Cavitation Bubbles In Liquid Research Articles

Laser trapping of cavitation bubbles in liquids

Cavitation has a significant impact on pulsed laser ablation of liquids. At high repetition rates of laser pulses, it tends to hinder laser breakdown and associated processes. Here, we report on the particular case of the cavitation process occurring only at the elevated pulse repetition rate — the formation of a laser trapped bubble. The effect was observed in liquid hydrocarbons (n-hexane and ethanol) and water. The cavitation bubbles generated by picosecond pulses were captured in the caustic beam in front of the laser focus and stay there for a long time (several seconds). After growing up to ∼100μm in size, such a bubble completely blocks the laser radiation and stops all processes in the laser waist. The scenario of laser trapped bubble formation is investigated, the effects of pulse energy and pulse repetition rate are analyzed, and a possible mechanism for the observed effect is proposed. The special importance of laser trapped bubbles for the optimization of laser synthesis of new materials, particularly the linear carbon chains in hydrocarbons, is demonstrated.

Nonlinear propagation and anomalous absorption of ultrasound in liquid

Recent work has rendered possible the formulation for the nonlinear propagation of pressure waves in liquids by using the generalized Navier - Stokes equations and the modified equations of state, with the heat transfer and fluid viscidity taken into consideration. And the nonlinear approximation solution of the second order term is obtained. The conclusion concerns the acoustic pressure, phase speed, attenuation, and velocity distribution function. When the amplitude of driving acoustic pressure is higher than the cavitation threshold of the host liquid, the cavitation occurs. The cavitation bubbles will prevent the sound field from spreading in the liquid, and the acoustic energy accumulates near the cavitation zone. So when studying the transmission characteristics of acoustic wave in the liquid, the cavitation attenuation must be considered. Note that the particularity of cavitation bubble movement, cavitation bubble vibration and viscous force are simulated under the initial driving sound. Through the analysis, it is found that the transmission of sound is influenced by the viscosity of the fluid, heat transfer, driving sound pressure (amplitude, frequency, duration) and cavitation bubble in liquid. The physical mechanism is that the higher driving pressure causes the cavitation to turn stronger, the acoustic loss to be faster, the sound propagation distance to be smalletr and the vibration of bubbles to transfer energy from the fundamental wave to harmonics. As a result, the stronger absorption from the liquid causes abnormal phenomena, and the output sound is lower finally. It shows that the nonlinear radial motion of cavitation bubble is mainly responsible for the sound intensity attenuation.

In vivo and in vitro study of a novel nanohydroxyapatite sonocoated scaffolds for enhanced bone regeneration

There still remains a need for new methods of healing large bone defects, i.e., gaps in bone tissue that are too big to naturally heal. Bone regrowth scaffolds can fill the bone gap and enhance the bone regeneration by providing cells with a support to for new tissue formation. Coating of the scaffolds surface with nanocrystalline hydroxyapatite may enhance the osteoinductivity or osteoconductivity of such scaffolds. Here we present the sonocoating method to coat scaffolds with bioactive hydroxyapatite nanoparticles. We show a method, where the material to be coated is immersed in a colloidal suspension of nanoparticles with mean sizes of 10 nm and 43 nm in water, and high-power ultrasound waves are applied to the suspension for 15 min at 30 °C. High power ultrasounds lead to growth of cavitation bubbles in liquid, which implode at a critical size. The implosion energy propels the nanoparticles towards the material surface, causing their attachment to the scaffold. Using this technique, we produced a uniform layer of nanohydroxyapatite particles of thickness in the range 200 to 300 nm on two types of scaffolds: a porous β-TCP ceramic scaffold and a 3D-printed scaffold made of PCL fibers. In vivo tests in rabbits confirmed that the novel coating strongly stimulated new bone tissue formation, with new bone tissue occupying 33% for the nHAP-coated PCL scaffold and 68% for the nHAP-coated β-TCP after a 3-month test. The sonocoating method leads to formation of a bioactive layer on the scaffolds at temperature close to room temperature, very short time and in water. It is a green technological process, promising for bone tissue regeneration applications.

Simulation of heat transfer with the growth and collapse of a cavitation bubble near the heated wall

The growth and collapse behaviors of a single cavitation bubble near a heated wall and its effect on the heat transfer are numerically investigated. The present study is designed to reveal the mechanism of cavitation enhanced heat transfer from a microscopic perspective. In the simulation, the time-dependent Navier-Stokes equations are solved in an axisymmetric two-dimensional domain. The volume of fluid (VOF) method is employed to track the liquid-gas interface. It is assumed that the gas inside the bubble is compressible vapor, and the surrounding liquid is incompressible water. Mass transfer between two phases is ignored. The calculated bubble profiles were compared to the available experimental data, and a good agreement was obtained. Then, the relationship among bubble motion, flow field and surface heat transfer coefficient was analyzed. On this basis, the effects of such factors as the initial distance between the bubble and the wall, the initial vapor pressure and the initial bubble nucleus size on the heat transfer enhancement are discussed. The present study is helpful to understand the heat transfer phenomenon in presence of cavitation bubble in liquid.

