Frequency Of Bubble Formation Research Articles

Vapor bubbles departure frequency at ferrofluid boiling on a single nucleation site in a uniform horizontal magnetic field

The departure frequency of vapor bubbles at boiling of ferrofluid in a uniform stationary horizontal magnetic field is studied experimentally. The formation of bubbles occurs on a single nucleation site. Two different methods are used to measure the frequency of vapor bubble departure. One is visual and consists in observing bubbles emerging in a two-layer ferrofluid-non-magnetic fluid medium. The other method is inductive and is based on the generation of induction current in the coil turns through which the vapor bubbles move. It is found that the frequency of vapor bubble departure can decrease several times with increasing magnetic field strength, and the frequency will increase with increasing temperature of the heat-emitting surface. An analysis of the influence of the magnetic field on the frequency of vapor bubble formation during ferrofluid boiling based on a linear stability analysis of the liquid–vapor boundary is presented.

Dynamics of bubble formation in yield stress fluids in parallelized microchannels

The bubble formation in yield stress fluids in parallelized microchannels is investigated experimentally. Nitrogen and Carbopol gel are used as the dispersed and continuous phases, respectively. Due to the feedback effect of the downstream microchannels, the uniformity and stability of bubble formation strongly depends on the properties of gels and operating conditions. The effect of yield stress on the interface evolution during bubble formation is investigated under different mass factions of Carbopol (0.2 %, 0.13 %, 0.05 %) and flow rates of gas (0.1–400 mL·min−1) and liquid (0.03–0.2 mL·min−1). The activation rate of parallel microchannels for bubble production increases with the decrease in the concentrations of Carbopol. The increase of liquid flow rate and the decrease of gas flow rate benefit the uniformity of bubble formation frequency. However, under the double-channel bubble-generation flow pattern, reducing the liquid flow rate significantly improves the stability of bubble formation.

Experimental research on aerosol deposition phenomenon in single-sized rising bubble

Bubble filtration in pool scrubbing is an important physical process to reduce the release of aerosol in gas during a severe accident. In this paper, experimental research on the phenomenon of aerosol deposition in single-sized bubbles was carried out. Also, the characteristic parameters of bubble dynamics, such as bubble diameter, and rising velocity, are synergistically studied with the deposition efficiency, and the quantitative relationship between them was analyzed. The experiments have also revealed the presence of a most penetrating particle size between 125 and 150 nm. The results show that bubble size is a sensitivity factor affecting the deposition efficiency of aerosol, and the deposition efficiency is negatively correlated with bubble size. Under the bubbling condition with nozzle sizes of 0.8 mm and 1.26 mm, the deposition efficiency may decrease from 95% to 81% when the bubble diameter change from 3.1 mm to 6.1 mm. The effect of bubble size on efficiency is mainly reflected in the change in retention time and aerosol migration distance, and this change is caused by the rising velocity instead of the bubble aspect ratio. Moreover, the entrance effect of the bubble formation process is also found in the study, in which the aerosol deposition efficiency caused by the centrifugal effect is positively correlated with the injection velocity and bubble formation frequency.

Biodegradable magnesium fuel-based Janus micromotors with surfactant induced motion direction reversal

The speed and motion directionality of bubble-propelled micromotors is dependent on bubble lifetime, bubble formation frequency and bubble stabilization. Absence and presence of bubble stabilizing agents should significantly influence speed and propulsion pattern of a micromotor, especially for fast-diffusing molecules like hydrogen. This study demonstrates a fully biodegradable Janus structured micromotor, propelled by hydrogen bubbles generated by the chemical reaction between hydrochloric acid and magnesium. Six different concentrations of hydrochloric acid and five different concentrations of the surfactant Triton X-100 were tested, which also cover the critical micelle concentration at a pH corresponding to an empty stomach. The Janus micromotor reverses its propulsion direction depending on the availability and concentration of a surfactant. Upon surfactant-free condition, the Janus micromotor is propelled by bubble cavitation, causing the micromotor to be pulled at high speed for short time intervals into the direction of the imploding bubble and thus backwards. In case of available surfactant above the critical micelle concentration, the Janus micromotor is pushed forward by the generated bubbles, which emerge at high frequency and form a bubble trail. The finding of the propulsion direction reversal effect demonstrates the importance to investigate the motion properties of artificial micromotors in a variety of different environments prior to application, especially with surfactants, since biological media often contain large amounts of surface-active components.

