Cylinders flow around

Cyclotriphosphazene hosts, 14 177-178 Cyclotrisiloxanes, 20 242 Cyclotriveratrylenes, 14 178 24 37 organometallic derivatives of, 24 44-45 Cycopac, composition, 3 386t Cylinder oil, 15 594 Cylinder paper former, 15 118—119 Cylinders, flows around, 11 753-757 15 720t... 

Flow around a cylinder with axis normal to the flow provides a good example of the many unusual features of such flows. These are illustrated in Figure 3. 

When fluid flows around a curwe in a duct, or when fluid is confined between differentially rotating cylinders, secondary flows called Taylor vortices are generated. If a membrane is mounted on a rotating... 

Before we discuss some conjectures as to the onset of turbulence, let us first of all get a qualitative feel for the different stages of behavior as the Reynolds number is increased. Consider, for example, the viscous flow around a circular cylinder ([feyn64], [bat67]). 

Figure 2.47 Micro mixer based on the excitation of an electro-osmotic flow around a cylinder by an oscillatory electric field (top). The bottom of the figure shows particle traces on both sides of the liquid/liquid interface with no electric field (above) and with the electric field switched on (below), as described in [145].

A. Lamuraand G. Gompper, Numerical study of the flow around a cylinder using multi-particle collision dynamics, Eur. Phys. J. 9, All (2002). 

Free convection flow around horizontal cylinders and spheres is laminar for moderate values of GrSc (see Table VII, Part C) mass-transfer rates obey correlations of the same type as that for a vertical plate electrode, Eq. (29a) ... 

Impaction When an air stream containing particles flows around a cylindrical collector, the particle will follow the streamlines until they diverge around the collector. The particles because of their mass will have sufficient momentum to continue to move toward the cylinder and break through the streamlines, as shown in Figure 8.3. The collection efficiency by this inertial impaction mechanism is the function of the Stokes and the Reynolds number as ... 

To overcome weld line problems, the cross-head tubing die is often used. Here, the die design is similar to that of the coat-hanger die, but wrapped around a cylinder. This die is depicted in Fig. 3.17. Since the polymer melt must flow around the mandrel, the extruded... 

FIGURE 2 Particle motion in aerosol flow around obstacles (dashed line), (a) Flow around a cylinder of radius a (b) flow around a flat plate inclined at an angle to the aerosol flow. 

In catalyst packings transverse flow components arc automatically established as a result of the nonuniform arrangement and the twisted flow around the pellets. Hollow and full cylinders with a length-to-diameter ratio of 1 3 are particularly effective in this respect. Despite the fact that radial heat transport takes place... 

It should be noted specifically that is proportional to and not to (1)° , as in the case of the RDE. Laminar flow around a rotating cylinder does not enhance the rate of mass transport to it, because the... 

Kato, M. and Launder, B.E. (1993), The modeling of turbulent flow around stationary and vibrating square cylinders. Proceedings of 9th Symposium on Turbulent Shear Flows, Kyoto. 

The flow around and therefore the heat transfer around an individual tube within the bundle is influenced by the detachment of the boundary layer and the vortices from the previous tubes. The heat transfer on a tube in the first row is roughly the same as that on a single cylinder with a fluid in crossflow, provided the transverse pitch between the tubes is not too narrow. Further downstream the heat transfer coefficient increases because the previous tubes act as turbulence generators for those which follow. From the fourth or fifth row onwards the flow pattern hardly changes and the mean heat transfer coefficient of the tubes approach a constant end value. As a result of this the mean heat transfer coefficient over all the tubes reaches for an end value independent of the row number. It is roughly constant from about the tenth row onwards. This is illustrated in Fig. 3.26, in which the ratio F of the mean heat transfer coefficient Oim(zR) up to row zR with the end value am (zR —> oo) = amoo is plotted against the row number zR. 

Flow type Flow over a flat plate U() Flow in a pipe Flow around a cylinder... 

Krahn [76] explained how the rotation of the sphere would cause the transition from laminar to turbulent boundary layers at different rotational velocities at the two sides of a sphere. The direction of the asymmetrical wake was explained based on the separation points for laminar and turbulent boundary layers. Krahn studied the flow around a cylinder. For a non-rotating cylinder the laminar boundary layer separates at 82° from the forward stagnation point, while the turbulent boundary layer separates at about 130°. Due to the rotation the laminar separation point will move further back, while the turbulent separation point will move forward. For some value of v qaa/v between 0 and 1 the laminar and turbulent separation points will be at equal distance from the stagnation point. The pressure on the turbulent side will be smaller than on the laminar side causing a negative Magnus force. 

The boundary condition for particle diffusion differs from the condition for molecular dilTusion becau.se of the finite diameter of the particle. For certain classes of problems, such as flows around cylinders and spheres, the particle concentration is assumed to vanish at one particle radiu.s from the surface ... 

Referring to the nondimensional equation of convective diffusion (3.3), it is of interest to examine the conditions under which the diffusion term, on the one hand, or convection, on the other, is the controlling mode of transport. The Peclet number, dUfD, for flow around a cylinder of diameter r/ is a measure of the relative importance of (he two term.s. For Pe 1, transport by llte flow can be neglected, and the deposition rate can be determined approximately by solving the equation of diffusion in a non flowing fluid with appropriate boundary conditions (Carslaw and Jaeger, 1959 Crank, 1975). 

Flow around single cylinders is the elementary model for (he fibrous filter and is the geometry of interest for deposition on pipes, wires, and other such objects in an air flow (Chapter 3). The flow patterns at low and high Reynolds numbers differ significantly, and thi.s affects impaction efficiencies. For Re > 100. the velocity distribution outside the velocity boundary layer can be approximated by inviscid flow theory. This approximates the velocity distribution best over the front end of the cylinder which controls the impaction efficiency. The components of the velocity in the direction of the mainstream flow, x, and normal to the main flow, y, are... 

The analogous problem of impaction of particles on spheres has been studied for application to gas cleaning In packed beds and aerosol senibbing by droplets. Numerical computations of the impaction efliciency for point particles in in viscid flows around spheres have also been made. Before comparing the numerical computations with the available data, we consider theoretical limiting values for the Stokes number for impaction on cylinders and spheres. 

---