Rarefaction

About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.

Experimental Investigation of the Compressibility Effects on the Friction Factor of Gas Flows in Microtubes

Abstract: The numerical and experimental works dealing with the behaviour of gas flow through microchannels have shown results which are by no means univocal, sometimes agreeing with the classical correlations, and other times contradicting them. It is now agreed upon that the effects due to both rarefaction and compressibility must be accounted for. In addition, the experimental works have demonstrated that sometimes compressibility and rarefaction effects can be coupled in microchannels: since these two actions contrast each other, the scatter of the friction factor data for gaseous flows is remarkably large. This paper is aimed at determining the friction factor for commercial short and long Peek microtubes with nominal internal diameters between 300 and 100 μm and different values of the length-to-diameter ratio L/D, ranging between 167 and 5000. Nitrogen flows inside the microtubes, with a maximum value of the supply pressure equal to 10 bar. Very low Knudsen numbers (Kn<0.001) are considered in order to uncouple the rarefaction effects from the compressibility effects. The role of compressibility on the friction factor is analyzed and discussed in order to draw its limit of significance.Copyright © 2006 by ASME

Characterization of showerhead performance at low pressure

Abstract: The performance of showerheads used in semiconductor processing applications has been examined over a wide range of Knudsen number and Reynolds number. Both computational fluid dynamics and direct simulation Monte Carlo techniques have been used to characterize the showerhead flow with the intent of developing correlations between the upstream velocity and the pressure drop across the showerhead. Empirical correlations developed to account for entrance effects and rarefaction are also examined. Recommendations are made concerning boundary conditions and, when appropriate, correlations for given pressures and flow rates.

Thermal Lattice Boltzmann Model for Nonisothermal Gas Flow in a Two-Dimensional Microchannel

Abstract: In this paper, the Thermal Lattice Boltzmann Method (TLBM) is used for the simulation of a gas microflow. A 2D heated microchannel flow driven by a constant inlet velocity profile and nonisothermal walls is investigated numerically. Two cases of micro-Poiseuille flow are considered in the present study. In the first case, the temperature of the walls is kept uniform, equal to zero; therefore, the gas is driven along the channel under the inlet parameters of velocity and temperature. However, in the second one, the gas flow is also induced by the effect of temperature decreasing applied on the walls. For consistent results, velocity slip and temperature jump boundary conditions are used to capture the nonequilibrium effects near the walls. The rarefaction effects described by the Knudsen number, on the velocity and temperature profiles are evaluated. The aim of this study is to prove the efficiency of the TLBM method to simulate Poiseuille flow in case of nonisothermal walls, based on the average value of the Nusselt number and by comparing the results obtained from the TLBM with those obtained using the Finite Difference Method (FDM). The results also show an interesting sensitivity of velocity and temperature profiles with the rarefaction degree and the imposed temperature gradient of the walls.

Propagation of rarefaction pulses in particulate materials with strain-softening behavior

Abstract: We investigate rarefaction waves in nonlinear periodic systems with a 'softening' power-law relationship between force and displacement to understand the dynamic behavior of this class of materials. A closed form expression describing the shape of the strongly nonlinear rarefaction wave is exact for n = 1/2 and agrees well with the shape and width of the pulses resulting from discrete simulations. A chain of particles under impact was shown to propagate a rarefaction pulse as the leading pulse in initially compressive impulsive loading in the absence of dissipation. Compression pulses generated by impact quickly disintegrated into a leading rarefaction solitary wave followed by an oscillatory train. Such behavior is favorable for metamaterials design of shock absorption layers as well as tunable information transmission lines for scrambling of acoustic information.