JPH1096599A - Outdoor heat exchanger unit and air conditioner using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an increase in a ventilating resistance due to freezing of condensate by setting a fractal dimension on a surface of an exchanger to a specific range in a region of a cell size in box counting method to a 1 micrometer or less, and forming a hydrophobic group on a surface of a heat exchanger. SOLUTION: The outdoor heat exchanger unit 101 comprises a heat exchanger in which a plurality of heat transfer tubes 102 are inserted in a plurality of fins 103, and fins 104. The fins 103 allow a hydrated oxide layer 106 to be formed on a surface of an aluminum plate 105, set a fractal dimension D on a surface of the exchanger to a range of 2<D<=3 in a region of 1μm or less of a cell size in a box counting method, and forms a hydrophobic group 107 on the surface of the exchanger. After a dirt on the surface of the exchanger is removed, the exchanger is washed. Then, a hydrated oxide film is formed on the surfaces of the fins 103. Thereafter, the exchanger is washed, dried, dipped in perfluoroalkane solution, and then dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an outdoor heat exchanger unit.

[0002]

2. Description of the Related Art When an air conditioner is operated for heating, the surface temperature of the heat exchanger of the outdoor heat exchanger unit falls below the dew point of the outside air, and water vapor contained in the outside air condenses on the surface of the heat exchanger of the outdoor heat exchanger unit. However, depending on the temperature conditions, there is a problem that the condensed water freezes and the ventilation resistance of the heat exchanger increases.

[0003] In order to solve this problem, a technique for preventing the adhesion of condensed water droplets by making the fin surface of the outdoor heat exchanger unit a water-repellent structure is disclosed in, for example, Japanese Patent Laid-Open No. 3-100182 (hereinafter referred to as Conventional Technique 1). JP-A-6-123575
(Hereinafter referred to as “prior art 2”).

[0004] Among them, in prior art 1, in order to form unevenness exposing hydroxyl groups on the aluminum surface, a hydrophilic treatment is performed with any of a boehmite coating, an alumite coating, and a silicate coating, and then a fluorine-containing silane compound is formed. Is disclosed. Further, it is disclosed that the hydrophilic treatment method having the best water repellency is a boehmite film, and its contact angle is 159 degrees.

[0005] Further, in prior art 2, micron-order irregularities are previously formed on the air-side heat transfer surface of the heat exchanger, and a siloxane-based monomolecular film made of a substance containing a chlorosilyl group is formed. It is disclosed that a chlorosilane-based surfactant containing a linear fluorocarbon group at the other end is chemically adsorbed to accumulate a monomolecular film, thereby suppressing frost formation on the air-side heat transfer surface. I have.

On the other hand, it has been conventionally known that even when the hydrophobic groups on the surface are the same, the contact angle of the liquid droplets differs depending on the presence or absence of surface irregularities.
No. pp. 788-792, 1995) describes the relationship between the super-water-repellent surface and the fractal structure as a theoretical basis, and forms a super-water-repellent surface by applying a substance having a hydrophobic group other than a fluorine compound to a flat surface. A method for doing so is disclosed. According to the theory disclosed herein, as the fractal dimension D of the hydrophobic surface increases, the contact angle increases compared to a smooth surface having the same hydrophobic group,
It is said to exhibit super water repellency.

[0007]

In the above prior art, the contact angle or frost resistance of a water droplet is used as a criterion for evaluating the surface of the water-repellent structure. Has a diameter of at least about 1 millimeter, and has insufficient water repellency against fine water droplets such as condensed water droplets.

An object of the present invention is to provide an outdoor heat exchanger unit which exhibits sufficient water repellency even for fine water droplets such as condensed water droplets and prevents an increase in ventilation resistance due to freezing of condensed water. .

Another object of the present invention is to provide a surface treatment method for a heat exchanger used in an outdoor heat exchanger unit, which exhibits sufficient water repellency even for fine water droplets such as condensed water droplets. .

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors prototyped a test piece obtained by subjecting aluminum to various surface treatments, and placed this test piece under the same conditions as the outdoor heat exchanger unit. An experiment was conducted in which water droplets were condensed on the surface of the test piece by installing the apparatus.

