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International audience; The freshwater microalgae species Chlorella kessleri and Chlorella vulgaris, and the marine microalgae species Nannochloropsis oculata were cultivated in urban wastewater. The freshwater species demonstrated the possibility of growing in urban wastewater reaching high biomass production and nutrient removal when cultured in batch mode using a flat-panel airlift photobioreactor. Both microalgae species reached high biomass dry weights, 2.70 ± 0.08 g/L and 2.91 ± 0.02 g/L respectively, accompanied by nitrogen concentration reduction around 96% and 95%, and a phosphorous concentration reduction around 99% and 98% respectively. N. oculata was able to uptake nutrients from wastewater to grow but with less efficiency, indicating the need of microalgae acclimation or process optimisation to achieve high nutrient removals. During C. kessleri and C. vulgaris cultivation, the nitrogen consumption led to a progressive N-starvation process which increased the microalgae potential for biofuels production; both species produced 346 ± 3 mL CH 4 /g VS and 415 ± 2 mL CH 4 /g VS during anaerobic digestion, and 7.4 ± 0.2 g Biodiesel /100 g VS and 11.3 ± 0.1 g Biodiesel /100 g VS respectively.

International audience; Nannochloropsis has emerged as a promising alga for biodiesel production. However, the genus consists of 6 species and hundreds of strains making strain selection a challenge. Furthermore, oil productivity is instrumental to economic viability of any algal strain for industrial production, which is dependent on growth rate and oil content. In most cases, these two parameters have been studied independently. Thus, the goal of this study is to provide a combined method for evaluating strain performance in specially designed photobioreactors together with an in-depth lipidomic analyses. The nine strains of Nannochloropsis tested showed considerable variations in productivity and lipidomics highlighting the importance of strain selection. Finally, Nannochloropsis gaditana CCMP527 and Nannochloropsis salina CCMP537 emerged as the two most promising strains, with an oil content of 37 and 27 dry wt% after 11-day nitrogen starvation, respectively, resulting in TAG productivity of 13 × 10−3 and 18 × 10−3 kg m−3 d−1, respectively.

The effect of a liquid dispersed on the wall flow structure in static mixer is analyzed by using an electrochemical method. Both laminar and turbulent flows have been investigated. The axial wall velocity gradient and turbulent intensity have been studied along the static mixer in both flow regimes and for different dispersed phase concentrations. The spectral analysis of the wall velocity gradient fluctuations was analyzed in the turbulent regime. For volume fraction higher than 5%, the effect of the dispersed liquid phase is very important for all the studied parameters. The turbulence associated to the dispersed phase leads to an increase of the energy dissipation in the static mixer and also to a modification of energy dissipation mechanism.

The electrochemical technique is commonly used to measure the instantaneous mass transfer between a liquid consisting of an electrochemical solution and a small probe mounted flush in an inert wall. The local mass transfer allows the calculation of the instantaneous wall shear rate averaged on the probe surface. In practice, there are different models used for the calculation of the wall shear rate (Leveque solution, transfer function and Sobolik methods). The probe inertia is closely dependent on its length; a small probe allows to enlarge the band-width of the probe response. For small probes, the axial diffusion can become important in contradiction with the assumptions used in the different models. In this paper, an inverse sequential algorithm of the convection diffusion equation is applied to simulated periodic signals in order to obtain the “true” wall shear rate. A comparison between the different methods is made for different amplitudes and frequencies of wall shear rate oscillations. The influence of noise on the different methods for wall shear rate calculation is also investigated.

An ultra high-pressure homogenizer was used to treat whey protein isolate solutions (3%, w/w). The treated solutions (up to 300 MPa) were characterised for both physico-chemical properties (particle size distribution, surface hydrophobicity and structural conformation) and functional properties (solubility, foaming stability and interfacial rheology). Dynamic high-pressure treatment did not affect the conformation of the proteins (determined by micro-calorimetry, size-exclusion chromatography and electrophoretic technique). This treatment dissociated large protein aggregates leading to unmasking of the buried hydrophobic groups without affecting protein solubility. Interactions may then occur between these groups that enhance the viscoelasticity of air-water interfaces (assessed by drop tensiometry) and improve foam stability (evaluated by sparging method). Dynamic high-pressure-treated whey proteins showed better foaming and stabilising properties.

The effects of some operating conditions on oil loss and physical properties of products obtained by doughs containing almond flour extruded in a co-rotating twin-screw extruder were investigated. The results showed that the lowest loss of oil was obtained at low percentages of dough moisture and high values of screw speeds. The extrusion parameters that greatly influenced the structural characteristics of extruded products were dough moisture and screw speed. In particular, the best results were obtained by extruding at 36% dough moisture and 200 rpm screw speed. The operating conditions suitable to obtain both a low oil loss and a good product structure were low percentages of dough moisture and high values of screw speed and extrusion temperature.

