flow calculations for temperature

[Steve Roberts]

[color=#000000]I want to be able to calculate airflow through an orifice at different temperatures for my flow bench. I don

[larrycavan]

[quote="Steve Roberts"][color=#000000]I want to be able to calculate airflow through an orifice at different temperatures for my flow bench. I don

[slracer]

Steve, If you want to do it, check out the pitot tube calculator that Ed did here on the forum. The first part of the calculation is a density vs temp routine. You might want to modify it for *F instead of *C, but that is easy to do.



Doug

[Steve Roberts]

[color=#000000]Thank you for the info you guys. Larry, according to the efunda online orifice calculator there is about a 1% difference in cfm for every 10 degrees F change in temperature. My shop temperature can change 30 degrees on many days, maybe more. That

[86rocco1]

What type of a flow bench do you have? I ask because not all flow benches are the same. Pitot tube type bench require correction for ambient temperature and atmospheric pressure, orifice type flow benches do not. This is because orifice type flow benches do not actually measure the amount of air flowing rather they compare the air flow through the piece you're testing to the flow through a calibrated orifice so the test results are self compensating for temperature and pressure, they are always referenced to the calibration specs of your orifice. IOW, unless you've made some physical changes to the flow bench, the test results on an orifice type bench should be consistent from day to day, regardless of weather conditions.

[Steve Roberts]

[color=#000000]My bench is like this one, sort of

It has the thermometers like the one in the picture and a correction chart.

[86rocco1]

The temperature correction in that particular bench is NOT for ambient room temperature, it's corrects for increase in air temperature as the air flows from the test piece to the orifice caused by the air pump. If you redesign the flowbench to look like this where the air doesn't pick up any additional heat between the test piece and the orifice, that becomes unnecessary.This arrangement is the more common, it's used in the larger Superflow benches and most DIY benches including the PTS bench, the benches I'm aware of that match the first diagram are benches patterned after the Superflow 110/120.

[Malvin]

Hey that looks like my first flow bench!! I still have it to but the
the metering plenum is under the test plenum witch is a 35 gallon drum.

Thanks

Malvin

[Steve Roberts]

I finally got a chance to look into this thing. My surprise, the motors are not before the orifice. One temperature gauge is wired right next to the hole on the bench top. The other temperature gauge is wired under the orifice.
I found an aerospace company owned this bench. I am trying to find someone there that might know a little more about it.
Steve Roberts

[86rocco1]

[johno]

That seems very strange that your bench would have temp. guages in both plenums without the vac motor being in the centre of the 'flow-circuit'! Is it a commercial bench or home-made? ???