As a result, most of the condensed water droplets have a diameter of 500 μm or less in a test piece having a surface having irregularities in a wide range from nano-order to micron-order and exposing a hydrophobic group thereon. A phenomenon was found in which the droplets were separated from the surface almost vertically by combining with water droplets.

If the condensed water droplets on the surface of the heat exchanger come off spontaneously, there is no need to add an operation for removing the water droplets, and it is possible to prevent an increase in ventilation resistance.
The object of the present invention is solved by the following configuration in an outdoor heat exchanger unit including a heat exchanger and a fan for sending air to the heat exchanger.

(1) The fractal dimension D of the surface of the heat exchanger is the cell size in the box counting method.
2 <D ≦ 3 within a region of 1 μm or less, and a hydrophobic group is formed on the surface of the heat exchanger. (2) In (1), the hydrophobic group is a fluorine-containing organic compound.

(3) In (1) or (2), the fractal dimension D of the surface of the heat exchanger measured by an atomic force microscope is in a region where the cell size in the box counting method is 1 μm or less. 2 ≦ D ≦
3.0.

(4) 90% of the condensed water droplets present on the surface of the outdoor heat exchanger unit during operation under dew condensation conditions have a diameter of 500 micrometers or less.

(5) When the outdoor heat exchanger unit is operated under dew condensation conditions, condensed water droplets generated on the surface of the heat exchanger are separated from the surface of the heat exchanger. (6) When the outdoor heat exchanger unit is operated under the dew condensation condition, condensed water droplets generated on the surface of the heat exchanger unite with each other and simultaneously separate from the surface of the heat exchanger.

(7) In a heat exchanger in which a plurality of heat transfer tubes are inserted into a plurality of stacked fins, an electric insulating material is formed on a surface of the heat transfer tube that comes into contact with the fins. Another object of the present invention is solved by the following configuration. (8) A hydrated oxide film forming step of immersing the heat exchanger in a treatment liquid to which a basic substance is added, and a hydrophobic group forming step of immersing the heat exchanger in a solution of a compound having a hydrophobic group. .

(9) A hydrated oxide film forming step of immersing the heat exchanger in a treatment liquid at a temperature of 343 K or higher, and a hydrophobic group forming step of immersing the heat exchanger in a solution of a compound having a hydrophobic group. thing.

(10) A hydrated oxide film forming step of immersing the heat exchanger in the treatment liquid and a hydrophobic group forming step of depositing a compound having a hydrophobic group are provided. (11) In (8), (9) or (10), the treatment liquid is convected at the time of forming the hydrated oxide film.

With these configurations, the outdoor heat exchanger unit of the present invention operates as follows.

(A) The fractal dimension D of the surface of the heat exchanger is the cell size in the box counting method.
In a region of 1 micrometer or less, the range of 2 <D ≦ 3 is satisfied, and condensed water on the surface of the heat exchanger is condensed on the surface of the heat exchanger due to the formation of hydrophobic groups on the surface of the heat exchanger. 90% of the condensed water remaining on the surface of the heat exchanger has a diameter of 500 micrometers or less, thereby preventing an increase in ventilation resistance due to freezing of the condensed water.

This phenomenon occurs because if the fractal dimension D measured by an atomic force microscope in the region where the cell size is 1 μm or less is in the range of 2.2 ≦ D ≦ 3.0, the frequency of condensed water separation increases. It is possible to prevent an increase in ventilation resistance due to freezing of the condensed water, and if the fractal dimension D is within the range of 2.3 ≦ D ≦ 3.0, most of the condensed water is released, so that the ventilation due to the freezing of the condensed water is prevented. It has been found through experiments that it is possible to almost completely prevent an increase in resistance and that this phenomenon of condensed water separation occurs when condensed water on the heat exchanger surface comes into contact and coalesce.

As will be described later in detail, the box counting method is a method of calculating a fractal dimension D of a curved surface.

As described above, the fractal dimension D of the surface of the heat exchanger is within the range of 2 <D ≦ 3 in a region where the cell size in the box counting method is 1 μm or less, and the surface of the heat exchanger has It has been found through experiments that condensed water on the surface of the heat exchanger coalesces and separates from the surface of the heat exchanger when the hydrophobic group is formed.