An experimental investigation of a scaled-down model of an industrial exchanger, using an electrochemical technique, was undertaken in order to show the presence of hydrodynamic heterogeneities at low axial Reynolds number. Heterogeneities were revealed in the bowls with respect to the generalised Taylor number as the result of the perturbations added to the flow by blade rotation at both ends of the exchanger. Shear heterogeneities associated to flow visualisations were correlated to temperature heterogeneities observed in the bowls. Shear fluctuations were revealed in the scraped part describing two distinctive zones at low rotation speed caused by varying viscosity in the flow field. A complex spiral flow was observed by flow visualisation characterising a mass transfer evolution comprised between these two distinctive zones at low Taylor number.

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.

A torus reactor was used to perform hydrolysis of casein with a protease immobilized on beads. Chitosan beads with two different sizes were tested as immobilization matrices. The mechanical resistance of beads in the torus reactor was tested for different times and rotation speeds. Chitosan beads were considered to be suitable as an immobilizing support. The more stable hydrolysis rates in successive assays were obtained with the protease grafted onto the largest chitosan beads. The kinetics parameters of free and immobilized enzymes were determined and compared in batch stirred tanks and torus reactors. Immobilization decreased the enzyme activity to only 5% of the free enzyme activity. No significant differences for apparent kinetic constant ( Km) were observed between immobilized and free enzyme. The apparent reaction rate constant (Vmax) was 25 times less with immobilized enzyme in the torus reactor than with free enzyme in the batch reactor. © 2004 Elsevier Ltd. All rights reserved.

International audience; The light attenuation in a photobioreactor is determined using a fully predictive model. The optical properties were first calculated, using a data bank of the literature, from only the knowledge of pigments content, shape, and size distributions of cultivated cells which are a function of the physiology of the current species. The radiative properties of the biological turbid medium were then deduced using the exact Lorenz-Mie theory. This method is experimentally validated using a large-size integrating sphere photometer. The radiative properties are then used in a rectangular, one-dimensional two-flux model to predict radiant light attenuation in a photobioreactor, considering a quasi-collimated field of irradiance. Combination of this radiative model with the predictive determination of optical properties is finally validated by in situ measurement of attenuation profiles in a torus photobioreactor cultivating the microalgae Chlamydomonas reinhardtii, after a complete and proper characterization of the incident light flux provided by the experimental set-up.

Emulsions are of great importance to industry. They are involved in many engineering operations, including chemical reactions, extraction, emulsification and suspension polymerization, etc. However, an important problem for these processes is how to control the size distribution of the dispersed phase. Indeed, off-line analysis of the emulsion may generate uncertainties due to sampling and dilution of the product, which are likely to change the dispersion state and physico-chemical properties. In this work, an on-line optical method is proposed to characterize dispersed media in real flowing conditions. This method is based on the time-analysis of back-scattered light fluctuations. The present paper deals with the development of this method and its application to dispersions of alumina in water. The results obtained with the on-line optical method are compared with those acquired by classical laser light scattering and microscopy.

La formation d'emulsion huile dans l'eau capable de retenir et de proteger la fraction grasse dans une matrice extrudee est etudiee. Les mesures de conductibilite electrique, qui ont ete faites sur des melanges de farine de ble, de farine d'amande, d'eau et de deux additifs (lecithine de soja et mono- et diglycerides d'acides gras), ont montre que les deux emulsifiants favorisent la formation de l'emulsion a faible concentration (0,2 %). Des experiences d'extrusion ont ete faites avec les melanges a base de farines de ble pregelatinisees, farine d'amande, lecithine de soja et mono- et diglycerides d'acides gras dans des extrudeurs mono- et bi-vis. Les produits obtenus ont ete caracterises au moyen d'analyses physiques et chimiques. Les resultats obtenus, relatifs a la perte d'huile pendant l'extrusion, ont montre que les produits contenant de la lecithine de soja ont une concentration en matiere grasse plus importante (faible perte d'huile pendant l'extrusion) et que l'extrudeur bi-vis peut etre considere comme la machine la plus adaptee pour la realisation des snacks d'amande. Ceci est du essentiellement a deux raisons : une faible perte d'huile pendant le procede et un taux d'expansion plus eleve des produits obtenus.

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.

Viscous products treated in a scraped surface heat exchanger receive a thermal treatment as well as a mechanical treatment. The new method developed by Mabit et al. [J. Food Engrg. 57 (2) (2003) 165] using starch as a marker for the shearing treatment was performed in order to show the influence of blades movement and flow pattern on shearing conditions. Two different flow regimes with respect to the generalised Taylor Number Ta g were investigated: a laminar regime with Taylor vortices and a weakly turbulent one. The blade rotation without scraping in the annulus space can be sufficient to apply a shear treatment above 20,000 s −1 . The product is submitted to the highest shear treatment for high rotational speed with a laminar regime with Taylor vortices. Blades scraping creates high wall shear rates, Taylor vortices improve radial mixing and renew product to be treated at the wall surface. The quantity of stressed product is directly influenced by the flow behaviour and the product residence time in the exchanger.

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.

Melt expansion by extrusion-cooking was investigated when processing corn grits in a twin-screw extruder. A growth phase followed by a shrinkage phase were experimentally observed through an image processing method, and analysed by use of classical expansion indices: sectional, longitudinal and volumetric expansion indices, for both growth and shrinkage phases. It was shown that the expansion phenomenon was strongly dependent on the geometrical characteristics of the die insert, and particularly on die insert diameter. Melt growth developed more in the radial direction which revealed an important structural anisotropy of the expanding melt, due probably to the elastic properties of the biopolymer-based melt. Melt shrinkage which occurred further, contributed to a significant decrease in the bulk density of the expanding melt, and could arise from either surface tension forces, or from the recovery of melt elasticity.

Through a study of the effect of hydrodynamics on the cleanability of complex equipment, this work demonstrates the need for hygienic design to significantly improve food safety. A three-way valve was contaminated with Bacillus spores, isolated from a dairy production line and then suspended in custard. The valve was cleaned by a CIP procedure, including both alkaline and acid phases. The residual localized contamination was assessed directly on the internal surfaces in contact with the food product. Wall shear stress was measured in selected zones by an electrochemical method. Rubber materials (seat areas) are usually considered to be poorly cleanable, yet were found to be more cleanable than adjacent stainless steel zones. This observation emphasizes the importance of the geometry on the cleanability level, and the flow pattern during the cleaning process. Despite its low level, the contribution of the mean wall shear stress, together with its fluctuation rate, was demonstrated in a complex piece of equipment. This underlines the importance of the flow pattern in machinery and more generally in production systems which are automatically cleaned in place. In the upper part of the valve, cleanability was ensured by higher values of local mean wall shear stress, while near its outlet the same cleanability was obtained due to a wide variation in wall shear rates.

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.

Light is the main limiting factor in photoautotrophic-intensive production of microorganisms, and improvement of its use is an important concern for photobioreactor design and operation. Swirling flows, which are known to improve mass and photon transfers, were applied to annular light chambers of a photobioreactor and studied by simulation and microalgal culture. Two hydrodynamic conditions were compared: axial flow generating poor radial mixing, and tangential flow generating three-dimensional swirling motion. Batch and continuous cultures of the Rhodophyte Porphyridium cruentum were performed in a 100-L, 1.5-m 2 , fully controlled photobioreactor with eight light chambers. The inlet design of these chambers was modified to create the hydrodynamic conditions for comparison. Various intensities of swirling motion were used, characterized by the velocity factor (VF), defined as the ratio between annular chamber flow and inlet aperture sections. Experiments were performed within the range of photon flux densities (PFD) optimizing the yield of light energy transformation into living substance for the species and the temperature used. Culture kinetics with swirling flows generated by apertures of VF = 2, 4, and 9 were compared with pseudoaxial VF = 2 chosen as reference. Batch cultures with VF = 4 swirling flow showed no significant difference, whereas continuous cultures proved more discriminating. Although no significant difference was obtained for VF = 2, a 7% increase of steady-state productivity and a 26% decrease in time required to reach this steady state were obtained with VF = 4 swirling flow. This beneficial effect of swirling flow could have accounted for increased mixing. Conversely, VF = 9 swirling flow resulted in a 9% decrease of steady-state productivity and a 9% increase in the time required to reach this steady state, a negative effect that could have accounted for increased shear stress. CO 2 bioconversion yield at steady state showed a 34% increase for VF = 4. These results suggest that swirling motion makes microalgal cultures more efficient, provided that the resulting adverse effects remain acceptable. Experimental investigation was completed by a theoretical approach in which simulation of continuous cultures of P. cruentum was based on the hydrodynamic conditions achieved in the photobioreactor. Although the results obtained with pseudoaxial flow were correctly predicted, simulations with swirling flow showed a marked enhancement of productivity not observed experimentally. The influence of side effects induced by increased mixing (particularly hydrodynamic shear stress) was considered with respect to modeling assumptions. Comparison of experimental results with theoretical simulation provided a better understanding of the mixing effect, a key factor in improving the efficiency of such bioprocesses.

Centrifugal partition chromatography (CPC) was introduced in 1982 by Sanki Eng. And for almost 20 years this company remained the only one manufacturing such an apparatus. A CPC instrument or a CPC column is a series of channels linked in cascade by ducts and aligned in cartridges or disks in a circle around a rotor; setting the rotor in motion submits this assembly to a constant centrifugal field. The originality of CPC is that it uses any biphasic liquid-liquid system as mobile and stationary phases. The United States branch of Sanki contributed greatly to the worldwide acceptance of the technique. Recent works performed in the Netherlands and in France have, by means of visualization of flow-patterns in CPC channels, contributed to a better knowledge of hydrodynamics and mass transfer phenomena. Nowadays research in our laboratory focuses on speediness and scale-up of the technique.

