WO2002090859A1 - Heat-exchanging device comprising a surface-coated wall separating medium 1 from medium 2 - Google Patents

Abstract

The invention relates to a heat-exchanging device comprising a surface-coated wall which separates medium 1 from medium 2. The surface of the wall is at least partially coated with a thin layer containing at least one compound from the elements titanium, zirconium and/or hafnium and/or alloys of the same with nitrogen and/or oxygen and/or carbon and/or fluorine. The invention also relates to a method for producing the surface-coated heat-exchanging wall, and to the use of the inventive heat-exchanging device.

Description

 Heat exchanger device with a surface coated

Wall that separates medium 1 from medium 2

The present invention relates to a heat exchanger device having a surface-coated wall which separates medium 1 from medium 2, the surface of the wall being at least partially coated with a thin layer which comprises at least one compound of the elements titanium, zirconium and / or hafnium and / or alloys thereof with nitrogen and / or oxygen and / or carbon and / or fluorine. The present invention further relates to a method for producing the surface-coated heat exchanger wall and the use of the heat exchanger device.

The invention relates essentially to a surface-coated heat exchanger wall of a heat exchanger device for transferring heat from a warmer medium to a colder one. A medium is understood to be any gas or liquid. The heat exchanger wall is, for example, the walls of a plate which is connected to a heat transfer tube and is used, for example, in condensers of refrigeration systems, air separation systems, drying or humidification systems or moist air stills.

There are various suggestions for optimizing heat exchanger walls. Grooves in the surface are described in the documents DE-A-27 31 476, EP-A-0 136 148 and DE-A-26 00 821. By suitably choosing the shape, size and arrangement of these grooves, condensed steam should form a thinner water film than without these grooves. A thinner water film is a smaller heat barrier and leads to one more efficient heat exchanger. Another approach is described in DE-A-26 50 565, where a surface coated with "porous material", such as fiber fleece or plastic foam, is intended to minimize the water film. Heat exchangers are also used in plants for the reprocessing of brackish water, especially sea water. The media in these systems are corrosive and when treating seawater, it is required that the medium in contact with the heat exchanger wall is food-safe. Furthermore, the efficiency and thus the economic viability of such systems strongly depend on the effectiveness of the heat exchangers used. A device for extracting industrial water from contaminated water is described in German patent DE-C-43 40 745. Here, a plurality of vertically parallel to each other with the formation of channels, ie at a distance from each other fleece or fabric webs are used as evaporation surfaces for the previously heated contaminated water. The disadvantage here, however, is that drops are formed and no thin film, which reduces the efficiency of the system.

The object of the present invention is to provide a heat exchanger whose surface is modified in such a way that the efficiency of the heat exchanger is improved, corrosion problems when using corrosive media are reduced and the surface for use in the production of drinking water is food-safe.

This object is solved by the subject matter of claim 1. Further advantageous embodiments result from the subclaims.

The present invention relates to a heat exchanger device with a surface-coated wall which separates medium 1 from medium 2, the surface of the wall being at least partially coated with a thin layer which comprises at least one compound of the elements titanium, zirconium and / or hafnium and / or alloys thereof with nitrogen and / or oxygen and / or carbon and / or fluorine contains.

In a preferred embodiment, the

Surface coating a compound with the chemical formula Ti _x ZryHf _z N _a OkC _c (with x, y, z = 0 to 1 each; a, b, c = 0 to 2.5 each, with the proviso that x + y + z = 1 and a + b + c> 0). In a further preferred embodiment, the surface coating contains a compound with the chemical formula Ti _x ZryHfz ^ a ^ b ^ c (with x, y, z = 0 to 1 each; a, b, c = 0 to 2 each, with the proviso that x + y + z = 1 and a + b + c = 0.02 to 2.0). Specific compounds which are particularly preferred: TiO ₂ , TiN _a O _f oC _c , with a = 0.01 to 1.8; b = 0.2 to 1.98 and c = 0.01 to 1.5; ZrN _a OC _c , with a = 0.01 to 0.2; b = 0.8 to 1.89 and c = 0.1 to 1.5.

