Patent Description:
A heat exchanger used as an evaporator of a refrigerant in a refrigerant cycle apparatus, such as an air conditioning apparatus, is known.

In a case where the heat exchanger is used in an environment where the temperature and humidity satisfy specific conditions, frost adheres to the surface, and the growth of the frost may increase the air flow resistance of the heat exchanger.

When the air flow resistance of the heat exchanger increases in this way, the heat exchange efficiency in the heat exchanger decreases. Therefore, in a case where the amount of adhering frost increases, the air flow resistance in the heat exchanger can be reduced by performing operation for melting the frost (defrosting operation) or the like.

However, when the defrosting operation for melting the frost is frequently performed, original operation in which the heat exchanger is caused to function as an evaporator of the refrigerant to process the heat load is inhibited.

Regarding such a problem, <CIT> discloses a heat exchanger having a surface structure in which a plurality of protrusions having a predetermined shape and a water-repellent coating film are provided. In the surface structure, energy due to combination of condensed water (water droplets) having droplet diameters capable of maintaining a supercooled state even under a predetermined freezing condition can separate the droplets after the combination. Since the heat exchanger disclosed in <CIT> can suppress frost formation by separating (scattering) condensed water after the combination, it is possible to suppress the heat-load processing from being inhibited by frequent defrosting operation.

<CIT>, which is considered as the closest prior art, relates to a heat exchanger and an air conditioner each of which has a surface structure that can reduce adherence of frost by scattering condensed water even when used in a frosting environment. A heat exchanger includes a portion on whose surface a water-repellent coating is formed. The surface on which the water-repellent coating is formed has a surface structure that satisfies all of the following relationships: rw(entirety) > <NUM>/|cosθw|, rw(protrusion) > <NUM>/|cosθw|, <NUM> < d/L < <NUM>, L < <NUM>, and <NUM>° < θw < <NUM>°, where L is an average pitch of protrusions, d is an average diameter of the protrusions, rw(entirety) is an average area-enlargement ratio of an entire surface, rw(protrusion) is an average area-enlargement ratio of surface protrusions, and θw is a contact angle of water on a flat surface of the water-repellent coating.

<CIT> states that on a cooling face surface of the heat transfer fin, a plurality of pins isolated in an island shape are formed. In the plurality of pins on the cooling face surface, the pin interval d between the adjacent pins is set to be twice r* or less (d≥2r*). Wherein, r* is a radius of a condensed liquid droplet condensed on the cooling face surface determined based on an air condition corresponding to the atmosphere environment where the heat transfer fin is used and a heat transfer face surface temperature condition corresponding to the temperature of the cooling face surface <NUM>, and is a critical radius which is a critical value indicating whether or not the condensed liquid droplet continues to grow in the air condition and the heat transfer face surface temperature condition.

Although the heat exchanger disclosed in <CIT> can suppress frost formation to a certain extent, there is room for further improvement in the dimensions of the protrusions formed on the surface.

The present disclosure is made considering the above-described points. An object of the present disclosure is to provide a heat exchanger having a surface structure capable of effectively suppressing frost formation by scattering condensed water in a frost formation environment, a method for manufacturing the heat exchanger, and a refrigerant cycle apparatus.

A heat exchanger of a first aspect is a heat exchanger provided with a water-repellent coating film on part of a surface of the heat exchanger. The surface on which the water-repellent coating film is provided has a surface structure including a plurality of protrusions, and satisfies all relationships <MAT> <MAT> <MAT> <MAT> and <MAT>where.

A heat exchanger of a second aspect is the heat exchanger of the first aspect, in which the surface on which the water-repellent coating film is provided further satisfies a relationship <MAT>.

A heat exchanger of a third aspect is the heat exchanger of the first or second aspect, in which the surface on which the water-repellent coating film is provided further satisfies a relationship <MAT>.

Since these heat exchangers can scatter condensed water in a frost formation environment, frost formation can be effectively suppressed.

A heat exchanger of a fourth aspect is the heat exchanger of any one of the first to third aspects, and includes a plurality of heat transfer fins, and a heat transfer tube that is fixed to the plurality of heat transfer fins and in which a refrigerant flows. Further, the above-described surface structure is provided on surfaces of the heat transfer fins.

A refrigerant cycle apparatus of a fifth aspect includes a refrigerant circuit including the heat exchanger of any one of the first to fourth aspects and a compressor, and a control unit that makes the refrigerant circuit execute normal operation that makes the heat exchanger function as an evaporator of a refrigerant, and defrosting operation that melts frost adhering to the heat exchanger. The control unit switches to the defrosting operation in a case where a predetermined frost formation condition is satisfied during the normal operation.

Since in this refrigerant cycle apparatus, the specific surface structure is adopted in the heat exchanger, adhesion of condensed water can be suppressed, and thus adhesion of frost can also be suppressed. Thus, it is possible to suppress the frequency of the defrosting operation and to execute the normal operation for a longer time.

A refrigerant cycle apparatus of a sixth aspect includes the heat exchanger of any one of the first to fourth aspects, and a fan that supplies an air flow to the heat exchanger. The air supplied from the fan to the heat exchanger is sent in a horizontal direction.

Even in a case where in this refrigerant cycle apparatus, an air flow is supplied in a horizontal direction (that is not the self-weight direction of the condensed water), the specific surface structure of the heat exchanger can scatter the condensed water.

A method for manufacturing a heat exchanger of a seventh aspect is a method for manufacturing the heat exchanger of any one of the first to fourth aspects, and includes forming the surface structure of the heat exchanger using an anodic oxidation treatment.

A method for manufacturing a heat exchanger of an eighth aspect is the method for manufacturing a heat exchanger of the seventh aspect, in which the forming the surface structure includes an etching treatment performed after the anodic oxidation treatment.

A method for manufacturing a heat exchanger of a ninth aspect includes forming a material having a plate-shape into a predetermined shape by pressing, and after the pressing, performing a surface treatment to form a surface structure including a plurality of protrusions on a surface of the material.

According to the method for manufacturing a heat exchanger, since destruction of the protrusions after the surface treatment is suppressed, it is possible to efficiently manufacture a heat exchanger capable of effectively suppressing frost formation by scattering condensed water.

A method for manufacturing a heat exchanger of a tenth aspect is the method for manufacturing a heat exchanger of the ninth aspect, in which the surface structure promotes scattering of a droplet condensed on the surface of the material.

A method for manufacturing a heat exchanger of an eleventh aspect is the method for manufacturing a heat exchanger of the ninth or tenth aspect, in which the surface treatment includes an anodic oxidation treatment and etching.

A heat exchanger of a twelfth aspect is the heat exchanger of any one of the first to fourth aspects, wherein the heat exchanger scatters a droplet condensed on a surface of the heat exchanger. About the heat exchanger, a first particle diameter that is a maximum particle diameter of the droplet scattered from the surface is equal to or smaller than a second particle diameter that is a minimum particle diameter of the droplet that starts to freeze under a predetermined first condition under which the droplet condenses on the surface.

According to this heat exchanger, since it is possible to scatter, before freezing, droplets that are condensed and grow on the surface, it is possible to effectively suppress frost formation.

A heat exchanger of a thirteenth aspect is the heat exchanger of the twelfth aspect, in which the first condition includes a fact that a relative humidity of ambient air is <NUM>%, and a temperature of the surface is - <NUM>.

A heat exchanger of a fourteenth aspect is the heat exchanger of the twelfth or thirteenth aspect, in which the first particle diameter is <NUM>.

A heat exchanger of a fifteenth aspect is the heat exchanger of the fourteenth aspect, in which the first particle diameter is <NUM>.

<FIG> is a schematic configuration diagram of a refrigerant cycle apparatus <NUM> according to an embodiment. The refrigerant cycle apparatus <NUM> is an apparatus that conditions air in a target space by performing a vapor compression refrigerant cycle (refrigeration cycle).

The refrigerant cycle apparatus <NUM> mainly includes an outdoor unit <NUM>, an indoor unit <NUM>, a liquid-refrigerant connection pipe <NUM> and a gas-refrigerant connection pipe <NUM> that connect the outdoor unit <NUM> and the indoor unit <NUM> to each other, a plurality of remote controllers 50a as input devices and output devices, and a controller <NUM> that controls the operation of the refrigerant cycle apparatus <NUM>.

