Two Streamwise Drops Impinging onto a Hydrophobic Plate

Abstract

The Investigation of the dynamic effect of the water drop on the flat plate was performed The drops were generated using the free-falling drop technique with the drop generator and the drop severance device While performing the experiment water at 25°C (room temperature) was used as the working fluid and the drop impact velocity on the hydrophobic glass plate was 2 m/s In our experiment we have specifically focused on the effect of the initial drop diameter (di) and oblique angle (?) of the hydrophobic glass surface on the impact phenomena The investigation considers six different impingement conditions differentiated by the different time intervals (△t) namely Case 1: single drop impingement; Case 2: △t =△t1 (the leading drop starts to spread); Case 3: △t =△t2 (the leading drop spreads to maximum); Case 4: △t =△t3 (the leading drop starts to retract and form peak); Case 5: △t =△t4 (the leading drop retracts to from a dome shape); Case 6: △t =△t5 (the leading drop starts to stabilize) Notably all of the cases correspond to the approximate same initial drop diameter For the case of the single drop impingement on the different roughness surfaces the surface with high roughness don’t allow the drop to retract back much and the low surface roughness makes the drop rebound-off the surface The comparison of the 50 and 60 Weber number the impact characteristics were found similar However the two-stream wise drop impacting the low roughness surface hydrophobic glass surfaces will rebound-off the surface after spreading but if the time interval between the two drop increases the air gets trapped so the drop stays on the surface even after spreading For the oblique angle hydrophobic glass surface the two-stream wise drop impacting spreads less and rebounds - off the surface and takes relative long time in comparison with the flat surface to strike back to the surface However the two streamwise drops impacting on the low roughness surface hydrophobic glass surface will rebound-off the surface after spreading for the cases of △t1 and △t2 The results of △t3 to △t5 shows the merged drop stays on the surface even after spreading

Date of Award	2018 Aug 30
Original language	English
Supervisor	Ta-Hui Lin (Supervisor)