Optical Measurements Of Mixing Processes In Turbulent Fluid Flows
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Optical Measurements Of Mixing Processes In Turbulent Fluid Flows
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Author : Huixin Li
language : en
Publisher:
Release Date : 2023
Optical Measurements Of Mixing Processes In Turbulent Fluid Flows written by Huixin Li and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023 with categories.
Many processes in chemical engineering and oceanography rely on fluid mixing. This thesis focuses on optical measurement techniques to experimentally investigate miscible liquid-liquid mixing and gas-liquid mixing. Previous numerical studies have examined the turbulent small-scale mixing, which is experimentally challenging because of the limited spatial resolution of the measurement techniques. A further difficulty emerges for active fluid mixing. When fluids of different densities, such as water and ethanol are mixed, experimental measurements for the small-scale fluctuations in turbulence are impeded by the optical distortion due to the spatio-temporally varying refractive index field. In this thesis, in order to investigate small-scale liquid-liquid mixing, an upscaled T-mixer was built with a height of 40 millimetres. A planar laser-induced fluorescence (PLIF) with high resolution was employed in proof-of-concept experiments concerning the T-junction. The results indicate that measuring the small-scale mixing in the viscous-convective range where the velocity does not fluctuate, but the scalar does, is possible. Subsequently, long inlet channels were added to the T-junction and the particle image velocimetry (PIV) technique was used to verify the fully developed laminar flows and to investigate the flow regimes for different Reynolds numbers. It was found that the present setup can achieve inlet conditions with fully developed laminar flows when the Reynolds number is smaller than 1100. The setup was validated by repeating the flow regimes in previous studies. However, small temperature differences had a weak effect on flow regimes, which should be avoided in the next measurements. Overall, high-quality measuring of the small-scale mixing dynamics in the T-mixer is now within reach. For active mixing with fluids of different densities, mixing usually causes optical measurement errors. In this thesis, a ray tracing simulation method is used in a three-dimensional flow to quantify the measurement errors of the flow velocity and flow acceleration for tracer-based velocimetry, i.e., particle tracking velocimetry (PTV). The flow field is from a direct numerical simulation of single-phase turbulent mixing of two miscible fluids. The measurement errors increase with increasing the refractive index difference. The errors of both velocity and acceleration are attributed to the spatial and the spatio-temporal gradients of the refractive indices. Since PTV, PIV and PLIF share the same working principles based on geometric optics, the findings are also assumed to hold for the measurements of other techniques. The thermal effect in the T-mixer on the measurement errors is subsequently estimated and found to be negligible. Finally, gas-liquid mixing is examined, in which a weakly soluble gas is transferred across the gas-liquid interface. This process is related to the climate balance and depends on surface waves and turbulence underneath the water in the ocean. Utilizing the refraction at the interface and optical displacements, a synthetic Schlieren method is developed to measure the surface topography. This method is implemented in experiments and allows high-accuracy measurements of free surface waves. This makes it feasible to implement simultaneous measurements of surface waves, mass transportation and turbulence under the water.
A Method For The Measurement Of Mixing Properties In A Turbulent Jet Flow
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Author : C. Borrego
language : en
Publisher:
Release Date : 1979
A Method For The Measurement Of Mixing Properties In A Turbulent Jet Flow written by C. Borrego and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1979 with Jets categories.
Micro And Macro Mixing
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Author : Henning Bockhorn
language : en
Publisher: Springer Science & Business Media
Release Date : 2009-12-26
Micro And Macro Mixing written by Henning Bockhorn and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009-12-26 with Science categories.
The homogenization of single phase gases or liquids with chemical reactive components by mixing belongs to one of the oldest basic operations applied in chemical engineering. The mixing process is used as an essential step in nearly all processes of the chemical industry as well as the pharmaceutical and food ind- tries. Recent experimentally and theoretically based results from research work lead to a fairly good prediction of the velocity fields in differend kinds of mixers, where as predictions of simultaneously proceeding homogeneous chemical re- tions, are still not reliable in a similar way. Therefore the design of equipment for mixing processes is still derived from measurements of the so called “mixing time” which is related to the applied methods of measurement and the special - sign of the test equipment itself. The cooperation of 17 research groups was stimulated by improved modern methods for experimental research and visualization, for simulations and nume- cal calculations of mixing and chemical reactions in micro and macro scale of time and local coordinates. The research work was financed for a six years period within the recently finished Priority Program of the German Research Foundation (DFG) named “Analysis, modeling and numerical prediction of flow-mixig with and without chemical reactions (SPP 1141)”. The objective of the investigations was to improve the prediction of efficiencies and selectivities of chemical re- tions on macroscopic scale.
