Pressure Losses Experienced By Liquid Flow Through Pdms Microchannels With Abrupt Area Changes

Given the surmounting disagreement amongst researchers in the area of liquid flow behavior at the microscale for the past thirty years, this work presents a fundamental approach to analyzing the pressure losses experienced by the laminar flow of water (Re = 7 to Re = 130) through both rectangular straight duct microchannels (of widths ranging from 50 to 130 micrometers), and microchannels with sudden expansions and contractions (with area ratios ranging from 0.4 to 1.0) all with a constant depth of 104 micrometers. The simplified Bernoulli equations for uniform, steady, incompressible, internal duct flow were used to compare flow through these microchannels to macroscale theory predictions for pressure drop. One major advantage of the channel design (and subsequent experimental set-up) was that pressure measurements could be taken locally, directly before and after the test section of interest, instead of globally which requires extensive corrections to the pressure measurements before an accurate result can be obtained. Bernoulli\u27s equation adjusted for major head loses (using Darcy friction factors) and minor head losses (using appropriate K values) was found to predict the flow behavior within the calculated theoretical uncertainty (~12%) for all 150+ microchannels tested, except for sizes that pushed the aspect ratio limits of the manufacturing process capabilities (microchannels fabricated via soft lithography using PDMS). The analysis produced conclusive evidence that liquid flow through microchannels at these relative channel sizes and Reynolds numbers follow macroscale predictions without experiencing any of the reported anomalies expressed in other microfluidics research. This work also perfected the delicate technique required to pierce through the PDMS material and into the microchannel inlets, exit and pressure ports without damaging the microchannel. Finally, two verified explanations for why prior researchers have obtained poor agreement between macroscale theory predictions and tests at the microscale were due to the presence of bubbles in the microchannel test section (producing higher than expected pressure drops), and the occurrence of localized separation between the PDMS slabs and thus, the microchannel itself (producing lower than expected pressure drops)

Electrohydrodynamic Manipulation Of Liquid Droplet Emulsions In A Microfluidic Channel

This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding of how the electric field can affect flowing droplet dynamics. This work deals with two primary models used in electrohydrodynamics: the leaky dielectric model and the perfect dielectric model. The perfect dielectric model assumes that fluids with low conductivities do not react to any effects from the small amount of free charge they contain, and can be assumed as dielectrics, or electrical insulators. The leaky dielectric model suggests that even though the free charge is minimal in fluids with low conductivities, it is still is enough to affect droplet deformations. Finite element numerical results of stationary droplet deformations, implemented using the level set method, compare well both qualitatively (prolate/oblate and vortex directions), and quantitatively with results published by other researchers. Errors of less than 7.5% are found when comparing three-dimensional (3D) numerical results of this study to results predicted by the 3D leaky dielectric model, for a stationary high conductivity drop suspended in a slightly lower conductivity suspending medium. Droplet formations in a T-junction with no applied electric field are adequately predicted numerically using the level set finite element technique, as demonstrated by other researchers and verified in this study. For 3D models, droplet size is within 6%, and droplet production frequency is within 2.4% of experimental values found in the microfluidic Tjunction device. In order to reduce computational complexity, a larger scale model was solved first iii to obtain electrical potential distributions localized at the channel walls for the electrode placement configurations. Droplet deceleration and pinning is demonstrated, both experimentally and numerically, by applying steep gradients of electrical potential to the microchannel walls. As droplets flow over these electrical potential “steps,” they are pinned to the channel walls if the resulting electric forces are large enough to overcome the hydrodynamic forces. A balance between four dimensionless force ratios, the electric Euler number (Eue – ratio of inertial to electric forces), Mason number (M a – ratio of viscous to electric forces), electric pressure (P s – ratio of upstream pressure forces to electric forces), and the electric capillary number (Cae – ratio of electric to capillary forces) are used to quantify the magnitudes of each of these forces required to pin a droplet, and is consistent with a cubic dependency on the drop diameter. For larger drop diameters, effects of hydrodynamic forces become more prominent, and for smaller droplets, a greater electric forces is required due to the proximity of the droplet boundary with reference to the electrified channel wall. Droplet deceleration and pinning can be exploited to route droplets into different branches of a microfluidic T-junction. In addition, using steep electrical potential gradients placed strategically along a microchannel, droplets can even be passively binned by size into separate branches of the microfluidic device. These characteristics have been identified and demonstrated in this work

Antonia Sentner\u27s Fight Against Deportation: An Example of the Federal Government\u27s Fight Against Communism

In the 20th century, the United States government used deportation as a tool to circumvent certain Constitutional protections in order to crack down on radicalism. This tactic was used in both the first and second “Red Scares.” In the 1940 and 1950s, a St. Louis deportation case rose to national prominence as it progressed through the federal court system. Antonia Sentner was the wife of Communist Party U.S.A. member and local labor leader, William Sentner. Her requests for naturalization were denied, even though her husband and children were born in the United States and she had lived here since she was 8 years old. This denial was on the basis of a short time in the early 1930s when Antonia had briefly been a member of CPUSA. This case reached the Supreme Court where the decision to deport her was struck down. This study is based on previously uncited primary sources

