Velocities, axial

The design of a cross-flow filter system employs an inertial filter principle that allows the permeate or filtrate to flow radially through the porous media at a relatively low face velocity compared to that of the mainstream slurry flow in the axial direction, as shown schematically in Figure 15.1.9 Particles entrained in the high-velocity axial flow field are prevented from entering the porous media by the ballistic effect of particle inertia. It has been suggested that submicron particles penetrate the filter medium and form a dynamic membrane or submicron layer, as shown in... 

Pulverized coal is fed directly from a variable speed auger into the high velocity primary air stream which conveys it to the injector at the top of the furnace. The coal and primary air enter the combustor through a single low-velocity axial jet. Secondary combustion air is divided into two flows which enter the combustor coaxial to the primary stream. Part of the flow is introduced through a number of tangential ports to induce swirl which is necessary for flame stabilization. The remainder enters the combustor axially. The two secondary air streams are separately preheated using electrical resistance heaters. 

Blasco et al. [12] proposed two-dimensional mathematical model for the drying process of dense phase pneumatic conveying. However, heat and mass transfer were not considered and therefore their model may be used for dense phase pneumatic transport only. In their paper, both experimental and numerical predictions for axial and radial profiles for gas and solid velocity, axial profiles for solid concentration and pressure drop were presented. 

The reactor length The flow velocity Axial position along the reactor The adsorption coefficient of A... 

Increasing surfactant concentrations in the aeration cell has been found to decrease bubble diameter, bubble velocity, axial diffusion coefficient, but increase bubble s surface-to-volume ratio, and total bubble surface area in the system. The effect of a surface-active agent on the total surface area of the bubbles is also a function of its operating conditions. The surfactant s effect is pronounced in the case of a coarse gas diffuser where the chances of coalescence are great and the effectiveness of a surface-active solute in preventing coalescence increases with the length of its carbon chain. 

There is a minimum of the SLT for an intermediate value of the mobile phase velocity, as in linear chromatography [11]. At low velocities, axial dispersion is large due to the long migration time during which axial diffusion proceeds constantly to relax the concentration gradients, while at high velocities, the finite rate of the mass transfer kinetics causes the SLT to increase in proportion to the velocity. If we assume as above the Van Deemter equation for the axial dispersion term (Eq. 14.3Q2), we obtain for the optimum velocity for minimum SLT in displacement (imder isotachic conditions)... 

This review deals mainly with the discussion of various macroscopic hydro-dynamic, heat, and mass transfer characteristics of bubble columns, with occasional reference to the analogous processes in modified versions of bubble columns with a variety of internals. The hydrodynamic considerations include determination of parameters like flow patterns, holdup, mixing, liquid circulation velocities, axial dispersion coefficient, etc., which all exert strong influence on the resulting rates of heat and mass transfer and chemical reactions carried out in bubble columns. Different correlations developed for estimating the aforementioned parameters are presented and discussed in this chapter. 

Batch time Transport number Internal energy Fluid flow rate Fluid velocity Axial fluid velocity... 

The computed turbulent axial and radial normal stresses and shear stresses increase with increasing superficial gas velocity. Axial normal stresses are considerably higher than their radial counterpart and both exceed Reynolds shear stresses. The maximum in Reynolds shear stress increases remarkably as the gas velocity is raised from 6 cm/s to 10 cm/s and its location is in the neighborhood of the inversion point for the axial velocity profile. 

The structure of airflow inside the nozzle depends on the following factors angle at which air enters into the nozzle (or axial angle of air inlets), channel diameter (or yam channel diameter) and air pressure. From the simulation, airflow pattern, components of air velocity (axial, tangential and resultant) at different normal planes for various nozzles were obtained [1]. To get air velocity profiles on different normal planes of nozzles, various sections of the nozzle were considered at a distance of 1 mm, along the axis of the nozzle, details of which are described in Rengasamy et al. [13]. 

For our present purpose it is convenient to reformulate equation (4.11) as a condition on the mass mean velocity. Let us write the mean axial components of molecular velocities in the form... 

Eor a linear system f (c) = if, so the wave velocity becomes independent of concentration and, in the absence of dispersive effects such as mass transfer resistance or axial mixing, a concentration perturbation propagates without changing its shape. The propagation velocity is inversely dependent on the adsorption equiUbrium constant. 

For hquid systems v is approximately independent of velocity, so that a plot of JT versus v provides a convenient method of determining both the axial dispersion and mass transfer resistance. For vapor-phase systems at low Reynolds numbers is approximately constant since dispersion is determined mainly by molecular diffusion. It is therefore more convenient to plot H./v versus 1/, which yields as the slope and the mass transfer resistance as the intercept. Examples of such plots are shown in Figure 16. 

Fan Rating. Axial fans have the capabiUty to do work, ie, static pressure capabiUty, based on their diameter, tip speed, number of blades, and width of blades. A typical fan used in the petrochemical industry has four blades, operates neat 61 m/s tip speed, and can operate against 248.8 Pa (1 in. H2O). A typical performance curve is shown in Figure 11 where both total pressure and velocity pressure are shown, but not static pressure. However, total pressure minus velocity pressure equals static pressure. Velocity pressure is the work done just to collect the air in front of the fan inlet and propel it into the fan throat. No useflil work is done but work is expended. This is called a parasitic loss and must be accounted for when determining power requirements. Some manufacturers fan curves only show pressure capabiUty in terms of static pressure vs flow rate, ignoring the velocity pressure requirement. This can lead to grossly underestimating power requirements. 

Fig. 7. Axial density profiles in the (—) bubbling, (------) turbulent, and (----) fast and ( ) riser circulating fluidization regimes. Typical gas velocities for...

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