In addition, various experiments were conducted on the hydrophobic group, and it was confirmed that when the hydrophobic group was a fluorine-containing organic compound, the frequency of the condensed water separation phenomenon was increased. Experiments were performed on silane compounds and polymers as the fluorine-containing organic compounds, but the same effect was obtained in each case.

(B) By providing an insulating coating on the surface of the heat transfer tube in contact with the fins, direct contact of dissimilar metals is prevented, thereby preventing electrolytic corrosion and improving corrosion resistance. In addition, by using a plastic material as the insulating coating, it is possible to reduce the air layer existing on the contact surface between the heat transfer tube and the fin, thereby reducing the contact thermal resistance.

Further, with these configurations, the surface treatment method of the heat exchanger for the outdoor heat exchanger unit of the present invention operates as follows.

(C) a hydrated oxide film forming step of immersing the heat exchanger in a treatment liquid to which a basic substance is added, and a hydrophobic group forming step of immersing the heat exchanger in a solution of a compound having a hydrophobic group As a result, the fractal dimension D of the heat exchanger surface is within the range of 2 <D ≦ 3 in a region where the cell size in the box counting method is 1 μm or less, and a hydrophobic group is formed on the surface of the heat exchanger. The condensed water on the surface of the heat exchanger separates from the surface of the heat exchanger, and 90% of the condensed water remaining on the surface of the heat exchanger has a diameter of 5%.
It is not more than 00 μm, so that an increase in ventilation resistance due to freezing of condensed water can be prevented.

Examples of the basic substance to be added to the treatment liquid include ammonia, carbonate, oxalate, ethanolamine, hydrazine and the like. Further, the same effect can be obtained even when the temperature of the processing liquid is set to 343 K or higher instead of adding the basic substance to the processing liquid.

(D) Convection of the treatment liquid during the formation of the hydrated oxide film prevents gas generated during the formation of the hydrated oxide film from remaining in the gaps between the fins of the heat exchanger. The formation of a hydrated oxide film can be promoted. Examples of the convection means include forced convection of the heat treatment liquid, vibration of the heat exchanger, and installation of a heater below the liquid to generate natural convection in the processing liquid.

[0031]

Embodiments of the present invention will be described below. FIG. 1 is a schematic sectional view of an air conditioner showing an embodiment according to the present invention. The air conditioner includes an indoor unit 1, an outdoor unit 7, and refrigerant pipes 4 and 4 'connecting them. The indoor unit 1 comprises a heat exchanger 2 and a once-through fan 3, and the outdoor unit 7 comprises a water-repellent heat exchanger 8 and an axial fan 9. Usually, the compressor 5 and the expansion valve 6 are installed inside the outdoor unit 7, but in this figure, the refrigerant circuit is shown outside for easy understanding.

FIG. 2A is a partially sectional perspective view of an outdoor heat exchanger unit according to an embodiment of the present invention.
The outdoor heat exchanger unit 101 includes a heat exchanger in which a plurality of heat transfer tubes 102 are vertically inserted into a plurality of stacked fins 103, and a fan 104.

FIG. 2B is a partially enlarged schematic view of the fin 103. In this embodiment, the aluminum plate 1
A hydrated oxide layer 106 having a thickness of 0.2 to 1 μm is formed on the surface of
7 are provided. Corrosion holes 10 in aluminum plate 105
8 are formed, but the hydrated oxide layer 106 and the hydrophobic group 107 also exist inside the corrosion hole 108.

Next, the surface treatment method of the heat exchanger will be described. First, the heat exchanger provided with the heat transfer tubes 102 and the fins 103 is immersed in a 333 K basic degreasing solution for 10 minutes to remove dirt on the heat exchanger surface. Next, the heat exchanger is washed with water and immersed in a boiled 0.4 wt% ammonia aqueous solution for 10 minutes to form a hydrated oxide film on the surface of the fin 103. At this time, in order to prevent the gas generated by the reaction from staying in the gap between the fins of the heat exchanger,
It is desirable to vibrate the heat exchanger or make the processing liquid flow. It is also effective to install a heater in the lower part of the liquid so that the processing liquid flows to generate natural convection. After that, the heat exchanger is washed with water and dried. In this drying step, the drying time can be shortened by contacting hot air to such an extent that the crystal structure of the hydrated oxide film is not destroyed. And 3 of fluoroalkylsilane (structural formula CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ )
It is immersed in a wt% perfluoroalkane (C ₈ F ₁₈ ) solution for 30 minutes, dried at room temperature for 30 minutes, and then dried at 413K for 30 minutes.

