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Heat exchanger

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Air-cooled heat exchangers are usually used when the heat exchanger outlet temperature is at least 20 oF above the maximum expected ambient air temperature. – PowerPoint PPT presentation

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Title: Heat exchanger


1
Heat exchanger
  • The word exchanger really applies to all types of
    equipment in which heat is exchanged but
  • is often used specially to denote equipment in
    which heat is exchanged between two process
  • Streams.

2
These heat exchanger may be classified according
to
  • Transfer process
  • 1. Direct contact
  • 2. indirect contact
  • (a) Direct transfer type
  • (b) Storage type
  • (c) Fluidized bed

3
Surface compactness
  • 1. Compact (surface area density 700m2m3)
  • 2. non-compact (surface area density lt 700m2m3)

4
Construction
  • 1. Tubular
  • (a) Double pipe
  • (b) Shell and tube
  • (c) Spiral tube
  • 2. Plate
  • (a) Gasketed
  • (b) Spiral plate
  • (c) Welded plate
  • 3. Extended surface
  • (a) Plate fin
  • (b) Tube fin
  • 4. Regenerative
  • (a) Rotory
  • i. Disc-type
  • ii. Drum-type
  • (b) Fixed-matrix

5
Flow arrangement
  • 1. Single pass
  • (a) Parallel flow
  • (b) Counter flow
  • (c) Cross flow
  • 2. Multipass
  • (a) Extended surface H.E.
  • i. Cross counter flow
  • ii. Cross parallel flow
  • (b) Shell and tube H.E.
  • i. Parallel counter flow (Shell and fluid
    mixed, M shell pass, N Tube pass)
  • ii. Split flow
  • iii. Divided flow
  • (c) Plate H.E. (N-parallel plate multipass)

6
Number of fluids
  • 1. Two-fluid
  • 2. Three fluid
  • 3. N-fluid (N gt 3)

7
Transfer mechanisms
  • 1. Single phase convection on both sides
  • 2. Single phase convection on one side, two-phase
    convection on the other side
  • 3. Two-phase convection on both sides
  • 4. Combined convection and radiative heat
    transfer

8
Classification based on service
  • single phase (such as the cooling or heating of a
    liquid or gas)
  • two-phase (such as condensing or vaporizing).
  • Since there are two sides to an STHE, this can
    lead to several combinations of services.
    Broadly, services can be classified as follows
  • single-phase (both shellside and tubeside)
  • condensing (one side condensing and the other
    single-phase)
  • vaporizing (one side vaporizing and the other
    side single-phase) and
  • condensing/vaporizing (one side condensing and
    the other side vaporizing). The following
    nomenclature is usually used

9
  • Heat exchanger both sides single phase and
    process streams (that is, not a utility).
  • Cooler one stream a process fluid and the other
    cooling water or air. Dirty water can be used as
    the cooling medium. The top of the cooler is open
    to the atmosphere for access to tubes. These can
    be cleaned without shutting down the cooler by
    removing the distributors one at a time and
    scrubbing the tubes.
  • Heater one stream a process fluid and the other
    a hot utility, such as steam or hot oil.
  • Condenser one stream a condensing vapor and the
    other cooling water or air.
  • Chiller one stream a process fluid being
    condensed at sub-atmospheric temperatures
  • and the other a boiling refrigerant or
    process stream. By cooling the
  • falling film to its freezing point,
    these exchangers convert a variety of chemicals
  • to the solid phase. The most common
    application is the production of sized ice
  • and paradichlorobenzene. Selective
    freezing is used for isolating isomers. By
  • melting the solid material and
    refreezing in several stages, a higher degree of
  • purity of product can be obtained.
  • Reboiler one stream a bottoms stream
    from a distillation column and the
  • other a hot utility (steam or hot oil) or a
    process stream.
  • Evaporators These are used extensively
    for the concentration of ammonium nitrate, urea,
    and other chemicals sensitive to heat when
    minimum contact time is desirable.
  • Air is sometimes introduced in the tubes to
    lower the partial pressure of liquids whose
    boiling points are high.
  • These evaporators are built for pressure
    or vacuum and with top or bottom vapor removal.

