Experimental study of the thermal behavior of spark generated bubbles in water

In the paper thermal behavior of spark generated bubbles is studied experimentally using an optic sensor (a photodiode) and an acoustic sensor (a hydrophone). It is shown that there is plasma in the bubble interior during the whole first bubble oscillation. A simple method is used, based on several assumptions, which allows determining an estimate of the radiated optic energy and from it the surface temperature of the bubble when the thermal radiation reaches its maximum. This temperature can be then exploited when computing a number of other quantities. An example of the energy partition in the first bubble growth phase and in the first compression and the following expansion phases is given. The estimate of the surface plasma temperature when the bubble is compressed to its first minimum volume is also given and it has been found to be approximately 5900 K in a selected experiment. It is also shown that spark generated bubbles do not behave adiabatically and that the plasma in the bubble interior represents a highly non-homogeneous medium far from an equilibrium state, for which the equation of the state of an ideal gas cannot be used.