JP2023143804A - Member for heat exchanger, heat exchanger, indoor unit for air conditioner, outdoor unit for air conditioner, refrigerator, and washer with dryer - Google Patents

Abstract

To realize a member for a heat exchanger with high efficiency while imparting characteristics not found in a metal itself with a coating with excellent heat transfer to a metal surface.SOLUTION: A fin 112 is made of metal, and has a carbon nanotube-containing oxide film 112B having a thread-like structure 112C on a surface of the metal when a cross section of the surface of the metal is observed with a scanning transmission electron microscope (STEM). The carbon nanotube-containing oxide film 112B contains carbon nanotubes in a direction in which a thermal diffusivity in a film thickness direction is higher than a thermal diffusivity in a film surface direction of the carbon nanotube-containing oxide film 112B.SELECTED DRAWING: Figure 3

Description

The present invention relates to a heat exchanger member whose metal surface has properties other than those unique to the metal, and to equipment including this member.

When an air conditioner is in operation, condensation or frost forms on the surfaces of the heat exchange fins of the heat exchangers provided in the indoor and outdoor units. This dew condensation and frost formation on the surface of the heat exchange fins has negative effects such as a decrease in air blowing efficiency, a decrease in heat exchange performance, and an accompanying increase in power consumption of the air conditioner itself. In recent years, in the air conditioning field, the heat exchange fin surface has been made hydrophilic to prevent dew condensation and frost formation, thereby suppressing the decline in air blowing efficiency and heat exchange performance, and reducing the power consumption of the air conditioner itself. Technologies to reduce this are being actively studied. Such a technique is disclosed in Patent Document 1, for example.

Patent Document 1 describes that a hydrophilic resin coating film made of acrylic resin (polyacrylic acid, acrylamino, acrylamide, etc.), cellulose resin, polyvinyl alcohol resin, amide resin, amino resin, etc. is heated. This document describes a method of suppressing an increase in ventilation resistance due to dew condensation generated on the heat exchange fins by forming them on the surfaces of the heat exchange fins of the exchanger.

Japanese Patent Application Publication No. 5-322469

However, in the technology of Patent Document 1, acrylic resin (acrylic resin) has significantly lower thermal conductivity than aluminum, which is a common material for heat exchange fins of heat exchangers, or aluminum oxide, which is naturally formed on its surface. organic resins such as silica particles (approximately 1/20 of aluminum oxide's thermal conductivity), silica particles (approximately 1/20 of aluminum oxide's thermal conductivity), and zeolites (aluminum oxide's thermal conductivity of (approximately 1/180 of For this reason, the composition of the hydrophilic coating itself, which is supposed to be a measure against the increase in power consumption of air conditioners, has the problem of increasing the power consumption of air conditioners when the air conditioners are operated in environments where condensation does not occur. was there.

In addition, with hydrophilic technology that only reduces the contact angle, there is a problem in that water droplets generated by actual dew condensation remain attached and do not slide off, resulting in ventilation resistance.

Furthermore, in the case of an indoor unit in an air conditioner, for example, the method of Patent Document 1 is not effective at all during heating operation, where power consumption is higher, because the temperature difference between the outside temperature and the required room temperature becomes even larger. There was a problem.

The present invention has been made in view of the above problems, and its purpose is to improve the heat transfer coefficient (single layer) with air on the metal surface forming the heat exchanger or the heat exchange fins of the heat exchanger. A coating with excellent heat transfer coefficient (during flow) that provides properties not found in metal itself, and is used in highly efficient heat exchanger components, heat exchangers, indoor units for air conditioners, outdoor units for air conditioners, refrigerators, and The aim is to realize a washing machine with a dryer.

In order to solve the above problems, the heat exchanger member of the present invention is a heat exchanger member made of metal, and when a cross section of the surface of the metal is observed with a scanning transmission electron microscope (STEM), the metal has a metal oxide film having a thread-like structure on the surface of the metal oxide film, and carbon nanotubes are arranged in a direction in which the thermal diffusivity in the film thickness direction is higher than the thermal diffusivity in the film surface direction of the metal oxide film. Contains.

