Hot water flow from open pipe end

[KevinNZ]

Hi

What's a good reference for working out the flow of hot water from an open ended pipe. The upstream pressure means the flow is critical and hot water will flash to two phase at the discharge.

Thinking of dividing the line into segments and working out pressure drops and the flash point. Iteration required.

Thanks K

 

[LittleInch]

Some sort of transient analysis program.

It will start to flash in the pipe before the end point which complicates things.
Also looks like choked flow to me.
As you pressure goes down then Q will go down so everything is constantly changing.

How long is L?
A few metres or a few km?
How big is the volume compared to your pipe? X100 or x 10000?

Also 145C will be saturated steam at the outlet? Not much room for liquid at that temp and pressure.



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

 

[Latexman]

Are you pursuing a steady-state (infinite hot water supply) or dynamic solution?

Good Luck,
Latexman

 

[Latexman]

I have an old journal article (attached) that may be pertinent to your problem.

Good Luck,
Latexman

 

[Latexman]

Is the file upload function broken, or did I do something wrong? I just get a blank page when I click the link.

Good Luck,
Latexman

 

[danschwind]

Latexman,

I'm getting the blank page from your link too. Try uploading it again.


Kevin,

Not enough info to answer this question. Is the upstream conditions held constant or is this a depressuring problem?

Daniel
Process Engineer
Rio de Janeiro - Brazil

 

[Latexman]

I already uploaded it twice. Notice the [Post Deleted] above my 15:01 post.

One last try!

EDIT - Didn't work. I reported the malfunction.

Good Luck,
Latexman

 

[LittleInch]

Try this?

Or this

https://simpliengineering.com/uploads/short-url/bjSJq2O5NVhUpTV23Xdfhb5oelr.pdf

Or this

https://www.eng-tips.com/viewthread.cfm?qid=488280

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

 

[Latexman]

First one was blank. (Link is below signature.)

Second one is right. (Not sure this one will survive though. I think it may get scrubbed automagically.)

Third one does not contain the PDF I was trying to upload, but the attached articles are pertinent.

Good Luck,
Latexman

 

[georgeverghese]

See page 6-29 in Perry Chem Engg Handbook 7th edn. for 2 phase flashing critical flow calculations - homogenous equilibrium model which applies to L > 100mm.

 

[pierreick]

Hi,
It might be the document latexman is willing to share with you.
Pierre

 

[Latexman]

Same subject, but yours is 3 years more recent.

Good Luck,
Latexman

 

[KevinNZ]

Thanks for the input

L = 4m
looking for steady state flow.
The main pipe is can be regarded as an infinite water source

 

[casflo]

As the pipe is only 4m long, practically the flashing occurs at the pipe exit and you can consider that the critical pressure at the end of the pipe is the saturation pressure of the water with 146 ºC. Therefore, calculate simply the flow rate of water through a pipe 4m long and 100 mm diameter with the pressure drop of 26 bar less the saturation pressure.
Don´t forget add to the equivalent pipe length, K = 1 that corresponds to the pipe exit.

 

[LittleInch]

You must be into choked flow here and you're going to get a HUGE flow at sonic velocity which will pretty much destroy your pipe in minutes.

What is this about as it clearly isn't something practical or real??

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

 

[KevinNZ]

Yes the flow will be large. We are trying to see what would happen if the operator left this pipe (drain) open and started the plant. We already know from damage to the pipe run the thrust forces are high. Need to know the flow and then the thrust force to design the hold down support at the end of the pipe ( unlike the sketch the pipe has elbows)

 

[pierreick]

Hi Kevin,
Edit
Using the reference given by George, I got about 420 tons/h of a mixture with about 10% vapor coming from the pipe.
Does it make sense?
Using PR equation of state, I found that you need to reach #415 Kpa to start to flash the liquid.

Pierre

 

[LittleInch]

Well I just did this as 100mm orifice choked flow (I hope) calculation and get about 1200-1300m3/hr so about 45 m/sec.

Now how the flashing impacts this I don't know, but I think you're looking somewhere along those lines.

The 4m of line or the flashing may bring this down a bit, but I think you're looking in 1,000 m3/hr mark with an unlimited amount of 26 barg superheated water coming out of a 100mm hole.

How precise do you need to be?

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

 

[Latexman]

Hi Kevin,

I used my company's HEM program and got 1250 MT/hr. I got about the same result using the company's PSV program set up for an open vent, which is what this is. Similar to pierreick, my final flash (14.7 psia) was 8.5% vapor. Do you have access to Aspen? You could probably model this rigorously as an open vent or a RD with K[sub]RD[/sub] = 0 in the Safety Environment.

Surprisingly to me, backpressure just inside the pipe exit was high enough to prevent flashing in the pipe, so it's essentially a liquid pressure drop problem from 26 bar to 3.15 bar at 145 C. All the flashing occurs at/after the pipe exit. I guess the 1 velocity head loss at the exit put just enough backpressure on the hot water to keep it from flashing inside the pipe. I'll let you check that out.

If you want more info., go to the PSV forum, find my FAQ, and send me a comment. That should connect us. I have some output files (thrust is provided), if you want them.

Good Luck,
Latexman

 

[georgeverghese]

No need to reinforce piping supports. Bolt on a blind flange to the drain valve; then it would require the operator to get an approved work permit, signed off by the shift supervisor, to get the blind off. And this would trigger safety operating procedures. In addition, or otherwise, add a restriction orifice at the valve to keep velocity within limits of the piping supports or some safe upper operating limit.