Bubble diameter column

Figure 8-86. Typical bubble cap tray details 3-ft-O-in. diameter column, 4-in. caps.

Fair [183] relates sieve trays and includes valve tray remarks to the extensive work done for bubble cap trays. Figure 8-137 and 8-139 show flooding data for 24-in. spacing of bubble cap trays from [81] and represents data well for 36-in. diameter columns, and is conservative for smaller columns. Fair s work has been corrected to 20 dynes/ cm surface tension by ... 

The baffle patterns in the column can be segmental (simple) up to about 4-ft diameter column, and larger columns can use a disk and donut design as in heat exchangers, or the double segmented or even multi-segmented as in the layouts discussed under bubble caps earlier in this text. 

The column is designed as an ammonia rectifier-stripper using fundamental design techniques. A 48-in. diameter column will handle at least 500 tons of refrigeration system load for the above temperature range, using 10 bubble cap trays with 32, 4-in. pressed steel caps per tray (slot area = 7.81 in. /cap riser area 4.83 in. /cap 3 ft 0 in. weir length). Tray... 

Bubble column, 69, 149-150, 293-298 Bubble diameter, 28, 42 Butyric acid, 4, 5... 

Example 11.8 With highly reactive absorbents, the mass transfer resistance in the gas phase can be controlling. Determine the number of trays needed to reduce the CO2 concentration in a methane stream from 5% to 100 ppm (by volume), assuming the liquid mass transfer and reaction steps are fast. A 0.9-m diameter column is to be operated at 8 atm and 50°C with a gas feed rate of 0.2m /s. The trays are bubble caps operated with a 0.1-m liquid level. Literature correlations suggest = 0.002 m/s and A, = 20m per square meter of tray area. 

Fig. 2. Simulated positions and shape variations of a rising bubble in a water column. Initial bubble diameter 0.8 cm and time increment 0.05 s.

The simulation results on bubble velocities, bubble shapes, and their fluctuation shown in Fig. 3 are consistent with the existing correlations (Fan and Tsuchiya, 1990) and experimental results obtained in this study. Bubble rise experiments were conducted in a 4 cm x 4 cm Plexiglas bubble column under the same operating conditions as those of the simulations. Air and tap water were used as the gas and liquid phases, respectively. Gas is introduced through a 6 mm nozzle. Note that water contamination would alter the bubble-rise properties in the surface tension dominated regime. In ambient conditions, this regime covers the equivalent bubble diameters from 0.8 to 4mm (Fan and Tsuchiya, 1990). All the air-water experiments and simulations of this study are carried out under the condition where most equivalent bubble diameters exceed... 

Tests have been carried out on the rate of extraction of benzoic acid from a dilute solution in benzene to water, in which the benzene phase was bubbled into the base of a 25 mm diameter column and the water fed to the top of the column. The rate of mass transfer was measured during the formation of the bubbles in the water phase and during the rise of the bubbles up the column. For conditions where the drop volume was 0.12 cm3 and the velocity of rise 12.5 cm/s, the value of Kw for the period of drop formation was 0.000075 kmol/s m2 (kmol/m3), and for the period of rise 0.000046 kmol/s m2 (kmol/s m3). 

Bubble-cap columns or sieve trays, of similar construction to those described in Chapter 11 on distillation, are sometimes used for gas absorption, particularly when the load is more than can be handled in a packed tower of about 1 m diameter and when there is any... 

Compared to packed columns, open-tubular columns have no bubble formation problems because end-frits are not needed, small internal diameter columns are used, and the stationary phase is homogeneous. The column length can also be easily shortened. Excellent mass sensitivity can be achieved by using capillaries with smaller inner diameters. The EOF in an open-tubular column is higher than that in a packed column because a greater... 

For bubble columns, the Akita-Yoshida equation can be used for determining of bubble diameter (Shall et al., 1982 Koide, 1996) ... 

A 30 cm-diameter bubble column containing water (clear liquid height 2 m) is aerated at a flow rate of 10 m h . Estimate the volumetric coefficient of oxygen transfer and the average bubble diameter. The values of water viscosity = 0.001 kg m s , density p = 1000 kgm , and surface tension cr = 75 dyne cm" can be used. The oxygen diffusivity in water is 2.10 X 10 ... 

Ozturk et al. (1987) developed a new correlation on the basis of a modification of the Akita-Yoshida correlation suggested by Nakanoh and Yoshida (1980). In addition, the bubble diameter db rather than the column diameter was used as the characteristic length as the column diameter has little influence on The value of db was assumed to be approximately constant (db = 0.003 m). The correlation was obtained by nonlinear regression is as follows ... 

Because of the flow resistance of the caps and risers in bubble-cap columns, there is a decrease in liquid depth as the liquid passes across the tray. Figure 16-4 shows an extreme example in which this liquid gradient is so great that only one out of the form bubble caps is operating normally. In general, the dimensionless ratio of total liquid gradient to pressure-drop head caused by the bubble-cap assembly should be less than 0.4 in order to ensure adequate vapor distribution, and, for single-pass crossflow trays, the rate of liquid flow across the tray should be less than 0.22 ft3/(sXft) diameter. 

Roy, et al (2 ) empirically determined the gas velocity needed to completely suspend a given amount of solid in a 5 cm id x 1.52 m Lucite column using coal and quartz slurried in water, alcohol, or oil. The degree of suspension was found to depend on physical properties as well as gas holdup, volume fraction, bubble diameter, and the contact angle between the solid and liquid. 

The gas, solid, and liquid phases used in this study were nitrogen, glass beads, and either water, silicone oil, ethylene glycol, or aqueous ethanol, respectively. Two densities of solids were used (2420 or 3990 kg/m ) and three narrow particle size fractions having particle sizes of 48.5 ym, 96.5 ym, and 194 ym. Engineering parameters obtained from the gas-phase measurements include bubble area per unit volume of column and bubble diameter distribution. 

Gas absorption is a function of the gas and liquid mass transfer coefficients, the interfacial area, and the enhancement due to chemical reaction. The gas-liquid interfacial area is related to the Sauter mean bubble diameter and the gas holdup fraction. The gas holdup fraction has been reported to vary with radial position (7-11) for column internal diameters up to 0.6 m. Koide et al" Tl2), however, found that the radial distribution of gas holdup was nearly constant for a column diameter of 5.5 m. Axial distribution of average gas holdup has been reported by Ueyama et al. (10). The average gas holdup... 

Radial distributions of bubble diameters in a bubble column have been reported for column diameters up to 5.5 m (12). In all cases, the bubble size increased from the wall to the center of the column. The axial distribution of bubble diameters in bubble columns has only been reported by a few investigators ( 7, 10). Rigby et al. (7) observed that the average bubble length increased with axial position, whereas Ueyama et al. (10) did not observe a significant change in bubble diameter with axial position. 

The conductivity probe technique has been applied successfully to gas-phase measurements in a slurry bubble column. The presence of solids does not appreciably change the gas-phase characteristics for a volume fraction of solids less than 5 percent. The radial distribution functions of gas holdup and interfacial area increase significantly from the wall to the center of the column. The average Sauter mean bubble diameter is greater than the Sauter mean bubble diameter measured near the wall. 

Table III. Effect of Small Bubble Diameter Value on Predicted Conversions for a Column Length of 2.36 m...

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