1. Heat exchanger design KERN METHOD
By: Dr. M.R.Shahnazari
K.N.Toosi university of technology
Heat exchanger design KERN METHOD
HEAT EXCANGER DESIGN
Lecturer: Dr M.R. Shahnazari
K.N.Toosi university of Technology

2. By: Dr. M.R.Shahnazari

3. By: Dr. M.R.Shahnazari
DOUBLE PIPE HE

4. By: Dr. M.R.Shahnazari
DP EXAMPLE Solution

5. By: Dr. M.R.Shahnazari
DP EXAMPLE…..Solution

6. By: Dr. M.R.Shahnazari
DP EXAMPLE…..Solution

7. By: Dr. M.R.Shahnazari
DP EXAMPLE…..Solution

8. By: Dr. M.R.Shahnazari
SHELL AND TUBE
Kern method

9. Classification of heat exchangers depending on the applications
Recuperative
Regenerative
Rotary regenerator
Fixed-matrix
regenerator
Indirect
contact-type
Direct
Disk type
Drum type
Tubular
Plate
Extended surface
Double pipe
Spiral tube
Shell & tube
Finned tube
Finned plate
Gasketed plate
Spiral plate
Lamella
Removable bundle
Floating head
Fixed tubesheet
U-tube
Heat
Exchanger
Heat exchanger may have singe or two phase flow on each side
Flow
Parallel
Counter
Cross

10. LMTD CORRECTION FACTOR
By: Dr. M.R.Shahnazari
LMTD CORRECTION FACTOR

11. SAMPLE CORRECTION FACTOR
By: Dr. M.R.Shahnazari
SAMPLE CORRECTION FACTOR
one shell pass; two or more even

12. TUBE SIZE: : Birmingham Wire Gage
By: Dr. M.R.Shahnazari
TUBE SIZE: : Birmingham Wire Gage

13. By: Dr. M.R.Shahnazari
TUBE PATTERN

14. By: Dr. M.R.Shahnazari
TUBE PITCH

15. Why a Shell and Tube Heat Exchanger?
By: Dr. M.R.Shahnazari
Why a Shell and Tube Heat Exchanger?
Shell and tube heat exchangers are the most widespread and commonly used basic heat exchanger configuration in the process industries.
The reasons for this general acceptance are several.
The shell and tube heat exchanger provides a comparatively large ratio of heat transfer area to volume and weight.
It provides this surface in a form which is relatively easy to construct in a wide range of sizes.

16. By: Dr. M.R.Shahnazari
Better Concurrence….
It is mechanically rugged enough to withstand normal shop fabrication stresses, shipping and field erection stresses, and normal operating conditions.
The shell and tube exchanger can be reasonably easily cleaned, and those components most subject to failure - gaskets and tubes – can be easily replaced.
Shop facilities for the successful design and construction of shell and tube exchangers are available throughout the world.

17. Simple Shell & Tube Heat Exchanger
By: Dr. M.R.Shahnazari
Simple Shell & Tube Heat Exchanger

18. By: Dr. M.R.Shahnazari
Inner Details of S&T HX

19. Components of STHEs
By: Dr. M.R.Shahnazari
It is essential for the designer to have a good working knowledge of the mechanical features of STHEs and how they influence thermal design.
The principal components of an STHE are:
shell; shell cover;
tubes; tubesheet;
baffles; and nozzles.
Other components include tie-rods and spacers, pass partition plates, impingement plate, longitudinal baffle, sealing strips, supports, and foundation.

20. Types of Shells
By: Dr. M.R.Shahnazari

21. By: Dr. M.R.Shahnazari
Fixed tube sheet

22. By: Dr. M.R.Shahnazari
U-Tube STHE

23. Floating Head STHE TEMA S
By: Dr. M.R.Shahnazari
Floating Head STHE TEMA S

24. Floating Head STHE TEMA T
By: Dr. M.R.Shahnazari
Floating Head STHE TEMA T

25. Cross Baffles Baffles serve two purposes:
By: Dr. M.R.Shahnazari
Baffles serve two purposes:
Divert (direct) the flow across the bundle to obtain a higher heat transfer coefficient.
Support the tubes for structural rigidity, preventing tube vibration and sagging.
When the tube bundle employs baffles,
the heat transfer coefficient is higher than the coefficient for undisturbed flow around tubes without baffles.
For a baffled heat exchanger the higher heat transfer coefficients result from the increased turbulence.
the velocity of fluid fluctuates because of the constricted area between adjacent tubes across the bundle.

