Bubble Size Measurements Research Articles

Gas dispersion in the oxygen delignification process

There has been very little knowledge about the state of gas dispersion in the oxygen delignification process, even though this has a major impact on the performance of the reactor. This paper presents a new continu-ous inline method for measuring oxygen bubble size distribution in the reactor, as well as results from studies con-ducted in softwood and hardwood lines. This new measurement worked well, and new information about oxygen bubble size, as well as how different reactor conditions affected the distribution, was obtained. For example: • In the softwood line, the mean volume-weighted bubble size was about 0.1 mm, whereas in the hardwood line, this size was almost 10 times higher. For both lines, there was considerable variation in the measured bubble size over the long term. • For both lines, an increase in mixer rotation speed caused a discernible decrease in the bubble size, and an increase in oxygen charge caused a discernible increase in the bubble size. • In the softwood line, no coalescence of the bubbles in the reactor was observed, but in the hardwood line, some coalescence of the larger bubbles occurred. • In the test conducted in the hardwood line, the use of brownstock washer defoamer caused a discernible increase in oxygen bubble size. • In the hardwood line, reactor pressure had a noticeable effect on the amount of delignification, which indicated that improving mass transfer of oxygen (e.g., by decreasing the oxygen bubble size, in this case) should also have an increasing effect on the delignification.

The role of gas dispersion in the oxygen delignification process

Oxygen delignification is an essential part of the pulp production process. Delignification occurs with the aid of alkali and dissolved oxygen. Dissolved oxygen is obtained by dispersing oxygen gas into the pulp suspension by using efficient mixers. Little is known about the state of oxygen gas dispersion and its effect on oxy-gen delignification kinetics and efficiency. This paper will present the results for the effect of gas bubble size on the performance of oxygen delignification. The results are mainly based on detailed studies made in a Finnish hardwood mill where the oxygen bubble size distribution could be altered at the feed of the reactor. An essential aspect of these studies was the use of a new continuous inline gas bubble size measurement system to simultaneously determine the bubble size distribution at the feed and top of the reactor. Information about oxygen consumption in the reactor could also be obtained through the bubble size measurements. Accordingly, these studies quantify the effect of oxygen bubble size on the kappa reduction of the pulp. The effect of different chemical factors on the oxygen bubble size is also studied. Finally, the relationship between the gas bubble size and the liquid phase oxygen mass transfer coefficient (kLa) is presented. This connects the bubble size to the kappa reduction rate. Based on the presented modeling approach and the evaluation of practical factors that are not taken into account in the modeling, it was concluded that the volumetric average oxygen bubble size should preferably be smaller than 0.2 mm in practice. The information obtained with the new gas bubble size measurement system and the presented modeling approach give a very new basis for understanding, monitoring, adjusting, and designing oxygen delignification processes.

Biogas Upgrading to Biomethane by CO2 Removal using Water Absorber with Microbubble Technique

Biogas upgraded to biomethane can be utilized as a renewable energy source to substitute LPG in households and industry. This study explored biogas upgrading by CO2 removal from 20 - 75 % CO2-N2 simulated biogas mixture. The experimental unit using the microbubble technique combined with the water absorption column was set up and used for CO2 removal from the gas. Microbubble sizes of 20 - 30 µm were generated by a venturi ejector and measured with an automated bubble size measurement. The experiments confirmed that a microbubble with an inline mixer could enhance the effectiveness of the absorption process. The tests demonstrated over 85.80 % removal of CO2 from the simulated biogas by the experimental unit. The effects of various parameters, including the size of venturi ejector, gas flow rate, water flow rate, liquid-gas ratio, and initial concentration of CO2, were investigated. The results revealed that 2 L/min gas flow rate, 15 L/min water flow rate, L/G ratio 7.5, and venturi ejector size 0.50 inches are the optimum conditions. The use of the tube absorber gave much higher CH4 recovery than an absorption column. The appropriate operating conditions gave over 96 % CH4 concentration or less than 4 % CO2 concentration, matching the CH4 purity required by biomethane specifications. The results indicated that the new technique demonstrated in this study can upgrade biogas to biomethane.

