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Airflow across a orifice or nozzle

Airflow across a orifice or nozzle

Airflow across a orifice or nozzle

(OP)
I'm connecting a 200 gallon tank maintained at negative 13 psi to a mold and pulling a vacuum on that mold by actuating a solenoid valve. If the mold is sealed the resulting pressure drop in the tank is easily calculated with P1*V1 + P2*V2 = P3*V3. Where P1 is the pressure of the vacuum tank, V1 is the volume of the tank, P2 is the pressure in the mold (14.7 psi), V2 is the volume of the mold, P3 is the resulting pressure when the tank pulls vacuum on the mold and V3 is the combined volume of the mold and tank. This process cycles every 12 seconds and the vacuum on the tank needs to be regenerated every cycle.

My question is when the mold is not sealed and air is moving through qty. 400, 3/16" vacuum holes on the mold for approximately 1 second, what is the resulting pressure in the tank when the solenoid valve is closed. I can't seem to find an simple equation that gives the CFM of aiflow across an orifice or nozzle given a pressure differential. The mold holes could be considered sharp edged nozzles. The mold volume is about 34,560 in^3.

The end result is being able to spec the CFM that the tank needs to be evacuated at to get the vacuum level in the tank back to negative 13 psi in time for the next cycle.

RE: Airflow across a orifice or nozzle

.
Sammy:

Read the article "Source Terms For Accidental Discharge Flow Rates" by going to this website:

http://air-dispersion.com/source.html

At the website, first select whether you want to work in SI units or in customary USA units. The select "Gas Discharge From Pressure Source".

 Milton Beychok
mbeychok@home.com
http://www.air-dispersion.com
Visit my website to learn about "Fundamentals of Stack Gas Dispersion", a most comprehensive book on dispersion modeling of continuous, buoyant air pollution plumes. The site has published peer reviews and the complete Table of Contents.

RE: Airflow across a orifice or nozzle

The easy way to do it is to have a chart, like me.

For one 3/16 orifice at a pressure dif. of 15psi (my chart is in 5psi increments) the flow is 15.4 CFM. From the chart I would guess around 14.9-15 cfm for 13psi.

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