Gas velocity profile

Momentum Dissipation of a Gas-Solid Two-Phase Jet. Gas velocity profiles in a gas-solid two-phase jet inside a fluidized bed were determined at five different horizontal planes perpendicular to jet direction using a pitot tube (Yang and Keaims, 1980). The velocity profiles were integrated graphically, and gas entrainment into a jet was found to occur primarily at the base of the jet. 

Figure 29. Calculated axial and radial gas velocity profiles for Run GJ18.

FIGURE 4.32 General burning velocity and gas velocity profiles inside a Bunsen burner tube (from Lewis and von Elbe [5]). 

Laird (L3), 1954 Experimental study of pressure drop in gas stream in tubes with sine-wave oscillations of tube wall. Shows that large pressure drop is partly due to change in shape of gas velocity profiles. 

Typically, there are two types of boundaries in reacting flows. The first is a solid surface at which a reaction may be occurring, where the flow velocity is usually set to zero (the no-slip condition) and where either a temperature or a heat flux is specified or a balance between heat generated and lost is made. The second type of boundary is an inflow or outflow boundary. Generally, either the species concentration is specified or the Dankwerts boundary condition is used wherein a flux balance is made across the inflow boundary (64). The gas temperature and gas velocity profile are usually specified at an inflow boundary. At outflow boundaries, choices often become more difficult. If the outflow boundary is far away from the reaction zone, the species concentration gradient and temperature gradient in the direction of flow are often assumed to be zero. In addition, the outflow boundary condition on the momentum balance is usually that normal or shear stresses are also zero (64). 

Fig. 6. Gas velocity profile in pipe cross section — DEM/CFD simulation (at 0.4 s).

Figure 17 The effect of center (nebulizer) gas flow rate plasma temperature and gas velocity profiles. Calculations were performed by using a simulation program, HiFI 2.0. (From Ref. 424.)...

Fig. 30. Effect of average voidage on radial gas velocity profile (after Zhang, 1990).

For describing the gas-velocity profile in the spout, Lefroy and Davidson started with the assumption, already discussed in Section IV,C, that the pressure variation with height in a spouted bed follows a quarter-cosine curve ... 

Figure 1. Radial gas velocity profiles Data from Van Breugel"squares, Gs 390 kg/(m. s)", "triangles, Gs kg/(m, s)". Solid lines are computed with the engineering model for two-phase flow (Nieuwland et al. ") ... 

A parabolic gas velocity profile. As a result of the velocity profile a residence time distribution arises i.e. longer residence time near the wall (less dilution with inert gas) results in higher gas fractions. Parabolic gas velocity profiles are observed by a number of authors in comparable reactor configurations. ... 

The sampling procedure calls first of all for determination of the streaming gas velocity profile. For this purpose, a dynamic velocity probe is used (Prandtl or Pitot tube). This determines the dynamic pressure value at a particular measured point of the given profile. The gas flow rate at the i-the point, u, is directly proportional to the square root of the dynamic pressure at the same point according to the relationship ... 

Figure 4a shows the gas velocity profiles of k = 0 flows confined in 5.4, 10.8, and 16.2 nm height channels through the nondimensional height (y/H). For these dynamically similar flows, influence of the surface forces differs with the ratio of the wall force penetration depth to channel height. The MD-based velocity profiles agree well with the kinetic theory predictions from [8] in the middle of the channels. Better match between the MD results and... 

HYDRODYNAMIC MODELING, 278 Radial Gas Velocity Profiles, 278 Gas Mixing, 280 Radial and Axial Dispersion, 281 Core-Annular Flow, 284 Contact Efficiency, 285... 

The behavior of the gas phase is, however, extremely important, not only for design and scale-up, but also for reactor optimization. The radial gas velocity profile affects gas-particle backmixing, influences the radial solids volume fraction distribution, and solids velocity profile, which, in turn, regulates the rates of chemical reaction, and heat and mass transfer. 

Yang el al. developed Pitot-static tube probes to measure radial gas velocity profiles at different heights in their riser [68]. They encased 0.5 mm ID hypodermic needles in a 5 mm OD tube. The static tube was sealed at the tip, and two 0.5 mm holes were drilled perpendicular to the planes of the tube 10 mm from the tip. The tip of the impact tube was flush with the surface. Using a standard equation for Pitot static tubes gives the local velocity. 

Zethraeus et al. [82] described the observed gas velocity profiles in the core region of their riser with the I/ " power-law. In the annular region, they assumed gas travels upward at a constant and low velocity. 

In this chapter, we propose a simple expression for the radial gas velocity profile... 

Figure 9. Reduced gas velocity profile as a function of exponent a (Equation 4).

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