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TEMA Shell and Tube Heat Exchangers

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Introduction to Shell and Tube Heat Exchangers

Introduction

� General Description� Identifying Major Components� TEMA Standards� Vibration



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



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



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



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



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



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 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 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 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 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 B Type

Bonnet (integral cover)

TEMA C Type

Channel integral with tubesheet and removable cover



TEMA N Type

Channel integral with tubesheet and removable cover

TEMA D Type

Special High Pressure Closure



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 U Type

TEMA P, S, T and W TypesML

P

S T

W



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



Tube Bundle Construction

Heat Exchanger Tubes



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



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



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



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



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



Welded Only

Tubesheet

Tube

Weld

Expanded Only

Tubesheet

Tube



Welded and Expanded

Tubesheet

Tube

Weld

Back-Face Welding

Tubesheet

Tube

Weld



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



Pass Partitions

Pass partition

2-Pass, B-Type Head

Tubesheet

Drain hole

Weld

Gasket

Pass Lane

Pass Arrangements

4-Passquadrant

6-Passribbon-banded



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



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



Baffle Types

Single Segmental

Double Segmental

Baffle Pitch and CutPitch

hCut % = (h/Ds) x 100

End Space(often greater than pitch) Ds



No-Tubes-in-Window

Standard Single Segmental

No-Tubes-in-Window

Baffle Construction

Triple Segmental



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



Baffle Selection

� Selection depends on

– Pressure drop requirements

– Tube support requirements

– Heat transfer requirements

Typical Tubesheet Layout



Tubesheet Layout

Introduction to Shell and Tube Heat Exchangersmazlan/?download=Introduction+to+Shell+and+Tub… · A fixed-tubesheet exchanger has both tubesheets fixed ... Introduction to Shell

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