In a very preferred embodiment, fluorine is also present in the compound for the surface coating, the ratio of the fluorine atoms to the carbon atoms contained therein being 0.05 to 2.05. Such a compound has the chemical formula Ti _x ZryHfz ^N a ° b ^c c ^F d ( ^with XYZ = in each case

mit b=0 bis 1,5, c=0,l bis 1,8 und d=0,01 bis 0,8; TiN_aC_cF_d mit a=0 bis 2,5, c=0,l bis 2,5 und d=0,01 bis 0,8.0 to 1; a, b = 0 to 2 each; c = 0.05 to 2 and d = 0.01 to 2 with the proviso that x + y + z = 1, a + b + c = 0.02 to 2.0 and d / c = 0.005 to 2, 05). Compounds with small proportions of fluorine, d <0.3, are preferred. Specific connections that are particularly preferred:

with b = 0 to 1.5, c = 0, l to 1.8 and d = 0.01 to 0.8; TiN _a C _c F _d with a = 0 to 2.5, c = 0, l to 2.5 and d = 0.01 to 0.8.

Very preferred compounds are TiNO _t ICQ, ₅ F _{0, 01} , TiNOi, 1C0, 5F0, 1 / TiNOi, ιC ₀ , 5 ^ 0, 15 / TiNOi, ιC ₀ , 5 ^ 0, 3, TiNOa., ΙC ₀ , 5F0,, and TiOi, ₄ C ₀ , 5F0, 5 •

The hydrophilicity / hydrophobicity of the surface coating can be controlled particularly easily by means of the fluorine content. A higher fluorine content thus creates a more hydrophobic surface, which can be advantageous for applications in refrigeration technology. In industrial water technology, on the other hand, more hydrophilic surfaces are more advantageous, which can be caused by a low fluorine content or the omission of fluorine. The fluorine-containing layers preferably have CF and / or CF2 groups which in the ESCA spectrum lead to maxima at 290 ± 1 eV

(caused by the CF groups) or 293 ± 1 eV (caused by CF2 groups) (see FIGS. 1-6). In a preferred embodiment, the surface coating contains CF and CF2 groups, which lead to an intensity ratio of the two maxima (at 290 and 293 eV) of 0.5 to 8 in the ESCA spectrum.

The coating is located as a thin layer on a substrate suitable as a heat exchanger wall. This can be made of plastic, e.g. Polypropylene, polyester, polyamide, polyurethane, polyethylene, polytetrafluoroethylene or from a metal such as copper, aluminum, nickel, chromium, titanium, vanadium, niobium, iron or their mixtures or alloys. The coating formed as a thin layer is preferably applied to a structured surface. The thickness of the coating is preferably in the range from 20 nm to 2 mm, more preferably in the range from 200 nm to 1.5 mm and very preferably in the range from 500 nm to 1 mm.

The coating can completely or partially cover the surface of the heat exchanger wall. The heat exchanger wall is preferably coated with at least 85% of the coating.

In a preferred embodiment, an intermediate layer is provided between the heat exchanger wall and the coating, which brings about a higher adhesive strength. This intermediate layer preferably consists of a thermally conductive metal, preferably chromium, nickel, titanium, molybdenum or vanadium.

The heat exchanger wall is preferably coated in a vacuum coating chamber, in which titanium, zirconium and / or hafnium are evaporated by means of electron beam evaporation and the elements nitrogen, oxygen, carbon and / or fluorine are added in gaseous form by means of “mass flow controler”. A particularly preferred method is the introduction of the base material of the heat exchanger (plastic or metal) in the form of tape material, which is in rolls, in a vacuum chamber. This vacuum chamber (Fig. 11) consists of a winding mechanism through which the strip material can be rewound from one roll to another in a vacuum. Furthermore, the winding mechanism has at least one, preferably two, deflection rollers through which the strip material can be heated or cooled. The heating rollers are preferably heated by infrared emitters, the cooling rollers are preferably cooled by thermal oil. The strip material is exposed to steam between the deflection rollers.

