An Experimental Study On The Breakup Of Power-law Liquid Sheets Formed By Two Impinging Jets

The breakup and atomization of liquid jets are very important in theory and havebeen widely used in engineering. The impinging jets device has been widely appliedto many fields including engines and reactors for various chemical engineeringprocesses owe to its advantages such as low cost, simple structure, excellentatomization and mixing behaviors. As a kind of widely existed fluid, non-Newtonianfluid in which the relation between shear stress and shear strain is not linear is notsatisfactorily recognized in the research of theoretical and experimental understandingof the breakup of liquid jets due to its complexity and variety. Although someresearches on the breakup characteristics of power-law liquid sheets can be found,they are limited to round jets. Few researchers shed light on the expansion angle ofpower-law liquid sheets at different spray parameters, physical parameters andgeometry parameters. The objective of this study is to characterize the developmentand breakup processes of power-law liquid sheets formed by impinging jets.An experimental system which is comprised of four sub-systems which areliquid feeding system, jet impinging system, data acquiring system, and pulsecontrolling system is built to characterize the development and breakup processes ofpower-law liquid sheets formed by impinging jets. High quality spray images arecaptured with a high speed camera from the experiment. The breakup and atomizationcharacteristics of power-law liquid sheets, including breakup mode, breakup lengthand expansion angle are defined and studied.Five different breakup modes are observed with the increase of Weber number.The breakup length first increases at closed-rim mode and then decreases after sheetbreakup with the increase of Weber number while the expansion angle is consistentlyincreasing. Rectangle jets intensify the development of liquid sheets and hence a moreunstable sheet compared with round jets. The transition velocity between twoneighboring breakup modes for square jets is lower that for round jets and that for rectangle jets is the lowest. Moreover, the liquid sheets formed by two rectangle jetshave a greater expansion angle than those of round jets while that of square jets is inthe middle. Impinging angle plays a role in aggravating the disturbance of liquidsheets in all modes so as to decrease the breakup length while to increase theexpansion angle; a larger impinging angle advances the appearance of all modes. Theviscosity of fluid also has important impact on the breakup characteristic. The sheet ofthe fluid with higher viscosity has a greater sheet length, a smaller expansion angleand a greater transition velocity from moderate breakup modes to turbulent breakupmodes.