Velocity of gas flow

The residence time distribution of particles is related to the properties of the particles and the gas flow, including the size distribution, and the velocity of gas flow and its profile. In practically applicable impinging stream devices, the particles being processed usually have relatively narrower size distribution the diameter of the tube to particles size ratio, d Jd,h is normally very large ( 15) while the gas velocity is high... 

With Eq. (6.4), the radial distance of the position where the maximum radial velocity of gas flow appears, rmax, can be calculated to be 1.974 times the diameter of the accelerating tube, R.dC. Assume the particles are carried out of the impingement zone at r = 1.974R.dC with an initial radial velocity of zero. From the force balance, the movement equations of sphere particles after leaving the impingement zone can be obtained as... 

The linear velocity of gas flow in a vacuum is also dependent on the cross-sectional area of the reactor in which the flow takes place. Therefore, a parameter describing the linear velocity of a flow is given by FjA p, where A is the cross-sectional area (square centimeters). The value of FjA p for a flow of 50 seem in a bell jar of 50-cm diameter at 1 torr is 19.4cm/min, whereas the value of FjA p for a flow of 5 seem in a tube of 5-cm diameter at 0.1 torr is 1940cm/min. 

Velocity of forward flow through stage divider opening, m/s Superficial velocity of gas flow through stage divider opening, m/s... 

Pulmonary deposition of an aerosol preparation is determined primarily by its size. Aerosols with a mass median aerodynamic diameter of 1-5 xm produce the best therapeutic results and are the target particle size for inhalation therapy. These small particles penetrate deep within the respiratory tract to ensure drug deposition in peripheral airways. The cross-sectional area (cm ) of the lung increases dramatically at the level of the respiratory zone therefore, the velocity of gas flow during inspiration rapidly decreases at this level. Moderate-sized particles (5-10 (xm) frequently settle out by sedimentation in larger more central airways because the velocity of gas falls rapidly in the region of the terminal bronchioles. 

One may imagine that just above the distributor solid is entrained by the rising bubbles to form the bubble wake. This solid is carried up the bed with the bubbles at velocity Ub and is continually exchanged with fresh emulsion solid. At the top of the bed the wake solids rejoin the emulsion to move down the bed at velocity Ug. The upward velocity of gas flowing through the emulsion is thus ... 

According to (2.21), both planar and three-dimensional (helical) small bending perturbations increase with the same growth rate if the relative velocity of gas flow is... 

The ammonia conversion effldency, expressed as a percentage of the ammonia that is converted to NO, is mainly a function of the catalyst selectiwty and activity, temperature, pressure, thoroi hness of mixing of the incoming air and ammonia, and velocity of gas flow through catalyst I7I-... 

The velocity of gas flow in the CL is very small this allows us to neglect the convective term in the heat transport equation. The heat balance in the CL is, therefore, given by... 

In ammonia production, the space velocity is often (0.6—2) x 10 h. In axial flow converters, the velocity of gas flow can be up to several m s the effect of external diffusion should be absent, but the effect of intraparticle diffusion cannot be ignored. The gas flow area In a radial flow converter is very large, the gas velocity is very low, and thus both effects of external and intraparticle diffusion cannot be ignored. Among the many factors that influence diffusion, the particle size of catalyst is the most significant and can be easily adjusted. 

As the proportion of small ash particles (under 30 M in radius) increases the coefficient of contamination does likewise, particularly for low velocities of gas flow (see Fig. IX.7), which corresponds to the earlier views on the adhesion of particles arising from an air flow (see 34). 

Hence there are two special velocities of gas flow the first is v. below which both free-running and dense deposits are formed and above which there are only dense deposits the second is above which no deposits are formed at all. 6pik [455] considered that v should be of the order of 220 m/sec. However, we feel that this velocity is too low (see 31). 

Fig. 18.32 Streaklines coloured by velocity of gas flow past a sphere in the region of low Reynolds numbers...

If the rate of a gas—solid reaction is plotted against the velocity of gas flowing past the solid (catalyst), the rate will approach an upper limit as the velocity of flow increases. This upper limit occurs when the transfer of heat and mass between the outer surface of the solid and the main stream of the gas no longer exerts a significant effect on the rate. 

It is important that the manifolds that feed the gases to the cells and the manifolds that collect the rmused gases are properly sized. The cross-sectional area of the manifolds determines the velocity of gas flow and the pressure drop. As a rule of thumb, the pressure drop through the manifolds should be an order of magnitude lower than the pressure drop through each cell in order to ensure uniform flow distribution. 

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