Bubble Coalescence Research Articles

Experimental investigation of pressure fluctuation in a mixed-flow pump under gas–liquid two-phase flow conditions

The flow in mixed-flow pumps under gas–liquid operating conditions is complex, involving special phenomena such as secondary flow and bubble breakup and coalescence. As a result, its pressure fluctuation characteristic is far different from that under pure water conditions. In this work, the energy performance, pressure fluctuation characteristics, and flow pattern under different inlet gas volume fractions (IGVFs) are studied through a visualization test in a mixed-flow pump. The air pocket forms easily close to the suction side of diffuser vanes, where two pressure fluctuation monitoring points are set up. The pressure increment decreases continuously when the IGVF increases, and the flow pattern shows a transition from bubble, condensed bubble, and air pocket to separated flow. Moreover, the pressure fluctuation amplitude and peak-to-peak values increase. The main frequency under different IGVFs is maintained as the blade passing frequency. When the IGVF increases to 15%, the peak-to-peak amplitude at P1 reaches the maximum, which is 2.24 times that of the pure water condition. Some amplitudes at one frequency fluctuate at different times when the IGVF is higher than 10%. The findings contribute theoretical support in improving the stability of multiphase pumps.

Characterization of microbubble aggregation in a double-T microfluidic chip

The coalescence phenomenon of air bubbles affects the flow field, bubble morphology, bubble velocity, and mass transfer efficiency in bioreactors, air bubble generators, and other devices. This article combines the level set method with COMSOL to simulate the formation process of two-phase fluid bubbles in microfluidic chips. The result shows that when the contact angle exceeds 90°, significant agglomeration occurs and the size of bubbles decreases with the increase in liquid flow velocity. However, as the gas velocity increases, agglomeration does not occur at liquid flow rates below 0.1 m/s. In addition, the agglomeration phenomenon occurs above the threshold, and when the gas flow rate is less than 0.02 m/s, there is no agglomeration phenomenon. The numerical simulation results exhibit an error rate of less than 10% compared to the experimental values, indicating that microfluidic chips can accurately predict the process of bubble coalescence.

Simulation analysis of bubble coalescence behavior characteristics in Newtonian fluids based on the phase field method

Gas-liquid two-phase flow is widely used in various fields of chemical production because of its stability. The bubble coalescence behavior significantly impacts bubbles’ size, shape, and movement. These parameters are essential for interphase mass, heat transfer processes, and equipment performance. This paper presents a simulation study of the bubble coalescence behavior of Newtonian fluids using the phase field method through simulation software. The relative location of bubbles were divided into three types: vertical, parallel and random; and also the distribution of bubbles can be divided into three cases: symmetric, left-skewed and right-skewed. This paper focuses on the influence of the arrangements of the bubbles on their coalescence behavior in Newtonian fluids. The results show that the relative distance of bubbles is the crucial factor for the occurrence of bubble coalescence in Newtonian fluids, and different distributions show different laws on the motion of bubbles.

Hydrodynamic Insights on Floating Bubbling Fluidized Beds: Dynamic Solutions for Mitigating Gas Maldistribution

This study examined bubbling fluidized beds as an alternative to fixed-bed dry scrubbers on ships for reducing pollutants from marine fuels. It focused on overcoming the challenges of gas maldistribution/slug formation, especially under rough sea conditions. This research departed from traditional methods by introducing mobile internal elements into the bed emulsion phase and investigating their effectiveness in various settings, such as vertical, inclined, and rolling beds. A specialized hexapod-driven bubbling fluidized bed was developed to mimic marine operating conditions and to study the behavior of shipboard fluidized beds. Techniques such as digital image analysis (DIA) and particle image velocimetry (PIV) were used to observe bubble dynamics and granular phases, measuring local void fractions and particle velocities. A key finding is the effectiveness of moving internals in preventing bubble coalescence, which is critical for avoiding wall slugs, at different inclinations. Three types of packing were used as mobile internals: Super Raschig, Pall, and square rings. Super Raschig rings, which are characterized by high porosity, were the most efficient in reducing bubble coalescence, making them a preferred choice for offshore fluidized bed applications. This research contributes to the advancement of fluidized bed technology in marine applications and provides insight for future improvements.

