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Mass transfer measurements were conducted on a Parallel Plate Rheometer (PPR) using the limiting diffusion current method, i.e. the polarography technique. The database constructed was exploited for the validation of the inverse method under a well-controlled unsteady shear flow. This method is based on a numerical sequential estimation. It has been applied to determine of the wall shear rate in the upper disk of the PPR. It requires the numerical inversion of the convection diffusion equation in order to apply it to instantaneous mass transfer measurements. This requires the use of electrochemical probe, which allows the determination of the local mass transfer rate for known flow kinematics. A multi-segment electrochemical probe has been used. The directional characteristics of the three-segment probe were highlighted. The directional angle effect and the frequencies of oscillations effect were studied in order to test the robustness of the inverse method within the presence of such factors. The obtained results demonstrate that the inverse method allows a good determination of the shear rate, which follows the experimental one for different cases tested in a satisfactory way.

Adding product into the mixer exerts a strong and rapid impact during concrete mixing. Experimental data obtained from a planetary mixer in a full-scale concrete plant under laboratory conditions show that the state of mixture progress with mixing time is well described by the mixing power evolution. More specifically, a reliable method for detecting the time corresponding to the transformation of a mixture from a cohesive granular material into a granular paste (i.e. the so-called “transition time”), through use of a mixing power measurement, will be presented herein. Moreover, once this transition has been achieved, mixing power consumption will be related to mixture rheology and then to mixer geometry by means of a simplified hypothesis. This equation can also be obtained via a dimensionless analysis. Lastly, it will be shown that mixture behavior beyond the transition point is well fitted by a hyperbolic equation. The corresponding mixing power evolution can then be predicted by the level of power at this transition time. These results are suitable for application to online process monitoring.

Drop break-up process for the flow of liquid–liquid dispersion in a static mixer has been investigated. Two new theoretical models for the drop break-up at low and intermediate Reynolds number for variant viscosity ratio of the dispersed phase to the continuous phase have been developed assuming that the flow through the static mixer elements is analogous to the flow through porous media. This concept has recently been established by Morancais et al. (Chem. Eng. Commun. 179 (1999) 77) and Legrand et al. (Chem. Eng. Res. Des. 79 (2001) 949). The boundary-layer shear force concept has been applied to predict the drop break-up at low Reynolds number and at intermediate Reynolds number, the effect of inertia on the drop break-up has been considered. The predicted drop sizes are in reasonable agreement with experimental results.

As a preliminary study to flow modeling in torus reactors, simulations are carried out in well-known standard geometries, namely 90° and 180° bends. For the latter, two flow configurations are considered, with and without initial swirl motion so as to approach torus reactor conditions. Efficiency of the commercial CFD code FLUENT is investigated by comparing predicted results with experimental measurements available in the literature for both bended configurations. Different turbulent models and near-wall considerations are considered, including k – e and high Reynolds-stresses models, with the standard wall-function approach as well as the two-layer zonal model and low- Re k – e models. After validation of the numerical strategy, a parametric study is made to better understand the interactions between Dean vortices, involved by the bend curvature, and the main rotating motion generated by the swirl motion. Simulations are achieved for various values of the initial swirl intensity applied at the bend entry. Numerical simulations show different flow structures, resulting from the progressive Dean vortices perturbations with the increase of swirl intensity.

Calculation of the 6ow pattern in a new small homogenising valve design (Stansted, U.K.), able to reach operating pressure as high as 350 MPa, was investigated in the :rst part of this paper using a Computational Fluid Dynamics method. Numerical simulation results are used in the present paper to better understand the emulsi:cation process in the Stansted high-pressure homogeniser. Deformation of drops is supposed to occur in the intense elongational 6ow caused bythe restriction between the piston and the seat of the valve. Deformation maybe mainlyfollowed bydrop disruption in the narrow valve gap. Break-up probablyalso occurred in the highly turbulent region, located just at the exit of the gap, and underlined bythe numerical investigation. Cavitation and the rate of recoalescence, :rst assumed from numerical results, are determined thank to experimental methods. Intensities of both phenomena stronglyincrease with homogenising pressure. Final droplet size of model oil-in-water emulsions is then the result of equilibrium between droplet break-up and recoalescence, which stronglydepends on operating pressure. ? 2004 Elsevier Ltd. All rights reserved.