10
  • Absorbers These have a two-phase flow system.
    The absorbing medium is
  • put in film flow during its fall downward
    on the tubes as it is cooled by a cooling
  • medium outside the tubes. The film absorbs
    the gas which is introduced into
  • the tubes. This operation can be cocurrent
    or countercurrent.
  • Falling-Film Exchangers Falling-film
    shell-and-tube heat exchangers have been
    developed for a wide variety of services and are
    described by Sack The fluid enters at the top of
    the vertical tubes. Distributors or slotted
    tubes put the liquid in film flow in the inside
    surface of the tubes, and the film adheres to the
    tube surface while falling to the bottom of the
    tubes. The film can be cooled, heated,
    evaporated, or frozen by means of the proper
    heat-transfer medium outside the tubes. Tube
    distributors have been developed for a wide range
    of applications. Fixed tube sheets, with or
    without expansion joints, and outside-packed-head
    designs are used.
  • Principal advantages are high rate of heat
    transfer, no internal pressure
  • drop, short time of contact (very
    important for heat-sensitive materials), easy
  • accessibility to tubes for cleaning, and,
    in some cases, prevention of leakage
  • from one side to another.

11
Classification by construction
  • The principal types of heat exchanger are listed
    again as
  • 1. Tubular exchanger
  • 2. Plate exchanger
  • 3. Extended surface
  • 4. Regenerative

12
2.1.1 Tubular heat exchanger
  • Tubular heat exchanger are generally built of
    circular tubes. Tubular heat exchanger is
  • further classified into
  • Double pipe heat exchanger
  • Spiral tube heat exchanger
  • Shell and tube heat exchanger

13
Double pipe heat exchanger
  • Constructon - This is usually consists of
    concentric pipes. One fluid flow in the inner
    pipe and the other fluid flow in the annulus
    between pipes.
  • The two fluid may flow concurrent (parallel) or
  • in counter current flow configuration
    hence the heat exchanger are classified as
  • counter current double pipe heat exchanger
    cocurrent double pipe heat exchanger
  • Advantages -
  • Is Easily by disassembly, no cleaning problem
  • ii Suitable for high pressure fluid, (the
    pressure containment in the small diameter pipe
  • or tubing is a less costly method compared to a
    large diameter shell.)
  • Limitation
  • The double pipe heat exchanger is generally used
    for the application where
  • the total heat transfer surface area required is
    less than or equal to 20 m2 (215 ft2) because
  • it is expensive on a cost per square meter (foot)
    basis.

14
Spiral tube heat exchanger
  • Spiral tube heat exchanger consists of one or
    more spirally wound coils fitted in a shell .
    Heat transfer associated with spiral tube is
    higher than that for a straight tube .
  • In addition, considerable amount of surface area
    can be accommodated in a given
  • space by spiraling. Thermal expansion is no
    problem but cleaning is almost impossible.

15
  • Advantages
  • Inexpensive
  • True countercurrent or co-current flow
  • Easily designed for high pressure service
  • Disadvantages
  • Difficult to clean on shell side.
  • Only suitable for small sizes. They are
    generally not economical if UA gt 50,000
    Btu/hr-oF.
  • Thermal expansion can be an issue.
  • Typical Applications
  • Single phase heating and cooling when the
    required heat transfer area is small.
  • Can be used for heating using condensing steam if
    fabricated with elbows to allow expansion.

16
  • HAIRPIN HEAT EXCHANGERS
  • The hairpin heat exchanger design is similar to
    that of double pipe heat exchangers with multiple
    tubes inside one shell. The design provides the
    flexibility of a U-tube design with an extended
    shell length that improves the exchangers
    ability to achieve close temperature approaches.
  • Advantages
  • Good countercurrent or co-current flow good
    temperature approach. Can be designed with
    removable shell to allow cleaning inspection.
    Use of finned tubes results in compact design for
    shellside fluids with low heat transfer
    coefficients. Easily designed for high pressure
    service. Able to handle large temperature
    difference between the shell and tube sides
    without using expansion joints. All connections
    are at one end of the exchanger.
  • Disadvantages Designs are proprietary
    limited number of manufacturers. Relatively
    expensive. Limited size Not economical if UA
    gt 150,000 Btu/hr-oF.
  • Applications
  • Single phase heating and cooling when the
    required heat transfer area is relatively small.
    Often found in high pressure services and where
    there is a large temperature difference between
    the shell and tubeside fluids.

