Prediction of Main Regime Transition with Variations of Gas and Liquid Phases in a Bubble Column

Abstract

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.

Novel Identifier of Transitions in Bubble Columns Operated with Water and Aqueous Alcohol Solutions

“…Note that the main transition velocity identified in Fig. 2a is very close to the prediction of Im et al (0.048 m s −1 ) 26. Based on simulations, Wang et al 33 have shown that the transition velocity for an air‐water system is 0.04 m s −1 .…”

“…They used a ring sparger with six legs (star-like cross). It is noteworthy that the second transition velocity U trans-2 is very close to the prediction of another correlation (0.048 m s -1 ) [26].…”

“…Under these conditions the correlation of Reilly et al is applicable 34. On the other hand, when a ring sparger (ERT data) is used, then the main transition velocity U trans‐1 is predictable by the correlation of Im et al 26. These results imply that the semi‐empirical correlations are still not very effective and the experimental determination of the main transition velocities based on new reliable reconstruction methods is the preferable approach in order to avoid serious miscalculations for the FR boundaries.…”

“…The methods without signal reconstruction involve calculation of average absolute deviation (AAD) [2], average cycle time [20], drift flux [26], etc. These simple methods are capable of identifying only the first transition (critical) velocity.…”

Numerical Slug Flow Model of Curved Pipes with Experimental Validation

“…The development of the gas–liquid two-phase flow has been an important research for many years. In the earlier periods, studies of two-phase flow in the vertical pipe were concentrated on the partition of different flow patterns by experiments, and then researchers obtained several steady-state models about pressure, density, and liquid holdup along the pipe. − Later on, some researchers proposed different flow patterns, new flow pattern transition criteria, and new steady-state models to predict liquid holdup and pressure drop, and they conducted experiments to validate these models. − …”