Download or read book Toward the Improved Simulation of Microscale Gas Flow written by Matthew James McNenly and published by . This book was released on 2006 with total page 924 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rarefied Gas Dynamics written by Ching Shen and published by Springer Science & Business Media. This book was released on 2006-03-30 with total page 406 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerodynamics is a science engaged in the investigation of the motion of air and other gases and their interaction with bodies, and is one of the most important bases of the aeronautic and astronautic techniques. The continuous improvement of the configurations of the airplanes and the space vehicles aid the constant enhancement of their performances are closely related with the development of the aerodynamics. In the design of new flying vehicles the aerodynamics will play more and more important role. The undertakings of aeronautics and astronautics in our country have gained achievements of world interest, the aerodynamics community has made outstanding contributions for the development of these undertakings and the science of aerodynamics. To promote further the development of the aerodynamics, meet the challenge in the new century, summary the experience, cultivate the professional personnel and to serve better the cause of aeronautics and astronautics and the national economy, the present Series of Modern Aerodynamics is organized and published.

Download or read book Rarefied Gas Flows in Microscale Geometries written by Stephanie Y. Docherty and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Accurate predictions of the flow behaviour in microscale geometries are needed, for example, to design and optimise micro devices, and to ensure their safety/reliability. Rarefied gas flows in such geometries tend, however, to be far from local thermodynamic equilibrium, meaning that the flow behaviour cannot be described by conventional fluid mechanics. Alternative approaches for modelling 'non-equilibrium' gas flows have been proposed in recent years; because analytical solution methods are subject to significant limitations, the direct simulation Monte Carlo (DSMC) method is, at present, the most practical numerical simulation tool for dilute gases. Unfortunately, the computational expense of tracking and computing collisions between thousands (or perhaps millions) of DSMC particles means that simulating the scales of realistic flow problems can require months (or even years) of computing time. This has resulted in the development of continuum-DSMC 'hybrid' methods, which aim to combine the efficiency of a conventional continuum-fluid description with the detail and accuracy of the DSMC method. This thesis focuses on the development of a continuum-DSMC method that offers a more general approach than existing methods. Using a heterogeneous framework with a field-wise coupling strategy, this new method is not subject to the limitations of the well-known domain decomposition framework, or the restrictions of the heterogeneous point-wise coupling approach. The continuum-fluid description is applied across the entire flow field, while the DSMC method is performed in dispersed micro elements that can be any size and at any location; these elements then provide the continuum description with updated constitutive and boundary information. Unlike most methods in the literature, the coupling strategy presented here is able to cope with heat transfer, and so non-isothermal flows can be simulated. Testing and validation of this new continuum-DSMC method is performed by simulating a number of benchmark cases and comparing the results with full DSMC solutions of the same cases. Two 1D flow problems are considered: a micro Fourier flow problem tests the energy coupling procedure of the method, and a high-speed micro Couette flow problem demonstrates the full coupling algorithm. In general, the method's accuracy is found to depend on the arrangement of the micro elements - with sufficient micro resolution, good agreement with the equivalent full DSMC simulations can be obtained. Although the hybrid method offers no computational speed-up over the full DSMC simulations for several of these 1D test cases and only modest speed-ups for the others, both of these 1D ow problems are simulated only to validate the coupling strategy of the method. Considerable speed-ups are offered by the method when simulating a larger and more realistic flow problem: a microchannel with a high-aspect-ratio cross-section acts as a representative geometry for modelling a gas flow through a narrow microscale crack. While the limitations of existing hybrid methods preclude their use for this type of high-aspect-ratio geometry, the new hybrid method is able to model this problem under isothermal and non-isothermal conditions. The implementation of the method is simplified to 2D by assuming that the flow variation in the streamwise direction is negligible, i.e. the method is applied to the microchannel cross-section only. Accurate predictions of the mass flow rate and the streamwise velocity field are obtained for a number of test cases; accurate predictions of the temperature field are also obtained when there is a temperature difference between the bounding walls.

