Industrial bubble
columns mainly operate in a heterogeneous flow regime and identifying
transition from homogeneous to heterogeneous flow is important. This
work addresses the determination of flow regimes with gas–liquid
systems in a bubble column. Various parameters of gas holdup, volumetric
mass transfer coefficient, drift flux, and pressure standard deviations
were investigated to precisely determine the superficial gas velocity
at the transition regime. For a column aspect ratio (
H
/
D
: static liquid height to column diameter ratio)
of 2.5 to 5, the transitional superficial gas velocity generally became
higher with lower liquid height. However, the reverse trend was observed
with a low density gas system due to the difference in force balance
acting around the bubble. The weak body force and drag force in a
lower axial position interrupted the mass transfer process. The experimental
results showed similar ranges of the transitional superficial gas
velocity regardless of the choice of parameter for detecting it. Because
there is no precise correlation about transition regime properties,
we proposed new correlations to predict both transition regime superficial
gas velocity and gas holdup by taking the intersection of the two
regimes. The correlations precisely captured the transition regime
properties within 15% deviations even in gas–liquid systems
that are not tested in this work.
This work addressed liquid−liquid mass transfer for actual industrial conditions of high pH with coexisting salt. The Sauter mean diameter was determined from the direct measurement of a chlorobenzene droplet size using a borescope system. At a high NaOH concentration, the droplet size decreased significantly due to the reduced density difference between two phases, and it further decreased when NaOH and NaCl coexisted. A Sauter mean diameter correlation with a density difference term was proposed, and it successfully predicted the experimental results. To determine the mass transfer coefficient, the solubility and the concentration gradient of chlorobenzene in the aqueous phase were measured under various conditions. As the NaOH and NaCl concentration increased, the solubility of chlorobenzene and the rate of change of chlorobenzene concentration in the aqueous phase both decreased, but the decrease in solubility was more pronounced. Thus, the mass transfer coefficient increased with the NaOH and NaCl concentration.
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