Cavitation on MicroElectro Mechanical Systems

提出的研究将通过对基本微尺度配置（如孔板和风投板）中的空化流动的细致研究，极大地推进微系统中极其有限的空化基础知识。建立微尺度空化知识库将改善许多创新微流体系统的设计，如微火箭、微冷却器、微冰箱、微混合器、药物输送系统、微动力系统（包括运载火箭和高密度电源）、电子芯片冷却系统、化学微反应器、DNA合成分析和生物mems系统。当前最先进的MEMS技术已经能够将各种独立的微部件（如泵，阀和喷嘴）集成和组装到复杂的高速微流控机器中。这些新型系统的几何尺寸在1-1000微米范围内，比传统机器小103-104倍，并且在高达300米/秒的液体流速下运行。我们小组最近对微系统中的空化现象进行的研究产生了意想不到的结果，并且与传统的尺度行为有很大的不同。因此，对微流体系统中的空化现象进行广泛的科学研究对于许多新型微机械的实际实现是迫切而必要的。空化现象，即当压力低于蒸汽压时，液体中形成的蒸汽穴，一直是流体机械工程中关注的问题。空化对传统流体机械的有害影响在上个世纪得到了充分的证明和积极的研究。水力机械中的空化会限制性能，降低效率，改变流动的流体动力学，引起剧烈的结构振动，产生噪声，阻塞流动并造成灾难性的破坏。对空化现象的研究对改进大型水力机械的设计具有重要意义。在目前的情况下，缩小宏观机械中有关空化的现有信息并将其应用于微尺度设备的设计确实很有诱惑力。虽然已经研究了伴随空化的尺度效应，但在宏观尺度上，它们最多适用于原型和现实世界范例之间的尺度。因此，本研究的目的是建立对微系统中原子核对空化效应的定量和定性认识，评估传统比例模型在预测微器件中空化起始的适用性，并研究不同条件下与微流体系统相关的空化流动机制。为了实现这些目标，提出了一项全面的实验研究。拟议的工作将涉及微制造和随后的实验，在各种表面（地形和化学）和流动（流核）条件下，在一系列水力直径，表面几何形状和尺寸，流量，压力和功率水平上。本研究将采用两种常见的工作流体（乙醇和水）。将进行高速、微观流动可视化研究，以补充定量测量。在不同的表面和流动条件下，将研究空化的开始和发展，并绘制各种流动条件下的流动模式。然后将结果与为传统规模系统开发的模型进行比较。这些工作将为进一步了解和揭示微系统中空化的机制提供手段。拟议研究的智力价值将是建立开创性的工程知识，量化表面形貌、化学和流核对微系统中空化的影响。所得的工程信息将极大地阐明表面核和流核在微系统内部空化中的作用，并为合理设计微功率器件提供指导。此外，这项研究工作将促进微系统中空化的研究。这项研究的广泛影响将是为MEMS和空化社区提供重要的科学信息，并通过在国家和科学论坛上的研讨会和演讲来强调微系统中空化的有害影响。此外，拟议的工作将教育一名少数民族女研究生（来自波多黎各-马亚圭斯大学）在新兴的MEMS技术领域，特别是高速微流体。拟议研究工作的结果将在档案期刊和会议出版物中传播，并将纳入PI教授的本科和研究生课程。

ABSTRACT - 0520604Rensselaer Polytechnic InstituteThe proposed research will greatly advance the exceedingly limited fundamental knowledge ofcavitation in microsystems through a meticulous study of cavitating flows in rudimentary micro scale configurations such as orifices and venturis. Establishing a micro-scale cavitation knowledge base will ameliorate the design of numerous innovative microfluidic systems, such as micro-rockets, micro-coolers, micro-refrigerators, micro mixers, drug delivery systems, micro power systems including launch vehicles and high density power sources, electronic chip cooling systems, chemical micro-reactors, DNA synthesis assays and bio-MEMS systems. The current state-of-the-art technology in MEMS has enabled the integration and assembly of assorted independent micro components such as pump, valves, and nozzles into complex high-speed microfluidic machines. These neoteric systems posses geometrical dimensions in the range of 1-1000 microns, which are 103-104 times less than conventional machines, and operate at liquid flow speeds up to 300 m/s. Recent studies performed by our group on cavitation in Microsystems have yielded unexpected results and major deviations from conventional scale behavior. Therefore, an extensive scientific investigation of cavitation in microfluidic systems is exigent and imperative for the pragmatic realization of numerous novel micro machines.Cavitation, the formation of vapor pockets in liquid when the pressure falls below the vapor pressure, has long been a concern in the engineering of fluid machines. The deleterious effects of cavitation on conventional fluid machinery are well documented and have been aggressively researched in the last century. Cavitation in hydraulic machinery can limit performance, lower efficiency, modify the hydrodynamics of the flow, introduce severe structural vibration, generate acoustic noise, choke flow and cause catastrophic damage. Research on cavitation has contributed immensely towards improving the design of macro-scale hydraulic machinery. In the current scenario, it is indeed tempting to scale down the available information on cavitation in macro-scale machinery and employ it in the design of microscale devices. Although concomitant scaling effects of cavitation have been investigated, they are at best applicable for scaling between prototypes and real-world paragons at the macro-scale. Thus, the objectives of this research are to establish quantitative and qualitative understanding of nuclei effects on cavitation in microsystems, to assess the applicability of conventional scale models to predict cavitation inception in micro devices, and to study cavitating flow mechanisms pertinent to microfluidic systems under various conditions. To accomplish these objectives, a comprehensive experimental investigation is proposed. The proposed work will involve microfabrication and subsequent experiments on micro venturis and microorifices with various surface (topography and chemistry) and flow (stream nuclei) conditions, over a range of hydraulic diameters, surface geometries and dimensions, flow rates, pressures, and power levels. Two commonly encountered working fluids (ethanol and water) will be employed in this study. Highspeed, microscopic flow visualization studies will be undertaken to complement the quantitative measurements. Both cavitation inception and developed cavitation for various surfaces and flow conditions will be studied and flow patterns will be mapped under various flow conditions. The results will then be compared against models developed for conventional scale systems. All these tasks will provide means to enhance the understanding and unveil the mechanism of cavitation in microsystems.The Intellectual merit of the proposed research will be to establish pioneering engineeringknowledge quantifying the effects of surface topography and chemistry and stream nuclei on cavitation in microsystems. The derived engineering information will greatly clarify the role played by surface and stream nuclei in cavitation inside microsystems, and provide guidelines to properly design micro power devices. Additionally, this research work will stimulate research on cavitation in microsystems.The Broader impact of this research will be to provide vital scientific information to the MEMS and cavitation community and highlight the pernicious effects of cavitation in microsystems via seminars and presentations at national and scientific forums. Additionally, the proposed work will educate one minority female graduate student (from the University of Puerto Rico-Mayaguez) in the emerging field of MEMS technology, especially high-speed microfluidics. The results from the proposed research endeavor will be disseminated in archival journal and conference publications, and will also be incorporated into the undergraduate and graduate courses taught by the PI.