26. Types of Baffle Plates : Segmental Cut Baffles
By: Dr. M.R.Shahnazari
Types of Baffle Plates : Segmental Cut Baffles
The single and double segmental baffles are most frequently used.
They divert the flow most effectively across the tubes.
The baffle spacing must be chosen with care.
Optimal baffle spacing is somewhere between 40% - 60% of the shell diameter.
Baffle cut of 25%-35% is usually recommended.

27. Types of Baffle Plates Double Segmental Baffles
By: Dr. M.R.Shahnazari
Double Segmental Baffles
Triple Segmental Baffles
The triple segmental baffles are used for low pressure applications.

28. By: Dr. M.R.Shahnazari
Types of Baffle Plates

29. Types of Baffle Plates
By: Dr. M.R.Shahnazari
Disc and ring baffles are composed of alternating outer rings and inner discs, which direct the flow radially across the tube field.
§ The potential bundle-to-shell bypass stream is eliminated
§ This baffle type is very effective in pressure drop to heat transfer conversion

30. Therm-Hydraulic Analysis of Heat Exchanger
By: Dr. M.R.Shahnazari
Therm-Hydraulic Analysis of Heat Exchanger
Initial Decisions.
Tube side Thermal Analysis.
Thermal analysis for Shell side.
Overall Heat Transfer coefficient.
Hydraulic Analysis of Tube side.
Hydraulic Analysis of Shell side.

31. Fluid Allocation : Tube Side
By: Dr. M.R.Shahnazari
Tube side is preferred under these circumstances:
The higher velocities will reduce buildup
Mechanical cleaning is also much more practical for tubes than for shells.
Corrosive fluids are usually best in tubes
Tubes are cheaper to fabricate from exotic materials
This is also true for very high temperature fluids requiring alloy construction
Toxic fluids to increase containment
Streams with low flow rates to obtain increased velocities and turbulence
High pressure streams since tubes are less expensive to build strong.
Streams with a low allowable pressure drop

32. Fluid Allocation : Shell Side
By: Dr. M.R.Shahnazari
Fluid Allocation : Shell Side
Shell side is preferred under these circumstances:
Viscous fluids go on the shell side, since this will usually improve the rate of heat transfer.
On the other hand, placing them on the tube side will usually lead to lower pressure drops. Judgment is needed.
Low heat transfer coefficient:
Stream which has an inherently low heat transfer coefficient (such as low pressure gases or viscous liquids), this stream is preferentially put on the shell-side so that extended surface may be used to reduce the total cost of the heat exchanger.

33. General design consideration
By: Dr. M.R.Shahnazari
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. Flow Past Tube Bundles : Outside Film Coefficient
By: Dr. M.R.Shahnazari
Flow Past Tube Bundles : Outside Film Coefficient

35. Major Steps in Design Initial Decisions. Tube side Thermal Analysis.
By: Dr. M.R.Shahnazari
Major Steps in Design
Initial Decisions.
Tube side Thermal Analysis.
Thermal analysis for Shell side flow.
Overall Heat Transfer coefficient.
Hydraulic Analysis of Tube side.
Hydraulic Analysis of Shell side.

36. Initial Decisions Spatial allocation of fluid.
By: Dr. M.R.Shahnazari
Initial Decisions
Spatial allocation of fluid.
Determination of flow velocity.
Initial guess for number of tubes.
Correction for standard tube diameter.
Effect of number of tubes on tube length….