In the refrigerant cycle apparatus <NUM>, a refrigerant cycle is performed in which the refrigerant sealed in a refrigerant circuit <NUM> is compressed, cooled or condensed, decompressed, heated or evaporated, and then compressed again. In the present embodiment, the refrigerant circuit <NUM> is filled with R32 as the refrigerant for performing a vapor compression refrigerant cycle.

The outdoor unit <NUM> is connected to the indoor unit <NUM> via the liquid-refrigerant connection pipe <NUM> and the gas-refrigerant connection pipe <NUM>, and constitutes part of the refrigerant circuit <NUM>. The outdoor unit <NUM> mainly includes a compressor <NUM>, a four-way switching valve <NUM>, an outdoor heat exchanger <NUM>, an outdoor expansion valve <NUM>, an outdoor fan <NUM>, a liquid-side shutoff valve <NUM>, a gas-side shutoff valve <NUM>, and an outdoor casing 2a.

Further, the outdoor unit <NUM> includes a discharge pipe <NUM>, a suction pipe <NUM>, an outdoor gas-side pipe <NUM>, and an outdoor liquid-side pipe <NUM>, which are pipes constituting the refrigerant circuit <NUM>. The discharge pipe <NUM> connects the discharge side of the compressor <NUM> and a first connection port of the four-way switching valve <NUM> to each other. The suction pipe <NUM> connects the suction side of the compressor <NUM> and a second connection port of the four-way switching valve <NUM> to each other. The outdoor gas-side pipe <NUM> connects a third port of the four-way switching valve <NUM> and the gas-side shutoff valve <NUM> to each other. The outdoor liquid-side pipe <NUM> extends from a fourth port of the four-way switching valve <NUM> to the liquid-side shutoff valve <NUM> via the outdoor heat exchanger <NUM> and the outdoor expansion valve <NUM>.

The compressor <NUM> is equipment that compresses a low-pressure refrigerant in the refrigerant cycle to a high pressure. Here, used as the compressor <NUM> is a compressor having a closed structure in which a positive-displacement-type compression element (not illustrated), such as a rotary type or a scroll type, is rotationally driven by a compressor motor M21. The compressor motor M21 is for changing the displacement, and the operating frequency can be controlled by an inverter.

The four-way switching valve <NUM> can switch the connection states to switch between a cooling-operation connection state (and a defrosting-operation state) in which the discharge side of the compressor <NUM> and the outdoor heat exchanger <NUM> are connected to each other and the suction side of the compressor <NUM> and the gas-side shutoff valve <NUM> are connected to each other, and a heating-operation connection state in which the discharge side of the compressor <NUM> and the gas-side shutoff valve <NUM> are connected to each other and the suction side of the compressor <NUM> and the outdoor heat exchanger <NUM> are connected to each other.

The outdoor heat exchanger <NUM> is a heat exchanger that functions as a radiator of high-pressure refrigerant in the refrigerant cycle during cooling operation, and functions as an evaporator of low-pressure refrigerant in the refrigerant cycle during heating operation.

The outdoor fan <NUM> is a fan that generates an air flow for sucking outdoor air into the outdoor unit <NUM>, causing the air to exchange heat with the refrigerant in the outdoor heat exchanger <NUM>, and then releasing the air to the outside. The outdoor fan <NUM> is rotationally driven by an outdoor fan motor M25.

The outdoor expansion valve <NUM> is an electric expansion valve whose valve opening degree can be controlled. The outdoor expansion valve <NUM> is provided between the outdoor heat exchanger <NUM> and the liquid-side shutoff valve <NUM> in the outdoor liquid-side pipe <NUM>.

The liquid-side shutoff valve <NUM> is a manual valve arranged at a connection portion between the outdoor liquid-side pipe <NUM> and the liquid-refrigerant connection pipe <NUM>.

The gas-side shutoff valve <NUM> is a manual valve arranged at a connection portion between the outdoor gas-side pipe <NUM> and the gas-refrigerant connection pipe <NUM>.

Various sensors are arranged in the outdoor unit <NUM>.

Specifically, arranged around the compressor <NUM> of the outdoor unit <NUM> are a suction temperature sensor <NUM> that detects a suction temperature that is the temperature of the refrigerant on the suction side of the compressor <NUM>, a suction pressure sensor <NUM> that detects a suction pressure that is the pressure of the refrigerant on the suction side of the compressor <NUM>, and a discharge pressure sensor <NUM> that detects a discharge pressure that is the pressure of the refrigerant on the discharge side of the compressor <NUM>.

Further, the outdoor heat exchanger <NUM> is provided with an outdoor heat-exchange temperature sensor <NUM> that detects the temperature of the refrigerant flowing through the outdoor heat exchanger <NUM>.

In addition, an outside-air temperature sensor <NUM> that detects the temperature of outdoor air sucked into the outdoor unit <NUM> is arranged around the outdoor heat exchanger <NUM> or the outdoor fan <NUM>.

The outdoor unit <NUM> includes an outdoor-unit control unit <NUM> that controls the operation of each unit constituting the outdoor unit <NUM>. The outdoor-unit control unit <NUM> includes a microcomputer including a central processing unit (CPU), a memory, and the like. The outdoor-unit control unit <NUM> is connected to an indoor-unit control unit <NUM> of the indoor unit <NUM> via a communication line, and transmits and receives control signals and the like. Further, the outdoor-unit control unit <NUM> is electrically connected to each of the suction temperature sensor <NUM>, the suction pressure sensor <NUM>, the discharge pressure sensor <NUM>, the outdoor heat-exchange temperature sensor <NUM>, and the outside-air temperature sensor <NUM>, and receives signals from the respective sensors.

Note that each element constituting the outdoor unit <NUM> described above is accommodated in the outdoor casing 2a as illustrated in an external perspective view in <FIG> and a seen-from-above arrangement configuration diagram in <FIG>. The outdoor casing 2a is partitioned into a fan chamber S1 and a machine chamber S2 by a partition plate 2c. The outdoor heat exchanger <NUM> is provided in a posture of being erected in a vertical direction, with the main surface of the outdoor heat exchanger <NUM> expanding, in the fan chamber S1, at the back surface of the outdoor casing 2a and a side surface of the outdoor casing 2a on the side opposite to the machine chamber S2. The outdoor fan <NUM> is a propeller fan whose rotation axis direction is a front-rear direction, takes in air in a substantially horizontal direction toward the inside in the fan chamber S1 from the back surface of the outdoor casing 2a and from the side surface of the outdoor casing 2a opposite to the machine chamber S2, and forms an air flow that blows out in a substantially horizontal direction toward the front via a fan grill 2b provided in the front surface in the fan chamber S1 of the outdoor casing 2a (see two-dot-chain-line arrows in <FIG>). With the above-described configuration, the air flow formed by the outdoor fan <NUM> passes orthogonally to the main surface of the outdoor heat exchanger <NUM>.

The indoor unit <NUM> is installed on a wall surface, a ceiling, or the like in a room that is a target space. The indoor unit <NUM> is connected to the outdoor unit <NUM> via the liquid-refrigerant connection pipe <NUM> and the gas-refrigerant connection pipe <NUM>, and constitutes part of the refrigerant circuit <NUM>.

The indoor unit <NUM> includes an indoor expansion valve <NUM>, an indoor heat exchanger <NUM>, and an indoor fan <NUM>.

Further, the indoor unit <NUM> includes an indoor liquid-refrigerant pipe <NUM> that connects the liquid-side end of the indoor heat exchanger <NUM> and the liquid-refrigerant connection pipe <NUM> to each other, and an indoor gas-refrigerant pipe <NUM> that connects the gas-side end of the indoor heat exchanger <NUM> and the gas-refrigerant connection pipe <NUM> to each other.

The indoor expansion valve <NUM> is an electric expansion valve whose valve opening degree can be controlled, and is provided in the indoor liquid-refrigerant pipe <NUM>.

The indoor heat exchanger <NUM> is a heat exchanger that functions as an evaporator of low-pressure refrigerant in the refrigerant cycle during cooling operation, and functions as a radiator of high-pressure refrigerant in the refrigerant cycle during heating operation.

The indoor fan <NUM> sucks indoor air into the indoor unit <NUM>, causes the air to exchange heat with the refrigerant in the indoor heat exchanger <NUM>, and then generates an air flow for releasing the air to the outside. The indoor fan <NUM> is rotationally driven by an indoor fan motor M53.

