444 research outputs found

    Effect of the surfactant on complex multi-phase annular flows

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    In the modern world, the scale of industrial production within all sectors has reached unprecedented levels due to ever-growing demand and consumption of various products. A vast majority of industrial processes exploits the benefits brought by the multiphase flows whose complex dynamics are governed by the concoction of fundamental physics. Probing the details of such flows, experimentally and/or theoretically provides an ability to develop and optimise the needs of industrial applications. Yet, this progression is gradual as it depends on the advancement of measurement technologies that enable the investigation of the complex behaviour and topologies of many different possible combinations of phases utilised in industry. Use of the novel optical diagnostic techniques coupled with bespoke capacitance probes in the present study enables us to explore uncharted territory of two-phase gas-liquid annular flows in vertically orientated pipes. In the present study, a recently developed variant of laser-induced fluorescence (LIF) technique, termed structured-planar laser-induced fluorescence (S-PLIF), is used which allows us to eliminate biases commonly encountered during film-thickness measurements of gas-liquid flows due to refraction and reflection of the light at the interface. In parallel, a bespoke capacitance probe is also employed which permits us to conduct film thickness measurements with high temporal resolution along the perimeter of the pipe. Simultaneous application of these two measurement techniques provides an opportunity to study the subtle differences found in thin annular film structures caused not only by the function of liquid and gas flow rates, but also by the surface-active agents which are widely known to cause drastic changes in flow behaviour due to surface tension gradients. The flow characteristics are studied in terms of mean film thickness, roughness, probability density functions, time-scales of the flows, and gas entrainment in the liquid film. The analysis of the data reveals important changes in the flow characteristics due to the presence of soluble surfactant. Firstly, it is observed that surfactant promotes thinning of annular films at nearly all flow conditions investigated herein, hinting at its influence on the turbulence within the bulk flow. The behaviour of interfacial waves was also found to be notably altered by the surfactant where the film roughness and the time-scale of the waves increase in gas-sheared film flows with low to moderate turbulence and low gas entrainment. This corresponds to flows not in the `regular wave' regime. A decrease in both characteristics then follows upon an increase in turbulence to a sufficiently high level of the two phases. The high gas-shear rate not only limits the highest attainable wave amplitude downstream, but also results in high agitation of air and water phases, and thus, high gas and liquid entrainment. Ultimately, this smooths the base film populated with small-amplitude waves and substantially reduces the amplitude of large interfacial waves. Generally, good agreement with relevant literature correlations is found. The estimated time-scales of the wave dynamics and Marangoni flow showed that the surfactant plays an increasingly important role on waves with lower amplitudes. The sizes of the bubbles entrained in the surfactant-free liquid film are found to exhibit log-normal distributions that become flatter with a decrease in the gas Reynolds number, while this distribution is maintained for surfactant-laden flows. On the other hand, wider distributions in the bubble sizes are found for the surfactant-laden flows at the highest gas-shear rate for all liquid Reynolds numbers. The normalised location of the bubbles (quantified as the relative entrainment depth, i.e., distance of the bubble from the local air-water film height in the wall-normal direction divided by the local film thickness) follows a Gaussian distribution, where the majority of the bubbles accumulate in the middle of the thin film. Understanding the need for further development of the multiphase flows that involves the use of surfactants, motivated us to develop a method to prepare water soluble fluorescent surfactant, which is described in the present work. Furthermore, a detailed characterisation of the fluorescent surfactant is also provided, which may encourage further experimental and modelling investigations of the relevant surfactant-laden multiphase dynamics found in small- and large-industrial scale applications.Open Acces

    Impedance Sensors for Fast Multiphase Flow Measurement and Imaging

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    Multiphase flow denotes the simultaneous flow of two or more physically distinct and immiscible substances and it can be widely found in several engineering applications, for instance, power generation, chemical engineering and crude oil extraction and processing. In many of those applications, multiphase flows determine safety and efficiency aspects of processes and plants where they occur. Therefore, the measurement and imaging of multiphase flows has received much attention in recent years, largely driven by a need of many industry branches to accurately quantify, predict and control the flow of multiphase mixtures. Moreover, multiphase flow measurements also form the basis in which models and simulations can be developed and validated. In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10 000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10 000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry

