JPH11325792A - Heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat exchanger having excellent corrosion resistance for an ant's nest-like corrosion by engaging a tube with a fin, and interposing a metal zinc-containing coating film or a zinc-plating layer having a specified thickness between at least engaging interfaces of the engaging part. SOLUTION: The heat exchanger is constituted by inserting a tube 1 via fin collars 3 of laminated fins 2, and engaging the tube 1 with the fins 2. In this case, a metal zinc-containing coating film or a zinc-plating layer 4 having a mean thickness of 1 to 50 μm is interposed between engaging interfaces of the tube 1 with the fins 2. The fin 2 is previously covered on its overall surface with a hydrophilic film 5. Thus, the film 4 containing a metal zinc of a substance having a larger ionization tendency than that of a copper is formed in a gap (engaging interface) in the case of enlarging and connecting the tube 1 to the fin 2, thereby preferentially dissolving the zinc in an acid adhering water to change the water to an alkali side and make it harmless.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a heat exchanger.

[0002]

2. Description of the Related Art Heat exchangers are used for air conditioner indoor and outdoor units.
A cross fin type, which is used for an indoor unit of an air conditioner using cold and hot water, and in which a heat transfer tube made of copper or a copper alloy is expanded and joined to a fin usually made of aluminum or an aluminum alloy, is mainly used.

In such a heat exchanger, for example, a fin is formed by pressing an aluminum plate to form a collar portion (hereinafter referred to as a “fin collar”) through which a heat transfer tube passes.
After laminating a plurality of the fins so that the positions of the fin collars are aligned with each other, the heat transfer tubes are inserted into the fin collars, and the heat transfer tubes are further expanded to join them. By the way, when the heat exchanger acts as an evaporator like the indoor unit during the cooling operation or the outdoor unit during the heating operation, the fin surface temperature of the heat exchanger is lower than the surrounding air. As a result, the dew point on the fin surface decreases, and the water vapor in the atmosphere becomes dew water and adheres to the fin. Also, water droplets may adhere for some reason.

[0004] However, dew condensation and water droplets (hereinafter referred to as "adhered water") block the gaps between the fins to form bridges, increase ventilation resistance and noise, and cause a decrease in cooling and heating capacity.

[0005] In order to solve the above-mentioned problem, the fin surface is coated with a hydrophilic film so that the adhered water flows down along the hydrophilic film of the fin so that the gap between the fins is not closed. Is adopted. Conventionally, various materials having a water glass, a polar group or the like have been used as a material of the hydrophilic film having such a function. These films are composed of hydrophilic groups (-OH groups,> C
= O group, -NH ₂ group, -COOH group, etc.) are exposed, the contact angle between the adhered water and the film surface becomes smaller, and the adhered water flows down the surface as described above. It is easier to go.

[0006]

However, when the fin surface is coated with the hydrophilic film as described above, the following problems are likely to occur. In other words, the fin collar and the heat transfer tube do not completely adhere to each other even by the expansion joint, and a gap is formed between the two. When the fin and the heat transfer tube surface are coated with the hydrophilic film, the attached water can easily enter the gap. . If the adhering water contains a corrosive medium, local ant-nest corrosion occurs on the surface of the heat transfer tube in the gap.

In particular, recently, there has been a tendency to reduce the distance between the fins in order to reduce the size of the heat exchanger. In many cases, the heat transfer tubes are completely covered by the laminated fin collars and are not exposed to the outside. The surface of the heat transfer tube is exposed to the adhering water staying in the gap between the fin collar and the heat transfer tube for a long time.

On the other hand, in the part where the heat transfer tube is exposed and the fin is not mounted, the attached water easily evaporates, so that ant-nest corrosion hardly occurs.

By the way, ant-nest-like corrosion is caused by the dissolution of copper as a component of a heat transfer tube in an organic acid (a carboxylic acid such as formic acid or acetic acid). Since formaldehyde and alcohol generated from the adhesive for plywood and cloth are generated even when oxidized, the indoor unit of the air conditioner is often used when exposed to an environment containing a corrosive medium.

