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HEAT TRANSFER, HEAT EXCHANGERS, CONDENSORS AND REBOILERS, AIR COOLERS Reyad Awwad Shawabkeh Associate Professor of Chemical Engineering King Fahd University.

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Presentation on theme: "HEAT TRANSFER, HEAT EXCHANGERS, CONDENSORS AND REBOILERS, AIR COOLERS Reyad Awwad Shawabkeh Associate Professor of Chemical Engineering King Fahd University."— Presentation transcript:

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, Kingdom of Saudi Arabia 1

2 Contents  HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS2 HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS2  H EAT T RANSFER BY C ONDUCTION 3 H EAT T RANSFER BY C ONDUCTION 3  The Heat Conduction Equation9 The Heat Conduction Equation9  H EAT T RANSFER BY C ONVECTION 12 H EAT T RANSFER BY C ONVECTION 12  Forced Convection12 Forced Convection12  Natural Convection14 Natural Convection14  H EAT T RANSFER BY R ADIATION 15 H EAT T RANSFER BY R ADIATION 15  O VERALL HEAT TRANSFER COEFFICIENT 18 O VERALL HEAT TRANSFER COEFFICIENT 18  PROBLEMS22 PROBLEMS22  DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS23 DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS23  S IZE NUMBERING AND NAMING 23 S IZE NUMBERING AND NAMING 23  S IZING AND DIMENSION 27 S IZING AND DIMENSION 27  T UBE - SIDE DESIGN 32 T UBE - SIDE DESIGN 32  S HELL - SIDE DESIGN 33 S HELL - SIDE DESIGN 33  Baffle type and spacing33 Baffle type and spacing33  G ENERAL DESIGN CONSIDERATION 35 G ENERAL DESIGN CONSIDERATION 35  THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN37 THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN37  D ESIGN OF S INGLE PHASE HEAT EXCHANGER 37 D ESIGN OF S INGLE PHASE HEAT EXCHANGER 37  Kern’s Method45 Kern’s Method45  Bell’s method49 Bell’s method49  Pressure drop inside the shell and tube heat exchanger57 Pressure drop inside the shell and tube heat exchanger57  D ESIGN OF C ONDENSERS 65 D ESIGN OF C ONDENSERS 65  D ESIGN OF R EBOILER AND V APORIZERS 72 D ESIGN OF R EBOILER AND V APORIZERS 72  D ESIGN OF A IR C OOLERS 9 85 D ESIGN OF A IR C OOLERS 9 85  MECHANICAL DESIGN FOR HEAT EXCHANGERS MECHANICAL DESIGN FOR HEAT EXCHANGERS  D ESIGN L OADINGS 88 D ESIGN L OADINGS 88  T UBE -S HEET D ESIGN AS P ER TEMA S TANDARDS 90 T UBE -S HEET D ESIGN AS P ER TEMA S TANDARDS 90  D ESIGN OF C YLINDRICAL SHELL, END CLOSURES AND FORCED HEAD 91 D ESIGN OF C YLINDRICAL SHELL, END CLOSURES AND FORCED HEAD 91  REFERENCES95 REFERENCES95 2

3 HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS 3

4 Heat Transfer by Conduction W/m 2 W/m.K 4

5 Thermal Conductivity of solids 5

6 Thermal Conductivity of liquids 6

7 Thermal conductivity of gases 7

8 Example Calculate the heat flux within a copper rod that heated in one of its ends to a temperature of 100 o C while the other end is kept at 25 o C. The rode length is 10 m and diameter is 1 cm. 8

9 Example An industrial freezer is designed to operate with an internal air temperature of -20 o C when external air temperature is 25 o C. 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 m 2 ? 9

10 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

11 The Heat Conduction Equation 11

12 Heat Transfer by Convection 12

13 Reynolds and Prandtl Numbers Values of Prandtl number for different liquids and gases Re < 2100 Laminar flow Re > 2100 Turbulent flow 13

14 Flow through a single smooth cylinder This correlation is valid over the ranges 10 < Re l < 10 7 and 0.6 < Pr < 1000 where 14

15 Flow over a Flat Plate Re < 5000 Laminar flow Re > 5000 Turbulent flow 15

16 Natural Convection 16

17 Heat Transfer by Radiation q = ε σ (T h 4 - T c 4 ) A c T h = hot body absolute temperature (K) T c = cold surroundings absolute temperature (K) A c = area of the object (m 2 ) σ = (W/m 2 K 4 ) The Stefan-Boltzmann Constant 17

