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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                 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
 DESIGN LOADINGS                                             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
 Heat Transfer by Radiation                       17




  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
            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
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
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                                      40. Floating Head Support
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
                                                                             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                               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

• 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
Design loading   74
75
76
77

				
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