The extrusion of a model yield stress fluid imaged by MRI velocimetry

Breaking of non-Newtonian character in flows through a porous medium

“…1), are "broken" by the porous medium. This conclusion is further supported by the observation that the yielding character of a fluid is broken around the entrance in a small die, which well represents the situation continuously encountered inside a bead packing: far from the entrance there is a plug flow [14], but just after the entrance the velocity profile is close to that for a Newtonian fluid and only after some distance of the order of the conduit diameter the standard profile including a plug is recovered (see Fig. 4).…”

“…Thus, once again in contrast with yield stress fluid flows through simple geometry, V has no significant impact on the velocity distribution. Actually, such a phenomenon has already been observed for a complex flow (extrusion) of yield stress fluids [14] in a similar range of Bi: over a length of the entrance conduit approximately equal to its diameter, the velocity fields (in a longitudinal cross section) scaled by the piston velocity appear quite similar for different Bi.…”

Softening of aged fluids in start-up flows of dense suspensions

“…Here we consider the transport in a pipe of fluids with different shear histories, and thus with different rheological properties. Rabideau et al [32] examined the velocity field during extrusion using a yield stress fluid. Their system was composed of a chamber connected to a pipe, which is similar to our system.…”

Cardinal series to sort out defective samples in magnetic resonance data sets

“…Unlike Gaussian noise, they often appear as a limited number of chaotically dispersed sharp spikes in the time domain, have hardly identifiable spectrum patterns and thus are difficult to remove by using a linear low pass filter. Noise caused by a brushed DC electric engine, which we have observed in our rheological studies [6][7][8][9], has a significantly higher covariance than Gaussian electronic noise; and even though only about one of ten NMR data samples were thus affected, it greatly reduced the overall signal-to-noise ratio, while Gaussian noise level was very reasonable.…”

“…Certain experiments require that auxiliary electric devices should be placed near or inside the magnet of the NMR spectrometer, which may bring about severe extra distortions of measured NMR signals [2][3][4][5][6][7][8][9]. In rheological and fluid mechanics studies by NMR in particular, electric motors and various monitoring units are put underneath the magnet of the NMR tomographer.…”