Formula for flow out of a container through an apurtance. 2

[cybereng]

I refer to a post in 2004 by PEDARRIN2 as follows

"There is a formula for flow out of a container through an apurtance.
It is
Q=C(d)*A*(2gH)^.5
Q is flow rate in cubic meters per second
C(d) is .6014
A is area in meters
g is 9.81"

Can anyone please explain "C(d) is .6014"

 

[BigInch]

Discharge coefficient of flow through an orifice (in the side of the container). Cd varies with the geometry of the penetration, from 0.6 to 0.75 or so, depending on if it intrudes into the container, is flush mounted, the edges of the hole are rounded, if the hole is round or square or some other shape and if it has sharp edges or some other geometrical configuration.

you must get smarter than the software you're using.

 

[cybereng]

Many thanks for that enlightenment. In this case the outlet is flush, round and the edges are sharp. Would a discharge coefficient of .6014 still be correct. Sorry for being a pest but I am trying to get a report done before the deadline.

 

[cybereng]

Me again. Would the discharge coefficient be the result of vena contracta?

 

[PEDARRIN2]

Per Cameron Hydraulic Data, the C for a square edge round opening is 0.61.

The flow will vary depending on the height of the fluid in the container, decreasing as the fluid level drops.

 

[cvg]

Would a discharge coefficient of .6014 still be correct?

depending on the approach conditions, exit conditions, submergence, head, gate, tube or flat plate, round, square, slotted, and other geometric conditions - orifice coefficients can range from 0.49 up to nearly 1. so, yes - .6014 might still be correct.

 

[bimr]

The discharge coefficient is not a result of the vena contracta. The vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum, such as in the case of a stream issuing out of a nozzle.

In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge) is the ratio of the actual discharge to the theoretical discharge,[1] i.e., the ratio of the mass flow rate at the discharge end of the nozzle to that of an ideal nozzle which expands an identical working fluid from the same initial conditions to the same exit pressures.

http://en.wikipedia.org/wiki/Discharge_coefficient

 

[Latexman]

"The discharge coefficient is not a result of the vena contracta."

That's not correct. The discharge coefficient depends heavily on the vena contracta.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[cybereng]

I am most grateful for the info. Thank you.

 

[BigInch]

The discharge coefficient is the pressure drop that occurs as the result of the conversion of some static head within the container to velocity as the fluid accelerates into and through the opening.

you must get smarter than the software you're using.

 

[bimr]

To clarify this discussion, there are four hydraulic coefficients:
[ul]
[li] Coefficient of contraction, Cc[/li]
[li] Coefficient of velocity, Cv[/li]
[li] Coefficient of discharge (or Orifice Coefficient), Co[/li]
[li] Coefficient of resistance, Cr[/li]
[/ul]


The ratio of loss of head in the orifice to the head of water available at the exit of the orifice is known as coefficient of resistance (not discharge coefficient as someone posted). The loss of head in the orifice takes place, because the walls of the orifice offer some resistance to the liquid as it comes out. The coefficient of resistance is generally neglected, while solving numerical problems.

The ratio of actual velocity of the jet, at vena contracta, to the theoretical velocity is known as coefficient of velocity. The value of Coefficient of velocity varies slightly with the different shapes of the edges of the orifice. This value is very small for sharp-edged orifices. For a sharp edged orifice, the value of Cv increases with the head of water.

The ratio of the area of the jet, at vena contracta, to the area of the orifice is known as coefficient of contraction. The value of Coefficient of contraction varies slightly with the available head of the liquid, size and shape of the orifice. The average value of Cc is 0.64.

The ratio of a actual discharge through an orifice to the theoretical discharge is known as coefficient of discharge. Mathematically coefficient of discharge = Co = Cv * Cc

The value of coefficient of discharge varies with the values of Cv and Cc. An average of coefficient of discharge varies from 0.60 to 0.64.

The final form of the orifice equation becomes: Q = CcVA = CoA * (sq rt(2gH))

where: A = orifice area, Cc = contraction coefficient, Co = discharge coefficient = Cc * Cv, g = acceleration due to gravity = 32.2 ft/s2 or 9.80 m/s2, H = head , Q = flowrate (discharge), V = horizontal velocity through orifice.

http://www.lmnoeng.com/Tank/TankTime.htm

Vena contracta is the point in a fluid stream where the diameter of the stream is the least, and fluid velocity is at its maximum, such as in the case of a stream issuing out of a nozzle, (orifice). It is a place where the cross section area is minimum. The maximum contraction takes place at a section slightly downstream of the orifice, where the jet is more or less horizontal.

The size of the vena contracta is the result of the available head of the liquid, size and shape of the orifice.

 

[jgailla]

Star for you, bimr. Great explanation.

 

[BigInch]

Yes. I agree. You also have to use the Bernoulli equation writing from two points across the outlet and using the downstream flow as calculated from Q=Cd*A*(2gH)^.5 to actually see the pressure drop which accelerates the fluid from nothing inside the container to the outlet velocity.

you must get smarter than the software you're using.