Parallel Pipes exiting to STP (Hazen-Williams applicability)
Parallel Pipes exiting to STP (Hazen-Williams applicability)
(OP)
I'm working on a parallel pipe scenario where there is one inlet and multiple outlets all exiting to free air (STP). Do the constraints of the Hazen-Williams equation still apply (ie all hL values equal)? I've found solutions assuming so but in practice we have found that in a case where all pipes have identical ID, roughness, and length we will consistently see greater dispense volumes from the pipe farthest from the inlet.
A little background: inlet is horizontal, all dispense pipes are vertical exiting the bottom with all dispense inlets at same height. Prior to a timed dispense all pipes and inlet tube (manifold) have been primed and are assumed full of fluid (ie. no air volumes displaced at beginning of dispense).
Thanks in advance for any guidance,
Adam
A little background: inlet is horizontal, all dispense pipes are vertical exiting the bottom with all dispense inlets at same height. Prior to a timed dispense all pipes and inlet tube (manifold) have been primed and are assumed full of fluid (ie. no air volumes displaced at beginning of dispense).
Thanks in advance for any guidance,
Adam





RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Most likely, the main reason your calculations do not match reality is momentum changes were not included in the analysis.
Good luck,
Latexman
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
The only way you are going to balance all of the legs is to put control valves on all of the legs and drive each of the control valves based on a flow meter. Just relying on the pipe being "the same" will result in maldistribution.
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.
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
As soon as air gets in, forget HW.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Using Hazen Williams I've come up with solutions to the variance allowed due to the varying tubing ID's but as I see more threads on use of H-W they seem to all refer to parallel pipes with single inlets and outlets. Is my use of it with single inlet and multiple outlets appropriate or am I off base?
Thank you all for your input
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
HW does not apply to such small diameters where surface tension forces are immensely greater than friction.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Maybe you are not even talking about water for that matter.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Good luck,
Latexman
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Patricia Lougheed
******
Please see FAQ731-376: Eng-Tips.com Forum Policies: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Good luck,
Latexman
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Balancing resistances will not work; bubbles, rat hairs, and machining chips will screw it all up.
Speaking of which, bubbles can be used to advantage, e.g. with TFE tubes and optical meniscus detectors. ... but they can be troublesome, too.
Start retooling now for multiple positive displacement plunger/piston pumps, one per dispense stream.
Mike Halloran
Pembroke Pines, FL, USA
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
Why not work with dispensing equipment vendors?
Good luck,
Latexman
RE: Parallel Pipes exiting to STP (Hazen-Williams applicability)
We are manufacturing these assemblies ourselves. My investigation stems from intermittent failures that can plague the line for weeks at a time. It seems as though a redesign of the inlet may be the best solution at this time.