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See detailCFD-based Compartment model for description of mixing in bioreactors
Delafosse, Angélique ULg; Calvo, Sébastien ULg; Collignon, Marie-Laure ULg et al

in Chemical Engineering Science (2014), 106

In most bioprocesses, it is fundamental to accurately predict the hydrodynamics behavior of bioreactors of different size and its interaction with the biological reaction. Computational Fluid Dynamics can ... [more ▼]

In most bioprocesses, it is fundamental to accurately predict the hydrodynamics behavior of bioreactors of different size and its interaction with the biological reaction. Computational Fluid Dynamics can provide detailed modeling about hydrodynamics and mixing. However, it is computationally intensive, especially when reactions are taken into account. Another way to predict hydrodynamics is the use of “Compartment” or “Network-of-zones” model which are much less demanding in computation time than CFD. However, compartments and fluxes between them are often defined by considering global quantities not representative of the flow complexity. To overcome the limitations of these two methods, a solution is to combine compartment modeling and CFD simulations. The aim of this study is to propose a compartment model where the flow rates between two adjacent compartments are easily computed from the velocity fields obtained by CFD. The mixing evolution predicted by the CFD-based compartment model have been then compared with mixing experiment results. Unlike a CFD mixing simulation and a classical compartment model, the CFD-based compartment model proposed in this work reproduces with a good accuracy the spatial distribution of concentrations during the mixing process and this, without any adjustable parameters. [less ▲]

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See detailInvestigation of liquid flow morphology inside a structured packing using X-ray tomography
Janzen, Anna; Steube, Julia; Aferka, Saïd et al

in Chemical Engineering Science (2013), 12

In this work X-ray tomography is used to analyse the influence of liquid viscosity on liquid flow in a column filled with Mellapak Plus 752Y structured packing. Tomographic measurements are performed at ... [more ▼]

In this work X-ray tomography is used to analyse the influence of liquid viscosity on liquid flow in a column filled with Mellapak Plus 752Y structured packing. Tomographic measurements are performed at various column heights for different liquid flow rates. Water and glycerine aqueous solutions are successively used as working liquids in order to quantify the influence of liquid viscosity on hydrodynamic quantities such as liquid hold-up and gas-liquid interfacial area. As expected, both liquid hold-up and gas-liquid interfacial area increase with liquid flow rate. An increase of liquid viscosity has also a positive impact on liquid hold-up and on gas-liquid interfacial area. In all cases, the measured quantities are not constant along the bed height, leading to fluctuating axial profiles. Furthermore, tomographic images are used to identify different liquid flow patterns (films, contact-point liquid, flooded regions) in the irrigated cross section images. A method based on morphological techniques is proposed to quantify the fraction of liquid flow within each flow pattern depending on flow rate and liquid viscosity. [less ▲]

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See detailGas Flow Simulations in a Structured Packing by Lattice Boltzmann Method
Beugre, Djomice; Calvo, Sébastien ULg; Crine, Michel ULg et al

in Chemical Engineering Science (2011), 66

Numerical simulations of gas flow between two sheets of plastic MellapakTM 250 Y are performed using Lattice Boltzmann methods in laminar and turbulent regimes. Results are compared with experimental ... [more ▼]

Numerical simulations of gas flow between two sheets of plastic MellapakTM 250 Y are performed using Lattice Boltzmann methods in laminar and turbulent regimes. Results are compared with experimental measurements and with known correlations. They are also compared with simulations using a classical CFD code. In all cases, the agreement is very good. [less ▲]

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See detailReply to "Comments on Collignon et al. (Chem. Eng. Sci. 65 (2010) 5929-5941)"
Collignon, Marie-Laure ULg; Delafosse, Angélique ULg; Crine, Michel ULg et al

in Chemical Engineering Science (2011), 6

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See detailTomographic measurement of liquid hold up and effective interfacial area distributions in a column packed with high performance structured packings
Aferka, Saïd ULg; Viva, Aurora; Brunazzi, Elisabetta et al

in Chemical Engineering Science (2011), 66

In this paper, we report on the use of a high energy and high resolution X-ray tomograph to visualize and quantify the distribution of liquid hold up and of gas-liquid interfacial area in a 0.1m diameter ... [more ▼]

