Bubble Dynamic Characteristics Research Articles

Theoretical investigation of the nonlinear dynamics for cavitation bubbles inside liquid drops

The cavitation bubble dynamics inside liquid drops governed by a Rayleigh–Plesset-like equation is investigated theoretically. A strict qualitative analysis is made to determine the bubble dynamic behaviors. Analytical expressions of the collapse times and analytical solutions of the governing equation are derived for different initial conditions. The validity of these analytical solutions is studied by testing numerical algorithms and/or experimental data. As applications of the analytical solutions, analytical expressions in parametric forms for the evolutions of bubble oscillation velocity, oscillation acceleration, kinetic energy, and potential energy are also obtained. Furthermore, the relevant nonlinear bubble dynamic characteristics and motion laws are also revealed based on the obtained results.

Experimental investigation on the influence of lubricant oil on CO2 nucleate pool boiling heat transfer characteristics

As a natural working fluid, CO2 is considered the most promising alternative refrigerant to hydrofluorocarbons. In the fields of automotive air conditioning and commercial heat pumps, transcritical CO2 cycles show significant potential for performance enhancement. Although there are many studies on CO2 flow boiling in the open literature, few studies involve CO2 nucleate boiling heat transfer, which is the dominant mechanism of CO2 flow boiling heat transfer process. This study is proposed to conduct experimental investigations of CO2 nucleate boiling heat transfer. The influences of evaporation temperature, heat flux and lubricant oil addition on boiling heat transfer performance and bubble dynamic characteristics are discussed. The results show that in pure CO2 nucleate boiling, heat flux increase leads to higher bubble density and bubble diameter in bulk liquid, which in turn enhances boiling heat transfer. The effect of evaporation temperature increases on bubble diameter is significant. The reduction in bubble diameter weakens the convective heat transfer caused by bubble motion, which leads to less variation in the CO2 nucleate boiling heat transfer coefficient with evaporation temperature. Lubricant oil addition significantly changes the bubble dynamics of CO2 nucleate boiling process, leading to larger bubble density and smaller bubble diameter. Moreover, the oil diffusion at the phase interface notably affects the heat transfer performance, resulting in greater differences in the boiling heat transfer characteristics of the mixtures compared to that of pure CO2. The mixture boiling heat transfer coefficient is collectively influenced by evaporation temperature, heat flux and oil concentration. The experimental results suggest that the heat transfer coefficient of the mixture with an oil concentration of 0.5 % increases by an average of 25 % compared to pure CO2 at an evaporation temperature of 0 °C. At higher evaporation temperatures and high oil concentrations (>1%), oil addition leads to heat transfer deterioration. Findings from this work can provide a better understanding of oil effect on refrigerant boiling heat transfer and a fundamental basis for heat exchanger design of CO2 systems.

Experimental research on the bubble dynamic characteristics during carbon capture in the novel prepared functionalized porous ionic liquids

Porous ionic liquids have received widespread attention as one of the novel CO2 absorbers to reduce CO2 produced by the combustion of fossil fuels. Based on this, the CO2 capture experiments are conducted in ionic liquids ([TEP][MIm] and [TEP][FA]), and the porous ionic liquid (ZIF-8/[TEP][MIm]). The dynamic characteristics of CO2 bubbles in different concentrations of ZIF-8/[TEP][MIm] liquid are researched. The results show that the CO2 capture capacity of the aqueous solution with a concentration of [TEP][MIm] of 20 wt% reaching 2.06 mol/mol ILs. The optimal addition amount of ZIF-8 in the porous ionic liquid using the ethylene glycol as a cosolvent is 1.0 g/100 g, and the maximum CO2 capture amount is about 2.22 mol/mol. Furthermore, the aspect ratio and cross-sectional ratio of CO2 bubbles generated by the four nozzles decrease with the increase of ZIF-8 and [TEP][MIm] concentrations, and the difference between the extreme values of CO2 equivalent diameter under experimental conditions is about 0.513 cm. In addition, the Eo number decreases with the rise of CO2 bubble, and the maximum different value is about 2.94. This work explores the dynamic characteristics of CO2 bubbles in ZIF-8/[TEP][MIm] within a bubbling tower, aiming to optimize the CO2 capture process and provide a valuable reference for advancements in the carbon capture, utilization, and storage technology.

