Investigation on Oscillating Behavior of Laser-Induced Cavitation Bubble Near Wall in Room Temperature Water and Cryogenic Liquid

Abstract

Cavitation is bubbling phenomena caused by local pressure reduction or strong energy concentration in liquids. Cavitation is widely observed in fluid machinery and it causes vibration, noise, erosion, and loss of efficiency. In addition, cavitation occurs in laser treatment and causes the ruin of human tissues. There are a lot of researches on cavitation phenomena in room temperature liquids. It is known that laser-induced bubble generates pressure waves, and the bubble oscillates and collapses eventually. Recently, it is reported that cavitation occurs in cryogenic liquid such as rocket propellant. However, there are few researches about cavitation in cryogenic liquid. Generally, the thermo-physical properties such as surface tension and viscosity of cryogenic liquid are different from those of room temperature water, and cavitation in cryogenic liquid occurs near boiling temperature (low subcooling region). In our experiment, single bubble was generated by focused laser, and its behavior and pressure wave were visualized. The focusing point of the laser was also settled near a wall in the liquids by designated distance. Interacting behavior of laser-induced bubble with the wall was also investigated. We chose liquid nitrogen (LN2) as cryogenic liquid for safety. LN2 was pressurized in order to increase the degree of subcooling. These experiments show difference of oscillation periods between bubble in water at room temperature and in liquid nitrogen. In addition, there is difference of oscillating behavior of LN2 bubbles in low and high subcooling regions. We discuss influence of the degree of subcooling and stand-off distance. It is found that shapes of deformation and oscillation period of bubble are influenced by these parameters.