ani so tropic thermal behavior of porous carbonized wood

8/3/2019 Ani So Tropic Thermal Behavior of Porous Carbonized Wood

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Anisotropic Thermal Behavior ofPorous Carbonized Wood

Based Composites forThermal Management

on the Space Solar Satellite

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2

Introduction

Contents:

Heat problem, the need of thermal management on the SPS

Carbon based thermal conductive material: graphite and thenecessary improvement in the anisotropic thermal behavior

Carbonized wood, a turbostratic carbon

Composite with alternate layers of graphite and carbonized

wood for anisotropic thermal behavior improvement


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Thermal Management in the SPS

Heat problem in the SPS: when temperature increase exceed 100 C,the electric generation efficiency will be dropped.

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Solar Power Satellite

Heat distribution of the solar cell side(URSI white paper, 2007)


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Thermal Management in the SPS

Solar Power Satellite

Thermal management is necessary

to keep the high efficiency of

electric power generation of the

SPS by keeping the temperaturebelow 100 C

A thermal conductive material to

discharge the heat to radiators ,

retaining the increase in

temperature

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Thermal Conductive Materials

A preferable material:High thermal conductivity, considerably strength, lightweight(low SG) and anisotropic behavior

No Material KT(W/m.K)

Modulus(GPa) SG(g/cm3)

1 Aluminum 230 69 2.7

2 Cooper 400 117 8.9

3 Silicon 150 - 2.3

4 Graphite* // 140 - 1.9

225

D.D.L. Chung and C. Zweben, 2001; *A.I. Lutcov et.al. 1970

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Graphite

Planar structure of ABA stacking sequence of hexagonal graphite (Klett et al., 2004)

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Graphite consists of carbon layers (graphene layers) with covalent bonding withineach layer and are linked by van der Walls interactions.

Graphite is anisotropic, good electrical and thermal conductor within the layersand a poor electrical and thermal conductor perpendicular to the layers.


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Graphite

The High temperature treatment (HTT)

improves the crystallites size (Taylor,2000) and increase the thermalconductivity.

But the anisotropic behavior is notinfluenced

(Oberlin et al., 1980)Crystallite orientation of Non-Graphitizable

Carbon (Franklin,1951)

Random orientation of the crystallites arepresent in non-graphitizable carbons.

KH/KV or H/V ratio of natural and commercialgraphite = 1.15 3.2 (Slack, 1962)


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Carbonized Wood

SEM images of cell wallof wood before andafter carbonization at700 C (Ishimaru et al., 2007)

Dark field TEM image(Ishimaru et al., 2007)

Turbostratic structure of carbonwith local molecular orientationlike crumpled paper(Oberlin et al., 1980)


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Carbonized Wood

Relationship between carbonization temperaturewith electrical properties of carbonized wood(Ishihara, 1996)

Carbonized wood becomes aconductor at around 700-800 C

Thermal conductivity:- KH= 1.14 W/m.K- KV = 0.50 W/m.K

H/V ratio: 2.31


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Morphology of Carbonized WoodComposite

Carbon foam produced by blowing

process (Klett et al., 2004)Carbonized wood composite

Carbonized wood composites possesses morphology with a porous structure

Pores become important for thermal management application


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Composites with Alternate Layers of CarbonsExhibiting Different Microstructures

The alternating layers structure of graphitic and turbostratic carbons orientsgraphite in a macro-scale.

Carbonized wood with a turbostratic structure are used to control heat flow inthe composite.

Schematic structure of a three-layer laminated carbonizedwood-graphite (C/G) composite (Sulistyo et al., 2009)


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Experimental

CarbonizationAt 700 C, 4 C/min, 1 h

Granulation25-32 and 63-90 m

Alternate layering ofCarbonized Wood & graphite

Heat treatmentAt 700 C, 71 C/min, 50 MPa,

15 min, vacuum condition

Effect of weight fraction ofcarbonized wood and particlesize: 0 100 wt% use 25-32

and 63-90 m

Effect interlayerinterface:

2, 3,5, 7 and 9 layer

Characterization:-Morphology

- Microstructure- Thermal properties

30 & 10 mm, d= 1 mm

GraphiteCarbonizedwood


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Thermal Conductivity

Q: the absorbed quantity of heatd: the thickness: densityT0: the extrapolated temperature

increase

Thermal conductivity (k) (W/m K):a measure of the rate of heat flow through one unit thickness of a materialsubjected to a temperature gradient.

