Subcooled pool boiling on nanotextured surfaces is explored in this study.
The experiments are performed in an enclosed viewing chamber. Two silicon
wafers are coated with Multiwalled Carbon Nanotubes (MWCNT), 9 microns
(Type-A) and 25 microns (Type-B) in height. A third bare silicon wafer is used for
control experiments. The test fluid is PF-5060, a fluoroinert with a boiling point of
56°C (Manufacturer: 3M Co.). The apparatus is of the constant heat flux type. Pool
boiling experiments in nucleate and film boiling regimes are reported in this study.
Experiments are carried out under low subcooling (5 °C and 10 °C) and high
subcooling conditions (20°C to ~ 38°C). At approximately 38°C, a non-departing
bubble configuration is obtained on a bare silicon wafer. Increase in subcooling is
found to enhance the critical heat flux (CHF) and the CHF is found to shift towards
higher wall superheats. Presence of MWCNT on the test surface led to an
enhancement in heat flux.
Potential factors responsible for boiling heat transfer enhancement on heater
surfaces coated with MWCNT are identified as follows: a. Enhanced surface area or nano - fin effect
b. Higher thermal conductivity of MWCNT than the substrate
c. Disruption of vapor-liquid vapor interface in film boiling, and of the
“microlayer” region in nucleate boiling
d. Enhanced transient heat transfer caused by local quasi-periodic
transient liquid-solid contacts due to presence of the “hair like”
protrusion of the MWCNT
e. Enhancement in the size of cold spots
f. Pinning of contact line, leading to enhanced surface area underneath
the bubble leading to enhanced heat transfer
Presence of MWCNT is found to enhance the phase change heat transfer by
approximately 400% in nucleate boiling for conditions of low subcooling. The heat
transfer enhancement is found to be independent of the height of MWCNT in
nucleate boiling regime in the low subcooling cases. About 75%-120%
enhancement in heat transfer is observed for surfaces coated with MWCNT under
conditions of high subcooling in the nucleate boiling regime. Surfaces coated with
Type-B MWCNT show a 75% enhancement in heat transfer in the film boiling
regime under conditions of low subcooling.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1155 |
| Date | 15 May 2009 |
| Creators | Sathyamurthi, Vijaykumar |
| Contributors | Banerjee, Debjyoti |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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