Flow deceleration

Prokunin AN23,24). Flow deceleration effect. Two maxima in dependencies of force upon time undercoditions of x = const and respective flow deceleration (which... 

Current density. Figure 4.16 shows the current density distribution at the an-ode/electrolyte interface. The current density is not uniform, as it is affected by the hydrogen and oxygen distributions and by the electrolyte resistance which is, in turn, dependent on the temperature. Because of the previously discussed reasons, as emphasized in Figure 4.17 where a 2D representation is shown, the produced current is smaller under the ribs than elsewhere. Furthermore, around the ribs, it is possible to observe that the produced current is characterized by a local increase. This effect is related to the local flow deceleration which, in turn, causes a local increase in the species concentrations together with a greater species diffusion perpendicular to the cell plane. 

Here is the actual water depth at the location (x,y). A characteristic feature of the water flows is the presence of the free water surface which varies at different points of the flow plan. It is higher in the zones of flow deceleration and lower in the free... 

If a gas or air current passes along a furnace wall or load surfaces, it is retarded by both viscosity and turbulence. The retardation due to turbulence grows with the roughness of the surface of the wall. By the law of conservation of momentum, flow deceleration causes a rise in pressure. 

A physical picture of what happens to the solids in a gas-solid flow system as they approach and leave a bend is of interest. Assuming the overall flow to be at steady state, as the gas-solid flow approaches a bend the solid and gas flows decelerate. The solid and gas velocities will go to zero if they collide directly with the perpendicular surface of a right-angle turn. Undoubtedly, deflections of the solid particles take place that do not allow the solid velocity go to zero. If the bend is less than 90°, then the degree of deceleration decreases as the angle decreases. Mason and Smith (1972) have provided some interesting photographs of gas-solid flow in bends that show the... 

Coriolis-Type Flow Meters. In CorioHs-type flow meters the fluid passes through a flow tube being electromechanically vibrated at its natural frequency. The fluid is first accelerated as it moves toward the point of peak vibration ampHtude and is then decelerated as it moves from the point of peak ampHtude. This creates a force on the inlet side of the tube in resistance to the acceleration and an opposite force on the outlet side resisting the deceleration. The result of these forces is an angular deflection or twisting of the flow tube that is directly proportional to the mass flow rate through the tube. 

Equation 26 is accurate only when the Hquids rotate at the same angular velocity as the bowl. As the Hquids move radially inward or outward these must be accelerated or decelerated as needed to maintain soHd-body rotation. The radius of the interface, r, is also affected by the radial height of the Hquid crest as it passes over the discharge dams, and these crests must be considered at higher flow rates. 

Droplet Dispersion. The primary feature of the dispersed flow regime is that the spray contains generally spherical droplets. In most practical sprays, the volume fraction of the Hquid droplets in the dispersed region is relatively small compared with the continuous gas phase. Depending on the gas-phase conditions, Hquid droplets can encounter acceleration, deceleration, coUision, coalescence, evaporation, and secondary breakup during thein evolution. Through droplet and gas-phase interaction, turbulence plays a significant role in the redistribution of droplets and spray characteristics. 

Water Hammer When hquid flowing in a pipe is suddenly decelerated to zero velocity by a fast-closing valve, a pressure wave propagates upstream to the pipe inlet, where it is reflected a pounding of the hne commonly known as water hammer is often produced. For an instantaneous flow stoppage of a truly incompressible fluid in an inelastic pipe, the pressure rise would be infinite. Finite compressibility of the flmd and elasticity of the pipe limit the pressure rise to a finite value. The Joukowstd formula gives the maximum pressure... 

Closure at the instant of reversal of flow is most nearly attained in these valves. This timing of closure is not the whole solution to noise and shock at check valves. For example, if cessation of pressure at the inlet of a valve produces flashing of the decelerating stream downstream from the valve or if stoppage of flow is caused By a sudden closure of a valve some distance downstream from the check valve and the stoppage is followed by returning water hammer, slower closure may be necessary. For these applications, tilting-disk check valves are equipped with external dashpots. They are also available with low-cost insert Dodies. 

Pressure drop during condensation inside horizontal tubes can be computed by using the correlations for two-phase flow given in Sec. 6 and neglec ting the pressure recoveiy due to deceleration of the flow. 

Diffusion-blading loss. This loss develops because of negative velocity gradients in the boundary layer. Deceleration of the flow increases the boundary layer and gives rise to separation of the flow. The adverse pressure gradient that a compressor normally works against increases the chances of separation and causes significant loss. 

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