Evolution Of Cavitation Bubbles Research Articles

Experimental study on damage mechanism of blood vessel by cavitation bubbles

Ultrasound-induced cavitation in blood vessels is a common scenario in medical procedures. This paper focuses on understanding the mechanism of microscopic damage to vessel walls caused by the evolution of cavitation bubbles within the vessels. In this study, cavitation bubbles were generated using the low-voltage discharge method in 0.9% sodium chloride saline, and vessel models with wall thicknesses ranging from 0.7 mm to 2 mm were made using a 3D laminating process. The interaction between cavitation bubbles and vessel models with different wall thicknesses was observed using a combination of high-speed photography. Results show that cavitation bubble morphology and collapse time increased and then stabilized as the vessel wall thickness increased. When the cavitation bubble was located in vessel axial line, pair of opposing micro-jets were formed along the axis of the vessel, and the peak of micro-jet velocity decreased with increasing wall thickness. However, when the cavitation bubble deviated from the vessel model center, no micro-jet towards the vessel model wall was observed. Further analysis of the vessel wall deformation under varying distances from the cavitation bubble to the vessel wall revealed that the magnitude of vessel wall stretch due to the cavitation bubble expansion was greater than that of the contraction. A comparative analysis of the interaction of between the cavitation bubble and different forms of elastic membranes showed that the oscillation period of the cavitation bubble under the influence of elastic vessel model was lower than the elastic membrane. Furthermore, the degree of deformation of elastic vessel models under the expansion of the cavitation bubble was smaller than that of elastic membranes, whereas the degree of deformation of elastic vessel models in the contraction phase of the cavitation bubble was larger than that of elastic membranes. These new findings provide important theoretical insights into the microscopic mechanisms of blood vessel potential damage caused by ultrasound-induced cavitation bubble, as well as cavitation in pipelines in hydrodynamic systems.

Experimental investigation of cavitation characteristics for a high-speed inducer with a great flow rate

Cavitation performance is a key parameter for a mine high-speed rescue pump, which reduces the stability and reliability of the entire unit. In this study, an experimental method was used to investigate the cavitation characteristics of an inducer installed on the impeller upstream. Hydraulic performance without cavitation was determined along with the cavitation performance, and a visualization experiment was implemented. The inducer head slightly decreased when the cavitation number started to decline; however, it dropped significantly thereafter. At 4200 r/min, anti-cavitation ability of the inducer had no connection with the blade numbers. The anti-cavitation performance of the inducer with three blades was superior than that of the inducer with two blades. The law governing shaft power, cavitation number, and rotating speed disagreed with the similarity law theory. Moreover, the inducer efficiency was higher at greater speeds. The evolution of cavitation bubbles was categorized into the inception, developing, and developed stages. When the cavitation number decreased, vortex cavitation was induced along with the tip leakage vortex; subsequently, wedge-shaped sheet cavitation occurred, which was followed by back-flow vortex cavitation. The areas associated with wedge-shape sheet cavitation and back-flow vortex cavitation increased gradually, extending spirally along the axial direction until the entire flow passage was blocked. Overall, the heads declined by 1.1%–1.9% for the inducer with three and two blades, respectively.

Effect of Laser Wavelength on Laser-Induced Breakdown Spectrum and Evolution of Cavitation Bubble in Bulk Water

Effect of Laser Wavelength on Laser-Induced Breakdown Spectrum and Evolution of Cavitation Bubble in Bulk Water

Evolution of Cavitation Bubble in Tap Water by Continuous-Wave Laser Focused on a Metallic Surface

