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International Heat Transfer Conference 15

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

Enhanced Flow Boiling Heat Transfer in Microchannels with Structured Surfaces

DOI: 10.1615/IHTC15.nms.009508
pages 5695-5704

Yangying Zhu
Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA

Dion S. Antao
Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA; Massachusetts Institute of Technology, Cambridge, MA 02139, USA

Kuang-Han Chu
Department of Mechanical Engineering, Massachusetts Institute of Technology

Terry J. Hendricks
Department of Mechanical Engineering, Massachusetts Institute of Technology

Evelyn N. Wang
Device Research Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02149, USA


KEY WORDS: Two-phase/Multiphase flow, NEMS/MEMS, Thermal management

Abstract

High performance electronic devices are motivating the need for advanced thermal management strategies. Two-phase microchannel heat sinks are attractive because they utilize the latent heat of vaporization to dissipate high heat fluxes in a compact form factor. This paper reports fundamental studies of two-phase heat transfer in microchannels to investigate the effect of microscale surface structures on flow boiling. We fabricated and characterized 500 ?m × 500 ?m × 10 mm microchannels with micropillar arrays (heights of ~25 ?m, diameters of 5-10 ?m and pitches of 10-40 ?m) on the bottom channel wall, where heat was applied. We investigated the effects of the geometry of the micropillar arrays on the heat transfer performance with degassed, de-ionized water as the working fluid. The flow patterns were simultaneously visualized, which indicated that nucleation occurred primarily on the side walls. Small fluctuations in the measured heater surface temperature (± 3-8 °C) indicated increased flow stability. The maximum heat flux observed was 1470 W/cm2 with a mass flux of 1849 kg/m2·s and a heater temperature rise of 45 °C. When compared to the structured surfaces, higher fluctuations in both pressure and heater temperature were observed for a flat surface microchannel at lower heat fluxes. While the overall maximum heat flux values were comparable, the heat transfer coefficient for the structured surface microchannel was 37% higher. Our observations suggest that with these microchannel designs, two-phase heat transfer and fluid flow behavior can be decoupled. Bubbles are generated via the less hydrophilic sidewalls while the superhydrophilic microstructures at the bottom of the channel enhance the capillary wicking capability to prevent dry out. This approach can potentially increase the critical heat flux and is a first step towards understanding the role of microstructured surfaces in microchannels for high performance two-phase microchannel heat sinks.

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