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Author: Yu Lu Publisher: ISBN: Category : Microfluidics Languages : en Pages : 0
Book Description
Microfluidic systems attract attention because the benefit they offer such as very high surface area to volume ratio and the precise control of the flow features or droplets formation. However, the study of displacement flows has not been systematically explored. This thesis presents a study of the behaviour of liquid-liquid two-phase flows in microchannel during the displacement of one liquid by another. Liquid displacement using immiscible and miscible fluid pairs were carried out. The kinematic viscosities of the fluids used range from 1 to 100 cSt. Three types of straight channel and a T-junction channel were tested. The flow activities at the fluids interface, with the addition of surfactants, were mainly investigated. Flow regimes were identified and their occurrence was illustrated via flow pattern maps. CFD simulations are applied largely in the study of fluid mechanics aiming to confidently predict flow behaviour from computational methods. The experimental results were used to validate CFD simulations carried out using the Fluent package incorporating the VoF model. Good agreement between simulation and experiment results was achieved.
Author: Yu Lu Publisher: ISBN: Category : Microfluidics Languages : en Pages : 0
Book Description
Microfluidic systems attract attention because the benefit they offer such as very high surface area to volume ratio and the precise control of the flow features or droplets formation. However, the study of displacement flows has not been systematically explored. This thesis presents a study of the behaviour of liquid-liquid two-phase flows in microchannel during the displacement of one liquid by another. Liquid displacement using immiscible and miscible fluid pairs were carried out. The kinematic viscosities of the fluids used range from 1 to 100 cSt. Three types of straight channel and a T-junction channel were tested. The flow activities at the fluids interface, with the addition of surfactants, were mainly investigated. Flow regimes were identified and their occurrence was illustrated via flow pattern maps. CFD simulations are applied largely in the study of fluid mechanics aiming to confidently predict flow behaviour from computational methods. The experimental results were used to validate CFD simulations carried out using the Fluent package incorporating the VoF model. Good agreement between simulation and experiment results was achieved.
Author: Volfango Bertola Publisher: CISM International Centre for Mechanical Sciences ISBN: Category : Science Languages : en Pages : 450
Book Description
This is an up-to-date review of recent advances in the study of two-phase flows, with focus on gas-liquid flows, liquid-liquid flows, and particle transport in turbulent flows. The book is divided into several chapters, which after introducing basic concepts lead the reader through a more complex treatment of the subjects. The reader will find an extensive review of both the older and the more recent literature, with abundance of formulas, correlations, graphs and tables. A comprehensive (though non exhaustive) list of bibliographic references is provided at the end of each chapter. The volume is especially indicated for researchers who would like to carry out experimental, theoretical or computational work on two-phase flows, as well as for professionals who wish to learn more about this topic.
Author: Young I. Cho Publisher: Academic Press ISBN: 0123815304 Category : Science Languages : en Pages : 459
Book Description
Advances in Heat Transfer fills the information gap between regularly scheduled journals and university-level textbooks by providing in-depth review articles over a broader scope than in journals or texts. The articles, which serve as a broad review for experts in the field, will also be of great interest to non-specialists who need to keep up-to-date with the results of the latest research. This serial is essential reading for all mechanical, chemical and industrial engineers working in the field of heat transfer, graduate schools or industry. Provides an overview of review articles on topics of current interest Bridges the gap between academic researchers and practitioners in industry A long-running and prestigious series
Author: Milnes P. David Publisher: Stanford University ISBN: Category : Languages : en Pages : 151
Book Description
Two-phase microfluidic heat exchangers have the potential to meet the large heat dissipation demands of high power electronics and computing systems. Two-phase cooling systems face practical challenges brought on by the growth and advection of the vapor phase in the confined geometries, which lead to large pressure drops, increased thermal resistance and the formation of detrimental flow instabilities. One proposed solution to these issues is phase separation, whereby the vapor is locally separated from the two-phase flow through a porous hydrophobic membrane. This dissertation describes a series of studies conducted to develop an understanding of the factors that influence vapor separation and its impact on the hydraulic and thermal characteristics of two-phase heat exchangers. Flow phenomena are a critical component in developing this understanding of phase separation. High speed visualization of adiabatic and diabatic vaporizing flows was carried out in a single 124[Mu]m by 98[Mu]m copper microchannel with a 65[Mu]m thick, 220nm pore diameter hydrophobic PTFE membrane wall. During adiabatic air-water flow, wavy-stratified and stratified flow dominated lower liquid velocities, while plug and annular type flows dominated at the higher velocities. Analysis found that air removal could be improved by increasing the venting area, increasing the trans-membrane pressure or using thinner, high permeability membranes. Diabatic water-vapor experiments with mass flux velocities of 140 and 340 kg/s-m2 and exit qualities up to 20% found that stratified type flows dominate at lower mass fluxes while cyclical churn-annular flow became more prevalent at the higher mass-flux and quality. The observed flow regimes are hypothesized to play a significant role in determining the pressure drop and heat transfer coefficient during flow boiling. To study the impact of various geometric and membrane factors on the performance of a phase separating microchannel heat exchanger dissipating 100W of heat, a numerical model incorporating vapor separation and transport during two-phase flow boiling in a microchannel was developed. The impact of substrate thermal conductivity and thickness, membrane permeability and thickness, liquid channel density, liquid