Behavior Of Single Bubble Research Articles

Experimental Investigation of Nucleate Boiling on a Thermal Capacitive Heater Under Variable Gravity Conditions

In the present work the behavior of single vapor bubbles of FC-72, generated on a thermal capacitive heater element, has been investigated during microgravity. A newly developed heater design allows temperature measurements by highspeed infrared thermography on the backside of the heater surface at a distance of approx. 800 nm from the fluid/heater-interface. The employed heater was manufactured by Physical Vapor Deposition (PVD) of a chromium based layer for better emissivity (Slomski et al., Mater Sci Technol 41:161–165, 2010) and a pure chromium heating layer supplying the energy required for bubble generation and sustainment by electrical heating. The thermal diffusivity of the employed Calcium Flouride (CaF) heater substrate is comparable to the thermal diffusivity of stainless steel, which makes this heater design very close to technical applications. The acquired transient temperature fields of the heater surface allow numerical determination of the local heat flux from the heater surface to the fluid. A local temperature drop and high heat fluxes have been observed in the vicinity of the 3-phase contact line. This effect has already been reported by former publications for thin stainless steel foil heaters (Stephan and Hammer, Int J Heat Mass Transfer 30:119–125, 1994; Wagner et al., Int J Heat Mass Transfer 42:875–883, 2006) and is also confirmed for heaters with significantly higher thermal capacities.

Hydrodynamic Behavior of a Single Bubble Rising in Viscous Liquids

The rising behavior of single bubbles has been investigated in six systems with different viscosity and Morton number ( Mo) from 3.21×10 −11 to 163. Bubbles with maximum equivalent diameter of up to 16 mm were investigated. The bubble Reynolds number ( Re) ranged from 0.02 to 1200 covering 3 regimes in which two functions are obtained relating the drag coefficient, C D, with Re and Mo. It has been found that in the high Reynolds number regime the drag coefficient increases until the Reynolds number of about 1200. The classic expression of Jamialahmadi (1994) is improved and extended to high viscosity liquids. A new relationship for the aspect ratio of deformed bubbles in terms of Re, the Eötvös number and Mo, applicable to a wide range of system properties, especially in high viscosity liquids, is also suggested.

Single Bubble Behavior Induced by Nd:YAG Laser Focusing Near Solid Wall in Liquid Nitrogen

This paper deals with an experimental investigation and visualization on the dynamics of laser induced single bubble in liquid nitrogen near an aluminum wall in cryostat. The cryogenic liquid nitrogen has the characteristic feature of the low latent heat, surface tension, and viscosity, as compared with the normal temperature water. Cavitation phenomena in cryogenic liquid may be different from the phenomena in water at normal temperature. However, there have been only a few reports on the single bubble dynamics combined with laser beam irradiation in cryogenic liquid. In this experiment the plasma is produced by focusing of Nd:YAG laser beam of second harmonics in liquid nitrogen. Laser induced bubble dynamics and interaction with the solid wall have been studied by flow visualization. This paper also shows the comparison between the dynamics of laser-induced single bubble in liquid nitrogen and in distilled water. We have clarified that the behavior of laser induced bubble in liquid nitrogen is different from that in distilled water at normal temperature.

The Bubble Behaviour under Effect of Centrifugal Force

The fining process may be enhanced by acting of additive force on bubbles in the glass melt. This study deals with behaviour of single bubbles under effect of centrifugal force in a rotating discontinuous cylinder with glass melt. The model of a single bubble in the combined gravitational and centrifugal field has been set up and calculations of bubble behaviour in the cylinder have been performed for the model TV glass. Two mechanisms of bubble separation were indicated from results of calculations, i.e. the complete dissolution and separation by centrifugal force. The first mechanism is restricted to areas close to cylinder mantel and exhibits relatively long bubble dissolution times. The analysis of model and results revealed the potentially positive role of increasing cylinder radius and partial filling of rotating cylinder with glass melt. The bubble separation is considerably influenced by bubble dissolution or growth during centrifuging, thus the crucial role in this process plays temperature and the bubble initial composition. The until now results show that at lower temperatures the bubbles should contain low content of gases well soluble in glass, to admit higher rotation velocities. Whereas to be enabled the transport of chemically soluble gases from the melt into the bubbles at high temperatures, the bubbles have to be treated at lower rotation velocities (ω =25 – 50 s-1). The small bubbles tend to dissolve close to the cylinder mantle, but from other cylinder regions they have to be separated by centrifuging, and this is a very slow process. Some pretreatments of the glass melt is considered to get rid of bubbles having size under 0.1 mm.

