JP2023165503A - Aluminum fin material and heat exchanger - Google Patents

Abstract

To provide an aluminum fin material that has anti-frosting property, and to provide a heat exchanger including the aluminum fin material.SOLUTION: An aluminum fin material includes: an aluminum base material; a porous film provided at a surface of the aluminum base material; a water-repellent film provided at a surface of the porous film; and a lubrication oil layer provided at a surface of the water-repellent film. A heat exchanger includes the aluminum fin material.SELECTED DRAWING: Figure 1

Description

The present invention relates to an aluminum fin material and a heat exchanger.

Aluminum fin material is used in heat exchangers.
For example, Patent Document 1 discloses that the aluminum plate includes an aluminum plate, a corrosion-resistant film layer formed on the surface of the aluminum plate, and a hydrophilic film layer formed on the surface of the corrosion-resistant film layer, and has excellent hydrophilicity and stain resistance. An aluminum fin material that exhibits the following is described.
Note that Patent Document 2 discloses that an aluminum oxide film is provided on the surface of an aluminum member having a hierarchical structure consisting of an aluminum oxide film having hierarchical etching pits and nanopores present on the surface of the etching pits, and that the aluminum oxide film contains fluorine. An aluminum composite material used to suppress snow accumulation, which has a monomolecular layer of an organic phosphoric acid compound and a coating layer of fluorine-containing oil on top of this monomolecular layer, can be used to prevent the surface of aluminum wires of overhead power transmission lines from being damaged. It is described that it makes snow accretion.

JP 2021-116993 Publication JP 2019-85597 Publication

Aluminum fins for heat exchangers such as room air conditioners are placed one on top of the other at intervals of 1 to 2 mm, and play the role of exchanging heat with the air flowing between the fins. In addition, if condensed water adhering to the fin surface forms bridges between the fins and causes clogging, ventilation resistance increases and heat exchange efficiency decreases, so in order to prevent clogging, the aluminum fin surface is Generally, it is subjected to hydrophilic treatment. However, since dew condensation water easily wets and spreads on a hydrophilic surface, there is a problem in that frost tends to form on the surface and heat exchange efficiency decreases. In particular, frost formation during operation of heat exchangers in winter is a serious issue, and an aluminum fin material with excellent frost resistance (capable of delaying frost formation and easy defrosting) is required.
A water-repellent surface has the effect of delaying frost formation compared to a hydrophilic surface, so water-repellent treatment of the aluminum fin surface is effective in preventing frost formation, but the water-repellent surface developed by the uneven structure Since dew condensation water tends to be pinned to the surface, there are problems such as difficulty in water droplets falling off after defrosting operation.
Accordingly, the present invention provides an aluminum fin material that is water repellent, has a very smooth water-sliding surface coated with lubricating oil, and has excellent frost retardation effects and water drop removal properties.

An object of the present invention is to provide an aluminum fin material with excellent frost resistance, and a heat exchanger containing the aluminum fin material.

The present inventors have discovered that the above problem can be solved by the following configuration.

(1)
aluminum base material,
a porous membrane provided on the surface of the aluminum base material;
a water-repellent membrane provided on the surface of the porous membrane;
a lubricating oil layer provided on the surface of the water-repellent film;
Including aluminum fin material.
(2)
The aluminum fin material according to (1), wherein the porous film is an anodic oxide film.
(3)
The aluminum fin material according to (1) or (2), wherein the water-repellent film contains a fluorine-containing compound.
(4)
The aluminum fin material according to any one of (1) to (3), wherein the lubricating oil layer contains a fluorine-containing compound.
(5)
A heat exchanger comprising the aluminum fin material according to any one of (1) to (4).

According to the present invention, it is possible to provide an aluminum fin material with excellent frost resistance, and a heat exchanger containing the aluminum fin material.

FIG. 1 is a schematic diagram showing an example of an aluminum fin material of the present invention. It is a photograph of the frosting and defrosting test results of each sample. These are photographs of the results of repeated frosting and defrosting tests for each sample. This is a photograph of the results of measuring the mass of water droplets remaining on the surface of each sample. It is a photograph showing the size of water droplets remaining on the surface of each sample.

The present invention will be explained below. Each structure and combination thereof in the following embodiments are examples, and the present invention is not limited by the embodiments.
In the present specification, "~" is used to include the numerical values described before and after it as a lower limit value and an upper limit value.

