HEAT TRANSFER, HEAT
EXCHANGERS,
CONDENSORS AND
REBOILERS, AIR
COOLERS
ReyadAwwad Shawabkeh
Associate Professor of Chemical Engineering
King Fahd University of Petroleum & Minerals
Dhahran, 31261Kingdom of Saudi Arabia
1
Contents� HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS 2
� HEAT TRA NSFER BY CONDUCTION 3� The Heat Conduction Equation 9
� HEAT TRA NSFER BY CONVECTION 12� Forced Convection 12� Natural Convection 14
� HEAT TRA NSFER BY RADIATION 15� OVERALL HEAT TRA NSFER COEFFICIENT 18
� PROBLEMS 22
� DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS 23
� SIZE NUM BERI NG A ND NAMING 23� SIZING AND DIMENSION 27� TUBE-SIDE DESIGN 32� SHELL-SIDE DESIGN 33� Baffle type and spacing 33
� GENERAL DESIGN CONSIDERATION 35
� THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN 37
� DESIGN OF SINGLE PHASE HEAT EXCHA NGER 37� Kern’s Method 45� Bell’s method 49� Pressure drop inside the shell and tube heat exchanger 57
� DESIGN OF CONDENSERS 65� DESIGN OF REBOILER AND VAPORIZERS 72� DESIGN OF AIR COOLERS9 85
� MECHANICAL DESIGN FOR HEAT EXCHANGERS10 88
� DESIGN LOADINGS 88� TUBE-SHEET DESIGN AS PER TEMA STA NDA RDS 90� DESIGN OF CYLINDRICA L SHELL, END CLOSURES AND FORCED HEA D 91
� REFERENCES 95
2
HEAT TRANSFER LAW APPLIED TO
HEAT EXCHANGERS3
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
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.
8
Example
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?
9
The Heat Conduction Equation
Rate of heat
generation
inside control
volume
Rate of energy
storage inside
control volume
Rate of heat conduction
into control volume
+ =
Rate of heat
conduction
out of control
volume
+
10
The Heat Conduction Equation11
Heat Transfer by Convection 12
Reynolds and Prandtl Numbers
Values of Prandtl number for different liquids and gases
Re < 2100 Laminar flow
Re > 2100 Turbulent flow
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 Convection16
Heat Transfer by Radiation
q = ε σ (Th4 - Tc
4) 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
Surface MaterialEmissivity 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 0.95 - 0.963
Zink Tarnished 0.25
18
Overall heat transfer coefficient
For a wall
For cylindrical
geometry
19
Typical value for overall heat transfer coefficient
Shell and Tube
Heat ExchangersHot Fluid Cold Fluid U [W/m2C]
Heat Exchangers Water Water 800 - 1500
Organic solvents Organic Solvents 100 - 300
Lightoils Lightoils 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
Coolers Organic solvents Water 250 - 750
Lightoils 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
20
Heat Exchangers Hot Fluid Cold Fluid U [W/m2C]
Heaters Steam Water 1500 - 4000
Steam Organic solvents 500 - 1000
Steam Lightoils 300 - 900
Steam Heavy oils 60 - 450
Steam Gases 30 - 300
HeatTransfer (hot) Oil Heavy oils 50 - 300
Flue gases Steam 30 - 100
Flue gases Hydrocarbon vapors 30 -100
Condensers Aqueous vapors Water 1000 - 1500
Organic vapors Water 700 - 1000
Refinery hydrocarbons Water 400 - 550
Vapors with some non
condensableWater 500 - 700
Vacuum condensers Water 200 - 500
Vaporizers Steam Aqueous solutions 1000 - 1500
Steam Lightorganics 900 - 1200
Steam Heavy organics 600 - 900
HeatTransfer (hot) oil Refinery hydrocarbons 250 - 550
21
DESIGN STANDARDS FOR
TUBULAR HEAT EXCHANGERS
• 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.
