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Dynamic head, pressure drop formulas?

  1. Mar 30, 2008 #1
    My fluid dynamics is rather weak and i was wondering if someone could please tell me how to calculate dynamic head of the flow in the a tube and how to calculate pressure drop of a hole in a tube? Some formulas would be handy


  2. jcsd
  3. Mar 30, 2008 #2


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    Staff: Mentor

    Generally, you just use a table for certain materials and velocities. IIRC, we use a book put out by BOCA. And I'm not sure what you mean by a hole in the tube - an orifice?
  4. Mar 31, 2008 #3
    Please see my diagram the diameters of the hold are fixed it has a fluid running through it being injected outwards. The diameter of the holes is fixed. the tube shape chamber has a free stream velocity flowing round it can be assumed to be air. need method of calculating pressure drop and head loss.

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  5. Mar 31, 2008 #4


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    Staff: Mentor

    I'm still not completely clear on it, but if you have a certain flow rate through the holes in mind, you can use bernoulli's equation to calculate the pressure required to get it. Figure on a 50% nozzle coefficient (meaning whatever pressure you get, double it).
  6. Mar 31, 2008 #5
    well,the formula of the dynamic head is"H=P/W",where p:pressure&W:specific weight=density*acceleration"g",of the fluid passing in the tube.
    u can apply the bernouli's equation as russ watters mentioned in his reply,between two points,say point"1" at the surface of the tube and at point"2" at the centre of the tube&at the centre line of the 1st two holes,and ive noticed that the every two holes at the same horizontal line?,their centre line is at the same line?,
    so by using bernouli's:
    (P1/W1+Z1+V1^2/2g)-(P2/W2+Z2+V2^2/2g)=head lossed from point "1" to point "2".
    and according to my assumptions:taking the datumn at the holes centre line: Z1=the distance from point"1"to point"2"&Z2=0.0,
    according to ur givens u should calculate the head losses in the pipe by adding the head losses calculated everytime between the every two points.
    notice that the head losses formula is : "hl=flv^2/2gd" ,or "hl=0.8flq^2/gd^5" , where f:friction factor,l:tube length,v:fluid velocity in the tube,d:tube daimeter,q:fluid flow rate.
    and for the pressure drop:
    hope this help.
  7. Apr 7, 2008 #6
    Hi there:

    Check out eFunda.com at: http://www.efunda.com where you can find theoretical background information as well as online calculators on fluid mechanics.


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