Holdup and interfacial area measurements using dynamic gas disengagement

Abstract

The dynamic gas disengagement technique is discussed comprehensively in this paper. Also outlined is the procedure for estimating holdup structures and bubble rise velocities in a bubble column, which is extended to include the methodology for estimating the Sauter mean bubble diameter and therefore the specific gas-liquid interfacial area. The error limits for the estimated quantities are established using two extreme cases to describe the disengagement process: constant rate disengagement and interactive disengagement of bubbles. The analysis is done assuming a bimodal bubble size distribution; however, generalized equations for a multimodal bubble size distribution are also presented. Sensitivity of results to the two cases is illustrated using results obtained from experiments conducted with the air-tap water system in two bubble columns (0.05 and 0.23 m in diameter, 3 m tall). Sauter mean bubble diameters and specific interfacial areas estimated using the two approaches provide lower and upper limits for values reported in the literature.

Engineering Development of Slurry Bubble Column Reactor (Sbcr) Technology

“…If it is assumed that the small bubbles do not disengage in stage one due to the liquid backflow (Model 2), the initial small bubble holdup is simply the gas holdup at t 1 , i.e., at the end of stage one (Vermeer and Krishna, 1981). The other assumption made regarding the disengagement rate of bubbles is that the slip velocity between the gas and the liquid is constant (Patel et al, 1989). In this case, the calculated small-bubble holdup falls in between the values of Model 1 and Model 2.…”

“…The DGD technique was first used in bubble columns at low gas velocities (U g < 2 cm/s) by Sriram and Mann (1977) to quantify the bubble size and size distribution in the columns. Various models that relate gas disengagement phenomena to bubble size or size distribution have been proposed in the literature (Vermeer and Krishna, 1981;Schumpe and Grund, 1986;Patel et al, 1989;Daly et al, 1992). However, the reliability of the DGD technique applied to the slurry bubble columns operated at high pressure and high gas velocity depends on whether the models account for the transient characteristics of bubble flow during the DGD process.…”

Influence of medium composition on oxygen transfer rate in animal cell culture

“…Global value and axial profile of gas holdup are measured using eight non intrusive differential pressure probes P1 -P8 (Keller PR41 and PR25) are respectively located 4.530, 4.043, 3.507, 2.758, 1.756, 1.257,0.751 and 0.200 m above the sparger. P3 is also used to measured the distribution of gas bubble diameters using the gas disengagement technique, which is a method based on a bubble classification as a function of their upwards velocities (Patel et al, 1989). A fast response dissolved oxygen probe (OxyGuard Ocean Probe -DO522M18) is used to measure oxygen transfer rate.…”

Liquid phase fluid dynamic (methanol) run in the LaPorte alternative fuels development unit

“…Many previous researchers have measured these quantities, and some have done so in organic fluids and slurries (e.g. Krishna and Ellenberger, 1996;Wilkinson et al, 1992;Patel et al, 1989, Bukur et al, 1987and O'Dowd et al, 1987), but always in much smaller diameter columns and never under the same operating conditions found in the AFDU. Because of the inability to extend correlations, particularly those for multiphase flows, outside the region for which they were derived, gas holdup must be monitored continuously while the AFDU is operating.…”

“…For a bubbly flow with a homogeneous distribution, one would expect the bubbles to disengage uniformly, leading to a single slope. For churn-turbulent flow, it was shown by Patel et al (1989) that the two bubble classes usually lead to two distinct slopes: an initial steep slope for the large, high velocity gas pockets followed by the gradual slope of the slower moving small bubbles. These two slope regions are distinctly visible in Figure 19 but are not present in Figures 16 through 18.…”