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TEMA Shell and Tube Heat Exchangers
© Copyright Progressive Thermal Engineering All rights reserved.Page 1-1-1
Introduction to Shell and Tube Heat Exchangers
Introduction
� General Description� Identifying Major Components� TEMA Standards� Vibration
TEMA Shell and Tube Heat Exchangers
© Copyright Progressive Thermal Engineering All rights reserved.Page 1-1-2
Shell and Tube Heat Exchangers
Tubeside flow (four passes)
Typical Major Components
Floating head
Stationary head
Pass partitions
Pass partitionShellside flow,
one pass
Tubesheet
BaffleTube
Shell
TEMA Shell and Tube Heat Exchangers
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General Description
� The variety of designs and configurations are almost limitless
� Common features:– A collection of tubes manifolded together to
form a “tube bundle”– A chamber formed around the outside of the
tube bundle, the “shell”
� One stream flows inside the tube bundle, the other outside the tube bundle, contained by the shell
Identifying Major Components
� Tubesheets� Channels� Fixed and floating heads� Shell covers� Bundle
TEMA Shell and Tube Heat Exchangers
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Tubesheets
� Within the scope of TEMA, tubes are manifolded together with tubesheets or U-bends
� A tubesheet is a flat, circular plate drilled to allow the tubes to be inserted
� U-bends are used to connect pairs of tubes together to remove the need for a tubesheet at one end of the exchanger
Tubesheets / U-bends
TEMA Shell and Tube Heat Exchangers
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Straight Tube / U-tube
� An exchanger in which two tubesheets are used is called a straight tube exchanger
� An exchanger with one tubesheet and U-bend returns is called a U-tube exchanger
Channels
� In order to direct the tubeside flow in and out of the tubes, a chamber is attached to the tubesheet, called a channel
� Depending on the design this may also be called a bonnet or waterbox
� Selection of channel type is based on balancing access requirements for maintenance against cost
TEMA Shell and Tube Heat Exchangers
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Fixed / Floating Heads
� Tubesheet may be fastened to the shell, or free to move relative to the shell– A tubesheet which is fastened is called a
fixed head– A tubesheet which is free to move is called a
floating head
� A fixed-tubesheet exchanger has both tubesheets fixed
� A floating-head exchanger has one fixed head and one floating
Shell Cover
� In a floating head heat exchanger, a removable cover may be incorporated into the shell at the floating end
� Allows access to the floating head without disturbing the fixed head
TEMA Shell and Tube Heat Exchangers
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Bundles
� The tube bundle comprises:– tubesheets / tubes / U-tubes– baffles / support plates– tie-rods / spacers
� The tubes may be arranged for single pass or multi-pass, using pass partition plates in the channel(s)
Bundle Fabrication
TEMA Shell and Tube Heat Exchangers
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TEMA Size and Type
TEMA Designations
� The TEMA standard contains a coding system to allow the size and configuration of a heat exchanger to be expressed in a concise manner
� This description system is widely accepted and understood
TEMA Shell and Tube Heat Exchangers
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TEMA Type Code
� A three letter code is used to describe the configuration:
B E MB E MFront head
Shell type
Rear head
TEMA Shell Types
� Selection of shell type is primarily a process/thermal design decision
� Different types create different flow paths through the shell
TEMA Shell and Tube Heat Exchangers
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TEMA Shell Types
Divided flow
One-pass shell Two-pass shell, longitudinal baffle
E F
J
TEMA Shell Types
Double-split flowSplit flow
Crossflow
X
H
Kettle reboiler
K
G
TEMA Shell and Tube Heat Exchangers
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TEMA Front Head Types
� Selection of front head type is primarily a mechanical design decision
� Different types provide various levels of access for maintenance
� Cost and pressure-integrity become factors at higher pressure
TEMA A Type
Channel and removable cover
TEMA Shell and Tube Heat Exchangers
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TEMA B Type
Bonnet (integral cover)
TEMA C Type
Channel integral with tubesheet and removable cover
TEMA Shell and Tube Heat Exchangers
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TEMA N Type
Channel integral with tubesheet and removable cover
TEMA D Type
Special High Pressure Closure
TEMA Shell and Tube Heat Exchangers
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TEMA Rear Head Types
� Selection of rear head type is primarily a mechanical design decision
� Different types provide various levels of access for maintenance
� Types L, M and N imply a fixed-tubesheet construction
� Types P, S, T, U and W are floating head types (bundle free to expand relative to shell)
TEMA L, M and N Type
L M
N
TEMA Shell and Tube Heat Exchangers
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TEMA U Type
TEMA P, S, T and W TypesML
P
S T
W
TEMA Shell and Tube Heat Exchangers
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TEMA Size Code
� A two-number code� First number is the shell id to the nearest
whole inch� Second number is the tube length to the
nearest whole inch� Example: TEMA size 31-240
(31” ID shell with 240” (20’) tubes)
TEMA Size Code
� For U-tube exchangers, the tube length is the length of the straight leg
� For kettle reboilers, the shell diameter is expressed as two numbers, the port ID then the shell ID:
Length
Port IDShell ID
E.g. Size 17/43 - 192
TEMA Shell and Tube Heat Exchangers
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Tube Bundle Construction
Heat Exchanger Tubes
TEMA Shell and Tube Heat Exchangers
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Heat Exchanger Tubing
� Welded vs Seamless Tube� Average vs Minimum Wall� U-tube bending� Tube pitches
Seamless vs Welded
Drawn from a solid billet or forged
cylinder
Rolled from a flat strip and welded along longitudinal seam
TEMA Shell and Tube Heat Exchangers
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Which to use?
