WO2005052489A2

WO2005052489A2 - Heat exchanger

Info

Publication number: WO2005052489A2
Application number: PCT/EP2004/012783
Authority: WO
Inventors: Oliver Mamber
Original assignee: Behr Gmbh & Co. Kg
Priority date: 2003-11-26
Filing date: 2004-11-11
Publication date: 2005-06-09
Also published as: WO2005052489A3; EP1690058B1; EP1690058A2; JP2007512493A; ATE552471T1; US20070114011A1; DE10355833A1

Abstract

The invention relates to a heat exchanger, particularly an evaporator for air conditioners in motor vehicles, having a number of heat transfer surfaces made of metal, in particular, aluminum or aluminum compounds. The aim of the invention is to provide this heat exchanger with a surface coating that is improved compared to the prior art. To this end, a number of layers are applied to its heat transfer surfaces, and nanoparticles are used for the coating.

Description

heat exchangers

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.

In order to meet the requirements of the industry on components, for example those of the automotive industry on heat exchangers or heat exchangers, treatment of the material surfaces is often unavoidable. Surface treatment is intended to impart specific properties to the components in question, which in particular protect them from environmental influences in favor of improved performance and a longer service life. The specific area of application and structural conditions must be taken into account.

Heat exchangers, in particular evaporators, which are used in air conditioning systems - in particular in motor vehicles - usually consist of a plurality of disks or pipes which are arranged in a row and are connected to one another in a fluid-tight manner and between which corrugated fins are arranged in a tightly packed manner. On the one hand, these enable optimal heat transfer between the cold flowing through the panes or pipes. medium and the air flowing through the corrugated fin network are, however, predestined for the precipitation of condensate as well as dust or dirt. This moist, dirty heat transfer surface provides an ideal breeding ground for microorganisms, the settlement of which can result in undesirable odors. In addition, the damp soiling particularly favors damage caused by corrosion.

In order to avoid the accumulation of water and dirt on a surface, the surface of an object is usually given a hydrophobic finish. Because spherical water droplets form on the surface due to the hydrophobic design, these beads are basically dirt and water repellent. With a hydrophobically equipped surface of the heat exchanger described, however, the water drops cannot bead off because of the very densely packed corrugated fin structure. Instead, they get caught between the adjacent, narrow ribs and gills. This just prevents the desired self-cleaning effect due to the hydrophobic design. This also usually leads to a decrease in the overall performance of the heat exchanger.

In order to solve this problem while maintaining the design of the heat exchanger, a hydrophilic finish on the heat transfer surfaces is desired.

The hydrophilicity of a substance is characterized, among other things, by its polarity, a low interfacial tension with water and good wettability with water, which results from the fact that the adhesive forces that act between the molecules of the same substance are large at an interface compared to the cohesive forces that between Molecules of the same substance work. If a surface is well wettable, a liquid drop forms a contact angle on it that is less than 90 °, ie the liquid can spread more or less on the surface. A hydrophilic finish on a surface therefore leads to the formation of a thin, closed liquid film. The closed liquid film allows the dust and dirt particles to flow away, thereby reducing the permanent accumulation of dust and dirt. In addition, since the corrugated fin surface dries faster due to the comparatively thin water film formation, the settlement of microorganisms on the heat exchanger surface is also reduced.

For example, CN 13242732 discloses 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-protective and hydrophilic properties.

Furthermore, a heat exchanger is known from EP 1 154 042 A1, in which, after acidic cleaning, the heat exchanger surface is provided with a chromium- or zirconium-containing conversion layer and a hydrophilic polymer-based layer which contains silicate particles with a diameter between 5 and 1000 nm ,

With this type of coating, compromises are usually necessary so that, for example, optimum corrosion resistance and a permanently hydrophilic surface for self-cleaning cannot be achieved in the same quality.

The invention is therefore based on the object of providing a heat exchanger of the type mentioned above, the heat transfer surfaces made of metal, in particular aluminum or aluminum compounds, are provided with a surface coating which is improved compared to the prior art. Furthermore, a particularly suitable method for such a surface coating of the heat exchanger mentioned is to be specified.

With regard to the heat exchanger, the object is achieved according to the invention in that a plurality of layers are applied to its heat transfer surfaces, nanoparticles being used for the coating.

The invention is based on the consideration that the design objectives pursued equally in favor of a long service life and improved performance for the heat exchanger cannot be achieved, or at least not satisfactorily, through a single layer. This applies in particular to design goals that actually diverge from one another, namely, e.g. B. on the one hand for optimized corrosion protection and on the other hand for a hydrophilic surface finish. In principle, a hydrophilic or water-attracting and therefore moist surface favors the damage or destruction of materials by chemical or electrochemical reactions. In order to avoid corrosion, it is generally desirable to prevent material and water from coming into contact with one another by means of a hydrophobic finish. While, for effective self-cleaning of the heat transfer surfaces, as described above, a hydrophilic finish of a surface is desired in order to promote the formation of a thin, closed liquid film which allows the dust and dirt particles to flow away.

