Effect of liquid velocity

Figure 11.9 Effects of liquid velocity and molecular weight on Hs in gel chromatography (dp 44 pm, 1.6x30 cm column).

This effect is demonstrated in Fig. 7.6, in which the effect of liquid velocity is compared for several sensors of different dimensions of the membrane and of the electrode radius. 

The effects of liquid velocity (at least at low velocities), direction of flow and liquid properties are only minor for Newtonian fluids. Correlations on gas-liquid columns are given by Joshi [63], Field and Davidson [64] measured the dispersion in a large industrial column (de - 3.2 m, H — 19 m) and found agreement with the correlations of Dcckwer et al. [65] and Joshi [63] (Tabic 3). The influence of particles can be expected to be small, at least for low concentrations and small particles. This is confirmed by the early experiments of Kato et al. [15, 69], For particle sizes ranging from 63... 

The effect of liquid velocity can be qualitatively explained as follows. In the heterogeneous regime, liquid circulation is developed that is upward in the central region and downward in the annular region. With cocurrent liquid upflow, the downward annular flow is restricted, resulting into a reduction in the liquid circulation. Therefore, the cocurrent liquid flow delays the transition. The countercurrent liquid flow has the opposite effect. 

Figure 6. Effect of liquid velocity on the foam flow resistance.

Having set the factual effects of liquid velocity, gas velocity and particle size on mass transfer coefficients and interfacial area for Hg -=84mm, correlations were attempted for these characteristic parameters by non-linear regression analysis of the experimental results. Empirical correlations in S.I. units,obtained for... 

Figure 2.1.5. Effect of liquid velocity on the efficiency of catalyst utilization for the decotiposition over charcoal (after Koros, R. M. [34]). ...

Figure 2.1.6. Effect of liquid velocity on acetic acid oxidation (after Levee, J. and J. M. Smith [41]). Reproduced by permission of the American Institute of Chemical Engineers.

Figure 2.1.8. Effect of liquid velocity on the apparent reaction rate for a reaction in a fixed bed reactor limited by gas/liquid mass transfer. Hydrogenation of alpha methyl styrene on 2.5% Pd/Al203 (p and 0.75% Pd/Al203 (II). Calculated apparent rate assuming liquid contacting/mass transfer as the only limitations (I, II ) (after Herskowitz, M., R. G. Carbonell and J. M. Smith [24J. Reproduced permission AIChE.

Summarizing then, it has been shown that for at least three reactions, that under strong mass transfer control with a limiting gas phase conponent, liquid mass velocity effects on the global reaction rates showing a minimum can be obtained due to the countering effects of liquid velocity on gas/catalyst and liquid/cata-lyst contacting. 

Some quantification of the model can be accomplished. With respect to the effect of liquid velocities, it can be assumed that the number of particles, n, in a clump will decrease with increasing velocity to the limit of unity for full utilization as shown in Figure 3 2. At low velocities, ng -3-5 based on various tracer study results (Hochman [28], Colombo [10]). On the... 

Effects of Liquid Velocity. When a liquid passing over an aluminum surface exceeds a certain velocity, grooves can be worn in the surface, the probable result of mechanical and chemical action. This phenomenon does not usually occur on aluminum at velocities below 3 m/s (10 ft s). 

---