This steam is generated in a vacuum of approx. 10–5 mBar to which the non-metals of the compound are added as gases, so that the process takes place at a process pressure of approx. 0.1 to 3 * 10 ^" mBar. The gas mixture the supplied non-metals are preferably controlled by means of a “mass flow controler.” It may be advantageous for the process to add a noble gas, such as argon, for example. The metals are preferably vaporized from crucibles by means of electron beam guns. The metals in these are preferred Crucibles mixed in granular form, in the ratio as they are later present in the connection on the strip material. Preferred strip speeds are 1 to 60 m / min, particularly preferably speeds of 6 to 25 m / min. In the case of metallic strips, the strip is heated by means of the heating rollers heated to temperatures of 150 ° C to 450 ° C. For copper, a temperature range of 350 ° C to 420 ° C has proven to be particularly suitable other temperatures in the range of 20 ° C to 80 ° C to choose.

The coated heat exchanger wall can be used in the context of a heat exchanger device in condensers of refrigeration systems, air separation systems, drying or humidification systems or moist air stills, the use in moist air stills and refrigeration systems being preferred.

For use in moist air stills, it is advantageous that the surface coating is corrosion-proof and food-safe and that after evaporation no individual droplets are deposited, but a thin one continuous film is created, which contributes to the efficiency of the still. Hydrophilic surfaces are advantageous, so compounds with little or no fluorine and a low carbon content should preferably be selected. Compounds with TiN _a 0 _o C _c , with a = 0.01 to 1.8; b = 0.2 to 2.2 and c = 0.01 to 0.5. The increase in efficiency through these connections is e.g. B. can be seen in Figure 7.

For use in air conditioning systems, the fact that the surface coating is hydrophobic, corrosion-resistant and food-safe has an advantageous effect. In air conditioning systems, warm, often humid air is cooled. The excess water vapor condenses on the heat exchanger surfaces and reduces the efficiency of the heat exchanger. A hydrophobic surface leads to the formation of individual droplets that drip quickly, which is conducive to the efficiency of the air conditioning system, especially in humid climates. This process and the improved efficiency through these connections is e.g. B. can be seen in Figure 10. In addition, the condensate does not need to be treated further, since no contamination occurs on the surface. Hydrophobic surfaces are preferably realized using compounds with a high fluorine content. Compounds with TiO _b C _c F ^ with b = 0.1 to 1.5, c = 0.1 to 1.8 and d = 0.05 to 0.6, TiN _a C _c F _d with a are particularly preferred = 0.1 to 2.5, c = 0.1 to 2.5 and d = 0.05 to 0.6 and TiN _a O _b C _c F _d with a, b = 0.1 to 2.5 each , c = 0.1 to 2.5 and d = 0.05 to 0.6.

The present invention is further described with reference to the figures:

Fig. 1 to Fig. 6: ESCA spectra of various coated heat exchangers.

Fig.l: heat exchanger coated with i _t QOI, ICQ, ₅ F _0, 0 ₁

Fig. 2: Heat exchanger coated with TiNi, 0 ° l, _l ^c ₀ , 5 ^F 0, 1

Fig. 3: Heat exchanger coated with TiNi, 0 ° 1, l ^c o, 5 ^F o, 15

Fig. 4: Heat exchanger coated with iN, 0O1, l ^ o, 5 o, 3

Fig. 5: Heat exchanger coated with TiNi, 0 ° l, l ^c 0, 5 ^F o, 4 Fig. 6: Heat exchanger coated with OK, ₄ C ₀ , ₅ F ₀ , ₅

Fig. 7: Thermal conductivity

In a test arrangement, two heat exchangers were installed in a moist air still. One consisted of conventional PP material (prior art), the other coated with the coating according to the invention, TiNo, ₂ ^ ₁ , i ^c ₀ , 3. At a working temperature of 95 ° C, the graphic shows a 40-fold thermal conductivity between the evaporator and the cooling water. This value is the limiting guide value in today's systems.

8: wettability of heat exchanger wall coatings according to the invention for different designs of the surface a) 105 ° contact angle of a surface made of TiNi, ₀ ° _l , ₁ and a high porosity (40% empty spaces), b) 60 ° contact angle of a surface made of TiNi, ₀ ° ₁ , ₁ and a medium porosity (22% empty spaces), c) 8 ° contact angle of a surface made of iNi ₀ ° _l , ₁ and a low porosity (3% empty spaces).

