# HEAT_TRANSFER

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HEAT TRANSFER, HEAT
EXCHANGERS,
CONDENSORS AND
REBOILERS, AIR
COOLERS
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                 2
 HEAT TRANSFER BY CONDUCTION                                  3
 The Heat Conduction Equation                                9
 HEAT TRANSFER BY CONVECTION                                 12
 Forced Convection                                          12
 Natural Convection                                         14
 HEAT TRANSFER BY RADIATION                                  15
 OVERALL HEAT TRANSFER COEFFICIENT                           18
 PROBLEMS                                                    22
 DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS                23
 SIZE NUMBERING AND 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 EXCHANGER                       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
 TUBE-SHEET DESIGN AS PER TEMA STANDARDS                     90
 DESIGN OF CYLINDRICAL SHELL, END CLOSURES AND FORCED HEAD   91
 REFERENCES                                                  95
HEAT TRANSFER LAW APPLIED TO   3

HEAT EXCHANGERS
Heat Transfer by Conduction   4

W/m2   W/m.K
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                                            10

Rate of heat       Rate of heat         Rate of heat         Rate of energy
conduction         generation           conduction
+                    =                    +   storage inside
into control       inside control       out of control       control volume
volume               volume
volume
11
The Heat Conduction Equation
Heat Transfer by Convection   12
13
Reynolds and Prandtl Numbers

Re < 2100        Laminar flow

Re > 2100        Turbulent flow

Values of Prandtl number for different liquids and gases
Flow through a single smooth cylinder                                              14

This correlation is valid over the ranges 10 < Rel < 107 and 0.6 < Pr < 1000 where
Flow over a Flat Plate     15

Re < 5000   Laminar flow

Re > 5000   Turbulent flow
Natural Convection   16

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
Emissivity coefficient for several selected material                      18
Emissivity Coefficient
Surface Material
-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
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
Overall heat transfer coefficient   19

For a wall

For cylindrical
geometry
Typical value for overall heat transfer coefficient                          20

Shell and Tube
Hot Fluid              Cold Fluid            U [W/m2C]
Heat Exchangers

Heat Exchangers    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
Coolers            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
Heat Exchangers Hot Fluid                       Cold Fluid              U [W/m2C]
21
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
Condensers      Aqueous vapors                  Water                   1000 - 1500
Organic vapors                  Water                   700 - 1000
Refinery hydrocarbons           Water                   400 - 550
Vapors   with    some     non
Water                   500 - 700
condensable
Vacuum condensers               Water                   200 - 500

Vaporizers      Steam                           Aqueous solutions       1000 - 1500
Steam                           Light organics          900 - 1200
Steam                           Heavy organics          600 - 900
Heat Transfer (hot) oil         Refinery hydrocarbons   250 - 550
DESIGN STANDARDS FOR                                        22

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.
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
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
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
12. Shell Node
13. Shell Cover Flange
14. Expansion Joint
15. Floating Tube sheet
19. Split Shear Ring
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
27

Removable kettle type reboiler with pull through floating head
Tube sizing: Birmingham Wire Gage                               28
(B.W.G.)   (B.W.G.)           (B.W.G.)   (B.W.G.)
Gauge                   (mm)      Gauge               (mm)
(inches)                      (inches)
00000 (5/0)     0.500     12.7       23       0.025      0.6
0000 (4/0)      0.454     11.5       24       0.022      0.6
000 (3/0)      0.425     10.8       25       0.020      0.5
00 (2/0)       0.380      9.7       26       0.018      0.5
0          0.340      8.6       27       0.016      0.4
1          0.300      7.6       28       0.014      0.4
2          0.284      7.2       29       0.013      0.3
3          0.259      6.6       30       0.012      0.3
4          0.238      6.0       31       0.010      0.3
5          0.220      5.6       32       0.009      0.2
6          0.203      5.2       33       0.008      0.2
7          0.180      4.6       34       0.007      0.2
8          0.165      4.2       35       0.005      0.1
9          0.148      3.8       36       0.004      0.1
10          0.134      3.4       25       0.020      0.5
11          0.120      3.0       26       0.018      0.5
12          0.109      2.8       27       0.016      0.4
13          0.095      2.4       28       0.014      0.4
14          0.083      2.1       29       0.013      0.3
15          0.072      1.8       30       0.012      0.3
16          0.065      1.7       31       0.010      0.3
17          0.058      1.5       32       0.009      0.2
18          0.049      1.2       33       0.008      0.2
19          0.042      1.1       34       0.007      0.2
20          0.035      0.9       35       0.005      0.1
21          0.032      0.8       36       0.004      0.1
22          0.028      0.7
Tube sizing: Birmingham Wire Gage   29
Tube-side design                                        30

Arrangement of tubes inside the heat exchanger
Shell-side design                                                        31

(a) one-pass shell for E-type,                          types of shell passes
(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.
Shell-side design                                                       32

Shell thickness for different diameters and material of constructions
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                   35

HEAT EXCHANGER DESIGN

Design of Single phase heat exchanger

Design of Condensers

Design of Reboiler and Vaporizers

Design of Air Coolers
Design of Single phase heat   36

exchanger
Typical values for fouling factor coefficients   37
38
Temperature profile for different types of
heat exchangers
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   62

For Laminar flow

For turbulent flow,
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   65

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
Design of air cooler   71
72
Mechanical Design for HE                                              73

A typical sequence of mechanical design procedures is summarized
by the flowing steps

• 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