Does Volumetric flow rate remain constant?
Does Volumetric flow rate remain constant?
(OP)
Need to determine volumetric flow rate for compressed air
Any easier way to determine the volumetric flow rate?
So far I found this website http://www.rapidairproducts.com/flowrate.asp
I can probably estimate the length, but the cross section area decreased from the air compressor to the actual inlet, does the volumetric flow rate remain constant even if the cross sectional area decreases?
Thanks
Any easier way to determine the volumetric flow rate?
So far I found this website http://www.rapidairproducts.com/flowrate.asp
I can probably estimate the length, but the cross section area decreased from the air compressor to the actual inlet, does the volumetric flow rate remain constant even if the cross sectional area decreases?
Thanks





RE: Does Volumetric flow rate remain constant?
because air is compressible, volume flow rate doesn't need to be constant ... if it was incompressible (like water) then it would.
how gentle (or sudden) is the area change ?
how fast is the flow ? (near sonic ??, probably not)
temperature ? (RT ??)
pressure ??
RE: Does Volumetric flow rate remain constant?
Mass flow rate does remain constant as long as no mass is added or removed.
Volume flow rate at standard conditions remains constant under changing thermodynamic conditions because it is calculated at a constant (imaginary) set of conditions.
For air compressors it is common to use "actual" volume flow rate at suction conditions as a stand-in for "standard" conditions. This is kind of reasonable since "standard" is actually anything that the parties to an agreement say it is. You have to be really careful to state the compressor flow rate as "CFM at suction conditions" or "SCFM" if you used one of the widely used "standards" (there are several, most common in air compression is 14.696 psia at 60F, but 14.73 at 60F, 14.73 at 68F (20C), and 15.025 at 60F are also widely used).
David
RE: Does Volumetric flow rate remain constant?
Regards,
Cockroach
RE: Does Volumetric flow rate remain constant?
David
RE: Does Volumetric flow rate remain constant?
"what makes you thinkit is a sonic flow?" ... experience with posters leaving out important information untill something has been thrashed out.
the OP asked if volumetric flow rate was constant ? it might be, it very likely to be constant. he should have gas conditions (pressure and temperature) at both ends to understand if it is.
RE: Does Volumetric flow rate remain constant?
Dan
www.eltronresearch.com
Dan's Blog
RE: Does Volumetric flow rate remain constant?
"it might be, it's very likely not to be constant"
sigh
RE: Does Volumetric flow rate remain constant?
TTFN

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RE: Does Volumetric flow rate remain constant?
If you are doing some actual engineering see the above posts.
RE: Does Volumetric flow rate remain constant?
Volume flow rate at actual conditions is an arithemtical side show that is only useful as an intermediate step to calculate mass flow rate, volume flow rate at standard conditions, or velocity--other than that it should never be reported.
David
RE: Does Volumetric flow rate remain constant?
But from the question and linked site I'm envisioning that he is at the tool store staring at selection of compressors that have 10 CFM 100 PSI or 15 CFM @ 110 PSI painted on the side and a collection of various tools with some consumption rating listed on the box.
In that case, "constant enough" means that if the CFM number on the compressor is greater than the sum of the CFM numbers on whatever tools you think you'll operate at the same time then you'll be good to go.
But since the OP has run away and shed no additional light on what he is trying to do I guess we'll never know.
RE: Does Volumetric flow rate remain constant?
But since the OP hasn't been back, we can talk about him any way we want to. We can also morph the discussion into any direction we want to. Got a topic you want to talk about?
David
RE: Does Volumetric flow rate remain constant?
But yeah, depending on the gas states, could or could not be a constant flow rate. The OP should of written tighter.
Regards,
Cockroach
RE: Does Volumetric flow rate remain constant?
Supplier claims in order to have a nitrogen output of 25 SCFM, 75 SCFM of compressed air is needed into the generator.
I have the PSI of the compressed air, but the diameter of the pipe went from a 2" OD (By the compressor) to "1 OD inside the facility.
RE: Does Volumetric flow rate remain constant?
The pipe size is irrelevant unless you are also trying to calculate velocity. If I put 75 SCFM into a 2 inch pipe and then swedge down to 1-inch, I'll still get 75 SCFM out the other end.
David
RE: Does Volumetric flow rate remain constant?
I'd look at a chart more like this. Set it up for the pressure needed.
http:
At 100 psi from the compressor, a 1" line can deliver 75 CFM, only 75 feet. then you have pressure drop issues.
RE: Does Volumetric flow rate remain constant?
I really don't like the table you referred to, but then I don't like most of what I see at that site. It calls itself "Engineering Toolbox" but everything on there is so dumbed down that it is should be called "high school tinkerers toolbox". For that table to be meaningful it would be important to know what equation they used to fill it in, is the pressure referenced at the head or the foot, and what is the target dP. Without that information it is just a table that only the laziest of engineers would consider using.
David
RE: Does Volumetric flow rate remain constant?