Development of a novel method to investigate the dew line of binary mixtures using a modified two-sinker densimeter

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To understand the phase behavior of fluid mixtures and to develop models that precisely describe the phase boundary between liquid and vapor, accurate experimental data are essential. Such models are of increasing importance for research and industry, for example in the fields of natural gas processing and carbon capture and storage. With regard to experimental data, the dew line, separating the homogeneous vapor region from the heterogeneous two phase region, is very difficult to determine accurately. The resulting lack of accurate data obstructs a significant improvement of the theoretical models. Against this background the major objective of this project is to investigate a new technique for accurately measuring the dew line of binary mixtures. The instrument to be used is the highly accurate two-sinker densimeter of the National Institute of Standards and Technology. Binary mixtures are chosen because state of the art models for multicomponent mixtures are only fitted in terms of the constituent binary pairs. In a first set of experiments we intend to measure dew-point temperatures at different pressures of selected binary mixtures. Confounding adsorption and pre-condensation effects will be studied as well. With the first results it will be possible to verify the suitability of the applied technique for the measurement of dew-point temperatures. For a second set of experiments the two-sinker densimeter utilized will be modified by integrating a new pair of sinkers specifically designed to improve the technique for the special purpose of measuring dew-point temperatures. In contrast to the original sinkers, the new ones will be of same mass, same volume but different surface characteristics; this will allow a quantitative determination of the mass of sample adsorbed onto the sinker. The second experimental data set will include the same measurement points as the first data set. This will allow to check the idea of using a special pair of sinkers and to make a first uncertainty estimate. Both sets of measurements will provide completely new information about the application of a two-sinker densimeter as an accurate dew-point instrument. Moreover, this work will serve as introductory work for future research within the group for the accurate measurement of thermophysical properties at the chair of thermodynamics of Ruhr-University Bochum. Thereby a comprehensive study of measuring thermodynamic property data on the dew line shall be carried out.