Various sensors are arranged in the indoor unit <NUM>.

Specifically, arranged inside the indoor unit <NUM> are an indoor air temperature sensor <NUM> that detects the air temperature in the space in which the indoor unit <NUM> is installed, and an indoor heat-exchange temperature sensor <NUM> that detects the temperature of the refrigerant flowing through the indoor heat exchanger <NUM>.

Further, the indoor unit <NUM> includes the indoor-unit control unit <NUM> that controls the operation of each unit constituting the indoor unit <NUM>. The indoor-unit control unit <NUM> includes a microcomputer including a CPU, a memory, and the like. The indoor-unit control unit <NUM> is connected to the outdoor-unit control unit <NUM> via the communication line, and transmits and receives control signals and the like.

The indoor air temperature sensor <NUM> and the indoor heat-exchange temperature sensor <NUM> are each electrically connected to the indoor-unit control unit <NUM>, and the indoor-unit control unit <NUM> receives signals from the respective sensors.

The remote controller 50a is an input device for the user of the indoor unit <NUM> to input various instructions for switching the operation states of the refrigerant cycle apparatus <NUM>. Further, the remote controller 50a also functions as an output device for performing predetermined notifications, such as the operation state of the refrigerant cycle apparatus <NUM>. The remote controller 50a is connected to the indoor-unit control unit <NUM> via a communication line, and transmits and receives signals to and from each other.

In the refrigerant cycle apparatus <NUM>, the outdoor-unit control unit <NUM> and the indoor-unit control unit <NUM> are connected to each other via the communication line to constitute the controller <NUM> that controls the operation of the refrigerant cycle apparatus <NUM>.

<FIG> is a block diagram schematically illustrating a schematic configuration of the controller <NUM> and each unit connected to the controller <NUM>.

The controller <NUM> has a plurality of control modes, and controls the operation of the refrigerant cycle apparatus <NUM> according to the control mode. For example, the controller <NUM> has a cooling-operation mode, a heating-operation mode, and a defrosting-operation mode as the control modes.

The controller <NUM> is electrically connected to each actuator included in the outdoor unit <NUM> (specifically, the compressor <NUM> (the compressor motor M21), the outdoor expansion valve <NUM>, and the outdoor fan <NUM> (the outdoor fan motor M25)), and various sensors (the suction temperature sensor <NUM>, the suction pressure sensor <NUM>, the discharge pressure sensor <NUM>, the outdoor heat-exchange temperature sensor <NUM>, the outside-air temperature sensor <NUM>, and the like). Further, the controller <NUM> is electrically connected to actuators included in the indoor unit <NUM> (specifically, the indoor fan <NUM> (the indoor fan motor M53) and the indoor expansion valve <NUM>). Further, the controller <NUM> is electrically connected to the indoor air temperature sensor <NUM>, the indoor heat-exchange temperature sensor <NUM>, and the remote controller 50a.

The controller <NUM> mainly includes a storage unit <NUM>, a communication unit <NUM>, a mode control unit <NUM>, an actuator control unit <NUM>, and an output control unit <NUM>. Note that each unit in the controller <NUM> is implemented by respective units included in the outdoor-unit control unit <NUM> and/or the indoor-unit control unit <NUM> functioning together.

The storage unit <NUM> is constituted by, for example, a ROM, a RAM, a flash memory, and the like, and includes a volatile storage area and a nonvolatile storage area. The storage unit <NUM> stores control programs that define processing in each unit of the controller <NUM>. Further, each unit of the controller <NUM> appropriately stores predetermined information (for example, a detection value of each sensor, a command input into the remote controller 50a, and the like) in a predetermined storage area in the storage unit <NUM>.

The communication unit <NUM> is a functional unit that serves as a communication interface for transmitting and receiving signals to and from each equipment connected to the controller <NUM>. The communication unit <NUM> receives a request from the actuator control unit <NUM> and transmits a predetermined signal to the designated actuator. Further, the communication unit <NUM> receives signals output from the various sensors <NUM> to <NUM>, <NUM>, and <NUM>, and the remote controllers 50a, and stores the signals in a predetermined storage area of the storage unit <NUM>.

The mode control unit <NUM> is a functional unit that performs switching between the control modes, and the like. The mode control unit <NUM> switches and executes the cooling-operation mode, the heating-operation mode, and the defrosting-operation mode according to an input from the remote controller 50a and the operation situation.

The actuator control unit <NUM> controls the operation of each actuator (for example, the compressor <NUM> or the like) included in the refrigerant cycle apparatus <NUM> according to a situation in accordance with the control programs.

For example, the actuator control unit <NUM> controls the number of rotations of the compressor <NUM>, the connection state of the four-way switching valve <NUM>, the numbers of rotations of the outdoor fan <NUM> and the indoor fan <NUM>, the valve opening degree of the outdoor expansion valve <NUM>, the valve opening degree of the indoor expansion valve <NUM>, and the like in real time according to a set temperature, the detection values of the various sensors, the control mode, and the like.

The output control unit <NUM> is a functional unit that controls the operation of the remote controller 50a as a display device.

The output control unit <NUM> causes the remote controller 50a to output predetermined information in order to display, for a user, information related to the operation state and the situation.

Hereinafter, refrigerant flows in the cooling-operation mode, the heating-operation mode, and the defrosting-operation mode will be described.

In the refrigerant cycle apparatus <NUM>, the mode control unit <NUM> switches the control mode to the cooling-operation mode, so that the actuator control unit <NUM> switches the connection state of the four-way switching valve <NUM> to the cooling-operation connection state in which the suction side of the compressor <NUM> and the gas-side shutoff valve <NUM> are connected to each other while the discharge side of the compressor <NUM> and the outdoor heat exchanger <NUM> are connected to each other. Thus, the refrigerant with which the refrigerant circuit <NUM> is filled mainly circulates through the compressor <NUM>, the outdoor heat exchanger <NUM>, the outdoor expansion valve <NUM>, the indoor expansion valve <NUM>, and the indoor heat exchanger <NUM> in this order.

More specifically, when the operation mode is switched to the cooling-operation mode, in the refrigerant circuit <NUM>, the refrigerant is sucked into the compressor <NUM>, compressed, and then discharged.

The gas refrigerant discharged from the compressor <NUM> flows into the gas-side end of the outdoor heat exchanger <NUM> through the discharge pipe <NUM> and the four-way switching valve <NUM>.

The gas refrigerant that has flowed into the gas-side end of the outdoor heat exchanger <NUM> exchanges heat with outdoor-side air supplied by the outdoor fan <NUM> in the outdoor heat exchanger <NUM> to radiate heat and condense, becomes liquid refrigerant, and flows out from the liquid-side end of the outdoor heat exchanger <NUM>.

The liquid refrigerant that has flowed out from the liquid-side end of the outdoor heat exchanger <NUM> flows into the indoor unit <NUM> through the outdoor liquid-side pipe <NUM>, the outdoor expansion valve <NUM>, the liquid-side shutoff valve <NUM>, and the liquid-refrigerant connection pipe <NUM>. Note that in the cooling-operation mode, the outdoor expansion valve <NUM> is controlled so as to be in a fully open state.

The refrigerant that has flowed into the indoor unit <NUM> flows into the indoor expansion valve <NUM> through part of the indoor liquid-refrigerant pipe <NUM>. The refrigerant that has flowed into the indoor expansion valve <NUM> is decompressed to a low pressure in the refrigerant cycle by the indoor expansion valve <NUM>, and then flows into the liquid-side end of the indoor heat exchanger <NUM>. Note that in the cooling-operation mode, the valve opening degree of the indoor expansion valve <NUM> is controlled so that the degree of superheating of the refrigerant sucked into the compressor <NUM> becomes a predetermined degree of superheating. Here, the degree of superheating of the refrigerant sucked into the compressor <NUM> is calculated by the controller <NUM> using the temperature detected by the suction temperature sensor <NUM> and the pressure detected by the suction pressure sensor <NUM>. The refrigerant that has flowed into the liquid-side end of the indoor heat exchanger <NUM> exchanges heat with indoor air supplied by the indoor fan <NUM> in the indoor heat exchanger <NUM>, evaporates, becomes gas refrigerant, and flows out from the gas-side end of the indoor heat exchanger <NUM>. The gas refrigerant that has flowed out from the gas-side end of the indoor heat exchanger <NUM> flows into the gas-refrigerant connection pipe <NUM> via the indoor gas-refrigerant pipe <NUM>.

