Bubble Growth Rate Research Articles

Pool boiling on nano-textured surfaces

Pool boiling on nano-textured surfaces was studied experimentally and theoretically for ethanol and water as working fluids. The nano-textured surfaces were copper platelets covered with copper-plated electrospun nanofibers. In addition, for comparison pool boiling on the corresponding bare copper surfaces was experimentally studied. The results revealed that the heat flux and heat transfer coefficient in boiling on the nano-textured surfaces were about 3–8 times higher than those on the bare copper surfaces. This stems from the fact that nano-textured surfaces promote bubble growth by increasing the average temperature of fluid surrounding growing bubbles, as our experimental and theoretical results show. Hence, nano-textured surfaces comprised of copper-plated nanofibers facilitate bubble growth rate and, thus, increase bubble detachment frequency. On the other hand, the critical heat flux (CHF) on the nano-textured surfaces was found to be very close to its counterpart on the bare copper surfaces. However, the heat flux on the nano-textured surfaces in transition boiling was significantly higher than on the bare copper ones, since the presence of nanofibers prevented bubble merging and delayed formation of vapor film. The wall temperature is about 10°C lower on the nano-textured surfaces. In transitional boiling the heat flux on nanofiber mats reduces much slower than on the bare surfaces.

Volume of fluid method for bubble dynamics in a gas–solid jetting fluidized bed

Abstract Several recent studies have shown that numerical methods originally developed for simulating gas–liquid flow can be extended to simulate the hydrodynamics of gas–solid flow in gas-fluidized beds, thanks to the similarity between gas–liquid and gas–solid flows. In this study, the volume of fluid method which is widely used in the direct numerical simulations of gas–liquid systems, is used to study the bubbling dynamics in a dense gas–solid jetting fluidized bed. It was shown that the bubble dynamics in a gas–solid fluidized bed, including the bubble growth rate, the time-averaged porosity profiles at two different profiles and the time-averaged global porosity distribution, can be reproduced reasonably well.

Factors influencing the characterization of bubbles produced by coaxial gas–particle jet flow

The effect of particle mass flow rate and annular channel thickness on the formation and characteristics of the bubbles is investigated experimentally by high-speed digital photography. A criterion is proposed to determine the emergence of the bubbles. The experimental results demonstrate that the particle mass flow rate and the annular channel thickness are both crucial factors for the bubble-formation process. The bubble size, bubble growth rates and bubbling frequency are investigated by analyzing a large number of images. The radial growth rate of the bubble is still governed by the superficial air jet velocity. In addition, the radial velocity difference between the gas and particle phase is confirmed to be the main cause of bubbling.

Relating vesicle shapes in pyroclasts to eruption styles

Vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions. Although their numbers and sizes are used routinely to infer aspects of eruption dynamics, vesicle shape remains an underutilized parameter. We have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles, using the dimensionless shape factor $\Omega $ , a measure of the degree of complexity of the bounding surface of an object. For each of the seven eruptions, we have also estimated the capillary number, Ca, from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling. We find that $\Omega $ is smaller for eruptions with ${\rm{Ca}} \ll 1$ than for eruptions with Ca $\gg 1$ . Consistent with previous studies, we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth, such as coalescence and shape relaxation of bubbles by capillary stresses. Among the samples analyzed, Strombolian and Hawaiian fire-fountain eruptions have ${\rm{Ca}} \ll 1$ , in contrast to Vulcanian, Plinian, and ultraplinian eruptions. Interestingly, the basaltic Plinian eruptions of Tarawera volcano, New Zealand in 1886 and Mt. Etna, Italy in 122 BC, for which the cause of intense explosive activity has been controversial, are also characterized by ${\rm{Ca}} \gg 1$ and larger values of $\Omega $ than Strombolian and Hawaiian style (fire fountain) eruptions. We interpret this to be the consequence of syn-eruptive magma crystallization, resulting in high magma viscosity and reduced rates of bubble growth. Our model results indicate that during these basaltic Plinian eruptions, buildup of bubble overpressure resulted in brittle magma fragmentation.

