Conservation of Flow?
Conservation of Flow?
(OP)
I have system that consists of the following:
1. Permanently installed flow meter for whole system (incoming and outgoing)
2. Manifold where whole system is split into three branches
3. Orifice devices in two of the three branches to limit flow to approximately 1/2 of the 3rd branch
4. Temporary flow meters on each branch
5. Similar manifold where all three branches converge (but with no orifices)
A given set of data looks like this (all in GPM):
Permanent flow meter incoming = 3.1
Permanent flow meter outgoing = 3.1
Temporary flow meter incoming = 3.0 (test for meter calibration)
Temp flow meter exiting branch 1 = .6
Temp flow meter exiting branch 2 = .6
Temp flow meter exiting branch 3 = 1.1
Because these values total 2.3 GPM, and the flow into the manifold = approximately 3 GPM, there is a feeling that the manifold is somehow limiting flow. I understand that while it is probably limiting flow of the SYSTEM, it cannot cause a localized flow restriction that somehow disappears after reconvergence. How do I explain to my peers the measurement differences they are seeing?
Thanks,
Jay
1. Permanently installed flow meter for whole system (incoming and outgoing)
2. Manifold where whole system is split into three branches
3. Orifice devices in two of the three branches to limit flow to approximately 1/2 of the 3rd branch
4. Temporary flow meters on each branch
5. Similar manifold where all three branches converge (but with no orifices)
A given set of data looks like this (all in GPM):
Permanent flow meter incoming = 3.1
Permanent flow meter outgoing = 3.1
Temporary flow meter incoming = 3.0 (test for meter calibration)
Temp flow meter exiting branch 1 = .6
Temp flow meter exiting branch 2 = .6
Temp flow meter exiting branch 3 = 1.1
Because these values total 2.3 GPM, and the flow into the manifold = approximately 3 GPM, there is a feeling that the manifold is somehow limiting flow. I understand that while it is probably limiting flow of the SYSTEM, it cannot cause a localized flow restriction that somehow disappears after reconvergence. How do I explain to my peers the measurement differences they are seeing?
Thanks,
Jay





RE: Conservation of Flow?
-Mike
RE: Conservation of Flow?
(1) The "total flow" meters are in close agreement and are probably reasonably correct in that they verify each other.
(2) If the flow branches are geometrically similar *and dynamically similar* (refer to fluid mechanics definitions of dynamic similarity) then the two branch meters reading 0.6 appear to verify each other.
(3) I tend to suspect the third branch meter is off calibration; it seems to be the only one in the system without a benchmark to follow.
You could probably rent a temporary Doppler meter for a day to confirm the rates.
Regards,
SNORGY.
RE: Conservation of Flow?
The third branch SHOULD read differently than the other two, since the orifices in the three branches are different. Branch 3 has a larger orifice than the other two in order to induce more flow to that branch.
Thanks,
Jay
RE: Conservation of Flow?
Water is essentially incompressible, so 3.1 gpm in must result in 3.1 gpm out, assuming no leaks.
TTFN
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RE: Conservation of Flow?
Thanks,
Jay
RE: Conservation of Flow?
On the surface, it would appear to me that one or more of your "temporary flow meters" would be the culprit since your ingoing and outgoing meters agree and your "calibration test meter" agrees with your permanent incoming meter within roughly 3% (3.0 vs. 3.1). At 3 GPM, I assume these are very small lines (maybe 1/4" or 1/2" ?), so I assume you left yourself plenty of straight-run before the meter (no disturbances from elbows, the orifice plates, wall taps, etc.). What flow metering technology are you using for the main and branch lines? Whenever you "mix" metering technology, you have the potential for discrepencies.
I don't know your complete piping arrangement. Is there any way to block off #1 and #2 and run 100% flow through Branch 3 (the one with no restrictive o-plates). A 25% discrepancy in flow between your branch lines and the main lines is huge. Isolating the flow through one line should at least indicate whether or not the error is cumaltive.
Since the units are in GPM, I assume you are running a non-compressible fluid (density compensation not required at measurement points).
I'm sure we can help trouble-shoot your application, but I would ask for the following:
1) Start with Mike's questions above.
2) Identify what fluid you are measuring
3) Identify what type of meters you are using on all lines.
4) Indentify all line sizes and equations you are using to calculate flow (for example, if it is DP, are you taking the square root of the DP to calc flow).
5) Are the flow rates you are measuring within the specs of the meter (turndown of 3.1 GPM down to .6 GPM)
6) Is there adequate straight-run up and downstream of the meters?
There are hundreds of meters claiming to have accuracy of 1% or better. Only a small percentage can produce independent flow lab data to back it up.
Bottom line: If the flow in = flow out, and there are only 3 branch lines in between (all are being metered), then you should not have a 25% error.
I hope we can help.
RE: Conservation of Flow?
Jake
RE: Conservation of Flow?
Since the inflow physically equals the outflow, your difference is measurement. I would first look at the two meters reading 0.6 gpm. I've measured the flow on seemingly identical legs hundreds of times (looped flow meters on big gas wells, but it is the same principle) and have never once had accurate, repeatable meters read the same on the two "identical" legs. It never happens. 20% difference is quite common, 30% is not rare.
Any chance you can put a 3-ball manifold downstream of your meters to drop in a prover? One, two, or three of your outlet meters is really wrong. Your inlet meters may also be wrong, but it is rare for two meters in series to both be wrong the same amount in the same direction.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: Conservation of Flow?
Unless there is a leak or storage, what comes out must equal what goes in.
Ted
RE: Conservation of Flow?
RE: Conservation of Flow?
"Micromotion is a cubic equation"????????? Micromotion infers flow from linear displacement of the piping--i.e., a linear equation since the only thing they are measuring is the shift in the piping.
David
RE: Conservation of Flow?
RE: Conservation of Flow?
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RE: Conservation of Flow?
RE: Conservation of Flow?
a random number generatorlinear because it infers flow from a pulse counter.I was only referring to the number of variables sampled, not to the shape of a graph of flow.
David
RE: Conservation of Flow?
RE: Conservation of Flow?
David
RE: Conservation of Flow?
I was once involved with automating a batch cooling process where utility water would cool "stuff" in a batch cooling tank. The instrument and process engineers were trying to establish the sizing basis for a full-port snap-acting dump valve on the outlet of a 1.5" utility water line. I asked if the utility water was hazardous or toxic, and they looked at me like I was some kind of idiot and said, no, it's only water. So I picked up a 5-gallon pail, hung it on the end of the pipe that was being dumped to sewer, opened the ball valve, and filled the bucket in 10 seconds. I told them to size the valve for about 30 usgpm. Again, they looked at me like I was some kind of idiot.
They didn't ask me for any more help, so I never did find out what they actually installed.
Regards,
SNORGY.
RE: Conservation of Flow?