PIPEING PROBLEM, NEED HELP
PIPEING PROBLEM, NEED HELP
(OP)
I am need some help trying to figure if this setup is going to work. i am not as skilled in fluid dynamics as i should be. any help i can get would be welcome. thanks
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PIPEING PROBLEM, NEED HELP
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PIPEING PROBLEM, NEED HELPPIPEING PROBLEM, NEED HELP(OP)
I am need some help trying to figure if this setup is going to work. i am not as skilled in fluid dynamics as i should be. any help i can get would be welcome. thanks
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RE: PIPEING PROBLEM, NEED HELP
RE: PIPEING PROBLEM, NEED HELP
I meant to post some questions with it.
How does the oil on top of the water effect the head?
The riser pipe is under the top oil level, how does this rise and drop effect the suction need by the pump other than normal flow loss?
They have been burning up the pump and not sure what they should do.
Would a 6 in Line help?
lowing the Riser pipe?
Thanks
Michael
RE: PIPEING PROBLEM, NEED HELP
RE: PIPEING PROBLEM, NEED HELP
As to your questions:
How does the oil on top of the water effect the head? The oil adds to head according to (ft of oil)*(S.G. of oil).
The riser pipe is under the top oil level, how does this rise and drop effect the suction need by the pump other than normal flow loss? As long as the riser remains fully flodded with water, then normal friction is the only loss.
They have been burning up the pump and not sure what they should do. Would a 6 in Line help? Some, but not much - A 6" line would gain you about 2 feet of NPSHA.
lowing the Riser pipe? If it's kept flooded, only by the friction due to length of suction pipe removed.
RE: PIPEING PROBLEM, NEED HELP
RE: PIPEING PROBLEM, NEED HELP
I would join pennpiper to ask why you need this high point?
Another question: How pump operates? Constantly, or intermitent? How level of fluid changes inside tank during operation?
Regards,
Curtis
RE: PIPEING PROBLEM, NEED HELP
RE: PIPEING PROBLEM, NEED HELP
In normal conditions, the oil is at the oil outlet and the left hand leg of the weir piping is always full to the overflow. If a liter of liquid comes in, then a liter of liquid leaves out some combination of the oil outlet and the weir piping. The weir has to be vented to prevent siphoning the whole tank into the water system--the vent either just isn't shown or the gun barrel was designed to fail.
With this design, I'd figure on the centrifugal pump lasting a week or so. The only way these things work (and they can work amazingly well) is if both the oil and water go into atmospheric tanks (and you have the pump from them controlled with on/off floats). Trying to pump out of the weir piping is ALWAYS a disaster.
David
RE: PIPEING PROBLEM, NEED HELP
Don't suppose you have a suction gauge reading?
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: PIPEING PROBLEM, NEED HELP
Can you explain the purpose of the riser?
RE: PIPEING PROBLEM, NEED HELP
If the riser is not there, you have to use an oil/water interface level controller and a dump valve. This works better with light oil than heavy, but even in light oil it is still at risk from leaking or hung dump valves.
There are several ways to skin this cat, I've attached an extract from my 5-day course to show some considerations. On the second page there is a picture of a couple of kinds of gun barrel. They do the same thing--the external weir like we're talking about here is much less expensive, the internal weir is much more forgiving.
This "simple" process is really quite complex. I always design the weir with multiple overflow heights (with block valves on them) so that if the SG of the oil changes I can shift the weir height.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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RE: PIPEING PROBLEM, NEED HELP
HERE IS WHAT I CAME UP WITH.
RE: PIPEING PROBLEM, NEED HELP
RE: PIPEING PROBLEM, NEED HELP
Your inlet pipe is the same size as the water outlet pipe. Inlet velocity (disregarding the Cv as a first approximation) is q/A (the velocity equations you are using are generally used to determine a flow rate from pressures, you know the flow rate) or 5.57 ft/sec. That is the combined stream flow rate. Part goes into the water pipe and part goes into the oil pipe. Logic says that the water outlet velocity must be less than 5.57 ft/sec (since it is a lower mass flow rate), not 34 ft/sec.
I can't comprehend why you stated oil density at 140F and water density at 52.8F. The inlet stream is mixed and very likely at the same temperature. It is crucial have the two densities at the same temperature. I'll assume that the tank is heated and that everything is at 140F, so the density of the water (assuming SG=1.0 and density at 60F is 62.4 lbm/ft^3) is 61.34 lbm/ft^3.
Your weir height is pretty wrong. It is not a function of velocity, it is a function of hydrostatic pressure. Weir height is always greater than the height of the oil/water interface and less than the oil outlet. The height is:
hweir=(ρwater*hwater+ρoil*hoil)/ρwater
Which works out to 23.55 ft. I will generally try to get a bit more definition and in this problem I'd plan on the interface being at 15 ft instead of 20 ft. That works out to a weir height of 22.96 ft which is only 7 inches lower, but that can make a big difference.
David
RE: PIPEING PROBLEM, NEED HELP
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: PIPEING PROBLEM, NEED HELP
David
RE: PIPEING PROBLEM, NEED HELP
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso