ACCURATE MEASUREMENT OF THERMOPHORETIC EFFECT IN MICROGRAVITY

The behavior of particles under thermophoretic effect was examined exp erimentally by getting rid of the effect of natural convection utilizi ng microgravity environment. The microgravity environment was realized by using a drop tower facility, In this system, measurement fields wi th temperature gradient were established between two metal plates, In order to provide a steep temperature gradient within a limited experim ental duration, the preheated metal plate was forced to approach the c old 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 mo notonic temperature gradient were obtained, In these fields, no other forces than thermophoretic force which might induce the particles move ment were confirmed to exist. The fields ideal for the measurement of the thermophoretic effect were obtained in our experiments. The measur ed thermophoretic velocities were found to be higher than the correspo nding one estimated from previously proposed theoretical equations; co efficients included in which were determined on the basis of experimen tal data obtained using a less accurate method. (C) 1996 American Inst itute of Physics.