[Aluminum fin material]
The aluminum fin material of the present invention comprises an aluminum base material, a porous membrane provided on the surface of the aluminum base material, a water-repellent film provided on the surface of the porous film, and a water-repellent film provided on the surface of the water-repellent film. It is an aluminum fin material containing a lubricating oil layer.
The surface of the aluminum fin material of the present invention is preferably SLIPS (Slippery Liquid Infused Porous Surface).
In the present invention, frost resistance is imparted by making the surface of the aluminum fin material water-smooth. Since the surface of the aluminum fin material of the present invention has excellent water sliding properties, even if water droplets that cause frost adhere to the surface, they easily fall off, and the aluminum fin material has excellent frost resistance.

FIG. 1 is a schematic diagram showing an example of the aluminum fin material of the present invention.
The aluminum fin material 10 in FIG. and a lubricating oil layer 4 provided on the surface of 3.

(aluminum base material)
Aluminum used for the aluminum base material is not particularly limited, but examples thereof include 1000 series aluminum defined in JIS H 4000:2014, and specifically aluminum with alloy numbers 1050, 1070, and 1200 is preferable. Moreover, in the aluminum plate manufacturing process, it is most preferable to use aluminum that has been subjected to a temper annealing process. When an annealed aluminum plate is used, the water repellency (water contact angle) after forming the water repellent film can be 150° or more. On the other hand, an aluminum plate that has not been annealed tends to have a water contact angle of about 140°. The porosity of the porous membrane is largely involved in the water repellency of the surface after the formation of the water-repellent membrane, and it is thought that annealing can impart even better porosity. When the anodized surface of an annealed aluminum plate is used as an oil retaining layer, the lubricating oil retaining power becomes extremely high, so that the performance of SLIPS is fully exhibited.
The aluminum base material may be made of an alloy containing aluminum, but preferably contains 90% by mass or more of aluminum.
The thickness of the aluminum base material is not particularly limited, but may be, for example, 0.05 mm or more and 1 mm or less.

(porous membrane)
It is preferable that the porous membrane provided on the surface of the aluminum base material is in direct contact with the aluminum base material.
In the present invention, it is preferable to form a porous film by making the surface of the aluminum base material itself porous, for example, by chemically or physically roughening the surface of the aluminum base material. Preferably, it is formed by anodic oxidation or etching, and most preferably an anodic oxide film (aluminum oxide film) formed by anodic oxidation. The anodizing treatment can be performed by a known method.
The thickness of the porous membrane is not particularly limited, but may be, for example, 0.1 μm or more and 100 μm or less.
The size of the pores included in the porous membrane is not particularly limited, but may be, for example, 1 nm or more and 200 nm or less.

(Water repellent film)
The water-repellent film provided on the surface of the porous membrane is preferably in direct contact with the porous membrane.
A water-repellent membrane can be obtained by treating a porous membrane with a compound exhibiting water repellency (preferably a fluorine-containing compound). Specifically, a water-repellent film is produced by immersing an aluminum base material containing a porous membrane in a solution containing a fluorine-containing compound, or by applying a solution containing a fluorine-containing compound onto a porous membrane (for example, by spin coating). Alternatively, it can be obtained by vapor-depositing a fluorine-containing compound onto a porous membrane. By subjecting the porous membrane to water-repellent treatment in this manner, the affinity with the lubricating oil layer can be increased and the lubricating oil layer can be retained.
The water-repellent film preferably contains a fluorine-containing compound. Examples of the fluorine-containing compound include fluorine-containing organic phosphoric acid compounds and fluorine-based silane coupling agents. Examples of the fluorine-containing organic phosphoric acid compound include FPE-50 (AGC Seimi Chemical Co., Ltd.). Examples of the fluorine-based silane coupling agent include triethoxy-1H,1H,2H,2H-heptadecafluorodecylsilane.
The thickness of the water-repellent film is preferably at the level of a monomolecular film made of a fluorine-containing compound. If an excessive amount of the fluorine-containing compound is adsorbed, the porous membrane may disappear, so it is preferable to remove the excess amount by washing the surface with an appropriate solvent after the water repellent treatment.

(Lubricating oil layer)
The lubricating oil layer provided on the surface of the water-repellent film is preferably in direct contact with the water-repellent film. As mentioned above, the lubricating oil layer is preferably held on a porous membrane that has been treated to be water repellent (having a water repellent film provided on its surface). Specifically, the lubricating oil layer can be obtained by dipping an aluminum base material containing a porous film on which a water-repellent film is formed in lubricating oil, or by applying lubricating oil on the water-repellent film. can.
The lubricating oil layer preferably contains a fluorine-containing compound. Examples of the fluorine-containing compound include perfluoropolyether and fluoroalkylamine. For example, GPL oil 101 (Krytox) can be used.
The lubricating oil layer can also contain additives such as ultraviolet absorbers and antioxidants.
The content (retained amount) of the lubricating oil layer is not particularly limited, but may be, for example, 0.1 to 10 mg/cm ² as a mass per unit area of the aluminum fin material of the present invention.

