In this study, six benchmark experiments are conducted on bubbles at different growth stages to evaluate the assumptions of the existing microchannel flow boiling heat transfer models/hypothesis. The results show that the bubble ebullition process triggers a spike in the local surface heat flux due to the thin film evaporation and transient conduction heat transfer mechanisms. This enhancement in the surface heat flux is limited to a very small area at the bubble–surface contact region at the nucleation site limiting the overall heat transfer contribution of the bubble ebullition process. The contribution of these two mechanisms of heat transfer increases as the bubble–surface contact area becomes larger. As the bubbles length increases, the time period of activation of the microlayer evaporation mechanism substantially increases while that of the transient conduction mechanism remains relatively unchanged. When the microchannel is mostly occupied by bubbles, the thin film evaporation mechanism becomes the dominant heat transfer mode. The results clearly indicate that single-phase heat transfer mechanism active at surface regions not covered by bubbles is governed by the laminar flow theory (for the test conditions presented here). In essence, a measureable enhancement effect in the liquid phase due to bubbles growth and flow has not been observed. A comparison with the existing microchannel flow boiling models suggests that the three-zone flow boiling model can qualitatively describe the heat transfer events observed in this experiment but fails to accurately predict the magnitude of the heat transfer mechanisms.
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November 2017
This article was originally published in
Journal of Heat Transfer
Research-Article
Physics of the Microchannel Flow Boiling Process and Comparison With the Existing Theories
Sajjad Bigham,
Sajjad Bigham
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611
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Saeed Moghaddam
Saeed Moghaddam
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611 e-mail: saeedmog@ufl.edu
Search for other works by this author on:
Sajjad Bigham
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611
Saeed Moghaddam
Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611 e-mail: saeedmog@ufl.edu
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 21, 2016; final manuscript received February 23, 2017; published online June 21, 2017. Assoc. Editor: Peter Stephan.
J. Heat Transfer. Nov 2017, 139(11): 111503 (10 pages)
Published Online: June 21, 2017
Article history
Received:
September 21, 2016
Revised:
February 23, 2017
Citation
Bigham, S., and Moghaddam, S. (June 21, 2017). "Physics of the Microchannel Flow Boiling Process and Comparison With the Existing Theories." ASME. J. Heat Transfer. November 2017; 139(11): 111503. https://doi.org/10.1115/1.4036655
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