1. HEAT EXCHANGER DESIGN

2. Heat Transfer Equipment Types
Service
Double pipe exchanger
Heating and cooling
Shell and tube exchanger
All applications
Plate heat exchanger
Plate-fin exchanger
Spiral heat exchanger
Air cooled
Cooler and condensers
Direct contact
Cooling and quenching
Agitated vessel
Fired heaters
Heating

3. Double Pipe Heat Exchanger
Consists of two concentric pipes with one fluid flowing through the inner pipe while the other fluid flowing through the annular space

4. Shell and Tube Heat Exchanger
Consists of tube bundles enclosed in a cylindrical shell with one fluid flowing through the tubes and the other flowing outside of the tubes

5. Heat Transfer Equipment in Industries
Exchanger: heat exchanged between two process streams
Heaters and coolers: where one stream is plant service
Vaporiser: if a process stream is vaporised
Reboiler: a vaporiser associated with distillation column
Evaporator: if concentrating a solution
Fired exchanger: if heated by combustion gases
Unfired exchanger: not using combustion gases

6. Heat Transfer Equipment in Industries
MODES of HEAT TRANSFER
Conduction
Transfer of heat from one part of a body to another part of the same body or between two bodies in physical contact, without significant displacement of the particles of the two bodies
Convection
Transfer of heat from one point to another within a fluid or between a fluid and a solid or another fluid, by the movement or mixing of the fluids involved
Radiation
Transfer of heat by the absorption of radiant energy

7. BASIC THEORY
General equation for heat transfer across a surface for DPHE is:
Q =heat transferred per unit time, W
U=the overall heat transfer coefficient, W/m2oC
A= heat-transfer area, m2
Tm= the mean temperature difference,oC

8. BASIC THEORY
General equation for heat transfer across a surface for STHE is:
Q =heat transferred per unit time, W
U=the overall heat transfer coefficient, W/m2oC
A= heat-transfer area, m2
Tm= the mean temperature difference,oC
Y = geometric correction factor

9. Tube-Side Passes
One tube pass
Two tube pass
Three tube passes

10. Geometric Correction Factor
Also refer to Figure 11-4, Perry 7th Edition

12. Geometric Correction Factor
For design to be practical, Y ≥ 0.85

13. Logarithmic Mean Temperature Difference
If ΔT1 < ΔT2 and (ΔT2/ΔT1) ≤ 2, then ΔTlm is the arithmetic mean temp difference

14. Overall Heat Transfer Coefficient
Rearranging the General Equation in terms of driving force and total resistance:
Driving Force
Total Resistance

15. Overall Heat Transfer Coefficient
The overall coefficient is reciprocal of the overall resistance to heat transfer, which is the sum of several individual resistances. Individual resistance is the reciprocal of individual HTC.

16. Total Resistance the sum of several individual resistances
Individual resistance is the reciprocal of individual HTC.
Convection
Conduction
Convection
inside

17. Total Resistance
Conduction Heat Transfer is governed by Fourier’s Law!
k = thermal conductivity of the Solid (BTU/hr-ft2-(OF/ft))
A = Area perpendicular to the direction of heat transfer
x = distance of heat flow

18. Total Resistance
At Steady State:

19. Total Resistance
If k is constant:
Define R = Δx/kA
Thus, q= - ΔT/R

20. If k varies slightly with Temp:
Total Resistance
If k is not constant:
If k varies slightly with Temp:
**km is evaluated at the mean temperature

21. If A varies slightly with Thickness:
Total Resistance
If k is not constant:
If A varies slightly with Thickness:

22. q = hcA (T1 – T2) Total Resistance Convection Heat Transfer Where:
hc- convection heat transfer coefficient, Btu/hrft2°F
-similar to k/∆x
A – Heat transfer Area
T1 – temperature at surface 1
T2 – temperature at surface 2

23. q = (T1 – T2)/(1/hcA) Total Resistance
Convection Heat Transfer: Rearranging
q = (T1 – T2)/(1/hcA)
Where:
hc- convection heat transfer coefficient, Btu/hrft2°F
-similar to k/∆x
A – Heat transfer Area
T1 – temperature at surface 1
T2 – temperature at surface 2

