Open-channel capillary flow in helical support structures

美国国家科学基金会化学与运输系统分部？微粒与多相过程项目（1415）提案编号：0731230主要研究者：Thiessen， David隶属于：华盛顿州立大学提案题目：螺旋支撑结构中的开放通道毛细管流动这项工作将探索由微弹簧组成的新型开放微流体通道中的流动。将液体注入一个小的水平弹簧中，在相邻线圈之间形成一个连续的液体通道，暴露的液体表面桥接在一起。因此，微弹簧可以用作具有许多潜在应用的柔性微流体管道。在具有最小支撑结构的开放通道中，毛细管驱动的流动可以应用于小规模系统（微流体、强化过程）或微重力条件下的传热或传质过程。开放通道毛细管流动已被证明在螺旋支架包括流动伴随传质。流动对润湿流体和非润湿流体都是可能的。将高度湿润的液体垂直吸进开式线圈微弹簧中，已被证明可以产生大约10倍直径的毛细管上升。在提出的工作中要测试的一个主要假设是，流动的驱动力可以从静态条件下结构中可持续的稳定压力范围内预测。探索液体通道静态稳定性的方法建立在描述毛细管系统（如液体桥、垂坠液滴和固定在槽上的圆柱形表面）稳定性的大量工作的基础上。据PI所知，在PI和合作者（B. J. Lowry）的工作之前，没有研究过螺旋自由表面的稳定性。初始穿透流理论也是基于Lucas和Washburn的经典论文开始的大量工作。建立的动脉血流模型的结果可能有助于理解非定常强迫情况下的血流动力学。实验方法建立在PI和Co-I在毛细管桥稳定和控制方面的先前工作的基础上，以及PI在模拟零重力条件下对大尺度螺旋表面的研究。PI在使用图像分析分析毛细管表面静力学和动力学方面具有丰富的经验。更广泛的影响本工作中设想的流通道似乎在微通道处理以及其他更多推测应用中具有使用潜力，包括：芯片通过工程微尺度排芯系统冷却（期望的热流通量增加），与界面聚合一起使用，制造独特的小型膜系统用于分离，可变顺应性毛细管流动通道（通过改变弹簧的螺距改变顺应性），在微重力下进行化学处理任务的液气接触通道，对于那些关心各种平行纤维或盘绕纤维织物的排芯，以及空气中颗粒物质的收集和浓缩的人来说，基本物理学可能会引起他们的兴趣，其中颗粒粘附在液体表面并被气流对流到通道的一端。该提案包括一项计划，设计和建造一个气液接触盒，用于华盛顿州立大学化学工程领域由B. Van Wie开发的桌面学习模块，用于在本科工程课程中实施合作、动手、主动和基于问题的学习（CHAPL）。一名研究生将参与该项目，并将在理论和实验方面进行工作。

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.