Dynamics of Taylor bubble under chemical reaction enhanced mass transfer in minichannel

Taylor bubble dynamic characteristics of CO2 chemical absorption into MEA aqueous solution in a vertical minichannel were systematically investigated in this study. The generation, movement, and shrinkage of bubbles in the minichannel were visualized and monitored using a high-speed camera, and their dynamic behaviors were characterized by image analysis method. The effects of gas and liquid Re numbers and absorbent concentration on two-phase flow patterns, bubble generation frequency, initial bubble length, bubble length decrease rate, and bubble velocity were examined and analyzed. Results showed that chemical reaction-enhanced mass transfer hindered the bubble cap penetration into the main channel, and alleviated the bubble neck thinning, both effects inhibiting the bubble generation. A new Damköhler number (Da)-based correlation has been proposed to predict the initial Taylor bubble length, showing good prediction accuracy for experimental data in the literature using different absorbents. Results also showed that before the formation of sphere bubble at the end of absorption, an approximate linear relationship exists between bubble length decrease rate and bubble velocity, with the slop decided by chemical reaction rate that could be characterized by the Da number. Finally, a simple model has been developed to determine the effective channel length at a given operating condition, providing design guidelines for microchannel-based miniaturized CO2 absorbers.

Stability Analysis of Anionic-CO2-Soluble Surfactant Di-(2-ethylhexyl) Sodium Sulfosuccinate-Assisted Oily Foam Based on Statistical Analysis of Bubble Dynamic Characteristics.

Currently, oily foam stability in CO2 injection for heavy oil recovery exhibits inadequacies that considerably constrain its extensive application. Some scholars have conducted research demonstrating that CO2-soluble surfactants can assist in inducing heavy oil to form oil-based foams (oily foam). In this study, stability tests for the oily foam were conducted at different surfactant concentrations using a visualized PVT cell. Oily foam stability was assessed by calculating the comprehensive foam index (S) and analyzing the bubble images. The research indicates that AOT can effectively reduce the interfacial tension between oil and gas. At a concentration of 0.1 wt % AOT, the interfacial tension can be effectively reduced from 1.75 to 1.14 mN/m. The concentration of 0.3 wt % AOT represents a turning point, with an S of 16 101.7 mL·min. Beyond this concentration, the increase in S becomes less pronounced. As the concentration of CO2-soluble surfactant is increased from 0.1 to 0.5 wt %, the average bubble radius decreases from 2.74 to 0.43 mm, while the number of bubbles per unit area increases from 5.56 to 81.1 per cm2. With an increasing concentration of the CO2-soluble surfactant, the system generates more and smaller gas bubbles within the oily foam, resulting in a slower bubble coalescence. The findings of this study are poised to play a pivotal role in enhancing heavy oil recovery efficiency.

Experimental Study on Bubble Dynamics and Mass Transfer Characteristics of Coaxial Bubbles in Petroleum-Based Liquids.

Petroleum-based liquids are from an important petroleum-based polymer, whose application and preparation involve multiple operations related to gas-liquid two-phase flow. Due to insufficient research on gas-liquid two-phase flow, there is a gap in bubble dynamics and mass transfer characteristics in petroleum-based liquids. Accordingly, we have systematically investigated the bubble formation process, bubble rising dynamics, and mass transfer of coaxial bubbles. Herein, the contour of bubbles was obtained for analyzing the bubble formation process. It was found that the increase of gas flow rate contributed to the increase of bubble generation size, while the liquid viscosity had an inhibitory influence on the increase of bubble generation size. Moreover, the variation of bubble rising velocity was considered and the force analysis of the rising bubble was provided. A new model of drag coefficient applicable to petroleum-based liquids was proposed. Finally, variations in the amount of dissolved oxygen in the liquid were measured to analyze the mass transfer characteristics. The increase in nozzle inner diameter and gas flow rate both promoted mass transfer, but the increased liquid viscosity hindered mass transfer.

