Microbubble Dispersion Research Articles

Mechanistic insight into the colloidal gas aphrons stability in the presence of petroleum hydrocarbons

This study is primarily focusing on the development, generation, and characterization of a colloidal dispersion of microbubbles, known as colloidal gas aphrons as an effective flushing/invading agent during subsurface processes. A major challenge facing the subsurface applications of such colloidal systems, for example for the in-situ remediation of petroleum hydrocarbons contaminated soils or enhanced oil recovery, is the influence of petroleum constituents on colloidal gas aphrons’ structure, consequently their stability. To investigate this issue which was not considered before, first, a series of bulk-scale experiments to study and optimize the properties of colloidal gas aphrons in terms of chemical formulation, structure, stability, the size distribution of bubbles, and gas content were designed and conducted. Then, the effect of the presence of two types of hydrocarbons, namely asphaltenic crude oil, and kerosene, on colloidal gas aphrons’ properties was evaluated. Results show that the unique multilayer structure of the colloidal gas aphrons developed in this research prevents the severe entry and spread of petroleum hydrocarbons into and on the layers of this colloidal system and provides proper colloidal stability than conventional foams in the presence and absence of petroleum hydrocarbons. In the absence of petroleum hydrocarbons, the best colloidal gas aphrons sample had a half-life time of 1621.9 min. The value decreased to 1302.6 min and 699.7 min when crude oil and kerosene were present, respectively. Generally, the results reveal that colloidal gas aphrons’ stability is not considerably influenced by the presence of petroleum constituents, and this suggested colloidal dispersion could be a viable alternative to conventional foams and other chemical-based strategies used in subsurface processes.

Microbubble Intensification of Bioprocessing

Microbubbles are famed for their large surface area-to-volume ratio, with the promise of intensification of interfacial phenomena, highlighted by more rapid gas exchange. However, for bioprocessing, it has been recognised for many decades that surfactant-rich fermentation media hinders mass transfer and possibly other interfacial processes due to surfactant loading on the interface. This article focuses on the roles of microbubble size and bubble bank, dispersed microbubbles that are sufficiently small to be non-buoyant, in mediating other modes of interfacial transfer via collisions with microorganisms and self-assembled clusters of microorganisms and microbubbles. These provide a more direct route of mass transfer for product gases that can be released directly to the microbubble with ~104 faster diffusion rates than liquid mediated gas exchange. Furthermore, secreted external metabolites with amphoteric character are absorbed along the microbubble interface, providing a faster route for liquid solute transport than diffusion through the boundary layer. These mechanisms can be exploited by the emerging fields of symbiotic or microbiome engineering to design self-assembled artificial lichen dispersed structures that can serve as a scaffold for the selected constituents. Additionally, such designed scaffolds can be tuned, along with the controllable parameters of microbubble mediated flotation separations or hot microbubble stripping for simultaneous or in situ product removal. Staging the product removal thus has benefits of decreasing the inhibitory effect of secreted external metabolites on the microorganism that produced them. Evidence supporting these hypotheses are produced from reviewing the literature. In particular, recent work in co-cultures of yeast and microalgae in the presence of a dispersed bubble bank, as well as anaerobic digestion (AD) intensification with dispersed, seeded microbubbles, is presented to support these proposed artificial lichen clusters.

Internal Optimization for Enhancing the Microbubble Dispersion Characteristics of a Stirred Tank

Internal Optimization for Enhancing the Microbubble Dispersion Characteristics of a Stirred Tank

Mediating heat transport by microbubble dispersions: The role of dissolved gases and phase change dynamics