Fig. 9: Schematic representation of a humid still

Fig. 10: Thermal conductivity of a coated heat exchanger used in an air conditioning system: The graphic shows the quotients of the thermal conductivity of various coated heat exchangers for an uncoated heat exchanger. The operating point of the air conditioning system is the cooling and dehumidification of air with 28 ° C, 95% air humidity on the inlet side and 18 ° C, 20% air humidity on the outlet side. The coating consists of: a) TiNi, ₀ O ₁ , ₁ b) TiNi, ₀ Oι, ιC _0f 5 0, 01 C) TiNi, 0θι, ιC ₀ , 5 ^F 0, ₁ d) TiNi, ₀ Oι, ιC ₀ , 5 ^F 0, 15 e) ^' TiNι, ₀ Oι, ιC ₀ , ₅ ^F 0, ₃ f) TiNi, ₀ Oι, ιC ₀ , _{5 0} , ₄ Fig. 11: Cons drawing of the coating system

The invention is further described on the basis of the examples.

EXAMPLES

The heat exchangers are manufactured as follows: 0.3mm thick copper foils are coated in a vacuum coating chamber. Here titanium is evaporated by means of electron beam evaporation and N ₂ , O ₂ , CH ₄ , CO ₂ and fluorine are fed into the vacuum chamber. By controlling the composition of the gas supplied, the chemical composition of the coating can be controlled. The titanium and the gases condense to a solid coating on the copper strip. In a subsequent step, the copper strip is cut to the size of the heat exchanger. Two of these blanks are placed on top of each other with the coated side facing outwards. Before that, solder and a tube are inserted between the plates. The almost finished heat exchanger is soldered in a soldering oven.

The following heat exchangers were manufactured:

In a vacuum chamber (Fig. 11a, b), the tape to be coated runs 40 ± 5cm over the electron beam evaporators, in which titanium, zirconium and hafnium are evaporated.

a) Belt speed: 45 + 5mm / s evaporator rate: 50 + 10nm / s material: titanium

Substrate temperature (temperature of the belt): 350 ± 30 ° C total gas pressure: 10 hPa

Gases supplied: N ₂ , O ₂ in the ratio N ₂ / θ ₂ = 1000 This results in a coating with TiNi ₀ O ₁ , ₁ •

b) Belt speed: 45 ± 5mm / s Evaporation rate: 50 ± 10nm / s Material: titanium

Substrate temperature (temperature of the belt): 350 ± 30 ° C total gas pressure: 10 ^" hPa Gases supplied: N ₂ , CO ₂ , F in the ratio N ₂ / CO ₂ / F:

1000/50 / 0.1

This results in a coating with iNi, _θ ° i, _l Co, ₅ ^F _θ , _θl -

c) Belt speed: 45 ± 5mm / s Evaporation rate: 50 + 10nm / s Material: titanium

Substrate temperature (temperature of the belt): 350 + 30 ° C

Total gas pressure: 10 hPa

Gases supplied: N ₂ , C0, F in the ratio N ₂ / CO ₂ / F:

