Knudsen number

About: Knudsen number is a research topic. Over the lifetime, 5052 publications have been published within this topic receiving 104278 citations.

Observation of Knudsen and Gurzhi transport regimes in a two-dimensional wire

Abstract: We have observed electronic Knudsen and Poiseuille flow in a current heating experiment on electrostatically defined wires in (Al,Ga)As heterostructures. Current heating induces an increase in the number of electron-electron collisions in the wire, leading first to an increase (Knudsen regime) and subsequently to a decrease (due to Poiseuille electron flow, and known as the Gurzhi effect) of the resistance of the wire.

Rate of convergence in the multidimensional central limit theorem for stationary processes. Application to the Knudsen gas and to the Sinai billiard

Abstract: We show how Rio’s method [Probab. Theory Related Fields 104 (1996) 255–282] can be adapted to establish a rate of convergence in ${\frac{1}{\sqrt{n}}}$ in the multidimensional central limit theorem for some stationary processes in the sense of the Kantorovich metric. We give two applications of this general result: in the case of the Knudsen gas and in the case of the Sinai billiard.

Development of a nonisothermal Knudsen effusion method and application to PAH and cellulose tar vapor pressure measurement

Abstract: The Knudsen effusion technique has long been employed as an indirect method for determining the vapor pressures of low-volatility materials. The method is tedious and, if not carefully applied, subject to considerable errors in temperature measurement. It is also desirable to shorten the time of measurement in some cases, since when working with either mixtures or thermally labile materials the long time scales of the usual measurement can result in significant changes in composition while waiting for pseudo-steady state to obtain. For these reasons, a new method, based on the traditional Knudsen effusion technique, was developed. The resulting nonisothermal method is a straightforward modification of the usual Knudsen effusion technique, generally requiring few changes in equipment and only a limited change in procedures. The technique has been applied to polycyclic aromatics and pyrolysis tars.

Measurements of the tangential momentum accommodation coefficient in the transition flow regime with a spinning rotor gauge

Abstract: Gas‐surface interactions which are described with the accommodation coefficients play an important role in the determination of the mass, momentum, and thermal energy transport in rarefied gas flows, aerosol mechanics, and vacuum technology. While the thermal accommodation coefficient has been extensively studied, the investigations of the other coefficients have been limited, partly because of the difficulties that are associated with the available theories and control of surfaces. To further understand the tangential momentum accommodation coefficients, experimental investigations of the rotational motion of a freely suspended sphere in a variety of gases and over a range of pressures were undertaken. It was found that the experimental results are generally well described by recent theoretical works that have provided numerical solutions of the linearized Boltzmann equation. Further, the theory can be used to interpret experimental data in terms of the tangential momentum accommodation coefficient, α over the entire range of the Knudsen number. The values of α are near 1 for most of the gas types and vary only slightly with the pressure.

Application of a parallel DSMC technique to predict flow characteristics in microfluidic filters

Abstract: Using a parallel implementation of the direct simulation Monte Carlo (DSMC) method, periodic MEMS microfilters are studied in detail. The dependence of the flow characteristics on geometry, Knudsen number, pressure difference, spacing between the filter elements, and accommodation coefficients are investigated. By comparing DSMC results with the widely used analytical formulas, the validity range of the analytical approaches is evaluated. The simulation results show that velocity slip exists both on the filter channel walls and on the filter membrane and results in an increased flow rate. Velocity slip increases strongly with decreasing accommodation coefficients. For long channels, this results in a strong increase in flow rate; whereas for short channels, the increase in flow rate is limited. For the filter separations considered in this paper, we observe that separation between filter channels does not influence the flow rate within each channel.