Hemodynamics across the scales
A systematic experimental study of the emulsification of shear-thinning fluids (xanthan solutions) in an inertially turbulent microscopic flow is presented. Through the first part of the talk, I focus on a presumably simpler aspect: the dynamics of a single oil drop in the turbulent microscopic flow of a shear-thinning fluid. Two distinct dynamic phenomena undergone by the single oil drop are described in connection to the rheological behavior of the shear-thinning continuous phase: trapping and breakup. As a central result, we show that trapping events emerging in xanthan solutions with various concentrations emerge via an imperfect bifurcation. The dynamics of the breakup process are quantitatively described in terms of the characteristic breakup times, a number of emerging daughter droplets, and drop morphology are equally dependent on both the driving flow rates and the polymer concentration. Further physical insights into the intricate coupling between the flow conditions, the shear thinning rheology of the continuous phase, and the single drop dynamics are obtained in terms of a quantitative description of the kinematics of drop deformation. Through the second part of the talk, I discuss the dynamics of the emulsification process in a wide range of Reynolds numbers and within a broad range of xanthan concentrations. Measurements of the flow resistance performed for various xanthan concentrations indicate the emergence of the drag reduction phenomenon which is instrumental in producing emulsions at lower energetic costs. A full chart of the dynamic modes of emulsification is presented in terms of both the Reynolds number and xanthan concentration.
