The thermal diffusion in binary gaseous mixtures under pressures, II : a new thermal diffusion apparatus

Abstract

A new "two-bulb" type thermal diffusion apparatus has been constructed, in which the concentration of a mixture and its variation with time can be deduced continuously under high pressures, from the velocity of ultrasonics. The bottom chamber of the themal diffusion apparatus is designed to be a constant-volume, variable-path ultrasonic interferometer, which contains a quartz transducer, facing a reflector-piston that can be driven by means of a micrometer screw. The electrical circuits consist of a Hartley oscillator, an amplifier and a detector. And the position of nodes is recorded on a photographic paper by the light spot of a galvanometer. The frequency of the driving oscillator is determined by a heterodyne frequency-meter at the same time. The overall accuracy of this instrument would be 0.2% in the estimation of the velocity of sound, as shown by the data of that in argon at 25.0℃ under pressures up to 150 atm. After the evaluation of the relations between the velocity of sound and the composition in hydrogen-carbon dioxide system, thermal diffusion factor α in these mixtures of various compositions has been measured under 9.7～98.1 atm and at a mean temperature of 349.1°K. It has been found that α increases continuously with increasing pressure at a definite composition, and the effect of pressure is larger at the lower mole fraction of hydrogen.