Two Phase PipelinePart II
Ref.: Brill & Beggs, Two Phase Flow in Pipes, 6th Edition, 1991. Chapter 3.
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
1- Flow regimes boundaries: The flow regimes map is shown in Figure 3-10. The flow regimes boundaries are defined as a functions of the dimensionless quantities: Ngv, NLv, Nd, NL, L1, L2, Ls and Lm where:
- Ngv, NLv, Nd and NL are the same as Hagedorn & Brown method.
- Ls= 50 + 36 NLv and Lm= 75 + 84 NLv0.75
- L1 and L2 are functions of Nd as shown in Figure 3-11.
Bubble Flow Limits: 0 ≤ Ngv ≤ L1 + L2 NLv
Slug Flow Limits: L1 + L2 NLv ≤ Ngv ≤ Ls
Transition (Churn) Flow Limits: Ls < Ngv <Lm
Annular-Mist Flow Limits: Ngv > Lm
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
2- Pressure gradient due to elevation change: The procedure for calculating the pressure gradient due to elevation change in each flow regimes is:
- Calculate the dimensionless slip velocity (S) based on the appropriate correlation
- Calculate vs based on the definition of S:
- Calculate HL based on the definition of vs :
- Calculate the pressure gradient due to elevation change:
s
sLssmmsL
L
sL
L
sgs v
vvvvvvHHv
Hv
v2
4)(1
5.02
4 /)( LLs gSv
ggLLsscelevation
HHwheregg
ZP
dd
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
Correlations for calculating S in each flow regimes:Bubble Flow:
F1 , F2 , F3 and F4 can be obtained from Figure 3-12.
Slug Flow:
F5 , F6 and F7 can be obtained from Figure 3-14.
Mist Flow: Duns and Ros assumed that with the high gas flow rates in the mist flow region the slip velocity was zero (ρs= ρn).
dLv
gvLv N
FFFwhereN
NFNFFS 4
3'
3
2'
321 1
6'
627
'6
982.0
5 029.0)1(
)1( FNFwhereNF
FNFS d
Lv
gv
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
3- Pressure gradient due to friction:
Bubble Flow:
f1 is obtained from Moody diagram ( ), f2 is a correction
for the gas-liquid ratio, and is given in Figure 3-13, and f3 is an
additional correction factor for both liquid viscosity and gas-liquid
ratio, and can be calculated as:
Slug Flow: The same as bubble flow regime.
321 /2d
d ffffwheredg
vvfZP
tpc
msLLtp
friction
sL
sg
vv
ff50
1 13
L
sLL dvN
Re
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
Annular-Mist Flow: In this region, the friction term is based on the gas phase only. Thus:
As the wave height on the pipe walls increase, the actual area through which the gas can flow is decreased, since the diameter open to gas is d – ε.
After calculating the gas Reynolds number, , the two-
phase friction factor can be obtained from Moody diagram or rough
pipe equation:
2
22
,2d
dddvvddwhere
dgvf
ZP
sgsgc
sggtp
friction
g
sgg dvN
Re
05.0067.0)/27.0(log4
1473.1
210
dfor
ddftp
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
Duns and Ros noted that the wall roughness for mist flow is affected by the wall liquid film. Its value is greater than the pipe roughness and less than 0.5, and can be calculated as follows (or Figure 3-15):
Where
Duns and Ros suggested that the prediction of friction loss could be refined by using d – ε instead of d. In this case the determination of roughness is iterative.
dvNN
dNNfor
dvdNNfor
sgg
WeLWe
sgg
LWe
2
302.0
2
)(3713.0:005.0
0749.0:005.0
LL
L
L
sggwe N
vnumberWeberN
22
,)(
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
4- Pressure gradient due to acceleration:
Bubble Flow: The acceleration term is negligible.
Slug Flow: The acceleration term is negligible.
Mist Flow:
Pgvv
EWhereE
ZP
ZP
ZP
orZP
Pgvv
ZP
c
nsgmk
k
fele
total
totalc
nsgm
acc
1dd
dd
dd
dd
dd
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Duns & Ros)
Transition Flow: In the transition zone between slug and mist flow, Duns and Ros suggested linear interpolation between the flow regime boundaries, Ls and Lm , to obtain the pressure gradient, as follows:
Where
Increased accuracy was claimed if the gas density used in the mist
flow pressure gradient calculation was modified to :
MistSlugTransition ZPB
ZPA
ZP
dd
dd
dd
ALLLN
BLL
NLA
sm
sgv
sm
gvm
1,
m
gvgg L
N '
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)
Orkiszewski, after testing several correlations, selected the Griffith and Wallis method for bubble flow and the Duns and Ros method for annular-mist flow. For slug flow, he proposed a new correlation.
Bubble Flow
1- Limits: vsg / vm < LB
2- Liquid Holdup:
Where the vs have a constant value of 0.8 ft/sec.
13.0and/2218.0071.1Where 2 BmB LdvL
ssgsm
s
mL vvvv
vvH /4)/1(15.01 2
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)
3- Pressure gradient due to friction:
Where ftp is obtained from Moody diagram with liquid
Reynolds number: 4- Pressure gradient due to acceleration: is negligible in bubble
flow regimes.
Slug Flow
1- Limits: vsg / vm > LB and Ngv < Ls
Where Ls and Ngv are the same as Duns and Ros method.
dgvf
ZP
c
LLtp
friction 2dd 2
L
LL dvN
Re
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)2- Two-phase density:
The following procedure must be used for calculating vb:
1- Estimate a value for vb. A good guess is vb = 0.5 (g d)0.5
2- Based on the value of vb , calculate the
3- Calculate the new value of vb from the equations shown in the
next page, based on NReb and NReL where
4- Compare the values of vb obtained in steps one and three. If they
are not sufficiently close, use the values calculated in step three as
the next guess and go to step two.
