Heat exchange – With timer – programmer – time delay – or condition responsive... – Having heating and cooling capability
Reexamination Certificate
1997-12-29
2001-02-27
Beck, Shrive (Department: 1762)
Heat exchange
With timer, programmer, time delay, or condition responsive...
Having heating and cooling capability
C165S287000, C427S248100, C427S249700
Reexamination Certificate
active
06192979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the use of plasma polymer layer sequences as functional layers in material transport or heat exchanger systems, by means of which these functional surfaces have definitely adjustable wetting behavior. Their use is advantageous in many fields in which material transport or heat exchange systems are used.
2. Discussion of Background Information
The supply and dissipation of heat or material transport is of central importance for many process technical industrial processes. In the transmission of heat, it is advantageous to use phase transitions (condensation, evaporation) since in this way, very high heat flow densities can be achieved. This will be explained in detail in the procedure of condensation.
In the majority of technical condensers, the fluidization of vapor occurs as film condensation. The heat transfer coefficient can be increased by approximately one order of magnitude if the condensation is carried out as dropwise condensation. In order to achieve this, the surfaces on which the condensation takes place should have a definite wetting behavior which is distinguished by very low surface energies or by an edge angle of >60° relative to water.
It is known that the basic prerequisite for the dropwise condensation is the existence of hydrophobic surfaces (low surface energy) in the condenser. The definite production of condenser surfaces of low surface energy requires the use of specific coatings on the metal parts that are necessary for heat transmission reasons.
It is furthermore known that monomolecular layers based on Langmuir-Blodgett films can have low surface energies. The extremely low thickness of these layers and the low number of possibilities for optimizing their mechanical/corrosive properties make them largely unsuitable for use in technical condensers for longevity reasons.
Other layers are also unsuitable if they cannot withstand the mechanical/corrosive stresses. For the mechanical/corrosive resistance of the layer, if a layer thickness is required that is so great that the thermal resistivity connected with it does not, on the whole, lead to any intensification of the heat transmission capacity (possibly even to a worsening in comparison to the initial system), then this layer is also unsuitable.
Materials that adhere to the metallic base material via physical and/or chemical effects and have been used to achieve incomplete wetting for tests of dropwise condensation include organic compounds with hydrophobic groups, various plastics, inorganic substances, special alloys, and—not without contradictions of different results—precious metals as well. Table 1 represents only a few references for this purpose.
TABLE 1
represents the promoting agent, wherein promoter is understood here to
mean all substances effectively used to hydrophobize the base material,
to bring about dropwise condensation (the essential tasks, no claim as
to completeness). The examples from the literature numbered here are
taken from the list in Appendix 1.
Material/
substance
Notes
Reference
organic
37 different compounds,
Blackmann et al. (1)
compounds
16 of them tested
for 500 hours
montan wax
Watson et al. (2)
montan wax
Tanner et al. (3)
oleic acid
Finnicum & Westwater (4)
silicone oil
Mingdao and Jiliang (5)
diff. promoters, overview
Kast (6)
of different results
polymers
fluoroacrylic, parylene,
Marto et al. (7)
Emralon 333,
fluoroepoxy polymerized
Marto et al. (8)
triazine dithiol
films on Al/Mg tubes
Mori et al. (9)
PVC layers
PTFE layer
Haraguchi et al. (10)
PTFE wetting analysis
Utaka et al. (11)
Boyes & Ponter (12)
inorganic
sulfides and Se compounds
Erb & Thelen (13)
compounds
galvanic
dispersion layer, esp.
Cluistra et al. (14)
with PTFE dispersion
alloys
surface alloy, CU with
Zhang et al. (15)
Cr, Fe, Al, Bi, Sb, Sn,
Se, In
Ion implantation N, He,
Zhao et al. (16)
Ar, H
Ion implantation Cr, N
Zhao et al. (17)
in Cu
precious metals
Gold, according to this,
Bernett & Zisman (18)
pure gold surfaces can
and Smith (19)
be completely wet
Gold gilded with paraffin-
Wilkins et al. (20)
thio-silane, and mercaptan,
vacuum coated gold
coatings, partially
chemically treated silver,
dep. via electroplating
Tanasawa &
Westwater (21)
Woodruff &
Westwater (22)
Barthau (23)
O'Neill & Westwater (24)
In all of the tests of dropwise condensation, in addition to the clarification of purely heat technical questions, the test of conceivable promoters forms the basis of the achievement of dropwise condensation and constitutes the main focus of the research.
Out of all of the research results that indisputably demonstrate possibilities for achieving dropwise condensation, until now, no methodology has come into use in the practical construction of condensers. This is brought about by the still insufficient proofs as to the service life of promoter layers and the resulting lack of certainty of a long term maintenance of dropwise condensation.
It is now the object of the invention to find functional layers that can be deposited by means of conventional coating methods on the functional surfaces of the corresponding apparatuses and devices for these material transport or heat exchanger systems, e.g. condensers, whose use will eliminate the disadvantages of the prior art.
It is consequently the object of the invention to find functional layers of the type mentioned, which can be used in all material transport or heat exchanger systems, e.g. also or even especially in condensers, which in the event that the functional layers are used on condensers, force the dropwise condensation and can advantageously be used in the systems and apparatus construction.
According to the invention, this object is attained through the use of a plasma polymer layer sequence as a functional layer in material transport or heat exchanger systems.
In these material transport or heat exchanger systems with a definitely adjustable wetting behavior, the functional layers that are deposited on the base material of the functional surfaces of apparatuses for heat and material transfer, plasma-modified carbon—hydrogen layers (a-C:H layers or DLC (diamond-like carbon) layers). These plasma-modified carbon—hydrogen layers are comprised of a plasma polymer layer sequence as a hard material layer with a top layer as a functional layer as well as possibly an intermediary layer and a gradient layer, wherein for adjusting a definite wetting behavior, in addition to the base elements of carbon and hydrogen, the top layer contains other non-metallic or metalloid elements of the 1st, 3rd, 4th, 5th, 6th, and/or 7th main group of the periodic table of the elements (preferably 1 at % to 70 at % in relation to the carbon content). These layers can be produced using conventional PVD or CVD processes, e.g. a plasma-enhanced chemical vapor deposition (PECVD) process. These layers are known per se and are described in DE 44 17 235, even with regard to manufacturing possibilities.
It has surprisingly turned out that in particular assembly regions of the top layer, these layers can be used to excellent effect as functional layers in or on
plate heat exchangers (composition of the top layer: 1-40 at % F, Si, and/or O, 60-99 at % C, with a remainder of hydrogen up to max. of 30 at %)
tubular or tubular bundle heat exchangers (composition of the top layer: 1-40 at % F, Si, and/or O, 60-99 at % C, with a remainder of hydrogen up to max. of 30 at %)
filling bodies in filling body columns (composition of the top layer: 1-40 at % N,O and/or B, 60-99 at % C, with a remainder of hydrogen up to max. of 30 at %)
condensers for forcing dropwise condensation (composition of the top layer: 1-40 at % F, Si, and/or O, 60-99 at % C, with a remainder of hydrogen up to max. of 30 at %)
heat/material exchanging walls and apparatus walls lead to a deliberate influencing of the adhesion mechanisms in such a way that the soiling inclination, the depositing inclination, and the caking inclination are advantageously counteracted (composition of the top layer: 1-40 at % F, Si, and/or O, 60
Grischke Martin
Koch Gerd
Leipertz Alfred
Beck Shrive
Chen Bret
Fraunhofer-Gesellschaft zur Foderung der angewandten Forschung e
Greenblum & Berstein P.L.C.
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