1000/50/1

This results in a coating with ii, ₀ ° _l , _l ^c o, ₅ ^F o, ₁ •

d) Belt speed: 45 ± 5mm / s Evaporation rate: 50 + 10nm / s Material: titanium

Substrate temperature (temperature of the belt): 350 + 30 ° C

Total gas pressure: 10 hPa

Gases supplied: N ₂ , C0 ₂ , F in the ratio N ₂ / C0 ₂ / F =

1000/50 / 0.15

This results in a coating with iNi, ₀ ° _l , _l ^c ₀ , ₅ ^F _{0 15} •

e) Belt speed: 45 ± 5mm / s Evaporation rate: 50 ± 10nm / s Material: titanium

Substrate temperature (temperature of the belt): 350 ± 30 ° C

Total gas pressure: 10 hPa

Gases supplied: N ₂ , C0 ₂ , F in the ratio N ₂ / C0 / F =

1000/50 / 0.35

This results in a coating with TiNi, ₀ ° _l , i ^c ₀ , ₅ ^F ₀ , ₃ •

f) Belt speed: 45 + 5mm / s Evaporation rate: 50 ± 10nm / s Material: titanium

Substrate temperature (temperature of the belt): 350 ± 30 ° C

Total gas pressure: 10 hPa

Gases supplied: N ₂ , C0 ₂ , F in the ratio N ₂ / C0 ₂ / F =

1000/50 / 0.5

This results in a coating with iNi, ₀ ° ₁ , _l ^c ₀ , ₅ ^F ₀ , ₄ ■ ) Belt speed: 45 ± 5mm / s Evaporation rate: 50 ± 10nm / s

Material: titanium, zirconium in a ratio of 1: 0.1 substrate temperature (temperature of the strip): 350 ± 30 ° C total gas pressure: 10 ^" hPa

Gases supplied: N, O ₂ in the ratio N / 0 = 1000 This results in a coating with TiZrg, ₁ N ₁ , ₀ O ₁ , ₁ •

Heat exchangers with the coatings a-f are measured in FIG. 10.

Claims

claims 1. Heat exchanger device with a surface-coated wall that separates medium 1 from medium 2, the surface of the wall being at least partially coated with a thin layer that contains at least one compound of the elements titanium, zirconium and / or hafnium and / or alloys thereof with nitrogen and / or oxygen and / or carbon and / or fluorine. 2. Heat exchanger device according to claim 1, wherein the compound has the chemical formula Ti _x ZryHf _z ^N a ° b ^c c (with x, y, z = 0 to 1 in each case; a, b, c = 0 to 2.5, with the proviso that x + y + z = 1 and a + b + c> 0). 3. Heat exchanger device according to claim 1 or 2, wherein the compound has the chemical formula Ti _x Zr _y Hf ^^ 0 ^ 0, -. (with x, y, z = 0 to 1 each; a, b, c = 0 to 2 each, with the proviso that x + y + z = 1 and a + b + c = 0.02 to 2.0 ) Has. 4. The heat exchanger device according to claim 1, wherein the compound has the chemical formula Ti _x Zr _y Hf _za O; _b C _c F _d (with x, y, z = 0 to 1 each; a, b = 0 to 2 each, c = 0.05 to 2 and d = 0.01 to 2 with the proviso x, y, z = l, a, b, c = 0.02 to 2.0 and d / c = 0.05 to 2.05). 5. Heat exchanger device according to claim 4, wherein the compound contains CF and / or CF2 groups which in the ESCA spectrum to maxima at 290 ± 1 eV (caused by CF groups) or 293 + 1 eV (caused by CF2 ~ Groups). 6. Heat exchanger device according to one of claims 1 to 5, wherein the heat exchanger wall consists of a metal such as copper, aluminum, nickel, chromium, titanium, vanadium, niobium, iron or mixtures thereof or their alloys. 7. Heat exchanger device according to one of claims 1 to 5, wherein the heat exchanger wall made of plastic preferably polypropylene, polyester, polyamide, polyurethane, polyethylene, polytetrafluoroethylene. 8. Heat exchanger device, wherein the thin layer of the connection on the heat exchanger wall is 20 nm to 2 mm thick. 9. A method for producing the thin layer on the heat exchanger wall of the heat exchanger device according to one of claims 1 to 8, wherein the heat exchanger wall to be coated is introduced partially or wholly in a vacuum coating system, in which titanium, zirconium and / or hafnium is evaporated by means of electron beam evaporation and by means of "mass flow controler" the elements nitrogen, oxygen, carbon and / or fluorine are added in gaseous form. 10. The device for carrying out the method according to claim 9, characterized in that in the cover of a cylindrical vacuum chamber a support tube is attached to which a winding mechanism with at least two deflecting rollers, a unwinding and a winding roller is fastened, the vacuum chamber with electron beam guns and gas flow controllers ( mass flow controler). 11. Use of the heat exchanger device according to one of claims 1 to 8 in a humid still.