• Developed a new model for buoyant convection with a dispersed microbubble phase. • Predicts microbubble phase fraction controls additional HT mechanism. • Scale of the additional heat transfer ranges from 5–45% with phase fractions 2–20%. • Demonstrates that dominant feature for HT in larger domains is the boundary layer. • Conclusions hold qualitatively with simple model for gas exchange between phases. Recently a theory for additional heat convection by microbubbles was posited. The mechanism proposed is that the latent heat of vapor of the liquid is carried by microbubbles from hot zones that vaporize more liquid to cold zones where condensation releases the latent heat. In this paper, the proposition that the additional heat flux is controlled by the phase fraction of microbubbles, is tested by steady state solutions of the canonical hot wall / cold wall buoyant convection problem. The simulations show that the range of additional heat transfer varies monotonically with length scale of the cavity, between 5 and 45% with phase fractions varying from 0.02 and 0.2. The larger characteristic lengths introduce insufficient heat flux from the hot wall to maintain a “driven cavity” flow structure, so that the steady state structure that emerges is a stable stratification with thin boundary layers near the hot and cold walls, with weak shear flow convection. The stable stratification resultant at higher characteristic lengths suppresses the additional heat flux due to microbubble mediation, yet only moderately deviating from proportionality. These conclusions hold qualitatively for a variant of the model which simply treats the gas exchange between the microbubble phase and dissolved gases in the liquid, resulting in variation of the microbubble phase fraction with temperature, hence with position in the domain. Quantitatively, the percentage increases are 3–30% in the parameter regime above, with the effects of dissolved gases captured dynamically.

Steady State Heat Transport by Microbubble Dispersions Mediating Convection With Phase Change Dynamics

A new theory for additional heat transfer convected by a dispersed phase of microbubbles was posited recently. An additional convection term in the heat transport equation reflects the latent heat of vapor of the liquid carried by the microbubbles from hot zones that vaporize more liquid to cold zones where condensation releases the latent heat. This theory was shown to be consistent with analysis of observations of freezing times measured by in the original Mpemba effect study, by inferring heat transfer coefficients fitted by Newton’s law of cooling. In this paper, the scaling analysis, leading to the proposition that the additional heat flux is proportional to the phase fraction of microbubbles, is tested by steady state solutions of the canonical hot wall / cold wall buoyant convection problem. For phase fractions 0.02 and 0.1, the maximum ratio of additional Nusselt number emergent is five, occurring in the microfluidic regime. Increasing the characteristic length of the domain maintains the monotonicity of the increase in additional Nusselt number ratio over the case of no microbubbles present. The additional heat transfer due to the microbubble dispersion, ranging from 5-50%, is found to be nearly proportional to the microbubble phase fraction for the range of 0.02 to 0.2. However, larger characteristic lengths introduce insufficient heat flux from the hot wall to maintain a “driven cavity” flow structure, so that the steady state structure that emerges is a stable stratification with thin boundary layers near the hot and cold walls, with weak shear flow convection. The stable stratification resultant at higher characteristic lengths suppresses the additional heat flux due to microbubble mediation, but only moderately deviating from proportionality.

Analysis of stability of silica nano-particle-laden microbubble dispersion.

Microbubbles are small gas-filled bubbles which have wide application in various industries. The stability of microbubble is of primary concern for the application of microbubble. In this research, the stability of microbubble dispersion generated using CTAB surfactant is analyzed by drainage mechanism. The stability of microbubble dispersion is studied on the basis of the half-life of microbubble dispersion. Microbubble dispersion gas fraction and apparent rise velocity of interface of microbubble dispersion are also calculated. The size of microbubble is estimated from the apparent rise velocity of interface of microbubble dispersion. Further, silica nano-particles are added to the surfactants to study their effect on the stability of microbubble dispersion. The observed results clearly indicate that the stability of microbubble dispersion is significantly affected by the surfactant concentration and the weight of silica nano-particle in the liquid. Similar results were observed for the apparent rise velocity of interface and bubble size of dispersion. The present work may be beneficial for the application of microbubble in various chemical and biochemical industries and scientific community.

Bubble size distribution and stability of CO2 microbubbles for enhanced oil recovery: effect of polymer, surfactant and salt concentrations

Fluids incorporating carbon dioxide (CO2) microbubbles have been utilized to promote enhanced oil recovery from hydrocarbon reservoirs. The performance of such fluids in porous media is greatly affected by both the bubble size and stability. On this basis, the present study evaluated the effects of varying the concentrations of a xanthan gum (XG) polymer, a surfactant (sodium dodecyl sulfate: SDS) and sodium chloride (NaCl) on both the stability and bubble size distribution (BSD) of CO2 microbubbles. CO2 microbubble dispersions were prepared using a high-speed homogenizer in conjunction with the diffusion of gaseous CO2 through aqueous solutions. The stability of each dispersion was ascertained using a drainage test, while the BSD was determined by optical microscopy and fitted to either normal, log-normal or Weibull functions. The results showed that a Weibull distribution gave the most accurate fit for all experimental data. Increases in either the SDS or XG polymer concentration were found to decrease the microbubble size. However, these same changes increased the microbubble stability as a consequence of structural enhancement. The addition of NaCl up to a concentration of 10 g/L (10 g/1000g) decreased the average bubble size by approximately 2.7%. Stability was also reduced as the NaCl concentration was increased because of the gravitational effect and coalescence.

