High-velocity gas stream

It is possible to eliminate the mass transfer resistances in Steps 2, 3, 7, and 8 by grinding the catalyst to a fine powder and exposing it to a high-velocity gas stream. The concentrations of reactants immediately adjacent to the catalytic surface are then equal to the concentrations in the bulk gas phase. The resulting kinetics are known as intrinsic kinetics since they are intrinsic to the catalyst surface and not to the design of the pores, or the pellets, or the reactor. 

When a high velocity gas stream bearing particulates or liquid droplets enters tangentially into a vertical pipe, the particles or droplets will collect into two streams, one spiralling downwardly and the other... 

In a direct-current plasma source (DCP) initial heating of an inert gas, usually argon, is produced by a dc-arc. Experimentally it is arranged for the plasma to be established in a high-velocity gas stream. When the edges of the plasma are cooled with an inert gas vortex, the cooler outer parts have... 

The first mode may occur when a droplet is subjected to aerodynamic pressures or viscous stresses in a parallel or rotating flow. A droplet may experience the second type of breakup when exposed to a plane hyperbolic or Couette flow. The third type of breakup may occur when a droplet is in irregular flow patterns. In addition, the actual breakup modes also depend on whether a droplet is subjected to steady acceleration, or suddenly exposed to a high-velocity gas stream.[2701[2751... 

Suddenly exposed to a high-velocity gas stream, a droplet is deformed into a saucer shape with a convex surface to the gas flow. The edges of the saucer shape are drawn out into thin sheets and then fine filaments are sheared from the outer part of the sheets, which subsequently disintegrate into smaller droplets and are swept rapidly downstream by the high-velocity gas. Unstable growth of short wavelength surface waves appears to be involved in the breakup process. 21° This is known as shear breakup (Fig. 3.10)J246f... 

Williams, G.C., H.C. Hottel, and A. C. Scurlock. 1949. Flame stabilization and propagation in high-velocity gas streams. 3rd Symposium on Combustion, Flame and Explosion Phenomena Proceedings. Baltimore The Williams and Wilkins Co. 21-40. 

Stable fluidization requires a distribution of particle sizes, preferably in the range of a few hundred microns. Normally a size of 4 mm or so is considered an upper limit, but the coal dryers of Tables 9.15(a) and (b) accommodate sizes up to 0.5 in. Large and uniformly sized particles, such as grains, are dried successfully in spouted beds [Fig. 9.13(f)] Here a high velocity gas stream entrains the solid upward at the axis and releases it at the top for flow back through the annulus. Some operations do without the mechanical draft tube shown but employ a naturally formed central channel. 

Baffles in a High Velocity Gas Stream, Third Symposium on Combustion, Flame, and Explosion Phenomena, p. 40, Williams Wilkins, Baltimore, 1949. 

Scarlock, A. C., Flame Stabilization and Propagation in High Velocity Gas Streams, ... 

B) have found excellent correlation between the measured sizes of drops atomized by high-velocity gas streams with the equations developed by Nukiyama and Tanasawa (6L), so long as conditions are held within certain limits. The behavior of sprays of 7i-heptane, benzene, toluene, and other fuels has been studied by Garner and Henny (SB) by use of a small air-blast atomizer under reduced pressures. A marked increase in the Sauter mean diameter was obtained for benzene and toluene as compared with n-heptane, which parallels their poor performance in gas turbines. Duffie and Marshall (2B) give a theoretical analysis of the breakup characteristics of a viscous-jet atomizer and show high-speed photographs of the process. 

Twin-Fluid Air-Blast Atomizer. Twin-fluid atomizers can be divided into internal and external mixing systems. Atomization occurs by passing a high-velocity gas stream over a liquid sheet or by mixing in the form of a Y jet. The gas stream is usually air although steam has been used to improve the injection characteristics of heavy viscous fuels. The air stream is usually derived from the main air flow to the combustor, thus utihzing a portion of the combustor pressure drop. 

The empirical relationship of Nukiyama and Tanasawa (NT) is probably the best known and the most widely used to predict the average droplet size in pneumatic (gas-atomized) sprays. In this type of spray the stream of liquid is broken up or atomized by contact with a high-velocity gas stream. The original NT relationship is given by... 

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