A new high pressure homogeniser going up to 350 MPa was used to produce fine emulsions stabilised by methylcellulose for food applications. The objective of this study was to evaluate the effect of homogenising pressure on emulsifying and stabilising properties of methylcellulose, a food macromolecule extensively used as stabiliser in emulsions. Oil droplet size distributions of the emulsions were measured by laser-light scattering; rheological properties were characterised with a coaxial cylinder rheometer; and stability was evaluated by heating of the emulsions. Influence of homogenising pressure on interfacial properties (adsorption kinetics, interfacial tension and rheological behaviour) of the polymer was also studied at different pressure treatments. The results showed significant modifications in the structure and the texture of emulsions with increasing homogenising pressure. Homogenised methylcellulose solutions showed weaker thickening and stabilising properties compared to the one of the native methylcellulose.

This works deals with the mechanical treatment realised in a surface scraped heat exchanger (SSHE) and consequence on products. In this type of apparatus, the presence of high shear rates is demonstrated and added to the thermal treatment. An innovative method was developed to measure the quantity of product that is subjected to high shear in the SSHE. This method used a starch suspension, which was sensitive to mechanical treatment. The starch granule diameter increased with the shear rate applied to the suspension. The increase of granule diameter measured by laser granulometry yielded the volume fraction of stressed starch. This method indicated that granules started to swell at a rotational speed of 6.5 rps and that 37% of starch is stressed at 10 rps. These results are explained by the role of the blades and confirm the presence of high wall shear rates. It was shown that starch granules were stressed and that Taylor vortices did not generate sufficient high shear rates in a SSHE to modify the starch granules. The mechanical stress was correlated to the shear rates applied. The starch granules became sensitive to shear treatment at 20,000 s−1 and this value was exceeded in the SSHE by the rotation of blades.

An experimental study of the flow pattern in the wall region of an SMX static mixer was performed by using electrochemical shear rate sensors. Electrochemical signals were related to the local shear stress and the fluctuating rate of the velocity gradient. Signal fluctuation analysis allowed one to define the flow regimes inside the static mixers. The laminar flow was characterized by a time-constant evolution of the velocity gradient, while the turbulent flow corresponded to the stabilization of the fluctuating rate of the velocity gradient for high values of pore Reynolds number, defined by considering the static mixer as a porous medium and by using a capillary model. The transition from a laminar flow to an intermediate flow occurred at a pore Reynolds number of about 200. The turbulent flow was observed at a pore Reynolds number of between 1500 and 3000.

The objective of the work is to create a two-effect product composed by microcapsules containing insecticide suspended in concentrated disinfectant solution. A two-step microencapsulation process has been performed with a first step corresponding to the formation of an oil/water (o/w) dispersion in a static mixer and a second step to the microencapsulation by interfacial polymerisation in a stirred tank reactor. Microcapsules are characterized by a mean diameter of 30 μm in order to ensure their suspension in the disinfectant solution. Microcapsules wall is made of polyurea and release rates monitored by pH-measuring in the disinfectant solution, are found to be very low, allowing a good compatibility of insecticide and disinfectant.

The present work deals with the use of a torus mixer for the formation of liquid-liquid dispersion. The objective is to determine the performance of the torus reactor to form the primary emulsion of the microencapsulation process of an active product by a solvent evaporation technique. The encapsulated product is dissolved in an aqueous phase, which is emulsified into a solution of the polymer in methylene chloride to form a water/oil emulsion. The methylene chloride is gradually removed from the droplets by evaporation. Hard microcapsules are obtained when the solvent is completely removed. The formation of the water/oil primary emulsions is the key step to control the size distribution of the microcapsules.The characteristics of the dispersed phase of the water-in-oil emulsion produced in a torus mixer in batch and continuous conditions is determined by an optical method based on the use of the microscope connected to a CCD camera. The flow inside the torus mixer is directly linked to the rotation speed of the impeller. The effect of the rotation speed of the impeller and the dispersed phase volume fraction of the liquid-liquid dispersion is analyzed. The experimental data are expressed by a correlation giving the mean droplet diameter in function of the Weber number and dispersed phase concentration. The influence of the superimposed throughput, for the continuous process, on the size distribution of the dispersed phase is also taken into account.

