Two-phase fluid flowGUIDELINE TO PIPE SIZING FOR TWO-PHASE FLOW (LIQUID-GAS)

AUTHOR: VIKRAM SHARMADATE: 2nd MARCH 2017

Table of ContentsWhat is two-phase flow?Types of Gas-Liquid flowBaker’s map for gas-liquid flowCalculation methodologyReferences

What is two-phase flow?Single-phase flow → fluid flow in a single

stateMultiphase flow → simultaneous flow of

several fluid phasesCommon multiphase flow are (i) gas-liquid,

(ii) liquid-liquid or (iii) liquid-solid.Why is it so important? Severity of pressure

drop problems that may result to operational problems in a process

Types of Gas-Liquid flowBubble flow:Bubbles (gas) are dispersed throughout the

liquid & moves along the upper part of the pipe due to their buoyancy.

Velocity of the bubble of gas ≈ velocity of the liquid

Occurs when the gas content is 0.3 wt. frac. of the total volumetric flow & at high mass flow rates

Linear vel. of the liq. = 1.5-4.8 m/s (typical)Linear vel. 0f the vap. = 0.15-0.61m/s

(typical)

Types of Gas-Liquid flow (cont’d)Plug flow: Intermittent type two-phase flowAlternate plugs of liq. & gas where the gas

portion moves along the upper part of the pipe.

Liq. → along the bottom part of the pipeExpected to occur when liq phase is at 0.61

m/s and vapour phase is < 1.22 m/s

Types of Gas-Liquid flow (cont’d)Stratified flow:2 phases separated frm. by a common interfaceLiq phase stratified at the bottom of the piping due

to gravitySeen in horizontal & slightly inclined pipelines ↓ gas flow: smooth fluid interface or possible

rippling by small capillary waves of a few mm lengths

↑ gas flow: waves of small amplitude appears, droplets can be entrained, deposited at the wall or interface

Liq. vel < 0.15 m/s, gas vel: 0.15-3.05 m/s (typical)

Types of Gas-Liquid flow (cont’d)Wave flowSimilar to stratified flow, gas flow at ↑

velocity ↓ gas vel. – gas-liq. Interface is flatAs gas vel. increases – interface becomes

unstable due to small disturbances & waves are seen

Shape & size of waves α pipeline geometry & fluids flow rates

Types of Gas-Liquid flow (cont’d)Slug flowLiq. rich slugs - may or may not cover the

entire inner section of a pipeObserved when the rapidly moving gas

created waves & form froth slugsThis slugs travel along the pipeline @ vel.

Higher than ave. liq. Vel.Vibrations are due to ↑ vel. travelling against

fittingsLiq. vel ≈ 4.58 m/sGas vel.: 4.58-15.24 m/s

Types of Gas-Liquid flow (cont’d)Annular flowGas vel. further increases resulting to gas

flow through the liq. FlowLiq. Film @ the bottom of the pipe is thicker

due to gravityLiq vel. < 0.15 m/sGas vel. > 6.1 m/s

Types of Gas-Liquid flow (cont’d)Dispersed flowLiq. entrained as the fine droplets by the gas

phase in the gas-liq flowThe dispersed phase in both gas-liq. / liq.-liq.

- flow rates of both phases as the interface is deformable

The dispersed phase of the dispersed flow coalesces & become continuous phase with ↑ flow rate

Occur when the gas content is > 30% of the total weight flow rate

Baker’s map for two phase flowLiq. entrained as the fine droplets by the gas

phase in the gas-liq flow

Calculation procedureObtain physical properties of the fluid (mass

flowrate, density, viscosity and surface tension) for both gas and liquid.

Obtain piping layout. Piping is to be divided into segments as fluid regime and properties varies along the piping route

Determine the flow regime for 1st pipe segment

Perform ΔPfriction, ΔPelev. & ΔpfittingsRepeat the above calculations for other pipe

segments

Calculation procedure (cont’d)

Break the pipe into a couple of segments.For Segment 0-1, determine the fluid flow regime

by calculating Bx and By (refer to Slide #11). Intersection of Bx and By gives the fluid flow

regimeThe next step is to calculate the ΔP of individual

phase (ΔPL, bar/100m & ΔPG,bar/100m)

1 2 3 4 5 6 n

Fluid in

Fluid out

0

Calculation procedure (cont’d)The next step is to calculate the ΔP of individual

phase (ΔPL, bar/100m & ΔPG,bar/100m) (cont’d)

Darcy friction factor (fD) is expressed as:

fD can calculate for both laminar and turbulent flows

Calculation procedure (cont’d)Lockhart-Martinelli (LM) parameter, X is the

ratio of liquid and gas pressure drop. It is a function of mass fluxes, densities,

viscosities of the liq.. & gas and pipe diameter.

