Understanding of pore scale displacement processes for Newtonian and complex fluids through the interaction of fluid properties and pore geometry.

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The aim of this project is to understand the displacement behavior of non-Newtonian fluids in porous media (microfluidic model systems). This displacement behavior is determined by the interplay of (complex) fluid properties such as wettability, shear rate dependent viscosity and elasticity as well as geometric parameters such as size and shape of flow channels. The shear rate dependent fluid properties can lead to a "geometry dependent" viscosity distribution within a heterogeneous porous medium at a constant (global) volume flow, as well as to local elasticity effects. In order to understand the influence of complex fluid properties on the pore-scale instabilities and hence on the global displacement behavior, the global and local displacement behavior of the complex fluids will be compared with each other, as well as with the displacement behavior of Newtonian fluids with the same zero shear viscosity. The occurring geometry-dependent local shear rates and thus local viscosities shall be estimated by determining the flow fields. The experiments will be carried out for different pore space geometries and different flow velocities, for both wetting and a non-wetting invading (complex) fluids. The velocities are chosen in such a way that capillary, viscous and possibly elastic forces dominate, while inertial forces can be neglected. By using two cameras with different magnification optics, the global displacement patterns as well as the fast local meniscus instabilities will be observed simultaneously. The frequency of different local instabilities will be determined by numerical image analysis and used to explain the different displacement modi that lead to different global displacement patterns. The global patterns will be quantified by various statistical descriptors such as finger width. By comparing all the data obtained, the wetting-dependent influence of shear-thinning viscosity and elasticity, respectively the combination of both non-Newtonian properties, on the occurrence of certain local instabilities and thus ultimately on the global displacement behavior shall be determined.