An ultra high-pressure homogenizer (20 to 350 MPa) was used to realize fine food emulsions stabilized by soy proteins. The first aim of the work was to understand how dynamic high-pressure processing affects soybean globulin conformation. Then, the effect of homogenizing pressure on the emulsions structure and rheology was investigated. High-pressure homogenization caused denaturation of proteins due to strong mechanical forces and high temperatures encountered in the valve. Droplet sizes of emulsions were greatly reduced with high-pressure homogenization and Newtonian liquid emulsions were converted into shear-thinning emulsion gels by homogenization at pressures above 250 MPa. Hydrophobic interactions between proteins were supposed to cause the gel-like network structure of emulsions.

Centrifugal partition chromatography (CPC) is a support-free liquid-liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane-methanol two-phase system, three main flow regimes - stuck film, oscillating sheet, and atomization - are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Peclet number, partition ratio, and mass-transfer coefficient) are fitted on solute residence-time distribution. Off-column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed.

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.

Initially developed for the dairy industry, the very high pressure homogenisation (>100 MPa) is now also applied in the pharmaceutical sector and in biotechnology (breaking cells for biomass extraction). The use of this technology to make fine food emulsions and to modify functional properties of macromolecules seems to be promising. Thus the objective of this study was to understand the effect of homogenisation forces on the mechanical degradation of a model polymer extensively used in food, cosmetic and pharmaceutical preparations: the methylcellulose. Degradation of the polymer was studied in a pressure range in the homogenising valve from 20 to 350 MPa. It was observed that as the pressure imposed by the homogeniser increased, the intrinsic viscosity decreased. Intrinsic viscosity decrease was correlated to apparent changes in the average molecular weight of the polymers obtained by size exclusion chromatography coupled on-line with multi-angle laser light scattering and refractive index detection (SEC/MALLS/RI). The strong elongational flow encountered by the polymer at the entrance of the valve of the high pressure homogeniser device may bring sufficient energy to disrupt covalent bonds. Consequently, as shown by flow behaviour the thickening properties of this polymer were also reduced.

An experimental investigation was done by the use of visual observations and the electrochemical technique in order to study the appearance of hydrodynamic instabilities at low Re axg in the gap between two coaxial cylinders, with radius ratio R r / R s =0.615 and aspect ratio L / e =24. A motor drove the inner cylinder and the outer cylinder was fixed. A Newtonian fluid (Emkarox HV45) and two non-Newtonian fluids (aqueous solutions of guar and CMC) have been used. The analysis of the evolution of the size of the Taylor vortices is carried out for Re axg Re axg Ta g ≈80, and a stretching phase for Ta g >80. For higher Re axg , the contraction phase vanished and the vortices progressively stretched with increasing Ta g . A dimensionless representation was also proposed for wall friction generalized to non-Newtonian fluids following the Ostwald law.

The objective of this work is the study of the pyrolysis process of date palm biomass main constituents related to the Ghars (GH) and Deglet Nour (DN) cultivars, i.e., petiole (KER), palm (DJ), rachis (AD), spathe (KH), fibrilium (LIF), fruit bunch (ARJ), and his peduncle (SA). The pyrolysis behaviour of this lignocellulosic biomass and the determination of the kinetic constants were performed by Thermogravimetric analysis (TGA). The statistical approach used for the examination of TGA data is the Analysis of Variance and the Principal Component Analysis applied to thermal, kinetics, and chemical parameters. The results show that phoenicicole biomass appears much more interesting in comparison with the conventional solids biocombustibles. Indeed, the activation energy is estimated at the average of 24.27 kJ/mol for all studied biomass. Moreover, two types of phoenicicole residue are characterized by their thermal behaviour: initially, Lif characterized by a low calorific value and thermal stability due to...

Absolute concentrations of total macromolecules (triglycerides, proteins and carbohydrates) in microorganisms can be rapidly measured by FTIR spectroscopy, but caution is needed to avoid non-specific experimental bias. Here, we assess the limits within which this approach can be used on model solutions of macromolecules of interest. We used the Bruker HTSXT-FTIR system. Our results show that the solid deposits obtained after the sampling procedure present physical and chemical properties that influence the quality of the absolute concentration prediction models (univariate and multivariate). The accuracy of the models was degraded by a factor of 2 or 3 outside the recommended concentration interval of 0.5-35 µg spot(-1). Change occurred notably in the sample hydrogen bond network, which could, however, be controlled using an internal probe (pseudohalide anion). We also demonstrate that for aqueous solutions, accurate prediction of total carbohydrate quantities (in glucose equivalent) could not be made unless a constant amount of protein was added to the model solution (BSA). The results of the prediction model for more complex solutions, here with two components: glucose and BSA, were very encouraging, suggesting that this FTIR approach could be used as a rapid quantification method for mixtures of molecules of interest, provided the limits of use of the HTSXT-FTIR method are precisely known and respected. This last finding opens the way to direct quantification of total molecules of interest in more complex matrices.