As a technique for preventing corrosion of a copper pipe, a technique of forming a copper-zinc alloy on the surface of the copper pipe has been proposed (see Japanese Patent Application Laid-Open No. 62-1856).

However, ant-nest corrosion is corrosion in a severe environment in which a copper tube is exposed to an acidic solution for a long period of time, and is also a kind of crevice corrosion. It was difficult to effectively prevent nest corrosion.

The ant nest-like corrosion progresses at an extremely high speed, and corrodes inside the heat transfer tube in a short period of time, causing leakage of the refrigerant and losing the function of the air conditioner. I was From such a thing,
It has been strongly desired to develop a heat exchanger having excellent corrosion resistance against ant-nest corrosion.

An object of the present invention is to provide a heat exchanger which can solve the above-mentioned problems in a heat exchanger and has excellent corrosion resistance against ant-nest corrosion.

[0014]

In order to achieve the above object, according to the present invention, a tube and a fin body are fitted, and at least a fitting interface at a fitting portion between the tube and the fin body is provided. The present invention provides a heat exchanger characterized in that a metal zinc-containing coating film or a zinc plating layer having an average thickness of 0.1 to 50 μm is interposed. Further, there is provided a heat exchanger in which the tube is made of copper or a copper alloy, and the fin body is made of aluminum or an aluminum alloy.

[0015]

FIG. 1 is a sectional view showing an example of a basic configuration of a heat exchanger according to the present invention. In the figure, the heat exchanger is constituted by inserting the tube 1 through the fin collar 3 of the laminated fin 2 and fitting the tube 1 to the fin 2. Further, a metal-zinc-containing coating film 4 or a galvanized layer 4 is interposed at the fitting interface. The entire surface of the fin body 2 is previously coated with the hydrophilic film 5.

The material of the tube body and the fin body constituting the heat exchanger may be any material as long as it has a high thermal conductivity and is easy to process. For example, copper, copper alloy, nickel, nickel alloy, In addition to steel, stainless steel, etc., aluminum or aluminum alloy that forms a passivation on the surface can also be used. Particularly, copper, copper alloy, aluminum and aluminum alloy are suitable. Further, it is preferable to use copper or a copper alloy for the tubular body and to use copper, copper alloy, aluminum or an aluminum alloy, particularly aluminum or an aluminum alloy for the fin body.

When copper or a copper alloy is used for the tube, it is preferable that the tube be phosphorus-deoxidized copper in order to prevent hydrogen embrittlement during brazing of the tube.

Next, the metal zinc-containing coating film or galvanized layer of the present invention will be described in detail.

Ant nest-like corrosion of the heat transfer tube proceeds as described above, as copper contained in the components of the heat transfer tube dissolves in the attached water containing the organic acid.

Therefore, according to the present invention, the gap (fitting interface) generated when the tubular body is joined to the fin collar by pipe expansion contains metallic zinc itself or metallic zinc, which is a substance having a higher ionization tendency than copper. By forming a coating film and preferentially dissolving zinc in the acidic water, the water is changed to the alkaline side to render it harmless. As a result, copper elution is suppressed and the ant nest of the tube is formed. The technical idea is to effectively prevent state corrosion, which is different from simple electrolytic protection by dissolution of zinc. Here, the change of the attached water to the alkaline side is due to the cathode reaction accompanying the dissolution of the metallic zinc in the attached water.

Therefore, the present invention relates to Japanese Patent Application Laid-Open No. 62-1856.
Unlike conventional technologies such as No. 2, metal zinc, especially metal zinc powder, is not alloyed with the underlying copper, but remains in a state of a highly reactive metal. The present invention is based on a novel technical idea that promotes the accompanying alkalizing reaction and effectively prevents ant-nest corrosion.