The heat exchanger member of the present invention has the effect of adding a function to the heat exchanger member that improves the heat exchange efficiency of the heat exchanger not only during cooling but also during heating.

1 is a perspective view showing an indoor unit of an air conditioner using a heat exchanger member according to Embodiment 1 of the present invention. It is a figure showing the member for heat exchangers concerning Embodiment 1 of the present invention. FIG. 3 is a schematic diagram showing a cross section taken along the line aa in FIG. 2; 1 is a STEM cross section of the surface of a heat exchanger member according to Embodiment 1 of the present invention. FIG. 1 is a diagram showing equipment for manufacturing Embodiment 1 of the present invention. FIG. 3 is a diagram showing a time chart of load electrolytic density for manufacturing Embodiment 1 of the present invention. It is a schematic diagram showing a heat transfer coefficient measuring device (supervised by Professor Koichi Nishino of Yokohama National University). It is a schematic diagram showing a heat transfer coefficient and air resistance measuring device (supervised by Professor Koichi Nishino, Yokohama National University). 5 is a diagram showing the dependence of the Nusselt number on the Reynolds number in the fin 112. FIG. FIG. 3 is a diagram showing the dependence of the pipe friction coefficient on the Reynolds number in the fin 112.

[Embodiment 1]
Embodiments of the present invention will be described below based on FIGS. 1 to 7.

<Configuration of indoor unit of air conditioner with built-in components>
FIG. 1 is a diagram showing a cut model of an indoor unit 100 of an air conditioner. The indoor unit 100 of the air conditioner includes a heat exchanger 110, an air filter 120, a blower fan 130, a drain pan 140, a casing 150, and a control section and a drive section (not shown).

Heat exchanger 110 consists of refrigerant piping 111 and fins 112. The heat exchanger member of the present invention means a member that constitutes the heat exchanger 110 (refrigerant piping 111 and fins 112). In the following description, the heat exchanger member will be described as a member constituting the fins 112.

<Component configuration>
FIG. 2 and FIG. 3, which is a cross-sectional view taken along the line aa in FIG. 2, are diagrams showing fins 112 constituting the heat exchanger 110, which is a specific example of the heat exchanger member of the present invention. As shown in FIG. 3, when the cross section of the surface of the fin 112 is observed using STEM, a structure 112C that looks like a string is provided on a metal base 112A made of the main material (aluminum, copper, etc.) that forms the fin 112. A carbon nanotube-containing oxide film 112B is provided. The carbon nanotube-containing oxide film 112B having this structure 112C is a metal oxide film in which carbon nanotubes are contained in a direction in which the thermal diffusivity in the film thickness direction is higher than the thermal diffusivity in the film surface direction of the metal oxide film, A function is provided to improve the heat exchange efficiency of the heat exchanger 110 not only during cooling but also during heating.

Generally, the heat transfer coefficient is not a physical property value, and unless there are irregularities with a height difference of several hundred μm or more that would affect the flow of fluid flowing on the surface of the fins 112, changes in the state of the fluid such as dew condensation will occur. In the case where there is no heat transfer coefficient, it is assumed that the heat transfer coefficient remains unchanged (common sense in physics). However, although it has been confirmed at an academic level that the above structure improves the heat transfer coefficient between the air and the fins 112, the cause is unknown. However, the heat transfer coefficient of the fins 112 is improved by the above structure because the carbon nanotubes, which have extremely high thermal conductivity, are arranged in a direction where the thermal diffusivity increases in the film thickness direction rather than in the film surface direction. This is thought to be due to localized convection caused by localized temperature distribution.

The fins 112 are made of a rolled aluminum plate or a rolled copper plate. The thickness of the fins 112 may be 0.05 to 0.50 mm. Further, the thickness of the fins 112 is preferably 0.05 to 0.20 mm so that when configured as a heat exchanger, the surface area can be made larger than that of the fins 112 in a heat exchanger having the same volume. The size is appropriately determined depending on the purpose of use.

