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ICHMT DIGITAL LIBRARY ONLINE

ISSN 961-91393-0-5

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$246.00 (Must be sent to your home address)

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Year 2004

• 3Thermal Sciences 2004
Proceedings of The ASME - ZSIS International Thermal Science Seminar II, Bled, Slovenia, June 13-16, 2004

1032 pages

Volume price - $246.00

Thermo-Fluids Considerations in the Development of a Silicon-based Micro-scale Direct Methanol Fuel Cell

Shi-Chune Yao
Department of Mechanical Engineering, Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Gary K. Fedder
Institute for Complex Engineered Systems, Department of Electrical and Computer Engineering, Robotics Institute, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Xudong Tang
Department of Mechanical Engineering, Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Cheng-Chieh Hsieh
Department of Mechanical Engineering, Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Yousef M. Alyousef
Department of Mechanical Engineering, Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Michael L. Vladimer
Institute for Complex Engineered Systems, Department of Electrical and Computer Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

Cristina H. Amon
Department of Mechanical Engineering, Institute for Complex Engineered Systems, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA, USA

ABSTRACT

A silicon-based micro-scale Direct Methanol Fuel Cell (DMFC) system is under development at Carnegie Mellon University, as a substitute for lithium-ion batteries to power hand-held electronic devices. The DMFC is simple in design, operational in any orientation and environmentally benign. The air flow and the methanol circulation are both at a natural convection draft, while a passive gas bubble separator removes CO₂ from the methanol chamber. The design and operation of the passive gas separator system, which has been successfully fabricated and tested, is described.
Micro-scale Direct Methanol Fuel Cells have great potential for early applications in portable electronics due to their higher tolerance of power cost. However, challenges in system integration have to be overcome. A major issue is the development of micro-fluidics, which includes the micro pump for anode liquid re-circulation and for recycling the excess water from the cathode back to the anode, as well as the passive CO₂ gas bubble separation from the anode side liquids. In addition, the seamless integration of various micro-fluidic components and the electronic control system has been an essential concern for system reliability and cost reduction.
The DMFC is designed using MEMS technology. To achieve high energy density, the excess water at the cathode is collected and pumped back to the anode. This micro fuel cell contains several unique features. A silicon wafer with an array of etched holes selectively coated with a non-wetting agent is used at the cathode to collect the water effectively. A silicon membrane micro pump is developed for pumping the collected water back to the anode. Finally, a passive micro-scale CO₂ bubble separator is developed to remove the gas bubbles from the anode stream. All of these silicon-based components are fabricated with a set of common processes on the same silicon wafer, such that interconnections are eliminated and fabrication cost is minimized. The resulting micro-scale fuel cell has an energy density four times larger than that of current lithium-ion batteries.