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At least 19 recordsLinked to original sources
PubMed2003

Numerical simulation and PEPT measurements of a 3D conical helical-blade mixer: a high potential solids mixer for solid-state fermentation.

Helical-blade solids mixers have a large potential as bioreactors for solid-state fermentation (SSF). Fundamental knowledge of the flow and mixing behavior is required for robust operation of these mixers. In this study predictions of a discrete particle model were compared to experiments with colored wheat grain particles and positron emission particle tracking (PEPT) measurements. In the discrete particle model individual movements of particles were calculated from interaction forces. It was concluded that the predicted overall flow behavior matched well with the PEPT measurements. Differences between the model predictions and the experiments with wheat grains were found to be due to the assumption that substrate particles were spherical, which was in the model. Model simulations and experiments with spherical green peas confirmed this. The mixing in the helical-blade mixer could be attributed to (1) the transport of particles up and down in the interior of the mixer, and (2) dispersion or micro-mixing of particles in the top region of the mixer. It appeared that the mixing rate scaled linearly with the rotation rate of the blade, although the average particle velocity did not scale proportionally. It may be that the flow behavior changes as a function of the rotation rate (e.g., changing thickness of the top region); further study is required to confirm this. To increase the mixing performance of the mixer, a larger blade or a change in the shape of the mixer (larger top surface/volume ratio) is recommended.

Bioreactors↗
PubMed2002

Improvement of mass transfer characteristics and productivities of inclined tubular photobioreactors by installation of internal static mixers.

The feasibility of improving mass transfer characteristics of inclined tubular photobioreactors by installation of static mixers was investigated. The mass transfer characteristics of the tubular photobioreactor varied depending on the type (shape) and the number of static mixers. The volumetric oxygen transfer coefficient ( k(L)a) and gas hold up of the photobioreactor with internal static mixers were significantly higher than those of the photobioreactor without static mixers. The k(L)a and gas hold up increased with the number of static mixers but the mixing time became longer due to restricted liquid flow through the static mixers. By installing the static mixers, the liquid flow changed from plug flow to turbulent mixing so that cells were moved between the surface and bottom of the photobioreactor. In outdoor culture of Chlorella sorokiniana, the photobioreactor with static mixers gave higher biomass productivities irrespective of the standing biomass concentration and solar radiation. The effectiveness of the static mixers (average percentage increase in the productivities of the photobioreactor with static mixers over the productivities obtained without static mixers) was higher at higher standing biomass concentrations and on cloudy days (solar radiation below 6 MJ m(-2) day(-1)).

Absorption↗
PubMed1999

Chaotic mixing of granular materials in two-dimensional tumbling mixers.

We consider the mixing of similar, cohesionless granular materials in quasi-two-dimensional rotating containers by means of theory and experiment. A mathematical model is presented for the flow in containers of arbitrary shape but which are symmetric with respect to rotation by 180 degrees and half-filled with solids. The flow comprises a thin cascading layer at the flat free surface, and a fixed bed which rotates as a solid body. The layer thickness and length change slowly with mixer rotation, but the layer geometry remains similar at all orientations. Flow visualization experiments using glass beads in an elliptical mixer show good agreement with model predictions. Studies of mixing are presented for circular, elliptical, and square containers. The flow in circular containers is steady, and computations involving advection alone (no particle diffusion generated by interparticle collisions) show poor mixing. In contrast, the flow in elliptical and square mixers is time periodic and results in chaotic advection and rapid mixing. Computational evidence for chaos in noncircular mixers is presented in terms of Poincare sections and blob deformation. Poincare sections show regions of regular and chaotic motion, and blobs deform into homoclinic tendrils with an exponential growth of the perimeter length with time. In contrast, in circular mixers, the motion is regular everywhere and the perimeter length increases linearly with time. Including particle diffusion obliterates the typical chaotic structures formed on mixing; predictions of the mixing model including diffusion are in good qualitative and quantitative (in terms of the intensity of segregation variation with time) agreement with experimental results for mixing of an initially circular blob in elliptical and square mixers. Scaling analysis and computations show that mixing in noncircular mixers is faster than that in circular mixers, and the difference in mixing times increases with mixer size. (c) 1999 American Institute of Physics.