Since the sliding performance of SLIPS is expressed by the fluidity of the lubricating oil held in the surface layer, it is preferable to use an oil that has fluidity even in a low-temperature environment. There are many types of oils that are generally used as lubricating oils, but among them, fluorine-based lubricating oils are preferred because they exhibit fluidity in a wide temperature range down to extremely low temperatures. Examples of the fluorine-based lubricating oil include perfluoropolyether and fluoroalkylamine. Further, even if the frosted surface temperature is higher than the flow temperature of the lubricating oil, the viscosity of the oil increases as the temperature decreases, so the lower the flow temperature is, the more suitable it is. For example, in the GPL oil series (Krytox), it can be said that the preferred order is 100, 101>102>103>104>105, and 106>107.

[Heat exchanger]
The heat exchanger of the present invention includes the aluminum fin material described above.
In addition to the above-mentioned aluminum fin material, the heat exchanger of the present invention can include parts known as parts included in a heat exchanger (for example, heat exchanger tubes, etc.).

The present invention will be explained in more detail below based on Examples. The materials, usage amounts, proportions, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention.

<Example 1>
As the aluminum base material, a 0.5 mm thick aluminum plate made of A1050 specified in JIS H 4000:2014 and subjected to a temper annealing process was used.
The above aluminum plate is anodized in a 0.3 mol/L sulfuric acid aqueous solution at 22 V for 35 minutes, and then sealed in a dilute chromate solution to anodize the surface of the aluminum base material. A porous membrane consisting of a film was formed. The porous membrane had many pores with a size of about 100 nm.
Next, the aluminum base material having the porous membrane was placed in a simple autoclave together with triethoxy-1H, 1H, 2H, 2H-heptadecafluorodecylsilane, and the temperature was 80°C. A water-repellent film was formed on the porous film by vapor deposition for about 16 hours.
Furthermore, a lubricating oil layer was maintained by applying GPL oil 101, which is a lubricating oil, to the water-repellent film, and an excess amount of oil was removed by air spray to form a SLIPS surface. The amount of lubricating oil retained was approximately 0.8 mg/cm ² .
In this way, the sample of Example 1 was produced.

<Comparative example 1>
An A1050 aluminum substrate with a thickness of 0.5 mm was used as Comparative Example 1.

(Measurement of water contact angle)
The water contact angle of the prepared sample surface was measured using an automatic contact angle meter DMS-601 (Kyowa Interface Science Co., Ltd.). The amount of water droplets during measurement was 2 μL.

(Measurement of sliding angle)
The sliding angle for a 10 μL water droplet was measured using the same device as used for measuring the water contact angle.
When the sample surface is gradually tilted from a horizontal state, the angle of inclination at which water droplets begin to slide down is defined as the sliding angle.If the sample surface is tilted up to the vertical position and the water droplets remain inside the measurement camera, the sliding angle is defined as the sliding angle. The result was marked as "x".

The results are shown in Table 1 below.

(Frosting/defrosting test)
The samples of Example 1 and Comparative Example 1 were fixed to the surface of a cooling device installed vertically in a constant humidity and temperature chamber. Moreover, each sample used had a size of 3×6 cm. The temperature and humidity chamber was set at 10° C. and relative humidity at 80% RH.
After placing each sample in a cooling device preset at 25° C., the surface of each sample was brought to −10° C. using the cooling device, and the temperature of the sample surface was maintained at −10° C. for 20 minutes. Here, when the sample surface was visually observed and frost formation was evaluated, the time required for the sample to completely frost was approximately 15 minutes for Example 1 and approximately 7 minutes for Comparative Example 1.
Furthermore, in Example 1, dew condensation water was observed to slide down on the surface.
Subsequently, the temperature of the sample surface was increased from -10°C to 1°C at a rate of 2°C/min, and the temperature of the sample surface was maintained at 1°C for 3 minutes. Here, when the sample surface was visually observed and the defrosting was evaluated, it was found that in Example 1, relatively large water droplets were removed from the surface by sliding down, whereas in Comparative Example 1, most of the water droplets were removed from the surface. The result was that it remained. FIG. 2 shows photographs of the frosting and defrosting test results of Example 1 and Comparative Example 1. Each photo is at a different temperature and time. In each photograph, the left side is the sample of Example 1, and the right side is the sample of Comparative Example 1.

