1 Copyright © 2012 by ASME
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Nucleate pool boiling heat transfer has been
experimentally studied at ambient temperature, on a surface
with a novel nanofiber mat coating. The nano-textured surface
was made of alumina ceramic substrate covered by an
electrospun polymer nanofiber mat with a thickness of about 30
µm and immersed in saturated HCFC-123. The surfaces of the
individual polymer nanofibers in the mat were copper-plated.
Significant enhancements in nucleate boiling heat transfer as
well as reduction of surface temperature have been achieved for
the copper nanofiber-coated surface compared to a bare surface.
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As a very effective heat transfer mechanism [1] that can
provide a large heat transfer rate, the nucleate boiling of a pool
of liquid has been a subject of intensive research for several
decades. However, it should be kept in mind that pool boiling
on a plain surface still cannot supply high enough heat transfer
coefficient for many applications such as high-heat-flux
microelectronics and optoelectronics which are highly sensitive
to temperature increases and need to be further miniaturized.
The nucleate boiling heat transfer coefficient is an indicator of
the heat removal rate. The higher it is, the smaller temperature
difference between liquid saturation temperature and surface
temperature in boiling fluid will be, at a given heat flux.
Therefore, increasing the nucleate boiling heat transfer
coefficient in two-phase cooling systems is an appropriate
method to improve performance of high-heat-flux devices [2].
In recent years, efforts have been made to find an effective
means of enhancing nucleate pool boiling heat transfer
coefficient. One method of great interest is to increase the
number of small scale cavities on a surface and surface
roughness since it has been shown that modifying the surface
characteristics substantially affects performance enhancement
of nucleate pool boiling heat transfer. In order to create
appropriate surface structures, various techniques have been
proposed such as porous coatings and mechanical surface
machining. In principle, all of these surface treatment
techniques create microscopic geometries on surfaces which
serve to increase vapor/gas entrapment volume, surface
roughness and active nucleation site density during pool
boiling. It is believed that these increases combine to reduce the
incipient and nucleate boiling wall superheats, as well as
increase the nucleate boiling heat transfer coefficient [3,4].
Most previous techniques used for surface structure
modification are related to micro-sized dimension. However,
recent advances in nano-technology have allowed the
development of nano-textured surfaces with conspicuous
structures [3] and much research has been done to investigate
the pool-boiling enhancement due to these surfaces. many have
found favorable boiling heat transfer augmentation results and
demonstrated that the nano-textured surface lead to the increase
of some important boiling parameters such as nucleation site
density, bubble diameter and bubble departure frequency and
therefore result in a significant increase of pool boiling heat
transfer coefficient.
A brief review of select work done is this area is given in
the paragraphs that follow and in Table 1. Forrest et al. [3] have
demonstrated significant enhancement in the pool boiling
critical heat flux and nucleate heat transfer coefficient by
applying nanoparticle thin-film coatings to heater surface using
a layer-by-layer assembly method. Vemuri and Kim [4] carried
out an experimental study on the nucleate pool boiling heat
transfer of nano-porous surface made of aluminum-oxide with
thickness of 70 nm in saturated FC-72 dielectric fluid. From the
experimental data obtained, they found that the incipient wall
superheat for applied power for a nano-porous surface was
Proceedings of the ASME 2012 Summer Heat Transfer Conference
HT2012
July 8-12, 2012, Rio Grande, Puerto Rico
HT2012-58107
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