Energy partition at the collapse of spherical cavitation bubbles.

Spherically collapsing cavitation bubbles produce a shock wave followed by a rebound bubble. Here we present a systematic investigation of the energy partition between the rebound and the shock. Highly spherical cavitation bubbles are produced in microgravity, which suppresses the buoyant pressure gradient that otherwise deteriorates the sphericity of the bubbles. We measure the radius of the rebound bubble and estimate the shock energy as a function of the initial bubble radius (2-5.6mm) and the liquid pressure (10-80kPa). Those measurements uncover a systematic pressure dependence of the energy partition between rebound and shock. We demonstrate that these observations agree with a physical model relying on a first-order approximation of the liquid compressibility and an adiabatic treatment of the noncondensable gas inside the bubble. Using this model we find that the energy partition between rebound and shock is dictated by a single nondimensional parameter ξ=Δpγ6/[p(g0)1/γ(ρc2)1-1/γ], where Δp=p∞ - pv is the driving pressure, p∞ is the static pressure in the liquid, pv is the vapor pressure, pg0 is the pressure of the noncondensable gas at the maximal bubble radius, γ is the adiabatic index of the noncondensable gas, ρ is the liquid density, and c is the speed of sound in the liquid.