Download or read book Modeling of Microscale Gas Flows Using the Direct Simulation Monte Carlo Method written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Microscale Gas Flow written by Toby Thatcher and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Micro Gas Flows written by Nishanth Dongari and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The behaviour of gas flows in microscale systems cannot be accurately described by the Navier-Stokes-Fourier (N-S-F) equations of macroscale fluid dynamics. Micro and nano-scale gas flows often display non-standard fluid behaviour, and near a solid bounding surface they are dominated by the effect of gas molecule-surface interactions. This leads to the formation of a Knudsen layer (KL): a local thermodynamically non-equilibrium region of thickness of a few mean free paths (MFP) from the surface. Linear constitutive relations for shear stress and heat flux are no longer necessarily valid in the KL. To account for this, we investigate a power-law (PL) form of the probability distribution function for free paths of rarefied gas molecules in arbitrary wall confinements. PL based geometry dependent MFP models are derived for planar and non-planar geometry systems by taking into account the boundary limiting effects on the molecular free paths. Molecular dynamics (MD) numerical experiments are carried out to rigorously validate the PL model, under a wide range of rarefaction conditions. MD is the most appropriate simulation tool as it is deterministic, allowing for realistic molecular behaviour, i.e. molecular attractions, repulsions, movements and scatterings. The free path measurements of individual molecules convey that conventional form of exponential distribution function is not valid under rarefied conditions and follow Lévy type of flights, irrespective of the presence of the wall. MFP profiles of MD measurements and PL model for confined surfaces in the transition flow regime show sharp gradients close to the wall, while exponential model predicts shallower gradients. As gas transport properties can be related to the MFP through kinetic theory, the N-S-F constitutive relations, and the velocity slip and the temperature jump boundary conditions are then modified in order to better capture the flow behaviour in the Knudsen layers close to surfaces. The new modelling technique is tested for isothermal and non-isothermal gas flows in both planar and non-planar confinements. The results show that our approach greatly improves the near-wall accuracy of the N-S-F equations, well beyond the slip-flow regime. In general, the current method exhibits good agreement for velocity and temperature profiles up to Kn ~ 1, and for integral flow parameters up to Kn ~ 5, without tuning any slip and jump coefficients. The PL scaling can be readily extended to complex geometries, and straightforwardly incorporated into existing computational fluid dynamics (CFD) codes. The current work is significant from the numerical simulation point of view because simulation tools are better developed for N-S-F equations, when compared to other higher order equations such as Burnett, R26 etc.

Download or read book Numerical Simulations of Microscale Gas Flows Continuum Approach written by A. Chaudhuri and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Particle Simulation of Micro scale Gas Flows written by Iain D. Boyd and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Selected Papers from the ISTEGIM 19 written by Lucien Baldas and published by MDPI. This book was released on 2021-03-01 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Special Issue compiles 11 scientific works that were presented during the International Symposium on Thermal Effects in Gas Flow in Microscale, ISTEGIM 2019, held in Ettlingen, Germany, in October 2019. This symposium was organized in the framework of the MIGRATE Network, an H2020 Marie Skłodowska-Curie European Training Network that ran from November 2015 to October 2019 (www.migrate2015.eu). MIGRATE intends to address some of the current challenges in innovation that face the European industry with regard to heat and mass transfer in gas-based microscale processes. The papers collected in this book focus on fundamental issues that are encountered in microfluidic systems involving gases, such as the analysis of gas–surface interactions under rarefied conditions, the development of innovative integrated microsensors for airborne pollutants, new experimental techniques for the measurement of local quantities in miniaturized devices and heat transfer issues inside microchannels. The variety of topics addressed in this book emphasizes that multi-disciplinarity is the real common thread of the current applied research in microfluidics. We hope that this book will help to stimulate early-stage researchers who are working in microfluidics all around the world. This book is dedicated to them!