Single Bubble Behavior in Direct Current Electric Field

The investigation on bubble behavior in electric field helps to analyze the mechanism of electric enhancement of boiling heat transfer. Experiments were performed to investigate the bubble deformation in direct current (DC) electric field with bubbles attached to the orifice. The air bubbles were slowly generated in the transformer oil pool at different orifices, so that the effect of flow on bubble shape was eliminated. The results showed that the bubbles were elongated and the departure volume decreased when the electric field was intensified. The major and minor axes, aspect ratio and departure volume increased with increasing the orifice diameter. Both the electric field and orifice size have great influence on bubble behavior. The bubble deformation was also simulated to compare with the experimental results. The numerical and experimental data qualitatively agree with each other.

513 単一気泡の上昇挙動に関する実験的研究(流体工学VI)

513 単一気泡の上昇挙動に関する実験的研究(流体工学VI)

Transfer functions of US transducers for harmonic imaging and bubble responses

Current medical diagnostic echo systems are mostly using harmonic imaging. This means that a fundamental frequency (e.g., 2 MHz) is transmitted and the reflected and scattered higher harmonics (e.g., 4 and 6 MHz), produced by nonlinear propagation, are recorded. The signal level of these harmonics is usually low and a well-defined transfer function of the receiving transducer is required. Studying the acoustic response of a single contrast bubble, which has an amplitude in the order of a few Pascal, is another area where an optimal receive transfer function is important. We have developed three methods to determine the absolute transfer function of a transducer. The first is based on a well-defined wave generated by a calibrated source in the far field. The receiving transducer receives the calibrated wave and from this the transfer functions can be calculated. The second and third methods are based on the reciprocity of the transducer. The second utilizes a calibrated hydrophone to measure the transmitted field. In the third method, a pulse is transmitted by the transducer, which impinges on a reflector and is received again by the same transducer. In both methods, the response combined with the transducer impedance and beam profiles enables the calculation of the transfer function. The proposed methods are useful to select the optimal piezoelectric material (PZT, single crystal) for transducers used in reception only, such as in certain 3D scanning designs and superharmonic imaging, and for selected experiments like single bubble behavior. We tested and compared these methods on two unfocused single element transducers, one commercially available (radius 6.35 mm, centre frequency 2.25 MHz) the other custom built (radius 0.75 mm, centre frequency 4.3 MHz). The methods were accurate to within 15%.

Microbubble spectroscopy of ultrasound contrast agents

A new optical characterization of the behavior of single ultrasound contrast bubbles is presented. The method consists of insonifying individual bubbles several times successively sweeping the applied frequency, and to record movies of the bubble response up to 25 million frames/s with an ultrahigh speed camera operated in a segmented mode. The method, termed microbubble spectroscopy, enables to reconstruct a resonance curve in a single run. The data is analyzed through a linearized model for coated bubbles. The results confirm the significant influence of the shell on the bubble dynamics: shell elasticity increases the resonance frequency by about 50%, and shell viscosity is responsible for about 70% of the total damping. The obtained value for shell elasticity is in quantative agreement with previously reported values. The shell viscosity increases significantly with the radius, revealing a new nonlinear behavior of the phospholipid coating.

Microbubble spectroscopy of ultrasound contrast agents

We present a new optical characterization of the behavior of single ultrasound contrast bubbles. The method consists of insonifying individual bubbles several times successively sweeping the applied frequency and recording movies of the bubble response up to 25 million frames per second with an ultra-high-speed camera operated in a segmented mode. The method, termed microbubble spectroscopy, enables one to reconstruct a resonance curve of the oscillating bubble in a single run. We analyze the data through a linearized model for coated bubbles. The results confirm the significant influence of the shell on the bubble dynamics: shell elasticity increases the resonance frequency by about 50%, and shell viscosity is responsible for about 70% of the total damping. The obtained value for shell elasticity is in quantitative agreement with previously reported values. The shell viscosity decreases significantly with the dilatation rate, revealing the nonlinear behavior of the phospholipid coating.

