Abrupt inlet

Figure 4.4 shows the effect of an abrupt inlet to the pipeline. Notice the vena contracta formed just downstream of the inlet. 

Favored locations for erosion-corrosion are areas exposed to high-flow velocities or turbulence. Tees, bends, elbows (Fig. 11.5), pumps, valves (Fig. 11.6), and inlet and outlet tube ends of heat exchangers (Fig. 11.7) can be affected. Turbulence may be created downstream of crevices, ledges (Fig. 11.8), abrupt cross-section changes, deposits, corrosion products, and other obstructions that change laminar flow to turbulent flow. 

Figure 5-38 shows plots of the dynamic response to changes in the inlet concentration of component A. The figure represents possible responses to an abrupt change in inlet concentration of an isothermal CFSTR with first order irreversible reaction. The first plot illustrates the situation where the reactor initially contains reactant at and... 

Open end vessel One in which there are no discontinuities (abrupt changes) in concentration at die inlet and outlet where bodi bulk and dispersion flow occur. The boundary condidons are C = when z = 0 and 6C/6z = 0 when z =... 

Fig. 27. Abrupt contraction cell for flow visualization, birefringence and degradation measurements A inlet (from a peristaltic pump of a pressurized reservoir B outlet (atmospheric pressure or partial vacuum) C interchangeable metallic nozzle with a sapphire tip D capillary flow meter E glass window for flow visualization AP pressure drop (from pressure transducers)...

By using a tapered inlet instead of an abrupt constriction, different variations of convergent flow could be envisioned axisymmetric flow in a conical channel... 

Fig. 56. Schematic representation of the convergent flow apparatus < > = 180° (abrupt contraction), 14° or 5° (conical inlet)

Fig. 57. Entrance elongational strain rate (e ) calculated along the centerline of the flow tube for the different nozzle geometries (the origin of the abscissa is taken at the orifice entrance) (-----) abrupt contraction (-----) 14° conical inlet (---) 5° conical inlet...

Fig. 58. Degradation yield as a function of maximum entrance strain rate e(0) for different nozzle geometries (x) abrupt contraction with r0 = 0.175 mm (a) abrupt contraction with r0 = 0.25 mm (o) abrupt contraction with r0 = 0.34 mm ( ) abrupt contraction with r0 = 0.50 mm ( ) 14° conical inlet with r0 = 0.25 mm (a) 5° conical inlet with r0 = 0.25 mm...

A plausible assumption would be to suppose that the molecular coil starts to deform only if the fluid strain rate (s) is higher than the critical strain rate for the coil-to-stretch transition (ecs). From the strain rate distribution function (Fig. 59), it is possible to calculate the maximum strain (kmax) accumulated by the polymer coil in case of an affine deformation with the fluid element (efl = vsc/vcs v0/vcs). The values obtained at the onset of degradation at v0 35 m - s-1, actually go in a direction opposite to expectation. With the abrupt contraction configuration, kmax decreases from 19 with r0 = 0.0175 cm to 8.7 with r0 = 0.050 cm. Values of kmax are even lower with the conical nozzles (r0 = 0.025 cm), varying from 3.3 with the 14° inlet to a mere 1.6 with the 5° inlet. In any case, the values obtained are lower than the maximum stretch ratio for the 106 PS which is 40. It is then physically impossible for the chains to become fully stretched in this type of flow. 

Example 14.1 shows how an isothermal CSTR with first-order reaction responds to an abrupt change in inlet concentration. The outlet concentration moves from an initial steady state to a final steady state in a gradual fashion. If the inlet concentration is returned to its original value, the outlet concentration returns to its original value. If the time period for an input disturbance is small, the outlet response is small. The magnitude of the outlet disturbance will never be larger than the magnitude of the inlet disturbance. The system is stable. Indeed, it is open-loop stable, which means that steady-state operation can be achieved without resort to a feedback control system. This is the usual but not inevitable case for isothermal reactors. 

In FA experiments, the chromatographic coinmn has to be equilibrated with the solution of a known concentration of the stndied compound. Snccessive abrupt step changes of increasing concentration are performed at the coinmn inlet, and breakthrongh curves are determined. From the breakthrongh curves obtained in single-component FA experiments (Figure 10.16), the values of the stationary... 

In practice, the recirculation cells are often eliminated by increasing the inlet flow rate, a procedure that also improves film thickness uniformity. However, because of nonlinear interactions among buoyancy, viscosity, and inertia terms, the transitions between the flow patterns may be abrupt, and multiple stable-flow fields may exist for the same parameter values (24,195,... 

These devices are employed for fine powders (40-400 im) and also coarser particles. In the Franken or Vandenhoek inertial separators [13,14] (Fig. 4a) particle-air mixture enters from the top and falls down in the inlet pipe. The air turns abruptly to the outlet pipe inclined by about 45-50° and carries the fine particles. Coarse fraction proceeds straight down because of high inertia towards the discharge pipe. On its way this material undergoes repeated separation in a secondary air flow carrying fines into a curvilinear chamber. Then they exit via the outlet pipe with blades mounted for better air distribution. These classifiers, manufactured by Buell Co., are used for separation of pulverized limestone at cut size of 150 pra with feeds from a few pounds to 600 t/h [15], In the Buell s variant of this device [14] blades have different angles to increase the efficiency. Such devices were used for separation of 15-1000 pm particles. 

It is more compact and is commonly used in large flow applications. The tube consists of a short, straight inlet section followed by an abrupt decrease in the inside diameter of the tube. This section, called the inlet shoulder, is followed by the converging inlet cone and a diverging exit cone. The two cones are separated by a slot or gap between the two cones. 

Consists of a short, straight inlet section followed by an abrupt decrease in the inside diameter of the tube... 

Figure 5-38 shows plots of the dynamic response to changes in the inlet concentration of component A. The figure represents possible responses to an abrupt change in inlet concentration of an isothermal CFSTR with first order irreversible reaction. The first plot illustrates the situation where the reactor initially contains reactant at CA and at t = 0. The reactant flow at CAO begins until component A reaches a steady state condition. The second plot starts with CA in the reactor at t = 0. Tables 5-15, 5-16, and 5-17, respectively, show common equations for all reactor models involving a first order reversible reaction. 

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