Superficial phases velocities

In extraction column design, the model equations are normally expressed in terms of superficial phase velocities, L and G, based on unit cross-sectional area. The volume of any stage in the column is then A H, where A is the cross-sectional area of the column. Thus the volume occupied by the total dispersed phase is h A H, where h is the fractional holdup of dispersed phase, i.e., the droplet volume in the stage, divided by the total volume of the stage and the volume occupied by the continuous phase, in the stage, is (1-h) A H. 

Eddy dispersion coefficient Inverse residence time Inverse dispersion time Fractional phase holdup Superficial phase velocity... 

The phase saturation, Si, and the superficial phase velocity, tq, are used to characterize the volume fraction and flow velocity of the aqueous phase (1 = w) and of the oleic phase (1 = o). The net rate particle loss of species i in phase 1 is accounted for by the term (dait T/dt). The particle loss can be classified further particle loss due to deposition or re-entrainment (aiy d), particle loss due to pore throat blocking (transfer from one fluid phase to the next ([Pg.366]

Thus, experimental data of superficial phases velocities along the SS/SW transitional boundary can be used to extract the dynamic coefficient for a variety of two-fluid systems, tube diameters, and operational conditions. 

Fig. 8. (a) Schematic for an FCC unit showing where the various fluidization regimes are found and (b) a corresponding phase diagram for Group A powder (FCC catalyst) where the numbers on the curves represent the superficial soHd velocity in m/s. A represents the bubbling regime B, the turbulent ... 

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

Fluidized This is an expanded condition in which the sohds particles are supported by drag forces caused by the gas phase passing through the interstices among the particles at some critical velocity. It is an unstable condition in that the superficial gas velocity upward is less than the terminal setting velocity of the solids particles the gas... 

Mechanical agitation is needed to break up the gas bubbles but must avoid rupturing the cells. The disk turbine with radial action is most suitable. It can tolerate a superficial gas velocity up to 120 m/h. (394 ft/h) without flooding, whereas the propeller is limited to about 20 i7i/h (66 ft/h). When flooding occurs, the impeller is working in a gas phase and cannot assist the transfer of gas to the liquid phase. Power input by agitation and air sparger is 1 to 4 W/L (97 to 387 Btu/[fF-h]) of liquid. 

Siemes and Weiss (SI4) investigated axial mixing of the liquid phase in a two-phase bubble-column with no net liquid flow. Column diameter was 42 mm and the height of the liquid layer 1400 mm at zero gas flow. Water and air were the fluid media. The experiments were carried out by the injection of a pulse of electrolyte solution at one position in the bed and measurement of the concentration as a function of time at another position. The mixing phenomenon was treated mathematically as a diffusion process. Diffusion coefficients increased markedly with increasing gas velocity, from about 2 cm2/sec at a superficial gas velocity of 1 cm/sec to from 30 to 70 cm2/sec at a velocity of 7 cm/sec. The diffusion coefficient also varied with bubble size, and thus, because of coalescence, with distance from the gas distributor. 

Two-phase flow pattern maps, observed by Revellin et al. (2006), are presented in Fig. 2.31 in mass flux versus vapor quality, and superficial liquid velocity versus superficial vapor velocity formats calculated from the test results as follows ... 

Zhao and Bi (2001b) measured pressure drop in triangular conventional size channels d = 0.866—2.866 mm). The variations of the measured two-phase frictional multiplier with the Martinelli parameter X for the three miniature triangular channels used in experiments are displayed, respectively, in Fig. 5.29a-c. In Fig. 5.29 also shown are the curves predicted by Eq. (5.25) for C = 5 and C = 20. It is evident from Fig. 5.29 that the experimental data are reasonably predicted by the Lockhart-Martinelli correlation, reflected by the fact that all the data largely fall between the curves for C = 5 and C = 20, except for the case at very low superficial liquid velocities. 

Ghajar et al. (2004) studied heat transfer of two-phase flow in a horizontal tube of d = 25.4 mm and reported that the effect of superficial gas velocity on heat transfer depended on flow pattern and showed its own distinguished trend (Fig. 5.44). 

For the sake of developing commercial reactors with high performance for direct synthesis of DME process, a novel circulating slurry bed reactor was developed. The reactor consists of a riser, down-comer, gas-liquid separator, gas distributor and specially designed internals for mass transfer and heat removal intensification [3], Due to density difference between the riser and down-comer, the slurry phase is eirculated in the reactor. A fairly good flow structure can be obtained and the heat and mass transfer can be intensified even at a relatively low superficial gas velocity. 

The reactor, in which the gas phase will be virtually pure hydrogen, will operate under a pressure of 2 MN/m2 (20 bar). The catalyst will consist of porous spherical particles 3 mm in diameter, and the voidage, that is the fraction of bed occupied by gas plus liquid, will be 0.4. The diameter of the bed will be such that the superficial liquid velocity will be 0.002 m/s. The concentration of the aniline in the liquid feed will be 0.055 kmol/m3. 

Superelectrons, 23 819-820 Superfibers, 24 624 Superficial filtering velocity, 26 710 Superficial velocity, 11 766 Superfilling, 9 774 Superfinishing stones, 1 19 Superflex catalytic cracking butylenes manufacture, 4 417 Superfluid helium, 17 353-354 Superfluid phases, of helium-3,17 354-355 Superfluids, 17 352-354 Superfractionation, 23 333-334 Superfund Amendments and... 

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