17
Shell and tube heat exchanger
18
Shell and tube heat exchanger is built of round
tubes mounted in a cylindrical shell with the
tube axis parallel to that of the shell. One
fluid flow inside the tube, the other flow across
and along the tubes. The major components of the
shell and tube heat exchanger are tube bundle,
shell, front end head, rear end head, baffles and
tube sheets
19
  • The shell and tube heat exchanger is further
    divided into three categories as
  • 1. Fixed tube sheet
  • 2. U tube
  • 3. Floating head

20
Fixed tubesheet
  • A fixed-tubesheet heat exchanger has straight
    tubes that are secured at both ends to tubesheets
    welded to the shell. The construction may have
    removable channel covers , bonnet-type channel
    covers , or integral tubesheets.
  • Advantage
  • The fixedtubesheet construction is its low cost
    because of its simple construction. In fact, the
    fixed tubesheet is the least expensive
    construction type, as long as no expansion joint
    is required.

21
  • tubes can be cleaned mechanically after removal
    of the channel cover
  • or bonnet, and that leakage of the shell side
    fluid is minimized since there
  • are no flanged joints.
  • Disadvantage
  • This design is that since the bundle is fixed to
    the shell and cannot be
  • removed, the outsides of the tubes cannot be
    cleaned mechanically.
  • Thus, its application is limited to clean
    services on the shell side.
  • However, if a satisfactory chemical cleaning is
    designed can be employed, fixed-tubesheet
    construction may be selected for fouling services
    on the shell side.
  • In the event of a large differential temperature
    between the tubes and the shell, the tubesheets
    will be unable to absorb the differential stress,
    thereby making it necessary to
  • Incorporate an expansion joint. This takes away
    the advantage of low cost to a significant
    extent.

22
U-tube
  • As the name implies, the tubes of a U-tube heat
    exchanger are bent in the shape of a U.
  • There is only one tubesheet in a Utube heat
    exchanger. However, the lower cost for the single
    tubesheet is offset by the additional costs
    incurred for the bending of the tubes and the
    somewhat larger shell diameter (due to the
    minimum U-bend radius), making the cost of a
    U-tube heat exchanger comparable to that of a
    fixed tubesheet exchanger.

23
  • Advantage
  • U-tube heat exchanger as one end is free, the
    bundle
  • can expand or contract in response to stress
    differentials.
  • In addition, the outsides of the tubes can be
    cleaned, as the tube bundle can be removed.
  • Disadvantage
  • U-tube construction is that the insides of the
    tubes cannot be
  • cleaned effectively, since the U-bends would
    require
  • flexible-end drill shafts for cleaning. Thus,
    U-tube heat exchangers should not be used for
    services with a dirty fluid inside tubes.

24
Floating head
  • The floating-head heat exchanger is the most
    versatile type of STHE, and also the costliest.
  • In this design, one tubesheet is fixed relative
    to the shell, and the other is free to float
    within the shell. This permits free expansion of
    the tube bundle, as well as cleaning of both the
    insides and outsides of the tubes. Thus,
    floating-head SHTEs can be used for services
    where both the shell side and the tube side
    fluids are dirty-making

25
The standard construction type used in dirty
services, such as in petroleum refineries. There
are various types of floating- head construction.
The two most common are the pull-through with
backing device and pull through without backing
service designs. The design with backing service
is the most common configuration in the chemical
process industries (CPI). The floating-head cover
is secured against the floating tubesheet by
bolting it to an ingenious split backing ring.
This floating-head closure is located beyond the
end of the shell and contained by a shell cover
of a larger diameter. To dismantle the heat
exchanger, the shell cover is removed first, then
the split backing ring, and then the
floating-head cover, after which the tube bundle
can be removed from the stationary end.
26
  • In the design without packing service
    construction (Figure 2.8), the entire tube
    bundle, including the floating-head assembly, can
    be removed from the stationary end, since the
    shell diameter is larger than the floating-head
    flange. The floatinghead cover is bolted
  • directly to the floating tubesheet so that a
    split backing ring is not required.
  • The advantage of this construction is that the
    tube bundle may be removed from the shell without
    removing either the shell or the floatinghead
    cover, thus reducing maintenance time. This
    design is particularly suited to kettle reboilers
    having a dirty heating medium where Utubes cannot
    be employed. Due to the enlarged shell, this
    construction has the highest
  • cost of all exchanger types.

27
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28
Plate heat exchangers
  • These exchangers are generally built of thin
    plates. The plate are either smooth or have
  • some form of corrugations and they are either
    flat or wound in exchanger. Generally
  • theses exchanger cannot accomodate high
    pressure/temperature differential relative the
  • tubular exchanger.