The carbon nanotube-containing oxide film 112B is an oxide of the same or similar metal as the metal base material containing the carbon nanotubes, and when a cross section of at least a part of the surface is observed by STEM, it has a structure that appears thread-like (hereinafter referred to as It has a thread-like structure) 112C. The thickness of this carbon nanotube-containing oxide film 112B may be 30 nm to 1500 nm. Further, the thickness of the carbon nanotube-containing oxide film 112B is preferably 100 nm to 1000 nm in order to utilize the thermal conductivity of the carbon contained therein and improve corrosion resistance. The content ratio of the carbon component contained in this carbon nanotube-containing oxide film 112B may be 3 at % to 50 at % at a point 3 nm to 5 nm from the surface (the surface opposite to the surface in contact with the metal base 112A). Furthermore, the content ratio of carbon contained in this carbon nanotube-containing oxide film 112B is set such that the carbon nanotube-containing oxide film 112B has the characteristics imparted by the inclusion of carbon nanotubes and maintains the strength of the film. 5 at% to 40 at% at the point is preferable.

The carbon nanotubes contained in the carbon nanotube-containing oxide film 112B are preferably single-walled carbon nanotubes because they increase the thermal diffusivity in the film thickness direction and further improve the heat transfer coefficient with air.

Although multi-wall carbon nanotubes and single-wall carbon nanotubes are expensive, the single-wall carbon nanotube-containing oxide film 112B in which they are contained is extremely thin compared to so-called coatings, so the amount actually contained is It is also advantageous in terms of cost since the amount itself is very small.

An example according to the first embodiment will be described below based on FIGS. 5 and 6. The fins 112 in the example are made from an aluminum plate measuring 60 mm x 60 mm x 0.5 mm. An oxide film 112B having a thread-like structure 112C and containing carbon nanotubes in a direction in which the thermal diffusivity in the film thickness direction is higher than that in the film surface direction is formed on the surface of this aluminum plate (metal base 112A). In order to provide this, the following processing was performed.

First, this aluminum plate (metal base 112A) is ultrasonically cleaned with 99.5% purity ethanol (cleaning time: 5 minutes). Thereafter, as shown in FIG. 5, the aluminum plate (metal base 112A) connected to the electric circuit 400 and the SUS304 electrodes 404 and 405 connected to the electric circuit 400 are immersed in the bath 300 containing the treatment liquid 301. . The treatment liquid 301 in the bathtub 300 contains sodium hydroxide, a 0.2% carbon nanotube dispersion, and a conductivity modifier at concentrations of 1.7 g/l, 1.64 ml/l, and 0.44 g/l, respectively. It is added to purified water so that the liquid temperature is room temperature (20 to 30°C).

After that, when the current flowing in the direction of the arrow shown in FIG. 5 is defined as a positive voltage, a voltage is applied to the aluminum plate using the rectifier 401, the rectifier 402, and the changeover switch 403 in the pattern shown in FIG. .

Next, perform ultrasonic cleaning with purified water (cleaning time: 5 minutes). The aluminum plate is further immersed in hot water at 98°C for 15 minutes to hydrate the aluminum oxide on the surface of the aluminum plate, and finally dried with air blow. In this way, an oxidized carbon nanotube is formed which has a thread-like structure 112C on the surface of the aluminum plate (metal base 112A), and which contains carbon nanotubes in a direction in which the thermal diffusivity in the film thickness direction is higher than that in the film surface direction. An aluminum film was provided to form the fin 112.

<Demonstration test>
Here, the characteristics required of the fins that essentially constitute the heat exchanger in the air conditioner, other than the measures against dew condensation and frost formation described above, will be explained. In a heat exchanger in an air conditioner, a large number of fins for heat exchange are arranged with extremely narrow gaps between them. Then, the air between the fins is caused to flow by a fan or the like, and heat is transferred between the fins and the flowing air. Therefore, the heat transfer coefficient between the air and the fan is naturally directly linked to the heat exchange efficiency.

