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. 2019 Jan 16;4(1):1329–1343. doi: 10.1021/acsomega.8b02657

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

Hanjin Im 1, Jeil Park 1, Jae W Lee 1,*
PMCID: PMC6648151  PMID: 31459402

Abstract

graphic file with name ao-2018-026575_0017.jpg

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.

1. Introduction

The bubble column is an important gas–liquid contactor. It has been widely applied, such as in the petrochemical and mineral processing industries as well as in biomass production, because of their superior mass and heat transfer, simple construction, and flexible operation under various reaction conditions.1−6 A bubble column consists of a main body column and a gas sparger at the bottom of the column. Gas is distributed through the gas sparger, and gas–liquid flow development occurs upon introduction to the column. The bubble column can be operated in batch, semibatch, or continuous modes. In our work, batch operation of bubble column was analyzed. There are two types of flow regimes in the bubble column operation: homogeneous and heterogeneous.7,8 In the homogeneous flow regime, each bubble is uniformly distributed, and the uniform rise in velocity of each bubble results in limited frequencies of bubble coalescence.9 This flow regime is usually observed at a low superficial gas velocity. The homogeneous flow regime can be classified into monodispersed homogeneous and pseudohomogeneous flow regimes.10,11 The former has a flat local void fraction and the latter has a center-peaked bubble size distribution. At a higher superficial gas velocity, the flow regime shifts to the heterogeneous flow regime (or churn-turbulent flow). In that regime, there is an improved turbulent motion of gas bubbles. Higher gas input and the vigorous mixing of gas bubbles induce repeated bubble coalescence in the column. There is a considerable population of large bubbles, and so a wide distribution of bubble size is observed. Therefore, in the homogeneous regime, a uniform size of smaller bubbles can be observed, whereas larger bubbles are obtained in the heterogeneous regime.

Understanding the range of transition regimes is important in operating bubble columns with various liquid and gas phases because the mass transfer behavior between homogeneous and heterogeneous flow is considerably different. The region of the transition regime depends on the column dimension, sparger design, and gas–liquid properties. Previous work reported that both the column diameter and column height affect the transitional superficial gas velocity.12−14 It was demonstrated that the column diameter has an effect on gas holdup for the column diameter column smaller than 0.15 m.15 For the column with a column diameter greater than 0.2 m and a column height greater than 2.2 m, the aspect ratio of height to diameter does not affect the gas holdup.16 Therefore, the aspect ratio with a smaller diameter or height than these is important in observing the transitional superficial gas velocity. The effect of gas–liquid property on the transitional superficial gas velocity was also studied. It was understood that the higher viscosity of liquid phase hinders the homogeneous regime stability and reduces the gas holdup.17−19

A number of methods have been used in determining the transition regime point. The gas holdup profile can be one of the determining parameters because the trend of gas holdup profiles differs between the two flow regimes along the superficial gas velocity.20 The concept of drift flux, which can be derived with gas holdup and superficial gas velocity, can also predict the transition point.21 A specific band (3–5 Hz) is used as evidence of the incipient transition regime in the spectral analysis method based on the Fourier transform.22−24 In addition, a fractal method utilizing cyclic slow and rapid stochastic phenomena was applied to determine the flow regime transition.23,25

Although there have been general studies on the transitional superficial gas velocity, no definitive answer has been given to this problem specifically when the gas–liquid phases and the aspect ratio vary. Previous studies developed a model to predict the gas holdup at the transition regime using small bubble velocity.26,27 By calculating two parameters in their models, the transitional superficial gas velocity could be determined. However, the transitional superficial gas velocity presented in the literature digressed from experimental observation and needed more accurate prediction.

Therefore, the purpose of this work is to investigate the transitional superficial gas velocity and to suggest an accurate model to predict the superficial gas velocity at the transition regime. Experiments were carried out to identify the superficial gas velocity at the transition regime of various gas phases in the organic or aqueous bulk liquid phase. We did not employ an air–water system as gas–liquid phases because many studies have already investigated this system.17,24,27 In our work, the transition regime point was measured by the gas holdup, volumetric liquid-phase mass transfer coefficient, and drift flux profile. Furthermore, the pressure standard deviation was applied to investigate the transition regime. The empirical results of this work were compared with the predicted transitional superficial gas velocity by using both prior correlations and our proposed correlation.26,27 The comprehensive correlation proposed here accurately predicted the gas holdup and the superficial gas velocity by integrating the two models covering gas holdup at homogeneous and heterogeneous flow regimes.

