U.S. patent application number 14/268757 was filed with the patent office on 2015-02-19 for functional coatings enhancing condenser performance.
This patent application is currently assigned to The Board of Regents of the Nevada System of Higher Education on behalf of the University of Ne. The applicant listed for this patent is The Board of Regents of the Nevada System of Higher Education on behalf of the University of Ne. Invention is credited to Kwang J. Kim, Hyungkee Yoon, Bong June Zhang.
Application Number | 20150048526 14/268757 |
Document ID | / |
Family ID | 51843992 |
Filed Date | 2015-02-19 |
United States Patent
Application |
20150048526 |
Kind Code |
A1 |
Kim; Kwang J. ; et
al. |
February 19, 2015 |
FUNCTIONAL COATINGS ENHANCING CONDENSER PERFORMANCE
Abstract
Coatings for enhancing performance of materials surfaces,
methods of producing the coating and coated substrates, and coated
condensers are disclosed herein. More particularly, exemplary
embodiments provide chemical coating materials useful for coating
condenser components.
Inventors: |
Kim; Kwang J.; (Henderson,
NV) ; Zhang; Bong June; (Henderson, NV) ;
Yoon; Hyungkee; (Jejusi, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Board of Regents of the Nevada System of Higher Education on
behalf of the University of Ne |
Las Vegas |
NV |
US |
|
|
Assignee: |
The Board of Regents of the Nevada
System of Higher Education on behalf of the University of
Ne
Las Vegas
NV
|
Family ID: |
51843992 |
Appl. No.: |
14/268757 |
Filed: |
May 2, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61818631 |
May 2, 2013 |
|
|
|
Current U.S.
Class: |
261/75 ; 427/405;
427/435; 427/436 |
Current CPC
Class: |
B05D 1/185 20130101;
F28F 13/04 20130101; B05D 7/222 20130101; F28F 2245/04 20130101;
B05D 3/12 20130101; F28F 21/085 20130101; F28F 13/182 20130101;
B05D 1/18 20130101; B05D 5/00 20130101; F28F 13/187 20130101; F28F
21/089 20130101; B05D 7/146 20130101; B05D 3/102 20130101; F28F
13/185 20130101; B05D 7/22 20130101; B01D 5/0003 20130101 |
Class at
Publication: |
261/75 ; 427/405;
427/435; 427/436 |
International
Class: |
B01D 5/00 20060101
B01D005/00; B05D 1/18 20060101 B05D001/18 |
Claims
1. A condenser system, comprising at least one vapor condensing
surface having metal, metalloid, metal alloy organic or polymeric
particles distributed across the surface of the vapor-condensing
surface, wherein the particles have an average diameter of 50 nm to
5 .mu.m.
2. The condenser system of claim 1, wherein the particles provide a
contact angle on the vapor-condensing surface of between 90 and 110
degrees with deionized water at a temperature of 70-90.degree.
C.
3. The condenser system of claim 1, wherein the particles are
silver particles.
4. The condenser system of claim 2, wherein the contact angle is
between 100 and 110 degrees.
5. The condenser system of claim 1, wherein the particles are
polymer based particles.
6. The condenser system of claim 8, wherein the polymer based
particles are fluorinated polymers, olefinic polymers, sulfonated
hydrocarbon polymers, phosphonated hydrocarbon polymers, or
silicone polymers.
7. The condenser system of claim 8, wherein the polymer based
particles are polytetrafluorethylene.
8. The condenser system of claim 8, wherein the polymer based
particles are poly (phenylene-sulfide).
9. The condenser system of claim 1, wherein the surface is
copper.
10. The condenser system of claim 1, wherein the particles are a
single layered molecular coating.
11. A method of forming a condenser system comprising depositing
particles on a vapor-condensing surface, wherein the particles are
selected from the group consisting of metals, metalloids, alloys
thereof, and polymers, and wherein the particles are in a layer of
about 1 .mu.m or less.
12. The condenser system of claim 1, wherein the surface has a
surface energy of less than about 40 mJ/m.sup.2.
13. The condenser system of claim 17, wherein the surface has a
total surface energy of less than about 30 mJ/m.sup.2.
14. The condenser system of claim 17, wherein the total surface
energy is calculated by the formula
.gamma.=.gamma..sup.h+.gamma..sup.d. where .gamma..sup.h is a
surface energy component due to a hydrogen bonding and
dipole-dipole interactions and .gamma..sup.d is a dispersion
component of surface energy.
15. A substrate comprising at least one surface coated with silver
particles and a self-assembly monolayer of a polymer.
16. A method comprising contacting a metal substrate with a silver
solution and subsequently applying a polymer self-assembly
monolayer.
17. The substrate of claim 21 or method of claim 22, wherein the
substrate is copper or a copper alloy.
18. The substrate of claim 21 or method of claim 22, wherein the
polymer is a hydrocarbon or fluorocarbon.
19. The substrate of claim 21 or method of claim 22, wherein the
polymer is 1-dodecanethiol.
20. The method of claim 22, wherein the silver solution is silver
nitrate.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/818,631, filed May 2, 2013, the
contents of which is incorporated herein by reference.
FIELD
[0002] The present invention disclosure relates to the field of
coatings for enhancing performance of materials surfaces. More
particularly, exemplary embodiments provide chemical coating
materials useful for coating condenser components.
BACKGROUND
[0003] The effect of surfaces on changes of state in materials,
including condensation, boiling, freezing and thawing have long
been appreciated and investigated in the art. With the advent of
microtechnology and nanotechnology, even smaller scale implications
of surface structure, composition, porosity and texture have been
evaluated and determined.
SUMMARY
[0004] Heat-transfer surfaces are provided with metal or
polymer-based porous coatings to alter condensation and heat
transfer properties on, from and to those surfaces. The
polymers-based particles may have number average diameters of
between 50 nm and 5 microns and may further contain additives to
further modify the physical properties of the polymer-based
particles or to alter chemical properties to resist deterioration
of the particles during use. The surfaces of the metal particles
may be in the form of oxides or may be coated in a manner to
minimize reduction in thermal transfer properties. Better tailoring
of hydroscopic or hygroscopic surface properties of the particles
is enabled.
[0005] In exemplary embodiments, a condenser system is provided
comprising at least one vapor condensing surface having metal or
polymer-based particles distributed across the surface of the
vapor-condensing surface to form a porous coating on the
vapor-condensing surface. The particles preferably have an average
size distribution within a range of +100, +50% or +20% within an
average size range of 50 nm to 5 .mu.m, or within 100 nm to 3
.mu.m. The particles may provide a static water contact angle
(SWCA) on the vapor-condensing surface of between 90 to 160 degrees
or 100 and 160 degrees with deionized water at a temperature of
70-90.degree. C.