22
Heat exchanger nomenclatures23
The standard nomenclature for shell and tube heat exchanger
1. Stationary Head-Channel
2. Stationary Head-Bonnet
3. Stationary Head Flange-Channel or
Bonnet
4. Channel Cover
5. Stationary Head Nozzle
6. Stationary Tube sheet
7. Tubes
8. Shell
9. Shell Cover
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
20. Slip-on Backing Flange
21. Floating Head Cover-External
22. Floating Tube sheet Skirt
23. Packing Box
24. Packing
25. Packing Gland
26. Lantern Ring
27. Tie-rods and Spacers
28. Support Plates
29. Impingement Plate
30. Longitudinal Baffle
31. Pass Partition
32. Vent Connection
33. Drain Connection
34. Instrument Connection
35. Support Saddle
36. Lifting Lug
37. Support Bracket
38. Weir
39. Liquid Level Connection
40. Floating Head Support
24
Removable cover, one pass, and floating head heat exchanger
Removable cover, one pass, and outside packed floating head heat exchanger
25
Channel integral removable cover, one pass, and outside packed
floating head heat exchanger
26
Removable kettle type reboiler with pull through floating head
27
Gauge(B.W.G.)(inches)
(B.W.G.)(mm) Gauge
(B.W.G.)(inches)
(B.W.G.)(mm)
00000 (5/0) 0.500 12.7 23 0.025 0.6
0000 (4/0) 0.454 11.5 24 0.022 0.6000 (3/0) 0.425 10.8 25 0.020 0.500 (2/0) 0.380 9.7 26 0.018 0.5
0 0.340 8.6 27 0.016 0.41 0.300 7.6 28 0.014 0.42 0.284 7.2 29 0.013 0.33 0.259 6.6 30 0.012 0.34 0.238 6.0 31 0.010 0.35 0.220 5.6 32 0.009 0.26 0.203 5.2 33 0.008 0.27 0.180 4.6 34 0.007 0.2
8 0.165 4.2 35 0.005 0.19 0.148 3.8 36 0.004 0.1
10 0.134 3.4 25 0.020 0.511 0.120 3.0 26 0.018 0.5
12 0.109 2.8 27 0.016 0.413 0.095 2.4 28 0.014 0.4
14 0.083 2.1 29 0.013 0.315 0.072 1.8 30 0.012 0.316 0.065 1.7 31 0.010 0.317 0.058 1.5 32 0.009 0.218 0.049 1.2 33 0.008 0.219 0.042 1.1 34 0.007 0.220 0.035 0.9 35 0.005 0.121 0.032 0.8 36 0.004 0.122 0.028 0.7
Tube sizing: Birmingham Wire Gage28
29Tube sizing: Birmingham Wire Gage
Tube-side design
Arrangement of tubes inside the heat exchanger
30
Shell-side design
types of shell passes(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
Shell-side design
Shell thickness for different diameters and material of constructions
32
Baffle type and spacing33
General design consideration
Factor Tube-side Shell-side
Corrosion More corrosive fluid Less corrosive fluids
Fouling Fluids with high fouling
and scaling
Low fouling and scaling
Fluid temperature High temperature Low temperature
Operating pressure Fluids with low pressure
drop
Fluids with high pressure
drop
Viscosity Less viscous fluid More viscous fluid
Stream flow rate High flow rate Low flow rate
34
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 coefficients37
Temperature profile for different types of
heat exchangers
38
For counter current
For co-current
39
one shell pass; two or more even tube 'passes
40
two shell passes; four or multiples of four tube passes
divided-flow shell; two or more even-tube passes
41
split flow shell, 2 tube pass
cross flow heat exchanger
42
Shell-side heat transfer coefficient 43
44
Shell diameter 45
46
Bundle diameter clearance
47
Tube-side heat transfer coefficient 48
Tube-side heat transfer factor
49
Shell and Tube design procedure
• Kern’s Method
• 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
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.
50
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
61Design of Condensers
Direct contact cooler
• For reactor off-gas quenching
• Vacuum condenser
• De-superheating
• Humidification
• Cooling towers
62Condensation outside horizontal tubes
For turbulent flow,
For Laminar flow
63Condensation inside horizontal tubes
stratified flow
annular flow
64Design of Reboiler and Vaporizers
Forced-circulation reboiler
Thermosyphon reboiler
Kettle reboiler
• Suitable to carry viscous and heavy fluids. • Pumping cost is high
• 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
• 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
65Boiling heat transfer and pool boiling
Nucleate pool boiling
Critical heat flux
Film boiling
66
Nucleate
boiling heat
transfer
coefficient
67
Critical flux
heat transfer
coefficient
Film boiling
heat transfer
coefficient
Convection boiling 68
Effective heat transfer coefficient encounter the
effect of both convective and nucleate boiling
69
70
71Design of air cooler
72
73Mechanical 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
74Design loading
75
76
77