Comparison of systemic, compartmental and CFD modelling approaches: Application to the simulation of a biological reactor of wastewater treatment

Nowadays there exist two main approaches to simulate the hydrodynamics of chemical reactors: the systemic method, based on the description of a given reactor as a limited number of elementary reactors, and the more theoretical CFD approach, based on the resolution of the Navier-Stokes equations in a large number of computing cells. This work describes another recent modelling approach based on the description of the reactor as a network of both structural and functional compartments. The complete methodology to build such a model, using CFD simulations, tracer experiments, mass transfer and chemical processes, is described. The simulation results with such a model are then compared to those obtained with the systemic and CFD models in the case of a biological gas-liquid reactor for wastewater treatment, involving oxygen transfer and complex biological kinetics. This work shows that the compartmental model gives results very similar to those of a full CFD simulation but with lower calculation time (10 times in most cases) with the advantage of remaining almost as simple to manipulate as the systemic approach

The Success of Flow Diversion in Large and Giant Sidewall Aneurysms May Depend on the Size of the Defect in the Parent Artery

ABSTRACT BACKGROUND AND PURPOSE: Flow diverters are designed to occlude aneurysms while preserving flow to jailed arterial branches. We postulated that treatment success depended on the size of the aneurysm ostium or defect in the parent artery

In vivo biomolecular imaging of zebrafish embryos using confocal Raman spectroscopy

Zebrafish embryos provide a unique opportunity to visualize complex biological processes, yet conventional imaging modalities are unable to access intricate biomolecular information without compromising the integrity of the embryos. Here, we report the use of confocal Raman spectroscopic imaging for the visualization and multivariate analysis of biomolecular information extracted from unlabeled zebrafish embryos. We outline broad applications of this method in: (i) visualizing the biomolecular distribution of whole embryos in three dimensions, (ii) resolving anatomical features at subcellular spatial resolution, (iii) biomolecular profiling and discrimination of wild type and ΔRD1 mutant Mycobacterium marinum strains in a zebrafish embryo model of tuberculosis and (iv) in vivo temporal monitoring of the wound response in living zebrafish embryos. Overall, this study demonstrates the application of confocal Raman spectroscopic imaging for the comparative bimolecular analysis of fully intact and living zebrafish embryos

Cell-based screen for altered nuclear phenotypes reveals senescence progression in polyploid cells after Aurora kinase B inhibition.

Cellular senescence is a widespread stress response and is widely considered to be an alternative cancer therapeutic goal. Unlike apoptosis, senescence is composed of a diverse set of subphenotypes, depending on which of its associated effector programs are engaged. Here we establish a simple and sensitive cell-based prosenescence screen with detailed validation assays. We characterize the screen using a focused tool compound kinase inhibitor library. We identify a series of compounds that induce different types of senescence, including a unique phenotype associated with irregularly shaped nuclei and the progressive accumulation of G1 tetraploidy in human diploid fibroblasts. Downstream analyses show that all of the compounds that induce tetraploid senescence inhibit Aurora kinase B (AURKB). AURKB is the catalytic component of the chromosome passenger complex, which is involved in correct chromosome alignment and segregation, the spindle assembly checkpoint, and cytokinesis. Although aberrant mitosis and senescence have been linked, a specific characterization of AURKB in the context of senescence is still required. This proof-of-principle study suggests that our protocol is capable of amplifying tetraploid senescence, which can be observed in only a small population of oncogenic RAS-induced senescence, and provides additional justification for AURKB as a cancer therapeutic target.This work was supported by the University of Cambridge, Cancer Research UK, Hutchison Whampoa; Cancer Research UK grants A6691 and A9892 (M.N., N.K., C.J.T., D.C.B., C.J.C., L.S.G, and M.S.); a fellowship from the Uehara Memorial Foundation (M.S.).This is the author accepted manuscript. The final version is available from the American Society for Cell Biology via http://dx.doi.org/10.1091/mbc.E15-01-000

Experimental determination of the drag coefficient in a swarm of bubbles

International audienceSimultaneous measurements of liquid velocity by laser Doppler velocimetry and bubble velocity, diameter, and void fraction by a double optical probe are performed in a bubble column to study the influence of the void fraction on the relative velocity of a swarm of gas bubbles. Bubble diameters db vary from 2 to 10mm and local void fractions αloc can reach 35%. It is found that, for αloc < 15%, the relative bubble velocity is determined by the hindrance effect and consequently decreases with the void fraction. Beyond this critical value, the aspiration of bubbles in the wake of the leading ones dominates the hindrance effect and the relative velocity thus increases suddenly. The contribution of the bubble diameters to this evolution is also determined. Finally, a drag correlation, valid for the whole range of void fraction and for pure water-air systems, is proposed

CFD simulation of the flow field in a bubble column reactor: Importance of the drag force formulation to describe regime transitions

International audienceThis paper deals with the simulation of a quasi two-dimensional bubble column. In particular, the aim is to predict regime transitions occuring in bubble column reactors, which is very important for their design. It is shown that taking into account bubble–bubble interactions through a drag coefficient depending on the local void fraction [M. Simonnet, C. Gentric, E. Olmos, N. Midoux, Experimental determination of the drag coefficient in a swarm of bubbles, Chem. Eng. Sci. 62 (2007) 858–866] allows to predict the onset of the regime transitions. This has been verified both with the Eulerian and Lagrangian approaches. It is also shown that the use of this drag correlation allows to reproduce some typical characteristics of the different regimes (velocity profiles becoming parabolic in the transition regime, typical transient phenomena, accumulation of large bubbles in the column centre in the transition and heterogeneous regimes)

Flow field and residence time distribution simulation of a cross-flow gas-liquid wastewater treatment reactor using CFD

International audienceA three-dimensional Eulerian-Eulerian two-phase approach has been used for the simulation of a cross-flow gas-liquid wastewater treatment reactor. Two different turbulence models have been tested: the k-ε and Reynolds Stress Model (RSM) models. Bubble induced turbulence source terms have been added to these models. Numerical results have been validated using Laser Doppler Velocimetry (LDV) measurements. Simulations with both turbulence models successfully predicted the hydrodynamics of the reactor. Then particle tracking with a stochastic approach has been used to calculate residence time distributions (RTD) with the flow previously simulated. It has been shown that dispersion in the reactor is primarily due to turbulence. Results have been compared with experimental RTD for various liquid and gas flowrates both on a bench scale and full scale plant. The RSM model accurately predicted the dispersion whereas the standard k-ε model slightly underestimated the dispersion

Deformation of liquid-liquid interfaces by a rotating rod

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