Rarefied gas flow through channels of finite length at various pressure ratios

A rarefied gas flow through channels (i.e. flow through parallel plates) of finite length has been modeled based on the direct simulation Monte Carlo method. The reduced flow rate and the flow field have been calculated as function of the gas rarefaction, the length-to-height ratio and the pressure ratio upstream and downstream of the channel. The whole range of the gas rarefaction including the free-molecular, transitional and hydrodynamic regimes and a wide range of the length-to-height ratio representing both short and long channels have been considered. Several values of the pressure ratio between 0 and 0.5 have been used in the calculations. It is shown that the rarefaction parameter has the most significant effect on the flow field characteristics and patterns, followed by the pressure ratio, while the length-to-height ratio has a rather modest impact. The Mach belt phenomenon is discussed in detail.     

Changes in the NPL orifice conductance on a transition from molecular gas flow to transitional flow

The conductance of an NPL orifice in the molecular regime is constant and can be exactly calculated from the geometric dimensions. For smaller Knudsen numbers the conductance increases and correction functions are employed to reduce the uncertainty in this range of pressures. The conductance is also constant in the viscous regime during flow into a vacuum and can also be calculated. A suitable function has been chosen with one free parameter, which is constant for both very low and sufficiently high pressures and the parameter was determined on the basis of the experimentally measured course of the conductance at the borderline between molecular and transitional flow. The function fits the experimental data very well and can be used to calculate the conductance of the orifice up to Knudsen number ≈1.     

Experimental study of gas flow through a multi-opening orifice

Gas flow through an orifice can be determined with high accuracy based only on the geometrical dimensions of the orifice and the upstream and downstream pressures when the flow is purely molecular. An orifice with a number of smaller openings in parallel can be used to maintain the molecular flow at higher pressure and high total conductance of the orifice. The question of how close such openings can be without influencing each other is important for practical design. This problem was studied experimentally. Changes in the total conductance versus pressure were followed for a set of multi-opening orifices with regularly arranged differently spaced circular openings. The experimental results show that no influence on the flow through a single opening can be observed at sufficiently distant opening, over the entire pressure range. At centre-to-centre distances shorter than approximately three times the diameter of the opening, notable differences in the total conductance can be seen in the pressure range where the transition from the molecular to transitional flow regime occurs.     

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.     

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.     

Monte Carlo simulation of gas flow through the KATRIN DPS2-F differential pumping system

The Karlsruhe Tritium Neutrino experiment (KATRIN) is a large vacuum system and aims to measure the electron neutrino mass from the β decay of tritium with unprecedented sensitivity. To achieve this purpose, the tritium gas flow has to be significantly reduced along the beamline by means of a modular differential pumping system. This paper studies systematically the vacuum performance of one of the differential pumping systems (known as DPS2-F) based on turbomolecular pumps. The flow reduction rates in the complete system are described by a matrix equation as a function of the capture factor of the turbomolecular pumps employed. The results show that a total reduction factor greater than 10⁵ can be attained, which is one of the prerequisites to achieve XHV conditions in the spectrometers used in the downstream end of the experiment.     

气体大流量标准装置的扩展不确定度评定

本文根据《测量不确定度评定与表示》（JJF1059-1999）中的规范化要求和有关数据,对国家原油大流量计量站成都天然气流量分站的气体大流量标准装置的测量不确定度进行了评定,结果表明该装置经过技术改造后的扩展不确定度不大于0．05％（P=0．95）。同1996年装置建立时的扩展不确定度0．1％（P=0．95）相比,又进一步提高了测量准确度。     

中压天然气流量计实流标定中气体压力、温度的影响及控制方法

论述在中压天然气流量计实流标定中,调压及流量点调节弓{起检定用天然气各参数变化对测量准确度的影响。并讨论了中压天然气流量计实流标定中天然气压力和温度的控制调节方法,保证检定用天然气各参数的波动符合检定规程的要求。     

Rarefied gas flow through a zigzag channel

A rarefied gas flow through a channel of zigzag shape is calculated over the wide range of the gas rarefaction and for several values of the aspect ratio applying the linearized kinetic equation. In the hydrodynamic flow regime, the kinetic solution is compared with that obtained from the Stokes equation. An approach to calculate a flow rate through a chain composed from an arbitrary number of zigzags is proposed. It was found that in some situations, the flow rate through a zigzag channel is higher than that trough a straight channel of the same length.     