Pool boiling on vertical and horizontal heated plates with a dielectric fluid: Influence of vertical canal width

A closed system testbench has been developed to study pool boiling with a dielectric fluid at atmospheric pressure. The experimental setup consists in immerged horizontal and vertical adjacent heated plates, representing the corner of a parallelepipedal heating element. Both plates are 64x40mm2. The plates can be heated separately or simultaneously, with surface heat flux ranging from 0 to 20 W/cm2. Additionally, the canal width in front of the vertical heated plate is varied from 0.5 to 15 mm to study the influence of confinement. The opposite wall of the canal is made of transparent glass to allow optical visualization of the boiling on the vertical plate. A condenser at the top of the system controls the fluid subcooling. The wall temperatures are measured in steady-state regime in the middle of the plates, heat transfer coefficients are also determined. This configuration leads to complex flows, from natural convection to film boiling, including nucleate boiling. For low heat flux, smaller vertical canal widths enhance natural convection mixed with phase change phenomena: this conveys significantly higher heat transfer coefficients than in the vertical free configuration case. At higher heat flux, confinement does not enhance heat exchange on the vertical plate. When the vertical plate is confined, bubble coalescence and critical heat flux occur for lower heat flux compared to the free configuration. Visual observations on boiling regimes on the vertical plate are given depending on confinement. Finally, simultaneous heating of both plates is compared to isolated plate heating: boiling on the vertical plate improves heat exchange on the horizontal one, whereas boiling on the horizontal plate has no effect on the vertical one.

Fast simulation of industrial-scale bubbling fluidized beds using mesoscience-based structural model

Fast and accurate simulation of industrial-scale reactors is the first and critical step towards virtual process engineering. In this article, we show for the first time that a recently proposed mesoscience-based structural model, which treats the bubble phase and the emulsion phase as the two interpenetrating continua, is able to achieve fast and accurate simulation of the hydrodynamics of four industrial-scale bubbling fluidized beds, in terms of macroscopic distribution of parameters such as the bed expansion rate, the axial and radial profiles of solid concentration and velocity. On the other hand, due to the fact that the mesoscale bubbling structures have been averaged over during the model derivation and the mesh sizes used are comparative to or larger than the bubble diameter, it is impossible to correctly capture the evolution, coalescence and breakup of bubbles. Therefore, the mesoscience-based structural model is best used as a computational fluid dynamics based method for fast engineering simulations of gas-solid fluidization.

Surfactant foamulsion stability in the absence and presence of salt

Foamulsions are widely used in many fields but the stability of them is still not fully understood. We investigate the evolution of foamulsions in the absence and presence of inorganic salt. For the system without salt, it is found that the effect of oil on the foamulsion properties depends on the critical threshold concentration of surfactant (300 mM), below which the foamulsion aging is slowed down and above it its evolution is facilitated. When salt is added, the surfactant molecules precipitates to form crystals, foamulsions tend to be generated in regions where the surfactant concentration is not less than the salt concentration, but it is difficult to foam at salt concentrations higher than 200 mM, independent of the oil concentration, unless the surfactant concentration is very high. For the prepared stable foamulsions, the stabilization mechanism is due to the inhibition of coarsening and coalescence of bubbles and oil droplets by the adsorption of surfactant molecules and crystal particles onto their surfaces. The investigation of adsorption kinetics show that maybe the crystals move to the surface of bubbles is faster than oil droplets. The system consisting of surfactant, oil, salt and water is simple and temperature sensitivity, which could have many potential applications.