(Durability test)
In order to confirm the durability of Example 1, frosting and defrosting tests were repeated. Immediately after the above-described test, the sample surface temperature was subsequently cooled to -10°C, and the sample surface temperature was maintained at -10°C for 20 minutes. Here, when the sample surface was visually observed and frost formation was evaluated, it was found that the time it took for the sample to become completely frosted was about 13 minutes for Example 1 and about 4 minutes for Comparative Example 1. This resulted in the time difference becoming even wider. This is considered to be because in Comparative Example 1, the amount of water droplets adhering to the surface after defrosting was larger than in Example 1, and therefore the time until frost formation was significantly accelerated. On the other hand, in Example 1, most of the water droplets were removed during the defrosting stage, so it is considered that the time until frost formation was not significantly accelerated. Therefore, when repeated frosting/defrosting tests were conducted, it was found that the frosting retarding effect of the aluminum fin material with the sliding surface (SLIPS) of the present invention was further exhibited.
Next, when the temperature of the sample surface was raised from -10°C to 1°C using the same method as above, it was found that in Comparative Example 1, most of the water droplets remained on the surface, similar to the first defrosting test. In contrast, in Example 1, most of the water droplets were removed by sliding down.
Further, when frosting and defrosting were repeated up to 5 times, it was confirmed in Example 1 that water droplets slid down to the same extent after the 5th defrosting as in the 1st time. FIG. 3 shows photographs of the results of repeated frosting and defrosting tests for Example 1 and Comparative Example 1. In addition, when the sliding angle of the surface after the test was measured, it was found to be 1 to 5 degrees, which is the same level of water sliding property as before the test, indicating that it has durability against repeated frosting and defrosting.

(Measurement of mass of attached water droplets)
In order to measure the mass of water droplets remaining on the surface of each sample, three samples each of Example 1 and Comparative Example 1 were used, and after sufficiently frosting the surface of each sample in the same manner as above, Defrosted. The mass of the remaining water droplets was 0.033 g on average in Example 1, whereas it was 0.114 g on average in Comparative Example 1, resulting in a reduction in the amount of residual water droplets in Example 1 by about 70%. Figure 4 shows photographs of each sample used to measure the mass of water droplets remaining on the sample surface.
Furthermore, the height of water droplets remaining on the surface of each sample was evaluated. Since it was difficult to visually measure the height of the water droplet attached to the sample surface, it was calculated from the radius of the attached water droplet and the water contact angle of each sample surface using the following formula.

Here, h is the height of the water droplet, r is the radius of the water droplet, and θ is the contact angle of the water droplet on the sample surface. FIG. 5 shows photographs showing the size of water droplets remaining on the surface of each sample. The diameter of the water droplets attached to Example 1 was about 1.5 mm at maximum, and the height was about 1.1 mm. On the other hand, the maximum diameter of the water droplets that adhered to Comparative Example 1 was approximately 4.0 mm, and the height was approximately 2.1 mm. It was found that it was reduced by half. Therefore, when the aluminum fin material with the sliding surface (SLIPS) of the present invention is installed in a heat exchanger with a fin pitch of 2 mm, it prevents clogging between the fins due to adhesion of water droplets and reduces ventilation resistance. It is expected to have a suppressive effect. Furthermore, since the aluminum fin material of the present invention has excellent water repellency, it is easy to remove attached water that causes rust, so it can also be expected to have a rust-preventing effect.

From the above, it was found that the sample of Example 1 had excellent frost resistance. Therefore, it can be said that the aluminum fin material of the present invention has excellent frost resistance, can delay frost formation, and can be easily defrosted when applied to a heat exchanger.

1 Aluminum base material 2 Porous membrane 3 Water repellent membrane 4 Lubricating oil layer 10 Aluminum fin material

Claims (5)

aluminum base material,
a porous membrane provided on the surface of the aluminum base material;
a water-repellent membrane provided on the surface of the porous membrane;
a lubricating oil layer provided on the surface of the water-repellent film;
Including aluminum fin material. The aluminum fin material according to claim 1, wherein the porous film is an anodic oxide film. The aluminum fin material according to claim 1, wherein the water-repellent film contains a fluorine-containing compound. The aluminum fin material according to claim 1, wherein the lubricating oil layer contains a fluorine-containing compound. A heat exchanger comprising the aluminum fin material according to any one of claims 1 to 4.

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