Download or read book Efficient Numerical Techniques for Multiscale Modeling of Thermally Driven Gas Flows with Application to Thermal Sensing Atomic Force Microscopy written by Nathan Daniel Masters and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The modeling of Micro- and NanoElectroMechanical Systems (MEMS and NEMS) requires new computational techniques that can deal efficiently with geometric complexity and scale dependent effects that may arise. Reduced feature sizes increase the coupling of physical phenomena and noncontinuum behavior, often requiring models based on molecular descriptions and/or first principles. Furthermore, noncontinuum effects are often localized to small regions of (relatively) large systemsprecluding the global application of microscale models due to computational expense. Multiscale modeling couples efficient continuum solvers with detailed microscale models to providing accurate and efficient models of complete systems. This thesis presents the development of multiscale modeling techniques for nonequilibrium microscale gas phase phenomena, especially thermally driven microflows. Much of this focuses on improving the ability of the Information Preserving DSMC (IP-DSMC) to model thermally driven flows. The IP-DSMC is a recent technique that seeks to accelerate the solution of direct simulation Monte Carlo (DSMC) simulations by preserving and transporting certain macroscopic quantities within each simulation molecules. The primary contribution of this work is the development of the Octant Splitting IP-DSMC (OSIP-DSMC) which recovers previously unavailable information from the preserved quantities and the microscopic velocities. The OSIP-DSMC can efficiently simulate flow fields induced by nonequilibrium systems, including phenomena such as thermal transpiration. The OSIP-DSMC provides an efficient method to explore rarefied gas transport phenomena which may lead to a greater understanding of these phenomena and new concepts for how these may be utilized in practical engineering systems. Multiscale modeling is demonstrated utilizing the OSIP-DSMC and a 2D BEM solver for the continuum (heat transfer) model coupled with a modified Alternating Schwarz coupling scheme. An interesting application for this modeling technique is Thermal Sensing Atomic Force Microscopy (TSAFM). TSAFM relies on gas phase heat transfer between heated cantilever probes and the scanned surface to determine the scan height, and thus the surface topography. Accurate models of the heat transfer phenomena are required to correctly interpret scan data. This thesis presents results demonstrating the effect of subcontinuum heat transfer on TSAFM operation and explores the mechanical effects of the Knudsen Force on the heated cantilevers.

Download or read book Computational Techniques for Multiphase Flows written by Guan Heng Yeoh and published by Butterworth-Heinemann. This book was released on 2019-02-27 with total page 640 pages. Available in PDF, EPUB and Kindle. Book excerpt: Computational Techniques for Multiphase Flows, Second Edition, provides the latest research and theories covering the most popular multiphase flows The book begins with an overview of the state-of-the-art techniques for multiple numerical methods in handling multiphase flow, compares them, and finally highlights their strengths and weaknesses. In addition, it covers more straightforward, conventional theories and governing equations in early chapters, moving on to the more modern and complex computational models and tools later in the book. It is therefore accessible to those who may be new to the subject while also featuring topics of interest to the more experienced researcher. Mixed or multiphase flows of solid/liquid or solid/gas are commonly found in many industrial fields, and their behavior is complex and difficult to predict in many cases. The use of computational fluid dynamics (CFD) has emerged as a powerful tool for understanding fluid mechanics in multiphase reactors, which are widely used in the chemical, petroleum, mining, food, automotive, energy, aerospace and pharmaceutical industries. This revised edition is an ideal reference for scientists, MSc students and chemical and mechanical engineers in these areas. Includes updated chapters in addition to a brand-new section on granular flows. Features novel solution methods for multiphase flow, along with recent case studies. Explains how and when to use the featured technique and how to interpret the results and apply them to improving applications.

Download or read book Gas Flows in Microsystems written by Lucien Baldas and published by MDPI. This book was released on 2019-10-28 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last two decades have witnessed a rapid development of microelectromechanical systems (MEMS) involving gas microflows in various technical fields. Gas microflows can, for example, be observed in microheat exchangers designed for chemical applications or for cooling of electronic components, in fluidic microactuators developed for active flow control purposes, in micronozzles used for the micropropulsion of nano and picosats, in microgas chromatographs, analyzers or separators, in vacuum generators and in Knudsen micropumps, as well as in some organs-on-a-chip, such as artificial lungs. These flows are rarefied due to the small MEMS dimensions, and the rarefaction can be increased by low-pressure conditions. The flows relate to the slip flow, transition or free molecular regimes and can involve monatomic or polyatomic gases and gas mixtures. Hydrodynamics and heat and mass transfer are strongly impacted by rarefaction effects, and temperature-driven microflows offer new opportunities for designing original MEMS for gas pumping or separation. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel theoretical and numerical models or data, as well as on new experimental results and technics, for improving knowledge on heat and mass transfer in gas microflows. Papers dealing with the development of original gas MEMS are also welcome.

