The document discusses heat exchangers used in marine engineering. It describes the two main types - shell and tube heat exchangers and plate heat exchangers. Shell and tube heat exchangers consist of tubes bundled inside a shell, with water boxes at each end to distribute the cooling medium. Plate heat exchangers are made of pressed plates with corrugations to aid heat transfer, held within a frame. The document provides details on construction, materials used, temperature control, corrosion control and cleaning methods for both types of heat exchangers.

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Reynold’s No= Density x Velocity of fluid flow X Pipe diameter
Kinematic Viscosity
 Reynolds No < 2000 the fluid is Laminar
 Reynolds No > 2500 the fluid is Turbulent
Types of Flow
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For Water

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Flow Pattern
Heat exchanger is classified as heater
and cooler from the function point of
view, and as shell and tube and plate
type from structure point of view.
The heat exchanger mediums could be
two liquids or liquid and air or steam
and liquid or electricity and fluid. One
of cooler type may be immersed type as
duct cooler or keel cooler.
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Where :
 Q is total heat transfer
 K is the Thermal conductivity
 x is the wall thickness
 θ is the logarithmic mean temperature difference
Heat transfer
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Shell & tube type

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Construction
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Shell & Tube
Finned Tubes
In recent designs of tube heaters and coolers
the guided flow concept has been introduced,
i.e. a secondary heating or cooling, surface in
the form of radial fins integral with the tubes
between which flow is guided radially,
alternately out and in from section to section.
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The joint arrangements at the tube plate ends are different. At the fixed
end, gaskets are fitted between either side of the tube plate and the shell
and end cover. At the other end, the tube plate is free to move with seals
fitted either side of a safety expansion ring.

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Tubes
• Made of aluminum brass (76 per cent copper; 22 per cent zinc ; 2 per cent aluminum) are commonly used .
• The successful use of aluminum brass has apparently depended on the presence of a protective film formed along the
tube length by corrosion of iron in the system .
• Thus unprotected iron in water boxes and other parts, while itself corroding, has prolonged tube life .This was made
apparent when steel was replaced by other corrosion resistant materials or protected more completely .
• The remedy in these systems has been to fit sacrificial soft iron or mild steel anodes in water boxes or to introduce iron
in the form of ferrous sulphate fed into the sea water by dosing the sea water to a strength of 1 ppm for an hour per day
over a few weeks and subsequently to dose before entering and after leaving port for a short period .
• Early tube failures may be due to pollution in coastal waters or to turbulence in some cases.
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• Naval brass tube plates are used with aluminum brass tubes. Other materials found in service are gunmetal, aluminum
bronze and sometimes special alloys .
Tube Plates

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Tubes configuration
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WATER BOXES AND COVERS
• Easily removable covers on water boxes permit repairs and cleaning to be carried out.
• The covers and water boxes are commonly of cast iron or fabricated from mild steel.
• Where they have been coated with rubber or a bitumastic type coating, the iron or steel has been protected but has provided no
protection for the tubes and tube plate. Uncoated ferrous (iron) materials in water boxes provide a protective film on the tubes as
the unprotected iron itself corrodes, the products of corrosion coating the tubes. The iron also gives some measure of cathodic
protection.
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• Headers or water boxes surround the tube plates and enclose the shell. They are arranged for either a single pass or a double pass
of cooling liquid.
• The tube bundle has baffles fitted which serve to direct the liquid to be cooled up and down over the tubes as it passes along the
cooler. The baffles also support the tubes.
• Should either liquid leak past the seal it will pass out of the cooler and be visible. There will be no intermixing or contamination.
• The shell or cylinder is fabricated or cast . It is in contact with the liquid being cooled . This may be oil, with which
there is no corrosion problem, or water, which is normally inhibited against corrosion.

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Shell & Tube Type
Baffles
Shells
Tube plates
Tubes stack
C.W inlet
C.W outlet
Sacrificial anodes
Always Ensure laminar flow is maintained during operation!
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Plate type

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The plate-type heat exchanger is made up of a
number of pressed plates surrounded by seals and
held together in a frame. The inlet and outlet
branches for each liquid are attached to one end
plate.
Construction
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Construction
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The arrangement of seals between the
plates provides passageways between
adjacent plates for the cooling liquid and
the hot liquid. The plates have various
designs of corrugations to aid heat
transfer and provide support for the large,
flat surface. A double seal arrangement is
provided at each branch point with a drain
hole to detect leakage and prevent
intermixing or contamination.
Plate Type
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Joints
The joint material is normally nitrile rubber which is bonded to
the plate with suitable adhesive such as Plibond. Other joint
materials for higher temperatures are available, such as
compressed asbestos fiber.
The nitrile rubber is suitable for temperatures up to about
100°C. At high temperatures the rubber hardens and loses its
elasticity . The rubber joints are compressed when the cooler is
assembled and the clamping bolts tightened .
Overtightening can cause damage to the chevron corrugated
plates so the cooler stack must be tightened, and dimensions
checked, during the process
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Plates
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Plate Type
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 Compact and space saving, virtually no head room required.
 Easily inspected and cleaned, all the pipe connections are at the frame
plate hence they don't have to be disturbed when plates are dismantled.
 Variable capacity, plate number can be altered to meet capacity
requirements.
 With titanium plates there is virtually minimum corrosion or erosion
risk
 Turbulent flow (which is erosive) which takes place between the plates
will increase heat transfer and enable fewer plates to be used.
The major advantage over tube type coolers is that their higher
efficiency is reflected in a smaller size for the same cooling capacity.
Advantages
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HEs Selection
In selection of a heat exchanger certain points should be considered some are:
1. Quantity of fluid, maximum to minimum to be cooled.
2. Range of inlet and outlet temperature of fluid to be cooled.
3. As above for the cooling medium.
• Specific heat of the mediums.
• streamline of turbulent flow.
• Type of medium, corrosive or non corrosive for safety.
4. Operating pressures.
5. Maintenance fouling cleaning access.
6. Position in system and associated pipe work.
7. Cost, material
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Temperature Control

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Temperature control
 Temperature control of coolers is usually achieved by adjusting the cooling liquid outlet valve. The inlet valve is
left open and this ensures a constant pressure within the cooler.
 This is particularly important with sea water cooling where reducing pressure could lead to aeration or the
collecting of air within the cooler.
 Air remaining in a cooler will considerably reduce the cooling effect.
 Methods of controlling temperature of hot liquid when the cooling medium is Sea water are basically are:
1. Bypass a proportion or all of the hot fluid flow.
2. Bypass or limit the sea water flow (outlet v/v only)
3. By spilling part of the sea water discharge back into the pump suction
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Temperature control
M/E Cooler
P & I
controller
Temperature sensor
3-way valve
C.W
inlet
C.W
outlet
Oil inlet
Oil outlet
By pass
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Corrosion Control
1. By using Zinc anodes to avoid galvanic corrosion
2. Using iron headers to have a protective film on the tube stack
3. Avoiding aeration by controlling the flow by throttling on the liquid outlet.
4. Controlling the flow velocity and maintain laminar flow inside the H.E
5. Periodic maintenance and cleaning
6. Avoiding overheating, and hence avoiding scales formation.
7. If the H.E to be reserved for long period, it should be filled with fresh water
8. Tubes to be made of aluminium brass.
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Cleaning Methods
1. Mechanical Cleaning :
by soft brushes ( Avoid damage the protective
Film of the inside of the tubes or plates)
2. Chemical Cleaning:
By an Acid (Hydrochloric Acid) advised by the
maker (depending on the cooled liquid and
cooling medium)
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