Displacement of a pipeline

[Matt17]

Dear all,

my guess is to displace sea water from a long pipeline (kilometers) with fresh water without any physical separation. To do this I've to size an adequate pumping spread in order to assure a minimum velocity in order to avoid stratification along the pipeline. Any idea to roughly estimate this minimum velocity? ... I know the AGA indicates a minimum velocity as a function of density difference, but AGA speaks about gases ... Suggestions?

Tahnk you all

Regards

Matt17
Process Engineer

 

[BigInch]

Keep your flow in the turbulent range and not much mixing will occur.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Matt17]

Yes, thank you BigInch it's what I think too, but I'd like to have an equation behind for reference and sizing purpose. Any idea?

Matt17
Process Engineer

 

[Latexman]

You are kidding, right?

N_Re = Dv[ρ]/[μ] > 4000

Good luck,
Latexman

 

[Matt17]

Of course, Latexman ...

I mean an equation to estimate a minimum velocity to avoid stratification ... but thank you anyway ... it's never late to refresh my scholastic lectures

Matt17
Process Engineer

 

[Latexman]

OK, how about:

v > 4000[μ]/(D[μ])

Good luck,
Latexman

 

[Latexman]

Whoopsie!

v > 4000[μ]/(D[ρ])

Good luck,
Latexman

 

[Matt17]

Probably there's a misunderstanding ... forget Mr. Reynolds.
My guess would be to have a correlation between minimum velocity and something like difference of density between fluid to be displaced and fluid to displace.

Regards,

Matt17
Process Engineer

 

[1gibson]

Too easy to use a pig?

 

[BigInch]

No pigs required. Density is important when flow is LAMINAR or STOPPED. Basically you have very little density difference between SEA water and Fresh water anyway. The difference in density is only 2.5% After 150 km of Diesel/Jet Fuel at 400 m3/h in a 14" pipeline, density difference 17%, you'll get less than 200 barrels of mix.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[zdas04]

I've been doing some low pressure work lately that is making me question the stability of the transition region in Reynolds Numbers (I know I'm speaking hearsay, but that is what I'm seeing). On one project I saw very constant performance between Reynolds Numbers of 100 up to 9000. Then there was some pretty odd (transition) behavior up to about 15000, then it was pretty smooth again. I don't have high enough quality data to try to publish it, but I'm starting to think that if a process demands turbulent flow, then using >7000 is a touch risky (the 4000 number above has classically been then end of laminar and the start of transition) and I'm starting to use >20000 as an upper limit for transition. This usually isn't a problem for real flows because I mostly find values <<4000 or >>100000, but when I'm pushing the transition region I get more concerned than I used to.

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.

 

[BigInch]

I can't say as high as 15,000, but 8,000 to 10,000 can be possible with heavy crudes.
Here, with seawater and fresh water, it's probably not much more than 2000.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Latexman]

I pulled 4000 straight from the old college textbook, because it said that's where the turbulent regime starts, based on Reynold's work. I agree the start of turbulence can be a nebulus thing. In the past, I have used 10,000 just to be safe.

Good luck,
Latexman

 

[Matt17]

Ok, thank you all ... my only doubt is regarding the pipe diameter (>1 m), but if it's only a problem of Re I'll have no problem.

Regards,

Matt17
Process Engineer

 

[BigInch]

What volume is mixed is the result, not so much from density difference as it is from mixing at the pipe wall interface where the fluid ahead is cleaned off the wall by and adsorbed by the initial frontal advance of the fluid behind.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek