Thermophoretic measurements in presence of thermal stress convection in aerosols in microgravity conditions of drop tower |
| |
Authors: | A A Vedernikov F Prodi G Santachiara S Travaini F Dubois J C Legros |
| |
Affiliation: | (1) Microgravity Research Center, Université Libre de Bruxelles, 50, Avenue F.D.Roosevelt, CP 165/62, B-1050 Brussels, Belgium;(2) Institute ISAC-CNR, Clouds and Precipitation Group, Bologna, Italy;(3) Department of Physics, University of Ferrara, Dept. of Physics, Ferrara, Italy |
| |
Abstract: | The aim of the work is getting reference data on thermophoretic motion eliminating gravity-induced perturbation, developing
new instrumentation and procedures. A series of experiments on measuring phoretic velocities was performed in the Bremen drop
tower providing 4.7 s of high quality microgravity conditions, which allowed making negligible particle sedimentation and
buoyancy driven convection. Motion of aerosol particles was observed simultaneously at low resolution to control nongravity
convective motion in the cell and at high resolution by the digital holographic velocimeter in order to register particle
three-dimensional trajectories. By choosing appropriate cell size and experimental procedures the heat and mass transfer relaxation
processes were reduced to less than 0.3 s thus allowing measurements of particle velocities during more than 4 s. Side-wall
temperature creep created convective motion in the cell. Its influence was suppressed by choosing sufficiently flat cell geometry.
The values of the measured thermophoretic velocities for Knudsen number in the range 0.047–0.89 were found to be between predictions
of the classical models of Talbot et al 1] on one hand and Yamamoto and Ishiara 2] on the other hand. Particles of different
thermal conductivities (paraffin and NaCl) had about the same velocities. No negative thermophoresis was observed at these
conditions for NaCl. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|