Secondary flow Characteristics

Many materials of practical interest (such as polymer solutions and melts, foodstuffs, and biological fluids) exhibit viscoelastic characteristics they have some ability to store and recover shear energy and therefore show some of the properties of both a solid and a liquid. Thus a solid may be subject to creep and a fluid may exhibit elastic properties. Several phenomena ascribed to fluid elasticity including die swell, rod climbing (Weissenberg effect), the tubeless siphon, bouncing of a sphere, and the development of secondary flow patterns at low Reynolds numbers, have recently been illustrated in an excellent photographic study(18). Two common and easily observable examples of viscoelastic behaviour in a liquid are ... 

It is well known (15, 16, 17) that colled tube heat exchangers possess superior heat transfer characteristics because of secondary flow effects. At small curvatures, the Dean number, defin-N = N -V a... 

Srinivasan and Tien (18) have made an analytical study on the mass-transfer characteristics of reverse osmosis in curved tubular membranes. The increase in mass-transfer due to secondary flow resulted in a substantial reduction in the wall concentration (the polarization modulus) for Np =100 and a/R=0.01 (see Figure 39). Further, the production capacity (permeation rate) was markedly increased (see Figure 40). 

Grochowicz et al. modeled the secondary flow in serpentine and coiled tubes as the measure of the radial mixing using computational fluid dynamics techniques. They showed that flow characteristics in serpentine tubes result in considerably less band broadening per unit length than in linear tubes of the same inner... 

The laminar flow data of Figure 3.39 have a higher slope (0.52 than predicted by theory (0.33)-probably because of "secondary flow effects". The data were taken in a spiral flow thin channel device. Whenever fluid passes through a curved tube or channel, centrifugal forces tend to throw fluid outward from the center of the channel. It then recirculates inward along the walls of the channel (see Figure 3.40). It is well known that coiled tube heat exchangers possesses superior heat transfer characteristics because of secondary flow effects. 

The most prominent characteristic of flow in curved ducts and helicoidal pipes is the secondary flow induced by centrifugal force due to the curvature of the pipe. Consequently, the friction factor is higher in curved pipes than that in straight pipes for the same Reynolds number. The pitch of the helicoidal pipe also has an effect on the flow. As a result, the heat trans-... 

Samenfink W, ElsSPer A, Dullenkopf K, Wittig S (1999) Droplet inteiactimi with shear-driven liquid films analysis of deposition and secondary droplet characteristics. International Journal of Heat and Fluid Flow 20 462-469. 

At the present time the improvement of areal and vertical (volumetric) sweep efficiency takes a great deal of room in secondary and tertiary oil recovery. One of the widely used and perspective methods is mobility control by diluted aqueous solutions of different polyacrylamides (1,2). In the middle of the sixties some authors (3,4) proposed that the viscosity enhancement and the non-Newtonian flow behavior of the solutions were responsible for the reduction of phase mobility. Mungan (5,6), Gogarty (7), Dauben and Menzie (8) have pointed out, however, that the sorption phenomenon plays a decisive role in the flow characteristics of the polymer solutions and carrier phases. In the papers devoted to... 

ABSTRACT The characteristic of turbulent flow in jackets with triangular helical ducts was simulated and the velocity fields of fully developed turbulent fluid flow in the jackets were obtained. The features of the local coefficient of resistance C/Reiocai) on outer walls and inner wall were summed up and the effects of dimensionless curvature ratio and Reynolds number on the flow field and the flow resistance were analyzed. The results indicate that the structure of secondary flow is with two steady vortices at turbulent flow conditions. The distribution of/ eiocai on the outer walls differs from that of/ eiocai on the inner wall. The mean coefficient of resistance (/Rem) on the outer walls is about 1.41 1.5 7 times as much as that on the iimer wall. With the increase of dimensionless curvature ratio or Reynolds number,/Rem on the boundary walls increases. 

For thermosets, the velocity profile of the flow front has been established to be relatively flat and plug-shaped. A thin melt region exists between the charge core and mold surfaces, which ensures that core fluid layers move together in the direction of flow. In the case of thermoplastics, the flow front assumes a more parabolic shape, characteristic of laminar flow. However, due to the fact that solidification initiates in the material in contact with the cooler mold, resin at the core migrates toward the cavity surfaces creating a secondary flow pattern that is known as the fountain flow effect. 

The overall nucleation rate in a crystallizer is determined by the interaction of the secondary nucleation characteristics of the material being crystallized with the hydrodynamics of the crystal suspension. When crystallizing a given material, crystallizers of different size, agitation levels, flow patterns, etc. will... 

The central element of the slit plate micromixer is a structured metallic plate that carries a number of slits [35]. These slits generate a multilamellar structure of the liquids to be mixed with slit structures of characteristic dimensions as low as 25 pm. Further mixing between the two lamellate liquids occurs by diffusional processes and secondary flow effects. These secondary flow effects were studied by computational fluid dynamics (CFD) simulations... 

Vortices are induced by the viscoelastic characteristics of the converging fluid [71,72]. When extensional viscosity values are large, the balance of forces makes radial flow impossible, thereby giving rise to secondary flows in the form of vortices in order to provide stress relief. 

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