Dynamic head, pressure drop formulas?

In summary: Bernoulli's equation to calculate the pressure required to get a desired flow rate through a tube. Additionally, you can calculate pressure drop using Ohm's law.
  • #1
engineering
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0
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



thanks



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  • #2
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?
 
  • #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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  • #4
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).
 
  • #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 I've 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:
H1-H2=deltaP1>>2
H1-H3=deltaP1>>3
H1-4=deltaP1>>4.
hope this help.
thanks.
 
  • #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.

Thanks,

Gordan
 

1. What is the formula for dynamic head?

The formula for dynamic head is:
Dynamic head = (velocity head) + (pressure head) + (elevation head)

2. How is pressure drop calculated for a fluid system?

Pressure drop is calculated using the following formula:
Pressure drop = (fluid density) x (velocity of fluid) x (friction factor) x (length of pipe / diameter of pipe)^2

3. What is the difference between dynamic head and static head?

The main difference between dynamic head and static head is that dynamic head takes into account the movement of the fluid, while static head only considers the elevation of the fluid. Dynamic head is also affected by the velocity of the fluid, while static head is not.

4. How do you calculate the friction factor?

The friction factor can be calculated using the Colebrook-White equation, which takes into account the Reynolds number and the roughness of the pipe walls. Alternatively, it can be estimated using charts or tables based on the type of pipe and the flow rate.

5. Can dynamic head and pressure drop formulas be applied to any fluid?

Dynamic head and pressure drop formulas can be applied to any fluid as long as the properties of the fluid, such as density and viscosity, are known. However, these formulas are most commonly used for incompressible fluids, such as water and oil, and may not be accurate for compressible fluids like gases.

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