High-pressure homogenisation is a key unit operation used to disrupt fat globules or cells containing intracellular bioproducts (AIChE J. 43(4) (1997) 1100). Modelling and optimisation of a small homogenising unit are often restrained by a lack of information on the flow conditions within the homogeniser valve. A numerical investigation of the flow within such a new homogenising valve, capable to reach pressure as high as (Stansted Fluid Power Ltd, UK) is presented. Results are obtained using the finite-volume technique and a RNG k–e turbulence model with low Reynolds number near wall treatment conditions. An experimental measurement of the size of the valve gap is presented in order to validate mathematical relations that give valve gap sizes versus homogenising pressure. The modelling results give detailed information on the mechanical stresses and the high shear rates in small disruption valves, and also reveal other phenomena that could not be easily determined experimentally.

The electrodiffusion technique was performed in order to investigate the shear rate on a scraped surface heat exchanger. Microelectrodes were placed inside: the walls of the outer cylinder; the inlet and outlet bowls; the rotor and the blades. Highly viscous Newtonian fluid (Emkarox HV45 solutions) and non-Newtonian model fluid (aqueous solutions of CMC) were used. The electrodiffusion method allowed us to measure wall shear rates. Maximum shear rate was observed at the scraping surface and caused by blades scraping, high shear rate was also measured on the leading edge of the blades. In the other parts of the exchanger, shear rate remained low but the development of Taylor vortices completely modified the scraped surface heat exchangers behaviour inside the surface of the bowls. A dimensionless representation of the friction factor was established for the inner and outer wall surface of the exchanger.

Local wall shears stress analysis as well as cleanability experiments on di!erent pieces of equipment in various circuit arrangements were performed. Pieces of equipment used in this work, stainless steel made, were representative of production lines:straight pipes of di!erent diameters, sudden or gradual contraction or expansion pipes. Local wall shear stress values, obtained by an electrochemical method, were shown to be in9uenced by the loop arrangement. Geometry as the gradual expansion pipe had an e!ect on the upstream straight pipe where the wall shear stress values were two times lower than in other con:gurations as with a sudden expansion. In sudden geometry, the bacterial removal during cleaning was improved by the increase of the 9ow rate, corresponding to the increase of the mean local wall shear stress. However, in gradual expansion or contraction pipe, cleanability was not improved by the increase of 9ow rate. The e!ect of the mean wall shear stress on the removal has been con:rmed. Moreover, this work demonstrated a clear positive e!ect of an increase of the 9uctuation rate on the spore detachment. Low mean wall shear stress zones as in sudden expansion (around 0:15 Pa) could be cleanable because of the high 9uctuation rate (around 21%). These results underline the importance of the design and the 9ow con:guration. ? 2002 Elsevier Science Ltd. All rights reserved.

In this work, the #ow modelling of a toroidal reactor in batch or continuous operating modes is obtained by the experimental determination of the tracer concentration evolution in batch mode and the residence time distribution in continuous con"guration, for mixing Reynolds numbers between 15 and 8]104 with water and glucose solutions. The comparison of the mean circulation times measured at each rotation speed and #ow rate shows that for a ratio of the mean residence time to the mean circulation time lower than 20, the #ow is accelerated by the inlet}outlet #ow rate. Two di!erent #ow regimes are respectively obtained for Re m (3000 and for Re m ’6000 and a single correlation giving the volume #ow number, N v , as a function of Re m can "t both #ow regimes. The #ow behaviour is modelled by a dispersed plug #ow with recirculation. The value of the axial dispersion coe$cient is rather small and constant in the whole range of Re m and for the two con"gurations which means that the #ow for each rotation of the #uid in the torus reactor behaves like a plug one. ( 2000 Elsevier Science Ltd. All rights reserved.

Vertical upward cocurrent gas—liquid flow in a short annular rotating separator was experimentally investigated. The liquid film thickness was measured with a conductimetric method and the axial velocity profiles in the liquid phase were determined from laser measurement (LDA). The obtained axial velocity distributions at the outlet of the centrifugal separator allow satisfactory withdrawal of the separated liquid phase. A model, using a laminar gas/turbulent liquid scheme, is proposed to predict the position of the interface and the liquid axial velocity profile. The model is obtained from a parametric analysis of the gas—liquid flow with separated phases. The model results are rather satisfactory to predict the conditions leading to a good extraction of the liquid phase.