BRIEF DESCRIPTION OF THE FIGURES
[0006] FIG. 1(a) is a schematic view of an image of a film-wise
condensate mode.
[0007] FIG. 1(b) shows a schematic view of an image of a drop-wise
condensate.
[0008] FIG. 2 is a schematic view of a condensation heat transfer
experimental setup.
[0009] FIG. 2A is a schematic view of a detail of a condenser of
FIG. 2.
[0010] FIG. 3A is a SEM image of silver self-assembly on the
primary surface-treated copper in a silver nitrate solution
concentration of 1 mM.
[0011] FIG. 3B is a SEM image of silver self-assembly on the
primary surface-treated copper in a silver nitrate solution
concentration of 10 mM.
[0012] FIG. 3C is a SEM image of silver self-assembly on the
primary surface-treated copper in a silver nitrate solution
concentration of 100 mM.
[0013] FIG. 3D is a SEM image of silver self-assembly on the
primary surface-treated copper in a silver nitrate solution
concentration of 100 mM for 20 sec.
[0014] FIG. 3E is a higher magnification SEM image of silver
self-assembly on the primary surface-treated copper of FIG. 3A.
[0015] FIG. 3F is a high magnification SEM image of silver
self-assembly on the primary surface-treated copper of FIG. 3D.
[0016] FIG. 4 is a graph showing EDX element mapping of K.alpha.
and L.alpha. peaks of fluorine, sulfur, copper, and silver at 0.525
and 2.984 keV, respectively. The approximate atomic ratio is
Ag:O=1:1.
[0017] FIG. 5A is a photograph of static water contact angle
("SWCA") measurement of SANP on copper tubes (prior to
dodecanethiol coating) of a 1 mM Ag solution (SWCA=93.degree.)
[0018] FIG. 5B is a photograph of SWCA measurement of SANP on
copper tubes (prior to dodecanethiol coating) of 10 mM Ag solution
(SWCA=63.degree.).
[0019] FIG. 5C is a photograph of SWCA measurement of SANP on
copper tubes (prior to dodecanethiol coating) of 100 mM Ag solution
(SWCA=53.degree.).
[0020] FIG. 5D is a photograph of SWCA measurement of SANP on
copper tubes (prior to dodecanethiol coating) of (d) 100 mM Ag
solution (SWCA=31.degree.).
[0021] FIG. 6A is a photograph of SWCA measurement of dodecanethiol
(1 w/w) SAM-coated SANP on copper tubes of 1 mM Ag solution (water
contact angle ("WCA")=101.degree.).
[0022] FIG. 6B is a photograph of SWCA measurement of dodecanethiol
(1 w/w) SAM-coated SANP on copper tubes of 10 mM Ag solution
(WCA=101.degree.).
[0023] FIG. 6C is a photograph of SWCA measurement of dodecanethiol
(1 w/w) SAM-coated SANP on copper tubes of 100 mM Ag solution
(WCA=100.degree.).
[0024] FIG. 6D is a photograph of SWCA measurement of dodecanethiol
(1 w/w) SAM-coated SANP on copper tubes of 100 mM Ag solution
(WCA=120.degree.).
[0025] FIG. 7A is a photograph of an AWCA measurement with a plain
surface-water liquid.
[0026] FIG. 7B is a photograph of an AWCA measurement with a plain
surface-CH.sub.2I.sub.2 liquid.
[0027] FIG. 7C is a photograph of an AWCA measurement with a
SAM-coated surface-water liquid.
[0028] FIG. 7D is a photograph of an AWCA measurement with a
SAM-coated-CH.sub.2I.sub.2 liquid.
[0029] FIG. 7E is a photograph of an AWCA measurement with a
SANP-coated surface-water liquid.
[0030] FIG. 7F is a photograph of an AWCA measurement with a
SANP-coated surface-CH.sub.2I.sub.2 liquid.
[0031] FIG. 8A is a graph showing results for external condensation
test results of q'' vs. T.sub.sub.
[0032] FIG. 8B is a graph showing results for external condensation
test results of h vs. T.sub.sub.
[0033] FIG. 9A is a photograph from a video-recording of a
condensation experiment using a plain surface-FWC tube Scale bar
represents 1 cm.
[0034] FIG. 9B is a photograph from a video-recording of a
condensation experiment using a SAM-coated surface-mixed DWC and
FWC tube. Scale bar represents 1 cm.
[0035] FIG. 9C is a photograph from a video-recording of a
condensation experiment using a SANP-deposited surface-DWC tube.
Scale bar represents 1 cm.
[0036] FIG. 10A is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=2.06 (t=33 ms).
[0037] FIG. 10B is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=4.13 (t=66 ms).
[0038] FIG. 10C is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=29.13 (t=466 ms).
[0039] FIG. 10D is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=35.38 (t=566 ms).
[0040] FIG. 11A is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=2.06 (t=33 ms).
[0041] FIG. 11B is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=47.9 (t=766 ms).
[0042] FIG. 11C is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=54.1 (t=866 ms).
[0043] FIG. 11D is a photograph frame from a video of DWC of the
SAM copper oxide at T.sub.sub.about.5.2, with a condensate diameter
of 3.3 mm and height (mm) of t*=56.2 (t=900 ms).
[0044] FIG. 12A is a graphic representation of long term
performance of the SANP tubes during 500 hour test runs of q'' vs
T.sub.sub.
[0045] FIG. 12B is a graph of long term performance of the SANP
tubes during 500 hour test runs of h vs T.sub.sub.
[0046] FIG. 13A is schematic illustration of a spatial condensate
(contour) distribution at one time frame of a silver-coated
surface. In order to estimate the diameter, the condensate contour
was obtained from a video recorded image. The condensate perimeter
was then estimated by ImageJ analysis with a still frame taken at
4.2 seconds.
[0047] FIG. 13B is a schematic illustration of the corresponding
condensate population of FIG. 13A at one time frame of a
silver-coated surface. In order to estimate the diameter, the
condensate contour was obtained from video recorded images. The
condensate perimeter was then estimated by ImageJ analysis with a
still frame taken at 4.2 seconds.
[0048] FIG. 13C is a schematic illustration of the spatial
condensate (contour) distribution at a second time frame of a
silver-coated surface. In order to estimate the diameter, the
condensate contour was obtained from a video recorded image. The
condensate perimeter was then estimated by ImageJ analysis with a
still frame taken at 4.9 seconds.
[0049] FIG. 13D is a schematic illustration of the corresponding
condensate population of FIG. 13C at one time frame of a
silver-coated surface. In order to estimate the diameter, the
condensate contour was obtained from video recorded images. The
condensate perimeter was then estimated by ImageJ analysis with a
still frame taken at 4.9 second seconds.
[0050] FIG. 13E is a graph of the spatial condensate (contour)
distribution at a third time frame of a silver-coated surface. In
order to estimate the diameter, the condensate contour was obtained
from a video recorded image. The condensate perimeter was then
estimated by ImageJ analysis with a still frame taken at 5.3
seconds.