According to this surface treatment method, the fin surface has a contact angle of 160 ° or more in a normal contact angle measuring method.

In addition, an atomic force microscope (Nanoscope)
e IIIa, manufactured by Digital Instruments), the fractal dimension D was determined in the range from 10 nanometers to 1 micrometer. As a result, at least D ≧ 2.2 and in many cases D ≧ 2.3. Although the details will be described later, the fractal dimension D is a value representing the degree of surface unevenness, and takes a value between 2 and 3 for a curved surface.

When the heat exchanger thus manufactured is installed in an actual outdoor heat exchanger unit and is operated for heating, the water droplets generated on the fin surface are extremely small while being accompanied by the flow of air caused by the fan. Splashes downstream. Since these water droplets have a very small diameter, they have the advantage of being easily supercooled even below the freezing point and less likely to become frost on the heat transfer surface. For this reason, it is possible to suppress an increase in ventilation resistance of the heat exchanger due to water droplets or frost.

Additives to the treatment solution used in the above treatment are, in place of ammonia, carbonates, oxalates, triethanolamine, hydrazine, solutes in seawater, combinations of magnesium ions and hydrogen carbonate ions, Combination of magnesium ion, hydrogen carbonate ion and sulfate ion, combination of hydroxide ion and lithium ion, combination of hydroxide ion, lithium ion and silicate ion, combination of hydroxide ion and calcium ion, hydroxide ion , Lithium ions and nitrate ions can be used.

In the above processing, the same effect can be obtained by setting the temperature of the processing solution to 343 K or higher, or using hot water of 343 K or higher in place of the processing solution.

It is more effective to deposit fluoroalkylsilane on a heat exchanger in an atmosphere of 423K or more.
In addition, in this vapor deposition method, perfluoroalkane as a solvent is not required, which is advantageous in terms of cost.

FIG. 3 is an electron micrograph of the fin surface showing the water repellency of the heat exchanger according to one embodiment of the present invention. The magnification is 30,000 times. A 0.4 wt% aqueous ammonia solution is used as a treatment liquid for forming the hydrated oxide film. In this photograph, the white part is the ridgeline of the hydrated oxide layer 106 exposed on the fin surface, and it can be seen that the size is about several tens to hundreds of nanometers. Note that the hydrophobic group 107 on the fin surface cannot be observed from this photograph.

FIG. 4 shows the fin surface observed in FIG.
It is an electron micrograph at the time of observing at 000 times. In this photo, the darkened area is a micron-order depression probably caused by pitting. This corresponds to the corrosion hole 108 described with reference to FIG.

As described above, irregularities are formed on the fin surface in a range from the nano-order by the hydrated oxide layer 106 to the micron-order by pitting corrosion. This is the so-called fractal structure, and the hydrophobic groups are exposed on the surface, so that the fin surface of the heat exchanger exhibits very good water repellency.

FIG. 5 is an example of a photograph taken by enlarging a condensed water droplet on the fin surface exhibiting water repellency according to the present invention.

An aluminum plate (A1100, 25.times.50.times.3 millimeters) treated in the same manner as in the above heat exchanger was attached to a heat absorbing surface of a vertically installed electronic cooling element, and was set to an ambient temperature of 298 K and humidity. The photograph was taken under the condition of natural convection of 60%, where the aluminum plate was cooled to 273K and reached a steady state. In the process of photographing this, it was found that very small condensed water droplets were generated on the aluminum plate surface, and the phenomenon that they coalesced and separated almost perpendicularly from the surface was constantly repeated.

In the present embodiment, most of the condensed water droplets immediately before merging / separation have a diameter of 10 to 50 micrometers.
The diameter of condensed water droplets remaining on the surface ranged from a few micrometers to 500 micrometers. This phenomenon does not always occur on the surface of the water-repellent structure where the contact angle of the water droplet is 120 ° or more, and the fractal dimension D is high when the surface ranges from nano-order to micron-order.
This occurs when the surface has high-density hydrophobic groups on the surface.

