Velocity limiting liquid

Limit liquid velocity to minimize static buildup... 

For air and water, in a one inch tube, the superficial gas velocity limits for the film suspension region were about 31 ft./sec. to 41 ft./sec. (see Fig. 10 also). The value of 31 ft./sec. agrees with the value to be expected for the critical gas flooding velocity at zero liquid flow from an extrapolation of the results of Nicklin and Davidson. Hence, the approach of the latter workers in their analysis of unstable slug flow would seem to be valid for net liquid flows down to zero. 

Fig. 10. Correlation of film thickness with gas and liquid flow rates for air-water system in vertical flow, according to Zhivaikin (Zl). 1, 2 limits for onset of entrainment in downward and upward flow, respectively. 3, 3 limits for small effect of gas velocity on liquid flow (smooth wetted wall operation). 4, 4 region of film suspension. 5 limit for existence of film flow.

Various empirical correlations are available for the limiting liquid velocity, but there is poor agreement among them. One of these correlations, compared with published FRI data, appears to be reliable ... 

In order to select the pipe size, the pressure loss is calculated and velocity limitations are established. The most important equations for calculation of pressure drop for single-phase (liquid or vapor) Newtonian fluids (viscosity independent of the rate of shear) are those for the determination of the Reynolds number, and the head loss, -(16—18). 

Fig. 4 General solution for the dispersion equation on water at 25 °C. The damping coefficient a vs. the real capillary wave frequency o> , for isopleths of constant dynamic dilation elasticity ed (solid radial curves), and dilational viscosity k (dashed circular curves). The plot was generated for a reference subphase at k = 32431 m 1, ad = 71.97 mN m-1, /i = 0mNsm 1, p = 997.0kgm 3, jj = 0.894mPas and g = 9.80ms 2. The limits correspond to I = Pure Liquid Limit, II = Maximum Velocity Limit for a Purely Elastic Surface Film, III = Maximum Damping Coefficient for the same, IV = Minimum Velocity Limit, V = Surface Film with an Infinite Lateral Modulus and VI = Maximum Damping Coefficient for a Perfectly Viscous Surface Film...

Liquid Type of line Optimum pressure gradient, ( Pm)opt. Pa/ Ti Velocity limit, m/s... 

The results showed that the activity is improved by increasing the linear velocities and liquid-to-gas ratios. The absence of internal diffusion limitations was checked by means of the Weisz-Prater criterion. It appeared that internal gradients were negligible. 

Flow direction considerations for liquid systems are somewhat different than those for vapor flow. In liquid or dense-phase flow the buoyancy force of the Uquid must be considered as well as the pressure drop. During upflow adsorption, the flow velocity should be low so as to not cause bed expansion (fluidization). As the flowrate exceeds this limit, the pressure drop increase is small with increasing velocity. Sometimes liquid systems are designed with some bed expansion (10% at the most) when it is desirable to limit pressure drop. Upflow is preferred if the liquid contains any suspended solids, so that the bed will not become plugged. 

As Ihe inlet velocity is increased from very low values, the separation efficiency rapidly increases to a meximum in the 80-120 fl/s range. At higher velocities, the liquid on the wall can be re-entrained by gas shear into the rotating gas vortex, and the separation efficiency drops significantly. The design limitation should be on (he besis of gas shear which is proportkranl to pc - where pc is the gas density (in and V, is the inlet velocity (in ii/s) should be less than 1000. 

In summery, the downcomer can limit column capacity when liquid flow rains are high, as in absorbers and pressure fractionators. Two viewpoints are used (and these ate not necessarily independent of each other) height of froth baildup in the downcomer, obtained from a pressure balance, and residence time in the downcomer, obtained from an entrainment velocity limitation. When the downcomer backs up liquid, the vapor entrains more liquid, and a flooding condition can be approached. 

Thus, a string orifice is characterized by two critical velocities. The first critical velocity limits the size of drops being captured, and is found from the condition Scr = 0.25. The second critical velocity corresponds to the beginning of a secondary ablation of drops from the surface of the liquid film that is formed on strings. We can estimate the value of the second critical velocity. 

Area IV at CC, the upper loading limit of the packing flooding point, flood limit), liquids stow, change of phase distribution, with a further increase of the gas velocity blowing out of liquid... 

There are two capacity limits related to liquid loading, which are the downcomer baekup limit and downcomer veloeity limit. The downcomer backup limit is set at 80% of liquid settling height based on the froth level. The downcomer velocity limit is 75% of maximum velocity allowed to avoid downeomer choke. The number of tray passes is the most important parameter affeeting the downcomer loading and thus these two downcomer limits. 

Step 1 Determine capacity limits for spray, tray flooding, downcomer backup, downcomer velocity, weeping, liquid rates, and so on. 

Centrifugal separators have lower separation efficiency than vane separators. They must be provided with a trap device for liquid collection, and have a limited liquid handling capacity. Line-type units can be operated with velocities as low as 30 ft/sec without significant loss In separation efficiency. 

These reactor studies showed that trickle bed reactors operating with limiting liquid phase reactants may exhibit mass velocity sensitivities. These sensitivities are a function of the nature of the reaction, catalyst size and the reactor tube to catalyst size ratio. 

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