Centrifugal separation of a mixture

Schaflinger, Uwe

doi:10.1016/0169-5983(90)90014-p

Cited by 39 publications

(48 citation statements)

References 101 publications

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“…In case of gravity settling, power products of Reynolds number and Grashof number have to satisfy certain conditions [13], while in case of centrifugal settling the Ekman number and the Rossby number play analogous roles [15]. It should be mentioned, however, that inertial effects have been considered by Schaflinger [18,46,47], while the effects of viscosity on the bulk flow have been taken into account in the framework of kinematic-wave analysis by Smek [20]. Ekman layers have also been discussed [18].…”

Section: Pressure Gradient In the Mixturementioning

confidence: 99%

“…It should be mentioned, however, that inertial effects have been considered by Schaflinger [18,46,47], while the effects of viscosity on the bulk flow have been taken into account in the framework of kinematic-wave analysis by Smek [20]. Ekman layers have also been discussed [18]. With regard to viscosity effects in a more general context cf.…”

Section: Pressure Gradient In the Mixturementioning

confidence: 99%

“…The Boycott effect occurs also in centrifuges with compartments [14,15] and in rotating buckets [16]; cf. also the survey articles [17,18] and the monograph [19]. Generalizations to more than one spatial coordinate are also required to account for viscosity effects in the bulk flow [20], or to describe enhanced settling in centrifuges [21].…”

Section: Introductionmentioning

confidence: 99%

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On basic equations and kinematic-wave theory of separation processes in suspensions with gravity, centrifugal and Coriolis forces

Schneider

2017

Acta Mech

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Neglecting inertial and viscosity effects in the bulk flow is a common assumption in the analysis of separation processes in suspensions under the action of gravity or centrifugal and Coriolis forces. While there is a number of examples of particular solutions, the general form of the basic equations for three space dimensions, together with the appropriate boundary and initial conditions, is still uncertain and, with regard to certain aspects, even controversial. An essential point is a proper choice of the variables. Here it is proposed to introduce the mass density of the mixture, the mean mass velocity of the mixture and the total volume flux as a set of dependent variables. After some manipulations, a complete set of basic equations is obtained. It consists of two continuity equations, a generalized drift-flux relation, and two linearly independent components of a vector equation describing the total body force as irrotational. Then, by eliminating the mean mass velocity of the mixture from the set of unknowns, a generalized kinematic-wave equation is derived. It describes kinematic waves that are embedded in a bulk flow that may be one-, two-or three-dimensional. Concerning boundary conditions at solid walls, one has to ascertain whether the total body force at the wall points into the suspension or out of it. In the former case, a thin boundary layer of clear liquid is formed at the wall, whereas in the latter case a thin sediment layer may either stick at the wall or slide along it. Each of those three possibilities leads to a particular boundary condition for the bulk flow in terms of the dependent variables. In addition, initial conditions and kinematic shock relations are briefly discussed. Finally, the application of the kinematic-wave theory to the settling process in rotating tubes is outlined.

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Section: Pressure Gradient In the Mixturementioning

confidence: 99%

Section: Pressure Gradient In the Mixturementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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On basic equations and kinematic-wave theory of separation processes in suspensions with gravity, centrifugal and Coriolis forces

Schneider

2017

Acta Mech

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“…In order to further improve the uniformity of the size distribution, we use ultracentrifugal fractionation [12]. In the earth's gravitational field, the Brownian motion of the nanodroplets is so strong that gravitational buoyant forces do not cause appreciable creaming, even over long time scales.…”

Section: Methodsmentioning

confidence: 99%

Extreme emulsification: formation and structure of nanoemulsions

Mason¹,

Graves²,

Wilking³

et al. 2006

Condens. Matter Phys.