[0051] FIG. 13F is a graph of the corresponding condensate
population of FIG. 13E at one time frame of a silver-coated
surface. In order to estimate the diameter, the condensate contour
was obtained from video recorded images. The condensate perimeter
was then estimated by ImageJ analysis with a still frame taken at
5.3 seconds.
[0052] FIG. 13G is a graph of the spatial condensate (contour)
distribution at a fourth time frame of a silver-coated surface. In
order to estimate the diameter, the condensate contour was obtained
from a video recorded image. The condensate perimeter was then
estimated by ImageJ analysis with a still frame taken at 5.8
seconds.
[0053] FIG. 13H is a graph of the corresponding condensate
population of FIG. 13G at one time frame of a silver-coated
surface. In order to estimate the diameter, the condensate contour
was obtained from video recorded images. The condensate perimeter
was then estimated by ImageJ analysis with a still frame taken at
5.8 seconds.
[0054] FIG. 13I is a population histogram estimated from the still
frame of FIGS. 13A and 13B.
[0055] FIG. 13J is a population histogram estimated from the still
frame of FIGS. 13C and 13D.
[0056] FIG. 13K is a population histogram estimated from the still
frame of FIGS. 13E and 13F.
[0057] FIG. 13L is a population histogram estimated from the still
frame of FIGS. 13G and 13H.
DETAILED DESCRIPTION
[0058] Described herein are embodiments of coating materials,
methods of forming the coating materials, methods of coating a
substrate, surfaces (e.g., a condenser surface) coated with the
coating materials, and a coated article formed by methods disclosed
herein. Instead of forming a film on a surface, water forms as
droplets on coated surfaces as described herein.
[0059] In an illustrative embodiment, a coating of a metal
substrate (i.e., a transition metal) includes bound or embedded
metal particles and at least one layer of polymer. In an
embodiment, a metal substrate includes copper, zinc, nickel, iron,
aluminum, and alloys thereof. In an embodiment, the metal particles
can be nano particles. In an embodiment, the metal particles can be
of an average size of 200 nm to 3 .mu.m. The metal substrate can be
treated and then immersed in an aqueous solution comprising the
metal particles (e.g., a silver solution, e.g., AgNO.sub.3). In an
embodiment, metal particles (e.g., silver or gold) coat and/or
embed into the surface of the metal substrate. In an embodiment, a
polymer or combination of polymers coat a surface of the treated
metal. Thereby, a polymer or a combination of polymers coats a
surface that is embedded or bound with metal particles. In an
embodiment, the surface is an inside surface, an outside surface,
or both inside and outside surfaces. In an embodiment, a copper or
copper alloy substrate includes silver self-assembled nano
particles bound to the surface and further coated with a
polymer.
[0060] A polymer should be stable to a moist environment so that a
robust condensing surface is provided. Polymers may vary across the
spectrum of hydrophilicity and hydrophobicity and may include
fluorinated polymers (e.g., perfluorinated polymers of halogenated
polymers comprising at least 25% by number of the halogen atoms as
fluorine), olefinic polymers, sulfonated hydrocarbon polymers,
phosphonated hydrocarbon polymers, silicone polymers and the like.
Among specific polymers identified are poly(phenylene-sulfide),
polytetrafluorethylene, and the like. Other classes of polymers
useful in the practice of the present technology may include, by
way of non-limiting examples, silicone polymers, polysiloxanes, and
the like.
[0061] In an illustrative embodiment, the thickness of the coating
on a surface is less than about 2 .mu.m, about 1.9 .mu.m, about 1.8
.mu.m, about 1.7 about 1.6 .mu.m, about 1.5 .mu.m, about 1.4 about
1.3 .mu.m, about 1.2 about 1.1 .mu.m, about 1 about 975 nm, about
950 nm, about 925 nm, about 900 nm, about 875 nm, about 850 nm,
about 825 nm, about 800 nm, about 775 nm, about 750 nm, about 725
nm, or about 700 nm.
[0062] Properly promoted "drop-wise" condensation ("DWC") has been
known to improve substantially Condensation Heat Transfer
Coefficient ("CHTC") compared to that of the traditional
"film-wise" condensation ("FWC") (A. K. Das, H. P. Kilty, Marto,
ASME J. Heat Transfer 7, 109 (2000)). As schematically illustrated
in FIG. 1(a), representing an FWC mode, a large portion of liquid
condensate with poor thermal conductivity hampers efficient heat
transfer passage. Residing liquid film prevents refreshing the
surface and nucleating liquid condensates.
[0063] On the contrary, DWC mode shows discrete rupture of
drops/droplets on the heat transfer surface in FIG. 1(b).
Drop-shaped condensates roll-off and merge with adjacent premature
condensates during sweeping the surface. DWC mode leads to a
continuous cycle of condensate nucleation. Eventually, DWC mode
increases condensate detachment frequency, which reduces the effect
of thermal resistance due to condensate on the heat transfer
surface.
[0064] A hydrophobic coating with enhanced interfacial tension
induces neighboring tiny condensates to coalesce and leads to
droplet-shaped condensates. Research has focused on fabrication of
a hydrophobic surface/coating with high Water Contact Angle (WCA),
which is measured by a sessile drop. For instance, organic coating
materials with low surface energy have received considerable
attention since it is assumed that hydrophobic capabilities of the
coated-surface promote DWC. Due to superhydrophobic WCA
(>150.degree.), numerous droplets were shown throughout the axis
of the test tubes. However, condensates on the polymer-based
coatings rarely rolled-off and resided on the surface until they
reached critical radius.
[0065] A porous surface with hydrophobic coating escalate its WCA
into superhydrophobic regime and shows rolling-off motion (B. J.
Zhang, K. J. Kim, H. K. Yoon, Bioinsp. Biomim. 7, 036011 (2012). C.
Y. Lee, B. J. Zhang, J. Y. Park, K. J. Kim, Int. J. Heat Mass
Transfer 55, 2151 (2012)). During condensation phase change, vapor
cluster impinges onto the condensing surface. Numerous condensates
fill into the condensing surface. Eventually, condensate drops
experience additional drag and lead to longer retention on the
surface. Once a condensate surface becomes wet, additional driving
forces are needed to be separate out of the condensing surface (F.
C. Wang, F. Yang, Y. P. Zhao, Appl. Phys. Lett. 98, 053112
(2011)).
[0066] Thus, coatings and coated surfaces as described herein
achieve DWC augmentation. A silver nano particle deposited coating
(i) has low surface energy, (ii) reduces liquid drag, and (iii) can
optimize silver nano-particles for condensation. These features
promote effective DWC and lead to a substantial DWC enhancement by
increasing nucleating sites and liquid condensate detachment
frequency.