Journal Article↗
PubMed1997

[Defective gas mixers, a cause of retro-pollution of medical gas distribution pipelines].

A defective Air/O2 mixer of a ventilator located downstream of the gas outlets of two pipelines is a potential cause of retropollution. Retropollution of O2 with Air or vice versa carries a risk of either a) a hypoxic gas mixture delivery during anaesthesia, including O2-N2O administration, when the O2 pipeline supplies Air instead of O2, or b) a hyperoxic gas mixture delivery in the intensive therapy unit for neonates during administration of a O2-Air mixture, when the Air pipeline supplies O2 instead of Air. A defective O2/N2O flowmeter-mixer of an anaesthesia machine, with N2O flow control by O2 through a differential pressure manometer, can cause retropollution of O2 supply pipeline with N2O or vice versa. The prerequisite for retropollution is the association of three events: build-up of a pressure difference between the two gas lines; defective or absent back-flow check value in the circuit of the gas at a lower pressure; one of the following defects: a) the pressure equilibrating valves of the mixer cannot amend the pressure difference and allow a gas reflow at the gas mixture outlet; b) leak in the diaphragm of a pressure equilibrating valve; c) defective bypass supply valve. The optimal means for the recognition of a pipeline contamination by another gas is the O2 analyzer, especially in anaesthetic areas where the presence of N2O and Air carries the risk of a hypoxic gas mixture delivery. The mixer or flowmeter-mixer responsible for retropollution can be recognized in plunging successively the various quick couplers underwater into a glass, while the others remain connected to their outlets and the mixer set at a O2 concentration of 50 vol% or the flowmeters set at a similar flow. In case of retropollution, the gas reflow produces bubbles. It is recommended: a) in anaesthetic areas to set the O2 pressure at about 0.2 bar above that of Air and the latter at a pressure of about 0.2 bar above that of N2O; b) in intensive therapy units for neonates, to set the Air pressure at about 0.2 bar above that of O2; c) in all areas to disconnect from the gas outlets the devices equipped with a mixer or a flowmeter-mixer when not in use.

Anesthesia, Inhalation↗
PubMed2006

Optimization of a microfluidic mixer for studying protein folding kinetics.

We have applied an optimization method in conjunction with numerical simulations to minimize the mixing time of a microfluidic mixer developed for protein folding studies. The optimization method uses a semideterministic algorithm to find the global minimum of the mixing time by varying the mixer geometry and flow conditions. We describe the minimization problem and constraints and give a brief overview of the optimization algorithm. We present results of the optimization, including the optimized geometry and parameter sensitivities, and we demonstrate the improvement in mixing performance with experiments using microfabricated mixers. The dye-quenching experiments of the original and optimized mixer designs show respective mixing times of 7 and 4 mus, a 40% reduction. The new design also provides more uniform mixing across streamlines that enter the mixer. The optimized mixer is the fastest reported continuous flow mixer for protein folding.

Kinetics↗
PubMed2004

Structural and functional imaging of 3D microfluidic mixers using optical coherence tomography.

To achieve high mixing efficiency in microfluidic devices, complex designs are often required. Microfluidic devices have been evaluated with light and confocal microscopy, but fluid-flow characteristics at different depths are difficult to separate from the en face images produced. By using optical coherence tomography (OCT), an imaging modality capable of imaging 3D microstructures at micrometer-scale resolutions over millimeter-size scales, we obtained 3D dynamic functional and structural data for three representative microfluidic mixers: a Y channel mixer, a 3D serpentine mixer, and a vortex mixer. In the serpentine mixer, OCT image analysis revealed that the mixing efficiency was linearly dependent on the Reynolds number, whereas it appeared to have exponential dependence when imaged with light microscopy. The visual overlap of fluid flows in light-microscopy images leads to an overestimation of the mixing efficiency, an effect that was eliminated with OCT imaging. Doppler OCT measurements determined velocity profiles at various points in the serpentine mixer. Mixing patterns in the vortex mixer were compared with light-microscopy and OCT image analysis. These results demonstrate that OCT can significantly improve the characterization of 3D microfluidic device structure and function.