A one-dimensional combined multifluid-population balance model for the simulation of batch bubble columns

Bubble columns are widely used as multiphase reactors for gas–liquid reactions in industrial applications. For the sensitivity and usability analysis of the bubble column in the process development, a model is needed that incorporates couplings between the fluid dynamics, the population balance equation (PBE) and the thermodynamics. Thereby the model should be as fast and reliable as possible. A suitable candidate is the kinetic theory approach with size resolution (KTAWSR), as one of the most rigorous combined multifluid-PBE models.A steady-state and one-dimensional version of the KTAWSR model was used and extended to batch bubble columns. For this purpose, a new approach for the determination of the integral gas holdup was developed which does not require additional empirical correlations. The spectral orthogonal collocation method was used to solve the model equations. Different breakage and coalescence model combinations were calibrated, compared and investigated on the basis of measured bubble size distributions. To validate the model, the integral gas holdup and the bubble size distribution were measured at four axial positions at three gas volume fluxes reaching the transition flow regime in a batch water–air bubble column. The novel integral gas holdup calculation approach could be predictively confirmed with measured data.

Impact of bubble coalescence in the determination of bubble sizes using a pulsed US technique: Part 1 – Argon bubbles in water

A powerful experimental approach to measure the size distribution of bubbles active in sonoluminescence and/or sonochemistry is a technique based on pulsed ultrasound and sonoluminescence emission. While it is an accepted technique, it is still lacking an understanding of the effect of various experimental parameters, including the duration of the pulse on-time, the nature of the dissolved gas, the presence of a gas flow rate, etc. The present work, focusing on Ar-saturated water sonicated at 362 kHz, shows that increasing the pulse on-time leads to the measurement of coalesced bubbles. Reducing the on-time to a minimum and/or adding sodium dodecyl sulfate to water allows to reducing coalescence so that natural active cavitation bubble sizes can be measured. A radius of 2.9–3.0 µm is obtained in Ar-saturated water at 362 kHz. The effects of acoustic power and possible formation of a standing-wave on coalescence and measured bubble sizes are discussed.

Numerical simulation of the interaction of wave phase conjugation with bubble clouds

The interaction of the Wave Phase Conjugation (WPC) process with bubble cloud dynamics is investigated via numerical modeling in application to bubble size measurements. The WPC simulator by Modarreszadeh and Timofeev (Computers and Fluids 197, 104353) is used as a starting point. In the simulator, a modified version of the high-order Nodal Discontinuous Galerkin method is used for modeling of acoustic wave propagation in the active WPC conjugator and the surrounding linear or non-linear fluid in 2D/axisymmetric domains. The effects of bubble dynamics are incorporated with the help of induced volume fractions. The modified Keller–Miksis model is employed to simulate vibrations of bubbles subjected to acoustic waves. After thorough verification and validation of the numerical scheme and the physical model, the interaction of various bubble clouds, including poly-disperse ones, with the WPC process is examined with the help of some existing and newly suggested descriptive indicators, e.g., the amplification factor and the absolute and relative signal intensities. The results show that signals scattered from bubble-plane clouds, in which the bubbles are non-physically synced, are strong enough to affect the modulation process if the stimulation frequency is close to the natural frequency of bubbles. For more realistic bubble clouds, the modulation process is almost intact. However, conjugate waves do carry some signatures of bubble-cloud dynamics, e.g., signals with frequencies higher than the natural frequency of bubbles are significantly diminished. The study demonstrates that WPC-based techniques have a promising potential to be used for measuring bubble dimensions.