Single bubble ignition after shock wave impact

The ignition behavior of single bubbles during the first oscillation after a shock wave impact was investigated experimentally. The bubbles were created by injection of oxygen into liquid cyclohexane. High speed pressure and optical measurements were applied. The experiments were performed inside cyclohexane, at room temperature and at an initial pressure of 1 bar. It was found that an incident shock wave with a peak pressure of 85 bar ± 8.5 bar can ignite bubbles with equivalent initial diameters between 2.4 and 7.2 mm. Measurements related to the shock-induced bubble compression process, the jet formation inside the bubble, the ignition delay, the light illumination during the bubble explosion, as well as other aspects of the observed bubble behavior are presented. In addition to the experimental observations a theoretical analysis is presented. The set of equations for the theoretical estimation of the pressure and the temperature and of the gaseous mixture inside the bubble at the moment of the observed bubble ignitions is shown and explained.

Single and dual bubble behavior under the influence of electric fields

Single and dual bubble behavior under the influence of electric fields

Simultaneous Measurement of 3-Dimensional Shape and Behavior of Single Bubble in Liquid Using Laser Sensors

A novel sensing system of bubble shape, surface area, volume and rising velocity using three coupled laser sensors was developed. To confirm the reliability of the system, the bubble shape was simultaneously measured using both a high-speed video camera and this system for an identical rising single bubble. The bubble's outline analyzed using the laser scanning system corresponded well with that analyzed by the video image analysis. The measured rising velocities of bubbles agreed well over a wide range of liquid viscosity with the data of Grace (1973), and Bhaga and Weber (1981). Moreover, the measured surface area of a bubble agreed well enough with the estimation of Tadaki and Maeda (1961) under their experimental condition. With this system, not only rising velocity of a single bubble but also its three-dimensional shape and surface area could he more precisely and quickly measured in real-time.

Predictions for stable sonoluminescence in nonaqueous liquids

The oscillation behavior of single sonoluminescing bubbles, and therefore their stability and the intensity of light emission, depends on a multitude of material parameters, including viscosity, surface tension, and liquid vapor. It is shown in analytical and numerical computations how substitution of water by nonaqueous fluids affects the domain for stable and unstable sonoluminescing bubbles in parameter space.

On the onset of transient cavitation in gassy liquids

This paper deals with a numerical and experimental study of ultrasound induced cavitation. On the basis of a computational analysis of Gilmore’s equation for the individual bubble dynamics, a slight decrease in the pressure radiated by a single bubble immediately before reaching the transient cavitation regime is predicted. Experiments presented in this paper confirm this observation. Therefore, a new method to detect the inception of transient cavitation is proposed. The numerical analysis of a single bubble behavior, carried out for the different bubble sizes, suggests that two distinct “types” of transient cavitation may occur in a cavitation field in connection with the relative number of bubbles involved in the process. The experiments seem to confirm the theoretical hypothesis. The experimental work consisted mainly of insonifying distilled water, with a gas content of about 75% of saturation, at 20 kHz and analyzing the resulting acoustic emissions.

Bubble characteristics in three-phase systems used for pulp and paper processing

Experiments are conducted to study the hydrodynamic behavior of three-phase pulp slurry systems at consistencies ranging from 0.1 to 1.0% (weight percent pulp). The pulp phase is a low-density fibrous material which swells to several times its original volume in water. The overall hydrodynamic behavior, including the regime transitions, of a multi-bubble, three-phase pulp slurry is studied by measuring the overall gas holdup and by using a light transmittance probe to determine the bubble characteristics. The results demonstrate that the hydrodynamic behavior of a three-phase pulp slurry varies from the behavior of a gas-liquid system. The deviation in the behavior becomes more pronounced as the pulp consistency increases. The bubble characteristics of bubbles injected through a single bubble injector are studied in a small rectangular column through the use of flow visualization and a particle image velocimetry technique. The measured change in the behavior of single bubbles injected into the pulp slurry through a single injector, is the basis for a proposed mechanism for the increased bubble coalescence in a multi-bubble system.

