Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F13/04—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by preventing the formation of continuous films of condensate on heat-exchange surfaces, e.g. by promoting droplet formation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
  • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2245/00—Coatings; Surface treatments
  • F28F2245/02—Coatings; Surface treatments hydrophilic

Definitions

• the invention relates to a heat exchanger with surface-treated heat transfer surfaces. It also relates to a process for the surface treatment of heat exchangers.
• a surface treatment is intended to provide the associated components with specific properties which protect them in particular from environmental influences so as to achieve improved performance and a longer service life.
• the specific application area and structural conditions need to be taken into account.
• Heat exchangers in particular evaporators, which are used in air-conditioning systems—in particular in motor vehicles—usually comprise a plurality of disks or tubes which are arranged in a row, are connected to one another in a fluid-tight manner and between which are arranged tightly packed corrugated fins.
• these allow optimum heat transfer between the refrigerant flowing through the disks or tubes and the air flowing through the network of corrugated fins, they are inevitably subject to the precipitation of condensate and dust or dirt.
• This wet, contaminated heat transfer surface offers an ideal breeding ground for microorganisms, colonization of which can lead to the formation of undesirable odors.
• corrosion damage is promoted by the wet contamination.
• the surface of an object is generally rendered hydrophobic.
• spherical drops of water form on the surface as a result of the hydrophobic configuration thereof, and these drops then run off, these surfaces are fundamentally able to repel dirt and water.
• the water drops cannot run off, on account of the very closely packed corrugated fin structure. Instead, they remain in place between the adjacent, closely packed fins and gills. Therefore, the desired self-cleaning effect by the hydrophobic configuration is in fact prevented. Moreover, this usually leads to a decrease in the overall performance of the heat exchanger.
• the hydrophilicity of a substance is characterized, inter alia, by its polarity, a low interfacial tension with respect to water and good wetability with water, which results from the fact that the adhesion forces which act between the molecules of the same substance are high at an interface compared to the cohesion forces which act between the molecules of the same substance. If a surface can be successfully wetted, a drop of liquid forms a contact angle on said surface which is less than 90°, i.e. the liquid can spread out to a greater or lesser extent on the surface. Therefore, rendering a surface hydrophilic leads to the formation of a thin, continuous film of liquid. The continuous film of liquid allows the dust and dirt particles to flow off and therefore reduces long-term accumulation of dirt and dust. Since, moreover, the corrugated fin surface dries more quickly as a result of the relatively thin film of water which is formed, the colonization of microorganisms on the heat transfer surface is also reduced.
• CN 13242732 has disclosed an aluminum heat exchanger which is provided with a layer which, inter alia, contains nanoparticles based on macromolecular surfactants and crosslinkable, unsaturated monomers and has corrosion-resistant and hydrophilic properties.
• EP 1 154 042 A1 has disclosed a heat exchanger in which the heat exchanger surface, after acid cleaning, is provided with a chromium-containing or zirconium-containing conversion layer and a hydrophilic layer based on polymer which contains silicate particles with a diameter of between 5 and 1000 nm.
• This type of coating means that compromises are generally required, and consequently, for example, optimum resistance to corrosion combined at the same time with a permanently hydrophilic surface to provide a self-cleaning action cannot be achieved with the same quality.
• the invention is based on the object of providing a heat exchanger of the above type, the heat transfer surfaces of which made from metal, in particular aluminum or aluminum compounds, are provided with a surface coating which represents an improvement on the prior art. Furthermore, it is intended to specify a process which is particularly suitable for this type of surface coating of the abovementioned heat exchanger.
• the object is achieved, according to the invention, by a plurality of layers being applied to its heat transfer surfaces, with nanoparticles being used for the coating.
• the invention is based on the consideration that the design objectives of a long service life and an improved performance, which are pursued to equal extent for the heat exchanger, cannot be achieved, or at least cannot be achieved to a satisfactory extent, by a single layer.
• design objectives which are actually divergent with respect to one another, namely for example on the one hand an optimized resistance to corrosion and on the other hand a hydrophilically configured surface.
• a hydrophilic or water-attracting and therefore wet surface fundamentally promotes damage or destruction of materials by chemical or electrochemical reactions. Therefore, to avoid corrosion, it is fundamentally desirable to suppress contact between material and water by using a hydrophobic configuration.
• a hydrophilic surface is desirable for effective self-cleaning of the heat transfer surfaces, as described above, in order to promote the formation of a thin, continuous film of liquid which allows the dust and dirt particles to flow off.
• each layer being suitable for its own specific property.
• defects in the layer can lead to the metal being exposed, and consequently this location in the metal, in particular in the case of a hydrophilic layer, i.e. a layer which attracts liquid, offers a suitable surface for attack in respect of corrosion damage.
• a hydrophilic layer i.e. a layer which attracts liquid
• offers a suitable surface for attack in respect of corrosion damage offers a suitable surface for attack in respect of corrosion damage.
• the probability that defects in the layer will lie directly above one another and expose the metal is reduced. This has a correspondingly beneficial effect with a view to reducing corrosion damage.
• tailored structures play an important role for the desired functions of the coating systems, such as for example the adhesion forces which are active between the molecules of different substances.
• the dimensions or sizes of individual components and mixtures play a crucial co-determining role in the formation of functional coatings.
• the smallest nanoparticles are clusters of a few hundred molecules and are subject to the laws of quantum mechanics, whereas for larger nanoparticles the rules of traditional solid-state physics apply.
