Is the value of the discharge coefficient depends on the depth of opening and the pre

Discharge Coefficient

This coefficient is used in all kinds of engineering problems where it is of interest to know the flow rate. The oil that flows in a pipeline is measured with an orifice, for which the discharge coefficient is known.

A large oil pipeline can cary over 20,000 gallons per minute, so knowing flow, with good accuracy, is valuable knowledge for the billing department. A power plant burning a million pounds of coal per hour is diagnosed and "tuned up" by measuring the feedwater flow to the boiler, again with a high precision orifice or flow nozzle.

The ASME (American Society of Mechanical Engineers) has tables giving discharge coefficients for all kinds of orifices and flow conditions, and the coefficients are presented to four decimal places, high precision for many applications.

 

Thanks for your help！
Is it ？http://asmedigitalcollection.asme.org/index.aspx

 

Not wanting to change the direction of the thread but
due to the higher restriction and resulting backpressure that orifice flow meters can cause, most pipeline flow measurement for fluids use a Coriolis style meter. Extremely accurate and low backpressure are the main features.

When you purchase gasoline at a service station either vane/paddle or a positive displacement meter is used for accuracy

 

Is the meter useful If the size of orifice is very big？

 

You would have to run specific parameters to calculate how the orifice size translates to upstream pressure.

The pressure developed at the orifice will translate up to the pressure creating pump and cost money. Ie higher pumping pressure, higher cost to pump the fluid

 

Sorry Gonzo, I didn’t note your question immediately, but here come a few observations, fwiw. Some years ago I ran into the problem with oval openings in a wall; no pipes attached. The “hydraulic diameter approach” gave ridiculous results (I agree with fredrosse that you must be careful with its use; I should not have opened that can of worms here at all, I’m afraid….).

So I ended up doing some testing with round (AR=1), and oval (AR=2, AR=4, AR=9) openings in a water channel. For practical reasons there had to be an exit pipe, and I fixed the nozzle area ratio (Achannel/Anozzle) to 100:1; big enough to mimic opening in a wall. Reynolds number ~3e5. The volume flow and pressure difference were referring to the nominal nozzle area, An, giving the flow equation:

Q = α * An * √(2*pdiff/density);

With this approach, you do not have to worry about contraction factors; the influence is baked into the flow coefficient. As you can see in the diagram attached, there is an influence from the three dimensional flow contraction up to an AR of 4:1. From there on, the effect of the jet contraction is two-dimensional, which shows in the increase of the flow coefficient with increasing AR up to 4:1.

Practically all losses occur downstream of the jet detachment point, wherever that is, and there is a slight pressure recovery due to momentum exchange in the exit chamber. This means that there is an influence from the length/geometry of the receiver. I did not systematically check the length influence, but somewhere at a length/nozzle dia ratio of 30, there is a stagnation point at the wall, dividing recirculating flow and fluid leaving towards the channel exit. This means that the recovery is complete at that length, from there on there are only wall friction losses to be compensated for.

I later used some of the test values for a simple validity check of the Solidworks CFD code. The result from a run with a circular opening with rounded inlet (sharp outlet) is shown attached. The number of fluid mesh cells were between 65000 and 110000, with a denser mesh in a spherical region around the nozzle. Please note the low pressure in the first third of the exit pipe, the following pressure recovery, and the stagnation point at the wall.

 

Thanks. It helps a lot.

 

I'm a bit curious about what the different design/safety rules say about filling time (or sinking time...) in the perspective of flow capacity and the coefficients that we have discussed here. Any of the forum NA:s who would like to take the discussion a step further on this topic?