Moisture sorption kinetics for water-soluble substances. III: Theoretical and experimental studies in air

As an extension of the model of heat transport control developed for the kinetics of water sorption by water-soluble substances from an atmosphere of pure water vapor, equations have been developed to account for limitations of diffusion on mass transport of water vapor when air is present. Although the inability to determine the vapor diffusion layer thickness prevents using these equations to predict sorption behavior a priori, minimum water sorption rates can be calculated by assuming a diffusion layer thickness equal to the sample chamber radius. Combining heat transport and mass transport produces equations which describe very well the observed sorption by three water-soluble salts in one atmosphere of air. As in the absence of air, sorption rates are predicted and observed to be constant at a given atmospheric relative humidity.