Bio-inspired ultrasound assisted construction of synthetic sponges

A porous material with a system of cavities can be considered as a sponge. The amazing mechanical, optical, electrical and sorption properties of sponge-like silicon-, carbon- and metal-based materials arose interest in novel synthetic pathways of formation of the sponges which in addition gained value in many energy and climate related issues. Here, we present a prospective bio-inspired approach to fabricate synthetic sponges via intensive ultrasonication. Ultrasound of high intensity triggers formation of cavitation bubbles in liquid in a controlled way. Cavitation happens when a rapid change in pressure occurs. Cavitation in nature occurs in fast streams, produced by some shrimps, and in the xylem of plants. Ultrasonically induced cavitation bubbles can be considered as chemical microreactors providing high temperature and pressure at the microscopic scale and trigger formation of active species (including free radicals) from dissolved molecules. In the context of chemistry, cavitation has the unique potential of locally catalyzing high-temperature (up to 5000 K) and high-pressure (several hundreds of bars) reactions, while the system remains macroscopically near room temperature and ambient pressure. Ultrasound of high intensity has already been applied for the synthesis of structured organic and inorganic materials and composites. In this review we summarize the latest achievements in the application of ultrasonication for the formation of hierarchically ordered 3-D networks (sponges). The prospects of applications of sonochemically formed composites in catalysis, optics, hydrogen storage and corrosion protection are highlighted.

Time-resolved measurements of shock-induced cavitation bubbles in liquids

A novel experimental method for the measurement of cavitation bubble dynamics is presented. The method makes use of a collimated cw HeNe laser beam that is focused onto a photodiode. A cavitation bubble centered in the laser beam leads to refraction and thus changes the diode signal. With sufficient temporal resolution of the measurement, the evolution of the bubble dynamics, and in particular, the collapse, could be well resolved (limitation is only due to diode response and oscilloscope bandwidth). In the present work this is demonstrated with cavitation bubbles generated with high-power nanosecond and femtosecond laser pulses, respectively. Bubble evolution is studied in two different liquids (water and glycerine) and at different temperatures and pressures.

Cumulation during compression of cavitation bubbles in liquid

Cumulative effects under strong compression of cavitation bubbles in liquid are considered. The dependence of cumulation on small initial nonsphericity of bubbles is discussed in three cases. In the first case, the compression of the bubble in liquid is realized at a great distance from the liquid boundaries (free surface, rigid walls). In the second case, the influence of a nearby wall is considered. In the third case, the bubble is compressed in the presence of other bubbles in its vicinity.

Clarification of Cavitation Phenomenon in Liquid Fuel under Unsteady Pressure Field in Pipeline.

High-pressure injection systems have been installed for the purpose of reducing toxic exhaust gas from diesel engines in recent years. However, the cavitation phenomenon and erosion occur in the high-pressure pipe system due to the large pressure fluctuations at the end of fuel injection. Therefore, there is strong demand for clarification of the cavitation phenomenon under a fluctuating pressure field. For this reason, behavior of cavitation bubbles in liquid fuel under a fluctuating pressure field in a pipeline was investigated in the experiments presented here.

金属の電析におよぼすジェット流の理論的考察

The effects of ultrasonic waves on electrolysis consist mainly of cavitation action. The collapse of cavitation bubbles in liquid generate collapse pressure, jet flow and impulse pressure due to the jet flow. First, the collapsing motion of a single bubble near a electrode surface was modeled, and equations of motion for a spherical gas bubble were obtained. Next, the properties of deposits were studied on the basis of the equations of motion. The jet flow speed and liquid pressure due to water hammer were calculated using equations (33) and (34) in liquid. For example, when the jet flow speed was 120m·s-1, the water pressure was about 2000atm. The mass transfer on the electrode was a turbulent diffusion. The jet flow and pressure affected the entire mechanism of electrodeposition: the rate of deposition, current efficiency, hardness, roughness and particle size of deposits were affected.

Dynamics of two nonspherical cavitation bubbles in liquids

This paper deals theoretically with the interaction between two nonspherical cavitation bubbles in liquids by means of twin spherical expansions. Governing equations of bubble boundaries are derived by taking account of the translational motion of the bubbles in an incompressible liquid, and are exact to the order (Ri0/L)5 in which Ri0 (i = 1, 2) is the radii of the two bubbles and L the distance between the centers of the bubbles. The theory is extended to the case of a compressible liquid in which the compressibility effect is considered to the first order of the inverse of the sound speed in the liquid.A test computation is performed on the collapse of a single vapor bubble in the neighborhood of a plane rigid boundary and is compared with the result calculated by a fully numerical method. It is further confirmed by an experiment conducted in a water shock tube. A numerical example for the case of interaction between two nonspherical bubbles with initially different radii is also given.

High Speed Holographic Movie Camera

A high speed holographic movie camera system has been developed to investigate the dynamic behavior of cavitation bubbles in liquids. As a light source for holography, a high power multiply cavity-dumped argonion laser is used to record very long hologram series with framing rates up to 300 kHz. For separating successively recorded holograms, two spatial multiplexing techniques are applied simultaneously: rotation of the holographic plate or film and acousto-optic beam deflection. With the combination of these two techniques we achieve up to 4000 single holograms in one series.

Cavitation dynamics. I. A mathematical formulation

A set of equations has been derived to describe the dynamical motions of small cavitation bubbles in liquids set into motion by an acoustic pressure field. The mathematical formulation takes into account heat conduction inside a bubble and in the surrounding liquid, and the viscosity, compressibility, and surface tension of the liquid. The effect of vapor pressure may be determined as a function of the interfacial temperature. The formulation consists of nonlinear ordinary differential, integral, and algebraic equations, and has been programmed for solution on a digital computer. Subject Classification: 25.60; 35.68.