[0067] The metal particles may be any metal or metalloid that can
form and maintain solid particles within the operating temperature
range (about 20.degree. C. to about 280.degree. C. depending on the
type of material) of vapors and liquids to which they will be
subjected during use. The ability to form thin, oxide coatings on
the surface that will resist deep oxidation of the metal is
desirable, but not essential. Given that background,
metals/metalloids and alloys thereof such as aluminum, chromium,
copper, chrome-steel, stainless steel, iron, tin, titanium, or a
combination thereof can coat the inside, outside, or both the
inside and outside of tubes/tubing and fins used in various
condensation applications.
[0068] The size range of the particles may vary over an average
size range of 50 nm to 5 .mu.m, as stated above. Both smaller and
larger average diameter particles and averages may be used with
varying efficiencies.
[0069] The particles may be bound to the surface of the condenser
plate by fusion of the polymeric surface of the particles to the
condenser surface, a coating provided on the particles bonding the
particles to the condenser plate surface (the coating must provide
the surface properties to the particles that offer the benefits of
the technology) or a thin adhesive layer may be present on the
condenser plate to cause the particles to adhere to that
surface.
[0070] There are various general characteristics that can be
discussed within the concept of non-limiting estimations of
general, but not exclusive attributes, dimensions, parameters and
specifications within which the present technology may be
discussed. The thickness of the coatings may be in similar ranges,
although with smaller particles, multi-particle layer thickness is
more desirable, while with the larger diameter size particles
(e.g., 750 nm to 5 .mu.m), mono-particle layer thicknesses can be
more useful. As shown in FIGS. 3A-F, the SEM images show a
thickness of the particle coatings of 1-2 .mu.m.
[0071] The coating may be a monolayer or multiple-particle layer of
the metal, metalloid, or alloy substrate as described herein. A
coating can include a polymer or material comprising a silane or
thiol end group. One coating that can be used is 1-dodecanethiol,
which consists of saturated carbon backbone with a thiol (--SH)
group. In ethanolic solution, 1-dodecanethiol does not polymerize
with other particles. Once the solution is sprayed out on a metal
substrate, a thiol group can interact with hydrogen binding sites
on a metal substrate, and in particular metal particles (e.g.,
silver or gold) coated on or embedded in the substrate. Individual
monomers (e.g. 1-dodecanethiol) chemically interact (via covalent
interaction) and parallel align with each other, thereby forming
single-layered molecular level coating. Thickness of single-layered
molecular coating for that particular material, composition and
particle size is less or equal to about 1 .mu.m. In an embodiment,
the coating thickness is about 750 nm to about 1 .mu.M, about 800
nm to about 1 .mu.m, about 825 nm to about 1 .mu.m, about 850 nm to
about 1 .mu.m, about 875 nm to about 1 .mu.m, about 900 nm to about
1 .mu.m, about 925 nm to about 1 .mu.m, about 950 nm to about 1 or
about 975 nm to about 1 .mu.m. Coatings as described herein that
less or equal to about 1 remain durable.
[0072] Hydrophobic coatings (1-dodecanethiol) are not exclusively
polymer-based. To control surface wetting, hydroxyl
group-functionalized coating (mercapto-based) can be used. For
dropwise condensation application, hydrophilicity does not need to
be considered since it will not help condensation.
[0073] An aspect of the disclosure includes a method of forming the
coated material. In an embodiment, a metal substrate is contacted
with a metal particle solution. In an embodiment, the contacting is
substrate immersion in a liquid metal solution. In embodiment, the
metal substrate is copper or a copper alloy. In an embodiment, the
metal particle solution is a silver solution. In an embodiment, the
silver solution is silver nitrate. In an embodiment, the silver
nitrate solution is about 1 to about 100 mM, about 10 to about 100
mM, about 20 to about 100 mM, about 25 to about 100 mM, about 30 to
about 100 mM, about 40 to about 100 mM, about 50 to about 100 mM,
about 60 to about 100 mM, about 70 to about 100 mM, about 75 to
about 100 mM, about 1 to about 50 mM, about 1 to about 75 mM, or
about 10 to about 50 mM.
[0074] The nano particles in a silver solution can be about 200 nm
to about 3 .mu.m. In an embodiment, silver nanoparticles deposited
on, coated on, or embedded within a substrate service can be about
200 nm to about 3 .mu.m, 300 nm to about 3 .mu.m, 400 nm to about 3
.mu.m, 500 nm to about 3 .mu.m, 600 nm to about 3 .mu.m, 700 nm to
about 3 .mu.m, 800 nm to about 3 .mu.m, 900 nm to about 3 .mu.m, 1
.mu.m to about 3 .mu.m, 2 .mu.m to about 3 .mu.m, about 200 nm to
about 2 .mu.M, 300 nm to about 2 .mu.m, 400 nm to about 2 .mu.m,
500 nm to about 2 .mu.m, 600 nm to about 2 .mu.m, 700 nm to about 2
.mu.m, 800 nm to about 2 .mu.m, 900 nm to about 2 .mu.m, 1 .mu.m to
about 2 .mu.m, about 200 nm to about 1 .mu.m, 300 nm to about 1
.mu.M, 400 nm to about 1 .mu.m, 500 nm to about 1 .mu.m, 600 nm to
about 1 .mu.m, 700 nm to about 1 .mu.m, 800 nm to about 1 .mu.M, or
900 nm to about 1 .mu.m.
[0075] In an illustrative embodiment, silver particles are embedded
in the surface of the substrate. In an embodiment, the silver
particles both cluster on the surface of the substrate and are
embedded in the surface of the substrate. The silver particles
provide a binding platform for a coating (e.g., coating comprising
a silane or thiol end group). In an embodiment, areas of silver on
and/or embedded in the surface of the substrate are heavily
hydroxylized and can covalently bond to a self-assembly monolayer.
In an embodiment, the self-assembly monolayer is a hydrocarbon or
fluorocarbon. In an embodiment, the hydrocarbon or fluorocarbon is
silane-based or contains a thiol end group.
[0076] In an embodiment, the self-assembly monolayer is
1-dodecanethiol. In an embodiment, a copper or copper alloy
substrate comprises silver particles clustered on or embedded in at
least one surface, and further comprising a self-assembly monolayer
of 1-dodecanethiol. In an embodiment, the coated surface provides a
water contact angle of about 90.degree. to about 115.degree., about
95.degree. to about 115.degree., about 100.degree. to about
115.degree., about 105.degree. to about 115.degree., about
90.degree. to about 110.degree., about 95.degree. to about
110.degree., about 100.degree. to about 110.degree., about
101.degree. to about 110.degree., about 102.degree. to about
110.degree., about 103.degree. to about 110.degree., about
104.degree. to about 110.degree., about 105.degree. to about
110.degree., about 106.degree. to about 110.degree., about
107.degree. to about 110.degree., about 108.degree. to about
110.degree., or about 109.degree. to about 110.degree..
