Experimental determinations of transient conditions during cavitation

Abstract

The collapse of cavitation bubbles generates intense local energy release, resulting in extreme local heating, high local pressures, and high energy chemistry. Determining the local conditions formed during cavitation, however, has proved to be a difficult problem. In our work, sonochemical reactions and the sonoluminescence that results have been used as quantitative probes of both temperature and pressure during cavitation. The effective temperatures reached during cavitation can be probed by measurement of the relative rates of a series of chemical reactions whose temperature dependence is already known. Comparative rate thermometry of multibubble cavitation (immersion horn at 20 kHz and ≊30 W/cm2) yields effective temperatures of ≊5200 K in hydrocarbons [K. S. Suslick, Science 247, 1439 (1990)]. Consistent with this, sonoluminescence in these liquids closely resembles flame emission from excited states of C2; rotational and vibrational fine structure permits a spectroscopic determination of the emission temperature of C2 excited states at 5080±160 K [E. B. Flint and K. S. Suslick, Science 253, 1397 (1991)]. Sonoluminescence from excited state metal atoms is produced from sonolysis of organometallic compounds, for which the linewidth determines the collisional lifetimes of emitting atoms and the effective local pressures. For excited state Cr atoms produced from Cr(CO)6, emission lifetime is only 0.20 ps, corresponding to local densities of ≊0.15 g/cm3 or pressures of ≊1.5 kBar at 5000 K. [Supported by NSF.]