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International Heat Transfer Conference 11

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

FORCED-CONVECTION AND BOILING CHARACTERISTICS IN MICROCHANNELS

Xiao-Feng Peng
Laboratory of Phase Change and Interfacial Transport Phenomena, Department of Thermal Engineering, Tsinghua University, Beijing 100084

Bu-Xuan Wang
Laboratory of Phase Change and Interfacial Transport Phenomena, Department of Thermal Engineering, Tsinghua University, Beijing 100084, China

DOI: 10.1615/IHTC11.2820
pages 371-390

Abstract

A sequence of experiments was conducted to investigate the fluid flow and heat transfer characteristics in microchannels with/without phase-change in last few years. More attentions have been paid to understand the flow boiling heat transfer performance and phase-change transition mechanism in micochannels. In these experiments, the single-phase and flow boiling heat transfer of pure water, pure methanol and watermethanol binary mixtures flowing through eight rectangular and six triangular microchannels were observaed and measured. The microchannel size, geometrical configuration, and mole fraction of water-methanol binary mixtures were experimentally found to have critically significant impact on single-phase forced-eonvection, on flow boiling, especially nucleate boiling, and on bubble formation and growth in microchannels. A physical model accounting for the effect of channel size was proposed to theoretically analyzed the single-phase gas flow and heat transfer through microtubes. For flow boiling and nucleation in microchannels, two new concepts "evaporating space" and "fictitious boiling" were proposed to explain the unusual phase-ehange transport phenomena. A dimensionless number and related criterion, for determining the phase transition in microchannels, were derived theoretically. The dynamical analyses of the system indicated that nucleate boiling in microchannels is almost impossible, and the nature of this transport phenomenon is found to be thermodynamic nonequilibrium.

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