Heat Exchanger Design and Operation

HEAT EXCHANGERS
Mohd. Hanif Dewan, Senior Lecturer, IMA,
Bangladesh. 19-Apr-14

Basic Definitions:
- A heat exchanger is a device built for
efficient heat transfer from one medium
to another, whether the media are
separated by a solid wall so that they
never mix, or the media are in direct
contact.
Or, the equipment in which transfer of
heat takes place is called the heat
exchanger.

On board ships the lubricating oil, fresh
water and refrigerated gas are cooled by
sea water and the fuel oil heated by
steam.
Heat exchangers are often used in the
following applications:
 Liquid Cooler or
Air Radiator
 Fuel Preheater
Air conditioning evaporator and condenser
steam condenser Mohd. Hanif Dewan, Senior Lecturer, IMA,

Coolers
 On board ships, the main engine is cooled by
the jacket cooling water and lubricating oil.
These fluids are then passed through a cooler
where sea water is used as the cooling medium
to cool the fresh water and the lubricating oil.
After being cooled the fluids return back to the
main engine and the sea water is discharged
overboard.

Heaters
 Heaters are used for various purposes on board
ships.The most essential one is used for the fuel
oil heating.The temperature of the fuel oil is
raised by passing steam through the heating
tubes and the oil on the outside of these tubes.
Thus heat is transferred from the steam to the
fuel oil.

Thermodynamic characteristics
The total rate of heat transfer between the hot
and cold fluids passing through a plate heat
exchanger may be expressed as:
Q = UA∆Tm
where,
U= Overall heat transfer coefficient,
A= total plate area, and
∆Tm= the Log mean temperature difference.

Coefficient of heat transferred
(U) depends on :-
Type of fluid
Flow condition
Thermal conductivity of wall materials
Thickness of the wall
Cleanliness of the walls

Flow pattern
Parallel flow
Counter flow – the best thermodynamic
pattern
Cross flow
Mixed flow – in practice use

Parallel flow
Practically not used in marine industry
May be in a combination of flow pattern (mixed flow)
Inherently poorer heat transfer rates
Could be found in food processing industry
ADV: lower heat transfer surface temperature and more even heat transfer surface temp.

Counter flow

Cross flow

Mixed flow

Streamline flow
Turbulent flow

Selection of Heat Exchanger
Quantity of fluid to be cooled
Range of temperature (inlet and outlet) to be cooled
Range of fluid to be cooled as a cooling mediums (jacket
water)
Specific heat of medium
Type of medium – corrosive or non-corrosive – safety
Operating pressure
Maintenance – cleaning
Position in system and pipe work
Cost and material
Streamline (heat transfer low) or turbulent (erosion) flow

TYPE of HEAT
EXCHANGER
Consists: -
 i) Shell and tube type heat exchanger
(Tubular or shell and tube type)
 ii) Plate type heat exchanger

Types of Heat Exchangers
 In the shell & tube type heat exchanger one
medium flows through a set of tubes and the
other medium flows on the outside.Thus heat
transfer take place across the tube walls.
 In the plate type heat exchanger, a set of
corrugated plates are tightly packed with
spaces in between.The different mediums flow
on either sides of the plate and heat transfer
takes place across the plate.

Shell and tube type heat exchanger

Shell & Tube Type HE:
9-Apr-14
Bangladesh. 18

 Tubular exchangers are used in great numbers, far more
than any other type of exchanger.They are made in a
wide variety of sizes and styles, ranging from the tiny
units used in miniature cryocoolers to giant installations
containing thousands of tubes and used as condensers in
base-load power stations.
 Tubular exchangers are so widely used because the
technology is well established for making precision metal
tubes capable of containing high pressures in a variety of
materials.There is virtually no limit to the range of
pressures and temperatures that can be accommodated.

Typical Materials
 Tubes - Aluminum brass, cupro-nickel
 Tube plates – Cast Naval brass
 Casing and water boxes – Cast iron,
gunmetal
 Baffles – Cooper, rolled naval brass

Shell & Tube type HE:
9-Apr-14
Bangladesh. 21

Two passage type
Division plate
Water box
Baffle or support
plate
Neoprene rings
Tell-tale hole Contact strip
Sacrificial
anode
Tube stack
ShellInspection door
Fixed endMovable end
Drain
Vent
Hot fluid
inlet
Hot fluid
outlet
Coolant inlet
Coolant outletDistribution
belt
Tube plate

 The shell (cylinder) is usually made of
grained cast iron, with surfaces machined as
required. Gun metal of fabricated steel may
be used as alternatives depending upon
requirements.
 Inspection doors are fitted in the
distribution belts even at water box.
 End boxes with end access covers, are at
the same material as the shell. Sacrificial
anodes in rod or plug form and electrical
contact strip are fitted to minimize
corrosion
Cont-

 The tube stack is made up of stress
relieved aluminum brass tubes expanded
into Naval brass tube plates, one plate is
fixed and other ended is free to allow for
expansion of the stack.
 Brass circular baffles give radial flow to
the fluid and support to the tube stack.