The coalescence / separation phenomenon of the condensed water droplets is considered to be based on the following principle. FIG. 6 schematically illustrates a state in which fine condensed water droplets generated on the fin surface when the vertically installed water-repellent fin surface is cooled are united and separated from the fin surface. Fin surface 203
The two condensed water droplets 201 and 202 (FIG. 5)
(A)) is united at the moment of contact and separates from the fin surface like a water drop 221 through the state of a water drop 211 (FIG. 5 (b)) (FIG. 5 (c)). Water drops 201, 20 at this time
The radii of 2 and 221 are r ₁ , r ₂ and R, respectively, the surface tension of the water droplet is σ, the sum of the adhesion energy of the water droplet to the fin surface before coalescence is Ea, and the kinetic energy of the water droplet resulting from the coalescence is when Ek, the energy conservation law, the ^{_{Ek = 4πσ (r 1 2 +}} r 2 2 -R 2) -Ea this formula, when the adhesion energy Ea is small, it can be seen that the kinetic energy Ek caused by coalescence.

[0048] Further, each of the mass and the desorption rate of water droplet after coalescence, M, when is V, the Ek = MV ^2/2. Since M is proportional to r ³ and Ea is proportional to r ² ,
After all, V ² is proportional to r ~ ¹ . In other words, it can be seen that the finer the water droplet, the easier it is to detach, and the faster the detachment speed.

FIG. 7 shows an electron microscope of the surface of the fin when no additive is mixed with the processing solution used for forming the hydrated oxide film, that is, when the hydrated oxide film is formed using pure water. It is a photograph. The magnification is 1000 times. When FIG. 3 and FIG. 6 in which the additive is mixed with the treatment liquid are compared, FIG. 6 shows that the corrosion hole is smaller in FIG. 6 and no micron-order irregularities are formed.

Similarly, no difference was found when comparing electron micrographs at a magnification of 30,000. From this,
It was found that when the additive was mixed in the treatment liquid, the irregularities on the order of microns increased, and the irregularities were formed in a wide scale range in combination with the irregularities on the nano-order of the hydrated oxide.

FIGS. 8, 9 and 10 show ammonia, sodium oxalate and sodium carbonate, respectively.
The conditions for obtaining fins exhibiting good water repellency when the additive is used in the treatment liquid used for forming the hydrated oxide film are shown. The horizontal axis is the additive concentration, and the vertical axis is the vertical axis. The axis indicates the immersion time.

For example, when the additive is sodium oxalate as shown in FIG.
Good water repellency can be obtained by immersing in a wt% treatment liquid for 10 minutes or more. At this time, the pH of the processing solution was 7.
96.

Good water repellency refers to a state in which most of the condensed water present on the fin surface is released, and even if the condensed water remaining on the fin surface freezes, it does not affect the ventilation resistance. 90 of condensed water droplets existing on the fin surface
% Is 500 micrometers or less in diameter. This is because if the fin surface exhibiting water repellency is placed almost vertically and cooled to below the dew point of air, condensed water droplets of 500 micrometers or less on the fin surface will coalesce in a steady state.
This is because the withdrawal is repeated.

Here, the box counting method, which is one of the methods for calculating the fractal dimension D, will be described.

The procedure of the box counting method is as follows. (1) A curve for obtaining the fractal dimension D is surrounded by square cells (boxes), and the number of cells intersecting the curve is counted. (2) Change the cell size and count the number of cells that intersect this curve as in (1).

(3) The cell size is plotted on a log-log graph with the horizontal axis representing the cell size and the vertical axis representing the number of intersecting cells. (4) The absolute value of the slope of the graph created in (3) is the fractal dimension D.

In the case where the target line is a straight line, if the dimensions of the squares are halved, the number of intersecting squares is doubled, and the fractal dimension D is 1.

When the target line is a curve, the fractal dimension D is 1 or more. FIG. 11A shows a fractal dimension D.
11A is obtained by enclosing a curve for determining the fractal dimension D with a square cell having a side of X and enclosing a cell overlapping the curve with a square cell having a side of X / 2. The cells that are surrounded by cells and the cells that overlap the curve are hatched.

