Investigation on cavitation enhancement on flash boiling atomization using two-dimensional slit nozzles

Flash boiling and cavitation are two important topics in internal phase changing flow and spray atomization studies. They have been proven to be effective in improving spray breakup process, and hypotheses are proposed that these two phenomena could have coupled effects to achieve even better atomization. But few quantitative studies have made direct comparisons on whether the introduction of cavitation into flash boiling will result in finer droplets. This investigation aims to address this issue with optically transparent, two-dimensional slit nozzles with varied geometries. The round corner is introduced to suppress the generation of cavitation at the inlet, and thermal boundary conditions are adjusted to trigger flash boiling. Results from high-speed backlit imaging and phase doppler interferometry unveil that the introduction of cavitation can enhance the flash boiling process throughout the increment of superheat degree, yet the enhancement efficiency is different as thermal conditions change, and is strongly correlated with internal bubble spatial distributions. A model is proposed to explain the governing factor of cavitation enhancement on flash boiling atomization.