Turbulent Mixing In Nonreactive And Reactive Flows
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Author : S. Murthy
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-11-11
Turbulent Mixing In Nonreactive And Reactive Flows written by S. Murthy and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-11-11 with Science categories.
Turbulence, mixing and the mutual interaction of turbulence and chemistry continue to remain perplexing and impregnable in the fron tiers of fluid mechanics. The past ten years have brought enormous advances in computers and computational techniques on the one hand and in measurements and data processing on the other. The impact of such capabilities has led to a revolution both in the understanding of the structure of turbulence as well as in the predictive methods for application in technology. The early ideas on turbulence being an array of complicated phenomena and having some form of reasonably strong coherent struc ture have become well substantiated in recent experimental work. We are still at the very beginning of understanding all of the aspects of such coherence and of the possibilities of incorporating such structure into the analytical models for even those cases where the thin shear layer approximation may be valid. Nevertheless a distinguished body of "eddy chasers" has come into existence. The structure of mixing layers which has been studied for some years in terms of correlations and spectral analysis is also getting better understood. Both probability concepts such as intermittency and conditional sampling as well as the concept of large scale structure and the associated strain seem to indicate possibilities of distinguishing and synthesizing 'engulfment' and molecular mixing.
Quantitative Methods For The Measurement And Monitoring Of Mixing Flows Using A Computer Vision System
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Author : Matej Novak
language : en
Publisher:
Release Date : 2001
Quantitative Methods For The Measurement And Monitoring Of Mixing Flows Using A Computer Vision System written by Matej Novak and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
In numerous production processes, such as mineral wool and paper production process, there exists a need for the direct quantitative visualization of turbulent flows. Assessment of quantitative results obtained using such methods requires, however, comparison with other state-of-the-art measurement methods. In the present work the performance of a computer-aided visualization and digital image-processing method was investigated by application to a turbulent mixing flow in the wake of a prismatic bluff body in a non-return subsonic wind tunnel and compared with more conventional techniques. A high-speed camera was used to capture smoke visualization images in the wake of a bluff body. Qualitative analysis as well as quantitative analysis of digitised sequences at different Reynolds numbers was performed on time series, obtained by simultaneous digitisation of the grey level in several small areas (windows) of the overall image. The flow visualization and analysis technique employed has the advantage that it enables simultaneous observation and analysis of separate regions of the flow field, and the size, location, and number of these regions can be readily selected. These advantages were demonstrated in practise. The study formed part of a co-operative EU programme (Noviscam) designed to compare such the visualization systems with conventional measures, and to test different chaotic measures obtained from digital image-processing signals. To verify the computer-aided visualization method against conventional methods of the flow field analysis, two types of analysis were performed: comparative non-simultaneous analysis using results of FFT analysis and turbulence profile intensity analysis, and cross-correlation analysis of simultaneous measurements using both a hot-film anemometer probe and the digital image-processing technique. In the second part of the study, concerned with chaotic measures, correlation dimension of the chaotic attractor, the degree of average local deformation of the trajectories in phase portraits of the light intensity time series, box-count, and Hölder exponent in various windows were investigated. The results confirmed that power spectra from both computer-aided visualization, and hot-film anemometry methods identified the expected vortex structures in the bluff body wake. Small scale characteristics were also detected and the average local deformation of the trajectories in the phase portraits was found to increase in connection with increasing correlation dimension. This is linked with increased flow complexity near the axis zone behind the bluff body. The -5/3 power law in power spectra was well defined insome regions. The turbulence intensity, calculated either from digital image analysis concentration fluctuations or velocity fluctuation analysis, reaches a maximum at a downstream position in the wake and asymptotically falls to a lower value further downstream. The results of cross-correlation analysis agreed well for both methods. Several other processes were examined quantitatively using the visualization system and methods of analysis developed in this work.
