Breakup Mechanisms, Fluid Velocity and Dimension Characteristics in Impinging Liquid Jets

1. Breakup Mechanisms, Fluid Velocity and Dimension Characteristics in Impinging Liquid Jets Sunny Ri Li, Nasser Ashgriz Department of Mechanical and Industrial Engineering University of Toronto

2. Introduction When two cylindrical jets of equal diameters collide they form an expanding sheet in the plane at a right angle to the plane containing the axes of the two jets. Multiphase Flows and Spray Systems Laboratory

3. Experimental Method and Apparatus Multiphase Flows and Spray Systems Laboratory

4. Breakup Regimes Pre-sheet formation Regime I: Capillary Instability (Closed-rim sheet) Smooth sheet Ruffled sheet Open-rim sheet Regime II: Kelvin-Helmholtz instability Turbulent sheet Regime III: Impact-wave 1. High-frequency circumferential waves 2. Very high Reynolds number 3. High impinging angle Multiphase Flows and Spray Systems Laboratory

5. Breakup Regimes - Critical Single-Jet & Impingement Reynolds Numbers Multiphase Flows and Spray Systems Laboratory

6. Breakup Regimes - Critical Sheet Reynolds Numbers 90 deg. 120 deg. Impinging angle: 60 deg. …..Thickness of the impact region ….Edge thickness of the sheet Multiphase Flows and Spray Systems Laboratory

7. Surface Velocity - Experimental Method • The surface velocity, which is defined here as the stream velocity on the sheet, was determined by measuring the wave motion on the surface. • Measurement was made on two angular positions on the sheet: 0 and 25 degree. Multiphase Flows and Spray Systems Laboratory

8. Surface Velocity -Distribution of Surface velocity (Impinging angle 90 deg.) Multiphase Flows and Spray Systems Laboratory

9. Dimensional Characteristics - Equations The following equations are based on the work of Taylor [1959] and Ibrahim [1991], which assumed the fluid velocity throughout the sheet is equal to the mean jet velocity. ….Maximum length ….Maximum width Where β can be obtained by solving Multiphase Flows and Spray Systems Laboratory

10. Dimensional Characteristics - Total Length Multiphase Flows and Spray Systems Laboratory

11. Dimensional Characteristics - Maximum Width Multiphase Flows and Spray Systems Laboratory

12. Dimensional Characteristics - Review of Early Theory Taylor [1959] assuming the fluid velocity on the sheet equal to jet velocity To retain its validity for non-uniform fluid velocity on the sheet, : Fluid velocity on the sheet : Edge thickness of the sheet with non-uniform velocity distribution : Edge thickness of the sheet with uniform velocity distribution When , When , Multiphase Flows and Spray Systems Laboratory

13. Dimensional Characteristics – Edge Thickness 0.837 mm 0.084 mm Ibrahim [1991]: 1) The edge thickness of the sheet thickness cannot be predicted by assuming uniform velocity on the sheet. 2) The real edge thickness is has higher order of magnitude than the ideal thickness. 3) eliminates the drawback, hereby making the subsequently derived equations still valid. Multiphase Flows and Spray Systems Laboratory

14. Conclusions • Three major breakup regimes of the liquid sheet were identified in this work, namely capillary instability regime, Kelvin-Helmholtz instability regime and impact wave regime. • The distribution of fluid velocity on the sheet was examined and found not uniform throughout the sheet. • The dimensional characteristics of the spray sheet were investigated by reviewing early theories. It was found that the theories can predict the shape of the sheet but not the sheet thickness. Multiphase Flows and Spray Systems Laboratory