In order to meet several, often even contradictory, design goals, a multiple coating is therefore provided, with each layer being upgraded for its own specific property. With one shift Namely, defects in the layer expose the metal, so that this location of the metal, particularly in the case of a hydrophilic layer, that is to say a liquid-attracting layer, offers a suitable contact surface for corrosion damage. If there are several layers, the likelihood that defects in the layers lie directly one above the other and the metal will be exposed is lower. This has a correspondingly positive effect on reducing corrosion damage.

When using the material for the layers, customized structures for the desired functions of the coating systems, such as the adhesive forces that act between the molecules of different substances, play an important role. The dimensions or dimensions of individual components and mixtures are largely responsible for the formation of functional coatings. Particularly small particles, especially those with a size of a few millionths of a millimeter, are called nanoparticles. The smallest nanoparticles are clusters of a few hundred molecules and are subject to the laws of quantum mechanics, while the larger ones are governed by the rules of traditional solid state physics. Compared to larger particles with the same chemical composition, nanoparticles have a much smaller number of construction defects. Because of their geometrical and material-specific peculiarities, they therefore offer a particularly large and varied spectrum of effects. For this reason, nanoparticles are used for coating. '

Nanoparticles can be produced, for example, by plasma processes, laser ablation, gas phase synthesis, sol-gel processes, spark erosion or crystallization, among others. Nanoscale particles are characterized by a particularly large surface / volume ratio. Because the adhesive force and the binding of the particles increase with increasing surface area, the layers produced are generally particularly scratch and abrasion resistant. As a result, the surface equipped in this way does not offer a contact surface for damage to the protective coating, as a result of which, for example, corrosion damage can be minimized. Corrosion protection is also improved by appropriately selected nanoscale additives. Because of their hydrophilicity and the comparatively large surface area, these particles are hygroscopic. This means that their surface is moist and ensures a thin liquid film, which both allows the dust and dirt particles to drain off and also reduces the settling of microorganisms by quickly drying the thin liquid film. Each layer of the heat exchanger therefore preferably contains different nanoparticles.

In order to ensure improved performance and a longer service life of the heat exchanger, at least one layer preferably has anti-corrosion properties and at least one further layer has hydrophilic and thus self-cleaning properties.

In a particularly advantageous embodiment, in particular for reasons of corrosion protection, a corrosion-protective layer is preferably first arranged and advantageously a hydrophilic layer is arranged thereon. In order to achieve a particularly effective self-cleaning effect, the hydrophilic layer preferably forms the cover 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 less than or equal to 40 °. The wetting contact angle is determined by the so-called sessile drop method, which is an optical one Contact angle measurement to determine the wetting behavior of solids.

In a particularly advantageous embodiment of the heat transfer surfaces, chromium-free, non-toxic additives are expediently used for the surface coating. For this purpose, the nanoparticles are preferably dissolved from organic and / or inorganic compounds of aluminum, silicon, boron and / or transition metals, preferably from the IV and V subgroups of the periodic table, and / or cerium in inorganic and / or organic solvents and / or dispersed form used for coating.

For efficiency reasons, a particularly thin coating is expediently provided for use of the heat exchanger in air conditioning systems, in particular in motor vehicles, which does not lead to any significant increase in volume and weight. Therefore, each layer thickness is advantageously less than 1.5 μm or equal to 1.5 μm, preferably less than 1 μm or equal to 1 μm, and the total layer thickness is less than 5 μm or equal to 5 μm.

With regard to the method for the surface treatment of heat exchangers, the stated object is achieved by applying several layers to a number of heat transfer surfaces made of metal, in particular aluminum or aluminum compounds, with nanoparticles being used for the coating.

Advantageously, nanoparticles composed of organic and / or inorganic compounds of aluminum, silicon, boron and / or transition metals, preferably of the IV and V subgroups of the periodic stems, and / or cerium dissolved and / or dispersed in inorganic and / or organic solvents for coating.

The layers are advantageously applied by dipping, flooding or spraying, the individual layers, in particular for a particularly rapid layer build-up, directly one after the other, using what is known as wet-on-wet technology, with a single application. Drying can be applied.

In an alternative embodiment of the method, the individual layers are preferably applied in separate treatment steps with respective intermediate drying.