2. Results and Discussion

2.1. Transitional Superficial Gas Velocity

The transitional superficial gas velocity is an important issue in the operation of an industrial bubble column. Because homogeneous and heterogeneous flow regimes have different hydrodynamic properties, different equations estimating mass transfer parameters should be applied based on the delicately determined transitional superficial gas velocity. Thus, in this work, numerous experiments determining the transitional superficial gas velocity with various methods were carried out to confirm the accuracy of the data. After the investigation of the empirical transitional superficial gas velocity, the results were compared with an existing model in prior studies and a new estimation model was developed to precisely predict the transition regime.26,27

2.2. Gas Holdup

Gas holdup is an important design parameter, as it has a significant influence on the column hydrodynamic behavior and mass transfer. For the homogeneous flow regime, gas holdup quickly increases as the superficial gas velocity rises until it reaches the transitional superficial gas velocity. Once the superficial gas velocity reaches the transitional superficial gas velocity, the ascending rate of gas holdup is reduced and the transition point from homogeneous to heterogeneous regime can be clearly recognized. The determination of the transitional superficial gas velocity is shown in Figure 1 using a plot of gas holdup vs superficial gas velocity. Although the gas holdup itself did not show a linear relationship with the whole range of superficial gas velocity, the two separate linear estimations provide the superficial gas velocity at the transition point.

Figure 1.

Figure 1

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Determination of transitional superficial gas velocity (Ar–monoethylene glycol (MEG) 25 wt % system).

The investigation of the gas holdup data over different gas–liquid phases is illustrated in Figures 2–4. The determination of the overall transition regimes in the gas holdup can be referred to the Supporting Information (Figure S1). The regime transition can be observed as the superficial gas velocity varies between 0.03 and 0.08 m/s. According to the observation, the increasing liquid height resulted in the reduced transitional superficial gas velocity. It is concurrent with previous observations that higher static liquid heights induce lower transition regime velocities.13,20,28 Overall, the gas holdup was lower at the n-hexane system than at the MEG 25 wt % system regardless of gas species because of the higher viscosity of the MEG 25 wt % system.

Figure 2.

Figure 2

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Individual transition regime determined by the slope of argon gas holdup.

Figure 4.

Figure 4

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Individual transition regime determined by the slope of helium gas holdup.

Figure 3.

Figure 3

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Individual transition regime determined by the slope of nitrogen gas holdup.

2.3. Volumetric Mass Transfer Coefficient (kla)

Detecting the change of the volumetric mass transfer coefficient is another way to determine the transitional superficial gas velocity. The result of kla is displayed in Figures 5–7. The determination of the overall transition regimes by the kla can be seen in Figure S1. The result was similar to that of the gas holdup case. The n-hexane system showed higher mass transfer coefficients than the system of MEG 25 wt % solution. Also, the increasing liquid height decreased the transitional superficial gas velocity.

Figure 5.

Figure 5

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Individual transition regime determined by kla with argon gas.

Figure 7.

Figure 7

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Individual transition regime determined by kla with helium gas.

Figure 6.

Figure 6

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Individual transition regime determined by kla with nitrogen gas.

Regarding the experiments using n-hexane and helium, however, mass transfer was improved, although the static liquid height increased. The result using argon and nitrogen as a gas phase did not show this reverse tendency. The reason why the elevated static liquid height gave better mass transfer seems to be derived from the smaller density of helium. By taking a closer look at a force acting in the bubble, there is drag force (FD), body force (FB), pressure force (FP), virtual mass force (FVM), and lift force (FL).29 The following equations are detailed expressions of each force

2.3. 1
2.3. 2
2.3. 3
2.3. 4
2.3. 5

where CD, CL, and CVM are coefficients of each force.

