Open-channel capillary flow in helical support structures

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National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)Proposal Number: 0731230 Principal Investigators: Thiessen, David Affiliation: Washington State University Proposal Title: Open-channel capillary flow in helical support structures This work will explore flow in novel open microfluidic channels consisting of microsprings. Injecting a liquid into a small horizontal spring creates a continuous liquid channel with exposed liquid surface bridging between adjacent coils. A microspring can thus be used as a flexible microfluidic conduit with a number of potential applications. Capillary-driven flow in open channels with minimal support structures may have applications in heat- or mass-transfer processes in small-scale systems (microfluidics, intensified processes) or under microgravity conditions. Open-channel capillary flow has been demonstrated in helical supports including flow with concomitant mass transfer. Flows are possible for both wetting and nonwetting fluids. Vertical wicking of a highly wetting liquid into an open-coil microspring has been demonstrated to yield a capillary rise of around ten diameters. A primary hypothesis to be tested in the proposed work is that the driving force for flow can be predicted from the range of stable pressures sustainable in the structure under static conditions. Intellectual Merit The methods for exploring the static stability of the liquid channels builds on a body of work that has been developed to describe the stability of capillary systems such as liquid bridges, pendant drops and cylindrical surfaces pinned on a slot. To the PI's knowledge, the stability of helical free surfaces has not been studied prior to the work of the PI and collaborator (B. J. Lowry). The initial penetration flow theory is also based on a large body of work starting with the classic papers of Lucas and Washburn. Results from flow models developed for arterial blood flow may by useful to understand the flow dynamics in cases of unsteady forcing. The experimental methods build on prior work by the PI and Co-I on capillary bridge stabilization and control and by the PI on large-scale helical surfaces in simulated zero gravity. The PI has significant experience with the analysis of capillary surface statics and dynamics using image analysis. Broader Impacts The flow channels contemplated in this work certainly would seem to have potential for use in microchannel processing as well as other more speculative applications including: chip cooling via engineered microscale wicking systems (desired heat fluxes are increasing), use with interfacial polymerization to make unique small-scale membrane systems for separations, variable compliance capillary flow channels (compliance changed by changing the pitch of the spring), channels for liquid-gas contacting for chemical processing tasks in microgravity, the fundamental physics may be of interest to those concerned with wicking in various textiles with parallel fibers or coiled fibers, and the collection and concentration of airborne particulate matter in which particles stick to the liquid surface and are convected to one end of the channel by the flow. The proposal includes a plan to design and construct a gas-liquid contacting cartridge for use with desktop learning modules being developed in chemical engineering at WSU by B. Van Wie for implementing cooperative, hands-on, active and problem-based learning (CHAPL) in the undergraduate engineering curriculum. One graduate student will participate in this project and will work on both theoretical and experimental aspects.