37. By: Dr. M.R.Shahnazari
Avoid Developed Flow

38. Thermal Analysis of Heat Exchanger
By: Dr. M.R.Shahnazari
Thermal Analysis of Heat Exchanger
Known as heat exchanger specification problems and their solutions.
These are ‘rating’, ‘design’, and ‘selection’.

39. By: Dr. M.R.Shahnazari
Rating Analysis
The rating problem is evaluating the thermo-hydraulic performance of a fully specified exchanger.
The rating program determines:
the heat transfer rate and the fluid outlet temperatures for prescribed fluid flow rates, inlet temperatures, and
the pressure drop for an existing heat exchanger;
therefore the heat transfer surface area and the flow passage dimensions are available.

40. By: Dr. M.R.Shahnazari
The Rating Analysis

41. The Design (Sizing) Analysis
By: Dr. M.R.Shahnazari
‘Design’ is the process of determining all essential constructional dimensions of an exchanger that must perform a given heat duty and respect limitations on shell-side and tube-side pressure drop.
In the Design (sizing) Analysis,
An appropriate heat exchanger type is selected.
The size to meet the specified hot and cold fluid inlet and outlet temperatures, flow rates, and pressure drop requirements, is determined.
Constraints:
Minimum or maximum flow velocities,
Size and/or weight limitations,
Ease of cleaning and maintenance, erosion, tube vibration, and thermal expansion.
Each design problem has a number of potential solutions, but only one will have the best combination of characteristics and cost.

42. Basic Design Procedure
By: Dr. M.R.Shahnazari
Basic Design Procedure
K.N.Toosi university of Technology

43. Basic Design Procedure
By: Dr. M.R.Shahnazari
Basic Design Procedure
Heat exchanger must satisfy the Heat transfer requirements (design or process needs)
Allowable pressure drop (pumping capacity and cost)
Steps in designing a heat exchanger can be listed as:
Identify the problem
Select an heat exchanger type
Calculate/Select initial design
parameters
Rate the initial design
Calculate thermal performance and pressure drops for shell and tube side.
Evaluate the design.
Is performance and cost acceptable?

44. The Selection Analysis
By: Dr. M.R.Shahnazari
The Selection Analysis
‘Selection’ means choosing a heat exchanger from among a number of units already existing.
Typically, these are standard units listed in catalogs of various manufacturers.
Sufficient manufacturer’s data usually exist to allow one to select comfortably oversized exchanger with respect to both area and pressure drop.

45. Thermal Analysis for Shell-Side
By: Dr. M.R.Shahnazari
Thermal Analysis for Shell-Side
Conventional Methods are based on Non-dimensional Analysis…
Convection Heat Transfer demands Definition of
Nusselt Number – Output
Reynolds Number – Input
Prandtl Number -- Input

46. Shell Side Fluid Flow
By: Dr. M.R.Shahnazari

47. Shell-Side Reynolds Number
By: Dr. M.R.Shahnazari
Shell-Side Reynolds Number
Reynolds number for the shell-side is defined based on the equivalent diameter and the velocity based on a reference flow:

48. Simplified Classification of Shell Side Flow
By: Dr. M.R.Shahnazari

49. Fluid dynamic Similarity of Counter & Cross Flow Heat Transfer ?!?!?!
By: Dr. M.R.Shahnazari

50. Tube Layout & Flow Structure
By: Dr. M.R.Shahnazari
A Real Use of Wetted Perimeter !

51. Tube Layout
By: Dr. M.R.Shahnazari
Tube layout is characterized by the included angle between tubes.
Two standard types of tube layouts are the square and the equilateral triangle.
Triangular pitch (30o layout) is better for heat transfer and surface area per unit length (greatest tube density.)
Square pitch (45 & 90 layouts) is needed for mechanical cleaning.
Note that the 30°,45° and 60° are staggered, and 90° is in line.
For the identical tube pitch and flow rates, the tube layouts in decreasing order of shell-side heat transfer coefficient and pressure drop are: 30°,45°,60°, 90°.
The 90° layout will have the lowest heat transfer coefficient and the lowest pressure drop.