A condition of the same superficial gas velocity and the same liquid was applied, and only the gas phase was varied. vl is negligible because vl is mainly affected by liquid property and vg.2929 The variation of pressure is governed by the axial position, and so FP is not greatly affected by changing the gas-phase component. Also, correlations in previous studies on bubble diameters did not consider gas properties of density and viscosity.30,31 If a bubble size is independent of the axial position, the only variable parameters are vb and mb. Thus, the change of FP, FVM, and FL is negligible. The FB of helium is significantly smaller than that of the other gases because of the low density of helium (argon: 1.661; helium: 0.16442; nitrogen: 1.1496 kg/m3 at room temperature and atmospheric pressure).

Average bubble rise velocity was investigated to examine the change of FD, and the result is illustrated in Figure 8. In the experiment using argon as a gas phase, the average bubble rise velocity for the entire column was higher at all superficial gas velocity conditions for the experiment using an H/D ratio of 5 (hatched block and white block in Figure 8a). Therefore, better mass transfer can be observed at lower static liquid height because a slower average bubble rise velocity induces more gas–liquid mass transfer opportunity.

Figure 8.

Figure 8

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Average rise velocity with respect to different axial positions (velocity measured position/static liquid height of experiments): (a) argon and (b) helium.

For the experiment using helium as a gas phase, however, the static liquid height increase gave reduced average bubble rise velocity (Figure 8b). This is the reason why the improved kla was observed even though the static height was expanded. Additional evidence of the mass transfer increase can be obtained by splitting measuring regions of average bubble rise velocity. For the argon experiment, the average bubble rise velocity in the range of 0–2.5 H/D axial position was lower than that in the range of 2.5–5 H/D axial position as the superficial gas velocity increased (see the black and gray blocks in Figure 8a). However, the average bubble rise velocity gradually decreased as the axial position increased for the helium experiment. This decrease in the average bubble rise velocity can increase the drag force in eq 1, which acts in the opposite direction of bubble rise. As a result, the different flow development tendency provides different mass transfer behaviors. With this overall perspective, the rise of static liquid heights may grow the kla when less dense gas is used.

2.4. Drift Flux

The drift flux method was introduced by Wallis to analyze flow hydraulics and physical properties of two-phase systems.21 Drift flux can be given by the following equation

2.4. 6

The transitional superficial gas velocity can also be obtained by tracing the change in the slope of the gas holdup vs drift flux curve.13,23,32 Results of the investigation using drift flux analysis are illustrated in Figures 9–11. The overall transition regime with different gas–liquid systems was displayed in Figure S2. The overall trend of the effect of static liquid height and different gas–liquid systems on the transitional superficial gas velocity was concurrent with the former selection of gas holdup because the drift flux analysis is based on the gas holdup in eq 6.

Figure 9.

Figure 9

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Individual transition regime determined by drift flux with argon gas.

Figure 11.

Figure 11

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Individual transition regime determined by drift flux with helium gas.

Figure 10.

Figure 10

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Individual transition regime determined by drift flux with nitrogen gas.

2.5. Pressure Standard Deviation

Another method for determining the transitional superficial gas velocity is to investigate pressure fluctuations. There have been several studies using statistical analysis to identify the hydrodynamics of a bubble column.33−35 The main characteristic of a homogeneous flow regime is the generation of a uniform bubble size at the gas sparger. Thus, there will be small pressure fluctuations at the lower point of the column. However, at a higher axial position, bubble size distribution will gradually become disordered because a bubble has the possibility of coalescing with others during the bubble rise. Therefore, it can be inferred that the intensity of pressure fluctuation progressively increases along the rising axial position. However, in the heterogeneous flow regime, a clear difference compared to the homogeneous flow regime is the wide range of bubble size distribution through the whole column. Pressure fluctuations are independent of the axial position due to the release of large bubbles near the gas sparger and the eddies in the column. Hence, the investigation of pressure fluctuations can be utilized as another tool for finding the transitional superficial gas velocity.