Capacity
 Most heat exchangers are sized to provide about
30% more surface area for heat transfer than that
required.This extra allows for:-
 - to cope up with fouling and deposits, thereby
increasing the period between opening
 - to cope up with the plugging of defective tubes.
Usually 10% is the limit before the tube stack
requires changing or the tube renewing
 - to cope with overloading of the engine for short
period
 - Abnormal sea water temperature

BAFFLES
 It is important that all baffles are neat fit in
the exchanger casing as by-passing of the
baffles can lead to a substantial drop in
efficiency.
 Note that casings are machined internally
to allow a neat fit and that care must be
taken when stripping or assembling to
prevent damage
 The tube stack is fitted with baffles which
are design to:-

Why ?…….
 Control fluid flow ensuring optimum
contact between heat transfer surface and
fluid
 Increase the time the fluid is present in the
exchanger
 Prevent ‘coring’ in the fluid paths ( Coring
occurs when a large temperature difference
exists which alters the velocity of the fluid
causing a heavy build-up of slow moving
fluid to adhere to the tube surface)
Cont-

 Increase the surface area on the hot fluid
side.This is particularly important when
the fluid specific heat of the fluid (oil) is
approximately haft of the cooling agent to
assist in balancing the heat flow
 Reduce turbulence in the fluid flow to
reduce the pressure drop across the
exchanger

Type of baffle
 Segmental baffle
 Doughnut baffle
 Disc baffle

Baffle flow arrangement
 Segmental flow
 Radial flow
 Guide flow
 Axial flow

Causes of tube failure
 General wastage – over acidic water prevents the
formation of a stable oxide film
 Impingement attack – due to turbulence
 Deposit attack – the metal under the deposit
becomes anodic to the surrounding area and
corrodes
 Anaerobic attack – bacteria reacts with tube material
causing local attack leading to pitting or tube
perforation
 Erosion – due to abrasive solids such as sand, or air
bubble in the coolant

TURBULENCE
 Turbulence leads to erosion, pumping
losses and encourages corrosion by
preventing the growth of a thick oxide film.
 The effect on tubes of turbulence in the
water boxes is usually limited to a length
equal to 4 x diameter which suffer erosion
 It can be cause by as follow:-
Cont-

 Excessive water velocities due to
overloading the heat exchanger or total
blockage of a large % of tubes
 Partial blockage of tubes
 Poor design of water boxes (too shallow)
 Incorrect fitting of protector plates
(anodes)

Temperature control
 By-passing a proportion(%) of the hot
fluid
 By throttling the sea water flow (outlet
valve)
 By controlling the temperature of sea
water entering the heat exchanger. It is
done by spilling part at the heated
discharge back to the pump suction.

Cleaning cold fluid side (s w)
 Algae slimes – mechanical cleaning or flushing through
with copper sulphate solution
 marine growth – Mechanical cleaning or chlorination
 Scales – soft scale by mechanical cleaning but for hard
scales require circulation of an acid declare usually
sulphuric acid, hydrochloric acid or citric acid in
addition of inhibitors which protect the metal surface.
Neutralizing solution be circulated after descaling like
sodium carbonate or hydrazine.
 Silt, sand, rust etc – mechanical cleaning

Cleaning hot fluid side
 Fresh water creating scaling and deposits cause
by corrosion or be a sludge due to the
deterioration of corrosion inhibitor additive – be
removed by degreasant.
 Oil creating oily sludge due to oxidation, carbon
and contaminations were accumulate in the tube
stack, thus reducing the heat transfer efficiency –
be removed by either circulation of a degreasant
solution or by stripping the exchanger and
immersing the tube stack in a tank of cleaning
solution

Type of degreasant
 Alkaline – trisodium phosphate and
caustic soda
 Hydrocarbon solvent – trichlorothane
 Solvent emulsion – mixture of
hydrocarbons and
surfactants

Provision for Expansion
 1. Keeping the shell, tube plates and the water-
boxes or headers fixed, the tubes are allowed
to expand.
 2. Keeping the shell and header fixed, the
entire tube stack is allowed to expand in the
shell (that is, slide in the shell).
 3. Keeping the tubes, tube plates and header
fixed, the shell is allowed to expand or
contract by means of shell expansion joint or
bellows.