29
  • This type of exchanger is further classified as
  • Gasketed plate
  • Fixed plate
  • Spiral plate

30
Gasketed plate heat exchanger
  • Gasketed plate heat exchanger consists of a
    series of corrugated alloy material channel
    plates, bounded by elastomeric gaskets are hung
    off and guided by longitudinal carrying bars,
    then compressed by large-diameter tightening
    bolts between two pressure retaining frame plates
    (cover plates)

31
Construction
  • The frame and channel plates have portholes which
    allow the process fluids to enter alternating
    flow passages (the space between two
    adjacent-channel plates) Gaskets around the
    periphery of the channel plate prevent leakage to
    the atmosphere and also prevent process fluids
    from coming in contact with the frame plates. No
    inter fluid leakage is possible in the port area
    due to a dual-gasket seal.
  • Expansion of the initial unit is easily performed
    in the field without special considerations.
  • The original frame length typically has an
    additional capacity of 15-20 percent more
  • channel plates (i.e. surface area). In fact, if a
    known future capacity is available during
  • fabrication stages, a longer carrying bar could
    be installed, and later, increasing the
  • surface area would be easily handled.
  • When the expansion is needed, simply untighten
    the carrying bolts, pull back the frame plate,
    add the additional channel plates, and tighten
    the frame plate.

32
  • Applications
  • Most PHE applications are liquid-liquid services
    but there are numerous steam heater and
    evaporator uses from their old ages in the food
    industry.
  • Industrial users typically have chevron style
    channel plates while some food applications are
    washboard style.
  • Fine particulate slurries in concentrations up to
    70 percent by weight are possible with standard
    channel spacing's.
  • Wide-gap units are used with larger particle
    sizes.
  • Typical particle size should not exceed 75
    percent of the single plate (not total channel)
    gap.
  • Close temperature approaches and tight
    temperature control possible with PHEs and the
    ability to sanitize the entire heat transfer
    surface easily were a major benefit in the food
    and pharmaceutical industry.

33
  • Advantages -
  • Easily assembled and dismantled
  • Easily cleaned both chemically and mechanically
  • Flexible (the heat transfer can be changed as
    required)
  • Can be used for multiple service as required
  • Leak is immediately deteced since all plates
    are vented to the atmosphere, and the
  • fluid split on the floor rather than mixing
    with other fluid
  • Heat transfer coefficient is larger and hence
    small heat transfer area is required than STHE
  • The space required is less than that for STHE
    for the same duty
  • Less fouling due to high turbulent flow
  • Very close temperature approach can be obtained
  • low hold up volume
  • LMTD is fully utilized
  • More economical when material cost are high

34
  • Disadvantages -
  • Low pressure lt30 bar (plate deformation)
  • Working temperature of lt (500 F) 250 oC
    (maximum gasket temperature)

35
Welded- and Brazed-Plate exchanger
  • To overcome the gasket limitations, PHE
    manufacturers have developed welded-plate
  • exchangers. There are numerous approaches to this
    solution weld plate pairs together
  • with the other fluid-side conventionally
    gasketed, weld up both sides but use a horizontal
  • nickel brazing, diffusion bond then pressure form
    plates and bond etched, passage plates
  • Typical applications include district heating
    where the low cost and minimal maintenance
  • have made this type of heat exchanger especially
    attractive.

36
Most methods of welded-plate manufacturing do not
allow for inspection of the heattransfer surface,
mechanical cleaning of that surface, and have
limited ability to repair or plug off damage
channels. Consider these limitations when the
fluid is heavily fouling, has solids, or in
general the repair or plugging ability for severe
services.
37
PLATE FRAME HEAT EXCHANGERS A plate and
frame heat exchanger is a compact heat exchanger
where thin corrugated plates are stacked in
contact with each other, and the two fluids flow
separately along adjacent channels in the
corrugation. The closure of the stacked plates
may be by clamped gaskets, brazed (usually copper
brazed stainless steel), or welded (stainless
steel, copper, titanium), the most common type
being the first, for ease of inspection and
cleaning.
  • Advantages
  • Very compact design
  • High heat transfer coefficients (2 4 times
    shell tube designs)
  • Expandable by adding plates
  • Ease of maintenance
  • Plates manufactured in many alloys
  • All connections are at one end of the exchanger
  • Good temperature approaches
  • Fluid residence time is very short
  • No dead spots
  • Leakage (if it should occur) is generally to the
    outside not between the fluids
  • Low fouling due to high turbulence

38
  • Disadvantages
  • Designs are proprietary limited number of
    manufacturers
  • Gaskets limit operating pressures and
    temperatures require good maintenance
  • Typical maximum design pressures are 150-250
    psig.
  • Gasket compatible with fluids are not always
    available
  • Poor ability to handle solids due to close
    internal clearances
  • High pressure drop
  • Not suitable for hazardous materials
  • Not suitable in vacuum service.
  • Typical Applications
  • Low pressure and temperature single phase heating
    and cooling when fluids are not hazardous, a high
    pressure drop can be tolerated and alloys are
    required for the fluids being handled.