Experimental and theoretical study on liquid-vapor behavior characteristics near CHF

Liquid-vapor behavior characteristics near CHF conditions are investigated through flow visualization experiments and theoretical analysis. The detailed liquid-vapor behavior near CHF is captured by high-speed camera in this paper. With the increase of heat flux, the periodic vapor layer occurs due to numerous large bubble coalescence. A three-layer structure is observed close to CHF conditions, i.e., liquid film, vapor layer, and liquid core. The physical triggering mechanism of CHF is the complete evaporation at the liquid film wave trough position close to the end of the heating rod. Furthermore, based on the separated flow model and instability analysis, respective prediction models for essential liquid-vapor characteristics, including thickness of vapor layer, interfacial wavelength, and the maximum thickness of liquid film, are developed. The predicted results are in good prediction performance with MAE of 16.9 %, 12.8 %, and 26.1 % compared to experimental results, respectively. The relevant research in this paper provides an important foundation for further development of the mechanistic CHF model.

Differences in ultrasonic cavitation damage between new and used engine coolants with varying time in operation

This study investigates the cavitation erosion performance of heavy-duty engine coolants before and after operation in trucks using an ultrasonic test rig based on ASTM G32. Fresh coolants with 35% and 50% v/v glycol were compared with used coolants. One coolant was obtained from a gasoline-fueled vehicle with a mileage of 27000 km, and two from diesel-fueled vehicles with mileages of 16000 and 180 000 km, respectively. Surface tension and boiling point at atmospheric pressure were measured, a chemical analysis was carried out, and suspended particles were quantified by dynamic image analysis. The results showed that the used coolants caused a lower mass loss in ultrasonic cavitation testing than the fresh ones, and that they had higher boiling points, lower pH and a higher number of suspended particles, especially of those smaller than 30μm. Surface tension was higher for the used coolants from Diesel engines.The lower mass loss caused by all three used coolants can be attributed mainly to their high boiling point and high particle count. The presence of particles is believed to promote the heterogeneous nucleation of smaller, more stable bubbles, which may protect the exposed surface by shockwave absorption and microjet deflection. Some dissolved ions in the used coolants may help reduce their aggressivity by inhibiting bubble coalescence, reducing bubble collapse energy, despite increasing surface tension. Surface tension has complex interactions with the solutes, particles and bubble formation and cannot, in isolation, explain the differences in performance of the coolants.

Study on inhibition mechanisms of detachment of coal particles from oily bubbles in flotation column

The cyclonic microbubble flotation column is an efficient separation equipment in the beneficiation process of metallic and non-metallic minerals. However, the higher detachment rate of coarse particles in the pulp, pulp-froth interfacial zone, and froth zone is an issue that needs to be addressed urgently in column flotation. Compared with traditional air-water bubbles, oily bubbles have higher hydrophobicity, which is beneficial for strengthening the bubble-particle attachment and inhibiting the bubble-particle detachment. Therefore, oily bubbles were introduced into the cyclonic microbubble flotation column to reduce the particle detachment rate. Firstly, an improved cyclonic microbubble flotation column was set up, and traditional air-water bubbles were placed by oily bubbles through the combined use of an atomizer and a bubble generator during experiments. Subsequently, we investigated the feasibility of using oily bubbles as a flotation carrier to regulate the particle detachment rate, improve the particle recovery, and explore the mechanism behind this. Column flotation results showed that recovery rates generated from experiments with oily bubbles are higher than those with air-water bubbles under different operation conditions, and the particle detachment rate in the interfacial region was significantly reduced with the use of oily bubbles. Recoveries and flotation rate constants generated from collection zones for each particle size range indicated that the use of oily bubbles can increase the upper limit of flotation particle size compared with the use of air-water bubbles. Calculated detachment rates showed that the use of oily bubbles can effectively reduce the detachment probability of particles with different sizes in the collection zone. Combined with the observation of ultrasonic-assisted oscillation, it is proved that the oil coating film on the oily bubble significantly improves the resistance of oily bubbles to turbulent disturbance. In addition, the increase in hydrophobic force between oily bubbles and particles and the growth of the three-phase contact periphery are beneficial to reducing the particle detachment probability due to turbulent disturbance in the collection zone. Results from bubble coalescence experiments showed that the existence of oily bubbles significantly reduced bubble coalescence time and increased the damping coefficient. Compared with air-water bubbles, oily bubbles have a stronger damping effect on the oscillation caused by bubble coalescence, inhibiting the violent bubble surface deformation and the induced particle detachment during bubble coalescence. Therefore, the introduction of oily bubbles is a promising idea to reduce the detachment probability of coarse particles and increase the upper limit of particle size in column flotation.

