Numerical Study of Gas-surface Interaction Models for Micro Scale Rarefied Gas Flow Simulation PDF Download
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Author: Tengfei Liang
Publisher:
ISBN:
Category : Fluid dynamics
Languages : en
Pages : 111
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Book Description
Author: Tengfei Liang
Publisher:
ISBN:
Category : Fluid dynamics
Languages : en
Pages : 111
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Book Description
Author: Ching Shen
Publisher: Springer Science & Business Media
ISBN: 3540272305
Category : Science
Languages : en
Pages : 406
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Book Description
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.
Author: Daniel John Rader
Publisher:
ISBN:
Category :
Languages : en
Pages : 55
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Book Description
A combined experimental/modeling study was conducted to better understand the critical role of gas-surface interactions in rarefied gas flows. An experimental chamber and supporting diagnostics were designed and assembled to allow simultaneous measurements of gas heat flux and inter-plate gas density profiles in an axisymmetric, parallel-plate geometry. Measurements of gas density profiles and heat flux are made under identical conditions, eliminating an important limitation of earlier studies. The use of in situ, electron-beam fluorescence is demonstrated as a means to measure gas density profiles although additional work is required to improve the accuracy of this technique. Heat flux is inferred from temperature-drop measurements using precision thermistors. The system can be operated with a variety of gases (monatomic, diatomic, polyatomic, mixtures) and carefully controlled, well-characterized surfaces of different types (metals, ceramics) and conditions (smooth, rough). The measurements reported here are for 304 stainless steel plates with a standard machined surface coupled with argon, helium, and nitrogen. The resulting heat-flux and gas-density-profile data are analyzed using analytic and computational models to show that a simple Maxwell gas-surface interaction model is adequate to represent all of the observations. Based on this analysis, thermal accommodation coefficients for 304 stainless steel coupled with argon, nitrogen, and helium are determined to be 0.88, 0.80, and 0.38, respectively, with an estimated uncertainty of {+-}0.02.
Author: Anirudh Singh Rana
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
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.
Author: Nishanth Dongari
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author: Lei Wu
Publisher:
ISBN: 9789811928734
Category :
Languages : en
Pages : 0
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Book Description
This book highlights a comprehensive description of the numerical methods in rarefied gas dynamics, which has strong applications ranging from space vehicle re-entry, micro-electromechanical systems, to shale gas extraction. The book consists of five major parts: The fast spectral method to solve the Boltzmann collision operator for dilute monatomic gas and the Enskog collision operator for dense granular gas; The general synthetic iterative scheme to solve the kinetic equations with the properties of fast convergence and asymptotic preserving; The kinetic modeling of monatomic and molecular gases, and the extraction of critical gas parameters from the experiment of Rayleigh-Brillouin scattering; The assessment of the fluid-dynamics equations derived from the Boltzmann equation and typical kinetic gas-surface boundary conditions; The applications of the fast spectral method and general synthetic iterative scheme to reveal the dynamics in some canonical rarefied gas flows. The book is suitable for postgraduates and researchers interested in rarefied gas dynamics and provides many numerical codes for them to begin with.
Author: Felix Sharipov
Publisher: John Wiley & Sons
ISBN: 352741326X
Category : Technology & Engineering
Languages : en
Pages : 330
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Book Description
Aimed at both researchers and professionals who deal with this topic in their routine work, this introduction provides a coherent and rigorous access to the field including relevant methods for practical applications. No preceding knowledge of gas dynamics is assumed.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 110
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Book Description
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.
Author: Stephanie Y. Docherty
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author: Ricardo Brancher
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
This thesis is devoted to the experimental and numerical study of the interaction between gas and solid surface. Rarefied gas flows through a rectangular microchannel under both isothermal and non-isothermal conditions were experimentally evaluated. The tangential momentum accommodation coefficient for PEEK (Poly Ether Ether Ketone) material associated to five gases (helium, neon, nitrogen, argon, krypton) was extracted from both pressure and temperature gradient driven flows. Additionally, steady one-dimensional flows of a polyatomic gas in the presence of an adsorbing-desorbing surface kept at constant and uniform temperature are simulated by solving numerically the Boltzmann kinetic equation by the Direct Simulation Monte Carlo (DSMC) method. It is considered the flow of gas between two planar and infinite surfaces,where only one surface is able to adsorb and desorb molecules, while the other one is impermeable. Finally, experimental and numerical investigation were performed to analyze the BTEX (benzene, toluene,ethylbenzene and xylenes) species separation inside a chromatographic column. From calibrating the constants of adsorption and desorption, the retention time of each species can be predicted for different operating conditions using the numerical code developed.