Dynamics of bubble formation in spontaneous microfluidic devices: Controlling dynamic adsorption via liquid phase properties

HypothesisThe interplay of interface evolution and surfactant adsorption determines the formation and stabilization of bubbles, and can be controlled by the liquid phase properties. ExperimentsWe studied bubble formation in an Edge-based Droplet GEneration (EDGE) microfluidic device at relevant length and time scale, allowing investigation of sub-events in a single bubble formation cycle. We vary the properties of the continuous phase that contains whey proteins and study a range of trans-pore pressures (Pd∗). FindingsThe shallow pores highlight the crucial role of the Laplace pressure and dynamic adsorption of proteins to the meniscus. Bubble formation is divided into two regimes by the Laplace pressure of the bare meniscus inside the pore. At Pd∗<1400 mbar, pre-adsorption of proteins is required to lower the Laplace pressure; the bubble formation frequency f0 increases with increasing protein concentration and is hardly affected by velocity and viscosity. At Pd∗≥1400 mbar, bubble formation immediately occurs upon applying pressure, and f0 mainly decreases with increasing viscosity. In both regimes, the initial bubble size d0 mainly increases with the viscosity (~η1/3). Bubble coalescence is only observed at Pd∗≥1400 mbar and can be effectively suppressed by raising protein concentration and viscosity within certain boundaries, yet ultimately this is at the cost of higher polydispersity of the bubbles. Our insights into the formation dynamics of micrometer-sized bubbles at time scales down to tens of microseconds can be used for effective control of bubble formation and stabilization in practical applications.

Controlling Air Bubble Formation Using Hydrophilic Microfiltration Diffuser for C. vulgaris Cultivation.

In this project, a commercial polytetrafluoroethylene (PTFE) membrane was coated with a thin layer of polyether block amide (PEBAX) via vacuum filtration to improve hydrophilicity and to study the bubble formation. Two parameters, namely PEBAX concentration (of 0–1.5 wt%) and air flow rate (of 0.1–50 mL/s), were varied and their effects on the bubble size formation were investigated. The results show that the PEBAX coating reduced the minimum membrane pore size from 0.46 μm without coating (hereafter called PEBAX0) to 0.25 μm for the membrane coated with 1.5wt% of PEBAX (hereafter called PEBAX1.5). The presence of polar functional groups (N-H and C=O) in PEBAX greatly improved the membrane hydrophilicity from 118° for PEBAX0 to 43.66° for PEBAX1.5. At an air flow rate of 43 mL/s, the equivalent bubble diameter size decreased from 2.71 ± 0.14 cm for PEBAX0 to 1.51 ± 0.02 cm for PEBAX1.5. At the same air flow rate, the frequency of bubble formation increased six times while the effective gas–liquid contact area increased from 47.96 cm2/s to 85.6 cm2/s. The improved growth of C. vulgaris from 0.6 g/L to 1.3 g/L for PEBAX1.5 also shows the potential of the PEBAX surface coating porous membrane as an air sparger.

Особенности формирования «Big Bubble» при проведении глубокой передней послойной кератопластики