Effect of distributor type on microbubble dispersion in a pressurized bubble column

The effect of distributor geometry on bubble characteristics in an air–kerosene system of a pressurized bubble column was evaluated. The experiment was carried out using a cylindrical stainless column with an inner diameter of 0.097 m and a height of 1.8 m under a system pressure up to 3.5 MPa. The gas holdup was calculated under pressure taps from 0.05 m to 0.85 m above the distributor along axial direction of the column. Bubble size was measured with an optical probe installed 0.5 m above the distributor. Perforated plates with four different hole sizes including 0.8 mm (20 each), 1 mm (12 each), 2 mm (3 each), and 3.46 mm (1 each) fixed with the same opening fraction (ϕo = 0.128%) were evaluated. Different opening fractions at 0.223% (21 holes), 0.128% (12 holes), 0.074% (7 holes), and 0.032% (3 holes) were also tested with a constant hole size (1 mm). The effect of the distributor geometry on bubble characteristics was determined with seven different types of perforated plates. The number of microbubbles was increased with decreasing opening fraction of the distributor. Based on dynamic gas disengagement (DGD) analysis, microbubbles were rarely generated in all distributors under conditions of Psys = 0.1 MPa at Ug = 12.3 mm/s. However, a significant number of microbubbles were generated at ϕo = 0.032% despite a low flow rate at Psys = 3.5 MPa. Microbubble ratio varied from 36% to 40% at ϕo = 0.128 %, while this ratio varied from 38% to 73% at ϕo = 0.032%.

Towards a microbubble condenser: Dispersed microbubble mediation of additional heat transfer in aqueous solutions due to phase change dynamics in airlift vessels

Microbubbles dispersions in aqueous solutions can be long lived. For instance, 20micron size microbubbles take on the order of a day to rise one meter. Consequently, any currents in a reasonably sized vessel would be expected to entrain such a microbubble dispersion as the buoyant force is exceeded by the inertial force of liquid currents. This paper argues for the advantages of a microbubble dispersion mediated condenser with two benefits. The obvious advantage over fine bubble direct contact heating or cooling is that the microbubble phase, which can be engineered with a throughput of approximately a hectare per second of interfacial area flux per cubic meter of solution volume, should not be limited by heat transfer to and from the liquid and microbubble phase. Rather the limitation will be on the wetted area for heat transfer of the vessel to its heat exchange configuration. The second potential advantage follows from the theory proposed in this paper. Arranging the condenser in the microbubble mediated airlift configuration will introduce additional heat transfer from microbubbles vaporizing hotter water near the central plume and convecting that additional latent heat to the cold wall, which condenses the water vapor and releases the latent heat. This additional convection of latent heat is proposed as an additional source term for heat transport equation, and the magnitude of the effect is shown to be proportional to the phase fraction of microbubbles. This theory is shown to be consistent with analysis of observations of freezing times measured by Mpemba and Osborne [Phys. Educ. 4:172-5, 1969], that infer heat transfer coefficients from fitting Newton’s law of cooling. The inferred heat transfer coefficient ratio from the presumed highest microbubble phase fraction to the lowest is ~7.4:1. Whether or not that enhancement level persists to a microbubble condenser in an airlift vessel, the promise of additional heat transfer should be explored.

