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Thermal Management in Devices for Portable Hydrogen Generation

Brandon S. Blackwell, Chemical Engineering, Massachusetts Institute of Technology, 25 Ames St 66-501, Cambridge, MA 02139, M. A. Schmidt, Electrical Engineering and Computer Science, MIT, 39-521, Cambridge, MA 02139, and Klavs F. Jensen, Chemical Engineering, MIT, Cambridge, MA 02139.

The development of portable-power systems employing hydrogen-driven solid oxide fuel cells continues to garner significant interest among applied science researchers. The technology can be applied in fields ranging from the automobile to personal electronics industries. This work focuses on developing microreaction technology that minimizes thermal losses during the conversion of fuels such as light end hydrocarbons, their alcohols, and ammonia to hydrogen. Critical issues in realizing high-efficiency devices capable of operating at high temperatures have been addressed: specifically, thermal management, the integration of materials with different thermophysical properties, and the development of improved packaging and fabrication techniques.

A new fabrication scheme for a thermally insulated, high temperature, suspended-tube microreactor has been developed. The new design improves upon a monolithic design proposed by Arana et al.[1] In the new modular design, a high-temperature reaction zone is connected to a low-temperature (~50C) package via the brazing of pre-fabricated, thin-walled glass tubes. The design also replaces traditional deep reactive ion etching (DRIE) with wet potassium hydroxide (KOH) etching, an economical and time-saving alternative. A brazing formulation that effectively accommodates the difference in thermal expansion between the silicon reactor and the glass tubes has been developed.

[1] L.R. Arana, S.B. Schaevitz, A.J. Franz, Martin A. Schmidt, K. F. Jensen, A microfabricated suspended-tube chemical reactor for thermally-efficient fuel processing, J. MicroElectromechanical Systems, vol. 12, pp. 600-612, 2003.