Download 130140119088 raval sachin piyushbhai

Government Engineering College
HEAT EXCHANGER
Mechanical Engineering Department
Sub: Heat Transfer
Sub Code:2151909
Presented by:
130140119088 RAVAL SACHIN PIYUSHBHAI
Criteria for the selection of
heat exchanger
– Suitable on the grounds of operating pressure and
temperature, fluid-material compatibility, handling,
extreme thermal conditions
– Estimating the cost of those which may be suitable
General considerations
• Tubes and cylinders can withstand higher pressures than
plates
• If exchangers can be built with a variety of materials,
then it is more likely that you can find a metal which
will cope with extreme temperatures or corrosive fluids
• More specialist exchangers have less suppliers, longer
delivery times and must be repaired by experts
Double pipe heat exchanger
• Normal size
Double-pipe heat exchangers are competitive at
duties requiring 100-200 ft2
• Built of carbon steel where possible
Advantages/disadvantages of double-pipe HE
• Advantages
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Easy to obtain counter-current flow
Can handle high pressure
Modular construction
Easy to maintain and repair
Many suppliers
• Disadvantage
– Become expensive for large duties (above 1MW)
Scope of double pipe HE
• Maximum pressure
– 300 bar(abs) (4500 psia) on shell side
– 1400 bar(abs) (21000 psia) on tubeside
• Temperature range
– -100 to 600oC (-150 to 1100oF)
– possibly wider with special materials
• Fluid limitations
– Few since can be built of many metals
• Maximum ε = 0.9
• Minimum ΔT = 5 K
Shell and tube heat exchanger
• Size per unit 100 - 10000 ft2 (10 - 1000 m2)
• Easy to build multiple units
• Made of carbon steel where possible
Advantages/disadvantages of S&T
• Advantages
– Extremely flexible and robust design
– Easy to maintain and repair
– Can be designed to be dismantled for cleaning
– Very many suppliers world-wide
• Disadvantages
– Require large plot (footprint) area - often need
extra space to remove the bundle
– Plate may be cheaper for pressure below 16 bar
(240 psia) and temps. below 200oC (400oF)
Scope of shell and tube
(Essentially the same as a double pipe)
• Maximum pressure
– 300 bar(abs) (4500 psia) on shell side
– 1400 bar(abs) (21000 psia) on tubeside
• Temperature range
– -100 to 600oC (-150 to 1100oF)
– possibly wider with special materials
• Fluid limitations
– Few since can be built of many metals
• Maximum ε = 0.9 (less with multipass)
• Minimum ΔT = 5 K
Plate and frame heat exchanger
• Plates pressed from stainless steel or
higher grade material
– titanium
– incoloy
– hastalloy
• Gaskets are the weak point.Made of
– nitrile rubber
– hypalon
– viton
– neoprene
Advantages of plate and frame HE
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High heat transfer - turbulence on both sides
High thermal effectiveness - 0.9 - 0.95 possible
Low ΔT - down to 1K
Compact - compared with a S&T
Cost - low because plates are thin
Accessibility - can easily be opened up for inspection
and cleaning
• Flexibility - Extra plates can be added
• Short retention time with low liquid inventory hence
good for heat sensitive or expensive liquids
• Less fouling - low r values often possible
Disadvantages of plate & frame HE
• Pressure - maximum value limited by the sealing of
the gaskets and the construction of the frame.
• Temperature - limited by the gasket material.
• Capacity - limited by the size of the ports
• Block easily when solids in suspension unless special
wide gap plates are used
• Corrosion - Plates good but the gaskets may not be
suitable for organic solvents
• Leakage - Gaskets always increase the risk
• Fire resistance - Cannot withstand prolonged fire
(usually not considered for refinery duties)
Scope of plate & frame HE
• Maximum pressure
– 25 bar (abs) normal (375 psia)
– 40 bar (abs) with special designs (600 psia)
• Temperature range
– -25 to +1750C normal (-13 to +3500F)
– -40 t0 +2000C special (-40 to +3900F)
• Flow rates
up to 3,500 m3/hour can be accommodated in standard
units
• Fluid limitations
– Mainly limited by gasket
• Maximum ε = 0.95
• Minimum ΔT = 1 K
Principal Applications
 Gasketed plate and frame heat exchangers have a large
range of applications typically classified in terms of the
nature of the streams to be heated/cooled as follows:
 Liquid-liquid.
 Condensing duties.
 Evaporating duties.
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Gasketed units may be used in
refrigeration
heat pump plants and
extensively used in the processing of food and drinks.
Comparison with Shell and Tube Heat
Exchangers
In quantitative terms, 200 m2 of heat transfer surface
requires a plate and frame heat exchanger approximately
 3 metres long,
 2 metres high and
 1 meter wide.
For a tubular heat exchanger achieving the same effect, some
600 m2 of surface would be required in a shell
 5 metres long and
 1.8 metre in diameter,
 plus the extra length
 needed for tube bundle removal.