Review and Perspectives on CO2 Bubble Dynamic Characteristics in Different Liquids during Carbon Capture, Utilization, and Storage Process

Carbon dioxide (CO2) bubbles are common during carbon capture, utilization, and storage (CCUS) processes and have many impacts on water conservancy machinery, metallurgy, and the chemical industry. To explore the dynamic characteristics of CO2 bubbles in different liquids in CCUS, the motion mechanism of CO2 bubbles was integrated, and the effects of different liquid characteristics and different external conditions on the dynamic characteristics of CO2 bubbles were classified and summarized. At the same time, the research progress of numerical simulation on CO2 bubble dynamics is reviewed. Therefore, approaches and methods that can be further explored in theoretical analysis, experimental research, and numerical simulation of CO2 bubble dynamics are proposed, which can provide reference and guidance for engineering practice, especially CCUS technologies.

Bubble Dynamics and Heat Transfer Characteristics of Flow Boiling in a Single Pentagonal Rib Channel

Abstract Two-phase flow boiling is the preferred method for efficient heat dissipation in electronic equipment, so the bubble dynamics and heat transfer characteristics of flow boiling in a single pentagonal rib channel are numerically analyzed by the volume of fluid (VOF) model. Three typical rib structures are obtained, whose block ratios are 0.4, 0.75, and 0.25, and the corresponding length-diameter ratios are 1.72, 0.59, and 12.70, respectively. The Reynolds number is 14,000 and 28,000. The heat flux is set from 50 to 150 kW/m2. The results show that the starting position of the bubble is at the cone and sides of the rib, and its moving direction is related to the configuration of the rib, the heat flux, and fluid velocity. Additionally, the bubbles are shedding at the corner of the rib, and the short rib does not appear to be the vortex shedding phenomenon. The wall temperature and temperature fluctuation increase with the increase of heat flux and with the decrease of fluid velocity. The heat transfer coefficient decreases with the increase of heat flux and with the decrease of fluid velocity. The short rib channel has a higher heat transfer coefficient, approximately 14% and 50% higher than that of the median and long rib channels, respectively. Compared with the single-phase flow, the main frequency of the lift coefficient increases with the increase of the fluid velocity while decreasing with the increase of heat flux. The main frequency of the median rib without harmonic signal keeps constant, and that for long rib decreases by 38%. The study of the instantaneous characteristics of bubble growth in pentagonal rib channels is instructive to the efficient heat dissipation in electronic equipment.

Electrically enhanced activity of cationic surfactant for the bubble surface modification of solvent sublation to remove acetaminophen from water

In this article, the molecular dynamics (MD) calculation was carried out to investigate the influence of electric field (EF) on the adsorption of cationic surfactant Dodecyl Trimethyl Ammonium Chloride (DTAC) at the phase interface of bubble and the interaction between acetaminophen (APAP) and DTAC. The main components’ structural parameters, interaction energy, PMF, surface tension of gas–liquid interface and density distribution of marker atoms in DTAC molecules were analyzed. The results show that EF can weaken the restriction of water molecules on DTAC and acetaminophen, increase the van der Waals attraction between DTAC and APAP, reduce the surface tension of phase interface, thereby significantly improving the adsorption of DTAC at the phase interface, and further enhancing the adsorption between APAP and DTAC. In addition, the distribution of DTAC adsorbed on the bubble surface may be controlled through adjusting the direction of EF, which makes it possible to counteract the uneven distribution of adsorbate on the bubble surface caused by liquid velocity and further control the bubble dynamic characteristics in the adsorption process. Our study results are expected to propose a simple and low-cost method for the removal of APAP in water by solvent sublation.

Stability Analysis of Co2-Soluble Surfactant System Foamy Oil Based on Statistical Analysis of Bubble Dynamic Characteristics

Stability Analysis of Co2-Soluble Surfactant System Foamy Oil Based on Statistical Analysis of Bubble Dynamic Characteristics

