(406d) Application of a Combined PIV/PTV-Method to Analyze Suspensions in (non-)Newtonian Media in Stirred Tanks

Suspending solid particles in stirred tanks is a standard process and is therefore widely used. While for Newtonian liquids this process has already been extensively investigated, there is no comparable knowledge and database for solid suspension in non-Newtonian liquids.

Non-Newtonian flow properties are expressed, for example, in a viscosity that is dependent on shear rate. In polymer systems, e.g., additional elastic flow properties lead to the development of normal stress differences. Both properties influence the interaction between particles and fluid and thus also the suspension process in the stirred tank.

In order to quantify these effects, refractive index-matched solid-liquid systems are analyzed in this talk in a standard, flat bottomed acrylic glass tank (D=H=0.29) equiped with 6-bladed pitched blade turbine (s. Fig. 1). Glass spheres with a uniform diameter are used as solids. As liquid, an (aqueous) inverted sugar solution is used, which is additionally adjusted to the refractive index of the solids via salts. Non-Newtonian flow properties are created by the addition of polymers.

This system enables the simultaneous recording of velocities of the liquid phase via PIV and solid phase via Particle Tracking Velocimetry (PTV) in the laser cutting plane (s. Fig. 1). For PIV, small density-adapted tracer spheres, which reflect the laser light, are used. They can be selectively recorded with a band-pass filter with a wavelength range adjusted to the laser light (s. Fig. 2). PTV of the solid spheres is enabled by addition of rhodamine-6G: this colorant leads to fluorescence of the liquid in the laser cutting plane, which is selectively recorded using a long-pass filter (s. Fig. 2). The shadows caused by the solids in this plane then can be evaluated by PTV algorithms (s. Fig. 3).