Characteristics and correlation of nozzle internal flow and jet breakup under flash boiling conditions

摘要

Flash boiling sprays utilize superheated fluid to enhance spray breakup via eruption of flash boiling bubbles near the nozzle exit. Extensive efforts have been made to interpret the underlying complex phase change physics associated with flash boiling sprays. However, the dynamic interaction between the gas phase and liquid phase of the flash boiling sprays has not been adequately investigated yet. This work adopts a two-dimensional optical transparent nozzle to study in-nozzle multiphase flow characteristics as well as spray characteristics outside of the nozzle. Both high-speed and low-speed measurements were carried out using optical diagnostic methods, and flash boiling sprays at different superheat levels were studied. With the experiments, the correlation between the internal flow and spray liquid jet breakup is established and the impact of the gas-liquid correlation on the properties of flash boiling sprays is presented. Furthermore, dynamic interaction between the gas phase and liquid phase in the nozzle and out of the nozzle is analyzed with a center of mass scheme. It is found that the dynamic features of the flash boiling sprays are closely connected with the dynamics of the in-nozzle flow. Such observation suggests that modifying flash boiling bubble characteristics can potentially be utilized to actively control flash boiling sprays for improved spray performance.