Three Dimensional Velocity And Vorticity Measuring And Image Analysis Techniques
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Author : Th. Dracos
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-06-29
Three Dimensional Velocity And Vorticity Measuring And Image Analysis Techniques written by Th. Dracos and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-06-29 with Science categories.
The contents of this volume reflect to a large extent the efforts made by a group of Institutes at the ETH Zürich to develop new techniques for measurements of flows in fluids in the last decade. The motivation came from the study of tr~sport and mixing processes in natural and industrial systems. One of the characteristic properties of turbulence is its high mixing efficiency. The techniques developed are therefore suitable, although not exclusively, for turbulence measurements. They can be subdivided into point-measurements and field-measurements. The aim of the point-measurements developed is to determine the three components of the velocity and all their first derivatives with good temporal resolution and accuracy in turbulent flows. The old and weIl established method of hot-wire anemometry was used for this purpose. One of the main achievements in this context is the construction of miniature multi-wire probes. This technique was introduced to the Institute of Hydromechanics and Water Resources Management of ETH Zürich by Profs. A. Tsinober and E. Kit from Tel-Aviv University. This was made possible by the generous financial support by ETH, for which I would like to express my gratitude on this occasion. In addition, Dr. F.E. Joergensen from DANTEC contributed an example of recent developments in the hardware ofConstant Temperature Anemometry (CTA), for which I am very thankful.
Scientific And Technical Aerospace Reports
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Author :
language : en
Publisher:
Release Date : 1994
Scientific And Technical Aerospace Reports written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1994 with Aeronautics categories.
Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Flow Measurement For Engineers And Scientists
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Author : Nicholas P. Cheremisinoff
language : en
Publisher: CRC Press
Release Date : 2022-01-27
Flow Measurement For Engineers And Scientists written by Nicholas P. Cheremisinoff and has been published by CRC Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022-01-27 with Science categories.
This book discusses instrumentation and experimental methods for obtaining detailed information on the structure of various types of flows as well as standard process flow instrumentation suitable for industrial control applications. It assists research-oriented and process engineering personnel.
Optical Diagnostics For Flow Processes
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Author : P. Buchhave
language : en
Publisher: Springer
Release Date : 2013-07-18
Optical Diagnostics For Flow Processes written by P. Buchhave and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-07-18 with Science categories.
The origin of optical methods for fluid flow investigations appears to be nontraceable. This is no matter for surprise. After all seeing provides the most direct and common way for humans to learn about their environment. But at the same time some of the most sophisticated methods for doing measurements in fluids are also based on light and often laser light. A very large amount of material has been published in this area over the last two decades. Why then another publication? Well, the field is still in a state of rapid development. It is characterised by the use of results and methods developed within very different areas like optical physics, spectroscopy, communication systems, electronics and computer science, mechanical engineering, chemical engineering and, of course, fluid dynamics. We are not aware of a book containing both introductory and more advanced material that covers the same material as presented here. The book is the result of a compilation and expansion of material presented at a summer school on Optical Diagnosticsfor Flow Processes,held at RiS0 National Laboratory and the Technical University of Denmark in September 1993. The aim of the course was to provide a solid background for understanding, evaluating, and using modem optical diagnostic methods, addressing Ph. D. students and researchers active in areas of fluid flow research. The disciplines represented by the participants ranged from atmospheric fluid dynamics to biomedicine.
Optical Measurements
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Author : Franz Mayinger
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-03-14
Optical Measurements written by Franz Mayinger and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-03-14 with Science categories.
Increasing possibilities of computer-aided data processing have caused a new revival of optical techniques in many areas of mechanical and chemical en gineering. Optical methods have a long tradition in heat and mass transfer and in fluid dynamics. Global experimental information is not sufficient for developing constitution equations to describe complicated phenomena in fluid dynamics or in transfer processes by a computer program . Furthermore, a detailed insight with high local and temporal resolution into the thermo-and fluiddynamic situations is necessary. Sets of equations for computer program in thermo dynamics and fluid dynamics usually consist of two types of formulations: a first one derived from the conservation laws for mass, energy and momentum, and a second one mathematically modelling transport processes like laminar or turbulent diffusion. For reliably predicting the heat transfer, for example, the velocity and temperature field in the boundary layer must be known, or a physically realistic and widely valid correlation describing the turbulence must be avail able. For a better understanding of combustion processes it is necessary to know the local concentration and temperature just ahead of the flame and in the ignition zone.
