Accurate measurement of thermophoretic effect in microgravity

Abstract

The behavior of particles under thermophoretic effect was examined experimentally by getting rid of the effect of natural convection utilizing microgravity environment. The microgravity environment was realized by using a drop tower facility. In this system, measurement fields with temperature gradient were established between two metal plates. In order to provide a steep temperature gradient within a limited experimental duration, the preheated metal plate was forced to approach the cold plate quickly after the microgravity environment was established. Temperature distribution and the behavior of individual particles were observed simultaneously. The fields in an almost steady state with monotonic temperature gradient were obtained. In these fields, no other forces than thermophoretic force which might induce the particles movement were confirmed to exist. The fields ideal for the measurement of the thermophoretic effect were obtained in our experiments. The measured thermophoretic velocities were found to be higher than the corresponding one estimated from previously proposed theoretical equations; coefficients included in which were determined on the basis of experimental data obtained using a less accurate method.