Single bubble geometry evolution in micro-scale space

Two types of single vapour bubble growth in micro-scale space are experimentally investigated. Degassed pentane and FC-72 are used to study the bubble confined between superheated parallel plates without liquid flow. Liquid properties which are influential on bubble growth are discussed. Effects of plate superheating and plate gap on bubble growth rate are examined. Bubble growth during flow boiling in high aspect ratio micro-channels is also examined to extensively investigate the single bubble growth in a dynamic configuration. The hydraulic diameters of the tested channel are 571 μm, 762 μm and 1454 μm, with an aspect ratio of 20, 20 and 10 respectively. Transparent heating technique is utilised to provide heating power while ensuring sufficient transparency for visualisation. A three-stage bubble growth mode is presented. Moreover, bubble geometry evolution is found to be strongly related to channel cross-sectional geometry but slightly affected by heat flux or mass flux. Bubble growth critical time is defined. Bubble equivalent radius, bubble aspect ratio and width versus length trends are also discussed.

Spiky Development at the Interface in Rayleigh-Taylor Instability: Layzer Approximation with Second Harmonic

Layzer’s approximation method for investigation of two fluid interface structures associated with Rayleigh Taylor instability for arbitrary Atwood number is extended with the inclusion of second harmonic mode leaving out the zeroth harmonic one. The modification makes the fluid velocities vanish at infinity and leads to avoidance of the need to make the unphysical assumption of the existence of a time dependent source at infinity. The present analysis shows that for an initial interface perturbation with curvature exceeding , where A is the Atwood number there occurs an almost free fall of the spike with continuously increasing sharpening as it falls. The curvature at the tip of the spike also increases with Atwood number. Certain initial condition may also result in occurrence of finite time singularity as found in case of conformal mapping technique used earlier. However bubble growth rate is not appreciably affected.

Rectified growth of histotripsy bubbles.

Histotripsy treatments use high-amplitude shock waves to fractionate tissue. Such treatments have been demonstrated using both cavitation bubbles excited with microsecond-long pulses and boiling bubbles excited for milliseconds. A common feature of both approaches is the need for bubble growth, where at 1 MHz cavitation bubbles reach maximum radii on the order of 100 microns and boiling bubbles grow to about 1 mm. To explore how histotripsy bubbles grow, a model of a single, spherical bubble that accounts for heat and mass transport was used to simulate the bubble dynamics. Results suggest that the asymmetry inherent in nonlinearly distorted waveforms can lead to rectified bubble growth, which is enhanced at elevated temperatures. Moreover, the rate of this growth is sensitive to the waveform shape, in particular the transition from the peak negative pressure to the shock front. Current efforts are focused on elucidating this behavior by obtaining an improved calibration of measured histotripsy waveforms with a fiber-optic hydrophone, using a nonlinear propagation model to assess the impact on the focal waveform of higher harmonics present at the source's surface, and photographically observing bubble growth rates.

Bubble formation in an annular granular jet dispersed by a central air round jet

An annular granular jet surrounding an air jet at its core is studied experimentally using high‐speed digital photography. The experimental results show that particle bubbles in a periodic manner are formed whether the central air is swirling or not. This flow feature is induced by the intense interaction between the central air jet and the annular granular jet, and it is important for the dispersion of particles by the air jet in the near field. The interaction between the two phases is mainly intensified by higher superficial air jet velocity and the addition of swirl to the central air jet. The bubbling frequency, bubble size, bubble shape, and bubble growth rate are investigated by analyzing a large number of images. In addition, the dispersion angle of granular jet is found to be mainly governed by the radial growth rate of the bubble. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1882–1893, 2013

Bubble dynamics and flow boiling instabilities in microchannels

This work describes an experimental investigation of bubble dynamics and the effect on flow boiling instabilities and heat transfer in a multiple-microchannel heat sink. In this paper, results of the experimental investigation of bubble dynamics are presented and discussed. The microchannel heat sink contained 40 parallel, rectangular channels having hydraulic diameter of 194μm, and an aspect ratio of 0.549. The experiments were conducted with deionised water over a mass flux range from 71 to 204kg/m2s, and an inlet temperature of 71°C. Bubble growth rate and departure diameter under subcooled and saturated flow boiling are studied using a microscope and a high speed camera. The effects of mass flux and heat flux on bubbles growth characteristics are investigated and discussed. The results of this study demonstrate that the bubble growth rate in microchannels is different from that in macroscale channels. Confinement of microchannel and interaction between channels result in the unique bubble dynamic in microchannels.

