Lift forces Subject

For micrometer-sized particles subject to steric- or lift-hyperlayer-FFF, the driving forces are higher (10 14 to 10 8 N per particle) but are not balanced by back diffusion as in the normal FFF mode. Steric- and lift-hyperlayer-FFF provide powerful means for the investigation of hydrodynamic lift forces [79]. Here, retention times have been measured for well-characterized particles such as latex spheres under widely varying conditions, and the hydrodynamic lift force FL has been determined. 

Mechanical Fines Migration. A fine particle attached to the surface of the sand particle is subjected to several hydrodynamic forces (51, 65). The two major hydrodynamic forces that act on a fine particle are the lift force and the viscous-drag force (Figure 2). The lift force, Fl, acts in a direction normal to the flow direction ([/-direction) and its magnitude is (66)... 

The development of microfluidics makes the study of the movement of a small particle in a laminar flow an especially dynamic topic nowadays. The eontents of this ehapter, without having gone into the detail of theoretioal developments, show the eomplexity and difficulty of the subject. A pertinent modeling of the movement of a particle, in order to encompass phenomena such as the lesuspension of particles from walls or the migration of particles in a direction perpendicnlar to the flow streamlines, should incorporate the lift force exerted on a partiele, even though it is much weaker than the drag force. 

If a particle presents a face inclined at an angle to the direction of motion of the fluid, it may be subjected to an upward lift due to the aerofoil effect. In Figure 5.13 a flat plate is shown at an angle to a stream of fluid flowing horizontally. The fluid pressure acts normally at the surface and thus produces forces with vertical and horizontal components... 

Willetts and Murray [171] studied the lift on spheres fixed in turbulent flows. The spheres were located both near and far from a boundary. They found that particles near a wall experienced lift away from the wall, while a sphere in a shear flow away from a wall experienced a lift towards the wall. The forces were found to be of the same magnitude as the forces in laminar flow, and they were consistent with the laminar results of Segre and Silberberg [131, 132]. Spheres that were not close to a boundary, and not subjected to a velocity gradient, experienced randomly fluctuating instantaneous lift which was strongly associated with the wake deflection. They suggested that the lift... 

Forces Acting on Adherent Particles. When an air stream is flowing over a horizontal dust-covered surface, the particles are subjected to the action of the force of adhesion the particle weight P, the drag" F r, and the lift F f. The conditions for particle detachment can be expressed by the inequality [156]... 

Account must be taken of the combination of forces to which the lifting equipment will be subjected, as well as the weight of any lifting accessories. The equipment should include an appropriate factor of safety against failure. 

Forces Acting on Adhering Particles. On subjecting a dust-laden horizontal surface to a flow of air, the forces acting on the adhering particles include the adhesive forces Fad, the weight of the particle P, the head or frontal pressure Ff, and the lift FI. The conditions for the detachment of the particle may be expressed by the inequality... 

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