However, since heat transfer coefficient is not a physical property value, it is not possible to change the heat transfer coefficient itself, and it is common to increase the number of fins or change the shape to make them more in contact with air, but this is costly. At present, reductions in the power consumption of air conditioners have reached their limits, as the power consumption of the fan increases due to the increase in pressure loss at the fins. Therefore, it has been desired to improve the heat transfer coefficient between the fins and the air, which can essentially improve the heat exchange coefficient.

Although the detailed mechanism of the fins 112 constituting the heat exchange of the present invention is unknown, the heat transfer coefficient with air in a single layer flow state is improved.
In order to confirm the above, using a heat transfer coefficient measuring device 500 (supervised by Professor Koichi Nishino, Yokohama National University) shown in FIG. We measured aluminum plates with aluminum plates (all of the same size). The results are shown in Table 1.

Note that the heat transfer coefficient is measured by the following method.
The measurement target (fin 112 (treated aluminum plate), untreated aluminum plate, copper plate, silver-plated aluminum plate) is applied to the test plate mounting position 520 shown in FIG. 7 on the contact side of the stainless steel block 510. After the stainless steel block 510 is installed, a predetermined current is applied to the heater 511 provided inside the stainless steel block 510, and small fans 541 and 542 are operated to blow air onto each test plate. After that, the heat flux imparted to the measurement object is calculated from the temperature of each part measured by the thermocouples 512 to 519 after a sufficient period of time has passed and the steady state is reached, and the heat transfer coefficient of the measurement object is calculated. Derive.

From Table 1, it is generally said that the heat transfer coefficient does not change even if the material has a high thermal conductivity such as copper or silver, and even if the surface area increases due to minute irregularities. (measurement error range). On the other hand, the heat transfer coefficient of the fins 112 has increased beyond the error range, and it can be seen that the heat transfer coefficient has clearly improved. Therefore, the fins 112 according to the present invention essentially have the effect of improving the heat exchange efficiency of the heat exchanger.

In addition, it has been confirmed that carbon nanotubes (having a very high thermal diffusivity) are added to the oxide film 112B of the fin 112 based on the depth profile obtained by Raman analysis and XPS analysis. Furthermore, when the thermal diffusivity of the fin 112 was measured using a measuring device manufactured by Bethel Co., Ltd. using a periodic heating radiation thermometry method, the thermal diffusivity in the thickness direction of the oxide film 112B was 102×10 ⁻⁶ m. ² /s, and the thermal diffusivity in the film surface direction was 90×10 ⁻⁶ m ² /s. Further, the thermal diffusivity of untreated aluminum was 94×10 ⁻⁶ m ² /s in both the film thickness direction and the film surface direction. In other words, carbon nanotubes are contained in a direction where the thermal diffusivity in the film thickness direction is higher than the thermal diffusivity in the film surface direction of the metal oxide film, which is thought to improve the heat transfer coefficient. .

In this example, wet electrolytic treatment under the above conditions was used to form the carbon nanotube-containing oxide film 112B having a thread-like structure 112C on the surface, but the present invention is not limited to this. It may be formed under different conditions or other processing methods (such as sputtering or sol-gel method using a metal oxide target containing carbon nanotubes). However, wet electrolytic treatment is superior to other treatment methods in terms of cost.

As described above, the fins 112 of the present invention have an effect that the heat transfer coefficient is improved compared to the conventional hydrophilic treatment by forming a hydrophilic coat, and the heat exchange coefficient of the heat exchanger can be improved both during cooling and heating.

Furthermore, the first embodiment of the present invention is not limited to the fins 112, and may be, for example, a member constituting a cooling water pipe for a copper radiator or a water cooling jacket for cooling a power device. In this case, the same effect as the fin 112 is achieved. Further, the carbon nanotube-containing oxide film 112B also has the effect of improving the corrosion resistance of the member.

Further, a heat exchanger made of members such as the fins 112 has the same effects as the fins 112.