As an example of photon-matter interaction, we experimentally investigate the temporal evolution of a millimeter-sized cavitation bubble, induced by focusing a continuous-wave laser on a metallic plate in tap water. Our major interests are to understand the mechanism of bubble growth/shrinkage for a long time duration up to O(102) seconds and to draw the time-dependency relation of a bubble size, depending on the incident laser power. With the time passed after the laser with different power is focused, it is found that the phase change and/or transport of dissolved gas into the bubble play a dominant role in determining the bubble growth and shrinkage. Thus, we propose two stages in terms of time and three regimes depending on the incident energy, in which the evolutions of cavitation bubble in short and long time durations are distinctively identified. In regime I (lower incident power), the water nearby the focal point undergoes a phase change, resulting in an initial rapid growth of a bubble (first stage), but the convection flow due to locally heated surface causes the bubble to shrink at later times (second stage). As the laser power increases (regime III), more dissolved gas in the surrounding water enters the growing bubble and prevents the water phase from being absorbed into the bubble. Thus, the bubble growth is dominated by the dissolved gas. Between regimes I and III, there is a transitional regime II in which both the phase change of water and the dissolved gas contribute to the bubble evolution. We further our understandings by developing the relations about the time-dependency of bubble size for each stage and regime, which agree well with the measured data. The scaling relations are also validated with different conditions of liquid such as degassed water and NaCl solution. While previous studies have mostly focused on the nano- and/or microsized bubble generation in a very short time (less than 1 s), we think that the present results will extend our knowledge on how to predict and control the size of laser-induced cavitation bubble for longer time duration.

High fidelity visualization of multiscale dynamics of laser-induced bubbles in liquids containing gold nanoparticles

Cavitation in pure liquids and in liquids containing nanoparticles enables applications in mechanics, bio-medicine, and energy. Its evolution carries a significant interest. We describe the multiscale dynamic evolution of ultrafast-laser-induced cavitation in pure and gold-nanoparticles-doped liquids in one-dimensional geometries induced by non-diffractive ultrashort Bessel-Gauss laser beams. Covering the complete electronic and thermomechanical cycle, from the early plasma phase to bubble cavitation and collapse on ms timescales, we reconstitute, using time-resolved imaging with amplitude and phase sensitivity, the hydrodynamic phenomena concurring to bubble evolution. We indicate geometry-specific instabilities accompanying the collapse. The insertion of gold nanoparticles of 200 nm size has subtle effects in the process energetics. Albeit a moderate field enhancement minimizing the contribution to breakdown, the nanoparticles play a role in the overall relaxation dynamics of bubbles. The evolving bubble border in nanoparticles-containing liquids create a snow-plough effect that sweeps the nanoparticles at the gas liquid interface. This indicates that during the macroscopic cavity development, the nanoparticles were removed from the interaction region and dragged by the hydrodynamic movement. We thus shed light on the evolution of cavitation bubbles not triggered but perturbed by the presence of nanoparticles.

Pulsed laser ablation plasmas generated in CO2 under high-pressure conditions up to supercritical fluid

Pulsed laser ablation of solids in supercritical media has a large potential for nanomaterials fabrication. We investigated plasmas generated by pulsed laser ablation of Ni targets in CO2 at pressures ranging from 0.1 to 16 MPa at 304.5 K. Plasma species were characterized by optical emission spectroscopy, and the evolution of cavitation bubbles and shockwaves were observed by time-resolved shadowgraph imaging. Ni and O atomic emissions decreased with increasing gas pressure; however, near the critical point the intensities reached local maxima, probably due to the enhancement of the plasma excitation and effective quenching resulting from the large density fluctuation.

A new approach to nucleation of cavitation bubbles at chemically modified surfaces

Cavitation at the solid surface normally begins with nucleation, in which defects or assembled molecules located at a liquid-solid interface act as nucleation centers and are actively involved in the evolution of cavitation bubbles. Here, we propose a simple approach to evaluate the behavior of cavitation bubbles formed under high intensity ultrasound (20 kHz, 51.3 W cm(-2)) at solid surfaces, based on sonication of patterned substrates with a small roughness (less than 3 nm) and controllable surface energy. A mixture of octadecylphosphonic acid (ODTA) and octadecanethiol (ODT) was stamped on the Si wafer coated with different thicknesses of an aluminium layer (20-500 nm). We investigated the growth mechanism of cavitation bubble nuclei and the evolution of individual pits (defects) formed under sonication on the modified surface. A new activation behavior as a function of Al thickness, sonication time, ultrasonic power and temperature is reported. In this process cooperativity is introduced, as initially formed pits further reduce the energy to form bubbles. Furthermore, cavitation on the patterns is a controllable process, where up to 40-50 min of sonication time only the hydrophobic areas are active nucleation sites. This study provides a convincing proof of our theoretical approach on nucleation.