HEAT EXCHANGERS

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HEAT EXCHANGERS
GROUP B A.Merve TASKENTLI Tuba NALÇACI
Aysun OKTAY Zeynep ÖZGÜVEN
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OUTLINE

• Definition classification of heat exchangers
• Heat exchangers according to construction
• Plate heat exchangers
• Extended surface heat exchangers
• Tubular heat exchangers
• Heat exchangers according to phase change
• Condensers
• Evaporators

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WHAT IS A HEAT EXCHANGER?
They are devices specifically designed for the
efficient transfer of heat from one fluid to
another fluid over a solid surface.
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WHAT ARE HEAT EXCHANGERS USED FOR?

• They have the function to transfer heat as
  efficiently as possible. Heat exchangers are
  widely used in
• refrigeration
• air conditioning
• space heating
• electricity generation
• chemical processing

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CLASSIFICATION OF HEAT EXCHANGERS

• Heat exchangers may be classified according
  to the following main criteria
• Recuperators and regenerators
• Transfer processes direct contact and indirect
  contact
• Geometry of constructions tubes,plates and
  extended surfaces
• Phase change mechanisms condensers and
  evaporators
• Flow arrangements parallel, counter and cross
  flow

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RECUPERATORS

• The conventional heat exchangers with heat
  transfer between two fluids.
• Hot steam A recovers some of the heat from
  stream B.

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REGENERATORS

• Storage type heat exchangers. The same flow
  passage (matrix) is alternately occupied by one
  of the two fluids.
• Thermal energy is not transfered through the wall.

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TRANSFER PROCESSES
1. Direct contact type heat exchangers

• Heat transfer between the cold and hot fluids
  through a direct contact between these fluids.
• Examples Spray and tray condensers,cooling towers

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2. Indirect contact type heat exchangers

• Heat energy is exchanged between hot and cold
  fluids through a heat transfer surface.
• The fluids are not mixed

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FLOW ARRANGEMENTS

• 1. Paralel Flow Heat Exchangers

• Two fluid streams enter together at one end,
  flow through in the same direction, and leave
  through at the other end

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2. Counter Flow Heat Exchangers

• Two fluid streams flow in opposite directions.

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3. Cross Flow Heat Exchangers

• The direction of fluids are perpendicular to each
  other.

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BASIC CRITERIAS FOR THE SELECTION OF HEAT
EXCHANGERS

• Process specifications
• Service conditions of the plant environment,
  resistance to corrosion by the process
• Maintenance, permission to cleaning and
  replacement of components
• Cost- Effectiveness
• Site requirements, lifting, servicing,capabilitie
  s

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PLATE HEAT EXCHANCERS

• GASKETED PLATE
• SPIRAL PLATE
• LAMELLA

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• Limited to below 25 bar and 250ºC
• Plate heat exchangers have three main types
  gasketed ,spiral heat exchangers and lamella
• The most common of the plate-type heat exchangers
  is the gasketed plate heat exchanger

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GASKETED PLATE HEAT EXCHANGER

• The most common of the plate-type heat exchangers
  is the gasketed plate heat exchanger

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SPIRAL PLATE HEAT EXCHANGER

• Ideal flow conditions and the smallest possible
  heating surface

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LAMELLA

• Consisting of cylindrical shell surrounding a
  number heat transfering lamellas.
• Similar to tubular heat exchanger

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• ADVANTAGES
• Plate heat exchangers yield heat transfer rates
  three to five times greater than other types of
  heat exchangers.
• The design of the plate heat exchanger allows to
  add or remove plates to optimize performance, or
  to allow for cleaning, service, or maintenance
  with a minimum of downtime.
• Plate exchangers offer the highest efficiency
  mechanism for heat transfer available in industry.

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• DISADVANTAGES
• Plate exchangers are limited when high pressures,
  high temperatures, or aggressive fluids are
  present.
• Because of this problem these type of heat
  exchangers have only been used in small, low
  pressure applications such as on oil coolers for
  engines.

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2. EXTENDED SURFACE HEAT EXCHANGERS

• - PLATE FIN HEAT EXCHANGER
• - TUBE FIN HEAT EXCHANGER

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PLATE FIN HEAT EXCHANGER

• For gas to gas applications.
• Widely used in cryogenic, energy recovery,
  process industry, refrigeration and air
  coditioning systems.