Microfluidics↗
PubMed2003

Effect of turbulent gas-liquid contact in a static mixer on Cryptosporidium parvum oocyst inactivation by ozone.

Static mixers may be used to dissolve gaseous ozone in water treatment facilities in order to provide protection against the waterborne parasite Cryptosporidium parvum. The objective of this study was to determine the effect of a brief exposure to turbulent gas-liquid mixing conditions in a static mixer on inactivation of C. parvum oocysts by ozone. Inactivation measured in an ozone contacting apparatus that employed a static mixer for ozone dissolution was compared to predictions based on a previously published kinetic model of C. parvum inactivation by dissolved ozone in gently stirred batch reactors. Although initial contact in the static mixer had no immediate effect on the oocysts, a 20% increase in the rate of inactivation during subsequent contact with dissolved ozone was observed. Increasing the degree of turbulence within the static mixer did not yield additional inactivation. Use of static mixers for dissolution of ozone in drinking water treatment systems may provide limited enhancement of C. parvum inactivation by dissolved ozone.

Animals↗
PubMed2003

Ultrafast microfluidic mixer and freeze-quenching device.

The freeze-quenching technique is extremely useful for trapping meta-stable intermediates populated during fast chemical or biochemical reactions. The application of this technique, however, is limited by the long mixing time of conventional solution mixers and the slow freezing time of cryogenic fluids. To overcome these problems, we have designed and tested a novel microfluidic silicon mixer equipped with a new freeze-quenching device, with which reactions can be followed down to 50 micros. In the microfluidic silicon mixer, seven 10-microm-diameter vertical pillars are arranged perpendicular to the flow direction and in a staggered fashion in the 450-pL mixing chamber to enhance turbulent mixing. The mixed-solution jet, with a cross section of 10 microm x 100 microm, exits from the microfluidic silicon mixer with a linear flow velocity of 20 m/s. It instantaneously freezes on one of two rotating copper wheels maintained at 77 K and is subsequently ground into an ultrafine powder. The ultrafine frozen powder exhibits excellent spectral quality and high packing factor and can be readily transferred between spectroscopic observation cells. The microfluidic mixer was tested by the reaction between azide and myoglobin at pH 5.0. It was found that complete mixing was achieved within the mixing dead time of the mixer (20 micros), and the first observable point for this coupled device was determined to be 50 micros, which is approximately 2 orders of magnitude faster than commercially available instruments.

Animals↗
PubMed1999

Influence of chopper and mixer speeds and microwave power level during the high-shear granulation process on the final granule characteristics.

Although microwave drying technology has been used extensively, detailed studies in the pharmaceutical field are necessary to model the different operational parameters involved in microwave drying in combination with the high-shear granulation processes. The implications of the chopper and the mixer speeds during the granulation step and the microwave power level during the drying step on the final granule characteristics were investigated. alpha-Lactose monohydrate and microcrystalline cellulose were granulated at three different mixer and chopper speeds in a laboratory-scale high-shear mixer (Mi-Mi-Pro) and dried at three microwave power levels. The dried granules were characterized by friability tests, particle size analysis, bulk and tapped density studies, and porosimetry. Neither the mixer speed nor the chopper speed had a significant influence on the granule friability, which was low for all batches produced. The selected materials and experimental conditions induced a very robust granulation process, but the granule size distribution was influenced by the microwave power level. The reciprocal relationship between the dust formation and the microwave power level was analyzed using a central composite factorial design. The amount of dust remained low in all batches, but it influenced some of the inherent density properties and the volume reduction behavior of the granulation mass. In almost all cases, the Carr index decreased slightly with increasing microwave power. The major granule characteristics were not changed when different mixer or chopper speeds were changed, although the mixer speed did alter the intragranular pore size distribution.

Lactose↗
PubMed1998

A methodology for the optimization of wet granulation in a model planetary mixer.

