A unique channel surface enhancement technique via diffusion-bonding a layer of
conductive fine wire mesh onto the heating wall was developed and used to
experimentally study flow boiling enhancement in parallel microchannels. Each
channel was 1000 μm wide and 510 μm high. A dielectric working fluid, HFE
7000, was used during the study. Two fine meshes as well as two mesh materials
were investigated and compared. According to the flow boiling curves for each
channel, the amount of wall superheat was greatly reduced for all the mesh
channels at four stream-wise locations; and the critical heat fluxes (CHF) for
mesh channels were significantly higher than that for a bare channel in the low
vapor quality region. According to the plots of local flow boiling heat transfer
coefficient h versus vapor quality, a consistent increasing trend for h with vapor
quality was observed for all the tested channels until the vapor quality reached
approximately 0.4. However, the three mesh channels showed much higher values
of h than the bare channel, with the 100 mesh copper performing the best.
Visualization using a high-speed camera was performed thereafter to provide
some insights to this enhancement mechanism. A significant increase in
nucleation sites and bubble generation was observed, and departure rates inside
the mesh channels were attributed to the flow boiling enhancement. A sudden
increase of h for mesh channels can also be attributed to the characteristics of
nucleate boiling and indicates that nucleate boiling was the dominant heat transfer
mode. Another interesting point observed was that the 100 mesh bronze outperformed
the 200 mesh bronze for most of the studies. This suggests that
nucleations happened inside the mesh openings, instead of on the mesh openings.
In addition, an optimal mesh size should exist for HFE 7000 flow boiling. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28962 |
| Date | 17 April 2006 |
| Creators | Wang, Hailei |
| Contributors | Peterson, Richard B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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