52. In that case, a minimum cleaning lane of ¼ in. (6.35 mm) is provided.
By: Dr. M.R.Shahnazari
The square pitch (90° or 45°) is used when jet or mechanical cleaning is necessary on the shell side.
In that case, a minimum cleaning lane of ¼ in. (6.35 mm) is provided.
The square pitch is generally not used in the fixed header sheet design because cleaning is not feasible.
The triangular pitch provides a more compact arrangement, usually resulting in smaller shell, and the strongest header sheet for a specified shell-side flow area.
It is preferred when the operating pressure difference between the two fluids is large.

53. Tube Pitch The selection of tube pitch is a compromise between a
By: Dr. M.R.Shahnazari
Tube Pitch
The selection of tube pitch is a compromise between a
Close pitch (small values of PT/do) for increased shell-side heat transfer and surface compactness, and an
Open pitch (large values of PT/ do) for decreased shell-side plugging and ease in shell-side cleaning.
Tube pitch Pt is chosen so that the pitch ratio is 1.25 < PT/do < 1.5.
When the tubes are to close to each other (PT/do less than 1.25), the header plate (tube sheet) becomes to weak for proper rolling of the tubes and cause leaky joints.
Tube layout and tube locations are standardized for industrial heat exchangers.
However, these are general rules of thumb and can be “violated” for custom heat exchanger designs.

54. Identification of (Pseudo) Velocity Scale
By: Dr. M.R.Shahnazari
Identification of (Pseudo) Velocity Scale

55. Shell Side Pseudo Flow Area
By: Dr. M.R.Shahnazari
The number of tubes at the centerline of the shell is calculated by
where is Asthe bundle cross flow area, Dsis the inner diameter of the shell, C is the clearance between adjacent tubes, and B is the baffle spacing

56. Pseudo Shell side Mass Velocity
By: Dr. M.R.Shahnazari
Pseudo Shell side Mass Velocity
The shell-side mass velocity is found with

57. Selection of Shell Diameter
By: Dr. M.R.Shahnazari

58. By: Dr. M.R.Shahnazari
Shell Diameter
The number of tubes is calculated by taking the shell circle and dividing it by the projected area of the tube layout. That is
where Apro-tube is the projected area of the tube layout expressed as area corresponding to one tube, Ds is the shell inside diameter, and
CTP is the tube count calculation constant that accounts for the incomplete coverage of the shell diameter by the tubes, due to necessary clearances between the shell and the outer tube circle and tube omissions due to tube pass lanes for multitude pass design.

59. Projected area of Tube Layout
By: Dr. M.R.Shahnazari
Projected area of Tube Layout
Where PT is the tube pitch and CL is the tube layout constant.

60. Coverage of Shell Area
By: Dr. M.R.Shahnazari

61. The CTP values for different tube passes are given below:
By: Dr. M.R.Shahnazari
The CTP values for different tube passes are given below:

62. Pseudo Shell side Mass Velocity
By: Dr. M.R.Shahnazari
Pseudo Shell side Mass Velocity
The shell-side mass velocity is found with

63. Shell side Equivalent (Hydraulic) Diameter
By: Dr. M.R.Shahnazari
Shell side Equivalent (Hydraulic) Diameter
Equivalent diameter employed by Kern for correlating shell side heat transfer/flow is not a true equivalent diameter.
The direction of shell side flow is partly along the tube length and partly at right angles to tube length or heat exchanger axis.
The flow area at right angles is harmonically varying.
This cannot be distinguished based on tube layout.
Kern’s experimental study showed that flow area along the axis showed excellent correlation wrt
Tube layout, tube pitch etc….

64. Equivalent Counter Flow : Hydraulic or Equivalent Diameter
By: Dr. M.R.Shahnazari
Equivalent Counter Flow : Hydraulic or Equivalent Diameter
The equivalent diameter is calculated along (instead of across) the long axes of the shell and therefore is taken as four times the net flow area as layout on the tube sheet (for any pitch layout) divided by the wetted perimeter.