Heating surface material’s effect on subcooled flow boiling heat transfer of R134a

In this study, subcooled flow boiling of R134a on copper (Cu) and stainless steel (SS) heating surfaces was experimentally investigated from both macroscopic and microscopic points of view. By utilizing a high-speed digital camera, bubble growth rate, bubble departure size, and nucleation site density, were able to be observed and analyzed from the microscopic point of view. Macroscopic characteristics of the subcooled flow boiling, such as heat transfer coefficient, were able to be measured as well. Experimental results showed that there are no obvious difference between the copper and the stainless surface with respect to bubble dynamics, such as contact angle, growth rate and departure size. On the contrary, the results clearly showed a trend that the copper surface had a better performance than the stainless steel surface in terms of heat transfer coefficient. It was also observed that wall heat fluxes on both surfaces were found highly correlated with nucleation site density, as bubble hydrodynamics are similar on these two surfaces. The difference between these two surfaces was concluded as results of different surface thermal conductivities.

Bromine monoxide / sulphur dioxide ratios in relation to volcanological observations at Mt. Etna 2006–2009

Abstract. Over a 3-yr period, from 2006 to 2009, frequent scattered sunlight DOAS measurements were conducted at Mt. Etna at a distance of around 6 km downwind from the summit craters. During the same period and in addition to these measurements, volcanic observations were made by regularly visiting various parts of Mt. Etna. Here, results from these measurements and observations are presented and their relation is discussed. The focus of the investigation is the bromine monoxide/sulphur dioxide (BrO / SO2) ratio, and its variability in relation to volcanic processes. That the halogen/sulphur ratio can serve as a precursor or indicator for the onset of eruptive activity was already proposed by earlier works (e.g. Noguchi and Kamiya 1963; Menyailov, 1975; Pennisi and Cloarec, 1998; Aiuppa et al., 2002). However, there is still a limited understanding today because of the complexity with which halogens are released, depending on magma composition and degassing conditions. Our understanding of these processes is far from complete, for example of the rate and mechanism of bubble nucleation, growth and ascent in silicate melts (Carroll and Holloway, 1994), the halogen vapour-melt partitioning and the volatile diffusivity in the melt (Aiuppa et al., 2009). With this study we aim to add one more piece to the puzzle of what halogen/sulphur ratios might tell about volcanic activities. Our data set shows an increase of the BrO / SO2 ratio several weeks prior to an eruption, followed by a decline before and during the initial phase of eruptive activities. Towards the end of activity or shortly thereafter, the ratio increases to baseline values again and remains more or less constant during quiet phases. To explain the observed evolution of the BrO / SO2 ratio, a first empirical model is proposed. This model suggests that bromine, unlike chlorine and fluorine, is less soluble in the magmatic melt than sulphur. By using the DOAS method to determine SO2, we actually observe most of the emitted sulphur of Mt.~Etna. Regarding bromine, however, we are aware that by determining only the bromine monoxide (BrO) radical we might just observe a small or even a variable fraction of the total emitted bromine, which is most probable originally in the form of HBr. Therefore, we present first studies to justify the assumption that, despite the disadvantage just mentioned, the BrO / SO2 ratio can nevertheless serve as a new parameter to indicate the state of a volcano, when measurements are conducted under certain, but rather convenient, conditions.

Effect of viscosity and shear flow on the nonlinear two fluid interfacial structures

A nonlinear formulation is presented to deal with the combined action of Rayleigh-Taylor and Kelvin-Helmholtz instabilities as well as combined Ricthmyer-Meshkov and Kelvin-Helmholtz instabilities at the two fluid interface under the influence of viscosity and consequent shear flow. Using Layzer's model, the development of the interfacial structures like bubbles is investigated analytically and numerically. It is found that the growth and normal velocity of the structures are dependent on the relative velocity shear and the kinematic coefficient of viscosity of both the fluids. Both the bubble growth and growth rate are reduced significantly for fluids of higher viscosity coefficient with small velocity shear difference. It is also observed that, for viscous fluids, the transverse velocity of the perturbed interface becomes slower under certain conditions.