Column flotation of fine glass beads enhanced by their prior heteroaggregation with microbubbles

The application of microbubbles as flotation carriers in fine minerals beneficiation processes can be a promising approach for solving challenges of fine particles flotation. This study explores the efficiency of column flotation of fine glass beads (ballotini). In test runs ballotini were first mixed with the air-in-water dispersion in CTAB (cetyltrimethylammonium bromide) solution, and then they were fed into a flotation column via a tubular flotation reactor. Independent of the total concentration of the collector in a flotation reactor and a column, the maximum increased recovery is achieved when a volume dosage of microbubbles per floated particles weight unit is 0.3 mL/g. The paper also offers the theoretical substantiation for this effect. The findings have shown that the average shear rate in a flotation reactor significantly influence the dependence of recovery on treatment time. It is suggested that the best performance can be achieved in flotation reactors, which generate shear rates in the range 300–500 s−1, and the treatment time amounts to 8–10 s. These conditions facilitate formation of hetero-aggregates comprising particles and microbubbles, and the size of the aggregates reaches several millimeters. In the test runs with the tubular flotation reactor of 6 mm in diameter at the shear rate of 500 s−1 and treatment time of 8 s, the recovery rate of ballotini increased from 63.2% to 77.6%. It was shown that the effectiveness of treating the mixture of particles and microbubbles in the flotation reactor significantly depends on the method of CTAB collector feed. The best results were achieved when the total amount of collector was fed into the flotation reactor with the microbubble dispersion in the concentrated solution of CTAB collector. In this case, the adsorption of CTAB cations on the microbubble surface caused the positive charging of the surface. As the surface of glass beads initially has a negative charge, the delivery of positively charged microbubbles into the feed creates favorable conditions for forming coarse hetero-aggregates due to Coulomb attraction of particles and microbubbles.

Computational modeling of microbubble coalescence and breakup using large eddy simulation and Lagrangian tracking

AbstractThe flow of dispersed microbubbles was studied with an Eulerian–Lagrangian technique using large eddy simulation to predict the continuous liquid flow and Lagrangian tracking to compute bubble trajectories. The model fully accounts for bubble coalescence and breakup and was applied to horizontal and vertical channel flows. With low levels of turbulence, gravity in horizontal, and lift in vertical, channel flows govern the bubble spatial and collision distribution. When turbulence is sufficiently high to, at least partially, oppose bubble preferential concentration, more uniform collision and coalescence distributions are found, although these remain peaked near the wall in both configurations. Almost 100% coalescence efficiency was always found, due to bubbles colliding along similar trajectories, with breakup only recorded in a flow of low surface tension refrigerant R134a. Models like this can provide the required quantitative understanding of the microbubbles complex behavior, as well as supporting the development of more macroscopic modeling closures.

Motion behavior of micro-bubbles in a delta shape tundish using impact pad

Micro-bubbles were generated using gas injection through tiny orifices located at the upper part of the ladle shroud, for deep cleaning the liquid steel. An impact pad was employed to improve the dispersion of micro-bubbles in the liquid bath, reduce the collision between bubbles, as well as to achieve the conventional functions of a turbulent inhibitor. A 3-D numerical modeling was developed to predict the flow characteristics and bubble motion behaviors under the effect of the impact pad, with the bubble sizes obtained from the measurements in full-scale water experiments. For comparison, the corresponding numerical simulation was also carried out in the tundish with a conventional turbulent inhibitor. It was found that the impact pad promotes the spreading of micro-bubbles in the tundish bath, which could effectively reduce the coalescence of bubbles, so as to restrain the secondary bubble grow-up. The global efficiency of inclusion removal by bubble flotation was evaluated, considering the mechanism of repeated bubble sweeps in each element. The inclusion removal was raised by 14.33–37.09% due to the extended area of bubbles dispersion, even with the same bubble amount and size.

Micro-Particle Image Velocimetry Investigation of Flow Fields of SonoVue Microbubbles Mediated by Ultrasound and Their Relationship With Delivery

