Temperature effects on single cavitation bubble dynamics under the free field condition: Experimental and theoretical investigations on water

Abstract

This paper examines how water temperature affects the dynamics of a single cavitation bubble in free field conditions. Both experimental and theoretical approaches are employed to explore the bubble dynamics in water under different temperatures. A series of single bubble experiments are conducted in water using the capacitive discharge method, with water temperature ranging from room temperature to near boiling point under atmospheric pressure. A high-speed photography system is utilized to capture the bubble evolution during the experiments. The experimental results suggest that (1) At all temperatures, the bubble evolutions progress through expansion, shrinkage, and oscillation stages, with significant changes observed in bubble dynamics when temperatures are above 60 °C. (2) The maximum bubble radius and the oscillation period of the cavitation bubble increase with increasing temperatures. The minimum bubble radius remains almost constant at 1.00 mm for water temperatures below 60 °C, but a rapid increase occurs above 60 °C. Thus, the bubble shrinkage ratio (R_min/R_max) in the first cycle at 95 °C is 6 times more than that at 30 °C, corresponding to the weaker collapse. (3) Near the boiling point, the cavitation bubble hardly rebounds after the first cycle and the bubble breaks into multiple micro-bubbles which continue to oscillate instead of collapsing. Meanwhile, a theoretical model accounting for heat transfer, phase change, and compressibility has been used to quantify the vapor mass transfer rate, the bubble internal pressure, and the bubble internal temperature. It is found that the mass transfer rate at 30 °C is significantly higher than at 95 °C. As a result, the bubble boundary collapse velocity is dozens of times lower at 95 °C compared to that at 30 °C. Moreover, the bubble internal pressure and internal temperature significantly decrease with increasing temperature due to the weaker collapse. In general, high temperatures (above 60 °C) significantly reduce the non-equilibrium interphase mass transfer effect of the bubble, and the bubble boundary retraction speed is slower and the collapse is weaker. This investigation is essential for better clarifying and explaining how water temperature affects the single cavitation bubble dynamics.