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TUBE FIN HEAT EXCAHNGER

• For gas to liquid heat exchangers.
• Used as condersers in electric power plant, as
  oil coolers in propulsive power plants, as ir
  cooled exchangers in process and power industires.

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TUBULAR HEAT 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 no limit to the range of pressures and
  temperatures that can be accommodated.

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SHELL AND TUBE HEAT EXCHANGERS
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SHELL AND TUBE HEAT EXCHANGERS

• are the most commonly used heat exchangers in oil
  refineries and other large chemical processes.
• are used when a process requires large amounts of
  fluid to be heated or cooled.
• provide transfer of heat efficiently.
• use baffles on the shell-side fluid to
  accomplished mixing or turbulence.

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SHELL AND TUBE HEAT EXCHANGERS

• APPLICATIONS
• Oil refining,
• Vapor recovery systems,
• Permanent engines,
• Industrial paint systems.

• tube strong, thermally
• conductive, corrosion
• resistant, high quality
• outer shell durable, highly
• strong
• inner tube having effective
• combination of durability,
• corrosion resistant and
• thermally conductive

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• U - TUBE HEAT EXCHANGERS
• heat exchanger systems consisting of
  straight
• length tubes bent into a U-shape surrounded by a
• shell.

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• U - TUBE HEAT EXCHANGERS
• Both initial and maintenance costs are reduced by
• reducing the number of joints.
• They have drawbacks like inability to replace
• individual tubes except in the outer row and
  inability to
• clean around the bend.

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U - TUBE HEAT EXCHANGERS

• Examples reboilers, evaporators and Kettle
• type.
• They have enlarged shell sections for
• vapor-liquid separation.

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• FIXED TUBE HEAT EXCHANGERS
• have straight tubes that are secured at both
• ends to tube sheets welded to the shell.

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• FIXED TUBE HEAT EXCHANGERS
• They are the most economical type design.
• They have very popular version as the heads
• can be removed to clean the inside of the
• tubes.
• Cleaning the outside surface of the tubes is
• impossible as these are inside the fixed part.
• Chemical cleaning can be used.

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• FLOATING HEAD HEAT EXCHANGER
• one tube is free to float within the shell
  and the other is fixed relative to the shell.

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• FLOATING HEAD HEAT EXCHANGERS
• A floating head is excellent for applications
• where the difference in temperature between
  the
• hot and cold fluid causes unacceptable
  stresses
• in the axial direction of the shell and
  tubes.
• The floating head can move, so it provides the
• possibility to expand in the axial direction.
• Design allows for bundle to be removed for
  inspection,
• cleaning or maintenance.

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• FLOATING HEAD HEAT EXCHANGERS
• Examples kettle boilers which have dirty
• heating medium.
• They have the most highest construction cost of
• all exchanger types.

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• DOUBLE-PIPE HEAT EXCHANGERS
• They consist of one pipe concentrically located
  inside a
• second, larger one.
• Cold and hot liquid respectively
• flows in the gap of inner pipe
• and sleeve pipe.
• Structure is simple and heat
• transmission is large.

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DOUBLE-PIPE HEAT EXCHANGERS

• utilize true counter-current
• flow which maximizes the
• temperature differences
• between the shell side and
• tube side fluids.

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• DOUBLE-PIPE HEAT EXCHANGERS
• When the process calls
• for a temperature cross,
• it is the most efficient
• design and will result in
• fewer sections and less
• surface area.

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• DOUBLE-PIPE HEAT EXCHANGERS
• ADVANTAGES
• Operates in true counter current flow permitting
  extreme temperature cross.
• Economically adaptable to service differentials.
• Ideal for wide temperature ranges and
  differentials.
• Provides shorter deliveries than shell and tube
  due to standardization of design and construction.

