6 replies to this topic

[Engineer87]

Hi Members,

 

I'm doing Line sizing on VMGSim for the NGL flowing in the horizontal 3" pipelines. I used Colebrook correlation for the pressure drop.I found greater value using Colebrook for the pressure drop and it make sense as Colebrook used turbulent flow.

 

Any body knows about Dukler's Method for pressure drop calculations?. I have less pressure drop obtained using Dukler's method per 100 ft.

 

Can any body explain why?

 

Is Duckler's method take into account for laminar flow?

 

Regards,

[breizh]

Engineer87

 

Better to post your calculation , certainly someone will review it !

Breizh

[PingPong]

I don't know VMGSim, but as far as I know the Dukler method is for two phase flow, not single phase.

 

And it seems very unlikely to me that an NGL pipe would have laminar flow, unless it is severly oversized.

[Engineer87]

Thanks Ping Pong,

 

So it means that for NGL flow, Colebrook is the suitable correlation to used?

 

If I use very very small ( Negligible ) gas in the liquid, making flow two phase. Does it effects the pressure drop in Duckler's method?

[PingPong]

Use Colebrook for liquid or vapor flow.

 

Use Dukler only for two phase flow, if you have nothing better at hand.

 

Problem (in my opinion) with the Dukler method is that it uses the smooth pipe friction factor, and applies a correction factor (multiplier) to that to get the friction factor to be used. The value of that multiplier depends on the liquid volume fraction in the two phase stream. At a liquid volume fraction close to 1 the multiplier is also 1, so it means that for a stream that is liquid with only a small quantity of gas the Dukler method gives the pressure drop of a smooth pipe, which is (in my opinion) total nonsens, especially for large Reynolds number. Just look at a Moody chart.

[breizh]

http://switch2011.up...ow & Piping.pdf

 

To support the discussion the link attached . Equation 17-41

 

Breizh

Edited by breizh, 11 May 2014 - 09:46 PM.

[Engineer87]

Thanks Ping Pong and Breizh,

 

 

You seems correct here, as while doing pressure drop using high Re values, Colebrook friction factor give more pressure loss as compared to Ducklers Method may be because of reason that Duckler;s incorporates smooth friction factor as gives comparitivley less pressure drop ( for Fluid like NGL )