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Bubble holdup

In some way, introducing an increased particle drag by means of Eq. (17) resembles the earlier proposal raised by Bakker and Van den Akker (1994b) to increase viscosity in the particle Reynolds number due to turbulence (in agreement with the very old conclusion due to Boussinesq, see Frisch, 1995) with the view of increasing the particle drag coefficient and eventually the bubble holdup in the vessel. Lane et al. (2000) compared the two approaches for an aerated stirred vessel and found neither proposal to yield a correct spatial gas distribution. [Pg.196]

In spite of all the simplifications Bakker and Van den Akker applied and given the black box approach for the impeller swept domain, their simulations resulted in values for the bubble size just below the liquid surface, overall holdup, and average kfl values which are in good agreement with their experimental data (see Table II). The major step forward they made was the acquisition of the different spatial distributions of average bubble size (see Fig. 13), bubble holdup and kfl as effected by three common impeller types. As a matter of fact, their approach may be restricted to low values of the gas hold-up. [Pg.205]

An empirical relationship was introduced to relate the bubble holdup with the superficial gas velocity uq-... [Pg.472]

Figure 1. Parity Plot for Correlation of Small Bubble Holdup,... Figure 1. Parity Plot for Correlation of Small Bubble Holdup,...
The lateral distributions of bubble holdup in fluid beds are very similar to those of bubble columns for gas-liquid systems. Experimental results by Akehata et al. (A2), Pozin et al. (P6), Ivanov and Bykov (112), Yamagoshi (Y2), Miyauchi and Shyu (M31), Hills (H9), Kato et al. (K7) and Ueyama and Miyauchi (U3) are reasonably well expressed by Eq. (2-13). When a gas phase is distributed with a perforated plate or a nozzle sparger, the parameters in Eq. (2-13) for the bubble columns are in the range of n = 1.7-2.5. [Pg.301]

Several investigations have been made on the flow characteristics in multistaged fluid beds. Nishinaka et al. (N6, N8, N9) have measured the average bubble holdup, the lateral distribution of bubble holdup, and the longitudinal dispersion of solid particles in four- and eight-stage fluid beds installed with various horizontal baffles. As shown in Fig. 25 the average bubble holdup (except for beds baffled with tube plates) is correlated by the equation of Nishinaka et al., (N8) ... [Pg.308]

Fig. 25. Correlation of average gas bubble holdup in free and baffled fluid beds (N8). Fig. 25. Correlation of average gas bubble holdup in free and baffled fluid beds (N8).
The bubble holdup Cb for a bubble column or for a fluidized bed is easily obtained as a function of superficial gas velocity Uq. Useful information... [Pg.340]

In recent detailed studies of bubble columns, separate equations have been proposed for the small-bubble holdup and the holdup of large bubbles, which form above a critical gas velocity [13]. This is a more fundamental... [Pg.292]

Letzel HM, Schouten JC, van den Bleek CM, Krishna R. (1998) Influence of gas density on the large-bubble holdup in bubble coluum reactors. AICHEJ, 44 2333-2336. [Pg.500]

Figure 4.23 Effect of gas extraction and addition on (A) equivalent bubble diameter as a function of the bed height, (B) vertical bubble velocity as a function of the bubble diameter, (C) average bubble diameter as a function of the lateral position, and (D) bubble holdup as a function of the bed height. Data are shown for the series with constant background fluidization velocity. Reprinted from De Jong et al. (2011) with permission from Elsevier. Figure 4.23 Effect of gas extraction and addition on (A) equivalent bubble diameter as a function of the bed height, (B) vertical bubble velocity as a function of the bubble diameter, (C) average bubble diameter as a function of the lateral position, and (D) bubble holdup as a function of the bed height. Data are shown for the series with constant background fluidization velocity. Reprinted from De Jong et al. (2011) with permission from Elsevier.
The bubble rise velocity (Fig. 4.23B) as a function of the equivalent bubble diameter appears to be quite similar for all cases. The graphs of the lateral profile of the equivalent bubble diameter and the axial profile of the bubble holdup (Fig. 4.23C and D) provide more insight into the bubble behavior. [Pg.211]

For bubble columns there is an extensive literature that gives a host of experimental information, particularly on the bubble holdup and the mean bubble diameter. Many authors have attempted to correlate these with process parameters, such as the gas flow rate and the reactor dimensions, and with the physical properties of the system. It appears to be extremely difficult to incorporate all relevant physical properties in correlations that are generally applicable. [Pg.101]

The dependent variables are the bubble holdup e and the Eotvos number E 6 ... [Pg.102]