In this paper, we report on the use of a high energy and high resolution X-ray tomograph to visualize and quantify the distribution of liquid hold up and of gas-liquid interfacial area in a 0.1m diameter column filled with MellapakPlus 752.Y packing elements. A standard air-water system at room temperature and atmospheric pressure was used. Tomographic measurements have been carried out in a large number of packing cross sections situated at different heights between the top and the bottom of the packed column, giving access to the evolution of axial profiles of liquid hold up and of gas-liquid interfacial area as a function of the operating conditions. Gas-liquid interfacial area values were also measured by a chemical method (CO2 absorption from air into a caustic solution). For the first time, a whole set of gas-liquid interfacial area values evaluated from tomographic images are interestingly compared with values measured by a chemical method. A comparison is also presented with literature models. [less ▲]

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See detailEstimation of the turbulent kinetic energy dissipation in a culture cell stirred tank bioreactor
Delafosse, Angélique ULg; Collignon, Marie-Laure ULg; Dossin, Denis et al

in Chemical Engineering Science (2011), 66(8), 1728-1737

The turbulent dissipation rate is a key parameter in stirred tanks and its local values may have a strong influence on the performance of many processes. However, the local dissipation rate estimation is ... [more ▼]

The turbulent dissipation rate is a key parameter in stirred tanks and its local values may have a strong influence on the performance of many processes. However, the local dissipation rate estimation is far from easy in a stirred tank, especially near the impeller discharge where maximum values are encountered. The aim of this work is to estimate the dissipation rate in a vessel used for animal-cell cultures and stirred with a down-pumping axial impeller (Mixel TTP) from velocity fields measured by 2D-PIV. Special attention is paid to the assumptions necessary to estimate the dissipation rate from 2D measurements and to the influence of measurement spatial resolution on the estimated values. The analysis of isotropy ratios measured on vertical, horizontal and tangential planes shows that the turbulence in the impeller discharge is far from isotropic. Isotropy assumptions classically used to estimate the dissipation rate from 2D measurements may thus lead to erroneous values. Based on the measured isotropy ratios, a new relationship is proposed to estimate the dissipation rate in the impeller discharge. This relationship is then used to estimate the dissipation rate on a vertical plane located in the impeller discharge zone. In order to analyze the influence of the measurement spatial resolution on the estimated values of the dissipation, a total of 12 spatial resolutions are tested. Results show that if the spatial resolution is divided by a factor 2, the dissipation rate increases by 220%. For the smallest spatial resolution value used, the maximum dissipation rate estimated is 50 times higher than the mean overall dissipation rate and the corresponding minimum value of the Kolmogorov scale is nearly 3 times smaller than the Kolmogorov scale computed from the mean overall dissipation rate. [less ▲]

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See detailAXIAL IMPELLER SELECTION FOR ANCHORAGE DEPENDENT ANIMAL CELL CULTURE IN STIRRED BIOREACTORS: METHODOLOGY BASED ON THE IMPELLER COMPARISON AT JUST-SUSPENDED SPEED OF ROTATION
Collignon, Marie-Laure ULg; Delafosse, Angélique ULg; Crine, Michel ULg et al

in Chemical Engineering Science (2010), 65(22), 5929-5941

Animal cells, which are nowadays essential for the industrial production of proteinic compounds, are commonly cultivated inside stirred tank bioreactors. In case of anchorage dependent cells, they are ... [more ▼]

Animal cells, which are nowadays essential for the industrial production of proteinic compounds, are commonly cultivated inside stirred tank bioreactors. In case of anchorage dependent cells, they are usually fixed on microcarriers. The choice of agitation conditions (impeller type, rotational speed…) in this type of process is not an easy task as it has to fulfil three potentially conflicting goals: (1) maintaining microcarriers in complete suspension, (2) homogenizing the culture medium, and (3) limiting mechanical constraints generated by the hydrodynamics on the cells. The aim of this study is to present an original methodology to select the most appropriate axial impeller for this specific application. Seven propellers are preselected on basis of their characteristics available in the literature. Instead of comparing impellers at a given rotational speed or a given power input, they are compared at their respective minimum impeller rotational speed that leads to a complete microcarrier suspension, i.e. at their respective just-suspended speed Njs. They are then compared at higher rotational speeds N, expressed as multiples of Njs. The impeller classification is based on the intensity of mechanical constraints they produced, evaluated from: (1) the macro-shear rate quantified by the spatial derivative of time average velocity fields measured by P.I.V, (2) the micro-shear rate characterized by the ratio between the microcarrier diameter to the average Kolmogorov scale computed from power input measurements, and (3) the impact of microcarrier collisions on cells described via the Turbulent Collision Severity index also computed from power input measurements. Results show that the 125 mm diameter TTP impeller (Mixel) and the 150 mm diameter Elephant Ear impeller (Applikon) produce the smallest mechanical constraints at their just-suspended speed (50 rpm and 20 rpm, respectively). Moreover, the mechanical constraints they produce increase more slowly with the N/Njs ratio than the mechanical constraints produced by other impellers. These propellers are thus even more advantageous if rotational speeds higher than the just-suspended speed have to be used. [less ▲]