Theoretical and experimental study of bubble dynamics in underwater explosions

The development of analytical theory and experimental methods for understanding the correlation between the explosive properties and bubble dynamic characteristics in underwater explosions has important engineering application value for underwater weapons and ships. Based on the assumption of an instantaneous explosive detonation, we introduced the Jones–Wilkins–Lee equation of state to describe the high-pressure state in an explosion bubble and established the initial conditions for the bubble dynamics calculations. Considering the high-Mach-number flow and high pressure at the initial boundary of the explosion bubble, the Lezzi–Prosperetti equation with second-order Mach accuracy was used. Thus, an analytical model and a calculation method of the explosion bubble dynamics for an explosive detonation were established. This direct link between the detonation parameters and the bubble features is significant for the subtle design, selection, and optimization of explosives' properties. A micro-equivalent explosive bubble pulsation experiment was carried out in a water tank using a customized experimental system, which can offer nearly boundary-free condition to mitigate the reflective wave effects on bubbles. Three types of explosives were used in the experiment: the Research Department explosive (RDX), the Pentaerythritol tetranitrate (PETN), and the Hexanitrohexaazaisowurtzitane (CL20). Finally, the experimental results and the practicability of the experimental system were analyzed. The influence of the explosive type on the dynamic characteristics of the explosion bubbles and the differences between the theoretical and experimental results were compared. The results showed that the proposed explosion bubble dynamics model and calculation method have high accuracy and practicability. The proposed model can be used for explosives with known detonation parameters and equation of state parameters. The detonation parameters, velocity, and pressure are linked to the bubble features pulsation period and the maximum radius directly. The designed experimental system, which is capable of simulating an infinite water for the explosion of micro-equivalent explosives, was stable and easy to use. The work is significant for the subtle design, selection, and optimization of explosives' properties.

Generation of hydrogen bubble in biodiesel—Influence of non-uniform electric field

With regard to improving the blending performance of biodiesel with hydrogen, it is important to generate smaller hydrogen bubbles in biodiesel at low energy consumption. In this context, a strong non-uniform direct current (DC) electric field has been created between a needle-ring electrode configuration, which is used to study the effect of EHD on hydrogen bubble behaviors in biodiesel considering the various gas flow rates and applied voltages. The special geometry of gas cones similar to the Taylor cone in liquid droplets under an electric field is demonstrated. The hydrogen bubble features—which are characterized by the bubble heights, frequencies, velocities, bubble sizes, and shapes—show that the bubble geometry and dynamic characteristics in the electric field are performed in manners different from those reported in the literature. It is found that the hydrodynamic behavior of the bubbles is also modified by the EHD effect. The distributions of bubble size in different cases follow the Gaussian distribution. Small bubbles are more likely to be associated with high separation velocities. Further, the diversity of bubble shapes at the separation is demonstrated, and two regimes of impact mechanism based on the surface tension and electric forces are revealed.

Effects of surface tension on the dynamics of a single micro bubble near a rigid wall in an ultrasonic field

Acoustic cavitation is a very important hydrodynamic phenomenon, and is often implicated in a myriad of industrial, medical, and daily living applications. In these applications, the effect mechanism of liquid surface tension on improving the efficiency of acoustic cavitation is a crucial concern for researchers. In this study, the effects of liquid surface tension on the dynamics of an ultrasonic driven bubble near a rigid wall, which could be the main mechanism of efficiency improvement in the applications of acoustic cavitation, were investigated at the microscale level. A synchronous high-speed microscopic imaging method was used to clearly record the temporary evolution of single acoustic cavitation bubble in the liquids with different surface tension. Meanwhile, the bubble dynamic characteristics, such as the position and time of bubble collapse, the size and stability of the bubbles, the speed of bubble boundaries and the micro-jets, were analyzed and compared. In the case of the single bubbles near a rigid wall, it was found that low surface tension reduces the stability of the bubbles in the liquid medium. Meanwhile, the bubbles collapse earlier and farther from the rigid wall in the liquids with lower surface tension. In addition, the surface tension has no significant influence on the speed of the first micro-jet, but it can substantially increase the speed of second and the third micro-jets after the first collapse of the bubble. These effects of liquid surface tension on the bubble dynamics can explain the mechanism of surfactants in numerous fields of acoustic cavitation for facilitating its optimization and application.

