The measurements of thermophoretic deposition of aerosol particles in the continuum and slip flow regions

Abstract

The thermophoretic deposition of limestone particles onto a cold plate above which a temperature gradient was established has been measured. The experimental setup and methodology are described. The particle size distribution was measured by means of an Andersen impactor. The concentration of particles of different sizes was also measured. The Knudsen numbers (Kn) covered both continuum and slip flow regimes (Kn = 1 x 10-2 to 0.93). The theoretical expressions for thermal velocity of particles in the two regimes were calculated using the theories of Derjaguin and YalamQw and Brock, respectively. The measured concentration of particles of each size (0.4 - 9 ILm) along with theoretical values of thermal velocity were used to predict the total particle flux. The comparison between the directly measured particle flux and the predicted values showed good agreement. This result validates the thermophoresis theoretical expressions which have been proposed for both flow regimes involved in the present investigation.