[0077] In an embodiment, a surface coated as described herein
comprises a condensate detachment frequency of about 0.5 Hz to
about 2.0 Hz, 0.5 Hz to about 1.9 Hz, 0.5 Hz to about 1.8 Hz, 0.5
Hz to about 1.7 Hz, 0.5 Hz to about 1.6 Hz, 0.5 Hz to about 1.5 Hz,
about 0.5 Hz to about 1.4 Hz, about 0.5 Hz to about 1.3 Hz, about
0.5 Hz to about 1.2 Hz, about 0.5 Hz to about 1.1 Hz, 0.6 Hz to
about 1.5 Hz, about 0.6 Hz to about 1.4 Hz, about 0.6 Hz to about
1.3 Hz, about 0.6 Hz to about 1.2 Hz, about 0.6 Hz to about 1.1 Hz,
0.7 Hz to about 1.5 Hz, about 0.7 Hz to about 1.4 Hz, about 0.7 Hz
to about 1.3 Hz, about 0.7 Hz to about 1.2 Hz, about 0.7 Hz to
about 1.1 Hz, 0.8 Hz to about 1.5 Hz, about 0.8 Hz to about 1.4 Hz,
about 0.8 Hz to about 1.3 Hz, about 0.8 Hz to about 1.2 Hz, about
0.8 Hz to about 1.1 Hz, 0.9 Hz to about 1.5 Hz, about 0.9 Hz to
about 1.4 Hz, about 0.9 Hz to about 1.3 Hz, about 0.9 Hz to about
1.2 Hz, about 0.9 Hz to about 1.1 Hz, about 1 Hz to about 2 Hz,
about 1 Hz to about 1.9 Hz, about 1 Hz to about 1.8 Hz, about 1 Hz
to about 1.7 Hz, about 1 Hz to about 1.6 Hz, about 1 Hz to about
1.5 Hz, about 1 Hz to about 1.4 Hz, about 1 Hz to about 1.3 Hz,
about 1 Hz to about 1.2 Hz, or about 1 Hz to about 1.1 Hz.
[0078] Condensation is the change of the physical state of matter
from a gaseous phase into a liquid phase, and is the reverse of
vaporization. Condensers are used in a variety of technical fields.
They may be used for capturing specific vapors, and especially
water vapor, from the air, condensing steam in power generation
systems, such as nuclear reactors and coal burning generators. The
condensation systems may be powered or passive. Among the various
types of condensers includes air well or aerial well generators,
which are structures or devices that collect water by promoting the
condensation of moisture from air. Designs for air wells are many
and varied, but the simplest designs are completely passive,
require no external energy source and have few, if any, moving
parts.
[0079] Three principal designs are used for air wells: high mass,
radiative and active. High-mass air wells were used in the early
20th century, but the approach failed. From the late 20th century
onwards, low-mass, radiative collectors proved to be much more
successful. Active collectors collect water in the same way as a
dehumidifier; although the designs work well, they require an
energy source, making them uneconomical except in special
circumstances. New, innovative designs seek to minimize the energy
requirements of active condensers or make use of renewable energy
resources.
[0080] The vanes, blades, coils, tubes, fins, or other condenser
surfaces may be metals, alloys, composites, ceramic, metal oxides
and the like as known in the art. Such vanes, blades, tubes, fins,
coils, or other condenser surfaces may be coated with a coating as
described herein.
[0081] Coated surfaces as disclosed herein increase energy
efficiency of heat transfer materials (e.g., condenser based
systems). For example, embodiments of coated surfaces can increase
the heat coefficient by changing how water interacts with materials
(e.g., a condenser surface). Instead of forming a film on a
surface, water forms as droplets on coated surfaces as described
herein (e.g., condenser coils). The droplets roll off coated
surfaces as described herein faster, thereby allowing new water
droplets to form on the surface. Thereby the cycle of droplet
formation and collection occurs more quickly. Thus, heat can be
removed more efficiently. In embodiments as described herein, the
heat coefficient of coated surfaces is 100 to 150% greater than
uncoated surfaces.
[0082] The disclosed coating can also coat condenser fins, such as
those used in air conditioning units. For examples, condenser fins
can be located on an outdoor portion of an air conditioner near a
compressor. Air conditioner fins can be a part of the condenser
that assists heat in moving away from the air conditioner so that
the heat disperses more quickly. Condensers with at least one vapor
condensing surface coated as disclosed herein, can be included in
air conditioning units for multiple applications, such as
industrial air conditioners, consumer (e.g., home) air
conditioners, automotive air conditioners, aircraft air
conditioners, etc. In an embodiment, the water comes off of a
coated fin and collected at the bottom and not blown out of the air
conditioner.
[0083] In an embodiment, condenser systems include at least one
coated vapor condensing surface as discussed herein, wherein the
surface has a total surface energy of less than about 20 mJ/m.sup.2
to about 40 mJ/m.sup.2, 25 mJ/m.sup.2 to about 40 mJ/m.sup.2, 26
mJ/m.sup.2 to about 40 mJ/m.sup.2, 27 mJ/m.sup.2 to about 40
mJ/m.sup.2, 28 mJ/m.sup.2 to about 40 mJ/m.sup.2, 29 mJ/m.sup.2 to
about 40 mJ/m.sup.2, 30 mJ/m.sup.2 to about 40 mJ/m.sup.2, about 20
mJ/m.sup.2 to about 35 mJ/m.sup.2, about 25 mJ/m.sup.2 to about 35
mJ/m.sup.2, about 26 mJ/m.sup.2 to about 35 mJ/m.sup.2, about 27
mJ/m.sup.2 to about 35 mJ/m.sup.2, about 28 mJ/m.sup.2 to about 35
mJ/m.sup.2, about 29 mJ/m.sup.2 to about 35 mJ/m.sup.2, about 30
mJ/m.sup.2 to about 35 mJ/m.sup.2, about 20 mJ/m.sup.2 to about 30
mJ/m.sup.2, about 25 mJ/m.sup.2 to about 30 mJ/m.sup.2, about 26
mJ/m.sup.2 to about 30 mJ/m.sup.2, about 27 mJ/m.sup.2 to about 30
mJ/m.sup.2, about 28 mJ/m.sup.2 to about 30 mJ/m.sup.2, about 29
mJ/m.sup.2 to about 30 mJ/m.sup.2, about 20 mJ/m.sup.2 to about 29
mJ/m.sup.2, 25 mJ/m.sup.2 to about 29 mJ/m.sup.2, 26 mJ/m.sup.2 to
about 29 mJ/m.sup.2, 27 mJ/m.sup.2 to about 29 mJ/m.sup.2, 28
mJ/m.sup.2 to about 29 mJ/m.sup.2, about 20 mJ/m.sup.2 to about 28
mJ/m.sup.2, 25 mJ/m.sup.2 to about 28 mJ/m.sup.2, 26 mJ/m.sup.2 to
about 28 mJ/m.sup.2, or 27 mJ/m.sup.2 to about 28 mJ/m.sup.2. In an
embodiment, condenser systems include at least one coated vapor
condensing surface as discussed herein, wherein the surface has a
total surface energy of less than about 40 mJ/m.sup.2, about 39
mJ/m.sup.2, about 38 mJ/m.sup.2, about 37 mJ/m.sup.2, about 36
mJ/m.sup.2, about 35 mJ/m.sup.2, about 34 mJ/m.sup.2, about 33
mJ/m.sup.2, about 32 mJ/m.sup.2, about 31 mJ/m.sup.2, about 30
mJ/m.sup.2, about 29 mJ/m.sup.2, or about 28 mJ/m.sup.2. In an
embodiment, the total surface energy can be calculated according to
the formula .gamma.=.gamma..sup.h+.gamma..sup.d. where
.gamma..sup.h is a surface energy component due to a hydrogen
bonding and dipole-dipole interactions and .gamma..sup.d is a
dispersion component of surface energy. In an embodiment,
.gamma. h = ( 137.5 + 256.1 cos .theta. H 2 O - 118.6 cos .theta.
