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Research Papers: Multiphase Flows

Mitigation of Damage to Solid Surfaces From the Collapse of Cavitation Bubble Clouds

[+] Author and Article Information
Parag V. Chitnis1

Department of Aerospace and Mechanical Engineering and Department of Mechanical Engineering, Boston University, 110 Cummington Street, Boston, MA 02215pchitnis@rri-usa.org

Nicholas J. Manzi, Robin O. Cleveland, Ronald A. Roy, R. Glynn Holt

Department of Aerospace and Mechanical Engineering and Department of Mechanical Engineering, Boston University, 110 Cummington Street, Boston, MA 02215

1

Corresponding author. Also at F. L. Lizzi Center for Biomedical Engineering, Riverside Research Institute, 156 William Street, 9th Floor, New York, NY 10038.

J. Fluids Eng 132(5), 051303 (May 14, 2010) (6 pages) doi:10.1115/1.4001552 History: Received April 20, 2009; Revised March 30, 2010; Published May 14, 2010; Online May 14, 2010

The collapse of transient bubble clouds near a solid surface was investigated to test a scheme for mitigation of cavitation-induced damage. The target was a porous ceramic disk through which air could be forced. Transient cavitation bubbles were created using a shock-wave lithotripter focused on the surface of the disk. The dynamics of bubble clouds near the ceramic disks were studied for two boundary conditions: no back pressure resulting in surface free of bubbles and 10 psi (0.7 atm) of back pressure, resulting in a surface with a sparse (30% of area) bubble layer. Images of the cavitation near the surface were obtained from a high-speed camera. Additionally, a passive cavitation detector (3.5 MHz focused acoustic transducer) was aligned with the surface. Both the images and the acoustic measurements indicated that bubble clouds near a ceramic face without a bubble layer collapsed onto the boundary, subsequently leading to surface erosion. When a sparse bubble layer was introduced, bubble clouds collapsed away from the surface, thus mitigating cavitation damage. The erosion damage to the ceramic disks after 300 shock waves was quantified using micro-CT imaging. Pitting up to 1 mm deep was measured for the bubble-free surface, and the damage to the bubble surface was too small to be detected.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

A representative waveform of the SW measured at the focus of the electrohydraulic lithotripter using a fiber-optic probe hydrophone. The peak positive pressure was 32 MPa and the peak negative pressure was −12 MPa.

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Figure 2

The porous ceramic disk was mounted in a PVC housing to facilitate the gas flow through the ceramic disk

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Figure 3

The schematic of the experimental setup

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Figure 4

A sequence of high-speed camera images for a bubble cloud collapsing near a ceramic face without a bubble layer (0 psi (0 bars) back pressure). The SW is normally incident at the ceramic face and time=0 μs represents the firing of the SW.

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Figure 5

A sequence of high-speed camera images for a bubble cloud collapsing near a ceramic face with a sparse bubble layer (10 psi (0.7 bars) back pressure). The SW is normally incident at the ceramic face and time=0 μs represents the firing of the SW.

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Figure 6

Measurements of the acoustic emissions acquired using a passive cavitation detector (a focused 3.5 MHz transducer) confocal to the lithotripter: (a) no bubble layer, 0 psi (0 bar); (b) sparse bubble layer, 10 psi (0.7 bar). Both (a) and (b) depict all 300 waveforms acquired for each ceramic sample. Acoustic emissions detected between 600 μs and 1000 μs represent noise from inertial cavitation collapses within or near the sensing volume of the PCD, which is positioned confocal with the lithotripter focus.

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Figure 7

Representative X-ray tomography scans acquired after SW treatment for ceramic samples with hydrodynamically rigid and hydrodynamically compliant boundaries. The Z-coordinate is normal to the undamaged surface and projected inwards toward the ceramic. (a no bubble layer, 0 psi (0 bar)) Cavitation induced by the incident SWs resulted in significant quantifiable damage to the ceramic sample. (b sparse bubble layer, 10 psi (0.7 bar)). The ceramic sample with a sparse bubble layer did not suffer any cavitation-induced damage.

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