24. Total Resistance
Convection
Conduction
Convection
inside

25. Total Resistance
inside

26. Typical Fouling Factor (Foust, 1980)

27. Heat Transfer Without Phase Change

28. Double Pipe Heat Exchanger

29. Invidual Heat Transfer Coefficient
HT w/o Phase Change: DPHE
For Long Tubes (L/D) > 50, Tube-side
Applicabilty:
Non-metallic fluid
0.5 < NPr < 100
NRE > 10,000

30. Invidual Heat Transfer Coefficient
HT w/o Phase Change: DPHE
For Long Tubes (L/D) > 50, Annular Space
Applicabilty:
Non-metallic fluid
0.5 < NPr < 100
NRE > 10,000

31. Invidual Heat Transfer Coefficient
HT w/o Phase Change: DPHE
For Short Tube (L/D < 50)

32. Invidual Heat Transfer Coefficient
HT w/o Phase Change: DPHE
Laminar Flow, Forced Convection

33. Shell and tube heat exchanger

34. Invidual Heat Transfer Coefficient
HT w/o Phase Change: STHE, ho

35. Invidual Heat Transfer Coefficient
HT w/o Phase Change: STHE, hi

36. Heat Transfer WITH Phase Change

37. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Vertical Surface
Assumptions:
Pure vapor is at its saturation temperature.
The condensate film flows in laminar regime and heat is transferred through the film by condensation.
The temperature gradient through the film is linear.
Temperature of the condensing surface is constant.
The physical properties of the condensate are constant and evaluated at a mean film temperature.
Negligible vapor shear exists at the interface

38. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Vertical Surface, Laminar

39. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Vertical Surface, Turbulent

40. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface
 If the amount of condensate is unknown
For Nre > 40, h is multiplied by 1.2

41. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface
 If the amount of condensate is known
For Nre > 40, h is multiplied by 1.2

42. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface, Banks of Tubes
For Nre > 40, h is multiplied by 1.2

43. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface, Banks of Tubes

44. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface, Banks of Tubes
 w/o splashing

45. Invidual Heat Transfer Coefficient
HT w/ Phase Change: STHE
Film-type Condensation on Horizontal Surface, Banks of Tubes
 w/ splashing

46. Invidual Heat Transfer Coefficient
Film Temperature
Condensate Properties are evaluated at the Film Temperature
Tf = ½(Tsv + Tw) by Kern, D.Q., Process HT
Tf = Tsv ΔT by McAdams, W.H., Heat Transmission, rd. Ed.
ΔT = Tsv - Tw

47. Invidual Heat Transfer Coefficient
Film Boiling on Submerged Horizontal Cylinder or Sphere

48. Invidual Heat Transfer Coefficient
Film Boiling on Submerged Horizontal Cylinder or Sphere

49. Invidual Heat Transfer Coefficient
Film Boiling on Submerged Horizontal Cylinder or Sphere
Nusselt-type Equation by Rohsenow:
Cr varies from to 0.015

50. Invidual Heat Transfer Coefficient
Film Boiling on Submerged Horizontal Cylinder or Sphere
Nusselt-type Equation by Forster and Zuber:

51. HE DESIGN SPECS

52. TOTAL HEAT TRANSFER AREA
A compromise between NT and L is chosen based on (L/Dshell) between 5 to 10

53. HE DESIGN SPECIFICATION
No. of Tubes in Conventional Tubesheet Layout

54. TOTAL HEAT TRANSFER AREA
With an appropriate pitch to diameter ratio and optimum pipe diameter chosen and the total HT area,

55. HE DESIGN SPECIFICATION
LAYOUT AND PITCH ARRANGEMENT

56. HE DESIGN SPECIFICATION
LAYOUT AND PITCH ARRANGEMENT

57. HE DESIGN SPECIFICATION
LAYOUT AND PITCH ARRANGEMENT
Optimum Pitch to Diameter Ratio: to 1.50
Suggested clearance: mm
Tube layout normally follows symmetrical arrangement having the largest number of tubes at the center

58. HE DESIGN SPECIFICATION
BAFFLES
Used to support tubes against sagging and vibrations
Direct the flow of fluid and control velocities
Types:
Segmental
Disk and Doughnut Type

