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Sliding Bubble-Pumped Motion Induced by Surface Micro-Structure in Pool Boiling of a Dielectric Fluid Under Reduced Gravity

[+] Author Affiliations
Naveenan Thiagarajan

GE Global Research, Niskayuna, NY

Sushil H. Bhavnani

Auburn University, Auburn, AL

Vinod Narayanan

Oregon State University, Corvallis, OR

Paper No. IMECE2014-37714, pp. V08BT10A063; 10 pages
doi:10.1115/IMECE2014-37714
From:
  • ASME 2014 International Mechanical Engineering Congress and Exposition
  • Volume 8B: Heat Transfer and Thermal Engineering
  • Montreal, Quebec, Canada, November 14–20, 2014
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-4956-9
  • Copyright © 2014 by ASME

abstract

This paper reports bubble dynamics observed during pool boiling over micro-structures with an asymmetric saw-tooth cross-section, under reduced gravity. The periodic saw-toothed ratchets etched on a silicon surface include fabricated vapor bubble nucleation sites only on the shallow slope. Reduced gravity pool boiling experiments were conducted aboard a Boeing 727 aircraft (Zero-g Inc.) carrying out parabolic maneuvers to achieve reduced gravity. The fluid used was FC-72, a highly wetting dielectric fluid used as a coolant for electronics. Under microgravity, it was observed that the bubble diameters were six times larger than in terrestrial gravity. Also, self-propelled sliding bubble motion along the surface of the saw teeth was observed in reduced gravity. The velocity of the sliding bubbles across the saw teeth, following lateral departure from the cavities, was measured to be as high as 27.4 mm/s. A model for the sliding bubble motion is proposed by attributing it to the force due to pressure differences that arise in the liquid film between the vapor bubble and the saw-toothed heated surface. The pressure difference is due to difference in the radius of curvature of the interface between the crest and trough of the saw teeth. The surface modification technique has the potential to alleviate dry out caused due to vapor blanketing of heat sources in microgravity due to negligible buoyancy forces compared to the surface tension forces.

Copyright © 2014 by ASME

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