air vessel cfm value

[qualityguy28]

Hi Guys, My boss wants me to find a CFM value for a vessel we're building a test stand out of. the capacity of the vessel is approximately 75 cu.ft. with a 1" npt outlet. we want the CFM value at 1500 psi. is there a somewhat simple calculation I can use with just this info or do I need some more data to calculate CFM?

Thanks Fellas

 

[zdas04]

Did your boss also ask you to bring him a water hammer? CFM usually refers to "cubic feet per minute" which requires a pressure and temperature reference to mean anything at all. Sometimes the air compressor industry implies that volumes and rates should be taken back to suction conditions, but that is anything but universal.

Now if you had a velocity limit inside the vessel or through the inlet/outlet nozzles, then a capacity could be calculated, but it would be more appropriate to state it at SCFM (using an explicit definition of standard temperature and pressure).

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[LittleInch]

You need much more data.

Is the tank re-filled at the same rate or does it deplete over time?

What is the outlet pressure downstream of the tank?. Anything less than about 700 psig will result in choked flow at your rather small 1" nozzle, plus a LOT of noise.

What is the air feeding? Normally this question is the other way around, i.e. you now how much air you need / require and then design / check your system around it.

As zdas04 says, what conditions do you want you CFM in? - Standard (60F, 1 atm) or at your usage conditions, whatever these are.

currently what you're asking is like saying, I have a tank of fuel. what MPG will I get from it, without knowing the size of engine, power, etc

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[qualityguy28]

definitely need this to be the most rudimentary calculation, it would be SCFM for sure. this is a steam accumulation tank that should be maintained at a constant 1500 psi. assume the flow would be out of a 6" long 1" npt pipe into the atmosphere at STP. the tank will be used for testing small portable safety valves. unfortunately we don't know what the final setup in the shop is going to look like and my boss wants some ballpark figure numbers from me. and, as far as steam temp goes, look at minimum for superheated steam @1500psi

Thanks for the quick responses guys.

 

[LittleInch]

Ok, so this isn't an air vessel it's a pressure vessel with superheated steam.

You now want to vent this 1500 psig steam via a 6 inch long 1" pipe into an enclosed space straight to atmosphere(!!)

Given that this seems to be unbeleiveably dangerous I'm not going to even try and calcualte this other than to say you will hit choked (sonic) velocity and the steam will expand to a ridiculous degree and you'll burn or kill everyone in the shop, or deafen them at the very least.

When you think about this a bit more and then come back with some more sensible way of doing it you might get a more reasoned response.

Sorry if this isn't the answer you're looking for but the scenario laid out, in my opinion, is so dangerous that it should not be being considered, far less calcualted.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[qualityguy28]

Hi Guys. I realize that venting 1500 pound superheated steam to atmosphere is moronic and quite possibly deadly. I just need to calculate a number to put in a manual to make the national board happy is all. in no way shape or form would we ever actually do this.

 

[LittleInch]

I would just put in your explaination instead. Once you put in a number some moron will think it is possible.... A bit like putting in a valve and then saying, we'll lock it off and no one will open it. Once you put a valve in you have no way of guarenteeing it apart from not putting the valve in in the first place.

This is a steam question and I haven't looked at that since university - a looong time ago - so even if I wanted to I can't give you answer. Sorry.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[chicopee]

Normally, the relieving capacity of a safety valve on an accumulation tank should be based on the free delivery of the medium that the tank is to receive. By free delivery, I mean that the medium delivered by the supply pipe in your case has no restriction another the supply pipe would be open to atmosphere. So if the supply pipe delivers 1000lbs/hr of steam to atmosphere, then the relieving pipe should have a relieving capacity of 1000lbs/hr.