Acta Chimica 91. (1976)

2. szám - Tettamanti, K.–Török J.: Concentration dependence of diffusion coefficient in vapour-gas systems and the mechanism of vaporization

Acta Chimica Academiae Scientiarum Hungaricae, Tomus 91 (2), pp. 217—224 (1976) CONCENTRATION DEPENDENCE OF DIFFUSION COEFFICIENT IN VAPOUR GAS SYSTEMS AND THE MECHANISM OF VAPORIZATION (SHORT COMMUNICATION) K. TeTTAMANTI and J. TÖRÖK (Department of Chemical Unit Operations, Technical University, Budapest) Received January 29, 1976 Introduction The essence of our work is the recognition that the well-known vapour diffusion tube by Stefan [1] designed to measure interdiffusion in vapour—gas systems can, by selecting appropriate experimental conditions, be utilized as an excellent tool for studies of concentration dependence of diffusion coeffi­cient. By varying the pressure in the gas space of the Stefan vapour diffusion tube from the saturation pressure pt upwards to a total pressure of several atmospheres, the true value of diffusion coefficient for a given temperature can be measured, within a practically discretionary molar fraction range, against the vapour concentration in the gas space (Fig. 1). Most experiments described in the literature were carried out at atmo­spheric pressure only. Such experiments evidently yield average values [Pav]o_y to be interpreted as corresponding to the molar fraction range у = pt/760 to У = o. Winkelmann [3, 4] was the only one who performed experiments with the H20/air system at various pressures P ^ 60, 750 and 1600 torr (y 0.019, 0.323 and 0.475, resp.). His data, however, cannot be evaluated, owing to the significant temperature variations. The mode of calculation reported in the literature is based on the integra­tion of the first Fick—Stefan differential equation (cf. Eq. (2)) yielding the expression However, integration is inadmissible if it is assumed that diffusion coefficient is a function of y. Data in the literature are usually data reduced to 1 atnu [AwL — [ Aiv]p • Pn ctot h N в = Vl ■Qbl Mb -- [Dav]‘P ■ In 2 1 - J, Acta Chim. (BudapestJ 91, 1976

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