Study of the Relationship between Boundary Slip and Nanobubbles on a Smooth Hydrophobic Surface.
Surface nanobubbles, which are nanoscopic or microscopic gaseous domains forming at the solid/liquid interface, have a strong impact on the interface by changing the two-phase contact to a three-phase contact. Therefore, they are believed to affect the boundary condition and liquid flow. However, there are still disputes in the theoretical studies as to whether the nanobubbles can increase the slip length effectively. Furthermore, there are still no direct experimental studies to support either side. Therefore, an intensive study on the effective slip length for flows over bare surfaces with nanobubbles is essential for establishing the relation between nanobubbles and slip length. Here, we study the effect of nanobubbles on the slippage experimentally and theoretically. Our experimental results reveal an increase from 8 to 512 nm in slip length by increasing the surface coverage of nanobubbles from 1.7 to 50.8% and by decreasing the contact angle of nanobubbles from 42.8 to 16.6°. This is in good agreement with theoretical results. Our results indicate that nanobubbles could always act as a lubricant and significantly increase the slip length. The surface coverage, height, and contact angle are key factors for nanobubbles to reduce wall friction.
School of Mechanical and Electrical Engineering, Harbin Institute of Technology , Harbin 150001, China.|School of Mechanical Engineering, Heilongjiang University of Science and Technology , Harbin 150022, China.
Dayong
D
Li
School of Mechanical and Electrical Engineering, Harbin Institute of Technology , Harbin 150001, China.|School of Mechanical Engineering, University of Shanghai for Science and Technology , Shanghai 200093, China.
Dalei
D
Jing
School of Mechanical and Electrical Engineering, Harbin Institute of Technology , Harbin 150001, China.
Yunlu
Y
Pan
School of Mechanical and Electrical Engineering, Harbin Institute of Technology , Harbin 150001, China.|Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics (NLB2), The Ohio State University , 201 W. 19th Avenue, Columbus, Ohio 43210-1142, United States.
Bharat
B
Bhushan
School of Mechanical and Electrical Engineering, Harbin Institute of Technology , Harbin 150001, China.
Xuezeng
X
Zhao