Model-based Analysis of Diffusion Experiments in Binary Gas Mixtures in a Loschmidt Cell

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The research project aims at the identification of concentration-dependent binary diffusion coefficients in gases from a single experiment. The measurement database is provided by already existing as well as newly to be determined experimental data from the group of Prof. Fröba (Erlangen Graduate School in Advanced Optical Technologies). Measurements are performed in a Loschmidt cell combined with a holographic interferometer. The present project focuses on the data analysis procedure. Previously, data analysis was based on Fick's second law. Therefore, it could not account for the required concentration dependence of the diffusion coefficient and interaction effects in the gas mixture.To improve the data analysis procedure, a consistent model describing diffusion in the Loschmidt cell will be developed in the group of Prof. Bardow (Chair of Technical Thermodynamics, RWTH Aachen University). The model should include concentration dependencies, excess effects, and (if needed) sorption and gravity effects. Particular attention should be given to the suitable choice of reference frame. An output-least-squares-method will allow to include all measurement data at once and lead to the statically optimal diffusion coefficients. The analysis of the residuals offers the potential to reveal the needs for improvements in model and experiment. This procedure is promising because of the excellent database and because a similar analysis has already been successfully applied to diffusion in liquids. The model-based procedure developed in this project will provide access to unique data on the concentration dependence of diffusion in gas mixtures.