Oscillatory magnetogasdynamic slip flow in a microchannel

The problem of pressure-driven magnetogasdynamic (MGD) slip flow with small rarefaction through a long microchannel is considered. The flow is driven by a steady or oscillatory pressure gradient. The study of MGD flows in microchannels is of interest since they occur in many electromagnetic microscale devices. In obtaining the microfluidic solutions in the presence of a magnetic field, some additional physical, mathematical, and numerical issues need to be considered. These issues deal with the scaling laws for microscale MGD flows and the relevant parameters such as Mach number, Reynolds number, Hartmann number, magnetic Reynolds number, and Knudsen number. For planar constant area microchannels, it is possible to obtain the analytical solutions for both steady and oscillatory pressure-driven flows at low magnetic Reynolds numbers. The flow field is assumed to be quasi-isothermal, which is a good assumption in the absence of a strong electric field. As physically expected, at higher values of the magnetic field (that is at a higher Hartmann number) the velocity profile in the channel flattens, and the pressure varies nonlinearly along the channel.     

Measurements of the relative momentum accommodation coefficient for different gases with a viscosity vacuum gauge

The viscosity vacuum gauges are based on the gas momentum transfer phenomena between a moving part of the gauge and a stationary surface. Thus, they may be used for the study of the momentum accommodation coefficient for various combinations of gas species and surfaces. The aim of the present work is to determine the momentum accommodation coefficient by means of the viscosity vacuum gauge with vibrating metal ribbon. The relative accommodation coefficient was computed from the measurements for Xe, Ar, He and H₂ on the bronze ribbon of the gauge in the molecular conditions. The values of the relative coefficients were 0.90 for Xe, 0.95 for Ar, 1 for He (values were normalised to data obtained for He) and 0.94 for H₂.     

Heat transfer in plane Couette flow of a rarefied gas

Summary In this paper Shen's method is used for solving the problem of heat transfer in plane Couette flow of a rarefied gas. An approximate distribution function is assumed and the appropriate transfer equations, which exhibit the proper collision effect between the molecules, are used to determine the temperature jumps at the plates.     

Transient flow of rarefied gas through a short tube

A transient rarefied gas flow through a short tube is studied on the basis of the direct simulation Monte Carlo method. The mass flow rates through both inlet and outlet cross sections are calculated as a function of the time in the free-molecular, transitional and hydrodynamic regimes with respect to the gas rarefaction. Two values of the pressure ratio, i.e. 0.1 and 0.5, and two values of the aspect ratio, i.e. 1 and 5, are considered. A characteristic time equal to that needed to cross the tube radius with the most probable molecular speed is defined. A typical interval of time to establish the steady flow rates was calculated. It was found that this time is about ten and forty characteristic times for the shorter and longer tubes, respectively. The flow field for the longer tube is analyzed in details.     

Nonisothermal flow of a rarefied gas in a circular cylindrical channel

Using a method which averages the system of moment equations over the channel section, the authors have obtained expressions for Poiseuille flow and thermal creep flow in a capillary at intermediate Knudsen numbers (Kn?0.25).     

Pressure driven rarefied gas flow through a slit and an orifice

The flow of a monatomic gas through a slit and an orifice due to an arbitrarily large pressure difference is examined on the basis of the nonlinear Bhatnagar-Gross-Krook (BGK) model equation, subject to Maxwell diffuse boundary conditions. The governing kinetic equation is discretized by a second-order control volume scheme in the physical space and the discrete velocity method in the molecular velocity space. The nonlinear fully deterministic algorithm is optimized to reduce the computational effort by introducing memory usage optimization, grid refinement and parallelization in the molecular velocity space. Results for the flow rates and the macroscopic distributions of the flow field are presented in a wide range of the Knudsen number for several pressure ratios. The effect of the various geometric and physical parameters on the flow field is examined. Comparison with previously reported corresponding Direct Simulation Monte Carlo (DSMC) results indicates a very good agreement, which clearly demonstrates the accuracy of the kinetic algorithm and furthermore the reliability of the BGK model for simulating pressure driven flows.     

Theoretical investigation of nonisothermal flow of a rarefied gas in a cylindrical capillary

This paper calculates thermocreep and Poiseuille flow in a cylindrical capillary using the Bubnov-Galerkin method. Asymptotic formulas are obtained for flow in the viscous regime with slip.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 36, No. 1, pp. 86–93, January, 1979.     

Theoretical and experimental investigation of rarefied gas flow in molecular pumps

The article presents a theoretical model for calculating the gas flow through channels with moving walls in the molecular flow regime. The analytical equations are solved by iteration techniques. The calculated data for the pumping speed and the compression ration of a molecular pump are compared with the experimental results. The agreement between calculated and measured values is good.     

气体稀薄流域的流动模型研究

研究气体通过漏孔的泄漏过程,建立气体在稀薄领域里的统一流动模型,可以避免对流态判断的困难,方便工程应用.气体稀薄流域的统一模型适用于从粘滞流到分子流的全部流态的数学模型.从N-S方程出发,利用滑移边界条件以及修正黏度推出统一流动模型,进而建立漏孔漏率与压力边界之间的关系式,引出稀薄气体流域下的经验公式,并通过试验可确定其待定系数.而且利用四极质谱法和压升法试验验证了模型的使用性及正确性,为今后的研究应用提供了参考依据.     

Couette problem for a rarefied gas in a channel

A study is made of the influence of the accommodation coefficients of tangential momentum of molecules on the lower and upper plates on the behavior of the gas between moving plates with arbitrary mirror-diffuse boundary conditions. The solution is constructed in a wide range of Knudsen numbers. Expressions for the mass and heat fluxes, the friction force, and the mass velocity are obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 2, pp. 186–193, March–April, 2006.     

Effects of boundary slip and apparent viscosity on the stability of microchannel flow

The effects of boundary slip, apparent viscosity and their combined modification on the mean velocity and stability of plane microchannel flow are investigated. Two kinds of microchannel are considered in this approach. One is the channel wall made of the same material. The other is the channel wall made of different materials. The boundary slip is determined by Navier slip condition. Apparent viscosity is considered by a model, where the effects of channel wall on liquid viscosity are assumed as a function of the distance from channel wall. Numerical results show that the boundary slip always stabilizes the flow and the apparent viscosity destabilizes the flow. It also shows that the effects of boundary slip are reduced sharply by considering the apparent viscosity modification. It means that the interaction between the close-wall molecules of liquid and solid wall is strong enough to resist boundary slip.     

Mechanism of heat and mass transfer during sublimation in a forced flow of rarefied gas

The interaction of a flow of rarefied gas with the flow of vapor close to a surface undergoing sublimation is studied by a visualization method. The rate of sublimation and the intensity of convective heat transfer are expressed as functions of the velocity of the incident flow of rarefied gas.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 4, pp. 700–705, April, 1971.     

Heat exchange in the flow of a hypersonic rarefied gas stream over a blunt wedge

The cooling of the leading edge of a blunt wedge over which a hypersonic rarefied gas stream flows is studied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 28, No. 5, pp. 788–792, May, 1975.     

Mass transfer in a highly rarefied gas

Equations of mass exchange in closed high-vacuum systems are obtained on the basis of the analogy between processes of transfer of molecular particles in a highly rarefied gas and processes of radiation.

     

Computational study of a rarefied gas flow through a long circular pipe into vacuum

The paper presents an analysis of the non-linear rarefied gas flow through a circular pipe into vacuum. The main attention is given to the case of the large length to radius ratio. The problem is studied on the basis of the numerical solution of the S-model kinetic equation. Results are compared with the available DSMC data for short tubes as well as with the asymptotic solution corresponding to the infinitely long pipe.     

Experimental investigation into coefficients of momentum flow and friction accompanying a uniform outflow in a porous pipe

The results of an experimental investigation into a turbulent flow in a circular pipe with a uniform spread through a permeable wall are presented. A calculation formula for determining the coefficient of friction is proposed. The nature of the variation in the coefficient of momentum flow is established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 6, pp. 1003–1008, June, 1976.     

Glow discharge in external magnetic field in hypersonic flow of rarefied gas

A two-dimensional computational model is used to investigate the gasdynamic structure of a rarefied (pressure of several torr) hypersonic flow of molecular nitrogen in a plane channel, with a glow discharge maintained between two surfaces of this channel. An asymmetric configuration of electrodes is considered, namely, the cathode is a narrow strip located on the lower surface of the channel, and the upper surface of the channel is a continuous anode. The fundamental possibility is studied of using an external magnetic field transverse to the flow for modifying the shock-wave structure of flow in the channel.A two-dimensional conjugate electrogasdynamic model is given, which includes equations of continuity, Navier-Stokes equations, equations of conservation of energy, and equations of continuity of charged particles in ambipolar approximation. The real thermophysical and transport properties of molecular nitrogen are included.It is demonstrated that the use of a surface glow discharge in a rarefied hypersonic flow enables one to effectively modify the shock-wave structure of flow and, thereby, consider discharges of this type as additional means of control over rarefied gas flows.     

Statistical simulation of a steady-state rarefied gas flow via a pipeline vacuum system in a molecular-viscous regime

A physicomathematical model of transport processes of molecules in a molecular-viscous regime is described which is consistent with the knowledge of the random motion of molecules in a molecular regime and of a laminar flow in a viscous regime. The Monte Carlo method is applied for the statistical three-dimensional simulation of a steady-state rarefied gas flow via vacuum system elements of arbitrary geometry in a molecular-viscous regime. The results of computational experiments on the determination of the conduction of long and short cylindrical pipelines are reported.St. Petersburg State Technical University. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 63, No. 6, pp. 673–677, December, 1992.     

Adsorbed layers in the interaction of a rarefied gas flow with a deeply cooled optical surface

A method of direct modeling of adsorbed layers and estimation of the mean thickness o f the cryodeposit is considered. The theoretical results are compared with experimental data.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 60, No. 2, pp. 321–324, February, 1991.     

On the problem of rarefied gas flow past blunt axisymmetric bodies

Shock layer separation in flows of rarefied gas past axisymmetric models is determined by interferometric methods. The form of the density jump is established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 5, pp. 843–846, November, 1968.