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Types of Heat Exchangers and LMTD
Design Method
Professor Jung-Yang San
Mech. Engrg. Dept.,
National Chung Hsing University
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(1) Types of Heat Exchangers
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Counter-flow
Double-Tube
Heat Exchanger
Shell-and-Tube
Heat Exchanger
(Two Tube Passes
& One Shell Pass)
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Shell-and-Tube Heat Exchanger (Single Pass)
(Condenser/Evaporation)
Compactness?
Material Weight Minimization?
Reduction of Manufacturing Cost?
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Shell-and-Tube Heat Exchanger (Single Pass)
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TEMA (Tubular ExchangerManufacturers Association)
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Assembly of the Core of a Shell-and-Tube Heat Exchanger
baffles
86 !
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A Shell-and-Tube Heat Exchanger with Floating Head
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Baffle Types in
Shell-and-Tube Heat
Exchangers
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Baffle Cut
0.2 ~ 0.35 D
(Shell Diameter)
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Flow Patterns for Different Baffle Cuts
Optimum Baffle Spacing 0.3 D ~ 0.6 D
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Helical Baffle
One of The Largest Helical
Baffle Exchanger Ever Built
- 12,000 fin tubes: 22 m long- Shell I.D.: 3.8 m
- Shipping Weight: 165 Tons
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Flat-Tube Cross-Flow Heat Exchanger
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Flat-Tube Heat Exchanger with Fins Car Radiator
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Helical Coil Heat Exchanger
Single tube helical coil heat exchangers are suited for oil coolers, sump
coolers and other high pressure, high temperature, low flow applications.
Pressure ratings up to 345 bar and sample conditions up to 540C Compact and lightweight Highly resistant to thermal and pressure shock
Standard 316 SUS construction with other exotic materials available
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Helical Coil Heat Exchanger
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Special Double Pipe Heat Exchanger
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Plate Heat Exchanger
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Heat Pipe Heat Exchanger
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Spiral heat exchanger
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HELICAL COIL HEATER
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Twisted TubeTechnology
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Tube Bundles
baffles
(tube bank heat exchanger)
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Cross Flow Heat Exchanger (SUS 304)
NCHU
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Cross Flow Heat Exchanger (made of pp sheets)
Spacing = 2 ~ 5 mm ; Operating temperature < 900C
Sheet thickness = 0.1 mm ; k (pp-sheets) = 0.12 W/m-K
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Core: 300 x 300 x 150 mm
(pp)Hot air inlet temperature = 30C
Cold air inlet temperature = 15C
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Cross-flow micro heat exchanger
Channel dimensions: 100 x 70 m, 200 x 100 m, 200 x 200 m
Specific inner surface up to 30,000 m2m-3Heat exchange coefficient up to 20,000 W/mKPressure resistance > 100 barLeak rate (Helium) 10-8 mbar (l s)-1
Temperature resistance: up to 850CMaterial: Stainless (DIN 1.4301, 1.4435), Hastelloy,
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Outer dimensions:
80 x 80 x 25 mm 115 x 115 x 35 mm 200 x 200 x 45 mm
Inner volume per passage
Up to 0.3 cm Up to 2 cm Up to 6 cm
Thermal power (water)
Up to 20 kW Up to 50 kW Up to 200 kW
Throughput (water at P = 5 bar)Up to 1100 kg/h Up to 3500 kg/h Up to 6500 kg/h
Connectors:
Swagelok 8 mm Swagelok 18 mm Swagelok 25 mm
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Co/counter-current micro heat exchanger
Specific inner surface up to 30.000 mm-3Heat exchange coefficient up to 20.000 W/mKPressure resistance > 100 barLeak rate (Helium) 10-8mbar (l s)-1
Temperature resistance: up to 850CMaterial: Stainless (DIN 1.4301, 1.4435), Hastelloy,
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High throughput micro reactor for chemical production
The main element at the production site, i.e. the micro reactor, is madefrom a nickel alloy and is 65 cm long and 290 kg in weight. The possiblethroughput is 1700 kg/h of liquid reactants. The heat released by thechemical reaction, approx. 100 kW is transferred within the reactor to
again several ten thousands of micro channels at the cooling passage.
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Micro heat exchanger for coffee production
A micro heat exchanger of only 8 cm3 in size is working ina plant for coffee production.
Purpose: Cooling of liquid CO2 .
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Fabrication of Metallic Micro structured Devices
Glowing micro-structured foil
stack during diffusion bonding
Micro-structured foilmade of copper
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Mechanical Micro Fabrication
Micro drill Micro cutter
The typical surface roughness is like Ra = 0.2 m.
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Results of Mechanical Fabrication
Material Min. Aspect Hollow
Process Groove Size Ratio Accuracy
Steel Milling 100 m 4 3 m
200 m 7-15
NonFerrous Milling 50 m 1 (Carbide) 2 m
Alloys Milling 100 m 1 (Diamond), 4 (Carbide)
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The fabrication of metallic micro structured devices startswith processing of metallic foils.
Precision turning () and milling () are applied therefore
and together with partners micro etching()
and microembossing () are carried out.
The micro structured metal plates are then stacked betweentwo base plates and diffusion bonded under a well defined
press capacity and temperature in vacuum. By thisprocedure a microstructured body is yielded, whichcomprises of thousands of microchannels.
Materials which can not be diffusion bonded can be joined
by laser welding or soldering. However, these technologiesare under development.
The joined micro structured body gets welded into a housingwith tubes or fittings by electron beam welding, vacuum tight
and pressure resistant.
Micro Fabrication
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Packed-BedRegenerator
Rotary
Regenerator
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Selection of Heat Exchangers
The proper selection depends on several
factors: heat transfer rate
cost (maintenance and power)
pumping power size and weight type materials miscellaneous (leak-tight, safety and
reliability, quietness)
H t T f E h t T h i
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Heat Transfer Enhancement Techniques
T b ith I t l Fi d T b ith I t l
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Tube with Internal Fins and Tube with Internal
Roughened Surface
T b I t d ith T i t d T d C il d
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Tubes Inserted with Twisted Tape and Coiled
Spring
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Secondary Flow Induced by Coiled Spring
Fl Di ti C d b hiTRAN Wi
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Flow Disruption Caused by hiTRAN Wire
Matrix Turbulator
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Brazed, Soldered, Edge
Tension, Stamped
Extrusion
Circular Tube with External Spiral Fins
Ci l T b ith I t l d E t l
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Circular Tube with Internal and External
Spiral Fins
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Fin Height : 1.422 (mm)
Outside Diameter : 19.00 (mm)
Wall thickness : 1.32 (mm)
Copper-Nickel Alloys
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Corrugated Tubes
(NCHU) -
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(NCHU)
dt
2 mm p
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Tw
r
otameter
Ta ,Po o
outlet
pump
water bath
water
inlet
airblower
1
test tube
Tw4 3 2Tw Tw
heater
Ta ,Pi i
surgetank
electric
inverter
Correlation of Nu
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Correlation of Nu
International Journal of Heat and Mass TransferVol. 49, 2006, pp. 2965-2971
J CR (Mechanical Engineering) : 7/106
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Correlation of f
Correlation Results
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Correlation Results
4
0.26( / ) 1.44 10 Re0.0018( / ) (Re)p d xf e d e e
=
42.55 0.26( / ) 1.44 10 Re0.132( / ) (Re)p d xf e d e e =
1.05 0.15 0.333
0.0072(Re) ( / ) ( / )Nu p d e d
=
0.015 / 0.057e d
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