1
HEAT TRANSFER, HEAT
EXCHANGERS,
CONDENSORS AND
REBOILERS, AIR
COOLERS
Reyad Awwad Shawabkeh
Associate Professor of Chemical Engineering
King Fahd University of Petroleum & Minerals
Dhahran, 31261
Kingdom of Saudi Arabia
Contents
2
 HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS
 HEAT TRANSFER BY CONDUCTION
 The Heat Conduction Equation
 HEAT TRANSFER BY CONVECTION
 Forced Convection
 Natural Convection
 HEAT TRANSFER BY RADIATION
 OVERALL HEAT TRANSFER COEFFICIENT
 PROBLEMS
2
3
9
12
12
14
15
18
22
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23
23
27
32
33
33
35
37
37
45
49
57
65
72
85
88
88
90
91
95
DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS
SIZE NUMBERING AND NAMING
SIZING AND DIMENSION
TUBE-SIDE DESIGN
SHELL-SIDE DESIGN
 Baffle type and spacing
 GENERAL DESIGN CONSIDERATION
 THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN
 DESIGN OF SINGLE PHASE HEAT EXCHANGER
 Kern’s Method
 Bell’s method
 Pressure drop inside the shell and tube heat exchanger
 DESIGN OF CONDENSERS
 DESIGN OF REBOILER AND VAPORIZERS
 DESIGN OF AIR COOLERS9
 MECHANICAL DESIGN FOR HEAT EXCHANGERS10
 DESIGN LOADINGS
 TUBE-SHEET DESIGN AS PER TEMA STANDARDS
 DESIGN OF CYLINDRICAL SHELL, END CLOSURES AND FORCED HEAD
 REFERENCES
HEAT TRANSFER LAW APPLIED TO
HEAT EXCHANGERS
3
Heat Transfer by Conduction
W/m2
W/m.K
4
Thermal Conductivity of solids
5
Thermal Conductivity of liquids
6
Thermal conductivity of gases
7
Example
8
Calculate the heat flux within a copper rod that
heated in one of its ends to a temperature of 100 oC
while the other end is kept at 25 oC. The rode length
is 10 m and diameter is 1 cm.
Example
9
An industrial freezer is designed to operate with an internal air
temperature of -20 oC when external air temperature is 25 oC. The walls
of the freezer are composite construction, comprising of an inner layer of
plastic with thickness of 3 mm and has a thermal conductivity of 1 W/m.K.
The outer layer of the freezer is stainless steel with 1 mm thickness and
has a thermal conductivity of 16 W/m.K. An insulation layer is placed
between the inner and outer layer with a thermal conductivity of 15
W/m.K. what will be the thickness of this insulation material that allows a
heat transfer of 15 W/m2 to pass through the three layers, assuming the
area normal to heat flow is 1 m2?
The Heat Conduction Equation
Rate of heat
conduction
into control
volume
+
Rate of heat
generation
inside control
volume
=
Rate of heat
conduction
out of control
volume
+
10
Rate of energy
storage inside
control volume
The Heat Conduction Equation
11
Heat Transfer by Convection
12
Reynolds and Prandtl Numbers
Re < 2100
Laminar flow
Re > 2100
Turbulent flow
Values of Prandtl number for different liquids and gases
13
Flow through a single smooth cylinder
This correlation is valid over the ranges 10 < Rel < 107 and 0.6 < Pr < 1000 where
14
Flow over a Flat Plate
Re < 5000
Laminar flow
Re > 5000
Turbulent flow
15
Natural Convection
16
Heat Transfer by Radiation
q = ε σ (Th4 - Tc4) Ac
Th = hot body absolute temperature (K)
Tc = cold surroundings absolute temperature (K)
Ac = area of the object (m2)
σ = 5.6703 10-8 (W/m2K4)
The Stefan-Boltzmann Constant
17
Emissivity coefficient for several selected material
18
Surface Material
Emissivity Coefficient
-ε-
Aluminum Commercial sheet
0.09
Aluminum Foil
0.04
Aluminum Commercial Sheet
0.09
Brass Dull Plate
0.22
Brass Rolled Plate Natural Surface
0.06
Cadmium
0.02
Carbon, not oxidized
0.81
Carbon filament
0.77
Concrete, rough
0.94
Granite
0.45
Iron polished
0.14 - 0.38
Porcelain glazed
0.93
Quartz glass
0.93
Water
Zink Tarnished
0.95 - 0.963
0.25
Overall heat transfer coefficient