This metal zinc-containing coating film or galvanized layer may be formed by electrogalvanizing or hot-dip galvanizing heat transfer tubes or fins. However, a resin or paint in which metal zinc powder is dispersed is applied. Alternatively, it may be formed. In particular, in terms of simplifying the equipment and preventing the plating solution and the like from entering the inside of the tube,
It is preferable to perform the latter coating. In addition, when performing the coating, even if the hydrophilic film is coated on the object, it is not necessary to remove the hydrophilic film.Moreover, since the highly reactive zinc metal powder is appropriately dispersed in the coating film, It is also desirable in terms of accelerating the dissolution of zinc in the attached water. As such a resin or paint, for example, a paint using metallic zinc powder as a pigment, which is so-called zinc-rich paint, can be used. In addition, a material obtained by dispersing metallic zinc powder in an epoxy resin can also be preferably used.

The average thickness of the coating film or the plating layer is 0.1.
It is set in the range of 1 to 50 μm. When the thickness is less than 0.1 μm, the above-described anticorrosion effect due to dissolution of zinc in the attached water comes to disappear in a short time. Since it cannot be performed, it is wasteful as a whole, is uneconomical, causes an increase in cost, and is not preferable in terms of heat transfer performance.

The average thickness means an average value of a portion where the coating film or the plating layer exists, and as described later, the coating film or the plating layer does not exist on a part of the fitting interface between the fin collar and the heat transfer tube. If not, that part was excluded from the calculation of the average thickness.

The thickness of the coating film or the galvanized layer can be adjusted as follows. For example, in the case of a coating film, in addition to changing the number of coatings, it is only necessary to adjust the resin concentration by changing the mixing ratio of the resin or the paint to the solvent. In plating, the immersion time and the number of times of immersion may be changed.

Further, the content of metallic zinc powder in the coating film is as follows:
It is preferably at least 60% by weight in a dried state of the coating film.
This is because the higher the content of the metal zinc powder, the greater the amount of zinc dissolved in the attached water, and the greater the anticorrosion effect due to the alkalinization of the attached water. Therefore, it is preferable to increase the content of the metallic zinc powder within a range that does not affect the film forming property. The upper limit of the content in a general coating film is about 95% by weight.
The size of the metallic zinc powder should not be too large in view of solubility and uniform dispersibility, and is usually preferably set to an average particle size of 10 μm or less.

The metal-zinc-containing coating film or the galvanized layer only needs to be interposed at a part of the fitting interface between the fin collar and the heat transfer tube, and need not necessarily be interposed on the entire surface. This is because the water adhering to the gap between the fin collar and the heat transfer tube exists not in the form of water droplets but in the form of a liquid film. This is because the dissolution reaction proceeds. Here, when the area where the coating film or the plating layer is interposed on the fitting interface is reduced, the area where the heat transfer tube and the fin are in direct contact increases as shown in FIGS. On the other hand, if the interposed area is increased, the corrosion resistance is further improved. Therefore, the area to be interposed may be appropriately determined in consideration of these characteristics. However, in order to maintain the anticorrosion effect due to dissolution of zinc, it is preferable that the interposed area is set to 30% or more of the total area of the fitting interface.

The coating film and the plating layer may be formed on either the tube or the fin before fitting. This is because a coating film or a plating layer is interposed at the fitting interface when the pipe expansion joining is performed. Further, a coating film or a plating layer may be formed on both the tube body and the fin body, and in this case, a further anticorrosion effect can be expected.

FIGS. 5 to 8 show examples in which a coating film or a plating layer is formed on a part of a tubular body or a fin body. 5 and 6, the outer surface of the tube is formed linearly and spirally in the axial direction, respectively. On the other hand, in FIG. 7, it is formed linearly in the axial direction of the inner surface of the fin collar, and in FIG. 8, it is formed cylindrically on the inner surface of the fin collar. In any case, the area of the coating film or the plating layer on the tubular body or the fin body may be adjusted in advance so that the area interposed after the fitting becomes 30% or more.