This paper investigates a methodology for the optimization of wet granulation processes in planetary mixers. A model formulation was granulated in a planetary mixer (two different bowl sizes). The wet masses were characterized by their bulk density and consistency (as measured by mixer torque rheometry), and the feasibility of scale-up from one mixer bowl to the other was studied using a dimensionless numbers approach for the estimation of the power consumption at the granulation end point. Both bowls gave the same dimensionless power relationships (a relationship between the power number, Reynolds number, Froude number, and bowl fill ratio), which could therefore be used for calculating the power consumption level when the wet mass achieves its target values of density and consistency, i.e., the point at which granulation should be stopped. It was also shown that batches granulated in different conditions (batch size, blade speed) in two planetary mixers, but presenting similar wet mass characteristics (bulk density and consistency) led to dry granules of similar properties: granule size distribution, density, friability, and flow. This work suggests that it is possible to characterize the wet mass by only two parameters which describe the quality of the downstream granules. The scale-up procedure based on the use of dimensionless numbers was found to be applicable to planetary mixers, provided they give one common dimensionless power relationship.

Technology, Pharmaceutical↗
PubMed2006

Genomic profiling of mixer and Sox17beta targets during Xenopus endoderm development.

The transcription factors Mixer and Sox17beta have well-characterized roles in endoderm specification during Xenopus embryogenesis. In order to more thoroughly understand the mechanisms by which these endodermal regulators act, we expressed Mixer and Sox17beta in naïve ectodermal tissue and, using oligonucleotide-based microarrays, compared their genomic transcriptional profile to that of unaffected tissue. Using this approach, we identified 71 transcripts that are upregulated by Mixer or Sox17beta, 63 of which have previously uncharacterized roles in endoderm development. Furthermore, an in situ hybridization screen using antisense probes for several of these clones identified six targets of Mixer and/or Sox17beta that are expressed in the endoderm during gastrula stages, providing new and regional markers of the endoderm. Our results contribute further insight into the functions of Mixer and Sox17beta and bring us closer to understanding at the molecular level the pathways that regulate endoderm development.

Animals↗
PubMed1999

Evaluation of melt agglomeration properties of polyethylene glycols using a mixer torque rheometer.

Lactose was melt agglomerated in a mixer torque rheometer with polyethylene glycol (PEG) 2000, 3000, 6000, 8000, 10 000, or 20 000 as meltable binder. A longer massing time caused an increase in mean torque until a maximum value after which the torque decreased. A smaller particle size of the PEG gave rise to a faster initial rise in mean torque. The higher viscosity of the PEG 20 000 resulted in a higher mean torque, whereas no clear difference in mean torque was obtained with the other PEGs. The binder concentration could be varied within a rather wide range without causing overwetting, the range being wider with PEG 3000 than with PEG 20 000. The mean torque values obtained were found to be related to the liquid saturation of the agglomerates. The reproducibility of the experiments was found to be very dependent on the experimental conditions, the highest binder viscosities and binder concentrations giving rise to a poor reproducibility. The results were compared with a few melt agglomeration experiments with PEG 3000 in a high shear mixer. The mixer torque rheometer was found not to be suitable for predicting melt agglomeration properties in the high shear mixer because of a marked difference in the shear forces in the two mixers.

Agglutination↗
PubMed2003

Design of passive mixers utilizing microfluidic self-circulation in the mixing chamber.

This paper proposes the design of a passive micromixer that utilizes the self-circulation of the fluid in the mixing chamber for applications in the Micro Total Analysis Systems (microTAS). The micromixer with a total volume of about 20 microL and consisting of an inlet port, a circular mixing chamber and an outlet port was designed. The device was actuated by a pneumatic pump to induce self-circulation of the fluid. The self-circulation phenomenon in the micromixer was predicted by the computational simulation of the microfluidic dynamics. Flow visualization with fluorescence tracer was used to verify the numerical simulations and indicated that the simulated and the experimental results were in good agreement. Besides, an index for quantifying the mixing performance was employed to compare different situations and to demonstrate the advantages of the self-circulation mixer. The mixing efficiencies in the mixer under different Reynolds numbers (Re) were evaluated numerically. The numerical results revealed that the mixing efficiency of the mixer with self-circulation was 1.7 to 2 times higher than that of the straight channel without a mixing chamber at Re= 150. When Re was as low as 50, the mixing efficiency of the mixer with self-circulation in the mixing chamber was improved approximately 30% higher than that in the straight channel. The results indicated that the self-circulation in the mixer could enhance the mixing even at low Re. The features of simple mixing method and fabrication process make this micromixer ideally suitable for microTAS applications.