Figure 12 shows that the pressure fluctuation is measured by obtaining pressure standard deviations with different axial positions (H/D = 0.1, 1, 2.5, and 3.5). Another figure containing empirical data using argon and helium is shown in the Supporting Information (Figure S3). The left side of the figure represents the homogeneous flow regime, and the other side represents the heterogeneous flow regime. The empirical data of the pressure standard deviation showed an upward tendency as the axial position increased in the homogeneous regime. The transition regime began with the red lines in Figure 12a,c. No relationship between axial position and pressure standard deviation was observed in the graph representing heterogeneous flow regime. Observation of the pressure standard deviation in the other gas–liquid systems, and all the empirical results in the above sections about the transitional superficial gas velocity are displayed in Table 1. Various gas–liquid systems showed different transitional superficial gas velocity. The empirical data with various methods for determining the transition regime showed that the transitional superficial gas velocity decreased with the rising static liquid height. There was no big difference between the transition regime velocities from the four different analysis methods. Drift flux and gas holdup have similar tendency because drift flux is a term combining superficial gas velocity with gas holdup. A big difference between gas holdup and liquid-side mass transfer coefficient is present with the bubble diameter. If a gas slug or gas cap is created in a bubble column, liquid-side mass transfer is significantly reduced, although gas holdup is not affected a lot.36 Because the gas slug or gas cap cannot be created in this work, the transitional superficial gas velocity was similar with the four different analysis methods. Thus, the average of the transition regime velocities was employed to propose a correlation of the transitional superficial gas velocity in the following section.

Figure 12.

Figure 12

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Experimental pressure deviation on different gas–liquid systems (measured at 5 H/D axial position): (a, c) homogeneous flow regime and (b, d) heterogeneous flow regime.

Table 1. Transitional Superficial Gas Velocity Results with Different Detection Method under Variation of Static Liquid Height and Gas–Liquid Systema.

detection method gas holdup
 kla
 drift flux
 pressure standard deviation
axial position H/D=2.5 H/D=4 H/D=5 H/D=2.5 H/D=4 H/D=5 H/D=2.5 H/D=4 H/D=5 H/D=2.5 H/D=4 H/D=5
MEG 25 wt % Solution
He 4.83 3.72 3.72 4.83 3.72 2.97 4.83 3.72 3.36 4.83 3.72 2.97
N2 5.94 4.46 3.72 5.94 4.83 4.46 5.94 4.46 3.72 5.94 4.46 3.72
Ar 6.69 5.57 4.83 7.43 5.57 5.2 6.69 5.57 5.2 6.69 5.57 5.2
n-hexane
He 4.83 4.08 4.08 4.08 3.72 4.83 4.83 4.83 4.08 4.09 3.72 2.97
N2 6.69 4.83 4.83 5.94 5.57 4.83 6.69 5.57 5.2 5.94 5.2 4.83
Ar 7.43 6.69 5.94 6.69 5.94 5.57 7.43 6.69 5.94 7.43 6.69 5.2
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a

⟨cm/s⟩.

2.6. Correlation of the Transitional Superficial Gas Velocity

There have been a few studies concerned specifically with transitional superficial gas velocity, and each of their models was proposed to determine the transitional gas holdup and the small bubble velocity. By using the two parameters, the transitional superficial gas velocity could be obtained.26,27 In our experiment, the dispersed bubble diameter was small enough to be recognized as a small bubble near the superficial gas velocity of 0 m/s. Therefore, the average bubble rise velocity at this condition can be expressed as the small bubble velocity. The transitional superficial gas velocity, the gas holdup at the transition regime, and the small bubble velocity predicted by the previous models were displayed with our experimental data in Figure 13.26,27 The three calculated parameters appeared with a significant difference between the experiments and the model predictions. Thus, a new correlation was proposed, as described next.

Figure 13.

Figure 13

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Comparison of transition regime parameters: (a) transitional superficial gas velocity; (b) gas holdup at transition point; and (c) small bubble velocity.

The relation between the gas holdup and the superficial gas velocity was analyzed. Because a lot of previous literature expressed gas holdup as a power relationship with superficial gas velocity, the value of the exponent for gas holdup was considered.26,37,38

2.6. 7

It was found that exponent “a” was in the range of 0.7–1.2 for the homogeneous flow regime, and it was within 0.4–0.7 for the heterogeneous flow regime.39 In another study, 1.2 was used for the exponent in the homogeneous flow regime and 0.4 in the heterogeneous flow regime to provide a transition regime correlation.26 However, it was also reported that the value operating in the homogeneous flow regime was 0.58.40 Gandhi and Joshi collected all of the published 3374 data points over the past 45 years regarding the measurement of the gas holdup.