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See detailInterfacial area measurement in a catalytic distillation packing using high energy x-ray CT
Aferka, Saïd ULg; Marchot, Pierre ULg; Crine, Michel ULg et al

in Chemical Engineering Science (2010), 65(1), 511-516

In this paper, we report on the use of X-ray tomography to visualize and quantify the gas–liquid interfacial area in modular catalytic distillation packing elements. The calculation method is based on ... [more ▼]

In this paper, we report on the use of X-ray tomography to visualize and quantify the gas–liquid interfacial area in modular catalytic distillation packing elements. The calculation method is based on processing of tomographic images. It is validated by comparing specific surface area determined on dry packings (Mellapak™ 752Y and Katapak™ SP12) tomographic binary images (gas and solid) to values announced by manufacturers, based on geometrical considerations. These data agree fairly well. However, tomographic images show that the specific area is not distributed uniformly over the height of a packing element due to the presence of perforations in corrugated sheets and of wall wipers between the packing and the column wall. X-ray tomography is a unique technique to access to the spatial distribution of these geometrical details in a non-intrusive way. The method used to determine the specific surface area of dry packing is then applied to irrigated packing in order to determine the gas–liquid interfacial area. The axial distribution of the interfacial area is non-uniform and is correlated to the packing specific area. The maxima of the specific surface area correspond to the presence of wall wipers. The gas–liquid interfacial area averaged over the column length is determined. It increases logically with the liquid superficial velocity and slightly with the gas velocity. The effect of the gas velocity is however more pronounced when reaching loading point. [less ▲]

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See detailLaminar flow in radial flow cell with small aspect ratios: Numerical and experimental study
Detry, Jean; Deroanne, Claude ULg; Sindic, Marianne ULg et al

in Chemical Engineering Science (2009), 64(1), 31-42

Studies on the effect of wall shear stress on soil and biofilm attachment and removal from a surface are one of the many applications of radial axisymmetrical flow. The particular nature of this flow ... [more ▼]

Studies on the effect of wall shear stress on soil and biofilm attachment and removal from a surface are one of the many applications of radial axisymmetrical flow. The particular nature of this flow allows taking advantage of a wide range of wall shear Stress applied at the analyzed surface in a single experiment. This type of experiments provides a critical radius up to which soil removal occurs. Good models are, however, still needed to convert the experimental data into critical wall shear stress. Analytical models are already available for creeping flow but Computational Fluid Dynamics must be applied for experiments performed at higher Reynolds numbers. The present study is a numerical analysis of the radial axisymmetrical flow for aspect ratios of 0.125, 0.25, 0.5 and 1 with inlet pipe Reynolds numbers varying from 0 to 2000, aiming at computing the wall shear stress distribution at any distance from the center. The simulations provided a thorough description of the complex flow pattern encountered close to the inlet section, which were validated for the laminar regime by dye injection. A total of up to four recirculation zones were identified in both numerical and experimental investigations. The experimental positions of these recirculation zones corresponded well to the numerical predictions. Based on this work, a map of the flow for the different aspect ratios was developed, which can be particularly interesting for the design of experimental devices involving axisymmetrical flow. (c) 2008 Elsevier Ltd. All rights reserved. [less ▲]

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See detailIn situ measurements of the static liquid holdup in Katapak-SP12 (TM) packed column using X-ray tomography
Aferka, Saïd ULg; Crine, Michel ULg; Saroha, A. K. et al

in Chemical Engineering Science (2007), 62(21), 6076-6080

Static liquid holdup was determined in situ, in a column packed with Katapak-SP12 (TM) elements, using a non-intrusive X-ray tomographic technique. Experiments were performed in a 10 cm diameter PVC ... [more ▼]

Static liquid holdup was determined in situ, in a column packed with Katapak-SP12 (TM) elements, using a non-intrusive X-ray tomographic technique. Experiments were performed in a 10 cm diameter PVC column with the air-water system. The technique allows a local determination of the various liquid holdup as well as of the capillary height, without dismantling the elements. Results are in good agreement with correlations proposed in the literature. (C) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAnalysis of gas holdup in bubble columns with non-Newtonian fluid using electrical resistance tomography and dynamic gas disengagement technique
Fransolet, E.; Crine, A.; Marchot, Pierre ULg et al

in Chemical Engineering Science (2005), 60(22 Sp. Iss. SI), 6118-6123

This paper presents an experimental analysis of the influence of the liquid rheology on the gas flow pattern in a bubble column reactor. Aqueous solutions of xanthan are selected as an example of non ... [more ▼]

