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Summary: Vapor diffusion coefficients in polymeric membranes were evaluated from dynamic permeation experiments. A membrane separated the diffusion cell into two parts – upstream and downstream. At the start of the experiment the concentration change in the upstream part (feed side) was made by substituting the input stream of pure nitrogen by the stream of permeant vapors. The solution of the Fick's second law with the step input concentration function is used for the evaluation of diffusion coefficients. The realization of the step input function can be difficult and its imperfection can negatively influence the evaluation process. This contribution deals with the description of the experimentally obtained input function and the study of its influence on evaluated values of diffusion coefficients. The mathematical model, which includes the non‐perfect step input concentration function and the transport through a polymer was developed. The results of this study enable the estimation of diffusion coefficient evaluation errors as dependence on the experimental arrangements and on the membrane transport properties.Diffusion apparatus for measurement of the steady‐state permeation process.magnified imageDiffusion apparatus for measurement of the steady‐state permeation process.

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Despite its importance, experimental information on the Residence Time Distribution (RTD) of solid particles in continuousflow stirred vessels is still scant. In this work, experimental data on particle RTD in a high-aspect-ratio vessel stirred by three equally-spaced Rushton turbines, obtained by means of Twin Systems Approach (TSA), are employed to assess the suitability of the well known Axial-Dispersion Model to describe particle behavior in the investigated system. The data analysis and model parameter assessment are preceded by a discussion on the utility of self-recirculated systems in carrying out experiments concerning continuous slurry-fed apparatuses. In particular, the suitability of single recirculated systems is discussed and a way to extract numerical RTD data from the relevant experiments is proposed. The advantages and disadvantages of employing instead a couple of twin systems, as it was actually done to obtain the experimental data employed in this work, is shortly discussed.

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