Page 321 - Mechanical Engineers' Handbook (Volume 4)

310 Heat Exchangers, Vaporizers, Condensers

Figure 15 Condensation profiles illustrated.

Heat-Transfer Coefficients, Pure Components
For condensers, it is particularly important to be able to estimate the two-phase flow regime
in order to predict the heat-transfer coefficient accurately. This is because completely dif-
ferent types of correlations are required for the two major flow regimes.

Shear-Controlled Flow. The vapor shear force on the condensate is much greater than the
gravity force. This condition can be expected, according to Ref. 18, when
J 1.5 (27)
g
where
J (Gy) 2 0.5

g (28)
gD ( )
j
l
v
v
For shear-controlled flow, the condensate film heat-transfer coefficient (h ) is a function of
cƒ
the convective heat-transfer coefficient for liquid flowing alone and the two-phase pressure
18
drop :
h cƒ h ( ) (29)
20.45
l
l
h h (1 y) 0.8 (30)
l
i
or
h h (1 y) 0.6 (31)
o
l
C 1
1 (32)
2
l
X X 2
tt tt
C 20 (tubeside flow),
X C 9 (shellside flow)
0.1
0.5
0.9

1 y
v
l
tt
y t v (33)
liquid viscosity, vapor viscosity
l
v