In this way, the refrigerant flowing through the gas-refrigerant connection pipe <NUM> is sucked into the compressor <NUM> again through the gas-side shutoff valve <NUM>, the outdoor gas-side pipe <NUM>, the four-way switching valve <NUM>, and the suction pipe <NUM>.

In the refrigerant cycle apparatus <NUM>, the mode control unit <NUM> switches the control mode to the heating-operation mode, so that the actuator control unit <NUM> switches the connection state of the four-way switching valve <NUM> to the heating-operation connection state in which the suction side of the compressor <NUM> and the outdoor heat exchanger <NUM> are connected to each other while the discharge side of the compressor <NUM> and the gas-side shutoff valve <NUM> are connected to each other. Thus, the refrigerant with which the refrigerant circuit <NUM> is filled mainly circulates through the compressor <NUM>, the indoor heat exchanger <NUM>, the indoor expansion valve <NUM>, the outdoor expansion valve <NUM>, and the outdoor heat exchanger <NUM> in this order.

More specifically, when the operation mode is switched to the heating-operation mode, in the refrigerant circuit <NUM>, the refrigerant is sucked into the compressor <NUM>, compressed, and then discharged.

The gas refrigerant discharged from the compressor <NUM> flows through the discharge pipe <NUM>, the four-way switching valve <NUM>, the outdoor gas-side pipe <NUM>, and the gas-refrigerant connection pipe <NUM>, and then flows into the indoor unit <NUM> via the indoor gas-refrigerant pipe <NUM>.

The refrigerant that has flowed into the indoor unit <NUM> flows into the gas-side end of the indoor heat exchanger <NUM> through the indoor gas-refrigerant pipe <NUM>. The refrigerant that has flowed into the gas-side end of the indoor heat exchanger <NUM> exchanges heat with indoor air supplied by the indoor fan <NUM> in the indoor heat exchanger <NUM> to radiate heat and condense, becomes liquid refrigerant, and flows out from the liquid-side end of the indoor heat exchanger <NUM>. The refrigerant that has flowed out from the liquid-side end of the indoor heat exchanger <NUM> flows into the liquid-refrigerant connection pipe <NUM> via the indoor liquid-refrigerant pipe <NUM> and the indoor expansion valve <NUM>. Note that in the heating-operation mode, the valve opening degree of the indoor expansion valve <NUM> is controlled so as to be in a fully open state.

In this way, the refrigerant flowing through the liquid-refrigerant connection pipe <NUM> flows into the outdoor expansion valve <NUM> via the liquid-side shutoff valve <NUM> and the outdoor liquid-side pipe <NUM>.

The refrigerant that has flowed into the outdoor expansion valve <NUM> is decompressed to a low pressure in the refrigerant cycle, and then flows into the liquid-side end of the outdoor heat exchanger <NUM>. Note that in the heating-operation mode, the valve opening degree of the outdoor expansion valve <NUM> is controlled such that the degree of superheating of the refrigerant sucked into the compressor <NUM> becomes a predetermined degree of superheating.

The refrigerant that has flowed into from the liquid-side end of the outdoor heat exchanger <NUM> exchanges heat with outdoor air supplied by the outdoor fan <NUM> in the outdoor heat exchanger <NUM> to evaporate, becomes gas refrigerant, and flows out from the gas-side end of the outdoor heat exchanger <NUM>.

The refrigerant that has flowed out from the gas-side end of the outdoor heat exchanger <NUM> is sucked into the compressor <NUM> again through the four-way switching valve <NUM> and the suction pipe <NUM>.

As described above, in a case where the heating-operation mode is executed, when a predetermined frost formation condition is satisfied, the mode control unit <NUM> temporarily interrupts the heating-operation mode, and switches the control mode to the defrosting-operation mode for melting the frost that has adhered to the outdoor heat exchanger <NUM>.

Note that the predetermined frost formation condition is not limited, but can be, for example, a fact that a state in which the temperature detected by the outside-air temperature sensor <NUM> and the temperature detected by the outdoor heat-exchange temperature sensor <NUM> satisfy a predetermined temperature condition continues for a predetermined time or more.

In the defrosting-operation mode, the actuator control unit <NUM> drives the compressor <NUM>, with the connection state of the four-way switching valve <NUM> made similar to the connection state during the cooling operation, and with the driving of the indoor fan <NUM> stopped. After the defrosting-operation mode is started, in a case where a predetermined defrosting end condition is satisfied (for example, in a case where a predetermined time elapses after the defrosting-operation mode is started, or the like), the actuator control unit <NUM> returns the connection state of the four-way switching valve <NUM> to the connection state during the heating operation again, and restarts the heating-operation mode.

As illustrated in a schematic front view of the outdoor heat exchanger <NUM> in <FIG>, the outdoor heat exchanger <NUM> includes a plurality of heat transfer tubes <NUM> extending in a horizontal direction, a plurality of U-shaped tubes <NUM> connecting end portions of the heat transfer tubes <NUM> to each other, and a plurality of fins <NUM> (heat transfer fins) spreading vertically and in an air flow direction.

The heat transfer tubes <NUM> are composed of copper, a copper alloy, aluminum, an aluminum alloy, or the like. As illustrated in a schematic external view in <FIG> of the fin <NUM> as viewed in a direction normal to a main surface of the fin <NUM>, the heat transfer tubes <NUM> are fixed to the fins <NUM> and used, in such a manner that the heat transfer tubes <NUM> pass through insertion openings 43a provided in the fins <NUM>. Note that the U-shaped tubes <NUM> are connected to end portions of the heat transfer tubes <NUM> in order to turn back the refrigerant flowing inside.

The fin <NUM> includes a substrate <NUM> and a plurality of protrusions <NUM> provided on a surface of the substrate <NUM>, as illustrated in a schematic sectional view in <FIG> of the vicinity of a surface of the fin <NUM> in a case where the protrusions <NUM> have a conical frustum shape, and a schematic view in <FIG> of the fin <NUM> viewed in a plate thickness direction. Note that the protrusions <NUM> and the substrate <NUM> each have a water-repellent coating film on the surface layer.

The substrate <NUM> is a plate-like member, and the thickness of the substrate <NUM> is <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less. Further, examples of the material used for the substrate <NUM> include aluminum, an aluminum alloy, silicon, and the like. Note that a surface of the substrate <NUM> where the protrusions <NUM> are not formed is constituted by the water-repellent coating film.

The protrusions <NUM> are formed on both surfaces of the substrate <NUM>. The protrusion <NUM> can have a structure in which, for example, aluminum, an aluminum alloy, silicon, or the like is covered with the water-repellent coating film. However, the protrusion <NUM> is not limited to having the structure.

The plurality of protrusions <NUM> is formed so as to satisfy the relationship of Expression <NUM>, where L is the average pitch of the plurality of protrusions <NUM>, D is the average diameter of the plurality of protrusions <NUM>, H is the average height of the plurality of protrusions <NUM>, and θ is a contact angle of water on a smooth plane of the water-repellent coating film. <FIG> is a graph in which the vertical axis represents the average diameter D of the protrusions <NUM> and the horizontal axis represents the gap (L - D) between the protrusions <NUM>, and an area satisfying the relationship of Expression <NUM> is indicated by hatching.

It is preferable that the plurality of protrusions <NUM> is formed so as to further satisfy the relationship of following Expression <NUM>. <FIG> is a graph in which the vertical axis represents the average diameter D of the protrusions <NUM> and the horizontal axis represents the gap (L - D) of the adjacent protrusions <NUM>, and an area satisfying the relationship of Expression <NUM> is indicated by hatching. [Expression <NUM>] <MAT>.

It is preferable that the plurality of protrusions <NUM> is formed so as to further satisfy the relationship of following Expression <NUM>. [Expression <NUM>] <MAT>.

The shape of the protrusion <NUM> is not limited, and examples of the shape include a frustum, such as a conical frustum illustrated in <FIG> (a shape obtained by cutting a cone along a plane parallel to the bottom surface and removing a small cone portion), or a pyramidal frustum, a conic solid, such as a cone, a pyramid, or a quadrangular pyramid, a column solid (a tube-shaped solid having two congruent planes as the bottom surface and the top surface), such as a cylinder, a prism, or a quadrangular prism, or a constricted shape (a shape in which the area of the cross section perpendicular to the protruding direction of the protrusion <NUM> has a minimum value in the protruding direction, such as a shape obtained by removing part of a side surface of a cylinder, a prism, or a conical frustum).

