Fluid flow partially full pipe

[LLLRLLL]

Hello I am an instrumantaion/Electrical technician by trade so please excuse my lack of knowledge in fluid dynamics. I am looking at a pipng system in which various verical cylinder vessels, under pressure,(1100 PSIG) set at ground level, drain fluid from their bottoms, into a horizontal 4 inch pipe which traverses across the ground. at various places along this run, there are 4" tees (taps) on the top of the pipe where the 4" GOES VRTICAL 6 FT., horizontal for 15 feet, Then drops back down to ground level. just beyond this there is a control valve/check valve,which, when opened, is supposed to push fluid into a lower pressure (600 PSIG) vessel.
My question is that if the first horizontal run from the originating vessels is only partially full, is there any way liquid will be able to travel UP those vertical legs?Thanks in advance.

 

[LittleInch]

Yes there is.

The type of two phase flow is variable depending on the liquid fraction, liquid flowrate and gas flowrate and pressure / velocity

In very large pipes with relatively low liquid fraction and low gas velocity, you could easily get more gas or mostly gas coming off the top of the pipe so long as the liquid flow in the main branch continues flowing. however if the gas velocity is quite high then it will essentaillly pick up the liquid and bring it with the gas up the pipe.

See this for what it physically looks like, but if you can sketch your system and advise where the flows go at the same time we might get somewhere further.

https://www.youtube.com/watch?v=GMp9Oc0Dy_U

If the pipe is coming off the bottom of the vessels why is it two phase flow? The liquid will flush out the gas and flow up.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[zdas04]

In that video, the mass flow ratio was about 1/3 gas and 2/3 liquid. A drain system with that amount of gas is typically called "broken". More normally gas would be 1-2% of the mass. In the more normal case, the only flow is "filling flow". In other words, all of the pipe below any given point must be full of liquid before any liquid flows past that point. As the liquid goes over hills, it will tend to increase velocity (resulting in partially full pipe since the mass flow rate must remain constant, but once the increased velocity in the downhill drains the higher horizontal pipe, flow into the upper horizontal pipe will stop until it refills. In other words you can siphon fluids while you have a liquid seal on the high points and the first horizontal will always be full of liquid.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[LLLRLLL]

Thanks for the response. The fluid flow rate with this arrangement is VERY low, and based on your response, what i believe may be happenning, is that the system design is to only have liquid in the pipe. introducing gas into this drain syatem.(which can, and does happen), combined with the low flow rate, is causing the liquid to just lay in the lowest section of the system,with such low velocity its creating a trap.I think This can be proved out because there is a jumper pipe (with a manual valve) which allows us to divert, from the low section,up and into another vessel that is only 120 PSIG (as opposed to the normal 600 PSIG) when this valve is opened,we easily evacuate the liquid from the system, and from what you illustrated, this would be due to the much higher flow rate caused by the large differential. would you agree?

 

[LLLRLLL]

"In other words you can siphon fluids while you have a liquid seal on the high points and the first horizontal will always be full of liquid"....... This i think is athe root of the problem, with no liquid seal and the low velocity i think its just passing the gas through without crrying the liquid.

 

[LittleInch]

Hmmm, Difficult to see what you're doing here and connecting a vessel rated at 120 psig to one at 1100 with a manual valve doesn't sound good.....

But yes, once you get a gas velocity of probably >3m/sec, it will essentially pick up the liquid or create enough waves that it starts slugging. Once liquid gets in the vertical pipe it won't fall back out if you have enough gas velocity ( again about 2-3m/sec)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Latexman]

Gas has so much volume, it can act as a propellant for the liquid if it's velocity gets high.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.