In the case of the curve shown in FIG. 11, if the size of the cell is halved as shown in the figure, the number of intersecting cells becomes 12 to 2
The number increases to six, that is, becomes two times or more, and the fractal dimension D in this case becomes one or more.

When this concept is extended to a curved surface, the cell becomes a cube. When the curved surface is a plane, reducing the dimension of one side of the cube to half reduces the number of intersecting cubes to four times and the fractal dimension D to two. Then, in the case of an arbitrary curved surface, two or more fractal dimensions D can be calculated in the same manner as in the case of a curve.

As can be understood from the above idea, the fractal dimension D of the curved surface takes a value between 2 and 3, but becomes closer to 3 as the shape of the curved surface becomes more complicated.

FIG. 12 shows that the treatment liquid used for forming the hydrated oxide film is a 0.5 wt% aqueous solution of sodium oxalate.
The fractal dimension D of the surface of the water-repellent structure was measured with an atomic force microscope in several measurement ranges with a treatment time of 10 minutes, and the horizontal axis represents the length of one side of the measurement range, and the vertical axis represents the measurement range. Is plotted by taking the fractal dimension D.

From this figure, as the measurement range is reduced to increase the resolution, the fractal dimension D increases, and the fractal dimension D is D ≧ 2.
2. It is understood that D ≧ 2.3 in a measurement range of 1 μm or less. In other words, the surface of the water-repellent fin of the present invention also has a complex shape with nano-order irregularities,
It can be inferred that it not only shows water repellency to water droplets of about 1 mm, but also contributes to the coalescence / separation phenomenon of finer condensed water droplets.

The heat exchanger of this embodiment uses a copper material for the heat transfer tube and an aluminum material for the fins, but by providing an insulating coating on the contact surfaces of both, the direct contact between copper and aluminum is eliminated. Prevents electric corrosion and enhances corrosion resistance. In addition, by using a plastic material as the insulating coating, it is possible to reduce the air layer existing on the contact surface between the heat transfer tube and the fin, thereby reducing the contact thermal resistance.

The problem of electrolytic corrosion caused by the direct contact of the dissimilar metals can be solved by fabricating the entire heat exchanger only with aluminum. In this case, it is easy to weld the fin to the heat transfer tube, and the contact heat resistance can be extremely reduced. Further, the water-repellent coating can be formed not only on the fins but also on the surface of the heat transfer tube.

The fins exhibiting water repellency described above need to form a fractal structure having a large number of hydroxyl groups on the surface in the manufacturing process, but this structure is not limited to the above aluminum hydrated oxide. But, for example,
It is also applicable to glass containing silica as a main component and organic substances having a hydroxyl group.

[0067]

According to the present invention, there is provided an outdoor heat exchanger unit exhibiting sufficient water repellency even for fine water droplets such as condensed water droplets and preventing an increase in ventilation resistance due to freezing of condensed water. Can be. Further, according to the present invention, it is possible to provide a surface treatment method for a heat exchanger used for an outdoor heat exchanger unit, which can exhibit sufficient water repellency even for fine water droplets such as condensed water droplets. .

[Brief description of the drawings]

FIG. 1 is a schematic view of an air conditioner showing one embodiment of the present invention.

FIG. 2 is a perspective view of an outdoor heat exchanger unit according to one embodiment of the present invention.

FIG. 3 is an electron micrograph of a fin surface showing water repellency, which is one example of the present invention.

FIG. 4 is an electron micrograph of a fin surface showing water repellency, which is one example of the present invention.

FIG. 5 is an enlarged photograph of condensed water droplets on the fin surface showing water repellency, which is one example of the present invention.

FIG. 6 is a schematic view showing a mechanism of coalescing / separation of condensed water droplets on a fin surface exhibiting water repellency according to an embodiment of the present invention.

FIG. 7 is an electron micrograph of a fin surface when an additive is not mixed into a treatment liquid.

FIG. 8 is a diagram showing conditions for forming a hydrated oxide film when ammonia is added to a treatment liquid according to one embodiment of the present invention.

FIG. 9 is a diagram showing conditions for forming a hydrated oxide film when sodium oxalate is added to a treatment liquid according to an embodiment of the present invention.

FIG. 10 is a diagram showing conditions for forming a hydrated oxide film when sodium carbonate is added to a treatment liquid according to an embodiment of the present invention.

