Smooth exit

Brereton et al. characterized riser gas mixing with a pseudo-axial dispersion coefficient [96]. They concluded that axial dispersion increases with total pressure drop across the riser (approximately proportional to the suspension density). In addition, they found the smooth exit configuration increased axial dispersion coefficients compared to an abrupt exit. They attributed this phenomenon to a more uniform solids distribution in the case of the abrupt exit which, in turn, corresponds to a decreased irregularity in the upward and downward solids movement primarily responsible for the axial mixing of the gas. The experimental values, reported as DyU L, ranged between 0.01 and 0.18 (D = 6,600 to 119,000 cm /s). 

Gas dispersion is influenced by the entrance and exit structure of the riser, as well as its length and diameter. Brereton et al. (1988) showed that Dge tends to be higher for an abrupt exit than for a smooth one at a given C7g and Gj. On the other hand, Dgg from the smooth exit was higher than from the abrupt exit for a given apparent suspension density. 

Figure 5. A figure illustrating the impact of exit effects in circulating fluidised bed systems. The lines show density profiles for identical conditions of gas velocity (7.1 m/s) and circulation rate (73 kg/mh) for an abrupt exit (circles) and a smooth exit (triangles). The solids are returned 1.98 m above the gas distributor causing the "nose" in the profile, (Brereton, 1987).

Figure 7. Diagram showing how similar total pressure drops in smooth and abrupt exit columns result in different profile shapes. The smooth exit unit has a choked dense phase at the base which may be a zone of increased gas backmixing.

Smooth Exit Promotes high solids circulation rate (external) with a uniform RTD (plug flow) at a low pressure drop. Ideal for certain catalytic reactions involving catalyst deactivation e,g. fluid catalytic cracking. Also suited for flash pyrolysis. 

The melt flows from the extmder iato the die where it flows around the bend and around the core tube. On the far side of the core tube, it forms a weld. Melt sticks to and is pulled by the moving wire. Details of the sizes and shapes of the die parts ia contact with the melt are important ia obtaining a smooth coating at high rates. The die exit usually is the same diameter as that of the coated wire and there is Httle drawdown. Die openings are small and pressures iaside the die are high at ca 35 MPa (5000 psi). Wire takeup systems operate as high as 2000 m /min. 

The shape of the converging section is a smooth trumpet shape similar to the simple converging nozzle. However, special shapes of the diverging section are required to produce the maximum supersonic-exit velocity. Shocks result if the divergence is too rapid and excessive boundary layer friction occurs if the divergence is too shallow. See Liepmann and Roshko (Elements of Gas Dynamic.s, Wiley, New York, 1957, p. 284). If the nozzle is to be used as a thrust device, the diverg-... 

Venturi Meters The standard Herschel-type venturi meter consists of a short length of straight tubing connected at either end to the pipe line by conic sections (see Fig. 10-15). Recommended proportions (ASME PTC, op. cit., p. 17) are entrance cone angle Oti = 21 2°, exit cone angle Cto = 5 to 15°, throat length = one throat diameter, and upstream tap located 0.25 to 0.5 pipe diameter upstream of the entrance cone. The straight and conical sections should be joined by smooth cui ved surfaces for best results. 

The collection efficiency of cyclones varies as a function of particle size and cyclone design. Cyclone efficiency generally increases with (1) particle size and/or density, (2) inlet duct velocity, (3) cyclone body length, (4) number of gas revolutions in the cyclone, (5) ratio of cyclone body diameter to gas exit diameter, (6) dust loading, and (7) smoothness of the cyclone inner wall. Cyclone efficiency will decrease with increases in (1) gas viscosity, (2) body diameter, (3) gas exit diameter, (4) gas inlet duct area, and (5) gas density. A common factor contributing to decreased control efficiencies in cyclones is leakage of air into the dust outlet (EPA, 1998). 

If the pressure drop over the tubes is not to exceed 2 kN/m2, calculate the minimum number of tubes that are required. Assume that the tube walls are smooth and that entrance and exit effects can be neglected,... 

In contrast to this, the enzyme resin is stressed less by gas sparging than by stirring (see Fig. 18 and 20). The same activity losses were observed first with 1 to 8 times greater specific adiabatic compression power Pj/ V than the maximum power density necessary for stirring. As in the case of the smooth disc, the effects of power input are only weak. The type of gas sparger and therefore the gas exit velocity are of no recognisable importance. The behaviour of the enzyme resin particles is thus completely different from that of the clay min-eral/polymer floes and the oil/water/surfactant droplet system, which are particularly intensively stressed by gas sparging. 

The cell bodies of visceral motor neurons are found in the lateral horn. The axons of these neurons form efferent nerve fibers of the autonomic nervous system (ANS). The ANS innervates cardiac muscle, smooth muscle and glands (see Chapter 9). The axons of these neurons exit the spinal cord by way of the ventral root. 

Air and water flow at 8 x 10 3 kg/s and 0.4 kg/s upwards in a vertical, smooth-wall tube of internal diameter dt = 20 mm and length L = 1.3 m. Using the homogeneous flow model, calculate the pressure drop across the tube (neglecting end effects). The fluids are at a temperature of 20 °C and the expansion of the air may be assumed to be isothermal. The exit pressure is 1 bar. 

Figure 11.11—Multichannel detection, a) Multichannel detection with a diode array located in the focal plane. The light beam is diffracted by the concave dispersive system after travelling through the sample. Note the absence of an exit slit b) spectrum of a 1 1 000 solution of benzene in methanol. This spectrum represents a typical spectrum without smoothing and is obtained with commercial photodiodes (note in contrast to mid IR spectroscopy, interferometry followed by Fourier transform has led to few commercial achievements in this area).

The current picture of protein folding is nicely summarized in Figure 17.1. There are a multitude of pathways from the state of unfolded protein at the top of the figure to the native protein at the bottom. Without folding intermediates, the walls of the funnel to the bottom would be smooth. If the energy trough around a nonnative protein is too deep, the misfolded protein cannot exit this local minimum. 

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