How to Calculate the Diameter of an Orifice Plate?

[robsmith82]

Hello,

I am trying to figure out how to calculate the diameter of an orifice for a pill loop in an oil heater and pump. The hot oil is used to heat fuel in a heat exchanger, and is driven by a positive displacement pump. There is a spill loop with an orifice plate, and the requirement is that the orifice must spill a specific flow when the oil is at 200C and 25psig. the pipework either side of the orifice plate is 2", and the kinematic viscosity of the oil at 200C is 1.2 cSt. I think this is all the info that is needed? How do I calculate what orifice size will give me what flow?

 

[FredGarvin]

Since you're dealing with, what can be considered, an incompressible fluid and the orifice is to meter the flow, you can simply use Bernoulli across the restriction. Here is a pretty good derivation of the basic orifice calculation:http://en.wikipedia.org/wiki/Orifice_plate

Note that since this is a pretty viscous fluid and not a gas, you don't need to worry about the expansion coefficient. If you need some decent accuracy, you should utilize literature to establish a discharge coefficient to handle minor losses that do not get handled in the derivation above.

 

[stewartcs]

Here's and example spreadsheet I threw together to help you figure it out. Of course, the catch 22 is that you must know (or reasonably estimate based on your experience with orifices) what the differential pressure is. Just plug the values in blue into worksheet and it will give you the flow rate out of the orifice.

 

[stewartcs]

Apparently I can't attached spreadsheets in this forum! Sorry! Here is a jpeg instead!

 

[KristianCE]

Try the program FlowCalc. There is a free trial version for downloat at http://controlengineering.se/flowcalc/flowcalceng.htm

I hope this helps.

 

[stewartcs]

Yeah there's a lot of programs out there to do it, but for something this small hand calcs generally work fine.

 

[DecentMenace]

I have a similar scenario, where I am trying to calculate the orifice diameter... On using a couple of different softwares (Flow Cacl 32 and Instrucalc)... I'm getting two different results however I get the same error that my Reynolds number is too low...

Sizing for a liquid w/ SG=1.081, Operating Temp 93.30C, Operating Pressure 10203 kPag, Max. Flow = 2m3/hr and Normal Flow = 1.6m3/hr. Viscosity is 11.20 cP and the Dry Diff. Range = 0-250mbar. All of this is flowing through a 2" Sch 160 Pipe.

Any thoughts folks?

 

[Bolts]

I have a similar scenario, where I am trying to calculate the orifice diameter... On using a couple of different softwares (Flow Cacl 32 and Instrucalc)... I'm getting two different results however I get the same error that my Reynolds number is too low...

Sizing for a liquid w/ SG=1.081, Operating Temp 93.30C, Operating Pressure 10203 kPag, Max. Flow = 2m3/hr and Normal Flow = 1.6m3/hr. Viscosity is 11.20 cP and the Dry Diff. Range = 0-250mbar. All of this is flowing through a 2" Sch 160 Pipe.

Any thoughts folks?

The high pressure of 10.2 MPa combined with the low flow rate of 2m3/hr might create to small a pressure difference across the orifice to solve. Try increasing the flow rate and see if it solves and make a conclusion based upon that result and what you are asking to solve in the first case.

 

[FredGarvin]

The ASME spec (MFC-14M-2001) that covers orifice flow in small bores dictates a minimum Re>1000. A rough calc shows that your Re~4150 at your max flow. The low limit may be a limit in that particular program for its calcs. Your flow rates are very low though, so it doesn't surprise me. I would look at other methods of measurement like a hot wire anemometer or possibly a Coriolis flow meter.

 

[elmandilon11]

I need help, hope somebody can give me a hint

Determine the appropiate orifice sizes for uniform exit temperatures of 140F from the four units in 70F ambient/ sea level pressure? Components (50W, 500W, 1000W and 300W)

Thank you

 

[elmandilon11]

I need help, hope you can give me a hint

Determine the appropiate orifice sizes for uniform exit temperatures of 140F from the four units in 70F ambient/ sea level pressure? Components (50W, 500W, 1000W and 300W)

Thank you