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Draining a Closed Tank

  1. Sep 19, 2013 #1
    Supposing you had a tank mounted to the outside of a submersible vehicle.
    The tank lid is left open, and the vessel that taken down to 200m sea water depth, to top of tank.

    The tank lid is now closed at this depth; it is assumed that the tank is completely full, with no air gap/bubble on top.

    The interior atmosphere of submersible vehicle is at normal atmospheric pressure (1 bar). If the valve on the bottom of the tank is opened, how do you calculate the quantity of water that you can drain from the tank into the vessel (ignore pressure rise in the vessel due to the ingress of water) before the low pressure generated in the tank prevents further sea water egress?

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  2. jcsd
  3. Sep 19, 2013 #2


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    The denser liquid will always drain completely into the submersible. The space above the liquid in the external tank is not stable, i.e. air will flow up through the drain line as water is draining in the opposite direction. Otherwise, you could never drink the contents of a soda can or a beer can.
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