65. Process (thermal) design procedure of Heat Exchanger
[Kern method ]

68. If the tube-side pressure drop exceeds the allowable pressure drop for the process system, decrease the number of tube passes or increase number of tubes per pass. Go back to step #6 and repeat the calculations steps.
If the shell-side pressure drop exceeds the allowable pressure drop, go back to step #7 and repeat the calculations steps.
Step #15. Upon fulfillment of pressure drop criteria, go mechanical design.

69. Selection of Fluids for Tube and Shell Side
Routing of the shell side and tube side fluids has considerable effects on the heat exchanger design. Some general guidelines for positioning the fluids are given in Table
These guidelines are not ironclad rules and the optimal fluid placement depends on many factors that are service specific
Tube-side fluid
Shell-side fluid
Corrosive fluid
Condensing vapor (unless corrosive)
Cooling water
Fluid with large temperature difference (>40°C)
Fouling fluid
Less viscous fluid
High-pressure steam
Hotter fluid

70. Effect of Temperature Differences on Design of Shell and Tube Heat Exchanger
Countercurrent flow
Cocurrent flow
Cross
Approach
1-1 exchanger flow
1-2 exchanger flow

71. Pseudo Shell side Mass Velocity: Perpendicular Flow
By: Dr. M.R.Shahnazari
Pseudo Shell side Mass Velocity: Perpendicular Flow
The shell-side mass velocity is found with

72. Hydraulic or Equivalent Diameter : Axial Flow
By: Dr. M.R.Shahnazari
Hydraulic or Equivalent Diameter : Axial Flow
A Hydraulic radius based on cross flow cannot recognize the importance of tube layout.
The equivalent diameter is calculated along (instead of across) the long axes of the shell and therefore is taken as four times the net flow area as layout on the tube sheet (for any pitch layout) divided by the wetted perimeter.

73. Free Flow Area for Square Layout:
By: Dr. M.R.Shahnazari
Free Flow Area for Square Layout:
Free Flow Area for Triangular Layout:

74. Perimeter for square Layout:
By: Dr. M.R.Shahnazari
Perimeter for square Layout:
Perimeter for triangular Layout:
Equivalent diameter for square layout:
Equivalent diameter for Triangular layout:

75. Shell-Side Reynolds Number
By: Dr. M.R.Shahnazari
Reynolds number for the shell-side is based on the equivalent diameter (based on axial flow) and the velocity on the cross flow area at the diameter of the shell:

76. Correlation for Shell side Heat Transfer Coefficient
By: Dr. M.R.Shahnazari
Correlation for Shell side Heat Transfer Coefficient

77. Overall Heat Transfer Coefficient for the Heat Exchanger
By: Dr. M.R.Shahnazari
Overall Heat Transfer Coefficient for the Heat Exchanger
The overall heat transfer coefficient for clean surface (Uc) is given by
Considering the total fouling resistance, the heat transfer coefficient for fouled surface (Uf) can be calculated from the following expression:

78. Outlet Temperature Calculation and Length of the Heat Exchanger
By: Dr. M.R.Shahnazari
Outlet Temperature Calculation and Length of the Heat Exchanger
The outlet temperature for the fluid flowing through the tube is
The surface area of the heat exchanger for the fouled condition is :

79. and for the clean condition
By: Dr. M.R.Shahnazari
and for the clean condition
where the LMTD is always for the counter flow.
The over surface design (OS) can be calculated from :

80. The length of the heat exchanger is calculated by
By: Dr. M.R.Shahnazari
The length of the heat exchanger is calculated by

81. Hydraulic Analysis for Tube-Side
By: Dr. M.R.Shahnazari
Hydraulic Analysis for Tube-Side
The pressure drop encountered by the fluid making Np passes through the heat exchanger is a multiple of the kinetic energy of the flow.
Therefore, the tube-side pressure drop is calculated by
The second term in above equation is the additional pressure drop introduced by the change of direction in the passes.
The tube fluid experiences sudden expansions and contractions during a return that is accounted for allowing four velocity heads per pass.

