NDLI: Heat Transfer Mechanisms During Flow Boiling in Microchannels

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Satish, G. Kandlikar
Copyright Year	2003
Abstract	The forces due to surface tension, inertia, and momentum change during evaporation in microchannel govern the two-phase flow patterns and the heat transfer characteristics during flow boiling. These forces are analyzed in this paper, and two new non-dimensional groups, K1 and K2, relevant to flow boiling phenomenon are derived. These groups are able to represent some of the key flow boiling characteristics, including the CHF. The small hydraulic dimensions of microchannel flow passages present a large frictional pressure drop in single-phase and two-phase flows. In order to keep the pressure drop within limits, the channel lengths are generally shorter and the mass fluxes are generally lower than those with conventional channels (Dh>3 mm). The resulting lower mass fluxes, coupled with small Dh, lead to Reynolds numbers in the range 100–1000. Such low Reynolds numbers are rarely employed for flow boiling in conventional channels. In these low Reynolds number flows, nucleate boiling systematically emerges as the dominant mode of heat transfer. Aided by strong evaporation rates, the bubbles nucleating on the wall grow quickly and fill the entire channel. The contact line between the bubble base and the channel wall surface now becomes the entire perimeter at both ends of the vapor slug. Evaporation occurs at the moving contact line of the expanding vapor slug as well as over the channel wall covered with a thin liquid film surrounding the vapor core. The usual nucleate boiling heat transfer mechanisms, including liquid film evaporation and transient heat conduction in the liquid adjacent to the contact line region, play an important role. The liquid film under the large vapor slug evaporates completely at downstream locations thus presenting a dryout condition periodically with the passage of each large vapor slug. The flow boiling correlation by Kandlikar [1, 2] with (i) the nucleate boiling dominant region equation, and (ii) the laminar flow equation for single-phase all-liquid flow heat transfer coefficient hLO was successful in correlating the available R-134a data for parallel microchannels of 190 μm hydraulic diameter.
Sponsorship	Nanotechnology Institute
Starting Page	33
Ending Page	46
Page Count	14
File Format	PDF
ISBN	0791836673
DOI	10.1115/ICMM2003-1005
Volume Number	1st International Conference on Microchannels and Minichannels
Conference Proceedings	ASME 2003 1st International Conference on Microchannels and Minichannels
Language	English
Publisher Date	2003-04-24
Publisher Place	Rochester, New York, USA
Access Restriction	Subscribed
Subject Keyword	Lubrication theory Vapors Microchannel flow Transient heat transfer Critical heat flux Microchannels Bubbles Slug flows Two-phase flow Nucleate boiling Liquid films Heart failure Inertia (mechanics) Reynolds number Dimensions Momentum Evaporation Boiling Flow (dynamics) Laminar flow Pressure drop Flux (metallurgy) Surface tension Heat transfer coefficients Heat transfer
Content Type	Text
Resource Type	Article

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3	National Digital Library of India Office, Indian Institute of Technology Kharagpur	The administrative and infrastructural headquarters of the project	Mr. Siddhartha Mukherjee siddhartha@ndl.gov.in
4	Project PI / Joint PI	Principal Investigator and Joint Principal Investigators of the project	Dr. B. Sutradhar bsutra@ndl.gov.in Prof. Saswat Chakrabarti will be added soon
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