Types of Heat Exchangers and LMTD Design Method

Professor Jung-Yang San

Mech. Engrg. Dept., National Chung Hsing University

(1) Types of Heat Exchangers

Counter-flow Double-Tube Heat Exchanger

Shell-and-Tube Heat Exchanger

(Two Tube Passes& One Shell Pass)

Shell-and-Tube Heat Exchanger (Single Pass)(Condenser/Evaporation)

Compactness? Material Weight Minimization? Reduction of Manufacturing Cost?

Shell-and-Tube Heat Exchanger (Single Pass)

TEMA

(Tubular Exchanger Manufacturers Association)

Assembly of the Core of a Shell-and-Tube Heat Exchanger

baffles

86 !

A Shell-and-Tube Heat Exchanger with Floating Head

Baffle Types in Shell-and-Tube Heat Exchangers

Baffle Cut

0.2 ~ 0.35 D

(Shell Diameter)

Flow Patterns for Different Baffle Cuts

Optimum Baffle Spacing 0.3 D ~ 0.6 D

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

Flat-Tube Cross-Flow Heat Exchanger

Flat-Tube Heat Exchanger with Fins Car Radiator

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 540CCompact and lightweight Highly resistant to thermal and pressure shockStandard 316 SUS construction with other exotic materials available

Helical Coil Heat Exchanger

Special Double Pipe Heat Exchanger

Plate Heat Exchanger

Heat Pipe Heat Exchanger

Spiral heat exchanger

HELICAL COIL HEATER

Twisted TubeTechnology

Tube Bundles

baffles

(tube bank heat exchanger)

Cross Flow Heat Exchanger (SUS 304)

NCHU

Cross Flow Heat Exchanger (made of pp sheets)

Spacing = 2 ~ 5 mm ; Operating temperature < 900CSheet thickness = 0.1 mm ; k (pp-sheets) = 0.12 W/m-K

Core: 300 x 300 x 150 mm (pp) Hot air inlet temperature = 30C Cold air inlet temperature = 15C

Cross-flow micro heat exchanger

Channel dimensions: 100 x 70 m, 200 x 100 m, 200 x 200 mSpecific inner surface up to 30,000 m2 m-3Heat exchange coefficient up to 20,000 W/mKPressure resistance > 100 barLeak rate (Helium) 10-8 mbar (l s)-1Temperature resistance: up to 850CMaterial: Stainless (DIN 1.4301, 1.4435), Hastelloy,

Outer dimensions: 80 x 80 x 25 mm 115 x 115 x 35 mm 200 x 200 x 45 mm

Inner volume per passageUp 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

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) 10-8 mbar (l s)-1Temperature resistance: up to 850CMaterial: Stainless (DIN 1.4301, 1.4435), Hastelloy,

High throughput micro reactor for chemical production

The main element at the production site, i.e. the micro reactor, is made from a nickel alloy and is 65 cm long and 290 kg in weight. The possible throughput is 1700 kg/h of liquid reactants. The heat released by the chemical reaction, approx. 100 kW is transferred within the reactor to again several ten thousands of micro channels at the cooling passage.

Micro heat exchanger for coffee production

A micro heat exchanger of only 8 cm3 in size is working in a plant for coffee production. Purpose: Cooling of liquid CO2 .

Fabrication of Metallic Micro structured Devices

Glowing micro-structured foil stack during diffusion bonding

Micro-structured foil made of copper

Mechanical Micro Fabrication

Micro drill Micro cutter

The typical surface roughness is like Ra = 0.2 m.

Results of Mechanical Fabrication

Material Min. Aspect HollowProcess Groove Size Ratio Accuracy

Steel Milling 100 m 4 3 m 200 m 7-15

Non Ferrous Milling 50 m 1 (Carbide) 2 mAlloys Milling 100 m 1 (Diamond), 4 (Carbide)

The fabrication of metallic micro structured devices starts with processing of metallic foils.

Precision turning () and milling () are applied therefore and together with partners micro etching () and micro embossing () are carried out.

The micro structured metal plates are then stacked between two base plates and diffusion bonded under a well defined press capacity and temperature in vacuum. By this procedure a microstructured body is yielded, which comprises of thousands of microchannels.

Materials which can not be diffusion bonded can be joined by laser welding or soldering. However, these technologies are under development.

The joined micro structured body gets welded into a housing with tubes or fittings by electron beam welding, vacuum tight and pressure resistant.

Micro Fabrication

Packed-Bed Regenerator

Rotary Regenerator

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)

Heat Transfer Enhancement Techniques

Tube with Internal Fins and Tube with Internal Roughened Surface

Tubes Inserted with Twisted Tape and Coiled Spring

Secondary Flow Induced by Coiled Spring

Flow Disruption Caused by hiTRAN Wire Matrix Turbulator

Brazed, Soldered, Edge Tension, Stamped

Extrusion

Circular Tube with External Spiral Fins

Circular Tube with Internal and External Spiral Fins

Fin Height : 1.422 (mm)

Outside Diameter : 19.00 (mm)

Wall thickness : 1.32 (mm)

Copper-Nickel Alloys

Corrugated Tubes

(NCHU) -

d t

2 mm p

Tw

rotameter

Ta ,Po o

outlet

pump

water bath

water

inlet

air blower

1

test tube

Tw4 3 2Tw Tw

heater

Ta ,Pi i

surgetank

electricinverter

Correlation of Nu

International Journal of Heat and Mass TransferVol. 49, 2006, pp. 2965-2971JCR (Mechanical Engineering) : 7/106

Correlation of f

Correlation Results

40.26( / ) 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 0.3330.0072(Re) ( / ) ( / )Nu p d e d=

0.015 / 0.057e d