Enhancing thermal mixing in turbulent bubbly flow by inhibiting bubble coalescence

The presence of bubbles in a turbulent flow changes the flow drastically and enhances the mixing. Adding salt to the bubbly aqueous flow changes the bubble coalescence properties as compared to regular demineralized water. Here we provide direct experimental evidence that also the turbulent thermal energy spectra are strongly changed. Experiments were performed in the Twente Mass and Heat Transfer water tunnel, in which we can measure the thermal spectra in bubbly turbulence in salty water. We find that the mean bubble diameter decreases with increasing concentration of salt (NaCl), due to the inhibition of bubble coalescence. With increasing salinity, the transition frequency from the classical −5/3 scaling of the thermal energy spectrum to the bubble induced −3 scaling shifts to higher frequencies, thus enhancing the overall thermal energy. We relate this frequency shift to the smaller size of the bubbles for the salty bubbly flow. Finally we measure the heat transport in the bubbly flow, and show how it varies with changing void fraction and salinity: Increases in both result into increases in the number of extreme events.

Bubble-particle detachment behavior during bubble coalescence: Role of bubble size

Studies have reported that bubble coalescence causes particle–bubble detachment in the flotation pulp and foam phases. Most coalescence experiments have been conducted using bubble pairs with the same diameter; however, this is not the case in real flotation. In this study, particle–bubble detachment behavior during the coalescence of two bubbles with different sizes was investigated using a high–speed camera, and the variation of the coalescing bubble area was fitted to a damped oscillatory equation and analyzed. To explore the intrinsic detachment mechanism of the bubble size effect, the flow field variation in the bubble periphery was simulated using COMSOL 6.1. Results show that the particle–bubble detachment probability decreased with increasing bubble size difference. The released energy is greatest when the two equal bubbles coalesced, thus leading to the strongest oscillation and highest detachment probability. The simulation results show that turbulent kinetic energy affects particle-bubble stability and is an important reason for inducing particle-bubble detachment. Notably, particle–bubble detachment did not occur at the maximum turbulent energy, because there was a delay due to the time required for the sliding contraction of the three–phase contact line. The research finding provides new insights into the mechanism of particle–bubble detachment.

Interface behavior and pore distribution of Ti6Al4V/CFRTP joints affected by groove profile

This study investigated the effect of groove profile on interface behavior, pore distribution, and bonding mechanism between Ti6Al4V (TC4) and carbon fiber reinforced thermoplastic (CFRTP). Using an ultraviolet picosecond laser system, grooves with varying depth-width ratios (R) and distances between adjacent grooves (T) were precisely etched on the TC4 surface. Experiment results revealed that grooves effectively impede bubble coalescence and growth, reduce pore defects at the grooves’ outer interface, and promote closer bonding between TC4 and CFRTP, thereby enhancing joint strength. In this study, grooves significantly improved joint strength by 40.2 % to 147.5 %, primarily due to increased mechanical interlocking and bonding area. Differences in joint strength among grooved joints are mainly attributed to variations in interface behavior and pore distribution caused by R and T. Appropriate R and T are crucial for inhibiting large-volume pores and reducing pores at the grooves’ outer. When R = 1/5 and T = 360 μm, the joint with small-volume pores, no pores at the grooves' outer, and the lowest porosity exhibits the highest strength (2830.3 N). Grooves showed no significant impact on chemical bonding (CTi0.42V1.58 carburization phase and TiOS). Furthermore, no significant effect of grooves on the chemical bonding (CTi0.42V1.58 carburization phase and TiOS).