Research Progress and Prospects of Multi-Stage Centrifugal Pump Capability for Handling Gas–Liquid Multiphase Flow: Comparison and Empirical Model Validation

The working capability of multi-stage pumps, such as electrical submersible pumps (ESPs) handling multiphase flow, has always been a big challenge for petroleum industries. The major problem is associated with the agglomeration of gas bubbles inside ESP-impellers, causing pump performance degradation ranging from mild to severe deterioration (surging/gas pockets). Previous literature showed that the two-phase performance of ESPs is greatly affected by gas involvement, rotational speed, bubble size, and fluid viscosity. Thus, it is necessary to understand which parameter is actually accountable for performance degradation and different flow patterns in ESP, and how it can be controlled. The present study is mainly focused on (1) the main parameters that impede two-phase performance of different ESPs; (2) comparison of existing empirical models (established for two-phase performance prediction and surging initiation) with our single-stage centrifugal pump results to determine their validity and working-range; (3) gas-handling techniques applied to enhance the multiphase performance of ESPs. Firstly, it aims at understanding the internal flow mechanism in different ESP designs, followed by test studies based on empirical models, visualization techniques, bubble-size measurements, and viscosity analysis. The CFD-based (computational fluid dynamics) numerical analysis concerning multiphase flow is described as well. Furthermore, gas-handling design methods are discussed that are helpful in developing the petroleum industry by enhancing the multiphase performance of ESPs.

Microbubble enhanced mass transfer efficiency of CO2 capture utilizing aqueous triethanolamine for enzymatic resorcinol carboxylation.

The present study focuses on the aeration of aqueous triethanolamine acting as reaction medium for biocatalytic carboxylations. For enhancing mass transfer in a bubble column reactor, microbubble aeration is applied and compared to conventional macrobubble aeration. Application of a 0.5 μm porous sparger enables microbubble CO2 aeration with bubble size distributions below 150 μm in Sauter mean diameter, correlating with the highest measured mass transfer rates. During CO2 saturation of the aqueous triethanolamine, bubble size distributions changed according to the level of CO2 saturation. For microbubbles, less foaming was observed compared to macrobubble aeration by a 10 μm porous sparger. This microbubble effect is attributed to their accelerated dissolution assisted by the Laplace pressure lowering the amount of bubbles reaching the surface of the liquid. The experiments reveal that the rate of interfacial area generation, which is calculated based on measured bubble size distributions, influences the biocatalyst activity.

Effect of rheology on mass transfer and bubble sizes in a bubble column operated in the heterogeneous regime

AbstractA recently developed measurement method has been applied for the first time to the characterization of a bubble column operated in the heterogeneous regime and in presence of non‐Newtonian fluids. The resulting measurements of bubble size are completed with local gas holdup and global mass transfer characterizations. A strong impact of rheology on both bubble size and mass transfer is observed, at any tested superficial gas velocity. A dissociation of the liquid side mass transfer kL and the specific interfacial area (a) is proposed. Results show that the kL model previously validated in stirred tanks filled with complex fluids is satisfyingly extended to bubble columns. The incoming databank will be of great help to develop and validate multiphase hydrodynamic models, especially in the scope of biotechnology and associated systems of complex rheology.

The role of non-frothing reagents on bubble size and bubble stability

Xanthates are widely used for the flotation of most sulphide minerals. As well as xanthates, various reagents (e.g. sodium hydrosulphide, NaHS) are used in sulphide mineral flotation to improve selectivity. Both xanthates and NaHS target the solid–liquid interface and modify the surface to achieve sufficient difference in wettability between the gangue and target mineral. This study examines the role of potassium amyl xanthate (PAX) and NaHS at the air–liquid interface in the presence of a frother, methyl isobutyl carbinol (MIBC). The separate and joint effects of these reagents on the stability of bubbles were studied by measuring bubble size in a batch flotation cell and the lifetime of bubble pairs using a bubble coalescence apparatus. The results of the bubble coalescence experiment with the PAX/MIBC mixture showed that the presence of PAX in a concentration as low as 1 ppm significantly increased the bubble lifetime compared to the MIBC only solution. The lifetime of the bubbles was longer in the NaHS/MIBC mixture, although this might be due to the gain in the liquid viscosity in the presence of high NaHS concentrations. Depending on the concentration of PAX in the solution, the bubbles showed unstable, metastable and ultra-stable behaviors. The influence of PAX and NaHS on the Sauter mean diameter of bubbles was studied and both had a notable effect on inhibiting bubble coalescence, reducing the bubble size by 26%, while in the PAX/MIBC mixture, the size of the bubbles was largely dominated by the concentration of MIBC. Overall, the results strongly suggested that the role of PAX and the synergistic effect of PAX, NaHS and MIBC in modifying the air–liquid interface should be considered when using these reagent combinations.