and vent channel diameter and vent-to-liquid channel diameter ratio was studied and compared for a standard non-venting heat exchanger, a vapor venting heat exchanger and a non-venting heat exchanger occupying the same increased volume as the venting heat exchanger. The numerical study found that the venting heat exchanger had improved pressure drop and device temperatures for all tested conditions when compared against a standard heat exchanger but only under very limited conditions when compared against the volumetrically equivalent non-venting heat exchanger. The study indicates that the best venting heat exchanger performance is achieved when the membrane conductance is of the same order or higher than that of the microchannel; this can be achieved through the use of thin high permeability membranes coupled with small hydraulic diameter microchannels. Finally, a study was conducted to explore the fabrication methods to build a vapor separating heat exchanger and to quantify the operating performance of multichannel silicon and copper phase separating devices. A copper parallel microchannel heat exchanger with nineteen 130[Mu]m square microchannels was built and tested at heat fluxes of up to 820 kW/m2 and water mass fluxes of between 102 and 420 kg/s-m2. Normalized pressure drop was improved by as much as 60% and average substrate temperature by a maximum of 4.4°C between the non-venting control and vapor venting device under similar operating conditions. Comparison between the experimental results and simulation predictions found higher than expected pressure drop improvements at higher mass fluxes and poorer heat transfer coefficients at the lowest mass flux. Based on the flow phenomena study these discrepancies are believed to be due to the mass flux and vapor quality dependent two-phase flow structures. The encouraging experimental and numerical results motivate further study into phase separation methods, materials and flow physics. The development of a high performance phase separating heat exchanger, with the thermal benefits of two-phase boiling flow and the hydraulic benefits of single-phase liquid flow, would strongly enable the adoption and application of two-phase heat exchangers to provide effective and efficient cooling for next generation high power computing systems.
Author: S. Mostafa Ghiaasiaan Publisher: Cambridge University Press ISBN: 1316785300 Category : Technology & Engineering Languages : en Pages : 1322
Book Description
Providing a comprehensive introduction to the fundamentals and applications of flow and heat transfer in conventional and miniature systems, this fully enhanced and updated edition covers all the topics essential for graduate courses on two-phase flow, boiling, and condensation. Beginning with a concise review of single-phase flow fundamentals and interfacial phenomena, detailed and clear discussion is provided on a range of topics, including two-phase hydrodynamics and flow regimes, mathematical modeling of gas-liquid two-phase flows, pool and flow boiling, flow and boiling in mini and microchannels, external and internal-flow condensation with and without noncondensables, condensation in small flow passages, and two-phase choked flow. Numerous solved examples and end-of-chapter problems that include many common design problems likely to be encountered by students, make this an essential text for graduate students. With up-to-date detail on the most recent research trends and practical applications, it is also an ideal reference for professionals and researchers in mechanical, nuclear, and chemical engineering.
Author: Roger Scott Stanley Publisher: ISBN: Category : Heat Languages : en Pages : 0
Book Description
The purpose of this study was to investigate fluid mechanic and heat transfer characteristics of two-phase two-component flow in rectangular microchannels. Experiments were conducted using rectangular aluminum channels with hydraulic diameters ranging between 56 micrometers and 256 micrometers and aspect ratios which varied from 0.5 to 1.5. Both single- and two-phase tests were conducted using water and gaseous argon, helium, and nitrogen as the working fluids. The Reynolds number for both types of experiments ranged from approximately 50 to nearly 10,000. The Nusselt number ranged between 0.0002 and 70. The single- and two-phase experimental data were empirically correlated, using parameters derived from a dimensional analysis. Experimental data were also used to correlate the unknown variables in derived analytical expressions. Both single- and two-phase tests yielded excellent correlations of the friction factor. For Nusselt number, the correlations were fair to poor. Reynolds number and the combination of Reynolds number and Prandtl number were the dominant parameters in the prediction of pressure drop and heat transfer rate, respectively, in both single- and two-phase flows. The pressure drop predictions based on the semi-empirical relations by Martinelli for two-phase flows were shown to substantially over-predict the pressure drop measured in these experiments.
Author: Chao Yang Publisher: Academic Press ISBN: 0124115799 Category : Technology & Engineering Languages : en Pages : 322
Book Description
Numerical simulation of multiphase reactors with continuous liquid phase provides current research and findings in multiphase problems, which will assist researchers and engineers to advance this field. This is an ideal reference book for readers who are interested in design and scale-up of multiphase reactors and crystallizers, and using mathematical model and numerical simulation as tools. Yang and Mao’s book focuses on modeling and numerical applications directly in the chemical, petrochemical, and hydrometallurgical industries, rather than theories of multiphase flow. The content will help you to solve reacting flow problems and/or system design/optimization problems. The fundamentals and principles of flow and mass transfer in multiphase reactors with continuous liquid phase are covered, which will aid the reader’s understanding of multiphase reaction engineering. Provides practical applications for using multiphase stirred tanks, reactors, and microreactors, with detailed explanation of investigation methods Presents the most recent research efforts in this highly active field on multiphase reactors and crystallizers Covers mathematical models, numerical methods and experimental techniques for multiphase flow and mass transfer in reactors and crystallizers
Author: Yu Lu
Author: Yu Lu
Author: Volfango Bertola
Author: Jason Burr
Author: Shih-i Pai
Author: Young I. Cho
Author: Roger Scott Stanley
Author: Milnes P. David
Author: S. Mostafa Ghiaasiaan
Author: Roger Scott Stanley
Author: Chao Yang