The advantages achieved with the invention consist in particular in that a multiple coating of heat transfer surfaces, in which case nanoparticles are used for coating, provides a heat exchanger which ensures various, in some cases also diverging, requirements. The desired functionality of the heat transfer surfaces is achieved through the selected use of nanoscale particles made of different materials. In this way, the surface coating, for example, the corrosion protection or the hardness and scratch resistance can be improved, and self-cleaning and antimicrobial surfaces can also be produced. For both improved corrosion protection and at the same time an improved self-cleaning effect through hydrophilization of the heat transfer surfaces, at least one corrosion-resistant layer and at least one further, in particular arranged, hydrophilic layer are provided. As a result of the aforementioned improved properties, an increased use and / or performance of the heat exchanger is achieved. As an exemplary embodiment, a heat exchanger, in particular an evaporator for air conditioning systems in motor vehicles, is provided with a double coating of its heat transfer surfaces made of aluminum substrate. The nanoparticles for the respective layer are manufactured using a sol-gel process.

Of course, depending on the desired requirement profile, a multiple coating can also be applied to the heat transfer surfaces, and of course the nanoparticles, which are different in material for each layer, can also be laser ablated by processes other than the sol-gel process, such as, for example, the plasma process - on, gas phase synthesis, spark erosion or crystallization u. a., have it made.

In the exemplary embodiment, a first corrosion-resistant and non-hydrophilic layer or the correspondingly configured base layer is applied by immersion treatment in an organically modified inorganic sol-gel layer with water-based solvent. It is cured by subsequent drying at a temperature in the range of 100-150 ° C for 10 minutes. The layer thickness generated is less than 1 μm. A further organically modified inorganic sol-gel layer with water-based solvent is applied as a second layer or the top layer by immersion treatment. It differs in chemical composition from the layer below. The second layer or the top layer is cured again at 100-150 ° C for 10 minutes. Their surface has a hydrophilic character and has a wetting contact angle with water of less than 40 °. This hydrophilicity is also resistant to the long-term exposure to condensed water, so that the contact angle even after exposure to condensed water for more than 1000 hours after the constant condensation test according to DIN 50017-KK is still below 40 °. The total layer thickness of the layer structure consisting of the base and top layers is a maximum of 2 μm.

This ensures optimal protection against corrosion by the first layer or the base layer, and the water drainage on the heat transfer surface is improved by the production of the functional hydrophilic cover layer. This promotes the drainage of dust and dirt from the surface, and the comparatively thin water film formation ensures that the surface dries faster. These self-cleaning and quick drying properties minimize the growth of microorganisms. All of these factors improve the use and / or performance of heat exchangers with heat transfer surfaces coated in this way.

Claims

P a t e n t a n s r u c h e

Heat exchangers, in particular evaporators for air conditioning systems in motor vehicles, with a number of heat transfer surfaces made of metal, in particular aluminum or aluminum compounds, to which a plurality of layers are applied, nanoparticles being used for the coating.

Heat exchanger according to claim 1, wherein each layer contains different nanoparticles.

3. Heat exchanger according to claim 1 or 2, in which at least one layer has anti-corrosion properties and at least one further layer, preferably arranged thereon, has hydrophilic properties.

4. Heat exchanger according to claim 3, wherein the layer with hydrophilic properties has a wetting contact angle with water of less than or equal to 60 °, preferably less than or equal to 40 °.

5. Heat exchanger according to one of claims 1 to 4, in which the nanoparticles of organic and / or inorganic compounds of aluminum, silicon, boron and / or transition metals, preferably the IV. And V. subgroup of the periodic table, and / or cerium in inorganic and / or organic solvents in dissolved and / or dispersed form are used for coating.

6. Heat exchanger according to one of claims 1 to 5, in which each layer thickness is less than 1.5 μm or equal to 1.5 μm, preferably less than 1 μm or equal to 1 μm, and in which the total layer thickness is less than 5 μm or equal Is 5 μm.

7. A method for the surface treatment of heat exchangers, in particular according to one of claims 1 to 6, in which several layers are applied to a number of heat transfer surfaces made of metal, in particular aluminum or aluminum compounds, nanoparticles being used for coating.

8. The method according to claim 7, wherein the nanoparticles made of organic and / or inorganic compounds of aluminum, silicon, boron and / or transition metals, preferably the IV. And V. subgroup of the periodic table, and / or cerium in inorganic and / or organic solvents in dissolved and / or dispersed form can be used for coating.

9. The method according to claim 7 or 8, in which the layers are applied by dipping, flooding or spraying, the individual layers being applied in succession without any intermediate drying.

10. The method according to claim 7 or 8, in which the layers are applied by dipping, flooding or spraying, the individual layers being applied in separate treatment steps with respective intermediate drying.