• Nanoparticles have a greatly reduced number of structural defects than larger particles of the same chemical composition. Therefore, on account of their geometric and material-specific properties, they offer a particularly wide and versatile spectrum of actions. For this reason, nanoparticles are used for the coating.
• Nanoparticles can be produced, for example, by plasma processes, laser ablation, gas phase synthesis, sol-gel processes, spark erosion or crystallization, inter alia.
• Nanoscale particles are distinguished by a particularly large surface area/volume ratio. Because the sticking force and bonding of the particles increases with an increase in surface area, layers produced in this way are generally particularly resistant to scratching and abrasion. As a result, the surface configured in this manner does not offer any surface for attack with respect to damage to the protective coating, with the result that, for example, corrosion damage can be minimized.
• nanoscale additives which are selected to have corresponding compositions, moreover, the resistance to corrosion is improved. On account of their hydrophilicity and their relatively large surface area, these particles are hygroscopic.
• each layer of the heat exchanger preferably contains nanoparticles of different compositions.
• At least one layer to have corrosion-resistant properties and for at least one further layer to have hydrophilic and therefore self-cleaning properties.
• a corrosion-resistant layer in particular for corrosion prevention reasons, it is preferable for a corrosion-resistant layer to be applied first of all, which is advantageously followed by a hydrophilic layer.
• the hydrophilic layer preferably forms the top layer of the multiple coating.
• the layer with hydrophilic properties advantageously has a wetting contact angle with water of less than or equal to 60°, preferably of less than or equal to 40°.
• the wetting contact angle is in this case determined by what is known as the sessile drop method, which represents an optical contact angle measurement for determining the wetting properties of solids.
• the nanoparticles used for the coating are preferably formed from organic and/or inorganic compounds of aluminum, silicon, boron and/or transition metals, preferably from transition groups IV and V of the periodic system, and/or cerium dispersed and/or dissolved in inorganic and/or organic solvents.
• each layer thickness advantageously amounts to less than 1.5 ⁇ m or equal to 1.5 ⁇ m, preferably less than 1 ⁇ m or equal to 1 ⁇ m, and the total layer thickness amounts to less than 5 ⁇ m or equal to 5 ⁇ m.
• the abovementioned object is achieved by a plurality of layers being applied to a number of heat transfer surfaces made from metal, in particular from aluminum or aluminum compounds, with nanoparticles being used for the coating.
• nanoparticles of organic and/or inorganic compounds of aluminum, silicon, boron and/or transition metals preferably from transition groups IV and V of the periodic system, and/or cerium dissolved and/or dispersed in inorganic and/or organic solvents to be used for coating.
• the layers are applied by dipping, flooding or spraying, with the individual layers, in particular for particularly rapid layer build-up, being applied in direct succession, using what is known as the wet-in-wet technique, with just one drying operation.
• the individual layers are preferably applied in separate treatment steps, in each case with intermediate drying.
• the advantages achieved by the invention consist in particular in the fact that a multiple coating of heat transfer surfaces with nanoparticles used for the coating provides a heat exchanger which satisfies different and in some cases also divergent demands.
• the selected use of nanoscale particles of different materials achieves the desired functionality of the heat transfer surfaces.
• this form of surface coating it is possible, for example, to improve the resistance to corrosion or the hardness and scratch proofing, and furthermore it is possible to produce self-cleaning and antimicrobial surfaces.
• an improved self-cleaning effect brought about by rendering the heat transfer surface as hydrophilic, at least one corrosion-resistant layer and at least one further hydrophilic layer, in particular arranged thereon, are provided. Improved use and/or performance of the heat exchanger are achieved as a result of the abovementioned improved properties.
• a heat exchanger in particular an evaporator for air-conditioning systems in motor vehicles, having a double coating of its heat transfer surfaces made from aluminum substrate is provided as an exemplary embodiment.
• the nanoparticles for the respective layer are in this case produced using a sol-gel process.
• the nanoparticles of different compositions for each layer can also be produced by processes other than the sol-gel process, such as for example by the plasma process, laser ablation, gas phase synthesis, spark erosion or crystallization, inter alia.
• a first corrosion-resistant layer which is not hydrophilic, or the correspondingly configured base layer, is applied by dip coating in an organically modified inorganic sol-gel layer with water-based solvent. It is hardened by subsequent drying at a temperature in the range from 100-150° C. for 10 minutes. The layer thickness produced is less than 1 82 m.
• a further organically modified inorganic sol-gel layer with water-based solvent is applied by dip coating as the second layer or the covering layer. Its chemical composition differs from that of the layer below. The second layer or the covering layer is again hardened at 100-150° C. for 10 minutes. Its surface has a hydrophilic character and has a wetting contact angle with water of less than 40°.
• the total layer thickness of the layer structure comprising base layer and covering layer is at most 2 ⁇ m.
• the first layer or base layer ensures optimum resistance to corrosion, and the production of the functional hydrophilic covering layering improves the water run-off on the heat transfer surface. This helps dust and dirt to flow off the surface, and on account of the relatively thin film of water which is formed, faster drying of the surface is ensured. These self-cleaning and fast drying properties minimize the growth of microorganisms. All these factors improve the use properties and/or performance of heat exchangers having heat transfer surfaces which have been coated in this way.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Laminated Bodies (AREA)
• Paints Or Removers (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
• Other Surface Treatments For Metallic Materials (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Air-Conditioning For Vehicles (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2003
  • 2003-11-26 DE DE10355833A patent/DE10355833A1/de not_active Withdrawn
• 2004
  • 2004-11-11 US US10/580,656 patent/US20070114011A1/en not_active Abandoned
  • 2004-11-11 JP JP2006540259A patent/JP2007512493A/ja active Pending
  • 2004-11-11 WO PCT/EP2004/012783 patent/WO2005052489A2/de active Application Filing
  • 2004-11-11 AT AT04803126T patent/ATE552471T1/de active
  • 2004-11-11 EP EP04803126A patent/EP1690058B1/de not_active Not-in-force

Patent Citations (7)

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