Purpose. To determine the optimal channel parameters in the deep layers of the corneal stroma when performing deep anterior lamellar keratoplasty (DALK), providing the maximum frequency of air bubble formation, under the control of intraoperative optical coherence tomography. Material and methods. The study was performed at 30 patients (30 eyes) with a diagnosis of stage III keratoconus. The average age of patients is 31±7 years. All patients were divided into groups consisting of 10 patients, depending on the choice of the topographic orientation of the channel for pneumodissection in the deep layers of the corneal stroma when performing DALK: 1st group – the channel is located towards the center of the cornea; 2nd group – the channel is located paracentral to the temporal side; 3rd group – the channel is located paracentral to the nasal side. In all cases, DALK was performed with a femtosecond laser Femto LDV Z8 (Ziemer, Switzerland). The length of the formed femto channels were variable and amounted to 1.0, 1.5, 2.0, 2.5 and 3.0 mm in each group. Results. The use of intraoperative OCT demonstrated that in all 30 cases the depth of the channel for pneumodissection corresponded to preoperative calculations and amounted to 97±5µm to DM. It was found that the bedding of the channel at a distance of 100µm to the descemet membrane (DM) and its paracentral orientation is characterized by a greater frequency of formation of the «Big Bubble» in comparison with its central orientation: 3rd group – 90% and 2nd group – 80% against 1st group – 60% of cases. The study of the effect of the length of the channel for pneumodissection on the ease of formation of the "Big Bubble" demonstrated that more attempts are required to inject sterile air when channels of 2.0, 2.5, 3.0 mm being used than with short channels of 1.0, and 1, 5 mm (average 3 attempts versus 1.5 attempts, respectively). Conclusion. The paracentral orientation of the location of the channel for pneumodissection is accompanied by a higher percentage of formation of the "Big Bubble" than the central location of the channel. Manual extension of femtochannels having length of 1.0, 1.5 mm, directly with a microsurgical spatula 30G followed by inserting a metal cannula into the channel minimizes the number of attempts to inject sterile air, that facilitates the formation of the "Big Bubble". Performing DALK applying the function of intraoperative OCT allows to control the accuracy of all stages of the operation, including the stage of formation of a large air bubble. Performing DALK with the applying of the function of intraoperative OCT allows to control the accuracy of all stages of the operation, including the stage of formation of a large air bubble. Key words: deep anterior lamellar keratoplasty, Big Bubble, channel for pneumodissection

Deformation and Aspect Ratio of Bubbles Continuously Rising in Shear-Thinning Fluids

The shape deformation of three bubbles with equilateral triangle arrangement continuously rising in shear-thinning non-Newtonian fluids was numerically investigated using the three-dimensional volume of fluid method (3D-VOF). The shape deformation of three continuously rising bubbles was compared with that of a single bubble under consistent operations to analyze the effect of interaction between bubbles. The influences of bubble diameter, initial bubble distance, bubble formation frequency, and liquid rheological property on the aspect ratio of the bubble were investigated. The results indicate that the aspect ratio of the bubble for multi-bubble systems with greater bubble diameter, initial bubble distance, and more intense shear-thinning effect of the liquid decreases, and the shape of the bubble deforms flatter. However, as the bubble formation frequency increases, the deformation of the bubble weakens, and the bubble aspect ratio increases. In comparison with the single bubble rising freely, the aspect ratio of the bubble for the multi-bubble systems is larger. Moreover, a modified model of the aspect ratio of the bubble was proposed by considering the interaction between bubbles for the multi-bubble system.

General rules of bubble formation in viscous liquids in a modified step T-junction microdevice

The understanding of the microbubble formation characteristics in viscous solutions remains confused in terms of the evolution of bubble neck and formation frequency. In this work, the general rules of bubble formation in viscous liquids were systematically investigated in a modified step T-junction. Different viscous glycerol-water solutions and nitrogen were chosen as the continuous and dispersed phase, respectively. A very wide range of bubble formation frequency was determined, and the formation frequencies could be divided into four periods: slightly increased, dramatically increased, approximately linearly increased to the maximum, and gradually decreased as the continuous phase flow rate increased, and the maximum was close to the transition line of bubbly and Taylor bubble flow. To the best of our knowledge, it is the first time to report the general bubble formation frequency range. Finally, the bubble diameter was perfectly scaled with the gas-liquid flow rate ratio and the capillary number.

Computational Study in Bottom Gas Injection Using the Conservative Level Set Method

This paper presents a computational study on bottom gas injection in a cylindrical tank. The bubble formation at submerged orifices, bubble rising, and interactions between bubbles and bubbles with the free surface were studied using the conservative level set method (CLSM). Since the gas injection is an important technique in various fields and this process is quite complicated, the scenario was chosen to quantify the efficacy of the CLSM to describe the gas-liquid complex interactions with fast changes in the surface tension force and buoyancy force. The simulation accuracy is verified with the grid convergence index (GCI) approach and Richardson Extrapolation (RE) and is validated by comparing the numerical results with experimental observations, theoretical equations, and published data. The results show that the CLSM accurately reproduces the bubble formation frequency, and that it can handle complicated bubble shapes. Moreover, it captures the challenging phenomena of interaction between bubbles and free surface, the jet of liquid produced when bubbles break through the free surface, and the rupture of the film of liquid. Therefore, the CLSM is a robust numerical technique to describe gas-liquid complex interactions, and it is suited to simulate the gas injection operation.

