Collapsing behavior of spark-induced cavitation bubble in rigid tube.

The phenomenon of cavitation within tubes is a common scenario in the fields of medicine and industry. This paper focuses on the effects of rigid circular tube length, diameter and the distance of bubble - tube port on the behavior of bubble in tube. The low-voltage discharge technique was utilized to induce a cavitation bubble in deionized water. The effects of rigid tube lengths, diameters, and bubble-tube port distances on the morphology of bubbles are observed using high-speed camera. It has been found that as the length of the rigid tube increases, so does the period, and this effect is more pronounced in tubes with smaller diameters. Conversely, the cavitation bubble period decreased and then stabilized as the tube diameter increased, the ratio of tube radius and the bubble radius exceeds 4.8, the period of bubble in tube is similar to that of bubble in free field. Further analysis of the influence of tube characteristics on microjets reveals that a pair of oppositely microjets were formed along the tube axis by the bubble near the midpoint of the tube axis. Moreover, when the non-dimensional tube length η < 3.5, the increase tube diameter results in a decrease microjet velocity. It has also been observed that as the bubble gradually approaches the interior of the tube, the velocity of microjets directed inward decreases. Additionally, the smaller the diameter of the tube, the greater the bubble-tube port distance required for the microjets to reach the same level of velocity as bubble near the center of the tube axis. These findings hold theoretical implications for improvement of targeted drug delivery efficiency in medicine and enhance the operational efficiency of inertial micropumps in industries.

Experimental study on influence of particle shape on shockwave from collapse of cavitation bubble.

The bubble dynamics under the influence of particles is an unavoidable issue in many cavitation applications, with a fundamental aspect being the shockwave affected by particles during bubble collapse. In our experiments, the method of spark-induced bubbles was used, while a high-speed camera and a piezoresistive pressure sensor were utilized to investigate how particle shape affects the evolution of shockwaves. Through the high-speed photography, we found that the presence of the particle altered the consistency of the liquid medium around the bubble, which result in the emitting of water hammer shockwave and implosion shockwave respectively during the collapse of the bubble. This stratification effect was closely related to the bubble-particle relative distance φ and particle shape δ. Specifically, when the bubble-particle relative distance φ < 1.34 e-0.10δ, particles disrupted the medium consistency around the bubbles and led to a nonspherical collapse and the consequent stratification of the shockwave. By measuring the stratified shockwave intensity affected by different particle shapes, we found that the stratified shockwave intensity experienced varying degrees of attenuation. Furthermore, as the particle shape δ increased, the attenuation of the particle on shockwave intensity gradually reduced. These new findings hold significant theoretical implications for elucidating cavitation erosion mechanisms in liquid-solid two-phase flows and applications and prevention strategies in liquid-solid two-phase cavitation fields.

Experimental study on the mesoscale causes of the influence of viscosity on material erosion in a cavitation field.

Cavitation is a very important hydrodynamic phenomenon in many scientific and engineering fields, such as acoustics, medicine, and hydraulics. The relationship between the physical characteristics of liquid media and the erosion status of materials in a cavitation field is a crucial concern for many researchers. In this study, we adopted underwater low-voltage discharge technology to generate cavitation bubbles. We studied the effect of the viscosity of liquid media on cavitation bubble dynamics at the mesoscale level by using high-speed photography and a transient stress test system to illustrate the mechanism and the characteristics of material erosion under viscosity changes at the macroscopic level. It was found that high liquid viscosity delays shrinkage of the cavitation bubble and increases the minimum volume to which the cavitation bubble shrinks. The shrinkage characteristics of a cavitation bubble in a solution with high viscosity can reduce the speed of micro-jet formation during the collapse of the cavitation bubble near a wall. In addition, they can delay the impact of the micro-jet on the wall surface and reduce the impact strength when the cavitation bubble collapses. The effect of viscosity on cavitation bubble dynamics at the mesoscale level can explain the erosion law of solid-wall surfaces in a cavitation field from a mechanical point of view. These conclusions present significant potential for cavitation application and prevention in the fields of ultrasonic cleaning, medicine, and hydraulic machinery.