ntb interstate university of applied sciences of technology buchs mnt institute for micro and...

Patrik Müller, Andres Bolleter, Aziz Ibzazene OneBat Discovery - Work Package 3: Thermal Management -

NTBINTERSTATE UNIVERSITY OFAPPLIED SCIENCES OF TECHNOLOGY BUCHS

MNTINSTITUTE FOR

MICRO AND NANOTECHNOLOGY

Work package 3

Thermal management

17. November 2005

Patrik Müller

Andres Bolleter



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ContentContent

- Resume thermal concept

- Theoretical thermal resistance

- Thermal measurement

- Redesign vacuum insulation

- Status WP3

- Next steps

- Miscellaneous to other WP



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Air

Exhaust

Air

Exhaust

Fuel

Stack

Vacuum insulation /insulation

Insulation

Separation of in- andoutlet (heat exchanger)

Resume thermalResume thermal conceptconcept

Vacuum insulation /insulation

~ 2 cm

< 1

cm

~ 2 cm

Shape cylindrical or cubical



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Resume thermal conceptResume thermal concept

600 °C

~ 40°C

~7e4 W/(m2) ~3e3 W/(m2)

Vacuum chamberVacuum insulation

Insulation material

Stack

Air / Gas

Exhaust

Separation of Gases

•Vacuum chamber

•Vacuum chamber filled with porous insulation (WDS)

•Insulation material (WDS, Aerogel)

Three insulation-possibilities



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Steel foilSteel foil

Inner Vacuum-Housing

Vacuum-Insulation

Stack

Air / Gas

Exhaust

Outer Vacuum-Housing



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Thermally self-sustained Thermally self-sustained SOFCSOFC

- Idea is to use the exothermic oxidation reaction to locally sustain the

500-600°C which is needed for the electrochemical reaction

- Fuel utilization of experiments at ~ 1%

- Therefore 99% is released as heat

- OneBat-project efficiency 40%

- Insulation needed

Comments on the paper “A thermally self-sustained micro solid

oxide fuel-cell stack with high power density” *

* Z. Shao, S. M. Haile, J. Ahn, P. D. Ronney, Z. Zhan, S. A. Barnett, “A thermally self-sustained micro solid-oxide fuel-cell stack with high

power density”, 2005, Nature Publishing Group



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Theoretical thermal resistanceTheoretical thermal resistance

Simulation

“Stack”

1 2Th

W

T TR

I

Measurements

T2

T1

Insulation



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Thermal measurementThermal measurement

Dummy stack

Pmax ~ 12 W

Ø 8 x 4 mm

Microtherm Super G

Thermal conductivity

0.028 W/m*K @ 400°C

Aim: determination of thermal resistant



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Measurements Silica AerogelMeasurements Silica Aerogel

t1: 500°C

t2: 48°C

t3: 147°C

t4: 23°C

Dimensions: 14 x 30 x 45 mm

( : 8 °C)

t1

t2

t4

t3



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Measurements vacuum insulationMeasurements vacuum insulation

t1: 500°C

t2: 148°C

t3: 102°C

t4: 23°C

Pressure: 2*10-3 mbar

Dimensions: Ø 22 x 2 mm

( : 8 °C)

t1

t2

t4

t3



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Measurements vacuum insulationMeasurements vacuum insulation

Dummy-Stack Temperature

450

460

470

480

490

500

510

1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03

Vacuum [mbar]

Tem

per

atu

re [

°C]

Ptotal: 1.6 W to keep the stack temperature

t1

t2

t3

t4



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Redesign vacuum insulationRedesign vacuum insulation

Reduced buckling

- Matching thermal expansion

- Pre-stressing

Compact design

- Dimension: adaptation on simulation results

- Slimmer frame

Not tested yet: reliability



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Silica Aerogel reliabilitySilica Aerogel reliability

untreated

24 hours @ 600°C

1 hours @ 700°C

1 hours @ 800°C

1 hours @ 900°C

1 hours @ 1000°C

1 hours @ 1100°C

SEM picture by magic Brandon, MNW ETHZ

By now no information about long-term and insulation stability



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Status WP3Status WP3WP 3.1: Thermal System Design

Milestones

Month 3: - thermal insulation concept (T inside = 550°C, T outside = 50°C) (ZHW)Month 12: - system integration concept incl. thermal management concept heat exchanger design

compatible with GPU designs and micro-fabrication (ZHW)

Deliverables

Month 3: - design from ZHW NTB for fabrication

WP 3.2 Fabrication Concept of Thermal System

Milestones

Month 6: - test structures for validation of critical points of the concept (ΔT 500°C) (NTB)

Month 9: - test results of first designs

Month 12: - thermal system design demonstrator with simulated heat sources (dummy stack,

reformer, post-combustor) (NTB)

☺☺

☺☺

☺☺



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Next stepsNext steps

- Comparing first measurements with simulations

- If discrepancies to large: why ?

- Redesign of concept

- Reliability vacuum insulation

- Setup of second measurements: without gas-channels

- Closer to concept

- Comparing second measurements with simulations

- Third set of measurements with simulations



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WP 1: structuring Pt-ElectrodeWP 1: structuring Pt-Electrode

Process: combination of lift-off and shadow mask Parameter:

- Development time

- Resist thickness

- Exposing dose

- Adhesion



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WP 2: gas processing unitWP 2: gas processing unitTest device: Foturan cannel 1 x 1 x 5 / 10 / 15 mm

Input needed for fabrication (month 6):

Final reformer design

3 designs of post-combustor

Drawings with all dimensions (CAD-File, dxf etc..)



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Thermo-mechanical simulationsThermo-mechanical simulations

What could be gained out of simulation

- Sensitivity of parameters can be evaluated

- Source of stresses can be localized easier then by

measurement

- Design-criteria



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What inputs would these simulations require?

- Geometry

- Expansion coefficients

- E-module, Poisson Ratio

Where could thermo-mechanical simulations be used

- As an additional tool for system design

- To support cell-measurements, gaining insights



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Questions ?Questions ?



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“ Resulting from elevated temperatures the major structural problem

foreseen with planar SOFCs is their thermal stresses” *

“ The stresses occurring in both cells are lying beyond the limit” *

“ principal stress peak arises at the beginning of the process (startup

process).” *

“ Largest stress occurs in a ceramic cell fuelled with prereformed

methane and it is located in the electrolyte layer at interface with the

anode”

* A. Selimovic, M. Kemm, T. Torisson, M. Assadi, “Steady state and transient thermal stress analysis in planar solid oxide fuel cells”,

Journal of Power Sources, 2005

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