Multi- and Single- Bubble Sonoluminescence: Difference in Nature of Light Emission
M.Margulis (Department of Sonochemistry, N.N. Andreyev Acoustics Institute, Moscow, Russia)
Sonoluminescence (SL) from usual multibubble cavitation field due to electric micro- discharges inside the cavitation bubbles at their deformations and fragmentation. Single bubble SL is a high temperature light emission from the single spherical non deformed bubble. Consequently, the first type of light emission has luminescent nature, and the second one is a thermal glow. Using the results on laser cavitation, we obtained the critical index of cavitation Kcr at that interaction between bubbles leads to absence of high temperatures at their compression. For water even at moderate sound intensities index of cavitation K = 0.01- 0.9 >> Kcr = 1,2.10-3. So, even in weak multibubble systems interaction between bubbles is substantial, practically all cavitation bubbles are deformed and high temperatures, that could produce SL and sonochemical reaction, are absent. At nonlinear oscillations the bubble.s forward motion affects magnificently on radial one. Forward motion damps adiabatic bubble .collapse. considerably, it decreases maximum temperature Tmax in 3 times (to 2800 K) and maximum radial velocity in 4 times (to 140 m.s-1). So, if heat exchange, lose of sphericity, interaction with other bubbles and flows of liquid are taken into account additionally, in the field of progressive sound wave Tmax <= 1000 K.
Section : 11