Study of Drag Forces on a Designed Surface in Bubbly Water Lubrication Using Electrolysis

[+] Author and Article Information
Haosheng Chen

State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084 Chinachenhs@mail.tsinghua.edu.cn

Jiang Li

Department of Mechanology, University of Science and Technology, Beijing, 100083 China

Darong Chen

State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084 China

J. Fluids Eng 128(6), 1383-1389 (May 08, 2006) (7 pages) doi:10.1115/1.2354531 History: Received November 15, 2005; Revised May 08, 2006

To study the drag reduction effect of a bubbly fluid, a pin-disk experiment is performed on the Universal Micro Tribotester system. Bubbles are generated by water electrolysis in holes that are specially designed on the disk surface. Experiment result shows that the drag force experiences a dynamic process, both drag reduction and drag increment effects appear in the process depending on the bubble behavior. This process is numerically simulated using computational fluid dynamics (CFD), and the explanations for the drag variation are given based on the analysis of drag forces on each wall of the disk surface. The drag reduction occurs when the bubble fills the hole, as the viscous drag on the air-liquid surface is small, and the pressure drag is reduced as the side wall of the hole is covered by the bubble. The drag increment is thought to be caused by the increment of the fluid viscosity when the bubble leaves the hole and flows in the fluid.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Structure of the two-layer printed circuit board

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Figure 2

Experimental system schematics

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Figure 3

Drag forces on the designed surface under difference supply voltages: (a) Friction forces at 1.0V voltage under 50g load, (b) average friction forces at 1.0V voltage under 50g load in 300s, and (c) average friction forces under 50g load in 60s

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Figure 4

Models for the bubbly lubrication in different stages

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Figure 5

Preprocessing and residuals for numerical simulation: (a) mesh and walls of model B and (b) residuals of the numerical results

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Figure 6

Numerical simulation on drag force variation process

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Figure 7

Drag forces on different walls of the surface



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