Experimental study on the discharge characteristics with downward moving bubbles in a two-dimensional aerated hopper

The characteristics of bubble behaviors during powder discharge process in a two-dimensional aerated hopper were studied by a high-speed camera system. The experimental results show that there are three typical discharge states with the rise of the aeration gas velocity. Correspondingly, three critical aeration gas velocities were all tested including the minimum bubbling, the maximum discharge rate and the minimum bubbling for downward moving to the outlet. The downward moving bubble formation frequency increases with the growth of gas velocity, and its proportion finally stabilizes at about 90%. This tendency is similar with that of the discharge rate. Resultantly, the bubble formed in the powder bed can promote the discharge by provide the interstitial gas to the powder bed, but plays a negative role as it gets larger and substantially moves downward.

Controlled Generation of Vapor/Liquid Slug Flows by Local Boiling in Microgravity

We design, construct, and test a device for controlled boiling by means of local vapor bubble formation in a cavity that injects vapor bubbles in a capillary crossflow. The outcome of the device is a regular slug flow of approximately monodisperse bubbles that can be used for a variety of applications. The setup is designed to be independent of gravity level and is tested succesfully both in normal gravity and in microgravity using drop tower experiments. The device is calibrated by a systematic study determining the size and frequency of bubble formation as a function of pressure and flow conditions. Results turn out to be virtually independent of gravity. Different regimes of operations are identified and described, and basic properties of the behavior of the bubbles inside the nucleation cavity are discussed. The slug flow downstream the crossflow is characterized and shows some differences depending on gravity. Finally, we illustrate the use of a controlled regular slug flow generated by our device by using it as an input of a serpentine heat exchanger. This emphasizes an important virtue of our method for practical applications, namely, the ability to separate the process of bubble formation from the actual heat exchange by phase transformation in the region of interest.

Numerical simulation of underwater air bubble formation under rolling conditions

Underwater gas bubbles are universal phenomenon in various industries. These bubbles appear under ocean conditions especially rolling conditions, that affect the mass transfer and produce different acoustic signals. The bubble formation and oscillation frequency characteristics under rolling conditions were investigated in this study by using a numerical method. Results showed that the bubbles followed two basic steps under rolling conditions, namely, expansion and detachment. The bubble detachment surface area and shape exhibited periodic changes because of the periodical motion of the surrounding water. A correlation was established to predict the bubble detachment surface area under rolling conditions. Similar to the bubble detachment surface area, the bubble oscillation frequency periodically changed. The oscillation mode of the bubbles under rolling conditions was the same as those under motionless condition, that is zeroth mode. A modified Minnaert formula was established to predict the bubble oscillation frequency under rolling conditions.

Study on the formation characteristic of microbubbles used in sewage treatment

Microbubble usually has very small volume, and it is difficult to rise in the water, so it can be used to wrap ozone for sewage treatment. In the present study, the experiments of bubble formation in a mechanical microfluidic device are developed. The effect of liquid flow rate and gas pressure on bubble formation characteristic was obtained through experiments. By observing experimental phenomena, it can be concluded that bubble growth process can be divided into three stages, and the law of the detachment volume and formation frequency of microbubbles under single variable factor was investigated by the control variable method. The investigation of bubble formation characteristic can help to control bubble detachment volume and formation frequency precisely.

Bubble generation by micro-orifices with application on activated sludge wastewater treatment

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 37 μm to 225 μm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with current state of the art of rubber membrane diffusers, bubbles generated from the micro-orifices transfer up to 22% more oxygen content into the continuous phase at up to 51% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency.

Dynamics of bubble formation in highly viscous liquid in co-flowing microfluidic device

In this work, the dynamics of bubble formation in a highly viscous liquid in a co-flowing microfluidic device is experimentally investigated. The evolution of gaseous thread in the co-flowing device is recorded using a high-speed camera. The bubble formation process can be divided into three stages: retraction stage, expansion stage, and collapse stage. According to an analysis of the forces acting on the gaseous thread, the bubble formation in the co-flowing device is a competitive result of the surface tension, pressure difference and shearing effects. The surface tension effect plays an important role in the retraction stage. In the expansion stage, the pressure difference effect dominates the bubble’s growth. While in the collapse stage, the shearing effect leads to the interface breakup. Three empirical correlations are proposed according to the experimental data and can be used to predict bubble formation frequency, the diameter and length of the generated bubbles.