    Microfluidics and Nanofluidics Handbook

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    The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

    BioMEMS

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    As technological advancements widen the scope of applications for biomicroelectromechanical systems (BioMEMS or biomicrosystems), the field continues to have an impact on many aspects of life science operations and functionalities. Because BioMEMS research and development require the input of experts who use different technical languages and come from varying disciplines and backgrounds, scientists and students can avoid potential difficulties in communication and understanding only if they possess a skill set and understanding that enables them to work at the interface of engineering and biosciences. Keeping this duality in mind throughout, BioMEMS: Science and Engineering Perspectives supports and expedites the multidisciplinary learning involved in the development of biomicrosystems. Divided into nine chapters, it starts with a balanced introduction of biological, engineering, application, and commercialization aspects of the field. With a focus on molecules of biological interest, the book explores the building blocks of cells and viruses, as well as molecules that form the self-assembled monolayers (SAMs), linkers, and hydrogels used for making different surfaces biocompatible through functionalization. The book also discusses: Different materials and platforms used to develop biomicrosystems Various biological entities and pathogens (in ascending order of complexity) The multidisciplinary aspects of engineering bioactive surfaces Engineering perspectives, including methods of manufacturing bioactive surfaces and devices Microfluidics modeling and experimentation Device level implementation of BioMEMS concepts for different applications. Because BioMEMS is an application-driven field, the book also highlights the concepts of lab-on-a-chip (LOC) and micro total analysis system (μTAS), along with their pertinence to the emerging point-of-care (POC) and point-of-need (PON) applications

    Summaries of FY 1997 engineering research

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    Summaries of FY 1996 engineering research

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    Summaries of FY 1995 engineering research

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    BioMEMS

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    As technological advancements widen the scope of applications for biomicroelectromechanical systems (BioMEMS or biomicrosystems), the field continues to have an impact on many aspects of life science operations and functionalities. Because BioMEMS research and development require the input of experts who use different technical languages and come from varying disciplines and backgrounds, scientists and students can avoid potential difficulties in communication and understanding only if they possess a skill set and understanding that enables them to work at the interface of engineering and biosciences. Keeping this duality in mind throughout, BioMEMS: Science and Engineering Perspectives supports and expedites the multidisciplinary learning involved in the development of biomicrosystems. Divided into nine chapters, it starts with a balanced introduction of biological, engineering, application, and commercialization aspects of the field. With a focus on molecules of biological interest, the book explores the building blocks of cells and viruses, as well as molecules that form the self-assembled monolayers (SAMs), linkers, and hydrogels used for making different surfaces biocompatible through functionalization. The book also discusses: Different materials and platforms used to develop biomicrosystems Various biological entities and pathogens (in ascending order of complexity) The multidisciplinary aspects of engineering bioactive surfaces Engineering perspectives, including methods of manufacturing bioactive surfaces and devices Microfluidics modeling and experimentation Device level implementation of BioMEMS concepts for different applications. Because BioMEMS is an application-driven field, the book also highlights the concepts of lab-on-a-chip (LOC) and micro total analysis system (μTAS), along with their pertinence to the emerging point-of-care (POC) and point-of-need (PON) applications

    Second Microgravity Fluid Physics Conference

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    The conference's purpose was to inform the fluid physics community of research opportunities in reduced-gravity fluid physics, present the status of the existing and planned reduced gravity fluid physics research programs, and inform participants of the upcoming NASA Research Announcement in this area. The plenary sessions provided an overview of the Microgravity Fluid Physics Program information on NASA's ground-based and space-based flight research facilities. An international forum offered participants an opportunity to hear from French, German, and Russian speakers about the microgravity research programs in their respective countries. Two keynote speakers provided broad technical overviews on multiphase flow and complex fluids research. Presenters briefed their peers on the scientific results of their ground-based and flight research. Fifty-eight of the sixty-two technical papers are included here
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