We also estimated the exponents by utilizing our 270 data points, as shown in Table 2. Because the column dimension may influence the gas–liquid flow up to the aspect ratio of 5, only the transitional superficial gas velocity measured at the aspect ratio of 5 was applied for developing a prediction model.9,41 The average value of a was 0.8422 operating in the homogeneous flow regime and 0.557 operating in the heterogeneous flow regime. The slope change at the transition regime can be well-defined between the gas holdup and the superficial gas velocity, as shown in Figures 2–4. Therefore, based on the experimental data, the correlation to estimate the gas holdup for each flow regime was established to find the transitional superficial gas velocity. Because gas and liquid viscosity, surface tension, and density have a considerable influence on the gas holdup, their properties were included as a parameter. The gas holdup prediction models for each regime were built by multiple regressions, as shown below.

Table 2. Determined Values of the Exponent, a, in Power Law Relationship for Each Gas–Liquid System.

gas–liquid system homogeneous flow regime heterogeneous flow regime
Ar–MEG 25 wt % 0.8547 0.5258
Ar–n-hexane 0.8639 0.5306
N2–MEG 25 wt % 0.7567 0.5982
N2–n-hexane 0.7909 0.57
He–MEG 25 wt % 0.9004 0.5847
He–n-hexane 0.8866 0.5298
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In the homogeneous flow regime

2.6. 8

In the heterogeneous flow regime

2.6. 9

The parity plot between the experimental and the estimated value is shown in Figure 14 to confirm the validity of both correlations. All of the data were within the range of 15% error. The intersection between the two gas holdup models for the homogeneous and the heterogeneous flow regimes can be the gas holdup at the transition regime. To simplify the equation, the model equation can be expressed as a power law model

2.6. 10
2.6. 11

Because A, B, a, and b were known values in eqs 8 and 9, the intersection point can be easily expressed as

2.6. 12
2.6. 13

Therefore, the equation to estimate the specific gas holdup and the superficial gas velocity values at each transition regime can be obtained

2.6. 14
2.6. 15

eqs 14 and 15 were derived by eqs 8 and 9 for the parameters having the following experimental ranges; ρg = 0.16442–1.661 kg/m3, ρl = 655–1027.71 kg/m3, μ = 0.000326–0.001289 Pa s, and σ = 0.0184–0.071 N/m. The comparison of experimental and correlated data is illustrated in Figure 15. Data from previous literature were compared with the calculated values from our proposed correlations.14,22,42,43 The new model revealed a good prediction capability for the gas–liquid systems like water–air and 80 wt % MEG–air that are not tested in this work. The calculated values of superficial gas velocity and gas holdup at the transition regime fitted well with the empirical data. Therefore, the proper selection of the value of exponent a in superficial gas velocity gives a proper prediction of superficial gas velocity and gas holdup at the transition point. Because this experiment was carried out at ambient conditions, the given correlations may not work for pressurized systems. More investigations in various conditions should be carried out to further improve the correlations.

Figure 14.

Figure 14

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Parity plot of experimental data and gas holdup estimated by eqs 8 and 9.

Figure 15.

Figure 15

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Comparison between experimental and calculated transitional superficial gas velocity (estimated by eq 15).

3. Conclusions

This work was performed to accurately determine the transitional superficial gas velocity with several different gas–liquid systems. Several different methods employing gas holdup, volumetric liquid-phase mass transfer coefficient, drift flux, and pressure standard deviation showed similar results in the transitional superficial gas velocity. Increase in the static liquid height can lower the transitional superficial gas velocity. However, in a lower gas density case such as with helium, it was observed that the increased static height caused a higher transitional superficial gas velocity. The relationship between gas holdup and superficial gas velocity was carefully observed to develop a new model based on the empirical result. After establishing a gas holdup model for the homogeneous and heterogeneous flow regimes, a new model to predict superficial gas velocity and gas holdup at the transition point was established. The established model displayed an overall error of less than 15% when compared to the empirical results of this work. By considering liquid and gas phase physical properties, the proposed model offers flexible prediction capability for various gas–liquid mass transfer systems.