Furthermore, an indoor unit for an air conditioner, an outdoor unit for an air conditioner, a refrigerator, or a washing machine with a dryer, which is provided with a heat exchanger made of members such as the fins 112, also exhibits the same effect as the fins 112. Since this is obvious, the effect is that power consumption can be reduced as a result.

<Demonstration test 2>
Further, although the detailed mechanism of the fins 112 constituting the heat exchange of the present invention is unknown, the heat transfer coefficient with air in a single-layer flow state is improved without increasing air resistance.
In order to confirm the above, as part of the flow path of the heat transfer coefficient measuring device 600 (supervised by Professor Koichi Nishino, Yokohama National University) shown in FIG. Set sample 1 as a pipe, or sample 2 as a square pipe by combining four untreated aluminum plates, and let air flow from upstream of the channel at varying flow rates as shown in the figure. By energizing the sample, we created a situation in which heat was transferred to the flowing air, and measured the temperature of each part with thermocouples.As shown in Figure 8, we created a situation in which heat was transferred to the flowing air, and as shown in Figure 8, we measured the slight difference in pressure between the upstream and downstream sides of the flow path. By measuring with a pressure gauge, the Nusselt number, which is a dimensionless number of the heat transfer coefficient, and the pipe friction coefficient (the dimensionless number of air resistance (pressure loss) in the pipe) can be converted to the Reynolds number (a dimensionless number that expresses the state of flow). number). The results are shown in Figures 9 and 10.

From FIGS. 9 and 10, it can be seen that the heat transfer coefficient, which is academically said to remain unchanged, has been improved beyond the range of measurement variation without increasing air resistance. This is fundamentally different from, for example, a method in which notches are provided in the fins to increase air resistance and thereby improve the heat transfer coefficient, which creates a trade-off with the increase in power consumption of the fan motor due to the increase in air resistance. The fins 112 according to the present invention essentially have the effect of improving the heat exchange efficiency of the heat exchanger.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

INDUSTRIAL APPLICATION This invention can be utilized for the member for heat exchangers which performs heat exchange with air by ventilation.

100... Indoor unit of air conditioner 112... Fin 112A... Metal base 112B... Carbon nanotube-containing oxide film (metal oxide film)
112C... Thread-like structure 300... Bathtub 400... Electric circuit

Claims (14)

A heat exchanger member made of metal,
When a cross section of the surface of the metal is observed with a scanning transmission electron microscope (STEM), the surface of the metal has a metal oxide film having a structure that looks like a thread,
A member for a heat exchanger, characterized in that the metal oxide film contains carbon nanotubes in a direction in which the thermal diffusivity in the film thickness direction is higher than the thermal diffusivity in the film surface direction of the metal oxide film. The heat exchanger member according to claim 1, wherein the content ratio of carbon contained within a range of 3 nm to 5 nm from the surface of the metal oxide film is 3 at% or more and 50 at% or less. The heat exchanger member according to claim 1, wherein the metal oxide film has a thickness of 30 nm or more and 1500 nm or less. The heat exchanger member according to claim 1, wherein the carbon nanotube is a single-wall carbon nanotube. A heat exchanger comprising heat exchange fins made of the heat exchanger member according to any one of claims 1 to 4. A heat exchanger comprising a heat exchanger refrigerant tube made of the heat exchanger member according to any one of claims 1 to 4. An indoor unit for an air conditioner, comprising the heat exchanger according to claim 5. An indoor unit for an air conditioner, comprising the heat exchanger according to claim 6. An outdoor unit for an air conditioner, comprising the heat exchanger according to claim 5. An outdoor unit for an air conditioner, comprising the heat exchanger according to claim 6. A refrigerator comprising the heat exchanger according to claim 5. A refrigerator comprising the heat exchanger according to claim 6. A washing machine with a dryer, characterized in that the heat exchanger according to claim 5 is provided. A washing machine with a dryer, characterized in that the heat exchanger according to claim 6 is provided.

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