Diffusion of impurities against the direction of gas flow can be a significant source of contamination in the ultrapure gas systems. The mechanism and the kinetics of impurity transport due to back-diffusion is studied both experimentally and theoretically. A model is developed to simulate the process and calculate the extent of impurity transport due to back-diffusion. Experiments for measuring oxygen back-diffusion in a nitrogen carrier stream are conducted. The data and the model predictions are in good agreement. Back-diffusion involves both bulk and surface diffusion and is higher for lower pressures, lower flow rates, larger tube diameters, and for smaller nonadsorbing molecules.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry