Effect of an electric field on an intermittent granular flow

The enzymatic modification of whey-proteins for spray drying encapsulation of Ginkgo-biloba extract

Ginkgo biloba extract (GBLE) contains many bioactives including flavonoids and terpene trilactones that play some pharmacological roles. These compounds are sensitive to operating conditions; so, encapsulation is a suitable approach to protect them. In this study, different carriers including maltodextrin (MD), and its combination with gum-Arabic (MD-GA), whey protein concentrate (MD-WPC), and whey-protein hydrolysate (MD-HWPC) were used to encapsulate GBLE. Powder production yield, physicochemical/functional characteristics, physical stability and flowability of particles were affected by the type and composition of carriers. FTIR results indicated the placement of phenolic compounds in the carrier matrix. The SEM images also showed the morphological changes of particles (especially the size, indentation and surface shrinkage) under the influence of various carriers. Microencapsulated powders formulated using MD-HWPC showed the highest values of TPC, DPPH, and ABTS and a lighter color which determined the suitability of this wall material (due to the improvement of surface activity and emulsifying properties of protein as a result of partial enzymatic hydrolysis) to protect the antioxidant properties of GBLE during spray-drying, improving the production yield and preserving physical and functional characteristics of the encapsulated powders.

Packing dynamics of powders at high temperature

In industrial powder processing, precise control of environmental temperature is difficult especially for large production facilities. A better knowledge of powder behavior modification due to temperature variation will help to improve product quality and consistency. From a fundamental point of view, the effect of temperature on powder flow and packing dynamics is still poorly understood. In particular, because temperature modifies the complex interplay between the different forces acting at the contact between the grains. The packing dynamics of a set of different powders (lactose, cacao and dried milk powder) has been investigated with a tapping experiment. After the filling procedure, the sample is heated and the evolution of the density is measured after each tap. We show that the packing dynamics is drastically influenced even for low temperature changes. Slight increase of temperature affects both the packing kinematics and the packing range characterised by the classical Hausner ratio analysis. Finally, the different physical mechanisms that could explain these modifications are discussed. The results of this preliminary study demonstrate the importance of temperature in powder behaviour and strongly motivate further investigations.

Discharge of a 2D magnetic silo

We investigate experimentally the discharge of a 2D-silo, a Hele-Shaw cell, filled with a mono layer of ferromagnetic grains submitted to an external magnetic field B perpendicular to the cell plane. In this case the magnetic pair interactions are repulsive. We show that the granular flow rate decreases systematically with the amplitude of the external magnetic field applied. Interestingly, while the output flow rate remains constant during an experiment, we reveal very large spatio-temporal fluctuations of the packing density within the cell, particularly evident for magnetic field of high amplitudes.

Intermittency and velocity fluctuations in hopper flows prone to clogging

We study experimentally the dynamics of granular media in a discharging hopper. In such flows, there often appears to be a critical outlet size D_{c} such that the flow never clogs for D>D_{c}. We report on the time-averaged velocity distributions, as well as temporal intermittency in the ensemble-averaged velocity of grains in a viewing window, for both D<D_{c} and D>D_{c}, near and far from the outlet. We characterize the velocity distributions by the standard deviation and the skewness of the distribution of vertical velocities. We propose a measure for intermittency based on the two-sample Kolmogorov-Smirnov D_{KS} statistic for the velocity distributions as a function of time. We find that there is no discontinuity or kink in these various measures as a function of hole size. This result supports the proposition that there is no well-defined D_{c} and that clogging is always possible. Furthermore, the intermittency time scale of the flow is set by the speed of the grains at the hopper exit. This latter finding is consistent with a model of clogging as the independent sampling for stable configurations at the exit with a rate set by the exiting grain speed [C. C. Thomas and D. J. Durian, Phys. Rev. Lett. 114, 178001 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.178001].

Geometry dependence of the clogging transition in tilted hoppers

We report the effects of system geometry on the clogging of granular material flowing out of flat-bottomed hoppers with variable aperture size D and with variable angle θ of tilt of the hopper away from horizontal. In general, larger tilt angles make the system more susceptible to clogging. To quantify this effect for a given θ, we measure the distribution of mass discharged between clogging events as a function of aperture size and extrapolate to the critical size at which the average mass diverges. By repeating for different angles, we map out a clogging phase diagram as a function of D and θ that demarcates the regimes of free flow (large D, small θ) and clogging (small D, large θ). We do this for both circular holes and long rectangular slits. Additionally, we measure four types of grain: smooth spheres (glass beads), compact angular grains (beach sand), disklike grains (lentils), and rodlike grains (rice). For circular apertures, the clogging phase diagram is found to be the same for all grain types. For narrow slit apertures and compact grains, the shape is also the same as for circular holes when expressed in terms of projected area of the aperture against the average flow direction. For lentils and rice discharged from slits, the behavior differs and may be due to alignment between grain and slit axes.

Flow of magnetized grains in a rotating drum

We have experimentally investigated the influence of a magnetic interaction between the grains on the flow of a granular material in a rotating drum. The magnetic cohesion is induced by applying a homogeneous external magnetic field B oriented either parallel or perpendicular to the gravity g. The drum rotating speed has been selected to obtain a continuous flow when the magnetic field is switched off. We show that, for both magnetic field orientations, the cohesion is able to induce a transition between the continuous flow regime to the discrete avalanche regime. The avalanche dynamics is periodic when B⊥g and irregular when B∥g. Moreover, the maximal angle of stability θ(m) increases strongly with the cohesion strength and could be higher than 90° when B⊥g. A toy model based on the stability of a magnetic block on a magnetic inclined plane is proposed to explain this behavior.