Journal Article↗
PubMed1998

Mixer, a homeobox gene required for endoderm development.

An expression cloning strategy in Xenopus laevis was used to isolate a homeobox-containing gene, Mixer, that can cause embryonic cells to form endoderm. Mixer transcripts are found specifically in the prospective endoderm of gastrula, which coincides with the time and place that endodermal cells become histologically distinct and irreversibly determined. Loss-of-function studies with a dominant inhibitory mutant demonstrate that Mixer activity is required for endoderm development. In particular, the expression of Sox17alpha and Sox17beta, two previously identified endodermal determinants, require Mixer function. Together, these data suggest that Mixer is an embryonic transcription factor involved in specifying the endodermal germ layer.

Animals↗
PubMed1979

[Automatic adder mixer for photometric cells: application to superprecipitation of myosin B. (author's transl)].

An automatic adder mixer for photometric cells was newly developed in our laboratory and was applied in experiments of superprecipitation of myosin B. The mixer has a reciprocating blade-type impeller with a pit for loading samples. The pit was cut so as to be just above the meniscus of the solution in a cell at the top dead point of the cam mechanism and so as to enter the solution at the bottom dead point. When 10 microliter of methylene blue solution was added, the mixing time was 0.6 sec. Myosin B was extracted from rabbit white muscle. Adding ATP (1 mM) to myosin B suspension and mixing was carried out by hand, using a mixing plunger, and also using the automatic adder mixer. The recordings obtained were then compared. Continuous recording of the initial reaction was successfully obtained only when the automatic adder mixer was used. Excellent results were also obtained with respect to reproducibility. The automatic adder mixer is easy to make, inexpensive, and can be utilized in conjunction with conventional spectrophotometers.

Chemical Precipitation↗
PubMed1998

Evaluation of the mixing effectiveness of a new powder mixer.

The effectiveness of the new powder mixer Canguro J tumbler was evaluated using lactose, microcrystalline cellulose, and salicylic acid as chemical indicator with the ratio 88:10:2 (w/w). The mixing time, the speed of the tumbler (rpm), its inclination, and filling percentage were varied in order to assess the limits of the mixer and the best parameters to use for obtaining a mixture as uniform as possible. The same experiments were then repeated after addition of 1% (w/w) magnesium stearate to the mixture of powders. The efficiency in the distribution of this lubricant was estimated by the progressive hardness reduction of the tablets derived from the compression of the powders, at a constant applied force. Finally, a comparison between Canguro J and a very efficient V-shaped mixer of the same capacity was performed. The results show that all investigated parameters influenced the mixing capability of Canguro J. The best effectiveness of the mixer occurred at the filling rate of 50% and a rotation speed of 20 rpm; in this case, Canguro J is even a little more effective than the V-shaped mixer. However, even at the filling rate of 70%, the same distribution uniformity of the powders can be obtained after a mixing time protraction of a few minutes.

Cellulose↗
PubMed2007

Quantitative characterization of magnetic separators: comparison of systems with and without integrated microfluidic mixers.

We present two new types of microfluidic passive magnetic bead separator systems as well as methods for performing quantitative characterizations of them. Both systems consist of a microfluidic channel with long rectangular magnetic elements of permalloy that are placed by the sides of the channel and magnetized by an external magnetic field. In one of the systems, a staggered herringbone microfluidic mixer is integrated in the channel. The characterization of the systems includes magnetic measurements of the capture-and-release efficiencies, estimates of distributions of captured beads in a channel from micrographs, and simulations and analytical models of bead trajectories, capture efficiencies, and capture distributions. We show that the efficiencies of both systems compare favorably to those in the literature. For the studied geometries, the mixer is demonstrated to increase the bead capture-and-release efficiency for a fixed flow rate by up to a factor of two. Moreover, high capture efficiencies can be achieved in the system with mixer at up to ten times higher flow rates than in the system without mixer.

Computer Simulation↗