Study and utilization of microscale phenomena for operation of microscale devices and high-temperature microreactors

Michael Mitchell, Paul J A Kenis

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The use of microscale devices has grown rapidly in the last decade because of the advantages these devices have over conventional devices. For instance, the larger surface area-to-volume ratios encountered at the microscale lead to the greater magnitude of surface forces relative to body forces, leading to phenomena that are not seen at the macroscale. Also, the shorter distances over which heat and mass transfer occur lead to improved transport at the scale of interest and faster transient behavior. Microreactors for H2 production are promising portable power sources. H2 can be produced by reactions such as the decomposition of NH3 or the steam reforming of hydrocarbons. High temperatures are required for both faster reaction kinetics and higher equilibrium conversion. Because heat must be supplied for this endothermic reaction, macroscale reactors are often limited by the heat transfer rate from a heat source to the reacting gas. By reducing the length scale over which the heat is transferred to the reactants, the heat transfer rate is increased, thus increasing the possible H2 production rate. This poster will describe efforts in fabricating macroporous SiC and SiCN catalyst supports with high-temperature stability and tailored pore size 1, and the integrating of these catalyst supports within an alumina housing. NH3 will also be decomposed within these reactors at temperatures up to 1000°C to show their use for H2 production. Interesting phenomena result from the importance of surface forces relative to body surfaces encountered at the microscale. Typically when fluids of different density flow side by side, the pressure mismatch at the vertical interface leads to immediate reorientation of the interface between the fluids such that the less dense fluid flows on top. At the microscale, however, the viscous force becomes more important and the reorientation occurs more gradually. This phenomenon is important for microfluidic devices using fluids of different densities, as devices such as T-sensors depend on the steams flowing side-by-side with a vertical interface. The work described here relates the extent of reorientation of the interface to two dimensionless numbers, Fr, the square root of the ratio of inertial to gravitational forces, and Re/Fr 2, the ratio of gravitational to viscous forces. The resulting equation shows that the extent of reorientation is independent of the ratio of inertial to gravitational forces, and aids in the design of microdevices using fluids of different densities by establishing conditions under which the reorientation of the interface can be avoided.

Original languageEnglish (US)
Title of host publication05AIChE
Subtitle of host publication2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings
Pages3460
Number of pages1
StatePublished - 2005
Externally publishedYes
Event05AIChE: 2005 AIChE Annual Meeting and Fall Showcase - Cincinnati, OH, United States
Duration: Oct 30 2005Nov 4 2005

Other

Other05AIChE: 2005 AIChE Annual Meeting and Fall Showcase
CountryUnited States
CityCincinnati, OH
Period10/30/0511/4/05

ASJC Scopus subject areas

  • Engineering(all)

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    Mitchell, M., & Kenis, P. J. A. (2005). Study and utilization of microscale phenomena for operation of microscale devices and high-temperature microreactors. In 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase, Conference Proceedings (pp. 3460)