Mapping the local viscosity of non-Newtonian fluids flowing through disordered porous structures

Flow of non-Newtonian fluids through topologically complex structures is ubiquitous in most biological, industrial and environmental settings. The interplay between local hydrodynamics and the fluid’s constitutive law determines the distribution of flow paths. Consequently the spatial heterogeneity of the viscous resistance controls mass and solute transport from the micron to the meter scale. Examples range from oil recovery and groundwater engineering to drug delivery, filters and catalysts. Here we present a new methodology to map the spatial variation of the local viscosity of a non-Newtonian fluid flowing through a complex pore geometry. We use high resolution image velocimetry to determine local shear rates. Knowing the local shear rate in combination with a separate measurement of the fluid’s constitutive law allows to quantitatively map the local viscosity at the pore scale. Our experimental results—which closely match with three-dimensional numerical simulations—demonstrate that the exponential decay of the longitudinal velocity distributions, previously observed for Newtonian fluids, is a function of the spatial heterogeneity of the local viscosity. This work sheds light on the relationship between hydraulic properties and the viscosity at the pore scale, which is of fundamental importance for predicting transport properties, mixing, and chemical reactions in many porous systems.

Effect of free fatty acids and phospholipids on growth of and product formation by recombinant baby hamster kidney (rBHK) and Chinese hamster ovary (rCHO) cells in culture

Recombinant BHK and CHO cells producing human antithrombin III (rh ATIII) were used to investigate the utilization of phospholipids and free fatty acids from low-serum (0.1% FBS) culture medium. Both cell lines show distinctly different patterns of fatty acid utilization. For rBHK ATIII cells it is shown that under low serum conditions several different combinations of free fatty acids (bound to bovine albumin) elicit an identical growth stimulatory effect although individual consumption and production rates of fatty acids are different. Increased fatty acid concentrations lead to increased uptake rates without any further effect on growth rate being observed. Recombinant antithrombin III formation is found to be a function of combinations and concentrations of fatty acids present in the culture medium.