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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Enhancing FC-72 Flow Boiling Heat Transfer Through Bubble Pumping from Imbalance Shear Flow Driven Rotating Beads

Shu-Lei Wang
National Chiao Tung University

Tsing Fa Lin
Department of Mechanical Engineering, National Chiao Tung University

DOI: 10.1615/IHTC15.fbl.008821
pages 2571-2582


KEY WORDS: Boiling and evaporation, Heat transfer enhancement, Electronic equipment cooling, Active method, Rotating beads, FC-72 flow

Abstract

In the present study a novel active-like passive method is proposed to enhance saturated FC-72 flow boiling heat transfer over a small heated plate through bubble pumping away from the boiling surface induced by imbalance shear flow driven rotating beads. Specifically, small plastic beads like rings are threaded by fine copper wires. The chosen beads have average outer and inner diameters of 1.45 and 0.65 mm, respectively, and thickness of 1.0 mm. The average weight of a bead is 0.0038 g. Straight parallel strings of the beads at selected pitch and height are placed above the plate normal to the upstream flow with their ends fixed at the rigs installed near the plate edges. The effects of the relevant parameters on the boiling heat transfer enhancement, including the imposed heat flux, string pitch, number of beads on each wire, and bead-plate separation distance are examined in detail. The experimental results indicate that the bubble pumping from the rotating beads can effectively enhance the boiling heat transfer in the flow. Besides, the enhancement in the boiling heat transfer is more pronounced when the beads are placed closer to the plate at the medium string pitch. Moreover, there exists an optimal number of beads threaded on each wire. The best enhancement in the boiling heat transfer coefficient in this study can be as high as 55 % for HB = 0, NS = 4 and NB = 5. Moreover, the rotating beads can substantially reduce the wall superheat for incipient boiling.

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