[0030]

EXAMPLES Examples 1 to 7 and Comparative Examples 1 to 3 Manufacture of tube and fin body (1) Fin body Aluminum strip coated with a silica-based hydrophilic film (JIS-A1200, 500 × 25 × 0.1 mm)
Was pressed to form 2 rows × 12 fin collars to obtain an aluminum fin body.

(2) Tube Heat transfer tube made of phosphorus-deoxidized copper without a hydrophilic film (JIS standard C1220T, outer diameter 7 × length 250 × wall thickness 0.3m)
m) was prepared.

2. Formation of Coating Film or Plating Layer on Tubular Body and Fin Body A coating film or a plating layer was formed on the surface of the tubular body and the inner surface of the fin collar under the conditions shown in Table 1.

(1) Formation of Coating Film Metallic zinc powder having an average particle diameter of 1 μm was mixed with an epoxy resin, and diluted with xylene to obtain a metal zinc-containing coating. This was applied to the inner surface of the fin collar or the surface of the tube, and then naturally dried to obtain a dried coating film. The coating was performed without removing the hydrophilic film on the inner surface of the fin collar.

The thickness of the coating film is changed by adjusting the mixing ratio of the resin and the solvent, and the film thickness is determined by using an eddy current type film thickness meter.
Three locations were measured per sample, and the average thickness was calculated.

When the coating was applied to the surface of the tubular body and a part of the inner surface of the fin collar, the coating area was adjusted as shown in FIGS. 5 and 7, respectively.

(2) Formation of plating layer A current density of 3 A / A was measured using a zinc plating solution (a zincate bath).
by changing the electrolysis time dm ² to form a galvanized layer of various thickness to the tube surface. The plating film thickness was measured at three locations per sample using an electrolytic plating thickness gauge, and the average thickness was calculated.

3. Assembly of heat exchanger sample The required number of aluminum fins were laminated with the fin collars aligned, a tube was inserted through the fin collars of the laminate, expanded by a mandrel, and the two were joined to heat. An exchanger (external dimensions 500 × 25 × 250 mm) was assembled. 4. Evaluation of heat exchanger samples The characteristics of each heat exchanger sample were evaluated according to the following specifications.

(1) Evaluation of Corrosion Resistance A 100% aqueous solution of 1% by volume formic acid was placed in a closed container having a content of 1 L.
into a 100 mL beaker so as not to come into direct contact with the liquid.
0 × 25 mm), and then placed in the closed container. Next, the atmosphere in the container was replaced with oxygen and kept at room temperature for 30 days. After the test, the heat transfer tube was separated from the heat exchanger sample and cut, and the maximum corrosion depth of the heat transfer tube at the cut surface near the fitting portion with the fin was measured by cross-sectional microscopic observation.

The smaller the value, the better the corrosion resistance.

(2) Evaluation of heat transfer characteristics For heat exchanger samples for which corrosion resistance has not been evaluated,
The air-side exchange heat during evaporation was measured under the following conditions.

(A) In-pipe refrigerant: R22 (b) Inlet air temperature (dry bulb temperature / wet bulb temperature): 27.0 ° C.
/19.0° C. (c) Wind speed: 1 m / s (d) Outlet refrigerant evaporation pressure: 5.4 kg / cm ² (e) Refrigerant temperature before expansion valve: 40.0 ° C. (f) Outlet refrigerant superheat degree: 5. 0 ° C. The measured value of a heat exchanger having neither a hydrophilic film nor a metal zinc-containing film or a galvanized layer was measured as 100.
Was evaluated as a relative value when

The larger the value, the better the heat transfer characteristics. From these facts, those with 95 or more were evaluated as good.

The results are shown in Table 1.

[0044]

[Table 1] The following is clear from Table 1.

(1) The heat exchanger of the present invention in which a coating film or a plating layer is interposed at the fitting interface between the tube and the fin collar,
Both corrosion resistance and heat transfer characteristics are good.