39
Spiral Plate Exchanger (SPHE)
  • SPHEs offer high reliability and on-line
    performance in many severely fouling services
    such as slurries.
  • CONSTRUCTION -
  • The SHE is formed by rolling two strips of plate,
    with welded-on spacer studs, upon each other into
    clock-spring shape and This forms two passages.
    Passages are sealed off on one end of the SHE by
    welding a bar to the plates hot and cold fluid
    passages are sealed off on opposite ends of the
    SHE.
  • A single rectangular flow passage is now formed
    for each fluid, producing very high shear rates
    compared to tubular designs. Removable covers are
    provided on each end to access and clean the
    entire heat transfer surface.

40
  • Pure countercurrent flow is achieved and LMTD
    correction factor is essentially 1.0.
  • Since there are no dead spaces in a SHE, the
    helical flow pattern combines to entrain any
    solids and create high turbulence creating a
    self-cleaning flow passage. There are no
    thermal-expansion problems in spirals. Since the
    center of the unit is not fixed, it can torque to
    relieve stress. The SHE can be expensive when
    only one fluid requires high alloy material.

41
  • Since the heat-transfer plate contacts both
    fluids, it is required to be fabricated out of
    the higher alloy. SHEs can be fabricated out of
    any material that can be cold-worked and welded.
    The channel spacings can be different on each
    side to match the flow rates and pressure drops
    of the process design. The spacer studs are also
    adjusted in
  • their pitch to match the fluid characteristics.
    As the coiled plate spirals outward, the plate
    thickness increases from a minimum of 2 mm to a
    maximum (as required by pressure)
  • up to 10 mm. This means relatively thick material
    separates the two fluids compared to tubing of
    conventional exchangers.

42
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43
  • Applications
  • The most common applications that fit SHE are
    slurries. The rectangular channel provides high
    shear and turbulence to sweep the surface clear
    of blockage and causes no distribution problems
    associated with other exchanger types.
  • A localized restriction causes an increase in
    local velocity which aids in keeping the unit
    free flowing. Only fibers that are long and
    stringy cause SHE to have a blockage it cannot
    clear itself.
  • As an additional antifoulant measure, SHEs have
    been coated with a phenolic lining. This provides
    some degree of corrosion protection as well, but
    this is not guaranteed due to pinholes in the
    lining process.

44
There are three types of SHE to fit different
applications
  • Type I is the spiral-spiral flow pattern It is
    used for all heating and cooling services and
    can accommodate temperature crosses such as
    lean/rich services in one unit. The removable
    covers on each end allow access to one side at a
    time to perform maintenance on that fluid side.
    Never remove a cover with one side under
  • pressure as the unit will telescope out like a
    collapsible cup.
  • Type II units are the condenser and reboiler
    designs One side is spiral flow and the other
    side is in cross flow. These SHEs provide very
    stable designs for vacuum condensing and
    reboiling services. A SHE can be fitted with
    special mounting connections for reflux-type
    ventcondenser applications. The vertically
    mounted SHE directly attaches on the column or
    tank.
  • Type III units are a combination of the Type I
    and Type II where part is in spiral flow and
    part is in cross flow. This SHE can condense and
    subcool in a single unit. The unique channel
    arrangement has been used to provide on-line
    cleaning, by switching fluid sides to clean the
    fouling (caused by the fluid that previously
    flowed there) off the surface. Phosphoric acid
    coolers use pond water for cooling and both sides
    foul water, as you expect, and phosphoric acid
    deposit crystals. By
  • reversing the flow sides, the water dissolves the
    acid crystals and the acid clears up the organic
    fouling. SHEs are also used as oleum coolers,
    sludge coolers/ heaters, slop oil heaters, and in
    other services where multiple flow- passage
    designs have not performed well.