Welded plates heat exchanger
• Wide variety of proprietary types each with one or
two manufactures
• Overcomes the gasket problem but then cannot be
opened up
• Pairs of plates can be welded and stacked in
conventional frame
• Conventional plate and frame types with all-welded
(using lasers) construction have been developed
• Many other proprietary types have been developed
• Tend to be used in niche markets as replacement to
shell-and-tube
Principal Applications
• As for gasketed plate and frame heat exchanger, but
extended to include more aggressive media.
• Welded plate heat exchangers are used for the
evaporation and condensation of refrigerants such as
ammonia and hydrochlorofluorocarbons (HCFCs), and
for different chemicals.
Comparison with Shell and Tube Heat Exchanger
• As for gasketed plate and frame units.
Plate Fin Exchangers
• Formed by vacuum brazing
aluminium plates separated
by sheets of finning
• Noted for small size and
weight. Typically, 500 m2/m3
of volume but can be 1800
m2/m3
• Main use in cryogenic
applications (air liquifaction)
• Also in stainless steel
Scope of plate-fin exchanger
• Max. Pressure
• Temperatures
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Fluids
Duties
Flow configuration
Multistream
Low ΔT
Maximum ΔT
High ε
90 bar (size dependent)
-200 to 150oC in Al
Up to 600 with stainless
Limited by material
Single and two phase
Cross flow, Counter flow
Up to 12 streams (7 normal)
Down to 0.1oC
50oC typical
Up to 0.98
use only with clean fluids
Principal Applications
The plate-fin heat exchanger is suitable for use over a wide
range of temperatures and pressures for
• gas-gas,
• gas-liquid and
• multi-phase duties.
Typically, these involve
• Chemical and petrochemical plant:
• Hydrocarbon off-shore applications:
• Miscellaneous applications:
Comparison with Shell and Tube Heat Exchanger
• A plate-fin heat exchanger with 6 fins/cm provides
approximately 1,300 m2 of surface per m3 of volume.
This heat exchanger would be approximately 10% of the
volume of an equivalent shell and tube heat exchanger
with 19 mm tubes.
Spiral heat exchangers
• The classic design of a spiral heat exchanger is simple
• the basic spiral element is constructed of two metal
strips rolled around a central core forming two
concentric spiral channels.
• Normally these channels are alternately welded,
ensuring that the hot and cold fluids cannot intermix
Operating Limits
 Maximum design temperature is 400oC set by the limits
of the gasket material.
 Special designs without gaskets can operate with
temperatures up to 850oC.
 Maximum design pressure is usually 15 bar, with
pressures up to 30 bar attainable with special designs.
Applications
• It is ideal for use in the food industry as well as in
brewing and wine making.
• Spiral heat exchangers have many applications in the
chemical industry including TiCl4 cooling, PVC slurry
duties, oleum processing and heat recovery from many
industrial effluents.
• Spiral heat exchangers also provide temperature control
of sewage sludge.
Comparison with Shell and Tube Heat Exchanger
• Spiral designs have a number of advantages compared to
shell and tube heat exchangers:
• Optimum flow conditions on both sides of the exchanger.
• An even velocity distribution, with no dead-spots.
• An even temperature distribution, with no hot or coldspots.
• More thermally efficient with higher heat transfer
coefficients.
• Small hold up times and volumes.
• Removal of one cover exposes the total surface area of one
channel providing easy inspection cleaning and
maintenance.
PLATE AND SHELL HEAT EXCHANGERS
• The plate and shell heat exchanger combines the merits
of shell and tube with plate heat exchangers
• Current plate and shell heat exchanger models
accommodate up to 600 plates in a shell 2.5 m long with
a 1 m diameter
Operating Limits
• The maximum operating temperature of a plate
and shell heat exchanger is 900oC
• maximum working pressure is 100 bar
• handle flow rates of 11 litres per second on the
shell side.
Principal Applications
• The principal applications for plate and shell
heat exchangers are:
• · Heating including district heating.
• · Cooling including cryogenic applications.
• · Heat recovery.
• · Combined exchanger/reactors vessels.
• · Condensation/evaporation
Comparison with Shell and Tube Heat Exchanger
• For heat exchangers of equivalent area and capacity,
plate and shell designs are smaller due to the higher
ratio of heat transfer area and specific volume. It is
claimed that the plate and shell heat exchanger will
occupy only 20 to 30% of the footprint of equivalent
capacity shell and tube types.
• The maximum operating pressure of the plate and shell
unit will also be higher.
Stream Location
(Rules of thumb)
• more corrosive fluid goes tube-side
– saves costs when using alloys, cheaper to construct
tubes from alloys rather than the shell and tubesheet
• higher pressure stream goes tube-side
– small diameter tubes handle stress better than large
diameter shells.
• more severely fouling fluid goes tube-side
– easier to clean tube-side using high pressure water
lance, brushing, chemical cleaning, etc.
• fluid with lower film coefficient goes shell-side
– allows use of finned tubing to increase Aoho
• fluid with low ΔPmax goes shell side