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Inertial Lift

The velocity, viscosity, density, and channel-height values are all similar to UF, but the diffusivity of large particles (MF) is orders-of-magnitude lower than the diffusivity of macromolecules (UF). It is thus quite surprising to find the fluxes of cross-flow MF processes to be similar to, and often higher than, UF fluxes. Two primary theories for the enhanced diffusion of particles in a shear field, the inertial-lift theory and the shear-induced theory, are explained by Davis [in Ho and Sirkar (eds.), op. cit., pp. 480-505], and Belfort, Davis, and Zydney [/. Membrane. Sci., 96, 1-58 (1994)]. While not clear-cut, shear-induced diffusion is quite large compared to Brownian diffusion except for those cases with very small particles or very low cross-flow velocity. The enhancement of mass transfer in turbulent-flow microfiltration, a major effect, remains completely empirical. [Pg.56]

If the external field strength is kept so low that the particles are significantly elevated from the wall by the action of the hydrodynamic lift forces, the fluid inertial contribution of the hydrodynamic lift force R. can be investigated [289-291,301]. Observed inertial lift forces were in reasonable agreement with values predicted by the inertial lift force theory expressed by ... [Pg.136]

Eor a given crossflow filtration, the dominant particle back transport mechanism may depend on the shear rate and the particles size [4]. Brownian diffusion is only important for particles smaller than only a few tenths of a micron in diameter with relative low shear, whereas inertial lift is important for particles larger than several tens of microns with higher shear rates. Shear-induced back transport appears to be important for intermediate particle sizes and shear rates. Li et al. [7] reported that the shear-induced mechanism was able to predict fluxes comparable with the critical fluxes identified by the DOTM. [Pg.196]

TABLE 8.1 Coefficient Coefficients in Equation 8.1 for Different Mechanisms Brownian Diffusion Shear-Induced Diffusion Inertial Lift ... [Pg.196]

J. A. Schonberg and E. J. Hinch, Inertial migration of a sphere in Poiseuille flow, J. Fluid Mech. 203, 517-524 (1989) E. S. Asmolov, The inertial lift on a small particle in a weak-shear parabolic flow, Phys. of Fluids 14, 15-28 (2002) P. Cherukat, J. B. McLaughlin, and D. S. Dandy, A computational study of the inertial lift on a sphere in a linear shear flow field, Int. J. of Multiphase Flow, 25, 15-33 (1999). [Pg.510]

The data of Theodore (T3a) for the lift force on a nonrotating sphere in a Poiseuille flow, and, to a lesser extent, the comparable data of Oliver (02), show that lateral forces arise at small Reynolds numbers even in the absence of particle rotation. Thus, inertial lift forces can arise from slip-shear as well as from slip-spin. That the character of these two forces is very different is shown clearly by the theoretical analysis of Saffman (SIa). [Pg.390]

Three mechanisms are important for the backtransport of particles from a membrane. For small solutes and submicron colloids. Brownian Diffusion (determined by the Stokes-Einstein equation (Sethi and Wiesner (1997)) dominates backtransport of the colloids from the membrane into the bulk solution. Inertial Lift, which is caused by the presence of a wall is important for large particle sizes and high shear rates. Shear Induced Diffusion is an orthokinetic mechanism also more important for larger colloids. [Pg.69]

A unique interaction between fluid mechanics and transport exists for filtration processes. Such processes perform better than expected based on the predicted impact of concentration boundary layers. The improvement in performance, a rare occurrence for membrane processes, arises from a combination of hydrodynamic diffusion and inertial lift [51]. Hydrodynamic interactions between particles or colloids that accumulate in the concentration boundary layer lead to shear-induced diffusion away from the membrane surface. Shear-induced diffusion can be significantly larger than molecular diffusion and thereby reduce surface concentrations. For sufficiently large particles at high shear rates, inertial lift becomes the dominant mechanism for particle movement away from the membrane. [Pg.306]

Chcmikat P, McLaughlin JB (1994) The inertial lift on a rigid sphere in a linear shear-flow field near a flat wall. J Hnid Mech 263 1-18... [Pg.581]

In spiral, rectangular channels, cells and particles experience Dean drag forces in addition to inertial lift forces. The first conclusive research to analyze flow in curved channels was done by Dean in 1927 [10]. He showed that in curved channels/pipes, the plane Poiseuille flow is disturbed by the presence of centrifugal force (Fcf), and in this condition, the maximum point of velocity distribution shifts from the center of the channel toward the concave wall of the channel (Fig. 2a). This shift causes a sharp velocity gradient to develop near the concave wall between the point of maximum velocity and the outer concave channel wall where the velocity is zero. This causes decrease in the centrifugal force on the fluid near the concave wall which leads to... [Pg.3061]

As the particle size becomes larger, the phenomenon of inertial lift (Green and Belfort, 1980) becomes important. [Pg.581]

Microfiltration is used when suspended particles are present. For suspended particles, the theory presented for dissolved solids earlier is only valid for very small suspended particles up to approximately 1 /um in size [120]. Two different theories are presented for larger size particles, namely, a shear induced diffusion theory [121] and an inertial lift theory [122]. Details of these theories are beyond the scope of this book. Please refer to [121] [123] for more information. [Pg.167]


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