The investigation of wakes of bluff bodies in a channel is still relevant despite the large number of works devoted on it, in both experimental and numerical studies. This attractiveness is mainly due to its related applications and practical interest in varied engineering fields. The understanding of dynamic flow behavior and the topology of the instability structures occurring in the wake is essential in order to optimize the obstacle shape according to the desired objectives. A confined laminar flow around a square and a circle, placed in a channel is numerically investigated in this work using Lattice Boltzmann method. The study is then extended to 3D computations with horizontal cylinder within a square then a circular cross-section mounted inside a rectangular duct. The Reynolds number (Re), based on the maximum velocity and the cross-section height varies between 50 and 120 and the blockage ratio is r=1/3. This geometry is representative of a passive method to enhance mixing in the laminar channel flow. LBM was built up on the D2Q9 and D3Q19 model for respectively 2D and 3D computations. The single relaxation time approach called the lattice-BGK method was adopted. The topology of the vortex-shedding phenomena and wake behavior according the Reynolds numbers, for both geometries of the obstacle are focused. The effect of wall confinement on the flow transition to the vortex shedding regime is discussed. Velocity profiles and integral parameters such as recirculation length and Strouhal number were investigated. The numerical results are supported by literatures works results for the same configuration showing the performance of LBM as numerical tools simulation for such kind of flows.

International audience; In the simplest and original case of study of the Taylor Couette TC problems, the fluid is contained between a fixed outer cylinder and a concentric inner cylinder which rotates at constant angular velocity. Much of the works done has been concerned on steady rotating cylinder(s) i.e. rotating cylinders with constant velocity and the various transitions that take place as the cylinder(s) velocity (ies) is (are) steadily increased. On this work, we concentrated our attention in the case in which the inner cylinder velocity is not constant, but oscillates harmonically (in time) clockwise and counter-clockwise while the outer cylinder is maintained fixed. Our aim is to attempt to answer the question if the modulation makes the flow more or less stable with respect to the vortices apparition than in the steady case. If the modulation amplitude is large enough to destabilise the circular Couette flow, two classes of axisymmetric Taylor vortex flow are possible: reversing Taylor Vortex Flow (RTVF) and Non-Reversing Taylor Vortex Flow (NRTVF) (Youd et al., 2003; Lopez and Marques, 2002). Our work presents an experimental investigation of the effect of oscillatory Couefte-Taylor flow, i.e. both the oscillation frequency and amplitude on the apparition of RTVF and NRTVF by analysing the instantaneous and local mass transfer and wall shear rates evolutions, i.e. the impact of vortices at wall. The vortices may manifest themselves by the presence of time-oscillations of mass transfer and wall shear rates, this generally corresponds to an instability apparition even for steady rotating cylinder. On laminar CT flow, the time-evolution of wall shear rate is linear. It may be presented as a linear function of the angular velocity, i.e. the evolution is steady even if the angular velocity is not steady. At a ``critical'' frequency and amplitude, the laminar CT flow is disturbed and Taylor vortices appear. Comparing to a steady velocity case, oscillatory flow accelerate the instability apparition, i.e. the critical Taylor number corresponds to the transition is smaller than that of the steady case. For high oscillation amplitudes of the inner cylinder rotation, the mass transfer time-evolution has a sinusoidal evolution with non equal oscillation amplitudes. If the oscillation amplitude is large enough, it can destabilize the laminar Couefte flow, Taylor vortices appears. The vortices direction can be deduced from the sign of the instantaneous wall shear rate time evolution.

This study aims to understand the role of light transfer in triglyceride fatty-acid (TG-FA) cell content and productivity from microalgae during nitrogen starvation. Large amounts of TG-FA can be produced via nitrogen starvation of microalgae in photobioreactors exposed to intense light. First, spectral absorption and scattering cross-sections of N. oculata were measured at different times during nitrogen starvation. They were used to relate the mean volumetric rate of energy absorption (MVREA) per unit mass of microalgae to the TG-FA productivity and cell content. TG-FA productivity correlated with the MVREA and reached a maximum for MVREA of 13 μmol hν/gs. This indicated that TG-FA synthesis was limited by the photon absorption rate in the PBR. A minimum MVREA of 13 μmol hν/gs was also necessary at the onset of nitrogen starvation to trigger large accumulation of TG-FA in cells. These results will be instrumental in defining protocols for TG-FA production in scaled-up photobioreactors.