CH 2 I 2 44.92 ) 2 ##EQU00001## and ##EQU00001.2## .gamma. d = (
139.9 + 181.4 cos .theta. CH 2 I 2 - 41.5 cos .theta. H 2 O 44.92 )
2 . ##EQU00001.3##
[0084] In an embodiment, the nanoparticle coating on a surface with
a total energy as described above is self-assembled. In yet another
embodiment, a condenser component (e.g., a fin, a coil, etc.) is
coated with silver nanoparticles and/or has silver nanoparticles
embedded into a surface and is further coated with a polymer. In an
embodiment, the polymer coating is a hydrocarbon or fluorocarbon
polymer. In an embodiment, the coating is 1-dodecanethiol.
[0085] Condenser systems having at least one coated vapor
condensing surface as discussed herein have various applications.
Such condenser systems can be utilized in dehumidification,
desalination, electric power plants, refrigeration, water
generation, and chemical separation processes. For example, water
desalination systems typically comprise a) an evaporator for
evaporating saline to produce water vapor and b) a condenser for
condensing the water vapor. In an embodiment, a water desalination
system comprises tubes (e.g., stainless steel) arranged either
horizontally or vertically in a condenser-evaporator chamber. The
energy to evaporate the water can be obtained from film or
drop-wise condensation of desorbed water vapor. A water
desalination system can include a condenser system comprising at
least one vapor condensing surface coated according to the
disclosure herein. In another embodiment, water desalination
includes vapor compression where feed water can be preheated (e.g.,
in a heat exchanger) outside tubes of a condenser-evaporator. After
heating (e.g., boiling), the vapor release is compressed and
directed to condense inside the tubes of the condenser-evaporator.
Such tubes can be according to the disclosure herein.
[0086] Condenser systems as disclosed herein can also be utilized
in steam power generation (e.g., air-steam, pure steam, etc.). For
example, a condenser system as disclosed herein in a steam powered
turbine can include an exhaust gas inlet part that introduces
turbine exhaust gases containing steam and non-condensable gases.
In another embodiment, a geothermal steam turbine comprises a
condenser system as disclosed herein. For example, a condensing
system as disclosed herein can be connected to a steam jet ejector
for condensing geothermal steam into geothermal water including
substantially no non-condensed gas by directly contacting the steam
to the condensate from the main condenser. In another embodiment, a
low pressure condensing steam turbine includes a condenser system
as disclosed herein. The condenser converts exhaust back to water
and thereby condensation of the steam and the change of the steam
from a vapor to water creates a partial vacuum that pulls the
exhaust through the last stages of the low pressure turbine. These
examples are non-limiting as a condenser system as disclosed herein
can be used in a multitude of steam power generators.
[0087] In an embodiment, a condenser component is formed by
contacting a liquid metal solution to at least one surface of the
condenser component. In an embodiment, the condenser component is a
tube, coil, fin, or vane. In an embodiment, the liquid metal
solution is a silver solution. In an embodiment, the silver
solution is silver nitrate. In an embodiment, the contacting is
immersion in the metal solution. In an embodiment, the contacting
is spraying at least one surface of the condenser component with a
metal solution. The method further comprises depositing a
self-assembly monolayer of a polymer on the treated condenser
component. The polymer can be a hydrocarbon polymer or a
fluorocarbon polymer. In an embodiment, the self-assembly monolayer
can be 1-dodecanethiol.
[0088] A further embodiment includes a method of forming a
condenser system as disclosed herein. In an illustrative
embodiment, at least one vapor condensing surface is etched. The
surface is initially cleaned with deionized water and then dried
with compressed air. Once dry, the surface is submerged into an
acid solution for 5 minutes. In an embodiment, the acid solution
comprises a 1:1 mixture (by weight) of 70 wt % nitric acid and 1 M
sulfuric acid.
Examples
[0089] Coated copper alloy tubes were produced according to methods
disclosed herein and tested for surface properties.
[0090] Silver Nano Particle Deposition:
[0091] Copper alloy 122 tubes with an outside diameter of 15.9 mm
and a thickness of 0.813 mm were primary surface-treated by using
emery sand paper (#320) and subsequently by wire wool. The tubes
were thoroughly rinsed with deionized water and ethanol. To prepare
aqueous silver nitrate stock solution, silver nitrate (99.9% metal
basis, Alfa Aesar) was dissolved in DI water at different
concentrations (1-100 mM). Silver self-assembled nano particles
were introduced via a wet chemistry process. Scalability of silver
nano particle was governed by a self-assembly process, which was
proportional to concentration of silver nitrate and immersion time.
Silver self-assembled nano particles (SANPs) were examined by Field
Emission-Scanning Electron Microscopy (FE-SEM) and Energy
Dispersion X-ray (EDX).
[0092] Water Contact Angle (WCA) Measurements:
[0093] The contact angles of liquids (i.e. water, methyliodide) on
the surfaces were measured by a CAM-100 type contact angle
apparatus (KSV Instruments, Finland) with an accuracy of
.+-.0.5.degree. at room temperature to assess wetting
characteristics. A standard syringe was used to introduce
approximately a volume of 5 .mu.l drop onto the surfaces.
[0094] Surface Energy Measurements:
[0095] Surface energies of different surface-treated coatings were
estimated from the WCA measurements using two different fluids:
water (H.sub.2O) and methylene iodide (CH.sub.2I.sub.2).
