Two separate constructions used in advanced microfluidics are combined to achieve controlled mixing and mass transport at maximum efficiency over minimal distance. One is the use of grooves to enhance mixing -an intensively investigated technique employed in electronic components cooling. So far, only grooves of ectangular cross-sections were used. The other construction builds on the well known effect of partial rectification in axially asymmetric channels and has been employed for valvless pumping. It is now shown that a cascade of axially asymmetric grooves retains and even improves the rectification efficiency of a single nozzle while offering the potential of simultaneous mixing enhancement by a factor of more than 2. The latter is achieved in a certain range of moderate Reynolds numbers characterized by self-induced oscillations at much higher frequency than that of flow actuation. Tuning the pressure drop provides precise control of the effective flow rate, up to suppression or reversion. The duration and intensity of mixing and shearing can thus be adjusted within a broad range and effected in very short channels without additional actuators. In the regime of self-induced oscillations, a few identical sensors with sufficient temporal resolution for temperature or concentration allow reliable determination of the flow rate as well as of the admixture composition of the transported fluid.It is well known that the flow in channels with walls patterned by closely spaced "roughness elements" (shallow grooves) or "constrictions" (grooves of depth comparable to the channel diameter) becomes unstable at significantly lower Reynolds numbers compared to channels with straight walls, giving rise to spontaneous (self-induced) oscillations [1,2]. This transition to time-dependent flow is a "normal" (supercritical) bifurcation (as opposed to the subcritical instability found in straight channel flows) in the bulk Reynolds number Re = D h U m /4ν (here U m is the average, or bulk velocity, D h the hydraulic diameter, ν the kinematic viscosity). The critical number Re c depends on the groove shapes, thus being different for the two possible flow directions along a channel with groove trains that are systematically asymmetric with respect to the channel axis. Interestingly enough, virtually all studies on this kind of instability have been focused on symmetric grooves, in some cases of wavy but mostly of rectangular shape. Thee objective of the present study is to explore the influence of assymetry -not only on Re c but also on the spectrum of induced oscillations and the mixing and transport quality of the respective flows. Typically, 200 < Re c < 600, consistent with similar flows, e.g. around polygonal obstacles (cylinders in 3D) or backward facing steps. In separate numerical studies at our Institute, self-sustained turbulent 3D flows were found for Re < 900 with square, and for Re < 600 with asymmetric obstacles of the kind shown in fig. 1. The dominant dynamical features were, in all cases, spanwise vortices with c...

The unwanted inclusions in food and beverages pose a threat to both consumer health and the business, including producer image and liability. Detection of such inclusions, in particular metal and glass particles of millimetre size, is an important element of quality control in such industries. Specific solutions usually are limited in their detection range or are investment and space intensive. The presented project investigates a principally new detection method for foreign particles in fluid media of different densities and transparencies. Proof of concept is provided for the important case of glass containers, but the method is applicable to other materials.

Unwanted foaming and liquid bridging inside structured packings have a negative effect on the pressure drop during thermal separation processes. A novel helical design of a packing column for preventing foaming is presented. The effective interfacial area is calculated by numerical simulations. Different designs are analyzed by varying geometrical parameters such as helix pitch, channel opening angle, and number of channels. Different F-factor values and liquid loads are evaluated. Packings with larger helix pitch exhibited lower pressure drop and reduced effective interfacial area. Smaller channel opening angles increased the pressure drop and promoted unstable flow conditions. The novel packings show lower effective interfacial area than existing structured packings, but no foaming was observed in a wide range of operating conditions.