Forced-flow rotational

J. Rotating cylinder in an infinite liquid, no forced flow... 

Forced-flow development enables the mobile phase velocity to be optimized without regard to the deficiencies of a capillary controlled flow system [34,35). In rotational planar chromatography, centrifugal force, generated by spinning the sorbent layer about a central axis, is used to drive the solvent... 

There are very many situations in which well-defined patterns of convection can be established, and analytical expressions for vf derived. Such situations usually involve forced convection, in which the movement of the liquid is determined by rotation, agitation, forced flow over a flat surface, etc. Once the functional form of vf is known, solutions for c as a function of x are sought so that values of the current can be found and compared with those obtained experimentally. 

Understandably, the baffles do not influence the power characteristics within the creeping flow region where viscosity forces prevent rotation of the liquid. However, their influence is extremely strong at Re > 5 X 10. Here, the installation of baffles under otherwise unchanged operating conditions increases the power consumption of the stirrer by a factor of 20. 

Fig. 6.16 Nondimensional velocity and temperature profiles in a finite gap with a rotating surface. In all cases the Prandtl number is 0.7 and the forced-flow Reynolds number is Rey = 100. The profiles are illustrated for four values of the rotation Reynolds number Re = G1L2/v. The viscous boundary layers are close to the surface. With the exception of the axial velocity, the plots show the range 0 < z < 0.2, with the small insets illustrating the entire gap 0 < z < 1.

G. Evans and R. Greif. Forced Flow near a Heated Rotating Disk A Similarity Solution. Numer. Heat Transf., 14(3) 373-387,1988. 

The shape of the molecule should differ from that of a sphere in this phase, as a sphere may always evade the reacting forces by rotation. Deformation produces a directional bias which enables the molecule to be aligned and fixed in the direction of flow and thus allows elongation to take place. As the coil shape must deviate from a... 

Consider heat transfer from a circular cylinder whose axis is normal to a forced flow and which is rotating at an angular velocity, o>. If the surface of the cylinder is maintained at a uniform temperature, find the dimensionless parameters on which the Nusselt number depends. 

Hydrodynamic voltammetry — is a voltammetry technique featuring an electrolyte solution which is forced to flow at a constant speed to the electrode surface. -> mass transport of a redox species enhanced in this way results in higher current. The forced flow can be accomplished either by agitation of the solution (solution stirring, or channel flow), or the electrode (electrode rotation, see -> rotating disk electrode or vibration,... 

Forced convection heat transfer is probably the most common mode in the process industries. Forced flows may be internal or external. This subsection briefly introduces correlations for estimating heat-transfer coefficients for flows in tubes and ducts flows across plates, cylinders, and spheres flows through tube banks and packed beds heat transfer to nonevaporating falling films and rotating surfaces. Section 11 introduces several types of heat exchangers, design procedures, overall heat-transfer coefficients, and mean temperature differences. 

J. Rotating cylinder in an infinite liquid, no forced flow ji> = — Ngf4 = 0.07911V j 30 V Results presented graphically to NRe = 241,000. A/jjg = where v = —= peripheral velocity P 2 [E] Used with arithmetic concentration difference. Useful geometry in electrochemical studies. 112 < NRe <, 100,000. 835 < NSc < 11490 k = mass-transfer coefficient, cm/s co = rotational speed, radian/s. [60] [138] p. 238... 

Rigid spheres sometimes experience a lift force perpendicular to the direction of the flow or motion. For many years it was believed that only two mechanisms could cause such a lift. The first one described is the so-called Magnus force which is caused by forced rotation of a sphere in a uniform flow field. This force may also be caused by forced rotation of a sphere in a quiescent fluid. The second mechanism is the Saffman lift. This causes a particle in a shear flow to move across the flow field. This force is not caused by forced rotation of the particle, as particles that are not forced to rotate also experience this lift (i.e., these particles may also rotate, but then by an angular velocity induced by the flow field itself). 

In a laminar flow at a definite shear rate, different parts of the polymer molecule move at different rates depending on whether they are in the zone of rapid or relatively slow flow, and as a result the polymer molecule is under the action of a couple of forces which makes it rotate in the flow. Rotation and translational movement of polymer molecules causes friction between their chain segments and the solvent molecules. This is manifested in an increase in viscosity of the solution compared to the viscosity of the pure solvent. 

Hannah, D.M., Forced Flow Against a Rotating Disk, British ARC R M 2772 (1952). 

Swirl-flow devices include a number of geometric arrangements or tube inserts for forced flow that create rotating and/or secondary flow inlet vortex generators, twisted-tape inserts, and axial-core inserts with a screw-type winding. 

Two general approaches are used for forced flow separations. Rotational planar chromatography uses centrifugal forces created by spinning the plate around a central... 

Pressure nozzles are usually operated with a feed pressure of 30-200 bar and lead to a certain flow velocity at the orifice of the nozzle. The feed is forced into rotation in a swirl chamber within the nozzle resnlting in a cone-shaped spray at the nozzle orifice. It readily integrates into a spray as it is unstable. An increase in the feed rate leads to a less homogeneous and coarse spray with an increase in the width of the droplet size distribution. The mean size of droplets is indirectly proportional to pressnre up to 690 bar (680 atm) and directly proportional to feed rate and feed viscosity. Working with pressure nozzles results in a particle size diameter between 50 and 500 pm. °... 

The separation of multiphase reaction system components in tubular turbulent diffuser-confusor devices occurs at high rates of flow. The peripheral area of a tubular turbulent diffuser-confusor device has a pressure gradient, which moves the particles in the opposite direction to the direction of the main flow (circulation zone). A liquid flow rotates in this area and an unusual effect appears centrifugal forces can lead to phase separation, which is mainly caused by the differences in the density of components participating in the dispersing process. Substantial differences in the densities of continuous and dispersed P2 phases and following the Pi < condition... 

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