The proposed research will greatly advance the exceedingly limited fundamental knowledge of cavitation 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 engineering knowledge 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.
