4. May 26, 2013 #3
    THANKS Simon!!

    I've been trying to figure out how to use Bournoulli's Theorem. Im very new to physics, LOVE science, especially physics..I've just never been formally taught beyond science 101 in high school...I went to a trade school. So please excuse any seemingly amateur questions. Anyways, I really appreciate your help.

    I think you are correct about the the release of the inner contents. My calculations show that the cylinders will hold a rough total of 3.8 ml. As the cylinders move through the water, I only want the fluid to exit at (.05 ml- .1 ml) every (.5-1 m) of travel. I think that is essentially the same thing as falling. Also, the cylinder is suspending at about 1.5 m below the surface of the water.
  5. May 26, 2013 #4

    Simon Bridge

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    Hmmm ... how fast will the thing be moving through the water?

    The situation is a bit different from pushing water through a pipe since the back-pressure means that not all the water immediately in front of the mouth of the pipe goes into the pipe.

    To release a drop of water every meter or so would be best achieved by having the valve just open and close at timed intervals. The effect would be to reduce the drag a little at those intervals.
    What is it you are trying to achieve here?
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