The average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM> can be measured by the following method using a scanning electron microscope (hereinafter abbreviated as a SEM). In the present disclosure, an S-<NUM> FE-SEM (Type II) manufactured by Hitachi High-Tech Corporation was used for the measurement. <FIG> is a diagram illustrating a method for measuring the average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM>.

First, a gray scale image is obtained with the SEM by observing a surface of the fin <NUM> including the plurality of protrusions <NUM> in a direction orthogonal to the substrate <NUM>. The observation conditions were that the acceleration voltage was <NUM> kV, the emission current was <NUM>µA, the working distance (the distance from the lower surface of the objective lens to the focus surface) was <NUM>, the inclination angle of the stage was <NUM>°, and the secondary electron detector was an upper detector.

In a case where in the observed SEM image, a blown highlight in which a bright portion whitens due to loss of gradation or black crush in which a dark portion blackens due to loss of gradation occurs, the brightness and the contrast may be appropriately adjusted. The resolution of the captured image is not limited, but is preferably <NUM> × <NUM> pixels or more. (a) of <FIG> is an example of the observed SEM image.

Next, the obtained SEM image is binarized to obtain a black-and-white binarized image. In the binarization processing, <NUM>% from the upper limit of the red, green, and blue (RGB) values of pixels constituting the SEM image is set as a threshold, pixels brighter than the threshold are set as white, and the other pixels are set as black to generate a black-and-white binarized image. (b) of <FIG> is a black-and-white binarized image obtained from the SEM image of (a) of <FIG>.

By binarizing the SEM image, the peripheries of the top portions of the protrusions <NUM>, which are brightly displayed in the SEM image because the top portions are close to the objective lens, are represented in white, and portions of the SEM image that are far from the objective lens except the top portions of the protrusions <NUM> are represented in black, so that the boundaries between the top portions of the protrusions <NUM> and the other area becomes clear.

Note that the above-described threshold is an example, and the threshold can be appropriately set in accordance with the shape of the plurality of protrusions <NUM>, or the like.

Next, line profiles of the obtained black-and-white binarized image are read to measure the average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM>. Specifically, a plurality of line profiles LP1, LP2, LP3. LPn extending in the same direction is drawn at equal intervals in the obtained black-and-white binarized image, pitches L1, L2, L3. Ln and diameters D1, D2, D3. Dn of the protrusions <NUM> are determined from each line profile LP, and the average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM> are calculated on the basis of the pitches L1, L2, L3 ··· Ln and the diameters D1, D2, D3. Dn of the protrusions <NUM>. The number of the line profiles LP is not limited, but is preferably <NUM> or more in a case of an image having the above-described resolution, (c) of <FIG> is a schematic view illustrating a state in which the average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM> are measured using the black-and-white binarized image in (b) of <FIG>.

Since the boundaries between the top portions of the protrusions <NUM> and the other area in the black-and-white binarized image are clear by the binarization processing, reading the pitches L <NUM>, L2, L3 ··· Ln and the diameters D1, D2, D3. Dn of the protrusions <NUM> using the line profiles is easier than a case of reading from the SEM image.

The average height H of the plurality of protrusions <NUM> is measured using an image obtained by observing a cross section of the fin <NUM> with the SEM. <FIG> is a diagram illustrating a method for measuring the average height H of the protrusions <NUM> using an image obtained by observing a cross section of the fin <NUM>.

As illustrated in <FIG>, the average height H of the plurality of protrusions <NUM> is calculated on the basis of the distances H1, H2, H3. Hn, in an extending direction of the protrusions <NUM>, between the top portions of the protrusions <NUM> and a surface of the substrate <NUM>, which can be read from an image obtained by observing the cross section of the fin <NUM>.

Note that the average height H of the plurality of protrusions <NUM> can also be observed under the same conditions as the conditions for the average pitch L of the plurality of protrusions <NUM> and the average diameter D of the plurality of protrusions <NUM>.

The water-repellent coating film constitutes surface layer portions of the protrusions <NUM> and the substrate <NUM>. Since the water-repellent coating film has a very small film thickness, the water-repellent coating film does not affect the surface structure of the fin <NUM> with the protrusions <NUM>.

Specifically, the film thickness of the water-repellent coating film constituting the surface layers of the protrusions <NUM> and the substrate <NUM> is, for example, <NUM> or more and <NUM> or less, and preferably <NUM> or more and <NUM> or less. Such a water-repellent coating film can be configured as, for example, a monomolecular film of a water-repellent agent.

Examples of the method for forming the water-repellent coating film include a method in which the bonding force between the protrusions <NUM> or the substrate <NUM> and the molecules of the water-repellent coating material is larger than the bonding force between the molecules of the water-repellent coating material, and after the water-repellent coating material is applied to the protrusions <NUM> and the substrate <NUM>, a treatment for cutting only the bonds between the molecules of the water-repellent coating material is performed to remove excess coating material.

As illustrated in <FIG>, a contact angle θw of water W on a smooth plane of the water-repellent coating film is <NUM>° < θw < <NUM>°. Thus, it is possible to reduce the contact area between a droplet (water droplet) and the fin <NUM>. Note that <NUM>° < θw < <NUM>° is more preferable from the viewpoint of sufficiently reducing the contact area between a droplet and the fin <NUM>.

The above water-repellent coating film is not limited, but is preferably an organic monomolecular film containing at least one of fluorine, silicone, or hydrocarbon, and more preferably an organic monomolecular film containing fluorine. A fluorine-containing monomolecular film can be selected from conventionally publicly known compounds, and for example, silane coupling agents having various fluoroalkyl groups or perfluoropolyether groups can be used. Note that examples of a product for forming a fluorine-containing monomolecular film include <NUM>,<NUM>,<NUM>,<NUM>-Heptadecafluorodecyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co. ) and OPTOOL DSX (manufactured by DAIKIN INDUSTRIES, LTD.

In the outdoor heat exchanger <NUM> of the present embodiment, the plurality of protrusions <NUM> satisfying the relationships of Expressions <NUM> to <NUM> is adopted in the surface structure of the fin <NUM>, and the water-repellent coating film having the specific water-repellency is further provided on the surface. Therefore, even in a case where condensed water is generated, a mechanism to be described later allows a droplet that has become large to spontaneously jump (scatter) from the fin <NUM> not by gravity but by release of excess surface energy. Accordingly, the outdoor heat exchanger <NUM> including the fins <NUM> can effectively suppress frost formation by scattering condensed water in a frost formation environment.

Therefore, even in a case where the outdoor heat exchanger <NUM> is used in a frost formation environment, frost formation can be suppressed by scattering condensed water, and a heating-operation time until a start of defrosting operation can be prolonged. Thus, it is possible to suppress deterioration of comfort in which the defrosting operation is frequently performed and the temperature of the space to be air-conditioned decreases.

Further, although the outdoor heat exchanger <NUM> of the present embodiment receives an air flow flowing in a horizontal direction from the outdoor fan <NUM> (although the outdoor heat exchanger <NUM> does not receive an air flow flowing in a vertical direction to promote drop of droplets), the adoption of the structure having the specific fine structure and the water-repellency allows droplets to be sufficiently removed from surfaces of the fins <NUM> only by supplying an air flow in a horizontal direction. In particular, the adoption of the above-described surface structure and water-repellency allows droplets to jump by themselves even in a location where an air flow is not generated or a location where an air flow is weak, and thus can effectively suppress adhesion of frost.

There is no limitation on the mechanism by which a droplet can jump spontaneously due to release of excess surface energy without depending on gravity when the droplet becomes large on a surface of the fin <NUM>, but the mechanism can be considered as illustrated in <FIG>, for example.

