Heat Exchangers Performance criterion.pdf

Performace critetia of heat exchangers...
Heat exchangers
Performace of HE

1. Heat and Mass Transfer
Lect. 8: Heat Exchangers Performance
Dr. Muhammad Ali Kamran

2. •These handouts are in no way,
whatsoever, a replacement of the
lectures or the book.
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
2

3. Cold Water at 20°C (C
p=4180 J/kgK) and
5000kg/hr is to be heated by Oil supplied at
100°C and 7000kg/hr (C
p=2200 J/kgK). You
selectfromamanufacturer’scatalogashelland
tube heat exchanger (1 Shell, 2 Tube pass)
havingaUAvalueof11600W/K.Determinethe
wateroutlettemperature.
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
3

4. Important equations
q= ṁ
hc
p( T
hi-T
ho)
q= ṁ
cc
p( T
co-T
ci)
q= U A He
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
4

5. Min and Max Fluids
•In a heat Exchanger, the fluids are also
classifiedbasedontheirHEATCAPACITIES
•The fluid withLOWER HEAT CAPACITYis
termedastheMinimumFluid
•The fluid withHIGHER HEAT CAPACITYis
termedastheMaximumFluid
LOW
ERH
EOW
ARH
A
•Minimum Fluidundergoes the higher
temperaturechangeintheheatexchanger
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
5

6. Inlet (°C) Outlet (°C)
Hot Fluid 140 100
Cold Fluid 30 90
Identify Min and Max Fluids
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
6

7. Which Fluid Appears to be the Minimum Fluid
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
7

8. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
8

9. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
9

10. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
10

11. Effectiveness of Heat Exchanger
siiblehtbrbnnTfwTf
cleuCOfUbCefNECrnibE
RCFhLuLfWgnnhIObfUbCefNECrnibE
TfH
"
N
"#
mN
"%
TfH
&
'N
&%
mN
&#
)
!
)#*
=!
"
Max Possible heat transfer will occur in a
COUNTERFLOWheatexchangerofINFINITElength
ffN
"%
TN
&#
If Hot fluid is Min Fluid
For =
)+,

)+,
=
!
)#*
(
N
"#
−
N
&#
)
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
11

12. Which Fluid Appears to be the Minimum Fluid
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
12

13. Effectiveness of Heat Exchanger
!
)#*
=!
&
ffN
&%
TN
"#
If Cold fluid is Min Fluid
For =
)+,

)+,
=!
)#*
'N
"#
mN
&#
)
TfH
"
N
"#
mN
"%
TfH
&
'N
&%
mN
&#
)
Hence
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
13

14. Effectiveness of Heat Exchanger
wT


)+,
Tf
!
"'N
"#mN
"%)
!
)#*'N
"#mN
&#)
=
!
&'N
&%mN
&#)
!
)#*'N
"#mN
&#)
TfH
"
N
"#mN
"%TfH
&'N
&%mN
&#)
If Hot fluid is Min Fluid
wT


)+,
Tf
f'N
"#mN
"%)
'N
"#mN
&#)
If Cold fluid is Min Fluid
wT


)+,
Tf
f'N
&%mN
&#)
'N
"#mN
&#)
w
=
H-Cr.bfhrfNbL/bECeuEbfgifRhrhLuLf0Ouh1
RCFhLuL
fNbL/bECeuEb
f2hiibEbrlb
fhr
f-
fUbCe
fsFl-Cr.bE
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
14

15. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
15

16. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
16

17. Effectiveness
•In addition to the type of heat exchanger,
Effectiveness depends on the following
parameters
Ees
5OxO,
)#*,!
)+,
•ThesecanbegroupedintoNonDimensional
Numbers
7m5e:
67
8
9:;
No. of Transfer Units
!
<=
8
9:;
89=>:Heat Capacity Rate Ratio
E
=

(
7m5
,
!
<
,
oTgf
:MAr=g.4TD
:mF1T
)
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
17

18. Parallel Flow Heat Exchanger
P.
m
@
m
A
e b5x
B
!
)#*
C
B
!
)+,
P.
m
@
m
A
= −
5x
!
)#*
BC
!
)#*
!
)+,
P.
∆
m
@
∆
m
A
=
−
7m5
B
C
!
<
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
18

19. Or
∆
N
@
∆
N
A
=
−
5N3
B
C
!
<
xN
@
xN
A
T DEFf'm5N3'BCH
<
))
xN
@
T N
"%
mN
&%
xN
A
T N
"#
mN
&#
xN
@
xN
A
=
N
"%
mN
&%
N
"#
mN
&#
If Cold fluid is Min Fluid
w T


)+,
Tf
f'N
&%mN
&#)
(
N
"#
−
N
&#
)
Add and subtract T
ci
in the numerator
xN
@
xN
A
=
N
"%
mN
&%
CN
&#
mN
&#
N
"#
mN
&#
xN
@
xN
A
=
N
"%
mN
&#
m'N
&%
mN
&#
)
N
"#
mN
&#
= !
"
N
"#mN
"%TfH
&'N
&%mN
&#)
!
)+,
N
"#mN
"%TfH
)#*'N
&%mN
&#)
N
"#mN
"%TfH
<'N
&%mN
&#)
N
"%TfN
"#−!
<'N
&%mN
&#)
xN
@
xN
A
=
N
"#
−!
<
'N
&%
mN
&#
(mN
&#
m'N
&%
mN
&#
)
N
"#
mN
&#
xN
@
∆
N
A
=
'N
"#
mN
&#
)−(BC!
<
('N
&%
mN
&#
)
N
"
#
−
N
&
#
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
19

20. xN
@
xN
A
T DEFf'm5N3'BCH
<
))
w
=


)+,
=
f
f(
N
&%
−
N
&#
)
'N
"#mN
&#)
∆
N
@
xN
A
=
(
N
"#
−
N
&#
)
−
(
B
C
!
<
)
(
N
&%
−
N
&
#
)
N
"#
mN
&#
xN
@
xN
A
T Bmw'BCH
<
)
Bmw'BCH
<
( T DEFf'm5N3'BCH
<
))
w T
BmDEFf'm5N3'BCH
<
))
BC!
<
If Cold fluid is Min Fluid
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
20

21. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
21

22. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
22

23. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
23

24. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
24

25. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
25

26. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
26

27. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
27

28. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
28

29. Heat Capacity Ratio = 0
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
29

30. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
30

31. Cold Water at 20°C (C
p=4180 J/kgK) and
5000kg/hr is to be heated by Oil supplied at
100°C and 7000kg/hr (C
p=2200 J/kgK). You
selectfromamanufacturer’scatalogashelland
tube heat exchanger having a UA value of
11600W/K. Determine the water outlet
temperature.
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
31

32. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
32

33. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
33

34. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
34

35. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
35

36. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
36

37. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
37

38. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
38

39. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
39

40. Objectives of this Study
•To understand the design process of a heat
exchanger
•To introduce parameters for assessing the
performance of a heat exchanger under prescribed
conditions
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
40

41. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
41

42. hi= 7543 W/m
2
K
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
42

43. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
43

44. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
44

45. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
45

46. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
46

47. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
47

48. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
48

49. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
49

50. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
50

51. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
51

52. Constant heat flux
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
52

53. Constant Surface Temperature T
s
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
53

54. Concentric Tube Annulus
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
54

55. Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
55

56. Concentric Tube Annulus
Dr. Muhammad Ali Kamran, Deptt. of Mech
Engg., UET Peshawar
56