82. Hydraulic Analysis for Shell-Side
By: Dr. M.R.Shahnazari
Hydraulic Analysis for Shell-Side
The shell-side fluid experiences a pressure drop as it passes through the exchanger, over the tubes, and around the baffles.
If the shell fluid nozzles (inlet and outlet ports) are on the same side of the heat exchanger, then the shell-side fluid makes an even number of the tube bundle crossings, but if they are on opposite sides, then it makes an odd number of the bundle crossings.
The number of bundle crossings therefore influences the pressure drop.

83. By: Dr. M.R.Shahnazari
Based on experiments, the pressure drop experienced by the shell-side fluid is calculated by
Where,

84. The wall temperature can be calculated as follows:
By: Dr. M.R.Shahnazari
μb is the viscosity of the shell-side fluid at bulk temperature, and μw is the viscosity of the tube-side fluid at wall temperature.
The wall temperature can be calculated as follows:
OR:

85. Evaluation & Fine tuning of Design
By: Dr. M.R.Shahnazari
Evaluation & Fine tuning of Design
Insufficient Thermal Rating
Insufficient Pressure Drop Rating

86. Insufficient Thermal Rating
By: Dr. M.R.Shahnazari
Insufficient Thermal Rating
If the output of the rating analysis is not acceptable, a geometrical modification should be made
If the required amount of heat cannot be transferred to satisfy specific outlet temperature,
one should find a way to increase the heat transfer coefficient or increase exchanger surface area
One can increase the tube side heat transfer coefficient by increasing the fluid velocity - Increase number of tube passes
One can increase the shell side heat transfer coefficient by decreasing baffle spacing and/or baffle cut
One can increase the surface area by
Increasing the heat exchanger length
Increasing the shell diameter
Multiple shells in series

87. Insufficient Pressure Drop Rating
By: Dr. M.R.Shahnazari
Insufficient Pressure Drop Rating
If the pressure drop on the tube side is greater than the allowable pressure drop, then
the number of tube passes can be decreased or
the tube diameter can be increased which may result to decrease the tube length – (Same surface area)
increase the shell diameter and the number of tubes
If the shell side pressure drop is greater than the allowable pressure drop then baffle spacing, tube pitch, and baffle cut can be increased or one can change the baffle type.
THERE IS ALWAYS A TRADE-OFF BETWEEN THERMAL & PRESSURE DROP RATINGS!

88. The Trade-Off Between Thermal Balance & Flow Loss
By: Dr. M.R.Shahnazari
The Trade-Off Between Thermal Balance & Flow Loss
Heat transfer and fluid friction losses tend to compete with one another.
The total energy loss can be minimized by adjusting the size of one irreversibility against the other .
These adjustments can be made by properly selecting physical dimensions of the solid parts (fins, ducts, heat exchanger surface).
It must be understood, however, that the result is at best a thermodynamic optimum.
Constraints such as cost, size, and reliability enter into the determination of truly optimal designs.

89. Roadmap To Increase Heat Transfer
By: Dr. M.R.Shahnazari
Increase heat transfer coefficent
Tube Side
Increase number of tubes
Decrease tube outside diameter
Shell Side
Decrease the baffle spacing
Decrease baffle cut
Increase surface area
Increase tube length
Increase shell diameter à increased number of tubes
Employ multiple shells in series or parallel
Increase LMTD correction factor and heat exchanger effectiveness
Use counterflow configuration
Use multiple shell configuration

90. Roadmap To Reduce Pressure Drop
By: Dr. M.R.Shahnazari
Roadmap To Reduce Pressure Drop
Tube side
Decrease number of tube passes
Increase tube diameter
Decrease tube length and increase shell diameter and number of tubes
Shell side
Increase the baffle cut
Increase the baffle spacing
Increase tube pitch
Use double or triple segmental baffles