This paper presents an experimental analysis of the influence of the liquid rheology on the gas flow pattern in a bubble column reactor. Aqueous solutions of xanthan are selected as an example of non-Newtonian shear thinning fluid. Averaged gas holdup is determined by two experimental techniques: parietal pressure probes and electrical resistance tomography (ERT). ERT is also used to provide 2D images of the gas phase distribution in a column cross-section. Bubble size distributions are evaluated by a gas disengagement technique using the parietal pressure probes. All these techniques clearly show the gas flow pattern is different in Newtonian and non-Newtonian fluids. Gas holdup values decrease when increasing the liquid viscosity and reach a minimum or a plateau. Homogeneous flow regime, observed in water at low gas velocities, tends to disappear when viscosity increases. This evolution is visualized by a much less isotropic distribution of the gas phase within cross-section of the column and by the appearance of much larger bubbles due to an increased coalescence phenomenon. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailGas-liquid mass transfer in a circulating jet-loop nitrifying MBR
Kouakou, Edouard; Salmon, Thierry ULg; Toye, Dominique ULg et al

in Chemical Engineering Science (2005), 60(22 Sp. Iss. SI), 6346-6353

Based on airlift configuration, a novel circulating jet-loop submerged membrane bioreactor (JLMBR) adapted to ammonium partial oxidation has been developed. Membrane technology and combined air and water ... [more ▼]

Based on airlift configuration, a novel circulating jet-loop submerged membrane bioreactor (JLMBR) adapted to ammonium partial oxidation has been developed. Membrane technology and combined air and water forced circulation are adopted to obtain a high biomass retention time and to achieve a separate control of mixing and aeration. This study is intended to determine how gas-liquid mass transfer is affected by operating conditions. In a first approximation, liquid was assumed to be perfectly mixed. A classical non-steady state clean water test, known as the "gas out-gas in" method, was used to determine the gas-liquid mass transfer coefficient k(L)a. Air and recirculated liquid superficial velocities were gradually increased from 0.013 to 0.019m s(-1) and 0.0056 to 0.011 m s(-1), respectively. Subsequently, the gas-liquid mass transfer coefficient kLa varied from 0.01 to 0.02 s(-1). It appears to be influenced by the combined action of air and recirculated liquid flowrates in the range 0.72-1.03N m(3) h(-1) and 0.30-0.58 m(3) h(-1), respectively, for air and liquid. Correlations are proposed to describe this double influence. Experiments were performed on tap water and a culture medium used for the autotrophic growth of nitrifying bacteria, respectively. Oxygen transfer appeared to be not significantly affected by the mineral salt (0.48 g 1(-1)) encountered in this medium. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailThe use of large scale computer assisted tomography for the study of hydrodynamics in trickling filters
Toye, Dominique ULg; Marchot, Pierre ULg; Crine, Michel ULg et al

in Chemical Engineering Science (1994), 49(24B), 5271-5280

In this paper, a new experimental technique is proposed, based on X-ray tomography, allowing the analysis of the gas-liquid-solid phase distribution in trickling filters. Tomography refers to the cross ... [more ▼]

In this paper, a new experimental technique is proposed, based on X-ray tomography, allowing the analysis of the gas-liquid-solid phase distribution in trickling filters. Tomography refers to the cross-sectional imaging of an object from data collected by illuminating this object from many directions. The experimental set-up allows the scanning of transverse sections of rather large filters: up to 0.8 m diameter and 2 m height can be irradiated. Experiments were carried out both without and with liquid flow. In the absence of liquid, the reconstructed images give a view of the non-uniformity of the solid phase distribution. The images obtained are very complex because they result from the superposition of several distributions with different spatial scales. The existence of a first spatial scale is shown which allows separation of the properties belonging to the individual packing elements from those belonging to the bed scale. When liquid is flowing through the packed bed, the distribution of the liquid hold-up is clearly evidenced, despite the very low liquid film thickness. [less ▲]

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See detailMacromixing versus hydrodynamics in trickle-flow columns
Crine, Michel ULg; Marchot, Pierre ULg; Lekhlif, B. et al

in Chemical Engineering Science (1992), 47

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