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Nanoemulsions are metastable dispersions of nanodroplets of one liquid that have been ruptured by shear in another immiscible liquid. The ruptured droplets are stabilized against subsequent coalescence by a surfactant. Because the nanodroplets do not form spontaneously, as they can in lyotropic "microemulsion" phases, the structure of nanoemulsions is primarily dependent on the history of the applied shear stresses relative to the interfacial restoring stresses. By applying extremely high shear rates and controlling the composition of the emulsion, we have been able to rupture microscale droplets down to diameters as small as 30 nm in a microfluidic process that yields bulk quantities suitable for commercial production. Following ultracentrifugal fractionation to make the droplets uniform, we study the structure of these emulsions using small angle neutron scattering (SANS) at dilute and concentrated volume fractions. We contrast the structure of a concentrated nanoemulsion with the structure factor of hard spheres at a similar volume fraction.

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“…Traditional techniques of particle manipulation rely on laminar flow (4) or differences in either particle mobility or equilibrium position in a flow with a variety of externally applied forces (5)(6)(7). Recently, microfluidic systems have been shown to be very useful for particle handling with increased control and sensitivity.…”

mentioning

confidence: 99%

Continuous inertial focusing, ordering, and separation of particles in microchannels

Carlo

Irimia

Tompkins

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

1,512

1,565

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Under laminar flow conditions, when no external forces are applied, particles are generally thought to follow fluid streamlines. Contrary to this perspective, we observe that flowing particles migrate across streamlines in a continuous, predictable, and accurate manner in microchannels experiencing laminar flows. The migration is attributed to lift forces on particles that are observed when inertial aspects of the flow become significant. We identified symmetric and asymmetric channel geometries that provide additional inertial forces that bias particular equilibrium positions to create continuous streams of ordered particles precisely positioned in three spatial dimensions. We were able to order particles laterally, within the transverse plane of the channel, with >80-nm accuracy, and longitudinally, in regular chains along the direction of flow. A fourth dimension of rotational alignment was observed for discoidal red blood cells. Unexpectedly, ordering appears to be independent of particle buoyant direction, suggesting only minor centrifugal contributions. Theoretical analysis indicates the physical principles are operational over a range of channel and particle length scales. The ability to differentially order particles of different sizes, continuously, at high rates, and without external forces in microchannels is expected to have a broad range of applications in continuous bioparticle separation, high-throughput cytometry, and large-scale filtration systems.cell manipulation ͉ Dean flow ͉ filtration ͉ hydrodynamic lift ͉ microfluidics C ontinuous manipulation and separation of microparticles, both biological and synthetic, is important for a wide range of applications in industry, biology, and medicine (1-3). Traditional techniques of particle manipulation rely on laminar flow (4) or differences in either particle mobility or equilibrium position in a flow with a variety of externally applied forces (5-7). Recently, microfluidic systems have been shown to be very useful for particle handling with increased control and sensitivity. Systems have been demonstrated that use scale-dependent electromagnetic forces (8-11), microscale hydrodynamic effects (12-14), or deterministic physical interactions and filters (15)(16)(17). However, the precision of microfluidic systems based on deterministic interaction with walls or posts may be limited by disturbances from random interparticle contact and spacing, and mechanical systems are prone to clogging. Additionally, throughput for particle manipulation based on external forces has been limited because the time for forces to act decreases with increasing flow rate. Inertial hydrodynamic forces that would increase along with flow rate have, in all but a few cases (18), not been considered in microfluidic systems. This is because of a widely held notion that small length scales require that the Reynolds number (Re), a measure of the relative importance of inertial to viscous forces, must be concurrently small, precluding any practically useful inertial effects.Inertial...

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Centrifugal separation of a mixture

Cited by 39 publications

References 101 publications

On basic equations and kinematic-wave theory of separation processes in suspensions with gravity, centrifugal and Coriolis forces

On basic equations and kinematic-wave theory of separation processes in suspensions with gravity, centrifugal and Coriolis forces

Extreme emulsification: formation and structure of nanoemulsions

Continuous inertial focusing, ordering, and separation of particles in microchannels

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