A dynamic model for the photoautotrophic growth of microalgae in photobioreactor that describes the main variables of the system and allows the precise prediction of the pH in the culture was proposed and validated. The dynamic behavior of the biological system was expressed through a multistate model in continuous-time formulation, based on mass-balance equations and local photosynthetic responses of the anisotropic medium, further associated with a set of algebraic equations that describes the thermodynamic properties of the ammonia—carbon dioxide—water ternary solute system. The global photoautotrophic growth model was validated on experimental data acquired from a torus reactor inoculated with Chlamydomonas reinhardtii cells. The model response was studied in simulation for all identified input variables (dilution rate, incident light intensity, temperature, and flow rates of input gases). © 2013 American Institute of Chemical Engineers AIChE J 60: 585–599, 2014

Velocity and concentration fields interaction has been experimentally investigated by mixing pure and salty water in a continuous stirred tank reactor. This has been achieved by coupling LDV and conductivity system which led to velocity–concentration correlations and to turbulent diffusivity. The axial velocity–concentration correlation coefficient does not exceed 5% in the turbine plan and below it. The knowledge of both concentration gradient and turbulent flux allowed the determination of turbulent diffusivity. The assumption of turbulence isotropy is discussed. Except in the immediate proximity of the stirrer, the probability density function of either velocities and concentration does not deviate significantly from Gaussian distribution indicating, in agreement with literature, local isotropy conditions particularly in the upper part of the tank with respect to the stirrer. The obtained results will contribute to refined mixing models while improving scale up procedures.

The electrodiffusion technique has been used to investigate reattaching and recirculating flows behind a backward-facing step. The instantaneous wall shear rate vectors were determined using the current signals provided by a three-segment electrodiffusion probe. The near-wall extents of two counter-rotating recirculation zones located behind the step were determined under turbulent flow conditions in a water channel. The near-wall flow inside these recirculation zones was found to be very unsteady, with strong low-frequency fluctuations. The streamwise profiles of the wall shear stress were measured at several values of the Reynolds number and a high level of skin friction was obtained in the reverse-flow region. The strong dependence of the peak value of skin friction on the Reynolds number confirms the viscous-dominated character of the reverse flow appearing inside the recirculation zone.

Break-up processes have been investigated in an SMX-Sulzer static mixer. Oil/water and water/oil dispersions have been studied over a range of Reynolds, Weber and viscosity numbers. A semiempirical model has been developed for the prediction of mean drop size by equating the disruptive force acting upon the drop to the cohesive forces due to surface and viscous resistance to breakage. To establish the model, the liquid–liquid dispersions are assumed to be pseudo-fluids and the energy dissipation rate is calculated from pressure drop measurements expressed through a capillary model. Experimental data are correlated with Reynolds and Weber numbers and are analysed in order to show the influence of surface and viscous resistance on the breakage process.

On a etudie la formation d'emulsions huile dans l'eau capables de retenir et proteger la fraction grasse dans une matrice extrudee. Les mesures de conductibilite electrique, qui ont ete faites sur des melanges de farines de ble et de riz pregelatinisees, farine d'amande, eau et differents additifs (lecithine de soja, farine de guar et gomme arabique), ont montre que la lecithine est plus efficace que les autres additifs pour favoriser la formation d'une emulsion huile dans l'eau. Des experiences d'extrusion ont ete faites avec les melanges a base de farines de ble et de riz pregelatinisees, de poudre d'amande torrefiee et de lecithine de soja. Les produits obtenus (en forme de grain et de flocon) ont ete caracterises au moyen d'analyses physicochimiques, rheologiques et sensorielles. Les resultats obtenus, relatifs a l'extraction d'huile pendant le procede d'extrusion, ont montre que la farine de ble peut etre consideree comme la farine de base la plus adaptee a la fabrication des snacks d'amande. Ces produits, en outre, ont ete juges les meilleurs par les tests sensoriels. Toutefois, les produits a base de farine de riz presentent les taux d'expansion les plus eleves.

This work is devoted to the numerical modeling of mass transfer on both cylinders of an annular cell subjected to swirling laminar decaying flow induced by means of a single tangential inlet greater in diameter, φ e =12.5 mm , than the annular gap thickness, e=7 mm . The complete diffusion–convection equation has been solved in a three-dimensional frame by means of the FIDAP finite element package using the velocity fields previously predicted by the same numerical technique. As for the flow-field, we have shown that a correct prediction of mass transfer coefficients in such a flow is strongly linked to an adequate mesh generation, especially when mass transfer occurs on the inner wall of the annulus, near which recirculating eddies exist. Numerical results have been found to be in good agreement with experimental data previously obtained on both cylinders of the annulus. A simulation study of the influence of the Schmidt number on the overall mass transfer on the outer cylinder has shown that the mean Sherwood number varies as Sc 0.44 . Even for forced convection, the numerical simulation of mass transfer is not directly obtained from the simulation of the dynamics of the flow. Due to the difference in mass and momentum boundary layer thicknesses, the mesh refinement has to be adapted to Schmidt number.