Investigation of Cavitation Bubble Dynamics Considering Pressure Fluctuation Induced by Slap Forces

Cavitation erosion is induced by the penetrating pressure from implosion of cavitation bubbles nearby solid boundary. The bubble evolution and the subsequent collapse pressure are especially important to evaluate the erosion degradation of solid boundary materials. The bubble dynamics equation taking into account the influence of distance between bubble and solid boundary is formulated to investigate the effect of boundary wall on bubble evolution process. The pressure fluctuation induced by slapping forces is adopted to evaluate the bubble dynamic characteristics. Negative pressure period which reflects the effect of vibration velocity and gap clearance also has large influence on bubble dynamics. The effects of standoff distance, initial radius and negative pressure period on bubble evolution and collapsing shock pressure are discussed. Maximum bubble radius increases with standoff distance and initial radius, while shock pressure increases with distance and decreases with bubble initial radius, and both of them increase with negative pressure period.

Composite porous surfaces of microcavities for enhancing boiling heat transfer

Enhancing boiling heat transfer by surface modification has the potential to increase the efficiency of energy systems and to address thermal management bottlenecks in electronics. In order to realize simultaneous enhancement of critical heat flux (CHF) as well as heat transfer coefficient (HTC) for boiling heat transfer processes, we developed a porous surface covered by microcavities (MCPS), which was fabricated by the three-step method of a powder sintering technique followed by chemical modification methods. The pool boiling heat transfer properties of MCPSs were systematically investigated in atmospheric pressure conditions, together with the bubble dynamics characteristics. The results showed that compared to plain Cu surfaces (PCSs), a 2.2 times higher CHF, a 2.5 times higher HTC as well as 85% lower onset of nucleate boiling (ONB) were demonstrated on the MCPSs. Owe to the formation of numerous microcavities and capillary-induced liquid rewetting, compared with PCPSs, the MCPS could increase the nucleation density, reduce bubble departure diameter and increase departure frequency. Finally, the wicking velocity of different surfaces obtained from the capillary wickability tests showed that there was a good linear relationship between the wicking velocity and CHF. The results showed that the liquid supply with capillary wickability could prevent the expansion of dry spots and maintain a higher CHF. This study provides a high-performance surface modification, which leads to significant industrial application prospects for high-power microelectronics cooling.

The experimental study on the boiling bubble behaviors and heat transfer performance of the deionized water across various pin fins

Microchannel heat sink is widely utilized as one of the effective heat dissipation methods with lower heat transfer temperature difference. In this paper, visual experiment study has been conducted to focus on the inner relationship between heat transfer/flow properties in macroscopic aspect with bubble dynamic characteristics in microcosmic aspect. Results show that along with the increases of Re, the value of convective heat transfer coefficient(h) increases as well. Correspondingly, the pressure drops show a tendency as increasing, decreasing lately, then increasing again. The bubbles in the undergo the same four process: film boiling process, transition process from film to nucleate boiling zone, nucleate boiling process and single-phase convection process. And the variation of pressure drop is one-to-one correspondence with the four heat transfer process. Besides, the triangle pin fin holds the higher heat transfer coefficient, which may be explained from the quantities and the sequence of appearance of bubbles in nucleate heat transfer process. The migration diameter as well as coverage rate of bubbles appears the tendency as ascending firstly then down lately with the increase of Re, which fit the conclusion in macroscopic aspect in heat transfer/flow properties. It could be found that the migration size is mainly influenced by the flow rate as well as the density of bubbles. In this way, the position of bubble occurred is the key point effecting bubble growth time and growth radium. Three zones have been divided to summarize the dynamic behaviors of bubbles in different positions: The migration diameter of bubbles in Zone I in the biggest, with that in Zone II moderate and that in Zone II lowest. The tail of pin fin (Zone I) makes the bubbles more easily to merge the surrounding new nucleated small bubbles to a bigger size, with more residence time to leave the bubble growing bigger. The general growth size of bubbles in ellipse pin fin is smallest, around 0.08 mm and with growth cycle short as 0.616 s. Simultaneously, that of the triangle one is biggest, with the size as 0.099 mm and growth time as 2.112 s.