Measurement of the air bubble size and velocity from micro air bubble generation (MBG) in diesel using optical methods

In this paper, we determine the bubble size and velocity from air bubble generation (MBG) in a diesel using optical methods. A KTM Series Pump was used to generate micro air bubbles in diesel. The air bubble radius and velocity measurements can be useful parameters to optimize the bubble generation process. Two optical systems were used for measurement air bubble sizes and their velocities in diesel. First, the optical system without an objective lens was used to determine the velocity of air bubbles in diesel. Another optical system with a 10× objective lens was used to obtain the size distribution of air bubbles generated in diesel. An available optical system with a 10× objective lens can detect a bubble diameter greater than 3.3 µm that air bubble images were processed using the ImageJ program. We measured the size distribution of air bubbles generated using the ImageJ program. The micro air bubble radius measured in diesel was found to be 6.26 µm in the sample after a month from air bubble generation. In addition, the particle image velocimetry (PIV) technique was used to measure the velocity field. Then, we used the OpenPIV program for PIV image processing. The highest velocity distribution was determined to be 90 mm/s for diesel without air bubbles and 20 mm/s for diesel with air bubbles after a month of the bubble generation.

Labelled Object Velocimetry: Simultaneous Measurements of Bubble Size and Velocity

This paper presents labelled-object velocimetry (LOV) – a technique to determine the velocities of labelled objects in multiphase flow. LOV is based on spatial correlations similar to those used in particle-image velocimetry (PIV) but employs grey-level shadowgraph images to determine object velocities. Object detection and labelling are performed using a classical image-processing algorithm. In contrast to PIV, interrogation areas in LOV are not uniformly distributed. Instead, these areas surround objects, and therefore, depend on object positions and sizes. Additionally, the proposed technique recalls a previously developed algorithm (Laupsien et al., 2019) to distinguish between single bubbles and complex situations, such as overlays, breakups and coalescences. This algorithm-based object selection (ABOS) provides a statistically reliable sample of the entire bubble swarm in terms of size and shape. Although both techniques are completely independent, they can be combined to link object velocities to their geometrical characteristics. Thus, the LOV technique can be used to ascertain velocity-object-diameter histograms.

Development of an efficient buoyant jet integral model of a bubble plume coupled with a population dynamics model for bubble breakup and coalescence to predict the transmission loss of a bubble curtain

The underwater noise radiated during the impact pile-driving of offshore foundations is a major threat to the habitat of several marine creatures. The bubble curtain is a widely used noise mitigation system. A major uncertainty in modeling the acoustic properties of a bubble curtain is the unknown local bubble size distribution. For an accurate estimation, a buoyant jet integral model of a bubble plume is coupled with an existing simplified model of the population dynamics for bubble breakup and coalescence. In this simplified model, the bubble population is divided into two fractions and two one-parameter distribution are used to approximate the overall bubble size distribution. Due to its formulation the resulting bubble formation model is efficient and the calculation time for a typical case is less than five seconds. In comparison to similar approaches, the model incorporates the bubble formation at the nozzle and the high gas fraction in close distance to the nozzle. The approach is validated with three different laboratory bubble size measurements. Subsequently, it is integrated into an existing model of the local acoustic wavenumber of the bubble curtain. The resulting approach is compared with measurements and allows for a prediction of the acoustic properties of a bubble curtain for different nozzle hose configurations, air flow rates and water depth.