First, as illustrated in (a), on a surface of the fin <NUM> of the outdoor heat exchanger <NUM> functioning as an evaporator of the refrigerant, fine droplets (having a diameter of about several nm) serving as nuclei are condensed and generated. Next, as illustrated in (b), the generated nuclei grow and the particle diameters of the condensed droplets increase. Thereafter, as illustrated in (c), the droplets further grow and are into a state in which the droplets adhere to the adjacent protrusions <NUM> while filling depressions between the protrusions <NUM> of the fin <NUM> with the liquid. In addition, as illustrated in (d), the droplets grow so as to extend between the plurality of adjacent protrusions <NUM>, and as illustrated in (e), the adjacent droplets combine together. At the time of the combination of the droplets, the surface free energy changes so as to exceed the binding force of the droplet to the surface of the fin <NUM>, and as illustrated in (f), the droplet spontaneously jumps.

Note that the kinetic energy Ek for the droplet to spontaneously jump can be expressed below by modeling the dynamic relationship where m is the mass of the droplet and U is the moving speed of the jumping droplet.

Here, ΔEs indicates the amount of change in the surface free energy at the time of the combination of the droplets, Ew indicates the binding energy received by the droplet from a solid surface, ΔEh indicates the amount of change in potential energy (substantially zero because the fin <NUM> of the present embodiment extends parallel to a plane orthogonal to a horizontal direction), and ΔEvis indicates the viscous resistance at the time when the liquid flows.

In the above relational expression, in a case where the droplet is small, the surface free energy generated at the time of the combination is small, so that a spontaneous jump does not occur. Note that at this stage, since the sizes of the droplets are small, even if the ambient temperature is <NUM> or less, the droplets are likely to be maintained in a supercooled state without freezing. Then, it is considered that the spontaneous jump occurs in a case where the surface free energy generated at the time of the combination of the droplets exceeds the binding force to the surface. As described above, it is considered that even in a situation where the sizes of the droplets become large and it is difficult for the droplets to maintain the supercooled state and the freezing easily starts, the droplets jump by the surface free energy generated at the time of combination of the droplets, and are less likely to remain on the surface, and frost formation can be suppressed.

Here, forming the plurality of protrusions <NUM> so as to satisfy the relationships of Expressions <NUM> to <NUM> suppresses the binding force of the surface of the fin <NUM> on the droplets, and allows the droplets to easily scatter from the fin <NUM>, due to the following reason.

In other words, in a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), the intervals between the adjacent protrusions <NUM> is not excessively narrow. Therefore, the generation of a capillary force between the adjacent protrusions <NUM> is suppressed.

In a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), the intervals between the adjacent protrusions <NUM> is not excessively wide. Therefore, the generation of an adhesive force between condensed water and the substrate <NUM> due to the condensed water entering between the adjacent protrusions <NUM> is suppressed.

In a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), the distances between the distal ends of the protrusions <NUM> and the substrate <NUM> are ensured, and thus condensed water adhering to the distal ends of the protrusions <NUM> is suppressed from coming into contact with the substrate <NUM>. Therefore, the generation of an adhesive force between condensed water and the substrate <NUM> due to the condensed water entering between the adjacent protrusions <NUM> is suppressed.

In addition, in a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), the increase in the particle diameters of droplets entering between the adjacent protrusions <NUM> is suppressed.

In this way, forming the plurality of protrusions <NUM> so as to satisfy the relationship of Expression <NUM> suppresses the generation of the capillary force and the adhesive force that are binding forces of the surface of the fin <NUM> on the droplets, and the increase in the particle diameters of the droplets. Therefore, in the fin <NUM> in which the plurality of protrusions <NUM> is formed so as to satisfy the relationship of Expression <NUM>, the droplets generated on the surface can easily scatter.

Further, in a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), condensed water entering between the adjacent protrusions <NUM> becomes smaller. Therefore, in the fin <NUM> in which the plurality of protrusions <NUM> is formed so as to satisfy the relationship of Expression <NUM>, the increase in the particle diameters of the droplets is further suppressed, and the droplets generated on the surface can more easily scatter.

In addition, in a case where the plurality of protrusions <NUM> is formed so as to satisfy the relationship of (<NUM>-<NUM>), since distances between the distal ends of the protrusions <NUM> and the substrate <NUM> are more ensured, condensed water adhering to the distal ends of the protrusions <NUM> is more reliably suppressed from coming into contact with the substrate <NUM>. Therefore, also in the fin <NUM> in which the plurality of protrusions <NUM> is formed so as to satisfy the relationship of Expression <NUM>, the generation of the binding force of the surface of the fin <NUM> on the droplets is further suppressed, and the condensed water can more easily scatter.

In this way, adjusting the average pitch, the average diameter, and the average height of the plurality of protrusions <NUM> can control the particle diameters of the droplets scattering from the surface of the fin <NUM>. In the present embodiment, a first particle diameter, which is the maximum particle diameter of droplets scattering from a surface of the fin <NUM>, may be equal to or smaller than a second particle diameter, which is the minimum particle diameter of droplets that start to freeze on the surface of the fin <NUM> under predetermined first conditions under which droplets condense on the surface of the fin <NUM>. Thus, it is possible to scatter (jump), by the above-described mechanism, droplets having the first particle diameter by condensing and growing on the surface of the fin <NUM>.

The first conditions are conditions under which droplets condense on a surface of the fin <NUM> when the refrigerant cycle apparatus <NUM> performs the refrigerant cycle. The first conditions include, for example, the relative humidity of air around the fin <NUM> and the temperature of a surface of the fin <NUM> when the refrigerant cycle apparatus <NUM> is in the heating-operation mode and the outdoor heat exchanger <NUM> functions as an evaporator. Specifically, the first conditions are a state in which the relative humidity of air around the fin <NUM> is <NUM>%, and the temperature of a surface of the fin <NUM> is - <NUM>.

The first particle diameter is the maximum particle diameter at which droplets that have condensed and grown on a surface of the fin <NUM> are scattered. As described above, the first particle diameter is controlled by adjusting the average pitch, the average diameter, and the average height of the plurality of protrusions <NUM>. Specifically, the first particle diameter is <NUM>, preferably <NUM>.

The second particle diameter is the minimum particle diameter of a droplet that begins to freeze on a surface of the fin <NUM>. In general, a droplet has a property that the smaller the particle diameter is, the higher the degree of subcooling is (the droplet is less likely to freeze). Therefore, as a droplet that has condensed on a surface of the fin <NUM> grows and becomes larger in particle diameter, the degree of subcooling decreases and the droplet is more likely to freeze. Therefore, in a case where a condensed droplet is grown under a predetermined temperature condition, the droplet whose particle diameter has exceeded a predetermined critical value starts to freeze. The second particle diameter is the minimum particle diameter of a condensed droplet that starts to freeze in a case where the droplet is grown under the first conditions. Specifically, the second particle diameter is <NUM>.

Since a droplet has a property that the smaller the particle diameter is, the higher the degree of subcooling is (a droplet is less likely to freeze), it is necessary to scatter generated droplets from a surface of the fin <NUM> while the particle diameters are small in order to suppress frost formation on the surface of the fin <NUM>. In the present embodiment, a first particle diameter, which is the maximum particle diameter of droplets scattering from a surface of the fin <NUM>, is set to be equal to or smaller than a second particle diameter, which is the minimum particle diameter of droplets that start to freeze under the predetermined first conditions under which droplets condense on a surface of the fin <NUM>. Thus, the outdoor heat exchanger <NUM> using the fins <NUM> can scatter, before freezing, droplets that condense and grow on surfaces of the fins <NUM> under the first conditions, and therefore can effectively suppress frost formation.

Next, a method for manufacturing the outdoor heat exchanger <NUM> will be described. <FIG> is a schematic view illustrating a method for manufacturing the outdoor heat exchanger <NUM>. The method for manufacturing the outdoor heat exchanger <NUM> according to the present embodiment includes uncoiling, pressing, forming the protrusions <NUM>, assembling, and brazing.

In the uncoiling, a band-shaped metal plate wound in a coil shape is uncoiled and sent to the pressing. The metal plate is made of, for example, an aluminum alloy.

In the pressing, the metal plate, which is a plate-shaped material, is pressed with a pressing machine to be formed into the shape of the fin <NUM> illustrated in <FIG> to be a substrate <NUM>. The substrate <NUM> is sent to the forming the protrusions <NUM>.

The forming the protrusions <NUM> includes performing a surface treatment to form a surface structure including a plurality of protrusions <NUM> on a surface of the substrate <NUM>. The surface treatment changes the substrate <NUM> into a fin <NUM>. The fin <NUM> is sent to the assembling. Details of the surface treatment in the forming the protrusions <NUM> will be described later.