A New Interpretation of Gas Viscosity for Flow through Micro-Capillaries and Pores

The Hagen–Poiseuille equation for gas flow had never been derived theoretically; it is rather a simple analogy of the same for liquid flow, and “gas viscosity” is a measure for overall resistance to flow. In this work, experimental flow data for different gases through capillaries and porous media, reported in literature by different groups, including those measured and treated by Knudsen are treated with Hagen–Poiseuille equation, but taking “gas viscosity” as an adjustable parameter. It is found that, at constant temperature, there exists an unambiguous relation between the viscosity (µ) of a given gas, and the product of average pressure (P_av) and capillary diameter (D). In addition, for P_av*D < 0.01, a universal linear relation exists between µ/M^0.5 (where M is molecular mass) for different gases and the parameter P_av*D. The new interpretation of gas viscosity avoids the differentiation of regimes into “Knudsen” and “viscous” flow as it is frequently done in literature. The concept can be applied to obtain a reliable data base for gas viscosities in different fields of applications, for example in microfluidic systems or the analysis of pore size distributions of filters and membranes by gas flow porometry.     

Benchmark problems in rarefied gas dynamics

In order to identify the most efficient and reliable methods and solvers for modeling of rarefied gas flows, it is proposed to choose few benchmark problems to be solved by different methods. The main requirements to such problems, such as geometrical simplicity and small number of determining parameters, are formulated in the present work. Two benchmark problems are proposed. A comparison between numerical and experimental data of these problems available in the open literature is performed.     

大型空分设备卧式垂直气流分子筛吸附器内的流场特征分析

为了更好地研究大型空分设备分子筛吸附器内的流场特征,建立了以单根、2根和3根多孔管结构为气流分布器的60000 m3/h空分设备卧式垂直气流分子筛吸附器结构的数学模型,并采用FLUENT软件对其内部速度场分布进行数值分析。比较计算结果显示,采用2根多孔管结构的分子筛吸附器在流场分布和生产成本上都比其他两种结构更优,与20000 m3/h空分设备卧式垂直气流分子筛吸附器相比,气流分布均匀性有所下降。     

音速喷嘴气体流量标准装置测量不确定度评定

各种流量计从研制到使用，必须对其特性进行研究，对其标称的流量性能进行试验，并给出试验结果。这些试验研究工作都需要在流量标准装置上进行。因此，流量标准装置的不确定度直接关系到试验结果的水平，对其研究是非常必要的。用临界流文丘利喷嘴做为流量标准，用比较法原理对流量计进行检定和校准，音速喷嘴法气体流量标准装置可对各种气体流量计的检测和校准，并对其检定和校准结果的不确定度进行评定。     

Numerical simulation of gas flow around a passive vent in a sanitary landfill

A numerical model, based on the Darcy law, was used to simulate the two-dimensional gas flow around a passive vent in a sanitary landfill. We follow Findikakis and Leckie [ASCE J. Environ. Eng. 105 (1979) 927] in modeling the biodegradation of the solid waste and assume the first-order biodegradation kinetics. The numerical results from the Fresh Kills landfill, New York, show that the well’s ability in extracting the landfill gas by the passive vent decays quickly with the increase of the radial distance from the well. The influence radius of the well is generally less than 20 m. The effects from the final soil thickness, well depth, and other parameters on the gas flow are also discussed.     

采用音速喷嘴的气体流量标准装置

建设流量标准装置是进行计量检定的基础工作，本文对当前的气体流量标准装置进行了分析比较，介绍采用音速喷嘴建设气体流量标准装置的理由和应用中的一些问题。     

On the gas flow rate through a Mach disk in an underexpanded jet

An air jet with an excess static pressure at a regime of escape into quiescent air is considered. The range of Mach number variation is 1–3, and that of the inefficiency ratio 1–1000. An analysis has been made on the basis of the well-known experimental-calculated approximation dependences for stationary expanding flows. We solve the inverse problem where the parameters at the nozzle exit and the geometric characteristics of the initial section of the jet are known and it is required to find the remaining quantities corresponding to them. In the present analysis, this is the rate of flow through a central discontinuity and the integral characteristic of the magnitude of the total pressure loss. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 320–325, March–April, 2009.     

基于流体诱发管道振动的气液两相流型识别

通过对不同流型的气液两相流流经管道时诱发的管道振动特性的实验研究,提出了基于流体诱发振动的非接触式在线两相流流型识别新方法.通过安装于测试管道外壁的振动传感器测量不同流型下气液两相流诱发的振动信号;采用小波包分析提取了表征流型变化的振动信号能量特征向量;以能量特征向量作为模型输入,建立了概率神经网络模型用于识别分层流、...     

Increasing the rate of heat transfer in ducts with a turbulent gas flow

Results are shown of a study concerning the heat transfer and the hydraulic drag in an air stream through ducts of various shapes with wavy rough walls and with boundary-layer breakers.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 981–986, June, 1972.     

Distortion of a turbulent-viscosity profile by large negative pressure gradients in gas flow through pipes

On the basis of tests performed at the Grenoble University, the profiles of turbulent viscosity are calculated as functions of the negative pressure gradient.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 5, pp. 913–918, May, 1972.