Page 172 - Design and Operation of Heat Exchangers and their Networks

160 Design and operation of heat exchangers and their networks

8 1=2
> 0:772 0:0214j ∗ +0:228 + 0:0214j ∗ Þ ρ =ρ , 20 j ∗ < 0
ð
< g l
C 0 ¼ 1=2
ð
> 0:00848 20 + j∗Þ 1 ρ =ρ
: 1+0:2e g l , j ∗ < 20
(4.46)
∗
j ¼ j=V gj (4.47)
Based on this drift flux model, Lokanathan and Hibiki (2018) developed
the following flow regime transition criteria for vertical downward flow:

Bubble to cap bubble : a 0:055 (4.48)
Cap bubble to slug : a 0:175 (4.49)

Slug to churn turbulent : a 0:45 (4.50)
2
ρ V d 0:11
g
gj
Churn turbulent to falling film : ð 1 aÞ 2 (4.51)
σ πf gi a 1=2
2
ρ j d 1 aÞ
ð
g g
To annular drop : We cr ¼ 0:5 (4.52)
4σ
The interfacial friction factor f gi in Eq. (4.51) is expressed with
h i
f gi ¼ 0:005 1 + 150 1 a 1=2 (4.53)
4.1.2.3 Flow pattern regimes in horizontal flow
The flow patterns in horizontal tubes have been recognized as bubble
flow, slug flow, stratified flow, wavy flow, slug flow, annular flow, and
mist flow. Taitel and Dukler (1976) presented a generalized flow regime
map for determining five flow regimes in horizontal tubes: dispersed bub-
ble flow, intermittent flow (plug/slug flow), stratified flow, stratified wavy
flow, and annular flow. They introduced three dimensionless parameters
defined by

1=2
2 3
ð dp=dzÞ l
T ¼ 4 5 (4.54)
g ρ ρ cosθ
l g
2 3 1=2
ρ j 2
g g
F ¼ 4 5 (4.55)
g ρ ρ dcosθ
g
l