For a wall
For cylindrical
geometry
19
Typical value for overall heat transfer coefficient
Shell and Tube
Heat Exchangers
Heat Exchangers
Coolers
Cold Fluid
U [W/m2C]
Water
Water
800 - 1500
Organic solvents
Organic Solvents
100 - 300
Light oils
Light oils
100 - 400
Heavy oils
Heavy oils
50 - 300
Reduced crude
Flashed crude
35 - 150
Regenerated DEA
Foul DEA
450 - 650
Gases (p = atm)
Gases (p = atm)
5 - 35
Gases (p = 200 bar)
Gases (p = 200 bar)
100 - 300
Organic solvents
Water
250 - 750
Light oils
Water
350 - 700
Heavy oils
Water
60 - 300
Reduced crude
Water
75 - 200
Gases (p = 200 bar)
Water
150 - 400
Organic solvents
Brine
150 - 500
Water
Brine
600 - 1200
Gases
Brine
15 - 250
Hot Fluid
20
Heat Exchangers Hot Fluid
Cold Fluid
U [W/m2C]
Heaters
Steam
Water
1500 - 4000
Steam
Organic solvents
500 - 1000
Steam
Light oils
300 - 900
Steam
Heavy oils
60 - 450
Steam
Gases
30 - 300
Heat Transfer (hot) Oil
Heavy oils
50 - 300
Flue gases
Steam
30 - 100
Flue gases
Hydrocarbon vapors
30 -100
Aqueous vapors
Water
1000 - 1500
Organic vapors
Water
700 - 1000
Refinery hydrocarbons
Water
400 - 550
Water
500 - 700
Vacuum condensers
Water
200 - 500
Steam
Aqueous solutions
1000 - 1500
Steam
Light organics
900 - 1200
Steam
Heavy organics
600 - 900
Heat Transfer (hot) oil
Refinery hydrocarbons
250 - 550
Condensers
Vapors
with
some
condensable
Vaporizers
non
21
DESIGN STANDARDS FOR
TUBULAR HEAT EXCHANGERS
22
•
Size of heat exchanger is represented by the shell inside
diameter or bundle diameter and the tube length
•
Type and naming of the heat exchanger is designed by
three letters single pass shell
The first one describes the stationary head type
The second one refers to the shell type
The third letter shows the rear head type
TYPE AES refers to Split-ring floating head exchanger with removable
channel and cover.
Heat exchanger nomenclatures
23
The standard nomenclature for shell and tube heat exchanger
24
1. Stationary Head-Channel
20. Slip-on Backing Flange
30. Longitudinal Baffle
2. Stationary Head-Bonnet
21. Floating Head Cover-External
31. Pass Partition
3. Stationary Head Flange-Channel or 22. Floating Tube sheet Skirt
32. Vent Connection
Bonnet
23. Packing Box
33. Drain Connection
4. Channel Cover
24. Packing
34. Instrument Connection
5. Stationary Head Nozzle
25. Packing Gland
35. Support Saddle
6. Stationary Tube sheet
26. Lantern Ring
36. Lifting Lug
7. Tubes
27. Tie-rods and Spacers
37. Support Bracket
8. Shell
28. Support Plates
38. Weir
9. Shell Cover
29. Impingement Plate
39. Liquid Level Connection
10. Shell Flange-Stationary Head End
11. Shell Flange-Rear Head End
12. Shell Node
13. Shell Cover Flange
14. Expansion Joint
15. Floating Tube sheet
16. Floating Head Cover
17. Floating Head Cover Flange
18. Floating Head Backing Device
19. Split Shear Ring
40. Floating Head Support
25
Removable cover, one pass, and floating head heat exchanger
Removable cover, one pass, and outside packed floating head heat exchanger
26
Channel integral removable cover, one pass, and outside packed
floating head heat exchanger
27
Removable kettle type reboiler with pull through floating head
Tube sizing: Birmingham Wire Gage
Gauge
00000 (5/0)
0000 (4/0)
000 (3/0)
00 (2/0)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
(B.W.G.)
(inches)
0.500
0.454
0.425
0.380
0.340
0.300
0.284
0.259
0.238
0.220
0.203
0.180
0.165
0.148
0.134
0.120
0.109
0.095
0.083
0.072
0.065
0.058
0.049
0.042
0.035
0.032
0.028
(B.W.G.)
(mm)
12.7
11.5
10.8
9.7
8.6
7.6
7.2
6.6
6.0
5.6
5.2
4.6
4.2
3.8
3.4
3.0
2.8
2.4
2.1
1.8
1.7
1.5
1.2
1.1
0.9
0.8
0.7
Gauge
23
24
25
26
27
28
29
30
31
32
33
34
35
36
25
26
27
28
29
30
31
32
33
34
35
36
28
(B.W.G.)