Acoustic Cavitation Behavior in Isopropyl Alcohol Added Cleaning Solution

As the semiconductor manufacturing technology for ultra-high integration devices continue to shrink beyond 32 nm, stringent measures have to be taken to get damage free patterns during the cleaning process. The patterns are no longer cleaned with the megasonic (MS) irradiation in the advanced device node because of severe pattern damages caused by cleaning. Recently, several investigations are carried out to control the cavitation effects of megasonic to reduce the pattern damages. The mechanism of damage caused by an unstable acoustic bubble motion was mainly attributed to the high sound pressure associated with violent bubble collapse [1]. In order to characterize the dominant factors affecting the cavitation, MS cleaning was conducted with various dissolved gas concentrations in water. It was reported that the cavitation phenomena relating to particle removal efficiency (PRE) and pattern damage were considerably changed with the addition of a specific gas [2]. This changing behavior may be due to the difference in the physical properties of dissolved gases associated with acoustic bubble growth rate as a function of their concentration. In particular, cavitation effects induced during MS cleaning was controlled by adjusting the acoustic bubble growth rate. Also the change of bubble growth rate is well explained by both rectified diffusion for single bubble and bubble coalescence for multi-bubble, respectively. Similarly, it is well-known that surface active solute (SAS) in the ultrasound field plays an important role in controlling the cavitation effects. A detailed explanation of the acoustic bubble growth rate, cavitation threshold and their relationship with various types of SAS and concentration of biomedical and chemical reactions perspective have been reported elsewhere [3,4]. Their studies demonstrated that the change of cavitation effects depends not only on the chain length of alcohol in the solution but also on the physical properties such as surface tension and viscosity of SAS solutions.

Numerical study of glass fining in a pot melting space with different melt-flow patterns

A numerical model of glass-melt flow and bubble removal was applied in a pot melting space with a different character of melt flow. The linear-temperature gradients with a higher temperature either near the space wall or in the center of the melt level were put on the melt level to simulate the melt circulations, corresponding to melt heating through the pot wall and from the top, respectively. The removal times of the small bubbles have been calculated at different intensities of evoked melt circulations and compared with the values attained in the quiescent glass melt. The results have shown that the melt circulations increased the rising time of bubbles and consequently led to higher energy consumption and lower melting performance. The impact of melt circulations became stronger with the increasing intensity of the circulations and weakened with the increasing bubble growth rate. The removal times of critical bubbles were generally lower in the case of heating from the top and the relevant values obtained in the space at very low bubble growth rates and relatively high melt circulation velocities attained even lower values than in the quiescent melt. The low values of the bubble fining times were described by the characteristic shapes of the critical bubble trajectories. The case may be utilized for the fining of special glasses without addition of fining agents.

Model for growth of bubbles during proofing of viscoelastic dough

A model for growth of bubbles during proofing of bread dough is presented for infinitely dilute as well as finite volume fraction gas dispersions. The model accounts for diffusion of CO2, produced by fermentation, along with the resistance to bubble expansion by the viscoelasticity of the dough as described by Oldroyd-B constitutive equation. The model predicts evolution of bubble size, bubble growth rate and the profiles of CO2 concentration and normal stresses in the vicinity of the gas bubble. The growth of bubbles exhibits a lag time followed by an exponential growth phase. The lag time is found to be smaller for larger dough relaxation time, larger surface tension, smaller dough viscosity, higher temperature, higher gas volume fraction and higher CO2 production rate. The bubble growth rate is larger for smaller bubbles resulting in crossover of bubble size at longer times.

Effect of Prepolymerization Time on Morphology and Properties of Epoxy-modified Bismaleimide Foams

Abstract Epoxy-modified bismaleimide (BMI) foams were prepared through prepolymerization and foaming. Density-adjustable BMI foams with closed-cell structures were produced. The influence of prepolymerization time on bubble growth and morphology, as well as the compressive and heat resistant properties of the foams, were thoroughly investigated. BMI prepolymerization was an effective method for controlling the bubble growth rate, the bubble size and its distribution, and the foam density. As the prepolymerization time increased, the matrix viscosity, the number of cells per unit volume and the foam density increased, whereas, the bubble growth rate and cell size decreased, and the cell size distribution became narrower. The compressive strength and modulus increased with increasing prepolymerization time. The dimensional stability temperatures of the BMI foams were all above 200°C, as determined by their base materials, and were unaffected by prepolymerization time.

Influence of magma ascent rate on carbon dioxide degassing at oceanic ridges: Message in a bubble