The bubble holdup follows from the total number of bubbles present in the liquid, and their diameter. The number of bubbles is determined by the gas flow rate, and by the average rising velocity of the bubbles, that is again a function of their diameter. However, the mean diamater is also determined by coalescence, that will increase with bubble holdup. This shows that both parameters are related in a complicated way. It follows from experimental work that the bubble holdup is simpler to correlate with various parameters than is the bubble diameter. Moreover, the measurement of the bubble holdup is simpler and more direct than the measurement of the mean bubble diameter, so that the results are generally more accurate. [Pg.102]

The constant is approximately 0.2 for pure liquids and 0.25 for electrolyte solutions. For high gas flow rates, eq. (4.55) predicts bubble holdups that are not quite so high as those predicted by eq. (4.54). Also, the gas holdup would be less sensitive to the surface tension and the viscosity of the liquid, than according to... [Pg.102]

These correlations were checked for atmospheric pressures only. Later it was found that the bubble holdup increases with gas density, for a given value of u see Wilkinson and Van Dierendonck (1990), Oyevaar and Westerterp (1991). Li a more recent publication, Krishna et al. (1991) propose the concept of the transition gas flow rate w indicated above. It is a function of a large number of physical properties, and can be determined experimentally for any given system. The bubble holdup is then a simple function of u and w ... [Pg.103]

Figure 4.11. The bubble holdup versus the superficial gas flow rate, for three values of the transition gas flow rate u = 0.015, 0.05 and 0,10 m/s,... Figure 4.11. The bubble holdup versus the superficial gas flow rate, for three values of the transition gas flow rate u = 0.015, 0.05 and 0,10 m/s,...
TTie best way to measure surface areas is by using rapid chemical reactions with known kinetics, that take place in a very thin zone close to the interface. Since the rate is proportional to the surface area, the latter can be calculated from rate measurements. The relevant principles are presented in section 5,42J. Surface areas can also be calculated from measured values of the bubble holdup and the mean bubble diameter, according to eq. (4.51). From the two empirical relations by Van Dierendonck (1970), eqs. (4.54) and (4.57), a third can be derived, giving the specific interfacial area a for solutions of electrolytes and liquid mixtures ... [Pg.104]

Considering the nature of the bubble behaviour, one would expect that the specific surface area a could be related to the superficial gas flow rate very much as the bubble holdup, as expressed by eqs. (4.56a) and (4.56b) ... [Pg.104]

This type of reactor consists of two parts, that are essentially different. In the venturi tube, a very effective gas/liquid dispersion is obtained, with unusually Itigh values of bubble holdup, specific surface area and volumetric mass transfer coefficients. However, its volume is small. In the tank itself, considerable coalescence will occur, but the volume is of course much larger. Both zones are effective with respect to mass transfer. In recent papers by Dirix and Van der Wiele (1990) and Cramers et al. (1992), the feasibility of this reactor type, which is still relatively new, is demonstrated convincingly. It follows from these studies, that for large gas/liquid reactors, that require a large surface area despite a relatively low gas flow rate, the venturi-loop reactor compares favourably with a stirred tank. However, for a reliable scale-up of this type of reactor a lot of experimental work has to be done, preferably under realistic conditions. [Pg.109]

The behaviour of the three scaled beds of Table 13.4 turned out to be closely matched when compared in terms of dimensionless variables minimum fluidization flux, bed expansion and bubble holdup all conformed in this respect. The dimensionless pressure fluctuations were also very similar, the best measure being provided by the dimensionless root mean square, pfppi. This is shown in Figure 13.7 as a function of dimensionless fluid flux, Uo/ut. the three matched systems (open symbols) form an essentially single curve sandwiched between those of the two unmatched systems (solid symbols). [Pg.161]

The essential interpretation of the experimental data may be readily appreeiated from the somewhat idealized representation of Figure 14.8 in addition to the dense-phase void fraction Sd, bubble holdup and interstitial gas flow rates may be estimated from this response. [Pg.182]


See other pages where Bubble holdup is mentioned: [Pg.102]    [Pg.531]    [Pg.143]    [Pg.149]    [Pg.289]    [Pg.298]    [Pg.298]    [Pg.298]    [Pg.299]    [Pg.305]    [Pg.337]    [Pg.346]    [Pg.365]    [Pg.436]    [Pg.278]    [Pg.153]    [Pg.169]    [Pg.443]    [Pg.102]    [Pg.104]    [Pg.179]    [Pg.286]   
See also in sourсe #XX -- [ Pg.255 ]

See also in sourсe #XX -- [ Pg.153 ]

See also in sourсe #XX -- [ Pg.95 , Pg.99 , Pg.103 ]




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