Twisting flow

M 75] [P 66] 3-D twisting flow is found for a mixer design with an array of multiple obliquely oriented, straight grooves [44]. 

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... 

Twisted Tube construction (Figure 6.32) eliminates the need for baffles altogether, since the tubes can be oriented ( tuned ) to contact surrounding tubes periodically along the exchanger. The shell-side flow is longitudinal, and special correlations have been developed for both heat transfer and pressure drop on both sides of the surface. Laminar flow inside the tube is enhanced by the secondary flow induced by the twisted flow path. 

Fig. 7 Three-dimensional twisting flow in a channel with obliquely oriented ridges on one wall, (a) Schematic of channel with ridges, (b) Optical micrograph showing a top view of a red stream and a green stream flowing on either side of a clear stream in the channel, (c) Fluorescent confocal micrographs of vertical cross sections of a microchannel such as in...

As the polymer flows off of the screw, it tends to retain the helical motion that it obtained traveling down the screw channel. This twisting flow could lead to aesthetic as well as structural defects in the extrudate. However, a breaker plate effectively hinders this motion, causing the flow downstream to be predominantly axial. 

Another type of viscometer which finds occasional use is the disk-plate viscometer (Fig. 16.8). A disk of radius R rotates with an angular velocity of CO relative to a parallel plate. The disk and plate are separated by a distance d(d R with the test fluid in between. The torque M on either the disk or plate is measured. This is known as torsional (twisting) flow, and is another example of a viscometric flow. 

Flow which fluctuates with time, such as pulsating flow in arteries, is more difficult to experimentally quantify than steady-state motion because phase encoding of spatial coordinate(s) and/or velocity requires the acquisition of a series of transients. Then a different velocity is detected in each transient. Hence the phase-twist caused by the motion in the presence of magnetic field gradients varies from transient to transient. However if the motion is periodic, e.g., v(r,t)=VQsin (n t +( )q] with a spatially varying amplitude Vq=Vq(/-), a pulsation frequency co =co (r) and an arbitrary phase ( )q, the phase modulation of the acquired data set is described as follows ... 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Coriolis-Type Flow Meters. In CorioHs-type flow meters the fluid passes through a flow tube being electromechanically vibrated at its natural frequency. The fluid is first accelerated as it moves toward the point of peak vibration ampHtude and is then decelerated as it moves from the point of peak ampHtude. This creates a force on the inlet side of the tube in resistance to the acceleration and an opposite force on the outlet side resisting the deceleration. The result of these forces is an angular deflection or twisting of the flow tube that is directly proportional to the mass flow rate through the tube. 

B23. Bundy, R. D., Gambill, W. R., and Wansborough, R. W., Heat transfer, burn-out and pressure drop for water in swirl flow through tubes with internal twisted tapes, Natl. Heat Transfer Conf, 4th, A.I.Ch.E., August 1960. 

Figure 7.27. Twisted-blade type of static mixer operating in the laminar flow regime (a) Distributive mixing mechanism showing, in principle, the reduction in striation thickness produced (f>) Radial mixing contribution...

Twisted tapes. These consist of a thin strip of twisted metal with the same width as the tube inside diameter that is slid into the tube. The flow is caused to spiral along the tube length. 

Static mixers. Static mixers are manufactured from thin metal strips with the same width as the tube internal diameter. In contrast with twisted tapes, the helix is not continuous. The flow is caused to twist through 180° and then twist in the reverse direction through 180°, and so on. The continuous splitting, reorientation and recombination of the fluid cause the enhancement as it flows through the insert. 

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