Simultaneous measurement of bubble size and growth with phase critical angle scattering

Simultaneous measurement of bubble size and its transient growth is of great importance for the study of bubble dynamics. Current methods based on Lagrangian tracking strategy cannot resolve nanoscale bubble growth within a short time interval. We have developed phase critical angle scattering (PCAS) and the theoretical derivation reveals the capability of PCAS to realize it. Nine air bubble cases are simulated based on a Lorenz-Mie scattering algorithm, and the results show that PCAS technique has a high resolution in size variation down to several nanometers and high accuracy with errors within 9%. Then the PCAS technique is applied to measure single growing bubble generated by electrolysis. By comparing the size measurement reults with results of the microscopic imaging, the size measurement accuracy of PCAS is evaluated to be around 7%. The PCAS technique has great potential in the characterization of bubble-like particle dynamics.

Experimental study of an initially pressurized water target irradiated by a proton beam

This experimental visualization study was conducted to investigate and define the phenomena of an initially pressurized liquid water target that can prevent the boiling of water when the target is irradiated with a 30-MeV proton beam produced using the MC-50 Cyclotron at Korea Institute of Radiological and Medical Sciences. At various initial pressures and proton beam currents, the behavior of the target water was investigated using a complementary metal–oxide–semiconductor camera. We confirmed that an appropriate initial pressure could indeed prevent local bulk boiling, and be determined by solving Rayleigh's equation and the Clausius–Clapeyron equation for homogeneous bubble growth using the measured bubble size generated at the Bragg-peak region. The saturation temperature of the initial pressure must be higher than the calculated local water temperature at the Bragg-peak region. The final pressure of the water target increased proportionally with the initial pressure and proton beam current. The penetration depth of the beam varied with beam current and slightly with the final pressure, as evidenced by the emission of blue light in all experimental cases.

Direct bubble size measurement in a mechanical flotation cell by image analysis and laser diffraction technique - A comparative study

Froth flotation is one of the most widely used methods to separate minerals. Although the bubble size of froth is a critical factor which affects the separation efficiency, accurate measurement of bubble size in a flotation cell brings its own challenges. Accordingly, in this study, the size distribution of the bubbles which were produced in a mechanical flotation was determined by both a new step-up system and the authentic laser diffraction (LD) technique. Image analysis (IA) as a typical technique for measuring bubble sizes was applied to validate the accuracy of the LD measurements and to compare the results. IA and LD outcomes in various bubble generation conditions were in a good agreement. Results revealed that LD technique is relatively faster, easier, and more accurate than IA. Therefore, measuring bubble size by LD can be considered as a reliable, alternative method to IA to determine the bubble sizes in different conditions in a mechanical flotation cell.

Discrimination of Six Flotation Kinetic Models Used in the Conventional Flotation and Carrier Flotation of -74 μm Coal Fines.

In this study, experimental results of conventional flotation and carrier flotation were characterized by six commonly used flotation kinetic models. Two statistical criteria (coefficient of determination, R2, and root mean square error, RMSE) were used for comparison of fitting performance of different models. All kinetic models tested gave good levels of goodness of fit, but the second-order model with rectangular distribution (model 6) provided the best fitting performance for the experimental data of conventional flotation and carrier flotation. On this basis, two parameters, that is, modified flotation rate constant (Km) and selectivity index (SI), were used to evaluate the difference in flotation separation selectivity between conventional flotation and carrier flotation. Comparisons of Km and SI values indicated that carrier flotation significantly improved the flotation rate constant of combustible materials and flotation separation selectivity of ultrafine coal (−74 μm). In addition, measurements of average bubble size and water recovery indicated that both the coalescence of bubbles and the drainage of liquid in the froth were promoted when coarse coal particles (contact angle >90°) were employed as the carrier to assist the flotation recovery of ultrafine particles, which in turn favored the inhibition effect of the entrainment of gangue materials in carrier flotation compared to conventional flotation.

