Cavitation on MicroElectro Mechanical Systems

Rensselaer理工学院这项拟议的研究将通过仔细研究微系统中基本的微尺度构型(如孔口和洞口)中的空化流动，极大地促进微系统中极其有限的空化基础知识的发展。建立微型空化知识库将改进许多创新微流控系统的设计，如微型火箭、微型冷却器、微型冰箱、微型混合器、药物输送系统、包括运载火箭和高密度电源在内的微型动力系统、电子芯片冷却系统、化学微反应器、DNA合成分析和生物微机械系统。目前最先进的MEMS技术使泵、阀和喷嘴等各种独立的微型部件能够集成和组装到复杂的高速微流体机器中。这些新系统的几何尺寸在1-1000微米范围内，比传统机器小103-104倍，并在液体流动速度高达300m/S的情况下运行。我们小组最近对微系统中的空化进行了研究，得到了意想不到的结果，并与传统的尺度行为有很大偏差。因此，对微流体系统中的空化现象进行广泛的科学研究，是实现众多新型微机械的迫切和必要的条件。空化，即当压力降到蒸汽压以下时，液体中形成汽泡的现象，长期以来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是有据可查的，并在上个世纪进行了积极的研究。水力机械中的空化会限制性能，降低效率，改变水流的流体动力学，引起严重的结构振动，产生声学噪声，堵塞水流，造成灾难性的破坏。空化研究对改进大型水力机械的设计有很大的贡献。在目前的情况下，减少宏观机械中有关空化的现有信息，并将其用于微尺度设备的设计，确实是很有诱惑力的。虽然已经研究了伴随的空化缩尺效应，但它们充其量只适用于宏观尺度上的原型和真实世界典范之间的缩尺。因此，本研究的目的是定量和定性地了解微系统中的空化核对空化的影响，评估传统尺度模型在预测微设备中空化开始时的适用性，并研究不同条件下与微流控系统相关的空化流动机理。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孔和微孔的微制造和后续实验，这些微孔和微孔具有不同的表面(地形和化学)和流动(流核)条件，涉及一系列水力直径、表面几何形状和尺寸、流量、压力和功率水平。本研究将使用两种常见的工质(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。将研究不同表面和流动条件下的空化起始和发展空化，并绘制不同流动条件下的流型图。然后将结果与为传统规模系统开发的模型进行比较。所有这些工作将为加深对微系统中空化机理的理解和揭示提供手段。拟议研究的智力价值将是建立开创性的工程知识，量化表面形貌和化学以及流核对微系统中空化的影响。所获得的工程信息将极大地阐明表面和流核在微系统内空化中所起的作用，并为正确设计微动力器件提供指导。此外，这项研究工作将促进对微系统中空化的研究。这项研究的更广泛的影响将是通过研讨会和在国家和科学论坛上的陈述，向MEMS和空化界提供重要的科学信息，并强调微系统中的空化的有害影响。此外，拟议的工作将教育一名少数民族女研究生(来自波多黎各大学-马亚圭兹大学)，学习新兴领域的MEMS技术，特别是高速微流控技术。拟议研究工作的成果将在档案期刊和会议出版物上传播，还将纳入国际和平研究所教授的本科生和研究生课程。

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.