3 replies to this topic

[krishnamurthy]

Can any please explain me the criteria for two phase (multiphase) line sizing ?  I know for two phase line sizing calculation, the calculated velocity should be lesser than the erosional velocity, but apart from this  , i would like to know what are the other parameters that needs to be considered for two phase line sizing calculation. Please explain me. 

[Vegeta]

There are multiple things to consider. One of these is what you mentioned. Also, you need to check the flow regimes.

The calculation might be complex especially if it is for an upstream production pipelines from wells.

[breizh]

Hi,

Let you consider the paper attached to support your work.

Note: you will be amazed using your favorite search engine, key words two phase flow

Good luck

Breizh

[shvet1]

Can any please explain me the criteria for two phase (multiphase) line sizing ? i would like to know what are the other parameters that needs to be considered for two phase line sizing calculation. Please explain me. 

ExxonMobil's doc. XIVD

 

FLOW REGIMES IN HORIZONTAL OR SLIGHTLY INCLINED PIPES

...

SLUG FLOW - when the vapor rate reaches a certain critical value, the crests of the liquid waves touch the top of the pipe and form frothy slugs. The velocity of these slugs, and that of the alternating vapor slugs, is greater than the average liquid velocity. In the body of a vapor slug the liquid level is depressed so that vapor occupies a large part of the flow area at that point. Uphill, slug flow is initiated at lower vapor rates than in horizontal pipe.

Downhill, it takes higher vapor rates to establish slug flow than in horizontal pipe, and the behavior is displaced in the direction of annular flow. SINCE SLUG FLOW MAY LEAD TO PULSATION AND VIBRATION IN BENDS, VALVES and other flow restrictions, it should be avoided where possible.

...

FLOW REGIMES IN VERTICAL PIPES

...

SLUG FLOW - as the vapor rate increases, bubbles coalesce into slugs which occupy the bulk of the cross-sectional area. Alternating slugs of vapor and liquid move up the pipe with some bubbles of vapor entrained in the liquid slugs. Surrounding each vapor slug is a laminar film of liquid which flows toward the bottom of the slug. As the vapor rate is increased, the lengths and velocity of the vapor slugs increase. Slug flow can occur in the downward direction, but is usually not initiated in that orientation. However, if slug flow is well established in an upward leg of a coil, it will persist in a following downward leg, provided that other conditions remain the same. 

IN DESIGNING FOR TWO-PHASE FLOW IT IS NORMAL PRACTICE TO TRY TO AVOID SLUG FLOW, since this regime can lead to serious pressure fluctuations and vibration, especially at vessel inlets and in bends, valves and other flow restrictions. This could lead to serious equipment deterioration or operating problems. When slug flow cannot be avoided (for instance, in thermosyphon reboilers), one should avoid flow restrictions and use long-radius bends to make turns as smooth as possible.

FROTH FLOW - as the vapor rate increases further, the laminar liquid film is destroyed by vapor turbulence and the vapor slugs become more irregular. Mixing of vapor bubbles with the liquid increases and a turbulent, disordered pattern is formed with ever shortening liquid slugs separating successive vapor slugs. The transition to annular flow is the point at which liquid separation between vapor slugs disappears and the vapor slugs coalesce into a continuous, central  core of vapor. Since froth flow has much in common with slug flow, the two regimes are often lumped together and called slug flow. In the downward direction, froth flow behaves much the same as slug flow does, except that the former is more easily initiated in this orientation, particularly if conditions are bordering on those for annular flow.

Edited by shvet1, 09 April 2023 - 10:51 PM.