Boris Ouriev

Novel ultrasound based time averaged flow mapping method for die entry visualization in flow of highly concentrated shear-thinning and shear-thickening suspensions

In this work a methodology for high-resolution time averaged two-dimensional flow mapping of converging flows was explored. Flow of non-transparent, highly concentrated shear-thinning and shear-thickening suspensions was circulating through the entrance flow adapter with adjustable position of the die entry. The entrance region was scanned with the distance resolution of 2.7 mm ? 1 mm, radial to axial displacement respectively. The time averaged flow map was composed from one-dimensional flow profiles measured along the ultrasonic sensor beam using the ultrasonic pulsed echo Doppler technique. Priory to die entry visualization an investigation of flow properties was performed using a novel in-line non-invasive measuring technique. The method is based on combination of the ultrasound velocity profiler velocity monitoring and pressure difference method. The rheological flow properties were derived from simultaneous recording and on-line analysis of the velocity profiles across the tube channel and related radial shear stress profiles calculated from the pressure loss along the flow channel. For the first time the entrance flow of shear-thickening suspension could be visualized. A comparison between the flow of the investigated model suspensions was qualitatively analysed. This method gives an opportunity for time averaged flow mapping of viscoelastic and viscous, non-transparent, multiphase and highly concentrated fluids.

Industrial application of ultrasound based in-line rheometry: Visualization of steady shear pipe flow of chocolate suspension in pre-crystallization process

In the present work an in-line ultrasonic method for investigation of the rheological flow behavior of concentrated suspensions was created. It is based on a nondestructive rheological measuring technique for pilot plant and industrial scale applications. Elsewhere the author discusses a tremendous need for in-line rheological characterization of highly concentrated suspensions exposed to pressure driven shear flow conditions. Most existing on-line methods are based on destructive macro actuators, which are not suitable for materials with sensitive to applied deformation structure. Since the process of our basic interest influences the structure of suspension it would be difficult to separate the effects of rheometric measurement and weakly pronounced structural changes arising from a fine adjustment of the process parameters. The magnitude of these effects is usually associated with the complex flow dynamics of structured liquids and is sensitive to density or temperature fluctuations around the moving r...

Transient flow of highly concentrated suspensions investigated using the ultrasound velocity profiler–pressure difference method

In the present work, the transient pressure driven shear flow of highly concentrated suspensions was investigated. The authors applied a novel Doppler-based ultrasound velocity profiler (Met-Flow SA)–pressure difference (UVP–PD) methodology (Ouriev B 2000 PhD Thesis Zurich ISBN: 3-905609-11-8, Ouriev B and Windhab E 2002 J. Exp. Fluids 32 204–11), for the investigation of concentrated suspensions in steady and transient flows. Model suspensions with two different solid phase concentrations and fluid matrixes were analysed in shear steady flow at different volumetric flow rates. Transient flow was initiated by abrupt flow interruption. Simultaneous recording of the pressure gradient (Windhab E 1986 Thesis VDI) and real time flow velocity profiles enables analyses of transient rheological flow properties. Both velocity and rheological information were simultaneously measured on-line and evaluated off-line. The rheological characteristics of the suspensions in transient flow are compared with those in steady flow and conclusions are drawn.

Industrial application of ultrasound based in-line rheometry: From stationary to pulsating pipe flow of chocolate suspension in precrystallization process

In-line visualization and on-line characterization of nontransparent fluids becomes an important subject for process development in food and nonfood industries. In our work, a noninvasive Doppler ultrasound-based technique is introduced. Such a technique is applied for investigation of nonstationary flow in the chocolate precrystallization process. Unstable flow conditions were induced by abrupt flow interruption and were followed up by strong flow pulsations in the piping system. While relying on available process information, such as absolute pressures and temperatures, no analyses of flow conditions or characterization of suspension properties could possibly be done. It is obvious that chocolate flow properties are sensitive to flow boundary conditions. Therefore, it becomes essential to perform reliable structure state monitoring and particularly in application to nonstationary flow processes. Such flow instabilities in chocolate processing can often lead to failed product quality with interruption of...

Influence of vibration on structure–rheological properties of a highly concentrated suspension

The influence of mechanical vibration on the flow properties of a highly concentrated multiphase food system is explored in this work. An experimental set-up was designed and adapted to a conventional rotational rheometer with precise rheological characterization capability. A number of calibration tests were performed prior to fundamental experiments with a highly concentrated chocolate suspension. Also, the prediction of wall slippage in shear flow under vibration was evaluated. Analysis of the boundary conditions shows that no side effects such as wall slippage or the Taylor effect were present during the shear experiment under vibration. It was found that superposition of mechanical vibration and shear flow radically decreases the shear viscosity. Comparison between reference shear viscosities at specified shear rates and those measured under vibration shows considerable differences in flow properties. Conversion of the behaviour of the concentrated suspension from strongly shear-thinning to Newtonian flow is reported. Also, the appearance of vibration-induced dilatancy as a new phenomenon is described. It is suggested to relate such phenomena to the non-equilibrium between structure formation and disintegration under vibration and hydrodynamic forces of shear flow. The influence of vibration on structure formation can be well observed during measurement of the yield value of the chocolate suspension under vibration. Comparison with reference data shows how sensitive the structure of the concentrated suspension is to vibration in general. The effects and observations revealed provide a solid basis for further fundamental investigations of structure formation regularities in the flow of any highly concentrated system. The results also show the technological potential for non-conventional treatment of concentrated, multiphase systems.

Rheology and Rheometry of Aluminum alloys: Influence of shear and vibration on aluminum flow properties

Understanding of flow properties and flow effects of liquid and semisolid aluminum became a key solution for know-how of casting process. Therefore such properties must be characterized a priory to layout of flow process parameters in order to predict structure formation of aluminum in flow. In order to reach target of material characterization it becomes essential to analyze materials under as close to real process conditions as possible. This task was solved by strong modification of commercial rotational rheometer and application of high-resolution temperature control. Besides understanding the flow properties it is essential to find the way of interactive structure control during flow process. Therefore controllable effects were generated and studied with the help of structure related rheological flow properties. For triggering structure formation an influence of mechanical vibration on flow properties of highly concentrated semisolid alloy is explored in this work. For that experimental set-up was designed and adapted to conventional rotational rheometer with precise rheological characterization capability. Priory to fundamental experiments with highly concentrated aluminum suspension a number of calibration tests were performed. Also prediction of wall slippage in shear flow under vibration was evaluated. Analysis of boundary conditions shows that no considerable side effects were present during shear experiment under vibration. The research reveals precise detection of transition temperatures with the help of steady and transient shear viscosity measurement besides selective measurement of full rheological curves within liquid and semisolid state temperature range. Rheological characterization was performed under shear flow conditions with and without presence of orthogonal to flow direction mechanical vibration. It was found that superposition of mechanical vibration and shear flow radically decreases shear viscosity but only in semisolid state. Liquid state rheological properties shows structural behavior but kept insensitive to application of mechanical vibration. For semisolid alloys, comparison between reference shear viscosities at specified shear rates and those measured under vibration shows considerable differences in flow properties. Conversion of concentrated suspension from strongly shear-thinning to almost Newtonian flow behavior is reported here. It is suggested to relate such phenomenon to non-equilibrium between structure formation and disintegration under vibration and hydrodynamic forces of shear flow. Influence of vibration on structure formation was also well observed during measurement of solidification process. Comparison to reference data shows how sensitive structure of concentrated suspension is to vibration in general and especially during solidification phase. The reveled effects and observations provide a solid bases for further fundamental investigations of structure formation regularities in flow of any highly concentrated systems.