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PHASE CHANGE HEAT EXCHANGERS
2.Condensers

• 1.Reboilers
• (Evaporaters)

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• 1)REBOILER
• to generate vapor to drive fractional
  distillation separation
• Most Common Reboilers Types
• Kettle Reboilers
• Forced Recirculation Reboilers
• Thermosiphon Reboiler

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Kettle Reboilers
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• Major factors influence reboiler type selection
• Plot space available
• Total duty required
• Fraction of tower liquid traffic vaporized
• Fouling tendency
• Temperature approach available
• Temperature approach required

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Kettle Reboilers

• Disadvantages
• All the dirt collects and non volatiles
  accumulate
• Shell side is difficult to clean
• Difficult to determine the degree of mixing
• Oversize shell is expensive

• Advantages
• Insensitive to hydrodynamics
• High heat fluxes are possible
• Can handle high vaporization
• Simple piping
• Unlimited area

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Thermosiphon Reboiler
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• Thermosiphon Reboiler
• operate using natural circulation with process
  flow on the shell side
• process flow on the tube or shell side in
  vertical units.
• not require a pump for recirculation
• have sensible heat transfer followed by nucleate
  boiling.

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Forced Recirculation Reboilers
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Forced Recirculation Reboilers

• These reboiler types have two mechanisms of heat
  transfer sensible heat transfer followed by
  nucleate boil-ing.
• Process flow is typically on the tube side of a
  standard exchanger in the vertical position.

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2)CONDENSERS

• b) Air- Cooled Condensers
• Phases
• de-super-heating
• Condensing
• Subcooling

• Water-Cooled Condensensers
• Horizontal shell and tube
• Vertical shell and tube
• Shell and coil
• Double pipe

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Single-Pass Condenser
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SELECT AN WATER-COOLED CONDENSER

• IF
• 1. Adequate water supplies are available from
  tower, city or well sources.
• 2. Water supply is of good quality.
• 3. Heat recovery is not practical or unimportant.
• 4. Plant ambient temperatures consistently exceed
  95F.
• 5. Ambient air is polluted with large dust and
  dirt particles.
• ADVANTAGE DISADVANTAGES
• 1. Offer lower capital investment.
• 2. Operates more efficiently on hot summer days.
• 3. Easier to operate.
• 4. Does not offer summer ventilation.

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SELECT AN AIR-COOLED CONDENSER

• ...WHEN
• 1. Adequate water supply not available from tower
  or well sources.
• 2. Water supply is not of good quality.
• 3. Heat recovery is practical and important.
• 4. Plant ambient temperature will not
  consistently exceed 95F.
• 5. Ambient air is not polluted with large dust
  and dirt particles.
• ADVANTAGE DISADVANTAGES
• 1. Somewhat more costly to purchase and operate.
• 2. Gives less cooling on hot summer days.
• 3. Consumes more electricity.
• 4. Offers summer ventilation and winter
  supplement heating.

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OUTLINE

• Definition classification of heat exchangers
• Heat exchangers according to construction
• Plate heat exchangers
• Extended surface heat exchangers
• Tubular heat exchangers
• Heat exchangers according to phase change
• Condensers
• Evaporators

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• REFERENCES
• Andreone, C.F., Tubular heat exchanger
  inspection, maintenance, and repair, McGraw-Hill,
  NY, 1998
• Couper JR,Penry W.R., Fair J.R., Walas S.M.,
  Chemical Process Equipment, Elsevier Inc, 2005
• Incropera,F.P.,Dewitt D.P., Fundamentals of Heat
  and Mass Transfer, 5th ed.,John Wiley Sons
  Inc., NY,2000
• Kakaç, S. Heat exchangers, CRC Press, Fla, 1998
• Shah, R.K.,Psekulis D., Fundamental of Heat
  Exchanger Design, John Wiley Sons Inc., NY,1999
• http//chentserver.uwaterloo.ca/courses/Che025Lab/
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• http//en.wikipedia.org/wiki/Heat_exchangerFlow_a
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• http//www.advantageengineering.com/fyi/110/advant
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• http//www.buildingdesign.co.uk/mech/guntner/dry-a
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• http//www.engineeringpage.com/heat_exchangers/tem
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• http//www.martechsystems.com/downloads/tech_manag
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• http//www.me.wustl.edu/ME/labs/thermal/me372b5.ht
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• http//www.pacificconsultant.net/compact_heat_exch
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• http//www.rwholland.com/hairpin.htm
• http//www.taftan.com/thermodynamics/EXCHANGE.HTM
• http//www.thomasnet.com/about/exchangers-heat-she
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