PPT: Heat Transfer in Boiling & Condensation | Heat Transfer - Mechanical Engineering PDF Download

 Page 2


Condensation and 
Boiling
?Until now, we have been considering 
convection heat transfer in homogeneous 
single-phase (HSP) systems
?Boiling and condensation, however, 
provide much higher heat transfer rates  
than those possible with the HSP systems
Page 3


Condensation and 
Boiling
?Until now, we have been considering 
convection heat transfer in homogeneous 
single-phase (HSP) systems
?Boiling and condensation, however, 
provide much higher heat transfer rates  
than those possible with the HSP systems
?
 
Condensation occurs when the temperature of a vapor is reduced 
below its saturation temperature
?
 
Condensation heat transfer
Film condensation
?
 
Heat transfer rates in drop wise condensation may be as much as 
10 times higher than in film condensation
Condensation
Drop wise condensation
Film
T
s 
<T
sat
Vapour
Drop
T
s 
<T
sat
Vapour
Page 4


Condensation and 
Boiling
?Until now, we have been considering 
convection heat transfer in homogeneous 
single-phase (HSP) systems
?Boiling and condensation, however, 
provide much higher heat transfer rates  
than those possible with the HSP systems
?
 
Condensation occurs when the temperature of a vapor is reduced 
below its saturation temperature
?
 
Condensation heat transfer
Film condensation
?
 
Heat transfer rates in drop wise condensation may be as much as 
10 times higher than in film condensation
Condensation
Drop wise condensation
Film
T
s 
<T
sat
Vapour
Drop
T
s 
<T
sat
Vapour
Laminar Film condensation on a 
vertical wall (VW)
Condensate Film
g
y
  ? y
x
T
sat
? (x)
A
T
?
y
x
A
A
y ?
y
y
u
l
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y y
y
u
l
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y gA )
v
l
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A
Page 5


Condensation and 
Boiling
?Until now, we have been considering 
convection heat transfer in homogeneous 
single-phase (HSP) systems
?Boiling and condensation, however, 
provide much higher heat transfer rates  
than those possible with the HSP systems
?
 
Condensation occurs when the temperature of a vapor is reduced 
below its saturation temperature
?
 
Condensation heat transfer
Film condensation
?
 
Heat transfer rates in drop wise condensation may be as much as 
10 times higher than in film condensation
Condensation
Drop wise condensation
Film
T
s 
<T
sat
Vapour
Drop
T
s 
<T
sat
Vapour
Laminar Film condensation on a 
vertical wall (VW)
Condensate Film
g
y
  ? y
x
T
sat
? (x)
A
T
?
y
x
A
A
y ?
y
y
u
l
?
?
?
?
?
?
?
y y
y
u
l
? ?
?
?
?
?
?
?
?
y gA )
v
l
( ? ? ? ?
A
Laminar Film condensation on a 
vertical wall (cont..)
4 / 1
l w sat
3
l v l fg
4 / 1
v l fg
l w sat l
) T T ( x 4
k ) ( g h
) x ( h
) ( g h
) T T ( xk 4
) x (
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fg
w sat L
fg
w sat L
4 / 1
l w sat
3
l v l fg
L
h
) T T ( A h
h
q
m               : rate on Condensati
) T T ( A h q        : rate fer heat trans Total
length. plate  the is L where
) T T ( L
k ) ( g h
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