Computational and experimental study of gas flows through long channels of various cross sections in the whole range of the Knudsen number

A new experimental setup for flow rate measurement of gases through microsystems is presented. Its principle is based on two complementary techniques, called droplet tracking method and constant-volume method. Experimental data on helium and argon isothermal flows through rectangular microchannels are presented and compared with computational results based on a continuum model with second-order boundary conditions and on the linearized kinetic BGK equation. A very good agreement is found between theory and experiment for both gases, assuming purely diffuse accommodation at the walls. Also, some experimental data for a binary mixture of monatomic gases are presented and compared with kinetic theory based on the McCormack model.

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“…This is the same assumption which allows the modeling of the flow as a linear fully developed flow (Sharipov 1999;Varoutis et al 2009). …”

Section: Values Of Coefficients C I Are Given Inmentioning

confidence: 99%

“…For the purposes of the present work, we focus on the mass flow rate, which is calculated from (Sharipov and Seleznev 1998;Varoutis et al 2009) by…”

Section: Kinetic Models-for Whole Knudsen Rangementioning

confidence: 99%

A novel experimental setup for gas microflows

Pitakarnnop

Varoutis

Valougeorgis

et al. 2009

Microfluid Nanofluid

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107

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“…The popularity of this approach is based on the fact that the model is simple, easily understood at both microscopic and macroscopic level, while the associated numerical effort for its implementation is minimal. For this purpose, it has been used in a variety of physical systems, providing good results in agreement with corresponding experimental findings [74,121]. However, in some cases, the gas may behave much differently.…”

Section: Boundary Condition Modelssupporting

confidence: 53%

“…Thus, we can discretize the kinetic equations in the physical and molecular velocity space and solve only for these specific discrete velocities in an iterative manner. This method has been used extensively in several works [73,74,75] and is particularly suitable when the distribution function can be linearized in terms of a small parameter [76,77].…”

Section: Methodsmentioning

confidence: 99%

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Simulation of transport phenomena in conditions far from thermodynamic equilibrium via kinetic theory with applications in vacuum technology and MEMS

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The approval of the current dissertation by the Department of Mechanical Engineering of the University of Thessaly does not imply acceptance of the author's opinions (Law 5343/32 number 202 paragraph 2). Also, the views and opinions expressed herein do not necessarily reflect those of the European Commission. There are several other people who I feel that have contributed in the writing of this dissertation.The most important contributions, along with several helpful conversations, were made by Prof. F.Sharipov, who provided the basic concept of the channel end effect study, and Dr. Chr. Day along with the KIT personnel, who briefly introduced me in the world of experimental rarefied gas dynamics. It was also a priviledge to discuss and work for a brief period of time with Prof. A. Grecos, who tirelessly discussed with me on various subjects of statistical mechanics. Financial support for this Ph.D. has been provided by the Euratom Association -Hellenic Republic, to which I am deeply indepted. Also, partial support for conference mobility expenses has been received from the GASMEMS Marie Curie programme. In this work, non-equilibrium transport phenomena have been examined via the kinetic theory of gases. The behaviour of the gas in low pressure conditions or in low-dimensionality systems can not be captured by the usual Navier-Stokes formulation, in conjunction with the constitutive laws of Newton-Fourier-Fick. The limited number of intermolecular collisions results in departure from equilibrium and the particulate nature of the gas must be taken into account, greatly increasing the computational effort.The problem is described by the integro-differential Boltzmann equation, which is used to determine the distribution of particles in physical and molecular velocity space, as well as in time.There are difficulties associated with the seven-dimensional nature of the distribution function, as well as with the complexity of the collision term, which is usually substituted by an appropriate model.The most widely used and successful numerical methodologies, the Discrete Velocity Method (DVM) and the Direct Simulation Monte Carlo (DSMC), are applied here in the whole range of the Knudsen number. It is important to employ approaches based on kinetic theory, since these are the only ones which are valid for any rarefaction level.In this work, several problems including non-equilibrium phenomena are considered. The interaction of gases with solid surfaces is considered for several problems according to the CercignaniLampis boundary conditions. The non-linear form of this scattering kernel, which had not been pre- viously used in the literature, is applied on the problem of heat transfer between parallel plates and coaxial cylinders. Its linearized form has also been employed for both flow and heat transfer problems and a comparison with relevant experiments has lead to surface characterization with respect to argon and helium flows.Non-linear heat conduction phenomena are also studied for the parallel plates and coaxial c...

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Effect of water saturation on gas slippage in circular and angular pores

Chen

et al. 2018

AIChE Journal

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A unified model for gas slip flow through circular and angular pores in both single phase flow and two-phase flow conditions is developed, and the effect of water saturation on gas slippage factors in different pore shapes are revealed. For circular pores, the water saturation retains as thin film binding on pore surfaces without changing the shape of the cross section, and the hydraulic diameters continuously reduce as water saturation increases, directly leading to an increase in the slippage factor. However, for angular pores, the water saturation retains as both films at boundaries and condensations at corners, and the film-water and corner-water gradually change their cross-section shape (from sharp corners to round corners), which further affects the gas slip behavior. Due to the presence of round corners, the ratio of the cross-sectional area and perimeter, which can also be regarded as the reciprocal of a specific surface area, can even increase at a low water saturation condition. Thus the collisions between gas molecules and pore boundaries weaken, resulting in a slight reduction in the gas slippage factor. This interesting finding in the angular pore case directly explains the contradiction of the published experimental results with the general knowledge (i.e., the gas slip factor always increases as water saturation increases). Thus, the validity of the common assumption regarding actual porous media as capillaries with a circular cross-section must be considered more carefully.

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Computational and experimental study of gas flows through long channels of various cross sections in the whole range of the Knudsen number

Cited by 92 publications

References 28 publications

A novel experimental setup for gas microflows

A novel experimental setup for gas microflows

Simulation of transport phenomena in conditions far from thermodynamic equilibrium via kinetic theory with applications in vacuum technology and MEMS

Effect of water saturation on gas slippage in circular and angular pores

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