FIG. 11 is a diagram illustrating a box counting method.

FIG. 12 is a diagram showing the measurement range dependency of the fractal dimension D of the fin surface according to one embodiment of the present invention.

[Description of Signs] 1 ... indoor unit, 2 ... heat exchanger, 3 ... cross-flow fan, 4, 4 '... refrigerant pipe, 5 ... compressor, 6 ... expansion valve, 7 ... outdoor unit , 8 ... water repellent heat exchanger, 9 ...
... axial fan, 10 ... fan duct, 11 ... airflow,
101: outdoor heat exchanger unit, 102: heat transfer tube,
103 fin, 104 fan, 105 aluminum plate, 106 hydrated oxide layer, 107 hydrophobic group, 108 corrosion pit, 201, 202 condensation water droplet,
203: Fin surface, 211, 221 ... Water droplets.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuhiro Yoshimura 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref.Mechanical Research Laboratories, Hitachi, Ltd. (72) Inventor Kensaku Oguni 390 Muramatsu, Shimizu-shi, Shizuoka Prefecture In-house Air Conditioning Systems Division, Hitachi, Ltd.

Claims (12)

[Claims] 1. An outdoor heat exchanger unit comprising a heat exchanger and a fan for sending air to the heat exchanger, wherein the fractal dimension D of the surface of the heat exchanger has a cell size of 1 in a box counting method. An outdoor heat exchanger unit, wherein the range of 2 <D ≦ 3 is satisfied in a region of micrometer or less, and a hydrophobic group is formed on a surface of the heat exchanger. 2. The outdoor heat exchanger unit according to claim 1, wherein said hydrophobic group is a fluorine-containing organic compound. 3. The method according to claim 1, wherein a fractal dimension D of the surface of the heat exchanger measured by an atomic force microscope is a cell size in a box counting method.
An outdoor heat exchanger unit, wherein 2.2 ≦ D ≦ 3.0 within a range of 1 μm or less. 4. An outdoor heat exchanger unit comprising a heat exchanger and a fan for sending air to the heat exchanger, wherein the outdoor heat exchanger unit operates under a dew condensation condition. An outdoor heat exchanger unit, wherein 90% of condensed water droplets present on the surface have a diameter of 500 micrometers or less. 5. An outdoor heat exchanger unit provided with a heat exchanger and a fan for sending air to the heat exchanger, wherein the outdoor heat exchanger unit operates under a dew condensation condition. An outdoor heat exchanger unit, wherein condensed water droplets generated on the surface of the heat exchanger are separated from the surface of the heat exchanger. 6. An outdoor heat exchanger unit comprising a heat exchanger and a fan for sending air to the heat exchanger, wherein the outdoor heat exchanger unit operates under a dew condensation condition. The outdoor heat exchanger unit, wherein the condensed water droplets generated on the surface of the heat exchanger unite and separate from the surface of the heat exchanger at the same time. 7. An outdoor heat exchanger unit comprising a heat exchanger in which a plurality of heat transfer tubes are inserted into a plurality of stacked fins and a fan for sending air to the heat exchanger. An outdoor heat exchanger unit, wherein an electric insulating material is formed on a surface of the heat transfer tube. 8. An air conditioner comprising the outdoor heat exchanger unit according to claim 1. 9. A hydrated oxide film forming step of immersing the heat exchanger in a treatment liquid to which a basic substance has been added, and a hydrophobic group forming step of immersing the heat exchanger in a solution of a compound having a hydrophobic group. A surface treatment method for a heat exchanger for an outdoor heat exchanger unit, the method comprising: 10. A hydrated oxide film forming step of immersing the heat exchanger in a treatment liquid at a temperature of 343 K or more, and a hydrophobic group forming step of immersing the heat exchanger in a solution of a compound having a hydrophobic group. A method for treating a surface of a heat exchanger for an outdoor heat exchanger unit, the method comprising: 11. The method according to claim 9, wherein the treatment liquid is convected during the formation of the hydrated oxide film. 12. A heat exchanger for an outdoor heat exchanger unit according to claim 9, further comprising a hydrophobic group forming step of depositing a compound having a hydrophobic group on said heat exchanger. Surface treatment method.