Third party funded individual grant
Start date : 01.01.2018
End date : 31.12.2020
The proposed research project focuses on the development of a shadowgraphy apparatus for the accurate and simultaneous determination of multiple transport properties in fluid mixtures over a large range of thermodynamic states. Here, shadowgraphy is applied for the analysis of non-equilibrium fluctuations (NEFs) which are caused by thermophoretic processes in fluid mixtures subjected to a stationary temperature gradient. The lifetimes of these NEFs are affected by several physical mechanisms and can be evaluated based on the hydrodynamic fluctuations theory. In principle, this allows an absolute determination of the thermal diffusivity, the mass diffusivity, the thermodiffusion or Soret coefficient, and the kinematic viscosity of the studied mixture in one single experiment. For the intended development of shadowgraphy as a reliable method for the accurate determination of multiple transport properties, it is necessary to design and realize a new generation shadowgraphy apparatus with maximum temporal resolution and maximum optical access to the integrated measurement cell. The experimental setup is planned to be validated by measurements with selected binary mixtures which cover a wide range of values for the accessible transport properties, e.g., between about 10-10 and 10-7 m2·s-1 for the diffusivities. The proposed mixtures include liquid/liquid, gas/liquid, and gas/gas systems at pressures up to 50 MPa and temperatures up to 573 K, where literature data as well as results from previous and ongoing dynamic light scattering (DLS) experiments should serve as reference data. These measurements with the new shadowgraphy apparatus are also designed to give information on the limitations of the technique as well as the uncertainties of the individual transport properties which can be expected for corresponding experimental conditions. Thus, the potential of shadowgraphy as a future routine measurement technique within thermophysical property research should be evaluated. Finally, the investigation of some systematically selected binary mixtures including light gases dissolved in liquids with varying molar mass as well as mixtures in supercritical state are planned. These measurements should demonstrate the ability of shadowgraphy to contribute to the development of a reliable database for transport properties of such mixtures, which is required, e.g., for modeling purposes or for the validation of available theories related to the accessible transport properties.