Vaporization and bubble growth dynamics of explosively boiling droplets at the superheat limit*

The explosive boiling of droplets of diethyl ether (0.5-4.0 mm in diameter) at the superheat limit was examined experimentally. Droplet explosion was studied using a heated host fluid column to bring test droplets to the superheat limit. The droplet fluid was diethyl ether (superheat limit 147 C at 1 bar) with glycerol employed as the host fluid. Imaging of the interfacial behavior during explosive boiling was performed using a high-speed camera at a frame rate of 100,000 frames per second.  Tests were carried out at pressures between 1-5 bar absolute.  At 1-2 bar the relatively rough vapor-liquid interface inside the droplet suggests unstable boiling.  Stable boiling was encountered between 4-5 bar; at 3 bar a transition from stable to unstable boiling was sometimes observed.  The speed of the vaporization front within the droplet rises rapidly after nucleation before decaying.  The mean wavelength at the vapor-host liquid interface appears in all cases to show a modest variation with each subsequent vapor bubble oscillation.  Direct Numerical Simulations were performed at Southern Illinois University Carbondale to compliment the experiments.