Thermophoresis in Rarefied Gas Flows

Abstract

Numerical calculations are presented for the thermophoretic force acting on a free-molecular, motionless, spherical particle suspended in a rare ed gas ow between parallel plates of unequal temperature. The rare ed gas ow is calculated with the direct simulation Monte Carlo (DSMC) method, which provides a timeaveraged approximation to the local molecular velocity distribution at discrete locations between the plates. A force Green's function is used to calculate the thermophoretic force directly from the DSMC simulations for the molecular velocity distribution, with the underlying assumption that the particle does not in uence the molecular velocity distribution. Perfect accommodation of energy and momentum is assumed at all solid/gas boundaries. Earlier work for monatomic gases (helium and argon) is reviewed, and new calculations for a diatomic gas (nitrogen) are presented. Gas heat ux and particle thermophoretic forces for argon, helium, and nitrogen are given for a 0.01 m spacing between plates held at 263 and 283 K over a pressure range from 0.1 to 1000 mTorr (0.01333 -133.3 Pa). A simple, approximate expression is introduced that can be used to correlate the thermophoretic force calculations accurately over a wide range of pressures, corresponding to a wide range of Knudsen numbers (ratio of the gas mean free path to the interplate separation).

Investigation of thermophoretic protection with speed-controlled particles at 100, 50, and 25mTorr

“…The thermophoretic effect on particle deposition has been a long time topic for experimental [2][3][4][5] and numerical [6][7][8] investigations. The thermophoretic effect on particle deposition has been a long time topic for experimental [2][3][4][5] and numerical [6][7][8] investigations.…”

“…On the numerical calculation side, Gallis et al [6][7][8] presented many articles for thermophoresis on rarefied gas flows. Gas heat flux and particle thermophoretic forces for Ar, He, and N 2 were given for 1 cm spacing between a cold plate and a warm plate over a pressure range from 0.1 mTorr to 1 Torr.…”

Numerical analysis for the thermophoretic coagulation of monodisperse particles at continuum regime

“…The movement of the particle resulted from this force is called thermophoresis. Thermophoresis is of practical interest in a wide range of applications including dust collectors (thermal precipitators) [1,2] and protection of critical surfaces from contaminant particles [3,4]. Over a century ago, Tyndall [5] observed that dust particles suspended in a gas with inhomogeneous temperature tend to move out of the hot regions.…”

Comment on "Thermophoresis of a Near-Wall Particle at Great Knudsen Numbers"

“…The force on a particle was determined by applying the force Green's function to the molecular velocity distribution computed by DSMC (Gallis et al 2001). Care was taken to ensure that the numerical parameters yielded accurate results (Gallis et al 2001(Gallis et al , 2002a(Gallis et al , 2002b; in particular, the simulations were run for long times to minimize the statistical uncertainties inherent in molecular gas dynamics methods.…”