We have to determine the frictional pressure drop multipliers for both liq. (φ2

L) and gas (φ2G).

The multipliers are a factor of fluid Reynolds number (turbulent, laminar (viscous)).

Transitional flow is considered as TURBULENT.

Calculation procedure (cont’d) Transitional flow is considered as TURBULENT (cont’d)

φ2L decreases with increasing X, φ2

G increases with increasing X

Extracting data is cumbersome, may lead to inaccurate date.

Calculation procedure (cont’d)Extracting data is cumbersome, may lead to

inaccurate date (cont’d).Chisholm (1967) incorporated the effect of

interfacial shear forces in the LM correlation.New correlation ensures engineers to

determine the hydraulic diameters of the phases more accurately compared to LM.

It do not require the use of graph (refer to Slide #16)

Chisholm (1967) correlations in terms of Lockhart-Martinelli (1949):

Calculation procedure (cont’d)Chisholm (1967) correlations in terms of

Lockhart-Martinelli (1949) (cont’d)

The frictional pressure drop can be calculated based on either liquid phase or gas phase.

The next step is to calculate the ΔPstatic due to elevation

Calculation procedure (cont’d)The next step is to calculate the ΔPstatic due to

elevation (cont’d)We have to include pressure drop due top

fittings. We rely on equivalent length method to

determine the pressure drop.This method approximates the pressure drop

of fittings based on hypothetical piping length

Calculation procedure (cont’d)The next step is to calculate the ΔPstatic due to

elevation (cont’d)We have to include pressure drop due top

fittings. We rely on equivalent length method to

determine the pressure drop.This method approximates the pressure drop

of fittings based on hypothetical piping length

Calculation procedure (cont’d) This method approximates the pressure drop of

fittings based on hypothetical piping length (cont’d) Consider the effect of erosion-corrosion on piping. In certain flow regimes, liq vel approach or exceed

gas vel & this leads to erosion-corrosion Determine if erosion-corrosion may occur at a

particular velocity.

Total pressure drop is:

P1 of Segment 0-1 is obtained: ΔP0 – ΣPTP..

Calculation procedure (cont’d)P1 of Segment 0-1 is obtained: ΔP0 – ΣPTP..

(cont’d)The properties for Segment 1-2 is based on

Point 1. Repeat the above calculations to determine the total pressure drop of horizontal pipe straight length.

Do not segmentized pipe fittings! Choose your segments appropriately.

References Akiwi, S. (2010, September 7). Dispersed Flow. Retrieved

February 23, 2017, from THERMOPEDIA: A-to-Z Guide to Thermodynamics, Heat & Mass Transfer, and Fluids Engineering: http://www.thermopedia.com/content/5/

Alain, L., & Fabre, J. (2011, February 9). Stratified Gas-Liquid Flow. Retrieved February 21, 2017, from THERMOPEDIA: A-to-Z Guide to Thermodynamics, Heat & Mass Transfer, and Fluids Engineering: http://www.thermopedia.com/content/266/

Coker. (2007). Fluid Flow. In Applied Process Design for Chemicals and Petrochemical Plants (4th ed., Vol. 1, pp. 133-302). Burlington: Elsevier Inc.

Hewitt, G. F., & Taylor-Hall, N. S. (2013). Flow regimes in horizontal and inclined flow. In Annular Two-Phase Flow (p. 7). Oxford: Elsevier.

McCready, M. J. (n.d.). Flow regimes in gas-liquid flows. Retrieved February 22, 2017, from https://www3.nd.edu/~mjm/flow.regimes.html

References Mekisso, H. M. (2004). Comparison of Frictional Pressure Drop

Correlations for Isothermal Two-Phase Horizontal Flow. Stillwater: Oklahoma State University.

Sreenivas, J. (2011, February 11). Wavy Flow. Retrieved February 21, 2017, from THERMOPEDIA: A-to-Z Guide to Thermodynamics, Heat & Mass Transfer, and Fluids Engineering: http://www.thermopedia.com/content/269/

Szilas, A. P. (1975). Selected topics in flow mechanics. In Production and Transport of Oil and Gas (p. 54). New York: Elsevier.

Thermal-FluidsCentral. (2010, July 9). Frictional pressure drop correlations based on the separated flow model. Retrieved March 1, 2017, from http://www.thermalfluidscentral.org/encyclopedia/index.php/Frictional_pressure_drop_correlations_based_on_the_separated_flow_model

Thome, J. R. (n.d.). 1: Two-Phase Flow Patterns and Flow Pattern Maps Chapter 12 (in Databook III) [Lecture Notes]. Retrieved February 14, 2017, from Two-Phase Flows and Heat Transfer: http://ltcm.epfl.ch/files/content/sites/ltcm/files/shared/import/migration/COURSES/TwoPhaseFlowsAndHeatTransfer/lectures/Chapter_12.pdf