The flow fields generated by the acoustic behavior of microbubbles can significantly increase cell permeability. This facilitates the cellular uptake of external molecules in a process known as ultrasound-mediated drug delivery. To promote its clinical translation, this study investigated the relationships among the ultrasound parameters, acoustic behavior of microbubbles, flow fields, and delivery results. SonoVue microbubbles were activated by 1 MHz pulsed ultrasound with 100 Hz pulse repetition frequency, 1:5 duty cycle, and 0.20/0.35/0.70 MPa peak rarefactional pressure. Micro-particle image velocimetry was used to detect the microbubble behavior and the resulting flow fields. Then HeLa human cervical cancer cells were treated with the same conditions for 2, 4, 10, 30, and 60 s, respectively. Fluorescein isothiocyanate and propidium iodide were used to quantitate the rates of sonoporated cells with a flow cytometer. The results indicate that (1) microbubbles exhibited different behavior in ultrasound fields of different peak rarefactional pressures. At peak rarefactional pressures of 0.20 and 0.35 MPa, the dispersed microbubbles clumped together into clusters, and the clusters showed no apparent movement. At a peak rarefactional pressure of 0.70 MPa, the microbubbles were partially broken, and the remainders underwent clustering and coalescence to form bubble clusters that exhibited translational oscillation. (2) The flow fields were unsteady before the unification of the microbubbles. After that, the flow fields showed a clear pattern. (3)The delivery efficiency improved with the shear stress of the flow fields increased. Before the formation of the microbubble/bubble cluster, the maximum shear stresses of the 0.20, 0.35, and 0.70 MPa groups were 56.0, 87.5 and 406.4 mPa, respectively, and the rates of the reversibly sonoporated cells were 2.4% ± 0.4%, 5.5% ± 1.3%, and 16.6% ± 0.2%. After the cluster formation, the maximum shear stresses of the three groups were 9.1, 8.7, and 71.7 mPa, respectively. The former two could not mediate sonoporation, whereas the last one could. These findings demonstrate the critical role of flow fields in ultrasound-mediated drug delivery and contribute to its clinical applications.

Simultaneous removal of NO and SO2 with a micro-bubble gas-liquid dispersion system based on air/H2O2/Na2S2O8

ABSTRACT A novel environment-friendly process was proposed to conduct the simultaneous removal of NO and SO2. In this process, a micro-bubble generator was utilized to generate the micro-bubble gas–liquid dispersion system (MBGLS) by inhaling mixed gas (NO, SO2 and/or air) and absorption liquid. The MBGLS was then sprayed into an oxidation absorption column reactor, in which NO and SO2 were oxidized and absorbed. As the additives, air, H2O2 and/or Na2S2O8 were brought into the MBGLS to investigate their effects on the simultaneous removal of NO and SO2. In addition, the effects of initial pH and temperature of the absorption liquid on the simultaneous removal of NO and SO2 were also explored. The performance of the MBGLS in removing NO and SO2 was excellent. Even if the MBGLS was composed of tap water, NO and SO2, the removal efficiencies of NO and SO2 respectively reached 78% and 94.4%. The additives significantly improved the removal performance of the MBGLS. Under the conditions of pH = 8 and room temperature and the addition of air, SO2 was removed completely and the NO removal efficiency reached 99.5% when Na2S2O8 to H2O2 molar ratio was 0.005/0.05. The effect of the absorbent temperature on the removal of NO and SO2 was insignificant. With the increase in pH, the removal of NO in both H2O2 aqueous solution and Na2S2O8 aqueous solution firstly increased and then decreased, but pH had no effect on the removal of SO2.

Bubble characteristics in pressurized bubble column associated with micro-bubble dispersion

Bubble characteristics of air-kerosene system and air-water system in a pressurized bubble column were analyzed. Experiments were carried out at system pressure up to 3.5 MPa on a cylindrical stainless column with an inner diameter of 0.097 m and a height of 1.8 m. Kerosene and tap water were used as liquids while air was used as gas. Bubble characteristics were observed by varying gas velocity up to 98 × 10−3 m/s at 0.1 MPa and up to 31.1 × 10−3 m/s at 3.5 MPa. Bubble chord length and bubble rising velocity were measured with a single tip probe installed at the top of the distributor at 0.5 m. In addition, pressure difference between the top and bottom of the column was measured with a differential pressure transducer to confirm gas holdup. In the air-kerosene system, gas holdup tended to increase with increasing system pressure. From the analysis of drift flux, transition from homogeneous to heterogeneous flow regime was observed only under atmospheric pressure. In the air-kerosene system, drift flux tended to be kept constant as gas holdup increased under pressurized conditions. The system pressure was varied from 0.1 MPa to 3.5 MPa to confirm micro-bubble generation under pressurized conditions. Dynamic gas disengagement (DGD) analysis and image analysis at the same time showed that gas holdup fraction of micro-bubbles was almost constant (εm/εg = 0.4) at atmospheric pressure. However, it was increased from 0.48 at gas velocity of 12.3 × 10−3 m/s to 0.57 with gas velocity of 32.1 × 10−3 m/s at 3.5 MPa.