18 Emissivity coefficient for several selected material Surface Material Emissivity Coefficient Emissivity Coefficient - ε - Aluminum Commercial sheet0.09 Aluminum Foil0.04 Aluminum Commercial Sheet0.09 Brass Dull Plate0.22 Brass Rolled Plate Natural Surface0.06 Cadmium0.02 Carbon, not oxidized0.81 Carbon filament0.77 Concrete, rough0.94 Granite0.45 Iron polished Porcelain glazed0.93 Quartz glass0.93 Water Zink Tarnished

19 Overall heat transfer coefficient For a wall For cylindrical geometry 19

20 Typical value for overall heat transfer coefficient Shell and Tube Heat Exchangers Hot FluidCold FluidU [W/m 2 C] Heat ExchangersWater Organic solvents Organic Solvents Light oils Heavy oils Reduced crudeFlashed crude Regenerated DEAFoul DEA Gases (p = atm) Gases (p = 200 bar) CoolersOrganic solventsWater Light oilsWater Heavy oilsWater Reduced crudeWater Gases (p = 200 bar)Water Organic solventsBrine WaterBrine GasesBrine

21 Heat ExchangersHot FluidCold FluidU [W/m 2 C] HeatersSteamWater SteamOrganic solvents SteamLight oils SteamHeavy oils SteamGases Heat Transfer (hot) OilHeavy oils Flue gasesSteam Flue gasesHydrocarbon vapors CondensersAqueous vaporsWater Organic vaporsWater Refinery hydrocarbonsWater Vapors with some non condensable Water Vacuum condensersWater VaporizersSteamAqueous solutions SteamLight organics SteamHeavy organics Heat Transfer (hot) oilRefinery hydrocarbons

22 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

23 Heat exchanger nomenclatures 23

24 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

25 Removable cover, one pass, and floating head heat exchanger Removable cover, one pass, and outside packed floating head heat exchanger 25

26 Channel integral removable cover, one pass, and outside packed floating head heat exchanger 26

27 Removable kettle type reboiler with pull through floating head 27

28 Gauge (B.W.G.) (inches) (B.W.G.) (mm) Gauge (B.W.G.) (inches) (B.W.G.) (mm) (5/0) (4/0) (3/0) (2/0) Tube sizing: Birmingham Wire Gage 28

29 29 Tube sizing: Birmingham Wire Gage

30 Tube-side design Arrangement of tubes inside the heat exchanger 30

31 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

32 Shell-side design Shell thickness for different diameters and material of constructions 32

33 Baffle type and spacing 33

34 General design consideration FactorTube-sideShell-side CorrosionMore corrosive fluidLess corrosive fluids Fouling Fluids with high fouling and scaling Low fouling and scaling Fluid temperatureHigh temperatureLow temperature Operating pressure Fluids with low pressure drop Fluids with high pressure drop ViscosityLess viscous fluidMore viscous fluid Stream flow rateHigh flow rateLow flow rate 34

35 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

36 Design of Single phase heat exchanger 36

37 Typical values for fouling factor coefficients 37

38 Temperature profile for different types of heat exchangers 38

39 For counter current For co-current 39

40 one shell pass; two or more even tube 'passes 40

41 two shell passes; four or multiples of four tube passes divided-flow shell; two or more even-tube passes 41

42 split flow shell, 2 tube pass cross flow heat exchanger 42

43 Shell-side heat transfer coefficient 43

44 44

45 Shell diameter 45

46 46

47 Bundle diameter clearance 47

48 Tube-side heat transfer coefficient 48

49 Tube-side heat transfer factor 49

50 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

51 Kern’s Method 51

52 Bell’s method 52

53 53

54 54

55 55

56 56 Figure 34 Baffle cut geometry

57 57

58 58

59 Pressure drop inside the shell 59

60 Pressure drop inside the tubes 60

61 61 Design of Condensers Direct contact cooler For reactor off-gas quenching Vacuum condenser De-superheating Humidification Cooling towers

62 62 Condensation outside horizontal tubes For turbulent flow, For Laminar flow

63 63 Condensation inside horizontal tubes stratified flow annular flow

64 64 Design 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

65 65 Boiling heat transfer and pool boiling Nucleate pool boiling Critical heat flux Film boiling

66 66 Nucleate boiling heat transfer coefficient

67 67 Critical flux heat transfer coefficient Film boiling heat transfer coefficient

68 Convection boiling 68 Effective heat transfer coefficient encounter the effect of both convective and nucleate boiling

69 69

70 70

71 71 Design of air cooler

72 72

73 73 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

74 74 Design loading

75 75

76 76

77 77


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