Analytical Study on Homogeneous Nucleation and Bubble Evolution Inside Monocomponent Fuel Droplet

Homogeneous nucleation and bubble evolution inside a fuel droplet trigger the occurrence of flash boiling, which shows a high potential to improve the droplet evaporation. To understand the bubble dynamic characteristics, an analytical study on homogeneous nucleation and bubble evolution has been performed, based on the flash boiling model proposed in our work. First, the nucleation rate graph of seven fuels within a wide range of operating temperatures is obtained according to the homogeneous nucleation model. Then the variation of homogeneous nucleation characteristics with fuel temperature and ambient pressure is discussed. Finally, the bubble evolution and boiling explosion of a single droplet are studied for different fuels at 490 K, 530 K, and 560 K, respectively. The results show that the nucleation characteristics are mainly affected by the fuel physical properties, especially the boiling point and surface tension. Moreover, the transitional and heat transfer controlled stages during bubble evolution are significantly affected by the nucleation rate, which causes temperature change and affects the boiling explosion time.

Dynamics of bubble formation on submerged capillaries in a non-uniform direct current electric field

In this paper, the dynamic behaviors of bubbles in ethanol were investigated with a needle-ring electrode rig in the presence of a direct current (DC) electric field. High-speed photography was used to capture the bubble dynamic characteristics under various electric field strengths. The obtained results show that the applied electric field accelerates the bubble formation speed and release frequency, but restricts the bubble release diameter. Meanwhile, high electric field strength causes the bubble shape being squeezed in horizontal direction and stretched in vertical direction, respectively. Quantitatively, the evolutions of the bubble non-dimensional size parameter δ reflect that producing the bubbles whose width are smaller than those of orifice is to judiciously control the electric field strength, which is not closely related to the capillary model. The bubble aspect ratio χ and the non-dimensional contact angle θb/θs depend primarily on electric field strength and show a desirable corresponding relationship with the bubble deformation and the triple-phase contact line, respectively. Furthermore, by combining the bubble evolution with the dimensionless Eötvös number (Eo), Weber number (We) and electrical Bond number (BoE), the main forces work on the bubble and surrounding liquid are evaluated and elaborated.

Wall heat flux partitioning during subcooled flow boiling of NaCl solutions and pure water

A careful evaluation on the wall heat flux partitioning is of great importance for the deep understanding the nucleate flow boiling heat transfer to saline solution. In this work, the portion of each heat transfer contribution was analyzed through wall heat flux partitioning model after model validation. The key parameters used in the model were discussed and the reasonable values were determined. The experimental data of bubble departure diameter, departure frequency, active nucleation site density, bubble waiting time and growth time, were combined into the model to eliminate the uncertainties of empirical closure sub-models. The comparison of heat flux partitioning of subcooled flow boiling between NaCl solution and pure water was presented under different operating conditions. The results showed that for the operating conditions of Qw > 180 kW/m2 or G < 400 kg/(m2·s), the contribution of single-phase liquid convection in the heat transfer of saline solution is greater than that in pure water, due to the bigger bubble diameter and more intensive bubble-induced turbulence. Quenching heat flux for NaCl solution is lower than that in pure water, owing to the smaller bubble departure frequency. For the lower heat flux or higher mass flux conditions, however, the contrary trend was observed. The dominant heat transfer mechanisms for solution and pure water during subcooled nucleate flow boiling were revealed. The interactions between bubble dynamic and heat transfer characteristics were carefully investigated.

EHD effects on periodic bubble formation and coalescence in ethanol under non-uniform electric field

This paper focus on the effects of electrohydrodynamic (EHD) on bubble dynamic characteristics generated on a submerged capillary in ethanol under non-uniform electric field, using high-speed photography and with a particular interest in the effect of electrical Bond number (BoE) on the bubble behaviors. The obtained results ranges of BoE from zero to 5.52 and Weber number (We) from 0.0006 to 0.1365 show that the bubble formation process associated with three stages at the low electric field strengths, including the nucleation, stable growth and necking stages, while the stable growth stage is absent for the high field strengths. With the increase of both We and BoE, the bubble period and waiting times are shortened rapidly, while the frequency is accelerated remarkably. The bubble dynamic behavior, which is characterized by the bubble volume and curvature radius, depends primarily on the BoE, and the increase in the We slightly raises the bubble volume and curvature radius at the departure time. Furthermore, it is found that with the increasing of BoE, bubbles coalescence evidenced at high We is weakened and eventually disappeared. Nevertheless, this phenomenon has the tendency to subsequently reappear at the higher We and BoE.