Large eddy simulation of microbubble dispersion and flow field modulation in vertical channel flows

Turbulent liquid–gas vertical channel flows laden with microbubbles are investigated using large eddy simulation (LES) two‐way coupled to a Lagrangian bubble tracking technique. Upward and downward flows at shear Reynolds numbers of Re τ = 150 and 590 are analyzed for three different microbubble diameters of 110, 220, and 330 μm. Predicted results are compared with published direct numerical simulation results although, with respect to comparable studies available in the literature, the range of bubble diameters and shear Reynolds numbers considered herein is extended to larger values. Microbubble concentration profiles are analyzed, with the microbubbles segregating at the wall in upflow conditions and moving toward the channel centre in downflow. The various forces acting on the bubbles, and the effect of the flow turbulence on the bubble concentration, are considered and quantified. Overall, the results suggest that the level of detail achievable with LES is sufficient to predict the fluid structures impacting bubble behavior. Therefore, LES coupled with Lagrangian bubble tracking shows promise for enabling the reliable prediction of bubble‐laden flows that are of industrial relevance. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1325–1339, 2019

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

Microbubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a downflow bubble column reactor with microbubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fraction and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal void fraction measurements are discussed and compared for a bubble column reactor with dispersed microbubbles. Empirical correlations are also proposed to predict the Sauter mean bubble diameter. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1000–4500 m2/m3) with sub-millimeter bubbles (500–900µm) and high overall void fractions (10–60%) in comparison with previous bubble column reactor designs.

A physics based multiscale modeling of cavitating flows.

Numerical modeling of cavitating bubbly flows is challenging due to the wide range of characteristic lengths of the physics at play: from micrometers (e.g., bubble nuclei radius) to meters (e.g., propeller diameter or sheet cavity length). To address this, we present here a multiscale approach which integrates a Discrete Singularities Model (DSM) for dispersed microbubbles and a two-phase Navier Stokes solver for the bubbly medium, which includes a level set approach to describe large cavities or gaseous pockets. Inter-scale schemes are used to smoothly bridge the two transitioning subgrid DSM bubbles into larger discretized cavities. This approach is demonstrated on several problems including cavitation inception and vapor core formation in a vortex flow, sheet-to-cloud cavitation over a hydrofoil, cavitation behind a blunt body, and cavitation on a propeller. These examples highlight the capabilities of the developed multiscale model in simulating various form of cavitation.

Microbubble assisted polyhydroxybutyrate production in Escherichia coli.

BackgroundOne of the potential limitations of large scale aerobic Escherichia coli fermentation is the need for increased dissolved oxygen for culture growth and bioproduct generation. As culture density increases the poor solubility of oxygen in water becomes one of the limiting factors for cell growth and product formation. A potential solution is to use a microbubble dispersion (MBD) generating device to reduce the diameter and increase the surface area of sparged bubbles in the fermentor. In this study, a recombinant E. coli strain was used to produce polyhydroxybutyrate (PHB) under conventional and MBD aerobic fermentation conditions.ResultsIn conventional fermentation operating at 350 rpm and 0.8 vvm air flow rate, an OD600 of 6.21 and PHB yield of 23 % (dry cell basis) was achieved. MBD fermentation with similar bioreactor operating parameters produced an OD600 of 8.17 and PHB yield of 43 % PHB, which was nearly double that of the conventional fermentation.ConclusionsThis study demonstrated that using a MBD generator can increase oxygen mass transfer into the aqueous phase, increasing E. coli growth and bioproduct generation.

Gas‐Liquid Mass Transfer Characteristics with Microbubble Aeration – I. Standard Stirred Tank

AbstractMore knowledge has to be acquired on the gas‐liquid mass transfer characteristics with microbubble aeration before an efficient bioreactor is designed. Experiments about this subject have been conducted in a stirred reactor. Some valuable conclusions were obtained: the shaft power consumption is little affected by the superficial gas velocity (vs) and the power consumption of the microbubble generator is rather high; the dispersion of microbubbles is more uniform compared to sparger aeration; surface aeration leads to a reduced microbubble number and the diameter of the microbubble increases with higher superficial gas velocity; when surface aeration happens, the kLa–vs curves turn quite abnormally different from that in the case of sparger aeration, and correlation‐based calculations fit well with the measurements.