In order to quantify the magma ascent rate beneath oceanic ridges, we propose a new method based on vesicle size distribution (VSD) and volatiles measurements (CO2 and H2O) on 65 fresh glasses from the global Mid-Ocean Ridge system. Comparisons of VSD between the main oceanic basins reveal that Mid-Ocean-Ridge-Basalts (MORB) from the Pacific Ocean have significantly higher bubble densities (148−124+739 bubbles/cm2) and initial population densities ln(n0)=19.6±2.8cm−4 but lower vesicularities (∼0.1%). We determine the residence time of bubbles in the magma using the linear relationship between the logarithm of the density population and the vesicle diameters. Assuming a constant bubble growth rate (G=1.5×10−7cm/s), we suggest that the transit times of the magmas through the oceanic crust are shorter beneath Pacific ridges (∼2 h) than elsewhere (∼15 h). In addition, the CO2 and H2O contents of the studied glasses allow the carbon saturation pressure to be calculated. Pacific MORB display a significantly lower carbon dioxide saturation pressure (Psat=843−221+300bars) than Atlantic and Indian MORB (Psat=1898−827+1466bars) but identical pressures of eruption (Pe∼310bars). Consequently, the distance traveled by bubbles from the vesiculation depth to the seafloor is shorter for the Pacific (∼1.9km) than for the Atlantic and Indian oceans (∼5.2km): the longer the transit time, the longer the distance traveled. A closer inspection of the data revealed that the decompression rate (dP/dt) varied from 5.0×102 to 2.3×104Pa/s and correlated positively with the measured bubble densities (nb/m3) as expected from experimental data and numerical modeling. At the global scale, most of the Pacific samples are characterized by high ascent rates (0.25−0.13+0.26m/s) relative to those from the Atlantic (0.11−0.06+0.15m/s) and the Indian samples (0.09−0.03+0.05m/s). However, at the local scale some samples from the Mid-Atlantic Ridge at 37 °N (where the reflections of seismic waves from crustal magma chamber have been observed) are not distinguishable from the Pacific data set having high ascent rates and large bubble densities. We suggest that the method presented in this study could be used to identify spots along the Mid-Oceanic-Ridge system where magma chambers are possibly present.

Pore shape development from a bubble captured by a solidification front

Development of the pore shape from a tiny bubble captured by a solidification front is fundamentally and systematically investigated in this study. Pore formation and its shape in solid influence not only microstructure of materials, but also contemporary issues of various sciences of biology, engineering, foods, geophysics and climate change, etc. In this work, the tiny bubble cap beyond the solidification front is considered to be spherical. As the dominant parameter, the bubble growth rate-solidification rate ratio, decreases, contact angle is found to approach 90°. An accepted criterion, stating that a pore becomes closed as long as the solidification rate is greater than bubble growth rate, is incorrect. This study also finds that the pore can be closed if the bubble radius at contact angle of 90° exhibits a local minimum. Since contact angle of 90° can maintain for a period of time, a subsequent positive bubble growth rate-to-solidification rate ratio readily gives rise to an isolated pore. The pore can be elongated, expanded, shrunk, rippled or closed, depending on the bubble growth rate-to-solidification rate ratio. Manipulating the bubble growth rate or solidification rate to control the pore shape in solid is therefore provided.

A model for growth and engulfment of gas microporosity during aluminum alloy solidification process

A new coupled approach is presented for modeling the hydrogen bubble evolution and engulfment during an aluminum alloy solidification process in a micro-scale domain. An explicit enthalpy scheme is used to model the solidification process which is coupled with a level-set method for tracking the hydrogen bubble evolution. The volume averaging techniques are used to model mass, momentum, energy and species conservation equations in the chosen micro-scale domain. The interaction between the solid, liquid and gas interfaces in the system have been studied. Using an order-of-magnitude study on growth rates of bubble and solid interfaces, a criterion is developed to predict bubble elongation which can occur during the engulfment phase. Using this model, we provide further evidence in support of a conceptual thought experiment reported in literature, with regard to estimation of final pore shape as a function of typical casting cooling rates. The results from the proposed model are qualitatively compared with in situ experimental observations reported in literature. The ability of the model to predict growth and movement of a hydrogen bubble and its subsequent engulfment by a solidifying front has been demonstrated for varying average cooling rates encountered in typical sand, permanent mold, and various casting processes.

Coarsening of a two-dimensional foam on a dome

In this paper we report on bubble growth rates and on the statistics of bubble topology for the coarsening of a dry foam contained in the narrow gap between two hemispheres. By contrast with coarsening in flat space, where six-sided bubbles neither grow nor shrink, we observe that six-sided bubbles grow with time at a rate that depends on their size. This result agrees with the modification to von Neumann's law predicted by J. E. Avron and D. Levine [Phys. Rev. Lett. 69, 208 (1992)]. For bubbles with a different number of sides, except possibly seven, there is too much noise in the growth rate data to demonstrate a difference with coarsening in flat space. In terms of the statistics of bubble topology, we find fewer three-, four-, and five-sided bubbles, and more bubbles with six or more sides, in comparison with the stationary distribution for coarsening in flat space. We also find good general agreement with the Aboav-Weaire law for the average number of sides of the neighbors of an n-sided bubble.