� Welded tube is cheaper and more readily available
� Quality of welded tube can be very high:– continuous testing of weld– Individual tube pressure testing– heat treatment of weld– no significant weld bead outside tube section
� Use seamless only for lethal service, very high integrity, or very high pressure
Wall Thickness Tolerance
� Important to understand the difference between minimum wall and average wall tubes
� Tolerances are controlled by the ASTM material spec. (e.g. SA-213 is a minimum wall spec., SA-249 is an average wall spec.)
� Min. wall usually -0% +20% thickness� Av. wall usually -10% +10% thickness
TEMA Shell and Tube Heat Exchangers
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U-tube Bending
� The process of forming a U-bend from a straight tube will:– thin the wall on the outside of the bend– tend to flatten the tube on the outside of the
bend– tend to crimp the inside of the bend– work-harden the tube material
� These effects limit the diameter of the bend to a minimum value (typically 3Do)
� Heat treatment may be required
U-Bend Forming
TEMA limits wall thinning to 17% for non-work hardening materials (equivalent to R = 1.5Do)
Crimping
Flattening
Thinning
R
Do
TEMA Shell and Tube Heat Exchangers
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Tube Pitches
60° layout
Pt
30° layout
Pt
90° layout
Pt
45° layout
Pt
Tube Pitch
� A minimum value of Pt must be maintained:– To retain mechanical strength in tubesheet– To allow any welding of tube end– To allow cleaning outside tubes
� Typical: Pt = 1.25 x Dt
TEMA Shell and Tube Heat Exchangers
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Tube-to-Tubesheet Attachment
� Tubes need to be attached to:– prevent interstream leakage– transmit mechanical loads
� Attachment may be by welding, expansion or both
� Type of attachment affects tube pitch requirement
� Attachment type has impact on ease of re-tubing
Types of Attachment
� Expansion:– Used as an attachment process providing
both sealing and strength functions– Light expansion used to remove crevice at
back face of tubesheet
� Welding:– Seal weld creates a better seal than
expansion, especially at high temperatures– Strength weld (weld strength ≥ tube strength)
provides both sealing and strength
� Explosive expansion and welding are also used
TEMA Shell and Tube Heat Exchangers
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Welded Only
Tubesheet
Tube
Weld
Expanded Only
Tubesheet
Tube
TEMA Shell and Tube Heat Exchangers
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Welded and Expanded
Tubesheet
Tube
Weld
Back-Face Welding
Tubesheet
Tube
Weld
TEMA Shell and Tube Heat Exchangers
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Tube Passes
Tubepasses
� Multiple passes are used to:– increase tubeside velocity– reduce overall length– allow U-tube/floating head designs
� Single pass designs used to retain counter-current flow
TEMA Shell and Tube Heat Exchangers
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Pass Partitions
Pass partition
2-Pass, B-Type Head
Tubesheet
Drain hole
Weld
Gasket
Pass Lane
Pass Arrangements
4-Passquadrant
6-Passribbon-banded
TEMA Shell and Tube Heat Exchangers
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Pass Arrangements
Quadrant(good for U-tubes)
Ribbon-banded(good pass lane
orientation)
1 2
4 3 1
2
3
4
56
1
2 3
45
6
H-banded(good tube count
distribution)
Pass Considerations
� Number of passes and arrangement is mainly driven by thermal design
� Limitations:– construction of pass partitions– thermal gradients– effect on tubecount (total and pass-to-pass)– gasket seating– shellside bypassing
TEMA Shell and Tube Heat Exchangers
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Baffles
Shellside Baffles
� Baffles have two main purposes:– To direct the shellside fluid in crossflow, to
improve heat transfer– To support the tubes against sagging and
vibration
� Described by type, cut and pitch
TEMA Shell and Tube Heat Exchangers
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Baffle Types
Single Segmental
Double Segmental
Baffle Pitch and CutPitch
hCut % = (h/Ds) x 100
End Space(often greater than pitch) Ds
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No-Tubes-in-Window
Standard Single Segmental
No-Tubes-in-Window
Baffle Construction
Triple Segmental
TEMA Shell and Tube Heat Exchangers
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Tie-Rod / Spacer
� This system allows accurate alignment of the baffles during construction
Tie-rod Spacer tube
Baffle
� Permits condenser drainage
� Better end zone distribution
� Prevents separation or stratification
Baffle Orientation
Perpendicular cut(perpendicular to nozzle centreline)
Nozzle
Baffle cut
Parallel cut(parallel to nozzle centreline)
Baffle cut
Nozzle
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Baffle Selection
� Selection depends on
– Pressure drop requirements
– Tube support requirements
– Heat transfer requirements
Typical Tubesheet Layout
TEMA Shell and Tube Heat Exchangers
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Tubesheet Layout