Investigation on dynamic characteristics and thermal effects of single cavitation bubble in liquid nitrogen

Abstract

The objective of this paper is to investigate the dynamic characteristics and thermal effects of the single cavitation bubble in liquid nitrogen. A fully enclosed experimental platform for the single cavitation bubble in free field is established. To analyze the impact of the strong thermal effects of cryogenic fluids on the evolution process of single cavitation bubble, the room-temperature water and the liquid nitrogen in the same ambient pressure are set for comparison. According to the experimental results, the evolutions of single cavitation bubble in the room-temperature water and liquid nitrogen both experience the expansion stage, shrinkage stage, and oscillation stage, respectively. To further analyze the unsteady dynamics, a theoretical model of single cavitation bubble considering the compressibility, temperature, and phase change is introduced. The results show that the bubble radius predicted by this theoretical model is in good agreement with the experimental data. During the expansion stage, the dynamic bubble behaviors in both the room-temperature water and liquid nitrogen are governed by the liquid inertia. During the shrinkage stage, the interphase mass transfer increases the shrinkage velocity of bubble. Compared to the room-temperature water bubble, the initial pressure difference and vapor mass transfer rate of the liquid nitrogen bubble are significantly smaller. Thus, the shrinkage velocity of the liquid nitrogen is small, corresponding to weaker liquid inertia. And the bubble behaviors in liquid nitrogen are dominated by the thermal effects. For the liquid nitrogen bubble, the minimum shrinkage radius is more than 3 times that of the bubble in room-temperature water; the maximum Mach number is about 0.2 times that of the room-temperature water bubble, and the influence of compressibility on the dynamic behaviors is weaker. Besides, the maximum pressure and temperature during the shrinkage stage of liquid nitrogen bubble are significantly smaller due to the weaker shrinkage of bubble. And the oscillation cycle and overall size of the liquid nitrogen bubble are significantly larger during the oscillation stage compared to the room-temperature water bubble.