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A high performance titanium sheet for plate type heat exchanger

October 6th 2010DAISUKE HAYASHI

Titanium Marketing & Technical Service SectionKOBE STEEL, LTD.

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Contents

The small thermal energy conversion, such as OTEC

Requirements to material for PHEPress formability development

with Pre-coated titaniumThe technology to improve the thermal

efficiency of vapor heat exchanger

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What’s the OTEC?

Ocean Thermal Energy Conversion (OTEC) is the power generation system with an extremely low emission of carbon dioxide.

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Principles of OTEC Technology

There is a temperature difference of over 20 degrees Celsius in the ocean.

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Principles of OTEC Technology

①Evaporator

②Turbine

③Condenser

④Working fluid pump

⑤Warmseawaterpump

⑥Cold seawaterpump

One major characteristic of OTEC is the use of a working fluid such as ammonia with low boiling point.

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Heat exchanger of Evaporator and Condenser

Titanium Plate Heat Exchanger is the best.

A cross section of tubular

Fluid

A cross section of plate channel

Fluid

Heat effective range Heat effective range

PHE can improve heat transfer efficiency.

Shell & tube heat exchanger Plate heat exchanger

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OTEC RoadmapPower Generation Output [MW]

C.Y. 2015 2020 2030 2050

Hawaii (U.S.A.) 1) 35 365

France 2) 200

Japan 3) 510 2550 81501) The Hawaii Clean Energy Initiative2) IFREMER3) New Energy and Industrial Technology Development Organization

Demand of titanium is estimated to be 18,000 MT/1000MW

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Requirements to material for PHE

Thermal resource isSeawater.

A working fluid isAmmonia.

Vapor pressure in plate channels is about 15MPa.

Plates are manufactured by Press forming.

Temperature Difference is small.

High corrosion resistance

Higher Strength

Good formability

High heat transfer rate

Requirements Solution

Titanium

with

Pre-coatedGr.2 titanium

Design optimizationof material & PHE

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Press formability development with Pre-coated titanium

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Lubricant for Press forming

Lubricant and press formability of Titanium Sheet

9.0

10.0

11.0

12.0

13.0

Eric

hsen

val

ue(m

m)

without lubricant oil film(P.E.)

MaterialGrade ASTM G1Thickness 0.8mmFinish 2B

Comparison of usual lubricant methodoil film

Press formability Not good GoodDimensional accuracy of products Good Not goodProductivity Good Not good

Pre-coated

?GoodGoodGood

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Design concept of coating

Hard to break after severe forming

Enough thin for forming accuracy

Easily removed after forming

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Contents of pre-coat layer

Pre-coat layer contains no harmful metal and organic chemicals.

Contents mass% Roll

Acrylic Resin 801) holds sufficient adhesive strength.2) maintains enough flexibility to severe

deformed surface.3) Dissolves easily into alkaline solution.

Silica ～10 1) gives moderate hardness

Polyolefin wax ～10 1) leads to low static/dynamic friction.

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Stretch formability of Pre-coated titanium

Pre-coated titanium shows excellent formability compared to one with polyethylene film as lubricant.

02468

101214

10kN 150kN

Blank Holder Force

Hei

ght t

o Fa

ilure

(mm

)with Press OilPre-coatedwith Polyethylene film

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In practical size die

Evaluation method of formability

A

A’4 : No Crack3 : Necking2 : Severe Necking1 : Small Crack0 : Large Crack

How to Score (Index for Press-formability)

２．Scoring at each point(E)

１．Evaluation Points and their number① Apex：18 (Concave) 18 (Convex) ② Ends of beams ：56

Score（％）＝（18×4×2 + 56×4 ）

ΣE①,② ×100

500

300

500

A’ Convex

Concave

A-A’Cross sectionA

14.9mmForming Height ：4.5mmRadius of beams ：3.4mmPitch between beams ：14.9mm

thickness：0.5mm

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Press formabilityin practical size die

20% stronger pre-coated titanium has same excellent press formability as a conventional CP titanium for PHE using press oil as a lubricant.

0

20

40

60

80

100

200 250 300 350 400 450Tensile Strength (MPa)

Sco

re (%

)

with Press oilPre-caoted

Gr.2Gr.1

Goodformability

Conventional CPtitanium for PHE

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Removable coating layer by alkali cleaner

Only 60 sec. dipping in alkali cleaner can remove pre-coating layer perfectly.

0

20

40

60

80

100

0 30 60 90 120 150Dipping time / sec

Rem

oval

rate

of c

oatin

g la

yer/

%

Weak Alkali CleanerStrong Alkali Cleaner

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Technology to improvethe thermal efficiencyof vapor heat exchanger

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Improvement process1.Elucidating and characterizing the behavior

of ammonia on a compact plate evaporator, a type of PHE

Because the boiling heat transfer performance of ammonia has not yet been elucidated.

2.Design optimization of material & PHE

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Experimental apparatus30 3040

2 2

850

380

250

175

Sight Glass

Wor

king

flui

d si

de fr

ame

War

m h

eat s

ourc

e si

de fr

ame

Spacer

100

Plat

e10

010

010

010

0

T.C. holes

Wor

king

flui

d

Hot

Wat

er

l1

T1T2

Twalll2

Working fluid（Tbulk）

Hot water

Urethane tube

Plate

Test plate

Thermocouple sheath

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Local boiling heat transfer

0 0.2 0.4 0.6 0.8 10

2000

4000

6000

8000

10000

quality x [-]

Loca

l hea

t tra

nsfe

r coe

ffic

ient

h l

oc

[W/(m

2 K)]

qav=20 kW/m 2

Pabs=0.8 MPa

Z= 1.0 0.9 G = 7.5 kg/m2s G = 10 kg/m2s G = 15 kg/m2s

Comparisons of local heat transfer coefficient on quality at different mass flux

Ammonia Ammonia / water mixture

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Visualization

G = 10kg/m2s, qav = 20kW/m2, Pabs = 0.7MPa

Quality 0.28 Quality 0.63

Quality 0.66

Flow

dire

ctio

n

Quality 0.26

Z=1.0 Z=1.0

Z=0.9 Z=0.9

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ConclusionsKOBE STEEL has been developing the high performance titanium for PHE of small thermal energy conversion.

There is a possibility to apply these technologies to the conventional heat exchanger.

Pre-coated titanium for good formability

Titanium with high heat transfer coefficient( under development )

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