(2) As is clear from the comparison between the embodiment and the comparative example 1, in the case of the comparative example 1 in which no coating film or plating layer is interposed at the fitting interface, the corrosion resistance is higher than that of the embodiment. Has dropped significantly.

(3) As is clear from the comparison between the example and comparative examples 2 and 3, in the case of comparative example 2 in which the thickness of the plating layer is small, the corrosion resistance is greatly reduced as compared with the example, and the comparative example is thick. Example 3
In the case of, the effect of improving the corrosion resistance is saturated as compared with Example 6. From this, it is understood that the average thickness of the coating film or the plating layer should be set to 0.1 to 50 μm.

Examples 8 to 13 Tubes and fins were manufactured in the same manner as in Examples 1 to 7, and a heat exchanger sample was assembled by forming a coating film only on the tubes under the conditions shown in Table 2. Was. Then, the corrosion resistance and heat transfer characteristics of this heat exchanger sample were evaluated.

The results are shown in Table 2.

[0050]

[Table 2] The following is clear from Table 2.

(1) As apparent from a comparison between Example 8 and Examples 9 and 10, Examples 9 and 10
Corrosion resistance is further improved as compared with. For this reason, it is preferable that the zinc content in the dried coating film is 60% by weight or more.

(2) As is clear from comparison between Example 11 and Examples 12 and 13, the corrosion resistance of Examples 12 and 13 is further improved as compared with Example 11. For this reason, the coating film or the plating layer is set at 30% of the mating interface.
It can be seen that it is preferable to interpose the above-mentioned area.

[0053]

As is apparent from the above description, according to the present invention, at least a metal interface having an average thickness of 0.1 to 50 μm is provided at the fitting interface at the fitting portion between the heat exchanger tube and the fin body. Since the zinc-containing coating film or the galvanized layer is interposed, it is possible to provide a heat exchanger that has excellent corrosion resistance against ant-nest corrosion and does not impair heat transfer characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of a heat exchanger according to the present invention, which is cut in an axial direction of a tubular body.

FIG. 2 is a cross-sectional view illustrating a second embodiment of the heat exchanger according to the present invention, which is cut in an axial direction of a tubular body.

FIG. 3 is a cross-sectional view showing a third embodiment of the heat exchanger according to the present invention, which is cut in an axial direction of a tubular body.

FIG. 4 is a cross-sectional view showing a fourth embodiment of the heat exchanger according to the present invention, which is cut in a radial direction of a tubular body.

FIG. 5 is a partial cross-sectional perspective view showing an example in which a coating film or a plating layer is formed on a part of the surface of a tube constituting the heat exchanger of the present invention.

FIG. 6 is a partially sectional perspective view showing another example in which a coating film or a plating layer is formed on a part of the surface of a tube constituting the heat exchanger of the present invention.

FIG. 7 is a partial cross-sectional perspective view showing an example in which a coating film or a plating layer is formed on a part of an inner surface of a fin collar of a fin body constituting the heat exchanger of the present invention.

FIG. 8 is a partial cross-sectional perspective view showing another example in which a coating film or a plating layer is formed on a part of a fin collar inner surface of a fin body constituting the heat exchanger of the present invention.

[Description of Signs] 1 tube 2 fin body 1 fin color 3 metal zinc containing coating or galvanized layer 1 hydrophilic coating

Claims (4)

[Claims] A fin body is fitted with a tube, and at least a fitting interface at a fitting portion between the tube and the fin body has a metal zinc-containing coating film having an average thickness of 0.1 to 50 μm or A heat exchanger having a galvanized layer interposed. 2. The heat exchanger according to claim 1, wherein the metal zinc-containing coating contains 60% by weight or more of metal zinc powder in a dry state. 3. The heat exchanger according to claim 1, wherein the metal-zinc-containing coating film or the galvanized layer is interposed in an area of 30% or more of the fitting interface. 4. The heat exchanger according to claim 1, wherein the tube is made of copper or a copper alloy, and the fin body is made of aluminum or an aluminum alloy.