45
SPIRAL PLATE HEAT EXCHANGERS Spiral plate
heat exchangers are fabricated from two metal
plates that are wound around each other. One
process fluid stream enters the exchanger at the
centre and flows outwards while the second fluid
enters on the outside and flows inward. This
creates almost a true countercurrent flow.
  • Advantages
  • Single flow paths reduce fouling rates
    associated with fluids containing solids.
  • Ability to handle two highly fouling fluids
  • No dead spots for solids to collect inside
    exchanger
  • Countercurrent flow
  • Manufactured in many alloys
  • Very low pressure drop

46
  • Disadvantages
  • Designs are proprietary limited number of
    manufacturers
  • Generally more expensive than shell tube
    designs
  • Typical Applications
  • 1. Liquid/liquid heating, cooling or heat
    recovery, where one or both of the fluids may
    cause fouling.
  • 2. Vapour/liquid condensing, particularly at
    very low pressure and/or high-volume flow.

47
  • SPIRAL TUBE HELIFLOW HEAT EXCHANGERS
  • Spiral tube type heat exchangers are fabricated
    from coiled tubing. In some cases the tubing is
    installed inside a fabricated bundle to provide a
    compact stand alone heat exchanger.
  • These exchangers are used primarily for small
    services such as pump seal fluid and sample
    coolers.
  • See attached article "Graham Spiral Flow Heat
    Exchangers.pdf" for a more detailed description.
  • Advantages
  • Compact very inexpensive exchanger for small
    applications
  • Can handle high pressures
  • Disadvantages
  • Designs are proprietary limited number of
    manufacturers

48
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49
AIR COOLED HEAT EXCHANGERS
  • locations where there is a shortage of cooling
    water.
  • Air-cooled heat exchangers are usually used when
    the heat exchanger outlet temperature is at least
    20 oF above the maximum expected ambient air
    temperature. They can be designed for closer
    approach temperatures, but often become expensive
    compared to a combination of a cooling tower and
    a water-cooled exchanger.
  • Air cooled heat exchangers use electrically
    driven fans to move air across a bank of tubes.
    There are two basic arrangements
  • Induced draft Fans draw air through the tube
    banks.
  • Forced draft Fans blow air through the tube
    banks.
  • Air cooled exchangers are expensive compared to
    water cooled exchangers due to their large size,
    low heat transfer coefficients on the air size,
    and structural and electrical requirements. In
    addition air cooler exchangers require large plot
    areas and must be designed to handle diurnal and
    seasonal changes in air temperature.
  • The very low heat transfer coefficient associated
    with air on the outside of the tubes is partially
    overcome through extensive use of finned tubes to
    increase the outside surface area.

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51
Changes in ambient air temperatures are often
handled by using variable speed or pitch fans to
adjust the air flow. In cold climates, it may be
necessary to design in the ability to recirculate
air to prevent freezing in the process. Smaller
units (similar to radiators) are available and
commonly used for small duty applications.
  • Advantages
  • Do not use water for cooling
  • Disadvantages
  • Requires large plot area
  • Expensive
  • Fins can plug in "dirty" environments
  • Fans can be noisy
  • Typical Applications
  • Cooling and condensing where cooling water is
    unavailable or is uneconomical to use.

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53
Extended surface
  • The tubular and plate exchangers described
    previously are all prime surface heat exchangers.
    The design thermal effectiveness is usually 60
    and below and the heat transfer area density is
    usually less than 300 m2/m3. In many application
    an effectiveness of up to 90 is essential and
    the box volume and mass are limited so that a
    much more compact surface is mandated.
  • Usually either a gas or a liquid having a low
    heat transfer coefficient is the fluid on one or
    both sides. This results in a large heat transfer
    area requirements. for low density fluid (gases),
    pressure drop constraints tend to require a large
    flow area. so a question arises how can we
    increase both the surface area and flow area
    together in
  • a reasonably shaped configuration. The
    surface area may be increased by the fins. The
    flow area is increased by the use of thin gauge
    material and sizing the core property.
  • There are two most common types of extended
    surface heat exchangers.

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Plate fin
  • Plate -fin heat exchanger has fins or spacers
    sandwiched between parallel plates (refereed to
    as parting plates or parting sheets) or formed
    tubes.
  • While the plates separate the two fluid streams,
    the fins form the individual flow passages. Fins
    are used on both sides in a gas-gas heat
    exchanger. In gas-liquid applications fins are
    used in the gas side.

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Tube fin
  • In tube fin heat exchanger, tubes of round,
    rectangular, or elliptical shape are generally
    used. Fins are generally used on the outside and
    also used inside the tubes in some applications.
    they are attached to the tube by tight mechanical
    fit, tension wound, gluing,
  • soldering, brazing, welding or extrusion.
    Tube fin exchanger
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