(inches)
0.025
0.022
0.020
0.018
0.016
0.014
0.013
0.012
0.010
0.009
0.008
0.007
0.005
0.004
0.020
0.018
0.016
0.014
0.013
0.012
0.010
0.009
0.008
0.007
0.005
0.004
(B.W.G.)
(mm)
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.5
0.5
0.4
0.4
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
Tube sizing: Birmingham Wire Gage
29
Tube-side design
Arrangement of tubes inside the heat exchanger
30
Shell-side design
(a) one-pass shell for E-type,
(b) split flow of G-type,
(c) divided flow of J-type,
(d) two-pass shell with longitudinal baffle of F-type
(e) double split flow of H-type.
31
types of shell passes
Shell-side design
Shell thickness for different diameters and material of constructions
32
Baffle type and spacing
33
General design consideration
34
Factor
Tube-side
Shell-side
Corrosion
More corrosive fluid
Less corrosive fluids
Fouling
Fluids with high fouling Low fouling and scaling
and scaling
Fluid temperature
High temperature
Low temperature
Operating pressure
Fluids with low pressure Fluids with high pressure
drop
drop
Viscosity
Less viscous fluid
More viscous fluid
Stream flow rate
High flow rate
Low flow rate
THERMAL AND HYDRAULIC
HEAT EXCHANGER DESIGN
Design of Single phase heat exchanger
Design of Condensers
Design of Reboiler and Vaporizers
Design of Air Coolers
35
Design of Single phase heat
exchanger
36
Typical values for fouling factor coefficients
37
Temperature profile for different types of
heat exchangers
38
39
For counter current
For co-current
40
one shell pass; two or more even tube 'passes
41
two shell passes; four or multiples of four tube passes
divided-flow shell; two or more even-tube passes
42
split flow shell, 2 tube pass
cross flow heat exchanger
Shell-side heat transfer coefficient
43
44
Shell diameter
45
46
47
Bundle diameter clearance
Tube-side heat transfer coefficient
48
49
Tube-side heat transfer factor
Shell and Tube design procedure
50
• Kern’s Method
This method was based on experimental work on commercial exchangers
with standard tolerances and will give a reasonably satisfactory prediction
of the heat-transfer coefficient for standard designs.
• Bell’s method
This method is designed to predict the local heat transfer coefficient and
pressure drop by incorporating the effect of leak and by-passing inside the
shell and also can be used to investigate the effect of constructional
tolerance and the use of seal strip
Kern’s Method
51
Bell’s method
52
53
54
55
56
Figure 34 Baffle cut geometry
57
58
Pressure drop inside the shell
59
Pressure drop inside the tubes
60
Design of Condensers
•
•
•
•
•
61
For reactor off-gas quenching
Vacuum condenser
De-superheating
Humidification
Cooling towers
Direct contact cooler
Condensation outside horizontal tubes
For Laminar flow
For turbulent flow,
62
Condensation inside horizontal tubes
63
stratified flow
annular flow
Design of Reboiler and Vaporizers
64
• Suitable to carry viscous and heavy fluids.
• Pumping cost is high
Forced-circulation reboiler
• The most economical type where there is no need for
pumping of the fluid
• It is not suitable for viscous fluid or high vacuum
operation
• Need to have a hydrostatic head of the fluid
Thermosyphon reboiler
• It has the lower heat transfer coefficient than the other
types for not having liquid circulation
• Used for fouling materials and vacuum operation with a
rate of vaporization up to 80% of the feed
Kettle reboiler
Boiling heat transfer and pool boiling
Nucleate pool boiling
Critical heat flux
Film boiling
65
66
Nucleate
boiling heat
transfer
coefficient
67
Critical flux
heat transfer
coefficient
Film boiling
heat transfer
coefficient
Convection boiling
Effective heat transfer coefficient encounter the
effect of both convective and nucleate boiling
68
69
70
Design of air cooler
71
72
Mechanical Design for HE
A typical sequence of mechanical design procedures is summarized
by the flowing steps
• Identify applied loadings.
• Determine applicable codes and standards.
• Select materials of construction (except for tube material, which
is selected during the thermal design stage).
• Compute pressure part thickness and reinforcements.
• Select appropriate welding details.
• Establish that no thermohydraulic conditions are violated.
• Design nonpressure parts.
• Design supports.
• Select appropriate inspection procedure
73
Design loading
74
75
76
77