In the assembling, heat transfer tubes <NUM> are inserted into insertion openings 43a and expanded to assemble the fins <NUM> and the heat transfer tubes <NUM>. The assembled fins <NUM> and heat transfer tubes <NUM> are sent to the brazing.

In the brazing, the fins <NUM> and the heat transfer tubes <NUM> are brazed together. Further, U-shaped tubes <NUM> are brazed to end portions of the heat transfer tubes <NUM>. Instead of the U-shaped tubes <NUM>, headers may be brazed. As a result, the outdoor heat exchanger <NUM> is completed.

<FIG> includes SEM images obtained by capturing surface structures formed on surfaces of the fins <NUM>. (a) of <FIG> includes a vertical-viewpoint image and a <NUM>°-inclined-viewpoint image of a surface of the fin <NUM> manufactured by the method for manufacturing a heat exchanger according to the present embodiment. On the other hand, (b) of <FIG> is a vertical-viewpoint image of a surface of the fin <NUM> subjected to the pressing performed after the performing the surface treatment to form the surface structure including the protrusions <NUM>. In other words, (b) of <FIG> is an image of a surface of the fin <NUM> formed by the method for manufacturing the outdoor heat exchanger <NUM> according to the present embodiment illustrated in <FIG> in which the order of the pressing and the forming the protrusions <NUM> is reversed.

In the images illustrated in (a) of <FIG>, it is confirmed that the protrusions <NUM> maintain upright shapes. On the other hand, in the image illustrated in (b) of <FIG>, it is confirmed that many of the protrusions <NUM> fall and the shapes of the protrusions <NUM> are not maintained. This is because the pressing after the performing the surface treatment to form the surface structure including the protrusions <NUM> crushes the protrusions <NUM> and destroys the surface structure. The fin <NUM> in which the protrusions <NUM> are crushed and the surface structure is destroyed limits the above-described function of scattering droplets.

As described above, the method for manufacturing a heat exchanger according to the present embodiment includes, after the pressing, the performing the surface treatment to form the surface structure including the protrusions <NUM>, the destruction of the protrusions <NUM> after the surface treatment is suppressed. Therefore, the present method for manufacturing a heat exchanger can efficiently manufacture a heat exchanger capable of effectively suppressing frost formation by scattering condensed water.

Further, a method for manufacturing a heat exchanger including the pressing after the performing the surface treatment sends a metal plate which is only uncoiled and whose shape is not formed, to the performing the surface treatment. On the other hand, the method for manufacturing a heat exchanger according to the present embodiment sends the substrate <NUM> whose predetermined shape has been formed by the pressing, to the performing the surface treatment. Thus, in the method for manufacturing a heat exchanger according to the present embodiment, the amount of the metal plate to be treated in the performing the surface treatment is smaller than the amount in a method for manufacturing a heat exchanger including the pressing after the performing the surface treatment. Therefore, in a case where a liquid chemical is used in the performing the surface treatment as in an anodic oxidation treatment or an etching treatment described later, the amount of the liquid chemical used can be reduced.

Next, the surface treatment in the forming the protrusions <NUM> will be described. <FIG> is a sectional view illustrating the surface treatment in the forming the protrusions <NUM>. In the present embodiment, a plasma etching treatment is used as the surface treatment.

First, as illustrated in (<NUM>), a substrate <NUM> that is a plate-shaped member having a smooth surface is prepared.

Next, as illustrated in (<NUM>), a layer having a specific thickness is formed on a surface of the substrate <NUM>. The layer is composed of an aluminum alloy, silicon, or the like.

Then, as illustrated in (<NUM>), masking is performed at specific intervals on the layer formed in (<NUM>), and plasma is radiated. The protrusion shape is controlled, such as the average pitch L controlled by the intervals of the masking, and the average diameter D of the protrusions <NUM> controlled by the shape of the masking. Among others, in a case where the protrusion <NUM> is shaped into a shape in which the area of the cross section perpendicular to the protruding direction of the protrusion <NUM> includes at least one minimum value in the protruding direction, the shape of each column forming the protrusion <NUM> is controlled by adjusting each of the radiation amount and the radiation time of the plasma.

Next, as illustrated in (<NUM>), etching is performed to form a protrusion shape having a specific shape and a specific pattern. Here, the height of the protrusions <NUM> is controlled by the etching time.

Note that the formation of the shape of the protrusions <NUM> is not limited to the plasma etching treatment, and for example, a publicly known method, such as an anodic oxidation treatment, a boehmite treatment, or an alumite treatment, can be used.

Finally, as illustrated in (<NUM>), a water-repellent coating film is formed on surfaces of the protrusions <NUM> and the substrate <NUM> on which the protrusions <NUM> are not formed. Note that selected as a water-repellent coating material for forming the water-repellent coating film is a water-repellent coating material having a bonding force between the protrusions <NUM> or the substrate <NUM> and molecules of the water-repellent coating material larger than a bonding force between molecules of the water-repellent coating material. After the water-repellent coating material is applied, excess coating material except the surface layer is washed away. In this way, the shapes of the protrusions <NUM> before the application can be substantially maintained.

The above-described embodiment can be appropriately modified as shown in the following modifications.

To describe the above embodiment, exemplified is a case where the specific fine protrusions <NUM> and the water-repellent coating film are provided on surfaces of the fins <NUM> of the outdoor heat exchanger <NUM>.

However, the specific fine protrusions <NUM> and the water-repellent coating film may also be provided at other locations to which condensed water may adhere. For example, the specific fine protrusions <NUM> and the water-repellent coating film described above may also be provided on surfaces of the heat transfer tubes <NUM> and surfaces of the U-shaped tubes <NUM> constituting the outdoor heat exchanger <NUM>. In this case, it is possible to suppress adhesion of condensed water at the locations and suppress adhesion of frost due to freezing of the condensed water.

In the above-described embodiment, the plasma etching treatment is used to form the protrusions <NUM>, but an anodic oxidation treatment and an etching treatment may be used as a method for forming the protrusions <NUM>. The formation of the protrusions <NUM> using the anodic oxidation treatment and the etching treatment can be performed as described below, for example.

First, a stainless steel material is attached to a cathode connected to a direct-current power source, and a substrate <NUM> is attached to an anode. In this case, an aluminum material can be used for the substrate <NUM>.

Next, the stainless steel material and the substrate <NUM> are immersed in a liquid chemical in which a predetermined liquid chemical type is adjusted to a predetermined concentration and temperature.

Next, an anodic oxidation treatment is performed by applying a voltage to the stainless steel material and the substrate <NUM> for a predetermined treatment time with the direct-current power source.

Used as the liquid chemical type of the liquid chemical used for the anodic oxidation treatment is phosphoric acid, pyrophosphoric acid, oxalic acid, malonic acid, etidronic acid, or a mixed solution thereof, but the liquid chemical type is not limited thereto. The concentration of the liquid chemical type in the liquid chemical is <NUM> mmol/L or more and <NUM> mol/L or less, preferably <NUM> mmol/L or more and <NUM> mol/L or less, and more preferably <NUM> mmol/L or more and <NUM> mol/L or less. The temperature of the liquid chemical is not limited, but is a room temperature (<NUM> or more and less than <NUM>).

The voltage applied during the anodic oxidation treatment needs to be <NUM> V or more, and is preferably a direct-current voltage of <NUM> V or more, more preferably <NUM> V or more and <NUM> V or less.

The treatment time for performing the anodic oxidation treatment needs to be <NUM> minutes or more, and is preferably <NUM> minutes or more. The upper limit of the treatment time is not limited, but can be less than <NUM> minutes from the viewpoint of production.

When the anodic oxidation treatment is finished, next, an etching treatment is performed by immersing the substrate <NUM> subjected to the anodic oxidation treatment for a predetermined treatment time, in a liquid chemical in which a predetermined liquid chemical type is adjusted to a predetermined concentration and temperature.

Used as the liquid chemical type of the liquid chemical used for the etching treatment is phosphoric acid, pyrophosphoric acid, oxalic acid, malonic acid, etidronic acid, or a mixed solution thereof, but the liquid chemical type is not limited thereto. The concentration of the liquid chemical type in the liquid chemical is <NUM> wt% or more and <NUM> wt% or less, preferably <NUM> wt% or more and <NUM> wt% or less, and more preferably <NUM> wt% or more and <NUM> wt% or less. The temperature of the liquid chemical is not limited, but is <NUM> or more and <NUM> or less, preferably <NUM> or more and <NUM> or less, and more preferably <NUM> or more and <NUM> or less.