59. HE DESIGN SPECIFICATION
BAFFLES
Segmental Baffles
Baffle Cut: 25 to 45% of disk diameter
Baffle Spacing: 20 to 100% of Shell Diameter

60. HE DESIGN SPECIFICATION
BAFFLES
Disk and Doughnut Baffles
Reduces pressure drop by 50-60%

61. HE DESIGN SPECIFICATION
BAFFLES

62. HE DESIGN SPECIFICATION
BAFFLES
Minimum unsupported tube span (in.) acc. to Perry = 74d0.75

63. HE DESIGN SPECIFICATION
BAFFLES THICKNESS: BENDING

64. HE DESIGN SPECIFICATION
BAFFLES THICKNESS: SHEARING

65. HE DESIGN SPECIFICATION
BAFFLES THICKNESS

66. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
Basic Equation for isothermal system
Tube friction losses only
jf = dimensionless friction factor
L’ = effective tube length
Di = inside tube diameter
ρ = density of fluid at bulk/film temperature
ut = velocity of fluid

67. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
For non-isothermal systems
Tube friction losses only

68. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
W/ pressure losses due to contraction, expansion and flow reversal
Suggestions for the Estimation of these Losses:
Kern (1950) suggests adding 4 velocity heads per pass
Frank (1978) considers this to be too high, and recommends 2.5 velocity heads
Butterworth (1978) suggests 1.8
Lord et al. (1970) take the loss per pass as equivalent to a length of tube equal to:
300 tube diameters for straight tubes
200 for U-tubes
Evans (1980) appears to add only 67 tube diameters per pass.

69. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
W/ pressure losses due to contraction, expansion and flow reversal
The loss in terms of velocity heads can be estimated by:
counting the number of flow contractions, expansions and reversals, and;
using the factors for pipe fittings to estimate the number of velocity heads lost

70. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
W/ pressure losses due to contraction, expansion and flow reversal
For two tube passes, there will be:
two contractions (0.5)
two expansions (1.0)
one flow reversal (1.5)

71. Pressure Drop Tube-Side Pressure Drop (Coulson and Richardson, 2005)
W/ pressure losses due to contraction, expansion and flow reversal

72. Pressure Drop
Shell-Side Pressure Drop (Coulson and Richardson, 2005)

73. Pressure Drop Shell-Side Pressure Drop (Coulson and Richardson, 2005)
Shell Equivalent Diameter (Hydraulic Diameter)
Square-Pitched Tube Arrangement, de in meter
Triangular-Pitched Tube Arrangement, de in meter

74. Pressure Drop Shell-Side Pressure Drop (Coulson and Richardson, 2005)
Shell-Side Friction Factor???

76. 1 ½ velocity heads for the inlet ½ for the outlet
Pressure Drop
Shell-Side Pressure Drop (Coulson and Richardson, 2005)
Shell-Side NOZZLE Pressure Drop
1 ½ velocity heads for the inlet
½ for the outlet

77. Pressure Drop
RULES OF THUMBS (Silla, 2003)

78. Pressure Drop
RULES OF THUMBS (Silla, 2003)

79. Pressure Drop
RULES OF THUMBS (Coulson and Richardson, 2005)

80. Pressure Drop RULES OF THUMBS (Couper, Penny, Fair & Wallas, 2010)
vacuum condensers be limited to 0.5–1.0 psi (25–50 Torr)
In liquid service, pressure drops of 5–10 psi are employed as a minimum, and up to 15% or
so of the upstream pressure

81. Heat Exchanger Temperature Limits
RULES OF THUMBS
At high temperature, water exerts corrosive action on steel and scaling is increased
To minimize scale formation, water temperature should not be more than 120ºF
To protect against fouling and corrosion, water temperature (outlet) should not be more than158F

82. Heat Exchanger Temperature Limits
RULES OF THUMBS
For the cooling water, on an open circulation systems, the temperature of the cooled water is 8-13ºF above the wet bulb temperature
When using cooling water to cool or condense a process stream, assume a water inlet temperature of 90oF (from a cooling tower) and a maximum water outlet temperature of 120oF

83. Heat Exchanger Temperature Limits
RULES OF THUMBS
the greatest temperature difference in an exchanger should be at least 36 degF, and;
the minimum temperature difference should be at least 10 degF