Dynamic gas disengagement

S.A. Patel, J.G. Daly, D.B. Bukur, Holdup and interfacial area measurements using dynamic gas disengagement, AIChE J. 35 (1989) 931-942. 

The key parameters in this model are the fractional gas holdups due to the large and small bubbles, the bubble rise velocities, and the bubble diameters. The fractional gas holdup structure due to different size bubbles has been determined by a number of investigators (3, 5 ) using the dynamic gas disengagement technique. This technique involves the measurement of the rate of drop in the dispersion height when the gas supply is instantly shut off ( 8 ) The following systems have been studied air-water (9 ), air-Soltrol-130 (a mixture of... 

Gas holdup can be measured by numerous invasive or noninvasive techniques, which have been reviewed by Kumar et al. (1997) and Boyer et al. (2002), and include changes in total bed expansion upon gassing, pressure drop measurements, dynamic gas disengagement (DGD), and tomographic techniques. 

Dynamic Gas Disengagement (DGD). DGD abruptly stops the aeration process in a gas-liquid or gas-Uquid-solid bioreactor and then records the liquid level or pressure at different locations as a function of time (Daly et al., 1992 Deshpande et al., 1995 Fransolet et al., 2005 Patel et al., 1989 Schumpe and... 

Figure 4.1 Sample data from a dynamic gas disengagement experiment (Krishna and Ellenberger, 1996).

Daly, J.G., Patel, S.A., and Bukur, D.B. (1992), Measurement of gas holdups and Sauter mean bubble diameters in bubble column reactors by dynamic gas disengagement... 

Fransolet, E., Crine, M., Marchot, P, and Toye, D. (2005), Analysis of gas holdup in bubble columns with non-Newtonian fluid using electrical resistance tomography and dynamic gas disengagement technique, Chemical Engineering Science, 60 6118-6123. 

Sriram, K., andMann, R. (1977), Dynamic gas disengagement A new technique for assessing the behavior of bubble columns, Chemical Engineering Science, 32 571-580. 

The gas holdup in slurry bubble columns at high pressures was also investigated by some researchers (Deckwer et al., 1980 Kojima et al., 1991 Daly et al., 1995 Inga, 1997 Luo et al., 1999). A dynamic gas disengagement technique has been proven suitable for the measurement of gas holdup in a slurry bubble column under high-pressure conditions (Luo et al., 1999). The pressure effect on the gas holdup in slurry bubble columns is similar to that in bubble columns. Elevated pressures lead to higher gas holdups in a slurry bubble column. The presence of particles reduces the gas holdup at both ambient and elevated pressures as shown in Fig. 15. An empirical correlation was obtained to estimate the gas holdup in high-pressure slurry bubble columns as... 

The existence of different bubble classes in churn-turbulent flow can be shown easily by dynamic gas disengagement measurements. Simplified evaluation of such measurements yields a splitting of the bubble phase into two bubble classes, i.e., one class of small bubbles with low rise velocity and another class of large bubbles with high rise velocity. Two bubble classes with such properties were also the starting point of a BCR model proposed by Joseph and Shah [41]. Experimental techniques and devices are now available to measure the entire bubble spectrum with regard to size and rise velocity. This information could form the basis of more realistic models of the gas phase flow in BCR. 

The method of dynamic gas disengagement (Sriram and Mann, 1977 Patel et al., 1989) to obtain an estimate of bubble size distribution is worthy of mention since it is convenient to use, sometimes even in real systems, especially for lower gas fractions. The impeller is stopped and the trend in the level measured against time. This trend indicates the bubble size distribution if terminal rise velocities are known and if coalescence is negligible. 

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