Thermal Expansion
 Keeping the shell, tube plate and end
cover fixed while allowing the tubes to
expands
Fiber packing ring
Metallic ring
Tube plate
Ferrule
nut
Clearance for expansion
Outlet end
serration
Inlet end

Leakage tell-tale hole
Rubber “O” rings
Movable tube plate
for free expansion
Keeping the shell and header fixed, the entire tube stack is
allowed to expand in the shell (that is, slide in the shell).

 Keeping the shell, end cover and tubes
while the tube plate is allowed to expands
Tell-tale hole
Tube plate
Neoprene ring
Contact strip

Keeping the shell, tube plates and the water-boxes
or headers fixed, the tubes are allowed to expand

Expansion arrangement
Keeping the tubes, tube plates and header fixed, the shell is allowed
to expand or contract by means of shell expansion joint or bellows.

 Keeping the tubes, tube plate and end
cover fixed while the shell is allowed to
expanded or contracted by means of shell
expansion joint – bellow type

LEAK TEST METHODS
 Water test
 Ultra-sonic test
 Fluorescein test
 Vacuum test

Water test procedure
 It chosen depends upon the equipment and
time available even type of exchanger.
 It can be done by opening the water boxes
and drying the tube plates.
 Filling the fluid space with water.
 for some extent, pressurize the space by
compressed air for a time interval
 Leakages will appear or can be seen by
pressure dropping.

Ultra-sonic test procedure
 Heat exchanger should be drained and any
necessary access doors removed.
 Electrical tone generators are then place in
the fluid space, care being taken to position
some in the air cooling section.(use slight air
pressure)
 The sound produced by these passes through
leaks to be detected by and ultra-sonic probe
moved over the tube plate (tube end)

Fluorescein test procedure
 Tube plates and tube should be cleaned in the
normal manner
 Flooded up the fluid space with water containing
small amount of fluorescein, thus water change to
green.
 Then the tube plate and tubes are then illuminated
by means of ultra-violet light.
 Any leakage will then be indicated by a fluorescent
glow.
 After testing, cleared the parts.

Vacuum test procedure
 Seal each end of tube plate to prevent any ingress
of air while the fluid part in vacuum.
 By having connection to ejectors, air in fluid space
will be suck thus creating vacuum.
 Leak can be now detected by spreading thin sheets
of polythene over the tube plates.
 Depressions in the sheets show the leaks even
ultra-sonic probe can be use too.

PLATE TYPE
HEAT EXCHANGER

A Plate Heat Exchanger , or PHE as it is more
commonly called as , is a type of heat exchanger
that uses metal plates instead of the conventional
pipes as in a Shell and Tube Heat Exchanger .
It was invented by Dr. Richard Seligman
way back in
1923 .
The plate heat exchanger revolutionized
the concept
of indirect heating or cooling of fluids .

Lateral bolts
Fixed plate/
frame
Plate pack
Carrying bar Movable pressure plate Lateral bolts
Fixed plate/
frame
Guide bar Distance pieces Adjustable feet
Support post

PLATE TYPE HEAT EXCHANGER

 The above picture illustrates the construction
AND liquid flow of a traditional Plate Heat
Exchanger. The RED arrows represent the flow
of the fluid which is hot , while the BLUE one
represents the flow of the fluid which is
relatively cooler. The metal plate can be either
welded or semi-welded or brazen , accordingly
to the industry in which the PHE is going to be
incorporated into.
 In place of pipes passing through a chamber ,
we have metal chambers , usually thin in depth
and seperated by gaskets .

PLATE TYPE HEAT
EXCHANGER

The flow of the liquids in the PHE that the
RED and BLUE fluid flow into alternating
chambers.The gaskets are so designed as to
allow the two fluids into successively
alternating metal chambers , facilitating
more surface area contact and thus , more
heat transfer efficiency.