Effects of high volumes of fly ash on cement paste

The study of high-volume fly ash (HVFA) concrete mixtures has become popular due to the significant environmental and economic benefits which the material may provide. By including fly ash at 50 percent or greater replacement levels, substantial benefits could be obtained. However, the inclusion of fly ash can have negative effects, including incompatibilities between constituents of a mixture. As the fly ash replacement level increases, the degree and likelihood of these problems increases. In this study, paste mixtures were made, as part of a larger HVFA concrete study, in order to determine the degree to which varying levels of fly ash would affect the paste mixtures and to determine potential methods of mitigating the negative effects of high volumes of fly ash on concrete mixtures. Five Type I or I/II portland cements were tested in combination with five Class C fly ashes at 0, 25, 50, and 70 percent replacement levels. The effects of gypsum, calcium hydroxide, and rapid set cement additions were evaluated at fly ash replacement levels of 50 and 70 percent, and the effects of a Type A/F water-reducing admixture were examined for all fly ash replacement levels. The paste properties that were evaluated included compressive strength, heat of hydration, consistency, and setting time. Analysis of the results showed general trends for increasing fly ash replacement levels, such as slower strength gain, decreased heat of hydration, delayed setting times, and increased fluidity of the paste at very early ages. However, there were also many inconsistencies in the results, which were attributable to sulfate imbalances and increased aluminate hydration at early ages. It was found that, in many cases, these sulfate imbalances were lessened by the addition of gypsum. The additions of calcium hydroxide and rapid set cement also showed improvements, such as increased rates of strength gain and accelerated setting times --Abstract, page iii

Entsorgungslogistik - neue Technik senkt Risiko und Kosten

Bis vor wenigen Jahren beschränkte sich die Logistik allein auf den Stoffstrom in der Produktion, also auf die Herstellung von Produkten und deren Verteilung. Fast unberücksichtigt blieben bei der Herstellung anfallende Neben- und Abfallstoffe, die eine Entsorgung verlangen. Dieser Sachverhalt ist auch deshalb bemerkenswert, weil für diese Entsorgung - ebenso wie für die anderen Stoffströme - förder-, lager- und handhabungstechnische Anlagen erforderlich sind, und zwar mit einem durchaus beachtlichen, ständig wachsenden Marktvolumen. Entsorgungslogistik wird immer wichtiger, allerdings bedarf es einer gründlichen Analyse des Produktionsbetriebs, um mit dem richtigen Konzept das Risikopotential und die Kosten senken zu können

Die Technik senkt Risiko und Kosten

Die Logistik beschränkte sich vor wenigen Jahren allein auf den Stoffstrom in der Produktion, auf die Herstellung von Produkten also und deren Verteilung. Fast unberücksichtigt blieben bei der Herstellung anfallende Neben- und Abfallstoffe, die eine Entsorgung verlangen. Dieser Sachverhalt ist auf der anderen Seite auch deshalb bemerkenswert, weil für diese Entsorgung genauso wie für die anderen Stoffströme förder-, lager- und handhabungstechnische Anlagen und Systeme erforderlich sind, mit einem sicherlich schon beachtlichen und ständig wachsenden Marktvolumen. Durch grundlegende Untersuchungen und technische Entwicklungen entstanden seit dem Jahre 1988 in der Entsorgungslogistik neue Systeme. Für derartige Konzeptionen ist eine ganzheitliche Betrachtung der Produktionsbetriebe entscheidend, um im Rahmen eines Entsorgungs-Consultings Risikopotentiale und Kosten zu senken

Entsorgungslogistik am Beispiel Sonderabfall

Das hier ausgewählte fiktive Sonderabfall-Zwischenlager zeigt, daß es möglich ist, sowohl zu einem ganzheitlichen, im Verbund stehenden logistischen System zu kommen und trotzdem unter Erhöhung der Sicherheitstechnik zu einer Vollautomatisierung und damit zu einer Erschließung der Rationalisierungspotentiale der Logistikfunktion Lagern im Entsorgungsbereich zu kommen

Entsorgung im Krankenhaus

Der Zwang zur Verwertung von Wertstoffen im Rahmen des Recyclings, möglichst unter Anwendung von automatisierten, d.h. kostengünstigen Systemen, ist bei der heutigen Abfallsituation unumgänglich. Dr. K.-H. Wehking, Geschaftsführer der LogTech GmbH, beschreibt den Einsatz eines neu konzipierten Systems in der von der Verwaltung der medizinischen Einrichtungen betriebenen Abfallzentrale innerhalb des Zentralklinikums

Technische Anforderungen an die Umsetzung des dualen Abfallwirtschaftssystems

Mit dem Konzept der "dualen Abfallwirtschaft" hat sich die Industrie einiges vorgenommen. Bis Ende 1993 soll das flächendeckende Sammel- und Verwertungssystem für verwertbare Verpackungsabfälle bundesweit, einschließlich der ehemaligen DDR, stehen. Entscheidend für den Erfolg wird sein, wie sauber die einzelnen Materialfraktionen separiert werden können. Neue Sammeltechniken sind gefragt

Orchestration of employees\u27 creativity: A phased approach

Digital innovation is a promising but challenging way for established organizations to achieve sustainable competitive advantage. A young research stream focuses on the development of innovations by means of employee involvement, which uses the knowledge and creativity of employees. Although it is clear that employees have been innovation drivers, studies on the roles of knowledge and creativity as foundations of employee-driven innovation are all but absent from the literature. Since not all individuals are equally creative, we investigate, through the analytical lens of the model of creativity and innovation, whether domain knowledge matters or if teams lacking domain knowledge can deliver satisfying results, too. The data collection is based on two design-thinking workshops including interviews, observations, and a survey with domain experts who evaluate the prototypes. Opposing to common assumptions of creativity techniques, domain knowledge is fundamental for developing digital innovations