Structure and breakup properties of sprays

Abstract

Multiphase flow phenomena relevant to spray combustion are reviewed, emphasizing the structure of the near-injector dense-spray region and the properties of secondary and primary breakup. Existing measurements of dense-spray structure are limited to round pressure-atomized sprays in still gases and show that the dispersed flow region is surprisingly dilute, that separated flow effects are significant because the flow is dilute and developing, and that atomization involves primary breakup at the liquid surface followed by secondary breakup, while effects of collisions are small. Available information about secondary breakup emphasizes breakup due to shock wave disturbances at large liquid/gas density ratios and shows that secondary breakup is a dominant feature of dense sprays that must be resolved as a function of time so that secondary breakup can be properly treated as a rate process. Finally, available information about primary breakup has been dominated by effects of disturbances in the injector passage; therefore, while some understanding of turbulent primary breakup has been achieved, more information about aerodynamic primary breakup is needed to address practical spray combustion processes.