Influence of ambient temperature on cavitation bubble dynamics

TL;DR

This work investigates how ambient temperature shapes the dynamics of spark-generated cavitation bubbles, spanning 23–$90\circ\mathrm{C}$. By combining hundreds of experiments with Keller-equation–based pressure estimation and compressible boundary-integral insights, it shows that higher $T$ raises internal vapour pressure and enlarges the maximum bubble radius while systematically weakening collapse and jetting. A novel secondary cavitation mechanism emerges above $70\circ\mathrm{C}$, driven by Blake-threshold–related nucleation that promotes Rayleigh–Taylor instabilities and bubble fission; near-wall dynamics further reveal reduced erosion potential at elevated temperatures, modulated by discharge energy. These findings advance the thermally mediated understanding of cavitation and offer practical guidance for erosion mitigation in high-temperature fluids.

Abstract

We investigate the influence of ambient temperature on the dynamics of spark-generated cavitation bubbles over a broad temperature range of 23 to 90$^\circ \text{C}$. Increasing temperature, the attenuation of collapse intensity of a bubble in a free field is quantitatively characterised through the Rayleigh factor, minimum bubble volume, and maximum collapse velocity. In scenarios where the bubble is initiated near a rigid boundary, this temperature-dependent weakening effect manifests further as a reduction in jet velocity and bubble migration. Additionally, our findings demonstrate that when ambient temperature exceeds 70$^\circ \text{C}$, secondary cavitation forms near the bubble surface around the moment of maximum bubble expansion, followed by coalescence-induced surface wrinkles. These perturbations trigger Rayleigh-Taylor instability and enhance bubble fission. We determine the internal gas pressure of the bubble at its maximum expansion via the Rayleigh-Plesset equation with the input of bubble radius from experimental measurements. It reveals that the secondary cavitation is derived from the gas pressure descending below the saturated vapor pressure, which provides nucleation-favorable conditions. This study sheds light on the physics behind erosion mitigation in high-temperature fluids from the perspective of cavitation bubble dynamics.

Figures (16)

• Figure 1: Representative high-speed images of spark-generated bubbles in a free field. (a) At $T= 23^\circ\mathrm{C}$, the bubble remains nearly spherical with a smooth surface during expansion, collapse and rebound. (b) At $T= 90^\circ\mathrm{C}$, the interface remains smooth during early expansion ($t=0.2$), then secondary cavitation bubbles emerge around the bubble ($t=0.35$). These secondary cavitation bubbles coalesce into the main bubble while it is still growing ($t=0.78$), creating surface wrinkles that intensify during collapse ($t=1.62$). Upon rebound, the wrinkles develop into pronounced Rayleigh–Taylor instabilities ($t=1.88$). The time displayed in the lower right corner is normalised by characteristic collapse time, $R_{max}\sqrt{\rho/(P_{\infty}-P_v)}$, where $R_{max}$ is the maximum bubble radius, $\rho$ the liquid density, $P_\infty$ the hydrostatic pressure at infinity, and $P_v$ the saturated vapour pressure; the resulting values are 1.11 and 2.60 ms, respectively.
• Figure 2: Experimental setup for cavitation bubble dynamics in various ambient temperatures. The bubble is generated by a underwater low-voltage electric discharge method. The temperature of water is controlled by two resistance-type heater arranged symmetrically.
• Figure 3: Three representative experiments conducted in the free field at different ambient temperatures. (a) The bubble was initiated at room temperature (23 $^\circ \text{C}$), maintaining a spherical shape throughout the oscillation process. (b) The bubble was initiated at 50 $^\circ \text{C}$. Its contraction intensity is weakened. (c) The bubble was initiated at 90$^\circ \text{C}$. During the expansion stage, secondary cavitation occurs near the bubble wall. During the collapse stage, the intensity of bubble contraction is further weakened, and fission occurs in the rebound process. Normalised times are indicated in the lower-right corners of each frame. The time scales for non-dimensionalization ($R_{max}\sqrt{\rho/(P_{\infty}-P_v)}$) are 1.11, 1.38 and 2.60 ms, respectively. $P_v$ is the saturated vapour pressure corresponding to the ambient temperature. The length of horizontal line indicated in the lower-left corner of first frame is 10 mm.
• Figure 4: Effect of ambient temperature on spark-generated bubbles. (a) Variation of the maximum bubble radius $R_{max}$ (blue triangles) and collapse time $t_c$ (red circles) as functions of ambient temperature $T$. Error bars indicate the standard deviation. (b) Pressure--temperature phase diagram for spark-generated bubbles. The dashed lines denote the spinodal, representing the thermodynamic limit of stability for the vapour and liquid phases. The solid line indicates the saturated vapour pressure. Blue and red symbols mark experiments conducted at 23 and 90 $^\circ$C, respectively. State A: liquid at local hydrostatic pressure and ambient temperature before discharge. State B: liquid after energy deposition, at the spinodal limit but before vaporisation. State C: the high temperature and high pressure vapour inside the initiated bubble, corresponds to the early expansion moment when the bubble reaches the same volume in both experiments.
• Figure 5: Effect of ambient temperature on bubble collapse. (a) Variation of the Rayleigh factor $\eta$ versus the ambient temperature $T$. The cycles denote the experimental data. (b) Variation of the non-dimensional minimum volume at the end of the first bubble collapse stage $R_{min}/R_{max}$ versus the dimensional ambient temperature $T$. The empty cycles represent the results of laser-induced bubbles from phan2022thermodynamic. The red crosses represent the results of spark-generated bubbles from geng2025. The upward triangles denote the experimental data. The squares represent the results computed by the Keller equation with initial pressures of 11, 16.5, 20.7, 22.4, 28, 32, 38, and 48 kPa, which are determined by the method described in $\S$\ref{['sec:2.2']}. Error bars indicate the standard deviation.