91. By: Dr. M.R.Shahnazari
Kern’s Method

92. By: Dr. M.R.Shahnazari
SHELL SIDE CROSSFLOW

93. By: Dr. M.R.Shahnazari
KERN METHOD

94. By: Dr. M.R.Shahnazari
KERN METHOD…con.

95. By: Dr. M.R.Shahnazari
KERN METHOD…con.

96. By: Dr. M.R.Shahnazari
KERN METHOD…con.

97. Fluid Allocation: Shell or Tubes?
Corrosion
Fouling
Fluid temperatures
Operating pressures
Pressure drop
Viscosity
Stream flow rates

98. Shell and Tube Fluid Velocities
High velocities give high heat-transfer coefficients but also high pressure drop.
Velocity must be high enough to prevent settling of solids, but not so high as to cause erosion.
High velocities will reduce fouling
For liquids, the velocities should be as follows:
Tube side: Process liquid 1-2m/s
Maximum 4m/s if required to reduce fouling
Water 1.5 – 2.5 m/s
Shell side: 0.3 – 1 m/s

99. Pressure Drop
As the process fluids move through the heat exchanger there is associated pressure drop.
For liquids: viscosity < 1mNs/m2 35kN/m2
Viscosity 1 – 10 mNs/m kN/m2

100. Tube-side Heat Transfer Coefficient
For turbulent flow inside conduits of uniform cross-section, Sieder-Tate equation is applicable:
C=0.021 for gases
=0.023 for low viscosity liquids
=0.027 for viscous liquids
μ= fluid viscosity at bulk fluid temperature
μw=fluid viscosity at the wall

101. Tube-side Heat Transfer Coefficient
Butterworth equation:
For laminar flow (Re<2000):
If Nu given by above equation is less than 3.5, it should be taken as 3.5

102. Heat Transfer Factor, jh
“j” factor similar to friction factor used for pressure drop:
This equation is valid for both laminar and turbulent flows.

103. Tube Side Heat Transfer Factor

104. Heat Transfer Coefficients for Water
Many equations for hi have developed specifically for water. One such equation is:
where hi is the inside coefficient (W/m2 0C)
t is the water temperature (0C)
ut is water velocity (m/s)
dt is tube inside diameter (mm)

105. Tube-side Pressure Drop
where ΔP is tube-side pressure drop (N/m2)
Np is number of tube-side passes
ut is tube-side velocity (m/s)
L is the length of one tube
m is 0.25 for laminar and 0.14 for turbulent
jf is dimensionless friction factor for heat exchanger tubes

106. Tube Side Friction Factor

107. Shell-side Heat Transfer and Pressure Drop
Kern’s method

108. Procedure for Kern’s Method
Calculate area for cross-flow As for the hypothetical row of tubes in the shell equator.
pt is the tube pitch
d0 is the tube outside diameter
Ds is the shell inside diameter
lB is the baffle spacing, m.
Calculate shell-side mass velocity Gs and linear velocity, us.
where Ws is the fluid mass flow rate in the shell in kg/s

109. Procedure for Kern’s Method
Calculate the shell side equivalent diameter (hydraulic diameter).
For a square pitch arrangement:
For a triangular pitch arrangement

110. Shell-side Reynolds Number
The shell-side Reynolds number is given by:
The coefficient hs is given by:
where jh is given by the following chart

111. Shell Side Heat Transfer Factor

112. Shell-side Pressure Drop
The shell-side pressure drop is given by:
where jf is the friction factor given by following chart.

113. Shell Side Friction Factor

114. (Figure 8 in notes)

120. (Table 3 in notes)
(Figure 10 in notes)

121. (Figure 12 in notes)

123. By: Dr. M.R.Shahnazari
KERN METHOD…con.

124. By: Dr. M.R.Shahnazari
KERN METHOD…example

125. By: Dr. M.R.Shahnazari
KERN METHOD…example

126. By: Dr. M.R.Shahnazari
KERN METHOD…example

127. By: Dr. M.R.Shahnazari
KERN METHOD…example

128. By: Dr. M.R.Shahnazari
KERN METHOD…example

129. By: Dr. M.R.Shahnazari
KERN METHOD…example