Previous works devoted to the development of the swirl flow generated by rotation of the marine screw impeller in the loop toroidal reactor show that the flow structure is characterized by the existence of a secondary flow. The deformation of the axial velocity profile, due to the bends curvature and the rotation of the agitator, modify considerably the friction and the transfer near the wall. The objective of this work is to study the toroidal flow and to characterize the wall turbulence. The wall shear stress distribution in the torus were performed by using an electrochemical method. The measurements of the wall shear stress were carried out in the inner and outer walls. The evolution of the wall velocity gradient with the longitudinal distance depends on the location in the torus. These results allow to obtain information about the friction factor, which is compared with the one measured directly by using piezometric connections. The experimental determination of the axial dispersion coefficient is ob...

Mixing in an axisymmetric concentrated KCl solution jet emerging in a less salty coflowing water has been experimentally investigated. This has been achieved by coupling laser Doppler velocimetry to a microconductimetry technique in view of measuring the turbulent fluxes cu and cv and deducing the turbulent diffusivity. The cross-correlation coefficient between radial velocity and concentration R cv reaches a maximum value of 0.77 when the one relative to axial velocity R cu gets smaller and does not exceed 0.37 under the same conditions. The total turbulence intensity, global microscale, kinetic energy dissipation rate, and turbulent diffusion coefficient in the radial direction have also been determined. In a jet section, the turbulent diffusion coefficient was found to vary from 180 to 2000 times the KCl molecular diffusivity D m .

The influence of different fluid inlet types, slits or tubes, on mass transfer in a rectangular reactor was studied. Measurements of mass transfer coefficients were made using the limiting diffusion current technique based on ferricyanide ion reduction at a large nickel electrode located downstream of abrupt expansions. The overall mass transfer coefficients obtained were 3 to 13 times greater than those obtained in fully developed flows. Overall mass transfer coefficients were correlated for Reynolds numbers ranging from 400 to 3500 by a unique equation by introducing a nondimensional expansion factor defined by the ratio of the fluid inlet cross-section to that of the reactor. The correlation equation obtained was compared with literature data.

International audience; Particle image velocimetry (PIV) has been used in order to measure the three mean components and turbulence intensities of the velocity vector in a swirling decaying flow induced by a tangential inlet in an annulus. This kind of flow motion is found to be very complex, exhibiting three-dimensional and non-axisymmetric characteristics coupled with a free decay of the swirling intensity along the flow path, thereby making it difficult to study. A method allowing the measurement of the three components of the velocity flow-field with a standard PIV system with two-dimensional acquisitions, is presented. The evolution of each velocity component between the inlet and the outlet of the annulus is obtained. Furthermore, the PIV technique is extended to the measurement of turbulent characteristics such as turbulent intensities and dimensionless turbulent energy. The main characteristics of the swirling flow are discussed and the swirl number is estimated as a function of the axial distance from the tangential inlet.

An experimental investigation of a scraped surface heat exchanger (SSHE) was undertaken using visual observations and the electrochemical technique in order to, firstly, study the transition between laminar and vortex flows and, secondly, evaluate the wall shear rates. Visual observations and the electrochemical technique had undergone preliminary testing in a SSHE without blades, a well-known reference annulus. Then, visual observations and wall shear rates was compared in both geometries. It was established that flow patterns in a SSHE are noticeably different from those observed in an annular space in the same conditions. In a SSHE, the formation of the vortices is thwarted by the rotation of the blades (and by the clips of the blades) and the transition between laminar and vortex flows occurs at Ta gc ≈80 ( Ta gc ≈45 in the annular space without blades). Local measurements of the shear rate at the tube wall of the SSHE showed that it is fully controlled by the rotation of the blades. Vortices have a negligible influence in comparison with that of blade scrapings. Wall shear rates due to blade scraping can reach up to 40 000 s −1 . Under these conditions, the lowest value of the clearance between the edge of the blades and the stator is about 50 × 10 −6 m.

This work is dedicated to an experimental study of the wall shear stress in a turbulent swirling decaying flow induced by means of a tangential inlet in an annular cell. The flow pattern near both cylinders of the annulus is analyzed by means of measurements of wall velocity gradients using an electrochemical method involving micro-electrodes working in inert wall. The analysis of the axial and circumferential evolutions of the mean wall velocity gradient and of its power spectral density emphasizes the complexity and highly three-dimensional nature of the flow pattern of the annular swirling decaying flow induced by means of a single tangential inlet. Near the inner wall of the annulus, a recirculating zone, consisting of several pairs of contra-rotating cells, develops following the main helical motion of the fluid along the flow path. Near the external wall of the annular cell, high local velocities and energetic turbulent structures are detected in the vicinity of the tangential inlet. These eddies rapidly decay along the flow path because of the decrease of the swirl intensity. The setup of a recirculation bubble near the inner wall induces a quasi-axisymmetric flow behavior at the outer cylinder of the annulus. Near both walls, the power spectral densities of the velocity gradient reveal a superposition of small turbulent eddies having a low energetic level in the high-frequency domain.