Pulse width measurements of sonoluminescence in cavitation-bubble fields

Recent studies involving sonoluminescence have focused on the properties and behavior of single bubbles in isolation. Some properties of single-bubble sonoluminescence (SBSL) appear to conflict with well-known properties of sonoluminescence from cavitation fields (MBSL). Direct comparisons between MBSL and SBSL have been difficult due to the difficulty in generating SBSL in nonaqueous solutions. A recent study comparing MBSL and SBSL [T. J. Matula etal., J. Acoust. Soc. Am. 96, 3252(A) (1994)] has shown that aqueous solutions of nonvolatile solutes show distinct differences in the corresponding spectra. The differences are attributed to differences in the relative symmetry of collapse of bubbles in cavitation fields versus in isolation. As part of the ongoing study to compare MBSL and SBSL, measurements were made of the apparent flash width of sonoluminescence from cavitation fields. Various well-defined cavitation regions were studied and compared to SBSL flash widths using an identical PMT for both cases. Both invasive and noninvasive mechanisms for generating MBSL were studied to determine the relative influence of ultrasonic horn immersion. Progress toward identifying the similarities and dissimilarities between MBSL and SBSL should lead to an improved understanding of sonochemical reactions. [Work supported by ONR.]

Heat transfer characteristics of the closed tube aerosyphon

The paper deals with heat transfer in the closed tube aerosyphon in which the upper section is cooled, the lower section is heated, and buoyancy forces are largely attributable to air bubbles introduced at the base of the device. Consistent with previous work, experimental data are used to demonstrate that substantial increases in heat transfer rates anse from increased advection and turbulence produced by the buoyant streaming. An attempt is made to describe the behaviour of the system in terms of bubble hydrodynamics. Predicted trends based on the behaviour of single bubbles are in general agreement with observations thus suggesting a simple physical basis for a complex convection system This flow model is consistent with the observed effects of aerator geometry and aeration rate, and may be used in establishing levels of confidence for extrapolation of an empirical correlation above or below the range of the variables measured.

Wall effect on the behaviour of single bubbles rising in highly viscous liquids.

The wall effect on the terminal velocity and the shape of single bubbles rising in highly viscous liquids has been investigated experimentally. The terminal velocities of single bubbles affected by the column wall are correlated with two dimensionless equations between ReM0.48/(l - λ1.5) and Eotvos number Eo, where λ is the bubble and column diameter ratio and 1 -λ1.5 is the wall effect function, which was also used for relatively low-viscosity liquids. The aspect ratio h/w defining the bubble deformation is found to be a function of Re and λ for Re ≥0.1, while it is a function of λ only for Re < 0.1. The bubble deforms from the sphere in the vicinity of Eo = 6, which corresponds to the border of dimensionless equations of bubble rising velocity.

Counting bubbles acoustically: a review

The acoustical resonance characteristics of bubbles are the key to their detection by backscatter, excess attenuation and sound speed dispersion in bubbly liquids. The linear, lumped-constant, behaviour of single bubbles is reviewed and formulated in terms of the physical constants of the medium liquid, the bubble gas and the interface between. Acoustical techniques for bubble counting are discussed using in-situ experiments at sea as an example.

Drag Coefficient and Wake Volume of Single Bubbles Rising through Quiescent Liquids

The behavior of single air bubbles rising through quiescent liquids, such as the shape, rising velocity and wake volume, is studied experimentally. The experiments which used seventeen kinds of aqueous glycerine solutions and glycerine-ethanol mixtures, are carried out in the Reynolds number range based on the equivalent spherical diameter 0.2-1000 and at the equivalent spherical diameter 0.2-1.8 cm. The wake volume is obtained from photographs using poster color.It is found that the bubble shape agrees with the equation of Tadaki et al., and the drag coefficient based on the major axis is correlated only with the Reynolds number based on the major axis. The effect of physical properties of liquids is not noticed. The volume ratio of the wake to the bubble is given as the function of the Reynolds number based on the equivalent spherical diameter and the Morton number, and the empirical equations are given.