Download or read book Numerical Simulation of Rarefied Gas Flow in Micro and Vacuum Devices written by Anirudh Singh Rana and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: It is well established that non-equilibrium flows cannot properly be described by traditional hydrodynamics, namely, the Navier-Stokes-Fourier (NSF) equations. Such flows occur, for example, in micro-electro-mechanical systems (MEMS), and ultra vacuum systems, where the dimensions of the devices are comparable to the mean free path of a gas molecule. Therefore, the study of non-equilibrium effects in gas flows is extremely important. The general interest of the present study is to explore boundary value problems for moderately rarefied gas flows, with an emphasis on numerical solutions of the regularized 13--moment equations (R13). Boundary conditions for the moment equations are derived based on either phenomenological principles or on microscopic gas-surface scattering models, e.g., Maxwell's accommodation model and the isotropic scattering model.Using asymptotic analysis, several non-linear terms in the R13 equations are transformed into algebraic terms. The reduced equations allow us to obtain numerical solutions for multidimensional boundary value problems, with the same set of boundary conditions for the linearized and fully non-linear equations. Some basic flow configurations are employed to investigate steady and unsteady rarefaction effects in rarefied gas flows, namely, planar and cylindrical Couette flow, stationary heat transfer between two plates, unsteady and oscillatory Couette flow. A comparison with the corresponding results obtained previously by the DSMC method is performed. The influence of rarefaction effects in the lid driven cavity problem is investigated. Solutions obtained from several macroscopic models, in particular the classical NSF equations with jump and slip boundary conditions, and the R13--moment equations are compared. The R13 results compare well with those obtained from more costly solvers for rarefied gas dynamics, such as the Direct Simulation Monte Carlo (DSMC) method. Flow and heat transfer in a bottom heated square cavity in a moderately rarefied gas are investigated using the R13 and NSF equations. The results obtained are compared with those from the DSMC method with emphasis on understanding thermal flow characteristics from the slip flow to the early transition regime. The R13 theory gives satisfying results including flow patterns in fair agreement with DSMC in the transition regime, which the conventional Navier-Stokes-Fourier equations are not able to capture.

Download or read book Geological disasters and its prevention in deep mining written by Shuren Wang and published by Frontiers Media SA. This book was released on 2023-02-02 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Study and Numerical Modeling of Gas Flow in Microchannels and Micronozzles written by and published by . This book was released on 2005 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the course of this research effort gas flows in microchannels and micronozzles were studied both experimentally and numerically. For the experimental study a flow visualization system was built and used to Study gas flows in microscale. Gas velocity measurements in microscope were conducted using both Laser Induced Fluorescence technique in conjunction with Image Correlation Velocimetry and Molecular Tagging Velocimetry technique. For the numerical study three different approaches were utilized. Continuum computational fluid dynamics was first used to study gas flows in microchannels and micronozzles. For micronozzles, effects of geometrical scaling down and different gas propellants were studied. For microchannels, slip versus no-slip boundary condition and compressibility and rarefaction effects were studied. Secondly, Direct simulation Monte Carlo (DSMC) method was used to study low Reynolds number flows in a conical micronozzle. The DSMC simulations were compared with the continuum model and available experimental data, and also used to study propellant gas temperature effect on the generated thrust Thirdly, a Unified Flow Solver that utilizes hybrid approach using deterministic Boltzmann solver for highly non-equilibrium flows at high Knudsen number and continuum solvers for low Knudsen numbers was tested and demonstrated for gas flows in microscale. Tested cases included gas flows in both microchannels and micronozzles.

Download or read book Fuel Cell Modeling and Simulation written by Gholam Reza Molaeimanesh and published by Elsevier. This book was released on 2022-11-15 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fuel Cell Modeling and Simulation: From Micro-Scale to Macro-Scale provides a comprehensive guide to the numerical model and simulation of fuel cell systems and related devices, with easy-to-follow instructions to help optimize analysis, design and control. With a focus on commercialized PEM and solid-oxide fuel cells, the book provides decision-making tools for each stage of the modeling process, including required accuracy and available computational capacity. Readers are guided through the process of developing bespoke fuel cell models for their specific needs. This book provides a step-by-step guide to the fundamentals of fuel cell modeling that is ideal for students, researchers and industry engineers working with fuel cell systems, but it will also be a great repository of knowledge for those involved with electric vehicles, batteries and computational fluid dynamics. Offers step-by-step guidance on the simulation of PEMFC and SOFC Provides an appendix of source codes for modeling, simulation and optimization algorithms Addresses the fundamental thermodynamics and reaction kinetics of fuel cells, fuel cell electric vehicles (FCEVs) and fuel cell power plant chapters

Download or read book Microscale and Nanoscale Heat Transfer written by Mourad Rebay and published by CRC Press. This book was released on 2016-01-06 with total page 499 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microscale and Nanoscale Heat Transfer: Analysis, Design, and Applications features contributions from prominent researchers in the field of micro- and nanoscale heat transfer and associated technologies and offers a complete understanding of thermal transport in nano-materials and devices. Nanofluids can be used as working fluids in thermal system