 The Plate Type Exchanger consists of:
Variable number of gasketed (titanium or
stainless steel/aluminum brass) plates –
clamped together between a movable
pressure plate and frame by lateral bolts.
Plates are suspended from upper bar and
located by the lower carrying bar
Plates thickness 0.6 – 0.8 mm each
Plates surface are corrugated – herring bone
pattern with vees pointing alternately up and
down, touching in a criss-cross pattern –
strength and additional heat transfer surface

Gasket (Nitrile rubber) bonded to the
plates and arranged so that in event of
failure the two fluids cannot mix
Plates distance are normally 3 – 5mm
Fluids enter and leave through duets
or port formed in the plates corner
Working pressure 14 bar, temperature
as a cooler 110oC and 220oC as a
heater

Bulkhead
Single
Twin frameTwin frame
FRAMETYPE

Top slot for carrying bar
Distribution area
Heat
transfer
area
Bottom slot
Gasket
Gasket
Plate stainless steel
titanium
Plate relief pattern
Leak channel
Heat
transfer
area

WHY PLATE ARE CORRUGATED?
 Provided strength
 Increase heat transfer surface
 Produce turbulent flow

Flow pattern in plate type
COUNTER FLOW

Maintenance of PHE:
 Plates – surfaces of each plates can be
mechanical or chemically cleaned – care
should be taken not to damaged or
scratch the plates (erosion)
 May required replacement from time to
time as per manufacturers instruction
 The only way to locate leaks is by visual
inspection of plate surfaces

Advantages of PHE
 Titanium plates (self healing) – no corrosion or erosion risk
 No velocity limit (High turbulent flow) reduces risk of fouling
thus increase heat transfer
 Easily inspection and cleaned – pipe connections are at the
frame plate
 Compact and space saving – no head room required
 Risk of leakage eliminated by the gaskets arrangement
 Adding or removing plates can alter size and capacity
 Lighter in weight
 Damaged plates can be renewed relatively easily
 Easy choice of flow patterns
 Single frame can be used for several cooling in different fluid –
central cooling Mohd. Hanif Dewan, Senior Lecturer, IMA,

Disadvantages of Plate Heat Exchanger:
 Deteriorating gaskets are difficult to remove and bending a
new joints
 Any scratches or markings – careless cleaning – erosion
which leads to perforation of the plate and contamination
 Heavier than equivalent size tubular heat exchanger
 Temperature and pressure limitation – pressure 14 bar,
temperature 110/220oC
 Narrow spaces between the plates can cause rapid fouling
thus required frequent cleaning
 i) Turbulent flow causes erosion of cooper based alloy
producing holes in plates, in this case contamination will
occur
ii) Turbulent flow causes large pressure drop

Advantages of Shell & Tube Type
Heat Exchanger:
 Extended heat transfer surface possible using
fins or baffles to compensate for different
specific heat of the fluid
 Defective tubes can be easily plugged
 Less expansive than plate type if using the
same materials

Disadvantages of Shell & Tube
Type Heat Exchanger:
 Fixed size – usually 30% excess
 Spare tube stack may be needed
 Any leakage may cause contamination
 Difficult to clean – tube can be mechanically
cleaned on inside, but outside likely to require
degreasant or descalant solution.

Why we use the PHE instead ofTHE?
- Shell and Tube Heat Exchangers cannot actually
perform in par when we have a low-temperature
or a low-pressure application , the design of the
Plate Heat Exchanger is such that it is best suited
for medium and low pressure fluids because the
driving factor in the concept is surface-area.

As compared to shell and tube heat exchangers, the
temperature approach in a plate heat exchangers may
be as low as 1 °C whereas shell and tube heat
exchangers require an approach of 5 °C or more. For
the same amount of heat exchanged, the size of the
plate heat exchanger is smaller, because of the large
heat transfer area afforded by the plates (the large
area through which heat can travel). Increase and
reduction of the heat transfer area is simple in a plate
heat-exchanger, through the addition or removal of
plates from the stack.

Flow distribution and heat transfer equation:
Design calculations of a plate heat exchanger include
flow distribution and pressure drop and heat transfer.
The former is an issue of Flow distribution in
manifolds.A layout configuration of plate heat exchanger
can be usually simplified into a manifold system with
two manifold headers for dividing and combining fluids,
which can be categorized into U-type and Z-type
arrangement according to flow direction in the headers,
as shown in manifold arrangement.

