Flow secondary

Using the described algorithm the flow domain inside the cone-and-plate viscometer is simulated. Tn Figure 5.17 the predicted velocity field in the (r, z) plane (secondary flow regime) established inside a bi-conical rheometer for a non-Newtonian fluid is shown. 

Figure 5.17 The predicted secondary flow field in the bi-conical viscometer...

Olagunju, D.O. and Cook, L. P., 1993. Secondary flows in cone and plate flow of an Oldroyd-B fluid. J. Non-Newtonian Fluid Mech. 46, 29-47. 

Secondary flows also occur in channels that have a noncircular cross section, but are otherwise straight. In these cases the secondary flows are directed outward into the corners and return along the waHs. 

A significant heat-transfer enhancement can be obtained when a nonckcular tube is used together with a non-Newtonian fluid. This heat-transfer enhancement is attributed to both the secondary flow at the corner of the nonckcular tube (23,24) and to the temperature-dependent non-Newtonian viscosity (25). Using an aqueous solution of polyacrjiamide the laminar heat transfer can be increased by about 300% in a rectangular duct over the value of water (23). 

Characterization and influence of electrohydro dynamic secondary flows on convective flows of polar gases is lacking for most simple as well as complex flow geometries. Such investigations should lead to an understanding of flow control, manipulation of separating, and accurate computation of local heat-transfer coefficients in confined, complex geometries. The typical Reynolds number of the bulk flow does not exceed 5000. 

A gas turbine used in aircraft must be capable of handling a wide span of fuel and air flows because the thmst output, or pressure, covers the range from idle to full-powered takeoff. To accommodate this degree of flexibiUty in the combustor, fuel nozzles are usually designed with two streams (primary and secondary flow) or with alternate tows of nozzles that turn on only when secondary flow (or full thmst power) is needed. It is more difficult to vary the air streams to match the different fuel flows and, as a consequence, a combustor optimized for cmise conditions (most of the aircraft s operation) operates less efficiently at idle and full thmst. 

One principal use of cyclohexanol has been in the manufacture of esters for use as plasticizers (qv), ie, cyclohexyl and dicyclohexyl phthalates. In the finishes industry, cyclohexanol is used as a solvent for lacquers, shellacs, and varnishes. Its low volatiUty helps to improve secondary flow and to prevent blushing. It also improves the miscibility of cellulose nitrate and resin solutions and helps maintain homogeneity during drying of lacquers. Reaction of cyclohexanol with ammonia produces cyclohexylamine [108-91-8], a corrosion inhibitor. Cyclohexanol is used as a stabilizer and homogenizer for soaps and synthetic detergent emulsions. It is used also by the textile industry as a dye solvent and kier-boiling assistant (see Dye carriers). 

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... 

Matching the flow between the impeller and the diffuser is complex because the flow path changes from a rotating system into a stationary one. This complex, unsteady flow is strongly affected by the jet-wake of the flow leaving the impeller, as seen in Figure 6-29. The three-dimensional boundary layers, the secondary flows in the vaneless region, and the flow separation at the blades also affects the overall flow in the diffuser. 

Boyce, M.P., Secondary Flows in Axial-flow Compressors with Treated Blades, AGARD-CCP-214 pp. 5-1 to 5-13, 1974. 

The process itself often sets requirements on the ventilation parameters, and it also affects the ventilation—for example, by secondary flows coming from moving wires or trucks. A very special case is clean rooms, where the high purity requirements set strict target conditions for ventilation. 

FIGURE 9.37 Secondary flow between the blades of a centrifugal fan. ... 

Bypass The provision for a secondary flow path from the main flow in duct or pipe flow. 

Bypass factor The ratio of the secondary flow to the sum of the main flow and secondary flow. 

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 ... 

Figure 7.14. Single-celled secondary flow with an anchor agitator...

Ide and White W studied the viscoelastic effects in agitating polystyrene solutions with a turbine. At concentrations below 50% PS, flow was normal. Abovfe 35%, the viscoelastic forces caused the flow to reverse, moving away from the impeller along the axis. At 30 to 35% PS, both occurred, causing a segregated secondary flow around the turbine. 

The dAc/dz term is usually zero since tubular reactors with constant diameter are by far the most important application of Equation (3.7). For the exceptional case, we suppose that Afz) is known, say from the design drawings of the reactor. It must be a smooth (meaning differentiable) and slowly varying function of z or else the assumption of piston flow will run into hydrodynamic as well as mathematical difficulties. Abrupt changes in A. will create secondary flows that invalidate the assumptions of piston flow. 

The density change on polymerization is typically about 20%, and this density gradient can cause significant secondary flows and natural convection effects. The experiments cited above for vinyl acetate polymerization were performed in a helical reactor. The centrifugal force in helical reactors induces secondary flows as well. The effects of helical flow have been analyzed, but were found to be less significant than the effects of natural convection [14]. 

It is also assumed that axial diffusion of mass, heat and momentum are negligible. The velocity profiles are assumed to be locally fully developed in length. For this simplified case the polymer concentration and secondary flows are determined by three dimensionless groups ... 

Figure 9. Secondary flow natural convection streamlines for a zeroth order reaction and uniform viscosity at GrSc = 1, 10 and 10 . ...

The secondary flows from natural convection can become larger than the primary flow, so it seems likely that the secondary flows might become turbulent or nonsteady. Shown in Tables 1 and 2 are the dimensionless groups at the inlet and outlet, based on cup-average quantities, as well as the Reynolds numbers for the primary and secondary flows (Reynolds numbers defined in terms of the respective total mass flowrate, the viscosity and the ratio of tube perimeter to tube area). 

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