Does anyone know who to size an orifice with the following parameters. What I am trying to find is the diameter of the orifice I need to have to drilled in a orifice plate in a swagelok fitting to allow 2 gpm flow with a .5 psig drop and the fluid is DI water. The value I came up with was 0.153 inches, but I am not very confident in this value.

flow rate - 2 gpm
tube size - 3/8"
Specific Gravity - 1
Beta - 0.4 to 0.6
Pressure drop across orifice - 0.5 psig

Is the 0.5 psi pressure drop the permanent pressure drop (i.e. are you designing a restriction orifice) or is this a flow measuring orifice with close tapping points?

What is the actual ID of the tube?  It will have an impact on the orifice sizing.

Just a note - pressure differentials are neither absolute nor gauge.  You should specify your pressure drop as 0.5 psi and not 0.5 psig.

Pertaining to katmar's question.
Is the 0.5 psi pressure drop the permanent pressure drop (i.e. are you designing a restriction orifice) or is this a flow measuring orifice with close tapping points?

Yes, it will be a permanent pressure drop with a constant pressure supplied from a header that should be a consistent 45 psig from a pump. I am trying to design this as a restriction orifice and it will not be monitored for flow. There are nine other taps off the main header that are cooling other equipment that also have restriction orifices in them. I have a total of 34 restriction orifices in this system. There are 4 in a 3 inch line, 2 in a 1-1/2 inch line, 20 in a 1 inch line, and 8 in a 3/8 inch line. This tubing and piping are cooling bus bars and a chamber that is being heated by induction coil and they keep the coils and bus bar and associated power units and load matching stations at a desirable temperature. I hope this helps explain what I am trying to do.

Another use is for slowing the air bleed rate on valves.  For example, you find that your liquid needle valve is in water hammer and you need to slow the closing, just pop 1 or 2 in and the vent, the valve slows up.  We kept several different Cv values of the disks around and used them as needed.

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