[0096] Condensation Heat Transfer Experiments:
[0097] Several surface-treated tubes were used in external
condensation tests using the experimental setup shown in FIGS. 2
and 2A. The test setup 10 consisted of three main parts: a test
section 20, a cooling loop 30, and a boiler 40. The test section 20
is composed of a condensing chamber 50 housing three condensing
tubes 52, 54, 56, view ports 58, valves with plumbing 60, and
measuring instruments 70 (not shown). The cooling loop 30 consisted
of a chiller/circulator (Affinity, RWE-012K) 80 and the outlet
temperature of which can be maintained within .+-.1.degree. C. of
the present value. The boiler 40 generated steam by a submerged
heating coil (not shown). Hot compressed water controlled by a
heater (Advantage Engineering, Sentra SK-1035 HE) 90 was flowing
inside of the heating coil of the boiler 40 to generate steam. The
coolant temperatures of the inlet 100 and outlet 110 were measured
by resistance temperature detectors (RTDs, OMEGA, class A,
+0.35.degree. C.), and the chamber 50 and steam temperatures were
measured by T-type thermocouples (.+-.0.5.degree. C.). The pressure
of the chamber 50 and boiler 40 were measured by pressure
transducers (AST, AST4300, 0-345 kPa, .+-.0.5%). The coolant flow
rate was measured by a rotameter (Blue & White, F-440, 0-5 GPM,
.+-.4% of full scale).
[0098] Before the test run, the condensing chamber 50 was fully
evacuated until the water could boil at vacuum pressure.
Non-condensable gases can be expelled to the atmosphere. Once the
system reached a steady state condition, relevant heat transfer
data were acquired. Pressure and coolant inlet temperature were
controlled at 97.8-67.5 kPa and 50-90.degree. C. during data
acquisition.
Results and Discussion
[0099] Surface Characterization:
[0100] Produced SANPs at different concentrations were examined by
FE-SEM and EDX. As shown in FIGS. 3A-D, the size of individual
SANPs was scalable by varying concentration of stock solutions and
immersion time. Each nano particle had a characteristic faceted
crystal and the average size of SANP was 200 nm-3 .mu.m.
[0101] For elemental analysis, EDX mapping was executed in FIG. 4.
The majority of elements consists of fluorine, sulfur, copper, and
silver. In aqueous silver nitration solution, silver and nitrate
were ionized. Individual ions interacted with copper and eventually
crystallize into silver:
Cu.sub.(s))+2Ag.sup.+.sub.(aq)+2NO.sub.3.sup.-.sub.(aq).fwdarw.2Ag.sub.(-
s)+Cu(NO.sub.3).sub.2(aq).
[0102] WCA Measurements:
[0103] Surface wetting is closely related to surface roughness and
surface energy. Scalability of SANPs influences surface wetting,
which was visualized by Static Water Contact Angle (SWCA) in FIGS.
5A-D. The reference surface (plain copper surface) has a SWCA of
approximately 77.degree.. As SANP concentration increased (1-100
mM), the SWCA decreased. It is assumed that enhanced wetting
phenomena was caused by hydrophilic SANP surface profiles and led
to the Wenzel effect.
[0104] As shown in FIGS. 3A-F, scalable nano- and micro-bumps on
the substrate can lead to surface wetting transition from a Wenzel
(wetting) surface to a Cassie-Baxter (less wetting) surface due to
hydrophobic coating. In general, a hydrophobic coating prevents
liquid impingement into surface profiles and entraps noncondensible
gas into surface roughness. Dodecanethiol consists of a hydrophobic
carbon backbone, which lowers surface energy and leads to
hydrophobicity. Dodecanethiol (1 w/w) was dissolved in ethanol and
was spray-coated several times.
[0105] As shown in FIGS. 6A-D, a hydrophobic coating dramatically
increased SWCA (.gtoreq.100.degree.). This result implies that a
hydrophobic coating prevents liquid from impinging into surface
roughness. A hydrophobic coating leads to a surface wetting
transition from a Wenzel surface to a Cassie-Baxter surface by
entrapping gas. Most surfaces showed SWCA of 100.degree.. This
phenomenon was assumed to be related to surface profiles as shown
in FIGS. 3A-F. Density of micro bumps at given surface area
increased with silver concentration. However, aspect ratio of micro
bumps is not significantly enhanced until exposure time increases.
To improve SWCA of structured-surfaces, aspect ratio of the
substructure was assumed to be the key (B. J. Zhang, K. J. Kim, H.
K. Yoon, Bioinsp. Biomim. 7, 036011 (2012); C. Y. Lee, B. J. Zhang,
J. Y. Park, K. J. Kim, Int. J. Heat Mass Transfer 55, 2151
(2012)).
[0106] Surface Energy Measurements:
[0107] In order to obtain a hydrophobic surface, surface roughness
and low surface energy were essential factors. The surface energy
of SANP was estimated using the formula suggested by Owen and Wendt
(D. K. Owen, R. C. Wendt, Appl. Polymer Sci. 13, 1741 (1967)):
.gamma.=.gamma..sup.h+.gamma..sup.d (1)
where .gamma. is the total surface energy. .gamma..sup.h is the
surface energy component due to a hydrogen bonding and
dipole-dipole interactions and .gamma..sup.d is a dispersion
component of surface energy.
[0108] As shown in FIGS. 7A-F, the SWCA of various surfaces (a
plain copper surface and self-assembly monolayer of copper) are
shown for comparison. For water, a wide range of SWCA)
(77.degree.-157.degree. occurred (FIGS. 7A-C). For methylene
iodide, SWCAs were almost halved) (33.degree.-75.degree. compared
to water (FIGS. 7D-F). Obtained results of SWCA measurements are
summarized in Table 2.
[0109] To obtain the surface energy using Eq. (1), individually
measured SWCAs of different polar liquids were plugged into
empirical formulations suggested by Baojin et al. (Q. Baojin, Z.
Li, X. Hong, S. Yan, Exp. Therm. Fluid Sci. 35, 211 (2011)):
.gamma. h = ( 137.5 + 256.1 cos .theta. H 2 O - 118.6 cos .theta.
CH 2 I 2 44.92 ) 2 ( 2 ) .gamma. d = ( 139.9 + 181.4 cos .theta. CH
2 I 2 - 41.5 cos .theta. H 2 O 44.92 ) 2 ( 3 ) ##EQU00002##
Estimated surface energies of various surfaces are summarized in
Table 2. For a SANP, the surface energy was significantly lower
(45%) than that of a plain surface.