Ck

0Td

QC

: density (g/cm3)C: specific heat capacity (J/g/K)

: thermal diffusivity (cm2/s)Specific heat capacity:

the amount of energy needed to increase one unit of mass one unit in temperature.

Thermal diffusivity: horizontal and vertical directiona measure of how quickly a material can absorb heat from its surrounding.

2/1

21388.0

t

d d: the thicknesst1/2: the time required for the temperature of

the rear face to increase to a half of themaximum temperature

Eff f W i h F i f


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Effect of Weight Fraction ofCarbonized Wood

C/G=10/90 C/G=20/80 C/G=33/67

C/G=60/40 C/G=70/30 C/G=80/20

Images by an optical microscope


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0.0

0.4

0.8

1.21.6

0 20 40 60 80 100

Weight fraction of carbonized

wood (wt%)

Sp

ecificheatcapacity

(J/g/K)

measured

calculated

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 20 40 60 80 100

Weight fraction of carbonized

wood (wt%)

Specificheatcapacity

(J/g/K)

measured

calculated

25-32 m

63-90 mGraphite

Carbonizedwood

A rough interlayerinterface


Specific Heat Capacity

CCGG

CCCGGG

vv

vCvCC

Calculated C:


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0

5

10

15

20

25

30

35

0 20 40 60 80 100

Weight fraction of carbonized wood

(wt%)

k(

W/mK)

measured kHcalculated kHmeasured kVcalculated kV

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25-32 m Thermal Conductivity

Calculated kHand kV:

HCtotalCHGtotalGHkddkddk

VCtotalCVGtotalG

V

kddkddk

11

1

0

2

4

6

8

10

12

0 20 40 60 80 100

Weight fraction of carbonized wood

(wt%)

H/Vratio


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Graphite

Carbonizedwood

Graphite

3000

3500

4000

4500

1100 1200 1300 1400 1500 1600 1700 1800

Raman shift (cm-1

)

Intensity(a.u.)

D band

G band

500

1000

1500

2000

2500

1100 1200 1300 1400 1500 1600 1700 1800

Raman shift (cm-1

)

Intensity(a.u

) D bandG band

Microstructure

H/V ratio = 3.8

H/V ratio = 1.9


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Optimum H/V

ratio

0

5

10

15

20

2530

35

40

0 20 40 60 80 100

k(W/mK)

0

2

4

6

8

10

12

0 20 40 60 80 100

H/Vratio

0

5

10

15

20

25

30

35

0 20 40 60 80 100

Weight fraction of

carbonized wood (wt%)

k(W/mK)

25-32 mkH

kV

0

2

4

6

8

10

12

0 20 40 60 80 100

Weight fraction of

carbonized wood (wt.%)

H/Vr

atio

63-90 mkV

kH

Eff f W i h F i f


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C/G=10/90

25-32 m

C/G=10/90

63-90 m

Morpholologyby SEM


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Effect of Interlayer Interfaces

Graphite

Graphite

Carbonized wood

Interlayer interfacePorous material withwood cellular structure

The role of interlayer interface andparticle size on thermal propertiesbecome important to be known


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Multilayer of C/G 10/90 images by an optical microscope



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0.70

0.75

0.80

0.85

0 2 4 6 8 10

No. of layer

Specificheatcapacity

(J/g/K)

0

5

10

15

20

25

0 2 4 6 8 10

No. of layer

k(W/mK)

Horizontal

Vertical

02

4

6

8

10

0 2 4 6 8 10

No. of layer

H

/Vratio



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Conclusions

1. Alternate layers of graphite and carbonized wood improvedthe anisotropic thermal conductivity2. The weight fraction of carbonized wood affected the

thermal conductivity and the H/V ratio. The optimum H/Vratio of 10.17 was obtained at 10 wt% of carbonized wood

3. Particle size affected the thermal conductivity and the H/Vratio in relationship with the morphology of carbonizedwood layer

4. The interlayer interface of graphite and carbonized wood

affected on the reduction of the thermal conductivity andthe H/V ratio


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Thank you very much

ani so tropic thermal behavior of porous carbonized wood

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