  We experimentally investigate the breakup mechanisms and probability of
Hinze-scale bubbles in turbulence. The Hinze scale is defined as the critical
bubble size based on the critical mean Weber number, across which the bubble
breakup probability was believed to have an abrupt transition from being
dominated by turbulence stresses to being suppressed completely by the surface
tension. In this work, to quantify the breakup probability of bubbles with
sizes close to the Hinze scale and to examine different breakup mechanisms,
both bubbles and their surrounding tracer particles were simultaneously
tracked. From the experimental results, two Weber numbers, one calculated from
the slip velocity between the two phases and the other one acquired from local
velocity gradients, are separated and fitted with models that can be linked
back to turbulence characteristics. Moreover, we also provide an empirical
model to link bubble deformation to the two Weber numbers by extending the
relationship obtained from potential flow theory. The proposed relationship
between bubble aspect ratio and the Weber numbers seems to work consistently
well for a range of bubble sizes. Furthermore, the time traces of the bubble
aspect ratio and the two Weber numbers are connected using the linear forced
oscillator model. Finally, having access to the distributions of these two
Weber numbers provides a unique way to extract the breakup probability of
bubbles with sizes close to the Hinze scale.
