84 research outputs found
Filtration characteristics of hollow fiber microfiltration membranes used in a specific double membrane bioreactor
The performance of the microfiltration in a specifically designed membrane bioreactor operating under various transmembrane pressures with periodic backwashing was investigated for model media. These media were representative of some usual components of a fermentation medium: BSA solution (2 g L−1), yeast suspension (8 g L−1, dry mass) and a mixture of BSA/yeast (2 g L−1/8 g L−1). In this system, the separation was provided by a 0.1 μm polysulfone hollow fiber membrane. The net permeate fluxes observed for yeast/BSA mixture were proportional to the transmembrane pressure applied (ΔP) but were less than those obtained with water osmosis, showing that, in spite of the periodic backwash, a small amount of irreversible fouling remained. This fouling can be assumed to be due to internal fouling by protein and/or external fouling by a residual yeast cake. Moreover, the net permeate flux obtained with the yeast/BSA mixture was higher than that obtained with the BSA alone, showing that a thin yeast cake probably acted as a primary filtration layer that could protect the polysulfone membrane against protein fouling. These experiments enable operating recommendations to be made for the use of this specific bioreactor concerning the transmembrane pressure value and the possible addition of inert particles
Conditional stability of particle alignment in finite-Reynolds-number channel flow
Finite-size neutrally buoyant particles in a channel flow are known to
accumulate at specific equilibrium positions or spots in the channel
cross-section if the flow inertia is finite at the particle scale. Experiments
in different conduit geometries have shown that while reaching equilibrium
locations, particles tend also to align regularly in the streamwise direction.
In this paper, the Force Coupling Method was used to numerically investigate
the inertia-induced particle alignment, using square channel geometry. The
method was first shown to be suitable to capture the quasi-steady lift force
that leads to particle cross-streamline migration in channel flow. Then the
particle alignment in the flow direction was investigated by calculating the
particle relative trajectories as a function of flow inertia and of the ratio
between the particle size and channel hydraulic diameter. The flow streamlines
were examined around the freely rotating particles at equilibrium, revealing
stable small-scale vortices between aligned particles. The streamwise
inter-particle spacing between aligned particles at equilibrium was calculated
and compared to available experimental data in square channel flow (Gao {\it et
al.} Microfluidics and Nanofluidics {\bf 21}, 154 (2017)). The new result
highlighted by our numerical simulations is that the inter-particle spacing is
unconditionally stable only for a limited number of aligned particles in a
single train, the threshold number being dependent on the confinement
(particle-to-channel size ratio) and on the Reynolds number. For instance, when
the particle Reynolds number is and the particle-to-channel height
size ratio is , the maximum number of stable aligned particles per
train is equal to 3. This agrees with statistics realized on the experiments of
(Gao {\it et al.} Microfluidics and Nanofluidics {\bf 21}, 154 (2017)).Comment: 13 pages, 13 figure
A numerical approach to study the impact of packing density on fluid flow distribution in hollow fiber module.
The aim of this study was to analyze the influence of hollow fiber module design, specially packing density, and filtration operating mode on the filtration performance. In order to perform this analysis, a model based on the finite element method was used to simulate numerically the flow and filtration velocity along the fiber. An annular region of fluid surrounding the fiber was considered in order to account for the packing density Φ of the module. The originality of this approach lies in the study of fiber density effect on the hydrodynamic conditions, both for inside/out (IO) and outside/in (OI) filtration modes. The numerical simulations of fluid flow have shown a modification of the axial filtration velocity profile with packing density. When the density of fibers was high, filtration took place preferentially in the bottom of the fiber. In contrast, when the packing density was low, permeate flow was higher at the top of the fiber, i.e. the filtration module. Two experimental hollow fiber modules with two packing densities were tested and showed good agreement with the numerical data. These results underline the variations of filtration velocity along the fiber that will allow some predictions on fouling deposit to be done
Modeling the effect of packing density on filtration performances in hollow fiber microfiltration module: a spatial study of cake growth
This study continues from a previous work on the impact of packing density on the fluid flow distribution in a hollow fiber module [1]. A numerical model was developed to simulate the growth of a particle cake along the surface of a hollow fiber membrane and the subsequent fluid flow during a microfiltration operation. The model accounts for the continuous change in porous domain (cake and porous wall) geometry and permeability as long as filtration occurs. The effect module packing density has upon cake growth is carefully analyzed both for inside/out (I/O) and outside/in (O/I) filtration modes. The results exhibit significant differences in the time variations of cake spatial distribution along the fiber as a function of packing density for both filtration modes. Then a confrontation between forward filtration and backward filtration velocities offers some conclusion on the effect of packing density on the backwash efficiency. This in turn underlines the importance of design parameters in the filtration performance of a hollow fiber module
Self-ordered particle trains in inertial microchannel flows
Controlling the transport of particles in flowing suspensions at microscale is of interest in numerous contexts such as the development of miniaturized and point-of-care analytical devices (in bioengineering, for foodborne illnesses detection, etc.) and polymer engineering. In square microchannels, neutrally buoyant spherical particles are known to migrate across the flow streamlines and concentrate at specific equilibrium positions located at the channel centerline at low flow inertia and near the four walls along their symmetry planes at moderate Reynolds numbers. Under specific flow and geometrical conditions, the spherical particles are also found to line up in the flow direction and form evenly spaced trains. In order to statistically explore the dynamics of train formation and their dependence on the physical parameters of the suspension flow (particle-to-channel size ratio, Reynolds number and solid volume fraction), experiments have been conducted based on in situ visualizations of the flowing particles by optical microscopy. The trains form only once particles have reached their equilibrium positions (following lateral migration). The percentage of particles in trains and the interparticle distance in a train have been extracted and analyzed. The percentage of particles organized in trains increases with the particle Reynolds number up to a threshold value which depends on the concentration and then decreases for higher values. The average distance between the surfaces of consecutive particles in a train decreases as the particle Reynolds number increases and is independent of the particles size and concentration, if the concentration remains below a threshold value related to the degree of confinement of the suspension flow
Development of a Microfluidic Device to Improve Microfiltration Process
When neutrally buoyant particles are subjected in laminar and continuous flow, one can observe that particles generally migrate across the streamlines in a particular way. Such lateral motion called “tubular-pinched effect” causes particles tend to migrate toward micro channel wall. The origin of this motion is due to the parabolic nature of the laminar velocity profile in Poiseuille flow. This phenomenon produces a shear-induced inertial lift forces which allows the scattered particles focused and form narrow annulus near the wall. The focalization of particles could improve the method of separation process by using microfiltration. Then, micro porous membrane is used for microfiltration which filters focused particles from a fluid by passage through it. In this work, we use this lift forces generated in laminar microfluidic systems to focus randomly distributed particles continuously. The form of particles deposition poon micro porous membrane hence was observed to determine the important parameter influencing the equilibrium position of the particles. A numerical simulation (COMSOL Multiphysics ®) has also first been developed to study the influence of channel and on the subsequent size of annulus formed by the focused particles on the membrane
Les analyses bilologiques (extraction de l'ADN) et chimiques (détection des xénobiotiques) réalisées sur le cheveu et leurs applications
CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF
Cicatrisation des plaies aigües et chroniques
CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF
Etude de la communication des fonds de teint anti-âge (produits de maquillage ou produits de soin)
CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF
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