Subcooled flow boiling in ultrahigh-aspect-ratio microchannels for high heat flux cooling

In present work, the numerical simulation and experimental investigations were performed on the subcooled flow boiling behavior in ultrahigh-aspect-ratio microchannel heat sink (AR = 25). As the heat flux is low, the unique discotic bubble expands the condensation area while ensuring an adequate evaporation area in the channel. When the heat flux increases, the violently fluctuating liquid-vapor interface forms a throat shape that effectively reduces the cross-section of vapor flow. Furthermore, the flow pattern of annular flow at the channel bottom and nucleate bubble at the channel top realizes a combined heat transfer mechanism (nucleate boiling and liquid film evaporation occurs simultaneously). Moreover, the phenomenon of “droplet inside the bubble” caused by bubble coalescence also significantly enhances the thermal process. The fluctuation of local pressure drop in UARM acts gently, which effectively inhibits the boiling instability, and its average value can be reduced by 68.9%. The maximum CHF reaches 1258.1 W/cm2 under a mass flux of 410.2 kg/(m2·s) based on the experimental data, indicating a tremendous potential for the efficient heat dissipation.

Prospects for the implementation of SWAG-technology to enhance oil recovery at the Rechitskoe field using flue and flare gases

This article proposes the introduction of SWAG-technology at the Rechitskoe oil field of RUE Belorusneft. An analysis of previously conducted research on the implementation of technology at the selected facility revealed a number of technological factors that reduced the effectiveness of the method. It is proposed to use pump-ejector systems –devices that will allow obtaining and pumping a water-gas mixture with the required pressure. To ensure rational gas content, it is advisable to add flare and flue gases to the water, which will reduce the carbon footprint. The addition of foaming surfactants helps to improve the characteristics developed by the booster pump, suppress the coalescence of gas bubbles and increase the efficiency of injection of the water-gas mixture.

Bubble flow analysis using multi-phase field method

In simulations of gas-liquid two-phase flows using conventional interface capture methods, we observed that when bubbles come close to each other, they tend to merge numerically, despite experimental evidence indicating that they would repel each other. Given the significant impact of sequential numerical coalescence on flow patterns, it is necessary to regulate the merging behavior of close bubbles. To address this issue, we introduced the Multi-Phase Field (MPF) method, which mitigates bubble coalescence by applying an independent fluid fraction function to each bubble. In this study, we employed the MPF based on the N-phase model [7] to minimize numerical errors associated with surface interactions at triple junction points. Additionally, we implemented the Ordered Active Parameter Tracking (OAPT) method [9] to efficiently store several hundreds of fluid fraction functions. To validate the MPF method, we conducted analysis of turbulent bubbly pipe flows and compared the results against experimental data from Colin et al [12]. The validation results showed reasonable agreements with respect to the bubble distribution and the flow velocity profiles.

Semi-mechanistic prediction of DNB heat flux based on global bubble coalescence concept

Semi-mechanistic prediction of DNB heat flux based on global bubble coalescence concept

Experimental and numerical investigation on the bubble breakup and coalescence characteristics in the highly efficient static mixers

CFD-PBM and experiment methods were applied to study the bubble dispersion characteristics in the static mixers with three twisted blades (TKSM). The gas-liquid velocity ratio was selected as drag correction factors. The simulation data was compared with experimental values at different superficial gas velocity and the results revealed that the modified model could effectively enhance the calculation accuracy of gas holdup. Furthermore, bubble size distribution (BSD) was well predicted by Luo-Prince model and the mean relative error (MRE) of axial d32 between the prediction of Luo-Prince model and experimental value was 2.86 %. Meanwhile, the influences of bubble collision mechanisms and coalescence correctors on the numerical prediction were quantitatively analyzed. The effects of turbulent fluctuation, viscous shear, wake entrainment and buoyancy driven were considered for the prediction of bubble collision frequency in TKSM. The prediction precision of cumulative probability distribution (CPD) was promoted by 17.26 % when the correctors obtained from Energy-Minimization Multi-Scale (EMMS) method were used. In addition, empirical parameter CDas was evaluated and the results showed that the Das coalescence model could accurately describe the BSD when CDas was 0.01–0.1. The backmixing performance of the gas phase in the TKSM exceeds that of the liquid phase, which is distinct from that in vortex unit.