Theoretical and Experimental Gas Volume Quantification of Micro- and Nanobubble Ultrasound Contrast Agents.

The amount of gas in ultrasound contrast agents is related to their acoustic activity. Because of this relationship, gas volume has been used as a key variable in normalizing the in vitro and in vivo acoustic behavior of lipid shell-stabilized bubbles with different sizes and shell components. Despite its importance, bubble gas volume has typically only been theoretically calculated based on bubble size and concentration that is typically measured using the Coulter counter for microbubbles and nanoparticle tracking analysis (NTA) for nanoscale bubbles. However, while these methods have been validated for the analysis of liquid or solid particles, their application in bubble analysis has not been rigorously studied. We have previously shown that resonant mass measurement (RMM) may be a better-suited technique for sub-micron bubble analysis, as it can measure both buoyant and non-buoyant particle size and concentration. Here, we provide validation of RMM bubble analysis by using headspace gas chromatography/mass spectrometry (GC/MS) to experimentally measure the gas volume of the bubble samples. This measurement was then used as ground truth to test the accuracy of theoretical gas volume predictions based on RMM, NTA (for nanobubbles), and Coulter counter (for microbubbles) measurements. The results show that the headspace GC/MS gas volume measurements agreed well with the theoretical predictions for the RMM of nanobubbles but not NTA. For nanobubbles, the theoretical gas volume using RMM was 10% lower than the experimental GC/MS measurements; meanwhile, using NTA resulted in an 82% lower predicted gas volume. For microbubbles, the experimental gas volume from the GC/MS measurements was 27% lower compared to RMM and 72% less compared to the Coulter counter results. This study demonstrates that the gas volume of nanobubbles and microbubbles can be reliably measured using headspace GC/MS to validate bubble size measurement techniques. We also conclude that the accuracy of theoretical predictions is highly dependent on proper size and concentration measurements.

Measurement of Bubble Size, Gas holdup and Interfacial Area in Bubble Columns using Image Processing Techniques

Bubble sizes in bubble column affect transfer processes. Therefore, it’s important to calculate bubble size and interfacial area. Bubble size distribution (BSD) in a bubble column of rectangular cross section with dimensions 0.2m x 0.02m was measured using photographic method (400 fps) for air-water system. Gas holdup, Sauter-mean bubble diameter, aspect ratio and specific interfacial area were estimated from BSD. Effect of superficial gas velocity and static bed height on these parameters was investigated. The bubble size distribution exhibited mono-modal distribution showing the presence of non-uniform homogeneous bubbling regime. The frames of video were analysed using image processing steps to obtain major and minor axis of elliptical bubbles. Values of d32, , and ai were estimated from the data. The value of d32 increased with increasing Ug but is independent of Hs. The values of d32 were somewhat higher than the values reported by other investigators. The value of ai increases with increasing Ug and with decreasing Hs. Present values of compared well with the data reported in literature.

Bubble size and liquid-side mass transfer coefficient measurements in aerated stirred tank reactors with non-Newtonian liquids

Oxygen transfer is a key element in aerobic fermentations, especially if the culture broth’s rheology is non-Newtonian, as in the case of cultures of filamentous fungi. Viscosity negatively affects the volumetric mass transfer coefficient (kLa), but mechanisms involved in terms of change of interfacial area (a) and liquid-side mass transfer coefficient (kL) have still not been clearly identified. This lack of knowledge is in part due to the difficulty in measuring bubble size in viscous fluids. In this study, an innovative technique was used to measure bubble Sauter diameter (d32) in water and in xanthan gum solutions. Additional experiments were carried out to obtain the volumetric mass transfer coefficient and the global gas holdup (αG). It was then possible to obtain the liquid-side mass transfer coefficient and to compare it with existing models. Finally, empirical correlations were proposed to estimate d32,αG,kLa and kL in a mechanically stirred tank.