TABLE-US-00001 TABLE 2 Estimated surface energy for various
surfaces Plain SAM-coated SANP-deposited surface surface surface
.theta..sub.H.sub.2.sub.O (.degree.) 77 157 101
.theta..sub.CH.sub.2.sub.I.sub.2 (.degree.) 33 75 58 .gamma..sub.sv
(mJ/m.sup.2) 44 33 28
[0110] Condensation Results:
[0111] Test tubes (inner and outer diameters were 14.3 and 15.9 mm,
respectively) were cleaned with acid solution (HCl:HNO.sub.3) to
remove any organic residues. After acid cleaning, the tubes were
thoroughly rinsed several times with distilled-water. A test tube
was chemically treated with 10 mM Ag solution and 2 wt % ethanolic
dodecanethiol was sprayed three times. As shown in FIGS. 8A-B, the
temperature of subcool (T.sub.sub) of the external condensation
heat transfer tests results were plotted with respect to heat flux
and the Condensation Heat Transfer Coefficient (CHTC). For
comparison, the test results of the SANP-deposited condenser were
compared to that of a plain copper tube and Self-Assembly Monolayer
(SAM) of copper. The CHTC of the SANP-deposited condenser was
approximately 2 to 2.5 times (100-150%) higher than non-surface
treated (FIG. 8B). For SAM-coated condenser, CHTC was approximately
25% less than non-surface treated.
[0112] All test-runs of all the test tubes were recorded for
condensation dynamics visualization. FIG. 9A shows a snapshot from
the video-recording for a plain surface. Once initial condensate
nucleates in the top part of tube, the condensate immediately
begins to coalesce with adjacent ones and forms liquid patches. On
the bottom of the tube, dangling condensates with a diameter up to
10 mm and height up to 9 mm were observed. After drop/droplet
detachment, very thin residues remained on the surface. A dangling
drop and thin liquid layer can play a role in thermal resistances.
As heat flux increases, complete FWC appeared along the axial
length of the tube.
[0113] In FIG. 9B, A SAM-coated surface had a different
condensation pattern compared to that of a plain surface (FIG. 9B).
In general, a hydrophobic coating provided nucleation site
improvement. In the top part of the tube, numerous condensates
nucleated and coalesced with neighboring condensates. Due to
enhanced surface tension on the droplet rim, a sweeping mode was
prevented and droplets grew horizontally. The residing droplet
retarded the nucleation of condensates and deteriorated heat
transfer performance. Similar phenomena were observed on the bottom
of the tube. To note, a larger droplet dangling on the surface
turned into a liquid patch, which induced FWC.
[0114] Still-frame of the SANP-deposited surface in FIG. 9C shows
DWC mode throughout the horizontal tube. Significant rolling-off
motion refreshed the entire surface and triggered immediate
nucleation of tiny condensates. The average diameter of detaching
condensates was estimated to be approximately 3 mm. The SWCA was
not a critical factor in determining DWC mode. As shown in FIGS.
7B-C, the SAM copper oxide was 50% enhanced WCA compared to the
SANP. Once the cavity of the superhydrophobic surface becomes wet,
additional driving force and/or energy are required. During
condensation test, most of superhydrophobic surface showed strong
WCA hysteresis, which restricted rolling-off motion and condensate
detachment.
[0115] To analyze dynamic condensate movement, the growth period of
the condensates was video-recorded and was normalized using the
characteristic length (l.sub.0), velocity (u.sub.0), and time
(t.sub.0) defined as (] Y. Nam, E. Aktinol, V. K. Dhir, Y. S. Ju,
Int. J. Heat Mass Transfer 54, 1572 (2011)):
l 0 = .sigma. g ( .rho. l - .rho. v ) ( 4 ) u 0 = g l 0 ( 5 ) t 0 =
l 0 u 0 ( 6 ) t * = t t 0 ( 7 ) ##EQU00003##
where .sigma., g, .rho..sub.l, and .rho..sub.v are surface tension,
gas constant, and density of liquid and solid, respectively.
[0116] t.sub.0=1.6.times.10.sup.-2 s and
l.sub.0=2.5.times.10.sup.-3 m was calculated for water at 1 atm. In
FIG. 10A, the flow-visualization of the SAM-copper oxide surface
showed condensate (arrowed) detachment at t*=2.06. During
detachment, the film partially detached (see the next frame FIG.
10B). Then, the droplet grew horizontally and vertically. At
t*=35.38, the droplet was removed from the surface again (FIG.
10D). The detachment frequency was approximately 1.7 Hz. The
drop-visualization of the SANP surface is shown in FIGS. 11A-D. At
t*=2.06, a droplet-shaped condensate (arrowed) was removed from the
test tube. At the same spot, several condensates are shown in FIG.
11B. These condensates instantaneously merged and detached from the
surface. Consecutive frame (FIG. 11D) shows that there is nearly no
residue left after detachment. The detachment frequency was
approximately 1.1 Hz (faster than the SAM copper oxide). The SANP
surface significantly increased droplet-detachment frequency and
also minimized the droplet-residuals, which led to an increase in
condensation heat transfer.
[0117] To check long term performance of the SANP tubes, longevity
test was performed for a 500 hours test run. As shown in FIG. 12A,
heat flux over subcool temperature was rarely influenced after 500
hours test run. Heat flux information was converted into a
condensation heat transfer coefficient (CHTC) and compared to the
initial condition in FIG. 12B. There was no significant change of
the SANP-deposited surface after 100 hours of operation.
[0118] FIGS. 13A-H depicts the contour of liquid condensate
distributions of the silver-coated surface, which were taken at
specified time periods. FIG. 13A shows that discrete liquid
condensates coalesced rolling off along the horizontal tube. Once
the liquid droplet began to roll off, the mean base radius was
approximately 2 mm. As the liquid droplet moved along the tube
surface, its mean base radius increased to about 3 mm. Growing
liquid condensate swiveled around and removed premature liquid
condensates (<1 mm) before reaching the critical radius to have
enough momentum to roll off. The time frames of FIG. 13A-H show the
renewal area. Instantaneously, micro-sized liquid condensates
nucleated over the condensing surface, as shown in FIG. 13B.
[0119] Considering that the contour of the liquid condensates was
outlined based upon a visually identifiable size, there might have
been millions of unidentified liquid condensates. In FIGS. 13E-F,
numerous liquid condensates densely populated the given surface
area. Before the liquid droplets were fully grown, the largest
droplet began to roll off and swivel around the adjacent premature
liquid droplets, as shown in FIGS. 13G-H.
[0120] The histogram shown below the contour map in FIGS. 13I-L
represents the amount of condensate droplet population. In FIG.
13I, droplets were distributed widely since large condensates were
swept already. Once nucleation began (FIGS. 13C-D), liquid droplets
grew homogeneously, and the population histogram localized within a
few microns regime (FIG. 13J). As droplets grew, the localized
histogram peak diminished (FIG. 13K). The histograms shifted and
were broadly distributed on a wide range of droplet radii. As shown
in FIG. 13L, by immediately merging adjacent liquids, population
peaks decreased significantly and histograms populated widely
(200-2,000 .mu.m).
* * * * *