Experimental estimations of thermophoretic velocity of spherical copper particles in nitrogen measured in microgravity conditions at the Bremen drop tower (Germany) at very low values of the Knudsen number (Kn ≈ 0.002) and very high thermal-conductivity parameter Λ ≈ 20 500 are presented. Comparison of the obtained data with the gas-kinetic theory, taking into account both thermal-creep flow and thermal-stress slip flow mechanisms of thermophoresis is carried out. The obtained results demonstrate indirectly the action of the thermal stress slip flow mechanism, however, negative thermophoretic velocities have not been recorded. The important role of energy accommodation coefficient for gas molecules on the particle surface for explanation of the obtained results is discussed. An additional analysis of experimental data is necessary, aiming at the increase of reliability of thermophoretic velocity estimates.
climatology, zonal averaging, stratosphere, vertical wind, aerosols