CENTRAL COOLING

Central Cooling Systems
 These have been design for diesel engine and
steam plant as per diagram shown
 Large sea water cooled heat exchangers, one in
operation the other stand-by are the central
coolers, which having excess cooling capacity to
allow for fouling
 A controlled by pass of the fresh water to be
cooled maintains it at a steady temperature of
35oC up to maximum sea water temperature
of 33oC
Cont - Mohd. Hanif Dewan, Senior Lecturer, IMA,

 Sea water temperature above 330C will
result in an increase in fresh water
temperature.
 The system is divided into low and high
temperature zones.
 The low temperature zone contains the
coolers which can be arranged in different
ways to suit requirements.
 Automatic by-pass valves are arranged
across each cooler unit which control the
upstream water pressure keeping it
constant irrespective of the number of
coolers

Advantages
 Reduced maintenance due to the fresh water
system having clean, treated water circulating.
The cleaning of the system and component
replacement are reduced to a minimum
 Fewer sea water pipes with attendant corrosion
and fouling problems
 With titanium plate heat exchangers used in the
central coolers cleaning of the coolers is
simplified and corrosion reduced
Cont - Mohd. Hanif Dewan, Senior Lecturer, IMA,

 The higher water speeds possible in the fresh
water system result in reduces pipe dimensions
and installation cost
 The number of valves made of expensive material
is greatly reduced, also cheaper materials can be
used throughout the fresh water system without
fear of corrosion or erosion problems
 With a constant level of temperature being
maintained, irrespective of sea water temperature,
this give stability and economy of operation of the
machinery – no cold starting since part of the
cooling system will be in operation. Reduced
cylinder liner wear, etc.

Disadvantages
 “Setting up” of the system may be difficult
 Leakage, causing contamination in one H/E
can foul the whole system
 Loss of fresh water due to pipe or fitting
failure will effect the whole system

Corrosion in Heat Exchangers:
 Uniform or general corrosion
 Galvanic or two-metal corrosion
 Pitting corrosion
 Selective leeching or de-alloying
 Erosion corrosion; fretting & cavitation
 Stress-corrosion cracking

Galvanic Corrosion
 Noble or Cathodic
 Platinum
 Gold,Titanium
 Silver
 Stainless steel
 Bronze/Copper/Brass
 Cast Iron
 Steel
 Aluminium
 Zinc
 Magnesium
 Active or Anodic
Electrolyte
Copper
Zinc

Isolation of dissimilar metals by electrical
insulation.

Prevention of Galvanic Corrosion
 Use a single material or a combination of materials that
are close in the galvanic series.
 Avoid the use of a small ratio of anode area to cathode
area. Use equal areas or a large ratio of anode to cathode
area.
 Electrically insulate dissimilar metals where possible.This
recommendation is illustrated in figure.A flanged joint is
equipped with bolts contained in insulating sleeves with
insulating washers under the head and nut. Paint, tape, or
asbestos gasket material are alternative insulations.
 Local failure of the protective coating, particularly at the
anode, can result in the small anode-to-cathode area
syndrome marked by accelerated galvanic corrosion.
Maintain all coatings in good condition, especially at the
anode.

 Decrease the corrosion characteristics of the fluid
where possible by removing the corrosive agents or
adding inhibitors.
 Avoid the use of threaded or riveted joints in favor of
welded or brazed joints. Liquids or spilled moisture can
accumulate in thread grooves or lap interstices and form
a galvanic cell.
 Design for readily replaceable anodic parts or, for long
life, make the anodic parts more substantial than
necessary for the given stress conditions.
 Install a sacrificial anode lower in the galvanic series than
both the metals involved in the process equipment.

Pitting Corrosion
 Pitting corrosion is the
phenomenon whereby an
extremely localized attack
results in the formation of
holes in the metal surface
that eventually perforate
the wall.The holes or pits
are of various sizes and
may be isolated or
grouped very closely
together.

Selective Leeching
 Selective leaching is the term used to describe a
corrosion process wherein one element is removed
from a solid alloy.The phenomenon occurs
principally in brasses with a high zinc content
(dezincification) and in other alloys from which
aluminum, iron, cobalt, chromium, and other
elements are removed.
 Grey cast iron is subject to leeching known as
graphitization, whereby the iron is dissolved leaving
behind a weak porous graphite network.

Prevention of Selective Leeching
 The only effective method of preventing corrosion
by selective leaching is to avoid the use of materials
known to be subject to it in association with the
fluids concerned. Brasses with high zinc content (>
35 percent) in acid environments are particularly
susceptible.

Erosion Corrosion
 Erosion corrosion is the term used to describe
corrosion that is accelerated as a result of an
increase in the relative motion between the
corrosive fluid and a metal wall.The process is
usually a combination of chemical or
electrochemical decomposition or dissolution
and mechanical wear action.

