Véronique Halloin

The radially vibrating horn : A scaling-up possibility for sonochemical reactions

Abstract A very strong dependence of sonochemical reactivity as a function of the transducer design is put into evidence. Moreover, this dependence is completely different when considering homogeneous, heterogeneous liquid–liquid or heterogeneous liquid–solid reactions. These surprising results, that show the complexity of sonochemical reactors, can be understood if a precise description of the reactor is undertaken. Different experimental tools were used and proved to be very useful in this way. Because of that complexity, the design and optimisation of sonochemical reactors is still an open problem and a very promising model that predict the acoustic field and the acoustic streaming is proposed and validated.

Hydrodynamics and mass transfer in a Couette–Taylor bioreactor for the culture of animal cells

Abstract A Couette–Taylor bioreactor device, commercialized by Synthecon for the culture of tissues, can exhibit interesting hydrodynamics and mass-transfer characteristics that could be well suited for the culture of animal cells in suspension. This is investigated through hydrodynamics and mass-transfer study on a plexiglass copy of the existing commercial equipment. Results of these studies show the potential of the Synthecon bioreactor for the culture of animal cells in suspension. The Synthecon bioreactor is then bought and actually used for the culture of CHO cells in suspension. First results confirm the approach developed on the plexiglass copy.

A new approach for the estimation of the melting enthalpy of metastable crystalline compounds using differential scanning calorimetry: Application to the two crystallographic forms of Etiracetam

This article focuses on the development of an innovative method, based on thermodynamic considerations and with the use of Differential Scanning Calorimetry (DSC), for the estimation of the melting enthalpy of crystalline compounds which are metastable near their melting temperature. The curves obtained, at various heating rates, are analysed in two steps. In the first step, the area of a zone generated by the melting endothermic peak is calculated following a specific method. In the second step, the melting enthalpy is extracted from this area through an enthalpy balance. This method is applied to both identified crystallographic forms, named form I and form II, respectively, of Etiracetam (UCB Pharma). The results show that the melting enthalpy of the stable form II compare well with the ones obtained using conventional methods. The curves of the metastable form I present thermal instabilities (partial solid–solid polymorphic transition and beta-recrystallization) near the form I melting peak leading to difficulties for a direct determination of the melting enthalpy by conventional methods. The proposed method is therefore very useful for the estimation of the form I melting enthalpy.

A multifunctional catalytic reactor suitable for the exothermal synthesis of condensable products

Abstract A new multifunctional catalytic reactor for the exothermal synthesis of condensable products is introduced. In this radial flow reactor, an annular packed bed of crushed catalyst particles is crossed by the reactants and the products of the reaction. A gaseous gap separates the catalytic bed from an external cooled envelope on which the products are condensed. The condensed products leave the reactor through a hydraulic seal, while the gas is kept inside the reactor. A mathematical model has been developed to provide a better understanding of the influence of the transfer phenomena in the gap on the behavior of the catalytic layer and vice versa. A first prototype was built, and the proof of technical feasibility was obtained from experiments on toluene hydrogenation; high conversions were obtained at atmospheric pressure. Several factors combine to keep the reaction rate large even in the outermost layers: low temperature, removal of reaction product, and presence of reactants at reasonably large partial pressures. The hydrogenation of benzene into cyclohexane, which is of great commercial interest, was also successfully operated. The use of this reactor for methanol or ammonia synthesis could bring significant cost savings through the possible suppression of the recycle loop.

A new technique for the experimental study of 3D velocity fields

A new photographic method has been developed for the experimental study of 3D velocity fields, by means of which the three components of velocity can be simultaneously determined from one single photograph. This technique is based on the usual PIV and PTV ones; the production of appropriate stroboscopic illumination enables to measure the third component of velocity in the direction orthogonal to the illuminated plane.The hardware required for its implementation is modest, and the evaluation of the measurements is simple. Until now, this technique was only applied to low Reynolds number flows.

Computational and experimental methods for the on-line measurement of the apparent viscosity of a crystal suspension

This paper proposes an experimental method, based on the Metzner and Otto concept, for the on-line measurement of the apparent viscosity of a crystal slurry during a crystallization process. The first step of this procedure consists of the determination of the N p-Re-Fr relation for Newtonian liquids, for two impeller-tank configurations, chosen such that this relation is a bijective one. This is achieved both experimentally and numerically, using Computational Fluid Dynamics. In the second step of the procedure, the same impeller-tank configurations are used for the determination of the evolution of the apparent viscosity of the crystal slurry (non-Newtonian liquid) during a reference pharmaceutical crystallization process (Etiracetam - UCB). The paper concludes on the influence of the Particle Size Distribution of the crystals on the apparent viscosity of the suspension. For a given crystal mass fraction, the bigger the crystals are - and then the less abundant they are - and the smaller the span is, the smaller the apparent viscosity of the suspension is.

PHYSICAL AND NUMERICAL SIMULATIONS OF CREEPING FLOW AND HEAT TRANSFER IN FOREHEARTHS

A forehearth is a shallow channel connecting the glass melting furnace to the gob dispenser in the glass bottles production process. Although the temperature of the molten glass has to decrease by several hundred degrees in the forehearth, the temperature distribution in the outlet section must be uniform. Due to the extremely convoluted character of the flow pattern, it is difficult to suggest the design rules and operational procedures that will ensure this uniformity without resorting to detailed experimental and numerical studies. Using a room temperature physical model, we have simulated the creeping flow of glass in a forehearth. The 3D temperature field and velocity field of the model fluid (silicon oil) were mapped. In particular, the complexity of the flow pattern immediately upstream of the outlet section was revealed, and more generally, the overriding importance of the gravity currents induced by the non uniformity of the temperature (hence density) field came to the fore. Numerical results ob...