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Design of a microbreather for two-phase microchannel devices

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dc.contributor.advisor Evelyn N. Wang. en_US
dc.contributor.author Alexander, Brentan R en_US
dc.contributor.other Massachusetts Institute of Technology. Dept. of Mechanical Engineering. en_US
dc.date.accessioned 2009-03-20T19:32:04Z
dc.date.available 2009-03-20T19:32:04Z
dc.date.copyright 2008 en_US
dc.date.issued 2008 en_US
dc.identifier.uri http://hdl.handle.net/1721.1/44919
dc.description Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. en_US
dc.description This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. en_US
dc.description Includes bibliographical references (p. 50-52). en_US
dc.description.abstract Multiphase flows in microchannels are encountered in a variety of microfluidic applications. Two-phase microchannel heat sinks leverage the latent heat of vaporization to offer an efficient method of dissipating large heat fluxes in a compact device. In microscale methanol-based fuel cells, the chemical reactions produce a two-phase flow of methanol solution and carbon dioxide gas. Differences in the underlying physics between microscale and macroscale systems, however, provide a new set of challenges for multiphase microscale devices. In thermal management devices, large pressure fluctuations caused by the rapid expansion of vapor are prevalent in the flow channels. In fuel cells, the gaseous carbon dioxide blocks reaction sites. In both of these cases, dry-out is a problem that limits device performance. We propose a design for a microscale breather that uses surface chemistry and microstructures to separate gas from a liquid flow to improve two-phase microchannel performance. To better understand the physics and governing parameters of the proposed breather, we have designed and fabricated test devices that allow cross-sectional visualization of the breathing events. We have conducted various experiments to examine the effects of device channel hydraulic diameters ranging from 72 [mu]m to 340 [mu]m and liquid inlet flow rates ranging from 0.5 cm/s to 4 cm/s on the maximum gas removal rate. We demonstrated a maximum breather removal rate of 48.1 [mu]l/min through breather ports with a hydraulic diameter of 4.6 [mu]m connected to a microchannel with a hydraulic diameter of 72 [mu]m, and a liquid inlet flow velocity of 0.5 cm/s. A model was developed that accurately predicts the exponential dependence of the maximum gas removal rate on a non-dimensional ratio of the pressure across the breather ports compared to the pressure drop in the main channel caused by the venting bubble. en_US
dc.description.abstract (cont.) These results serve as design guidelines to aid in the development of more efficient and sophisticated breathing devices. The successful implementation of a microchannel with an efficient breather will allow for new technologies with higher heat removal capacities or chemical reaction rates that can be effectively used by industry. en_US
dc.description.statementofresponsibility by Brentan R. Alexander. en_US
dc.format.extent 59 p. en_US
dc.language.iso eng en_US
dc.publisher Massachusetts Institute of Technology en_US
dc.rights M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. en_US
dc.rights.uri http://dspace.mit.edu/handle/1721.1/7582 en_US
dc.subject Mechanical Engineering. en_US
dc.title Design of a microbreather for two-phase microchannel devices en_US
dc.type Thesis en_US
dc.description.degree S.M. en_US
dc.contributor.department Massachusetts Institute of Technology. Dept. of Mechanical Engineering. en_US
dc.identifier.oclc 302251012 en_US


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