Temperature-driven transition in the unsteady evolution of cavitation bubble in subcooled liquid nitrogen

The objective of this study is to investigate the unsteady and thermodynamic characteristics of cryogenic cavitation bubble with various temperatures. The transient behavior of cavitation bubble in liquid nitrogen with various temperatures is experimentally obtained. In the experiment, the ambient pressure is set as 101.325 kPa. The liquid nitrogen temperature ranges from 66 K to 76.4 K, corresponding to a subcooling range of 0.95 K to 11.35 K. The experimental results show that, as the temperature of liquid nitrogen increases, the maximum radius of liquid nitrogen bubble increases, and the maximum values of both velocity and acceleration during the first collapse decrease. We unexpectedly found that the breakup time of bubble exhibits a negative exponential relationship with the subcooling degree of liquid nitrogen. Based on the experimental and theoretical analyses, this phenomenon is attributed to the transition from the thermal and re-evaporation model to the inertia model of bubble evolution. When the liquid nitrogen approaches its saturated state, the evolution of liquid nitrogen bubble is dominated by the thermal effects and re-evaporation, which prolongs bubble evolution time. As the subcooling degree decreases during this stage, the influences of both thermal effects and secondary evaporation on bubble diminish significantly, causing a sharp decline in bubble breakup time. When the liquid nitrogen is far from its saturated state, the dominant factor of bubble evolution shifts to the liquid inertia. During this stage, the change of subcooling degree has a weak impact on thermal effects, re-evaporation, and liquid inertia, resulting in bubble breakup time remaining nearly unchanged as the subcooling degree rises. A dimensionless parameter t_ITM is proposed to quantitatively evaluate and predict dynamic transition between these two models. Meanwhile, a mapping function between the breakup time and the liquid temperature is obtained based on t_ITM, which can predict the breakup time of liquid nitrogen bubble.