Basics of Double pipe heat exchanger(Heat Transfer slides)

7/30/2019 Basics of Double pipe heat exchanger(Heat Transfer slides)

1/38

IMRAN RASHIDLecturer

COMSATS

Heat Transfer

Basics of Shell and Tube Heat Exchanger

1


2/38

WHY SHELL AND TUBE HEAT

EXCHANGER

Large surface area in small volume

Good shape for pressure operation

Can be constructed from variety of materials Easily cleaned

Well established design procedures

Used for all applications Well established fabrication techniques


3/38

Classification Shell and tube heat exchanger

Most commonly used heat exchangers. These use baffles on the shell-side fluid to accomplished

turbulence, direct fluid flow, and support tubes.

Outer shell : durable, highly strong Inner tube : having effective combination of durability,

corrosion resistant and thermally conductive.


4/38

Shell & Tube

Heat exchangers

U- Tube Heat

exchangers

Fixed Tube Heat

exchangers

Floating Head Heat

exchangers


5/38

Classification U tube heat exchanger

U-Tube heat exchanger consisting of straight lengthtubes bent into a U-shape surrounded by a shell.

Advantages

Requires one tube sheet and is less expensive, alsomaintenance costs are less

Disadvantages

They have drawbacks like inability to replace

individual tubes except in the outer row and inability

to clean.


6/38

Classification


7/38

Classification Fixed tube heat exchanger

These have straight tubes that are secured at both endsto tube sheets welded to the shell.

They are the most economical type design.

They have very popular version as the heads can beremoved to clean the inside of the tubes.

Cleaning the outside surface of the tubes is impossibleas these are inside the fixed part.

Chemical cleaning can be used.

Limited to 80C and 8 Bar pressure applications


8/38

Classification

Fixed tube heat exchanger


9/38

Classification Floating head heat exchanger

One tube end is free to float within the shell.

A floating head is excellent for applications where the

difference in temperature between the hot and coldfluid causes unacceptable stresses in the axial directionof the shell and tubes.

The floating head can move, so it provides thepossibility to expand in the axial direction.

Easy inspection,cleaning or maintenance.


10/38

Classification

Floating head heat exchanger


11/38

Shell and Tube heat exchangerIt consist of tubular elements (tubes) inside a shell and installed wherelarge heat transfer are required.Maximum pressure

Shell 300 bar (4500 psia)Tube 1400 bar (20000 psia)

Temperature range

Maximum 600

o

C (1100

o

F) or even 650

o

CMinimum -100oC (-150oF)

Number of tubes per shell depends on shell diameter, tube diameter,and tube pitch

Tube lengths available in multiples of 4 ft, e.g.8, 12, 16, 20 ftFluidsSubject to materialsAvailable in a wide range of materials

Size per unit is 100 - 10000 ft2 (10 - 1000 m2)


12/38

TEMA terminology

Letters given for the front end, shell and

rear end types

Exchanger given three letter designation


13/38

Construction Bundle of tubes in large cylindrical shell

Baffles used both to support the tubes and

to direct into multiple cross flow

Headers

Types

Shell

Tubes

Baffle


14/38

TubesSmaller Tube Diameter

Compact exchanger, Cheaper exchanger

Large Tube Diameter

-easy for cleaning ,used for fouling liquids

Tube Thickness-to withstand internal pressure and for corrosion

allowance

Tube Length-more length, reduce shell dia and cost but

sagging


15/38


16/38

Plate Baffle Types


17/38

Plate Baffle Types (continued)


18/38


19/38


20/38

Avoiding vibration (cont.)

Inlet supportbaffles

Double-segmental baffles

No tubes in the window - with intermediate support baffles

TubesWindows

with no tubes

Intermediate baffles


21/38

ROD bafflesTend to be about 10% more expensive for the

same shell diameter


22/38

Front head type A-type is standard for dirty tube side

B-type for clean tube side duties. Use ifpossible since cheap and simple.

B

Channel and removable cover Bonnet (integral cover)

A


23/38

More front-end head types C-type with removable shell for hazardous tube-

side fluids, heavy bundles or services that needfrequent shell-side cleaning

N-type for fixed for hazardous fluids on shell side

D-type or welded to tube sheet bonnet for high

pressure (over 150 bar)

BN

D


24/38

Basic ComponentsShell Types

Front and rear head types and shell types are standardized by TEMA, identified by

alphabetic characters (Fig. 8.2)

E-shell is the most common

cheap and simple configuration

one-shell pass and one- or multiple-tubepasses

if one-tube pass, nominal counterflow is achieved

most common for single-phase shell fluid applications

F-shell used if are two tube passes and pure counterflow

longitudinal baffle results in two-shell passes

units in series, each shell pass represents one unit

higher pressure drop than that for E-shell


25/38

Shell Types (continued)

J-shell has divided flow

for low pressure drop applications normally, single nozzle for shell-fluid at tube

center, two nozzles near tube ends

when used for condensing the shell fluid, two inlets for shell-

side vapor and one central outlet for condensate (figure)

X-shell has cross flow

central shell-fluid entry and exit

no baffles are used

very low pressure drop

used for vacuum condensers

and low-pressure gases

G-shell and H-shell are single- and double-split flow

Divided Flow


26/38


27/38

Tube Bundle Types (rear head types)

Main objectives in design are to accommodate thermal expansion

and allow easy cleaning (or to provide the least expensiveconstruction)

U-tube configuration (Fig. 8.4)

allows independent expansion of tubes and shell

(unlimited thermal expansion)

only one tube sheet is needed (least expensive

construction)

tube-side cannot be mechanically cleaned even number of tube passes

individual tubes cannot be replaced (except those in

the outer row)


28/38


29/38

Tube Bundle Types (continued)

Fixed tube sheet configuration

allows mechanical cleaning of inside of tubes but not

outside because shell is welded to the tube sheets

low-cost

limited thermal expansion

individual tubes replaceable

Pull-through floating head

allows the tube sheet to float move with thermal

expansion

the tube bundle can be removed easily for cleaning

suitable for heavily fouling applications


30/38

Figure 8.2

TEMAs Standard Shell,

Front-end and Rear-end

Types


31/38

1-2 shell and tube Heat Ex.


32/38


33/38


34/38


35/38

ow

T b d T b P


36/38

Tubes and Tube Passes

A large number of tube passes are used to increase fluid velocity and

heat transfer coefficient, and to minimize fouling

Tube wall thickness is standardized in terms of the Birmingham Wire

Gauge (BWG) of the tube

Small tube diameters for larger area/volume ratios, but limited for in-

tube cleaning

Larger tube diameters suitable for condensers and boilers

Fins used on the outside of tubes when low heat transfer coefficient

fluid is present on the shell-side

Longer tubes fewer tubes, fewer holes drilled, smaller shelldiameter, lower cost. However limitations due to several factors

result in 1/5 1/15 shell-diameter-to-tube-length ratio


37/38

Tube layouts

Triangular layouts give more tubes in a given

shell Square layouts give cleaning lanes with close

pitch

pitch

Triangular

30oRotated

triangular60o

Square90o

Rotated

square45o


38/38

Documents

Basics of Double pipe heat exchanger(Heat Transfer slides)