Lbm
sggbsLLs vv
vvv
)(
L
bL dvNb
Re
L
mL dvNL
Re
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)
Use the following equations for calculation of vb:
30001074.8546.0 ReRe6
bLNfordgNvb
80001074.835.0 ReRe6
bLNfordgNvb
5.0
5.02 59.135.0
dvwhere
L
Lb
800030001074.8251.0 ReRe6
bLNfordgN
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)
The value of δ can be calculated from the following equations depending upon the continuous liquid phase and mixture velocity.Continuous
Liquid PhaseValue of vm Equation of δ
Water < 10
Water >10
Oil <10
Oil >10
)log(428.0)log(232.0681.0)log(013.038.1 dv
d mL
)log(888.0)log(162.0709.0)log(045.0799.0 dv
d mL
)log(113.0)log(167.0284.0)1log(0127.0415.1 dv
d mL
)log(63.0397.0)1log(01.0)log(
)log(569.0161.0)1log(0274.0
571.1
371.1
dd
vX
Xdd
Lm
L
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)
Data from literature indicate that a phase inversion from oil continuous to water continuous occurs at a water cut of approximately 75% in emulsion flow.
The value of δ is constrained by the following limits:
These constraints are supposed to eliminate pressure discontinuities between equations for δ since the equation pairs do not necessarily meet at vm=10 ft/sec.
L
s
bm
bm
mm
vvvvForb
vvFora
1:10)
065.0:10)
Two-Phase Flow CorrelationsVertical Upward Flow Pipeline (Orkiszewski)3- Pressure gradient due to friction:
Where ftp is obtained from Moody diagram with mixture
Reynolds number: 4- Pressure gradient due to acceleration: is negligible in slug
flow regime.
Transition (Churn) Flow Limits: Ls < Ngv <Lm
The same as Duns and Ros method.
Annular-Mist Flow Limits: Ngv > Lm
The same as Duns and Ros method.
bm
bsL
c
mLtp
friction vvvv
dgvf
ZP
2dd 2
L
mL dvN
Re
Two-Phase Flow CorrelationsBeggs and Brill
Beggs and Brill method can be used for vertical, horizontal and inclined two-phase flow pipelines.
1- Flow Regimes: The flow regime used in this method is a correlating parameter and gives no information about the actual flow regime unless the pipe is horizontal.The flow regime map is shown in Figure 3-16. The flow regimes boundaries are defined as a functions of the following variables:
738.64
4516.13
4684.242
302.01
2
5.0,10.0
10252.9,316,
LL
LLm
Fr
LL
LLgdvN
Two-Phase Flow CorrelationsBeggs and Brill
Segregated Limits:
Transition Limits:
Intermittent Limits:
Distributed Limits:
2
1
and 01.0or and 01.0
LNLN
FrL
FrL
32 and 01.0 LNL FrL
43
13
and 4.0or and 4.001.0
LNLLNL
FrL
FrL
4
1
and 4.0or and 4.0
LNLN
FrL
FrL
Two-Phase Flow CorrelationsBeggs and Brill
2- Liquid Holdup: In all flow regimes, except transition, liquid holdup can be calculated from the following equation:
Where HL(0) is the liquid holdup which would exist at the same conditions in a horizontal pipe. The values of parameters, a, b and c are shown for each flow regimes in this Table:
For transition flow regimes, calculate HL as follows:
LLcFr
bL
LLL HNaHHH )0()0()0()( :constraintwith ,
Flow Pattern a b c
Segregated 0.98 0.4846 0.0868
Intermittent 0.845 0.5351 0.0173
Distributed 1.065 0.5824 0.0609
ABLL
NLAHBHAH FrLLL
1,,23
3ent)(intermittd)(segregaten)(transitio
Two-Phase Flow CorrelationsBeggs and Brill
The holdup correcting factor (ψ), for the effect of pipe inclination is given by:
Where φ is the actual angle of the pipe from horizontal. For vertical upward flow, φ = 90o and ψ = 1 + 0.3 C. C is:
The values of parameters, d’, e, f and g are shown for each flow regimes in this Table:
)8.1(sin333.0)8.1sin(1 3 C
.0n that restrictio with ,ln)1( CNNdC gFr
fLv
eLL
Flow Pattern d' e f g
Segregated uphill 0.011 -3.768 3.539 -1.614
Intermittent uphill 2.96 0.305 -0.4473 0.0978
Distributed uphill No correction C = 0 , ψ = 1
All patterns downhill 4.70 -0.3692 0.1244 -0.5056
Two-Phase Flow CorrelationsBeggs and Brill
3- Pressure gradient due to friction factor:
fn is determined from the smooth pipe curve of the Moody
diagram, using the following Reynolds number:
The parameter S can be calculated as follows:
For and for others:
Sntp
c
mntp
f
effdg
vf
L
P
,
2d
d 2
42 )(ln01853.0)(ln8725.0ln182.30523.0
ln
yyy
yS
n
mn dvN
Re
)2.12.2ln(2.1/1 2)( ySHy LL
Two-Phase Flow CorrelationsBeggs and Brill
4- Pressure gradient due to acceleration: Although the
acceleration term is very small except for high velocity flow,
it should be included for increased accuracy.
sin,
1dd
dd
dd
dd
dd
scelec
ssgmk
k
fele
total
totalc
sgms
acc
gg
dLdP
Pgvv
EWhere
ELP
LP
LP
orLP
Pgvv
LP
Figure 3-10. Vertical two-phase flow regimes map (Duns & Ros).
F4
F4
F3
F2
F6
F5
Figure 3-16. Beggs and Brill, Horizontal flow regimes map.