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Water flow rate

  1. Aug 16, 2009 #1
    Please help i'm going round in circles!

    Water on tank 12m high, feeding pipe 200m long and 125mm diameter. Open end.

    Given friction factor of 0.008 for the pipe and total of 3.2K for various fittings.

    Asked to find water flow rate in Kg/s in the pipe.

    Been looking at this for ages now and have got really confused!

    So far :

    As the tank and the outlet are open to the atmosphere we can use v= √2gh to find the velocity of the water?

    V=√(2*9.81*12)

    V=15.34m/s

    Mass flow rate =pVA
    Where p is the density of water 1000kg/m3
    V is mean velocity 15.34m/s
    A is cross sectional area normal to the direction of flow 0.125mXπ2
    2
    m = 1000 x 15.34 x (0.125xπ2)
    2
     
  2. jcsd
  3. Aug 17, 2009 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi Sevy35! :smile:
    Yes … since last December, I see! … https://www.physicsforums.com/showthread.php?t=278890
    No, you can use ρgh, but only to find the contribution of the height to the Bernoulli's equation.

    As LowlyPion :smile: said, you must subtract the loss through friction.

    Remember the background: Bernoulli's equation is basically a conservation of energy equation (per unit mass, ie using density instead of mass), and if you have friction, you must subtract the energy lost from friction (equals the work done by friction). :smile:
     
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