Pseudo-binary molecular diffusion of vapors into air

A novel open-tube evaporation method was developed to determine the experimental diffusion coefficients of the vapors of various liquids diffused into air. The mass losses of the volatile liquids chosen for this study were measured with a balance rather than changes in the level of the liquid in a diffusion tube for various evaporation durations and no fresh air was passed over the top end of the diffusion path by forced convection, as opposed to the conventional open-tube evaporation method. A diffusion equation was developed which is suitable for the novel open-tube evaporation method. The experimental diffusion coefficient values obtained from the novel experimental diffusion methods were in reasonable agreement with the diffusion coefficient values predicted with both the Wilke-and-Lee method and the Fuller et al. method. The experimental diffusion coefficients of n-heptane diffused into air are independent of the lengths and the evaporation areas of the diffusion paths chosen for this study. The experimental diffusion coefficients of normal alcohols and hydrocarbons in air decrease with increased number of carbon atoms in their molecular formulas. The overall root mean squares of deviation of the diffusion values of this experimental study from those predicted with the Wilke-and-Lee method and the Fuller et al. method are 5.8 and 6.0%, respectively. (C) 2003 Elsevier Science Ltd. All rights reserved.