Full metadata
Title
A theoretical analysis of microchannel flow boiling enhancement via cross-sectional expansion
Description
Microchannel heat sinks can possess heat transfer characteristics unavailable in conventional heat exchangers; such sinks offer compact solutions to otherwise intractable thermal management problems, notably in small-scale electronics cooling. Flow boiling in microchannels allows a very high heat transfer rate, but is bounded by the critical heat flux (CHF). This thesis presents a theoretical-numerical study of a method to improve the heat rejection capability of a microchannel heat sink via expansion of the channel cross-section along the flow direction. The thermodynamic quality of the refrigerant increases during flow boiling, decreasing the density of the bulk coolant as it flows. This may effect pressure fluctuations in the channels, leading to nonuniform heat transfer and local dryout in regions exceeding CHF. This undesirable phenomenon is counteracted by permitting the cross-section of the microchannel to increase along the direction of flow, allowing more volume for the vapor. Governing equations are derived from a control-volume analysis of a single heated rectangular microchannel; the cross-section is allowed to expand in width and height. The resulting differential equations are solved numerically for a variety of channel expansion profiles and numbers of channels. The refrigerant is R-134a and channel parameters are based on a physical test bed in a related experiment. Significant improvement in CHF is possible with moderate area expansion. Minimal additional manufacturing costs could yield major gains in the utility of microchannel heat sinks. An optimum expansion rate occurred in certain cases, and alterations in the channel width are, in general, more effective at improving CHF than alterations in the channel height. Modest expansion in height enables small width expansions to be very effective.
Date Created
2011
Contributors
- Miner, Mark (Author)
- Phelan, Patrick E (Thesis advisor)
- Herrmann, Marcus (Committee member)
- Chen, Kangping (Committee member)
- Arizona State University (Publisher)
Topical Subject
- Mechanical Engineering
- critical heat flux
- cross-section
- divergent channel
- flow boiling
- Heat Transfer
- microchannel
- Heat flux--Mathematical models.
- Heat flux
- Water--Boiling--Mathematical models.
- Water
- Heat sinks (Electronics)--Mathematical models.
- Heat sinks (Electronics)
- Heat--Transmission--Mathematical models.
Resource Type
Extent
ix, 54 p. : ill. (some col.)
Language
Copyright Statement
In Copyright
Primary Member of
Peer-reviewed
No
Open Access
No
Handle
https://hdl.handle.net/2286/R.I.9081
Statement of Responsibility
by Mark Miner
Description Source
Viewed on Jul. 5, 2012
Level of coding
full
Note
Partial requirement for: M.S., Arizona State University, 2011
Note type
thesis
Includes bibliographical references (p. 50-54)
Note type
bibliography
Field of study: Mechanical engineering
System Created
- 2011-08-12 03:57:53
System Modified
- 2021-08-30 01:53:49
- 2 years 7 months ago
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