types of heat exchangers and lmtd design method

7/23/2019 Types of Heat Exchangers and LMTD Design Method

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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

types of heat exchangers and lmtd design method

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