The treatment time for performing the etching treatment is <NUM> minutes or more and <NUM> minutes or less, preferably <NUM> minutes or more and <NUM> minutes or less, and more preferably <NUM> minutes or more and <NUM> minutes or less.

Thereafter, a water-repellent coating film is formed on surfaces of the protrusions <NUM> and the substrate <NUM> on which the protrusions <NUM> are not formed in the same manner as in the above-described embodiment, although the description thereof is omitted.

Assessment plates according to Examples and Comparative Examples were produced, and Assessment <NUM> for confirming the effect of suppressing frost formation was performed. Hereinafter, Examples and Comparative Examples will be described, but the present disclosure is not limited thereto.

Used as an assessment plate according to Example <NUM> was a silicon substrate of <NUM> by <NUM> on which protrusions <NUM> were formed by performing a plasma etching treatment for a predetermined time, and then a water-repellent coating film containing a C8 fluorine-based water-repellent material was formed using chemical vapor deposition (hereinafter abbreviated as CVD).

Used as an assessment plate according to Example <NUM> was a silicon substrate of <NUM> by <NUM> on which protrusions <NUM> were formed by performing an anodic oxidation treatment and an etching treatment under predetermined conditions, and then a water-repellent coating film containing a C8 fluorine-based water-repellent material was formed using the CVD.

The liquid chemical used for the anodic oxidation treatment included etidronic acid as the liquid chemical type, and had a concentration of <NUM> mol/L, and a temperature of <NUM>. In the anodic oxidation treatment, a direct-current voltage of <NUM> V was applied for <NUM> minutes.

The liquid chemical used for the etching treatment included phosphoric acid as the liquid chemical type, and had a concentration of <NUM> wt%, and a temperature of <NUM>. The etching treatment was carried out for <NUM> minutes.

Used as an assessment plate according to Comparative Example <NUM> was an aluminum substrate of <NUM> by <NUM> not provided with protrusions and a water-repellent coating film.

Used as an assessment plate according to Comparative Examples <NUM> to <NUM> was a silicon substrate of <NUM> by <NUM> on which protrusions were formed by performing an etching treatment for a time different from the time in Example <NUM>, and then a water-repellent coating film containing a C8 fluorine-based water-repellent material was formed using the CVD. (Shape of Protrusion).

For each assessment plate, the average pitch L, the average diameter D, and the average height H of the plurality of protrusions were measured by the above-described method using an S-<NUM> FE-SEM (Type II) manufactured by Hitachi High-Tech Corporation.

As to the contact angle (static contact angle) of water on a smooth plane of the water-repellent coating film, the measurement was performed at five points on a sample with a water-repellent coating film including a C8 fluorine-based water-repellent material and formed using the CVD, with a contact angle meter Drop Master <NUM>, and water droplets of a volume of 2µl.

The contact angles of water on flat surfaces of the water-repellent coating film formed in Example <NUM> and Comparative Examples <NUM> to <NUM> were <NUM>°.

For each assessment plate, a "frost formation start time period" and a "moisture adhesion amount" were measured in a case where one of the surfaces was cooled while air flowing in a direction parallel to the other surface was applied to the other surface. Further, a "frost height" was measured for the assessment plates according to Example <NUM>, and Comparative Examples <NUM> and <NUM>.

The frost formation start time period is a time period from the start of the assessment to the start of frost adhesion to the other surface. The moisture adhesion amount is an adhesion amount of frost adhering to the other surface after the completion of the assessment. The frost height is a change in the height, in a plate thickness direction of the assessment plate, of the frost adhering to the other surface until two hours elapsed from the start of the assessment.

The assessment plates were cooled under the following conditions.

The assessment plate was cooled using a Peltier element, and the heat flux was measured with a heat flux sensor provided between the assessment plate and the Peltier element.

The moisture adhesion amount was obtained by measuring the difference in the weight of the assessment plate between before and after the assessment with an electronic balance.

The frost height was measured using a laser displacement meter.

Table <NUM> shows the shapes (the average pitches L - D, the average diameters D, and the average heights H), and the measurement results (the frost formation start time periods and the moisture adhesion amounts) of the plurality of protrusions of the assessment plates according to Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>. Further, the assessment plates according to Examples <NUM> and <NUM> and Comparative Examples <NUM> to <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are plotted on the graphs of <FIG> and <FIG>.

As shown in Table <NUM>, the frost formation start time period of the assessment plate according to Example <NUM> was <NUM> minutes, and the frost formation start time period of the assessment plate according to Example <NUM> was <NUM> minutes. Both of the assessment plates according to Examples <NUM> and <NUM> required a longer time before the start of frost formation than the assessment plates according to Comparative Examples <NUM> to <NUM>. Further, the moisture adhesion amount of the assessment plate according to Example <NUM> was <NUM>, and the moisture adhesion amount of the assessment plate according to Example <NUM> was <NUM>. Both of the assessment plates according to Examples <NUM> and <NUM> had a smaller moisture adhesion amount than the assessment plates according to Comparative Examples <NUM> to <NUM>. From the above assessment results, it was confirmed that the assessment plate according to Example <NUM> can effectively suppress frost formation. Further, it was confirmed that the assessment plate according to Example <NUM> can more effectively suppress frost formation.

<FIG> includes a diagram illustrating changes in frost heights of the assessment plates according to Examples <NUM> and <NUM> and Comparative Examples <NUM> and <NUM>, and images obtained by capturing the surfaces of the assessment plates according to Examples <NUM> and <NUM> and Comparative Example <NUM> after two hours from the start of the assessment.

As illustrated in <FIG>, it was confirmed that the assessment plates according to Examples <NUM> and <NUM> had less frost formation even after two hours than the assessment plates according to Comparative Examples <NUM> and <NUM>. In particular, it was confirmed that the assessment plate according to Example <NUM> had less frost formation after two hours than the assessment plate according to Example <NUM>.

Using the assessment plates prepared in Assessment <NUM>, Assessment <NUM> was performed to confirm the relationship between frost formation and the particle diameters of droplets.

In this assessment, the assessment plate of Example <NUM> and the assessment plate of Comparative Example <NUM> were used. For each assessment plate, in a case where one of the surfaces is cooled while air flowing in a direction parallel to the other surface was applied to the other surface, the sizes of droplets generated on the other surface was measured. The sizes of the droplets were measured by analyzing an image obtained by capturing the other surface from the front with a microscope.

The assessment plates were cooled under the following conditions. Note that the following conditions correspond to the above-described first conditions (conditions of humidity and temperature in the fin <NUM> at a time when the outdoor heat exchanger <NUM> functions as an evaporator).

The assessment plates were cooled using a Peltier element.

As a result of the above assessment, as to the particle diameters of the droplets generated on the assessment plate according to Example <NUM>, the average particle diameter was <NUM>, and the maximum particle diameter was <NUM>. Further, as to the particle diameters of the droplets generated on the assessment plate according to Comparative Example <NUM>, the average particle diameter was <NUM>, and the maximum particle diameter was <NUM>. From the above assessments, it was confirmed that the assessment plate according to Example <NUM>, which, in Assessment <NUM>, received a confirmation that the assessment plate was capable of effectively suppressing frost formation, was capable of scattering droplets having particle diameters larger than <NUM>. Further, it was confirmed that the assessment plate according to Comparative Example <NUM>, which, in Assessment <NUM>, received a confirmation that the assessment plate was capable of only limitedly suppressing frost formation, was capable of scattering droplets having particle diameters larger than <NUM>. Thus, it was confirmed that frost formation can be effectively suppressed by performing control to make smaller the particle diameters of the scattered droplets.

Claim 1:
A heat exchanger (<NUM>) provided with a water-repellent coating film on part of a surface of the heat exchanger (<NUM>), wherein
the surface on which the water-repellent coating film is provided has a surface structure including a plurality of protrusions (<NUM>), and satisfies all relationships <MAT> <MAT> <MAT> <MAT> and <MAT>
L: an average pitch of the plurality of protrusions,
D: an average diameter of the plurality of protrusions,
H: an average height of the plurality of protrusions, and
θ: a contact angle of water on a smooth plane of the water-repellent coating film.