Parametric Study of the Frequency of Bubble Formation at a Single Orifice With Liquid Cross-Flow

The bubble formation frequency from a single-orifice nozzle subjected to the effects of a crossflowing liquid was investigated using high-speed shadowgraphy, combined with image analysis and signal processing techniques. The effects of the nozzle dimensions, orientation within the conduit, liquid cross-flow velocity, and gas mass flow rate were evaluated. Water and air were the working fluids. Existing expressions in the literature were compared to the experimental values obtained. The expressions showed modest agreement with the experimental mean average frequency magnitude. It was found that increasing the gas injection diameter could decrease the bubbling frequency approximately 12% until reaching a certain value (0.52 mm). Further increasing the nozzle dimensions increase the frequency by around 20%. Bubbling frequency is more sensitive to the liquid velocity where changes up to 63% occurred when the velocity was raised from 3.1 to 4.3 m/s. Increasing gas mass flow rates decreased the gas jet breakup frequency in all cases. This phenomenon was primarily attributed to changes in the bubbling mode from discrete bubbling to pulsating and jetting modes. The nozzle orientation plays a role in modifying the bubbling frequency, having a higher magnitude when oriented against gravity.

Bubble formation from an orifice in liquid cross-flow

The formation of gas bubbles by submerged orifices in a cross-flowing liquid is encountered in many industrial applications. It is therefore important to understand the dynamics of bubble formation and to accurately predict the bubble detachment characteristics under such situations. In the present work, the process is numerically studied using the Local Front Reconstruction Method (LFRM), a Front Tracking Direct Numerical Simulation method that enables the simulation of interface merging and breakup. Experiments of bubble formation subjected to cross-flow induced shear are also performed to provide data for the validation of the numerical simulations. The predictions of the bubble shape and the detached bubble volume obtained by the numerical model show good agreement with the experimental results. The validated numerical model is then used to study the effects of volumetric gas flow rate and fluid physical properties on the bubble detachment characteristics under various shear rates in the quasi-static bubble growth regime. The simulation results show that the shear flow advances the bubble detachment and decreases the bubble size. Consequently, the bubble formation frequency and the detached bubble size can be controlled by exerting different shear rates. At higher shear rates, the simulated bubbles are highly deformed due to the drag force created by the tangential liquid flow and the influence of liquid properties on the bubble detachment characteristics becomes less significant.

Experimental characterization of two-phase flow patterns in a slit microchannel

At present, there is revolutionary development of microchannel systems. In such systems, it is extremely important to determine two-phase flow patterns depending on the gas and liquid flow rates. However, in most works there are no clear criteria for turning from one regime to another. In the present work, we have developed a new technique that makes it possible to measure the local void fraction, size of characteristic regions of the liquid films on the upper and lower walls of microchannel, frequency of bubble formation, and other quantitative characteristics. The two-phase flow patterns in a microchannel of 50-μm height and 10-mm width have been studied experimentally. Based on the developed methodology, criteria that accurately determine the boundaries between the two-phase flow regimes have been created. The features of a two-phase flow in a microchannel have been determined, and a new flow regime map has been created.

CFD study on Taylor bubble characteristics in Carreau‐Yasuda shear thinning liquids

AbstractIn the present study, Taylor bubble formation in two‐phase gas‐non‐Newtonian Carreau liquid flowing through a confined co‐flow microchannel is investigated. Systematic analyses are carried out to explore the influences of rheological properties, inlet velocities, and surface tension on Taylor bubble length, shape, velocity, and liquid film thickness. Aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations are considered as the non‐Newtonian liquids to understand the fundamentals of flow behaviour. With increasing solution viscosity and liquid phase inlet velocity, Taylor bubble formation frequency and velocity increased; however, the bubble length was found to decrease. Velocity profiles inside the Taylor bubble and liquid slug were analyzed, and distinct velocity distributions were found for different CMC concentrations. Flow regime maps are developed based on gas and liquid velocities for Carreau liquids in the co‐flow microchannel. This study essentially provides useful guidelines in designing a non‐Newtonian microfluidic system for precise control and manipulation of Taylor bubbles.