Experimental investigation on bubble dynamic behaviors in pool boiling of surfactant solutions

In this study, pool boiling experiments on copper surfaces with different roughness levels (Ra = 0.61 μm and Ra = 0.15 μm) using sodium dodecyl sulfate (SDS) solutions at various concentrations (0.1 CMC, 1 CMC, 5 CMC, and 10 CMC) are investigated. Our study focuses on the impact of SDS concentration, wall superheat, surface roughness, and bubble behavior on boiling heat transfer. The results show that an increase in SDS concentration could improve the heat transfer. However, when the SDS concentration reaches 10 CMC, there is a deterioration in heat transfer. Additionally, rough surfaces show better heat transfer performance compared to smooth surfaces. The presence of surfactant not only promotes bubble nucleation but also reduces the bubble departure diameter and inhibits bubble coalescence. Multiple bubbles are formed from the same nucleation site in surfactant solutions with high concentrations (5 CMC, 10 CMC). Various bubble dynamic parameters, including instantaneous size, departure diameter, growth time, waiting time, and departure frequency are obtained and compared with existing empirical correlations in the literature. It is found that the bubble growth in both deionized water (DI water) and surfactant solutions is mainly influenced by the near-wall thermal conditions, aligning with the thermal diffusion mechanism. In addition, the bubble departure diameters in both DI water and surfactant solutions gradually increase with increasing Jakob number (Ja). The growth time and waiting time in the surfactant solution both decrease with increasing Ja number, leading to a significant rise in the departure frequency. In contrast, the bubble growth time in DI water increased and the waiting time decreased with increasing Ja number, resulting in a relatively stable departure frequency. A new empirical formula is proposed for fDd0.5 based on the surface tension coefficient, surface roughness, and Ja number, which demonstrates good rationality.

Improved gas influx distribution estimation using interfacial area transport equation (IATE) enabled two-fluid model: An advanced modeling and full-scale experimental study

Gas influx management is a critical aspect of petroleum drilling operations, which aims to prevent the uncontrolled outflow of formation gas and the potential consequences caused by blowouts. This study investigates the distribution of gas influx and the interfacial area concentration (IAC) during gas influx circulation operations through a combination of full-scale experiments and advanced numerical simulations.Experiments were conducted to simulate downhole gas influxes by injecting Nitrogen gas into the base of a 5,160-foot-deep experimental wellbore, which was filled with water. A Distributed Fiber-Optic Sensing (DFOS) system was installed in the wellbore to obtain high-resolution acoustic and temperature data and monitor the gas influx behaviors when circulated out of the annulus. Various types of measurements were obtained to analyze the gas influx length, slip velocities, void fraction distribution, and dispersion behaviors. In addition, an advanced numerical simulator was developed based on a modified Two-Fluid Model and the Interfacial Area Transport Equation (IATE) to simulate the gas influx behaviors. The model estimations were compared to the experimental measurements for validation of accuracy and further insights.The numerical modeling framework, based on the interfacial area transport equation, effectively captured bubble interactions, including mechanisms including bubble breakage and coalescence, by estimating the interfacial area distribution. The gas influx dispersion during circulation was analyzed using both model estimations and experimental data. Good agreement was observed between the model predictions and experimental data, including multi-depths gauge measurements and the DFOS data.This is a novel application of the IATE in well-scale multiphase flow simulations, which has proved to be an effective tool for predicting the dynamics of gas influx distributions. The outcomes of this study provide critical insights into the design and optimization of gas influx management during Managed Pressure Drilling (MPD).