Compressible gas pipe flow rate 1

[MHind]

Good afternoon all,

I'm having some difficulty in sizing some components for a test rig and have now found myself in what appears to be an infinite loop!

I want to buy a flow meter, but to buy the flow meter I need to know what is the nominal and range of flow that my rig will be required to test... now since the rig is being designed to test components which don't have a known flow rate value, you can start to see my issue...

Anyways, my ideas is to get a rough idea of the maximum value required by determining the maximum flow rate for my maximum possible test case:

-1" steel tube
-10barg service pressure
-vented to atmosphere (0barg)

I've searched for some time to find a direction in which to look to solve this problem but I can't think of any theory that I'm aware of... albeit someone must know.

Kind regards

Matt

 

[LittleInch]

You're going to need to narrow it down more than that as the range is huge.

Is the meter measuring the 10 barg air or the 0 barg air? (10: 1 range there already)

How long is the tube?
What is your flow control ( might be able to work out a max flow fromt he valve CV when fully open
What is your air supply (you cn only flow what you can compress)
Your max will be sonic velocity in your 1" tube - a BIG number

The issue is if you buy a meter to handle say 10,000cfm, but your test flow is 100cfm, the repeatability and accuracy of your meter will be 100-200 cfm.

Your call

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

There is a flow measurement lab in Colorado (Colorado Experiment Engineering Station Inc,, CEESI). I've tested 2-inch tubes there, I've also tested 6-inch tubes, and once I tested a trailer with one 6-inch, one 4 inch, one 3-inch, and one two inch meter in parallel at max beta and max dP. They get that kind of turn down with 0.5% repeatability by using critical flow nozzles on the air exhaust. Biggest limitation is noise (this station is in a re-purposed missile silo out on the plains with no neighbors close). They also have a minimum pressure into the nozzle of 10 psig so anything being tested has to be rated for at least 30 psig. They have a number of nozzles that they can change out in a few seconds without changing instrumentation.

Don't even think about using an industrial flow meter like an AGA-3 Square Edged Orifice meter, V-Cone, turbine meter, Corriolis meter, ultrasonic meter, etc. All of these meters require the flow regime to be effectively incompressible (i.e., target dP range results in upstream and downstream density being within 1% of each other, with 0.5% preferred). To meet this requirement on the massively parallel test we had to run the trailer at 300 psig and depleted their air supply in under a half hour followed by an hour to recharge it. None of the industrial flow meters do well exhausting to atmosphere.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LittleInch]

I was being fixated a bit by the single meter concept. To cover any decent range of flows and pressures you really need some sort of interchangeable elements or multiple elements to bring on and off line.

I'm sure there's a lot more you can tell us about these mysterious "components", but without some sort of guide your max flow is sonic velocity out of a 1" nozzle. Many online calculators for that.

CEESI looks like a decent place David.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MHind]

I suppose the reason for my thread is two fold:

1) I obviously need an answer, which I can use to price up a flow meter with. I'm fully aware that this isn't the correct piece of kit for the job and realise that what I actually need is to measure the DP across orifice plates; but I've got to go through the motions to prove to management first.

2) Online calculators are fine... but I won't use them. As far as I'm concerned they fall into two categories: magic or programmed by a moron and hence I never use them unless I can verify their application by a hand calc. I need to see an example of how to find the flow rate of a air through a 1" pipe with a differential pressure of 10barg to 0barg. From that I'll understand some more and go about figuring out my next step from there.

As for more info on parts... not sure I can give you any details on that, not because I'm being coy but because they haven't been designed yet. All I know is they connect to pipework which is less than 1".

Regards

Matt

 

[zdas04]

MHind,
I'm not sure what your post is referring to. I can't see where "online calculators" was ever put forth as an option.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[MHind]

"I'm sure there's a lot more you can tell us about these mysterious "components", but without some sort of guide your max flow is sonic velocity out of a 1" nozzle. Many online calculators for that."

 

[LittleInch]

That was from me.

Try this

http://www.engineeringtoolbox.com/nozzles-d_1041.html

https://www.physicsforums.com/threads/velocity-of-air-coming-out-of-a-nozzle.694656/

Basically you need to search for critical flow or sonic flow through a 1" nozzle.

You don't say how long your tube is, but on the basis that it's in the region of mm and not km, a nozzle will give you a fairly good basis.

You might find restriction orifice a better bet - plenty of equations available, especially as you only want an initial number.

If you put your meter in the 10 bar end you're better off, but again - how is this flow being controlled for flow rate or pressure and where does your 10barg air come from?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MHind]

Thanks. That was what I was after really. After seeing the pressure ratios it's all come flooding back to me.

I've unfortunately spent all day not seeing the wood for the trees!

Regards

Matt

 

[LittleInch]

If you were prepared to have say 0.3 to 0.5 barg at the outlet and have space for a BIG pipe venting to atmosphere, you could easily have an orifice plate in that exhaust duct, just would need to be something like 36" to get the velocity down and keep the inlet pressure down. Then either that or a set of different sized exhaust ducts with orifice plates and an interchangeable set of DP sensors to get you a big flow range.

Just need space for the 15D upstream lengths / 5D downstream.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.