4. Methods

4.1. Bubble Column Setup

The detailed design of the bubble column experiment is illustrated in Figure 16. The transparent acrylic column had the inner diameter of 0.2 m and height of 1.8 m. At the bottom of the column, a ring sparger with 54 holes with a size of 0.001 m in diameter was installed to provide a consistent distribution of the gas phase. The gas sparger was made of 3/8″ stainless steel pipe and has a diameter of 0.12 m. A mass flow controller (MFC-Korea, TSCD245, Korea) was used to provide the gas phase. The superficial gas velocity was set to more than 0.01 m/s to avoid gas weeping near the gas sparger. To cover both homogeneous and heterogeneous flow regimes, superficial gas velocities were varied up to 0.133 m/s. To detect a pressure fluctuation during the experiment, four pressure sensors (Sensys, PHPG 0003BCTG, Korea) that offered ±0.035% precision under the range of 0–3 bars were installed at different axial positions. During the experiment, dynamic mass flow controller (MFC) signals were continuously recorded and delivered to the PC.

Figure 16.

Figure 16

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Schematic diagram of the bubble column.

4.2. Measurement Method

For the liquid phase, monoethylene glycol (MEG) aqueous solutions and n-hexane were used. Because pure MEG has a high viscosity, 25 wt % MEG aqueous solution was employed. Each of helium, nitrogen, and argon was chosen as a gas phase to cover various gas densities. All experiments were carried out in batch mode and experimental condition was atmospheric pressure and room temperature. The liquid phase was filled before the experiment, and the gas phase was injected through the sparger by MFC. The void fraction of the gas holdup (εg) was calculated by the ratio of the aerated liquid height to the difference between the static and the aerated liquid heights.

The volumetric mass transfer coefficient (kla) was determined by applying dynamic dissolved oxygen (DO) absorption and desorption method. There were already frequent references using a DO probe to obtain kla.44,45 Ahead of the experiment, oxygen gas was sufficiently provided to achieve the saturated condition to desorb the remaining gas in the liquid phase. After the complete replacement of the system gas by oxygen, the object gas was distributed, and the variation of DO in the system liquid was measured using a polarographic DO meter (Hanna Instruments, HI98193). The collected DO data were transferred to the PC, and the experimental kla was calculated by the following equation36,46,47

4.2. 16

Bubble velocity was measured by a stopwatch. Once a bubble was released above the sparger, exact time measurement began. The elapsed time was measured until the bubble passed the specific destinations (axial position of H/D = 2.5 and 5). Because it is hard to differentiate which bubble is a measuring objective, the first released bubble after the column operation was observed. For the accuracy of the experiment, more than 10 bubble velocity measurements were made per each data point. After the experiment, the remaining gas in the sparger was slowly released. This condition was represented as a small bubble velocity at 0 m/s superficial gas velocity. For the pressure deviation analysis, the dynamic pressure during the experiment was recorded and analyzed by the connected PC.

Acknowledgments

The authors are grateful for the financial supports from both the Hanwha Chemical R&D Institute through the KAIST-Hanwha Future Technology R&D Center and the Advanced Biomass R&D Center (ABC) as the Global Frontier Project funded by the Ministry of Science, ICT, and Future Planning, South Korea (ABC-2010-0029728).

Glossary

Nomenclature

Cf

final gas concentration, kg/m3

Ci

initial gas concentration, kg/m3

C*

concentration of gas at saturation, kg/m3

D

column diameter, m

d

bubble diameter, m

g

gravity acceleration, m/s2

j

drift flux, m/s

F

force, N

H

column height, m

kla

volumetric liquid-phase mass transfer coefficient, s–1

m

mass, kg

p

pressure, Pa

t

time, s

u

superficial gas velocity, m/s

v

velocity, m/s

V

volume, m3

Greek Letters

εg

gas holdup

μ

liquid viscosity, Pa s

ρ

density, kg/m3

σ

surface tension, N/m

Subscripts

B

body

b

bubble

D

drag

g

gas

L

lift

l

liquid

P

pressure

sb

small bubble

trans

transition regime

VM

virtual mass

Abbreviations

MEG

monoethylene glycol

MFC

mass flow controller

DO

dissolved oxygen

Supporting Information Available

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.8b02657.

  • Overall view of regime transition using gas holdup and kla in different gas–liquid systems; experimental pressure deviations on different gas–liquid systems (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao8b02657_si_001.pdf (542.3KB, pdf)

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