Erosion Corrosion of CondenserTubeWall

Prevention of Erosion Corrosion
 Use materials with superior resistance to
erosion corrosion.
 Design for minimal erosion corrosion.
 Change the environment.
 Use protective coatings.
 Provide cathodic protection

Cavitation Erosion
 Cavitation erosion is a special class of
erosion corrosion that is associated with
the periodic growth and collapse of
vapour bubbles in liquids.

Fretting Corrosion
 Fretting corrosion occurs at the contact points
of stressed metallic joints that are subject to
vibration and slight movement. It is also called
friction oxidation, wear oxidation, chafing, and false
brinelling. Fretting corrosion to be a special case
of erosion corrosion occurring in air rather
than aqueous conditions.

Tube-tube-sheet &Tube-baffle Fretting

Theories of Fretting Corrosion

Essential Elements for Fretting Corrosion
 A loaded interface.Tube-tube-sheet joints are
heavily loaded by the strains induced in rolling
the tubes in the tube-sheet.
 Vibration or repeated relative motion
between the two surfaces.
 The load and relative motion of the interface
must be sufficient to produce slip or
deformation on the surfaces.

Prevention of Fretting Corrosion
 Eliminate vibration
 Eliminate high-stress interface
 Lubricate the joint
 Use hard surface
 Increase friction at the interface
 Use soft metallic or non-metallic interface
gaskets

Stress Corrosion
 Stress corrosion is the name given to the
process whereby cracks appear in metals
subject simultaneously to a tensile stress and
specific corrosive media.The metal is generally
not subject to appreciable uniform corrosion
attack but is penetrated by fine cracks that
progress by expanding over more of the surface
and proceeding further into the wall.

Prevention of Stress Corrosion
 Reducing the fluid pressure or increasing the wall
thickness.
 Relieve residual stress by annealing.
 Change the metal alloy to one that is less subject to
stress-corrosion cracking. E.g. carbon steel is more
resistant than stainless steel to corrosion cracking in a
chloride-containing environment, but less resistant to
uniform corrosion. Replacing stainless steel with an alloy
of higher nickel content is often effective.

 Modify the corrosive fluid by process
treatment or the addition of corrosion
inhibitors such as phosphates.
 Apply cathodic protection with sacrificial
anodes or external power supply.
 Use shot peening to induce surface stress.
 Use venting air pockets to avoid
concentration of chloride in the cooling
water

Cleaning & inspection
 For efficient heat transfer, the surface through
which heat transfer take place, must be
maintained clean.
 Coolers and heaters can loose their efficiency
through accumulations of deposits like marine
growths, sludge, mud, sand etc. Such deposits
increase the thickness of the tubes thus
affecting heat transfer.This causes greater
temperature difference between the hot and
cold surfaces and results in high thermal stress
on the tubes.

Mechanical/Chemical Cleaning
 Mechanical by manual and by brush
 Chemical by circulation

Protection against Corrosion
 Sacrificial anodes
 Coating
 Impressed current
 Chemical

Sacrificial Anodes
 Galvanic action
 Sacrificial anodes – aluminium, zinc, soft
iron
 Anodes corrode away

Coating
 Coatings – rubber, bitumen or epoxy
 Also use for seawater pipes

Impressed Current System
 A technique to reduce corrosion of a
metal surface by passing sufficient
cathodic current to it to cause anodic
dissolution rate to become negligible
 Cathodic protection
 Inert anodes – lead silver with platinum
 Initial use to protect the hull

Ferrous Sulphate
 Protective film of oxide
 Self healing
 Break down if turbulence is too great

Usual Causes of Tube Failure
 Tube & tube plate
 General wastage
 Deposit attack
 Anaerobic attack
 Erosion

Protection Against Impingement Attack

Cleaning & Inspection
 Cold fluid side
◦ Algea slimes
◦ Marine growth
◦ Silt, sand
◦ Scales
 Hot fluid side
◦ Sludge

Alkaline
 Cheap
 Non-toxic
 Non-inflammable
 Requires heating to 70ºC to 100ºC
 Least efficient of the three degreasant types
 May attack aluminium and zinc
 Requires care-prevent contact with skin,
eyes, etc

Hydrocarbon
 Toxic and/or narcotic
 Some inflammable (except in chlorinated
ones)
 Highly volatile - ensure good ventilation of
space
 Use as cold liquid or vapour.
 More efficient than alkalis

Solvent Emulsion
 Toxic
 Generally used at 50º to 60ºC
 May be combined with acids or alkalis to
help scale removal or augment cleaning
process
 Most efficient of the three types.

Any Question?
Thank you.

Heat Exchanger Design and Operation

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Heat Exchanger Design and Operation