JP2012228670A - Water-repellent substrate, heat exchanger using water-repellent substrate, and method for producing water-repellent substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-repellent substrate having excellent water repellency to condensed water produced on a surface thereof, a heat exchanger using water-repellent substrate and a method for producing water-repellent substrate.SOLUTION: The water-repellent substrate is provided with a substrate 110, and a hydrophobic film 120 disposed upon the surface of the substrate 110, wherein a plurality of needle-shaped protrusions 111 extending in a needle shape is formed on the surface of the substrate 110. The hydrophobic film 120 comprises a plurality of minute protrusions 121 that are formed finer than the needle-shaped protrusions 111 on the surfaces of the needle-shaped protrusions 111 and the surface of the substrate 110 between the needle-shaped protrusions 111.

Description

  The present invention relates to a water-repellent substrate that repels condensed water generated from the surface of the substrate at a low temperature, a heat exchanger using the water-repellent substrate, and a method for producing the water-repellent substrate.

  As a conventional super water-repellent substrate, for example, one described in Patent Document 1 is known. The super water-repellent substrate of Patent Document 1 is applied to a window glass for a vehicle, and has a base film having fine irregularities on the surface of the substrate and a water-repellent film formed on the minute irregularities of the base film. And have. The water-repellent film has a surface shape reflecting the minute irregularities of the base film. Furthermore, the surface shape of the water-repellent coating is composed of particulate protrusions and columnar protrusions that are higher in height as measured from the surface of the substrate than the particulate protrusions.

  In Patent Document 1 applied to a window glass, CA ≧ 150 degrees, where CA is the contact angle of water droplets on the surface of the water-repellent coating, and TA is the falling angle as the critical angle at which the water droplets fall when dropped. In addition, TA ≦ 15 degrees, or 150 degrees> CA ≧ 145 degrees and TA ≦ 5 degrees, and the water repellency is excellent and water droplets hardly remain on the surface of the window glass.

Japanese Patent No. 4198598

  However, the super water-repellent substrate of Patent Document 1 is excellent in dropping water droplets dropped on a window glass or the like as described above. On the other hand, for example, when the base material is placed in a low temperature field, water vapor in the air that touches the base material is condensed and condensed water is generated from the surface of the base material. The substrate has a problem that good water repellency of condensed water cannot be obtained. That is, in the super water-repellent substrate of Patent Document 1, condensed water is generated from the inside of the recess formed between the particulate protrusions and the columnar protrusions, and the condensed water accumulates in the recess, and further outside the recess. Since the condensed water in each recess is connected to each other to form a large water film, it is difficult to obtain good water repellency of the condensed water and it is difficult for the condensed water to slide down.

  In view of the above problems, an object of the present invention is to provide a water-repellent substrate having good water repellency against condensed water generated on the surface, a heat exchanger using the water-repellent substrate, and a method for producing the water-repellent substrate. Is to provide.

  In order to achieve the above object, the present invention employs the following technical means.

In invention of Claim 1, a base material (110),
A water-repellent substrate comprising a hydrophobic coating (120) provided on the surface of the substrate (110),
A large number of needle-like protrusions (111) extending in a needle shape are formed on the surface of the substrate (110),
The hydrophobic film (120) is formed on the surface of the needle-like protrusions (111) and the surface of the base material (110) between the needle-like protrusions (111). It is characterized by being formed as a protrusion (121).

  According to the present invention, even if condensed water is generated from the bottom surface between the needle-like projections (111) under the condition that condensed water is generated on the surface of the base material (110), When they are combined and grown, the fine projections (121) are pushed out from the bottom side between the needle-like projections (111) toward the tip side, so that they stay between the needle-like projections (111). There is nothing. Therefore, the condensed water accumulates in the concave portions as in the prior art, and the condensed water in the concave portions is connected to each other outside the concave portions to form a large water film, so that the water is repelled as water droplets of condensed water. You can slide down.

  The invention according to claim 2 is characterized in that the fine protrusion (121) is a monomolecular film having a hydrophobic functional group.

  According to this invention, a large number of fine protrusions (121) can be easily formed on the surface of the needle-like protrusions (111) and the surface of the base material (111) between the needle-like protrusions (111).

  The invention according to claim 3 is characterized in that it includes at least one of an alkyl group and a fluoroalkyl group as a hydrophobic functional group.

  According to the present invention, a large number of fine protrusions (121) can be formed at a relatively low cost.

  The invention according to claim 4 is characterized in that the substrate (110) is made of metal or metal oxide.

  According to the present invention, when the substrate (110) is a metal or metal oxide, it becomes easy to form a hydroxyl group on the surface, so that a hydrophobic functional group can be firmly bonded, and a fine protrusion ( 121) can be reliably formed.

The invention according to claim 5 is an endothermic heat exchanger that absorbs heat from the air circulating outside the heat exchanging portion (210) by the heat medium flowing inside the heat exchanging portion (210),
At least one of the heat medium circulation tube (211) forming the heat exchange section (210) and the fin (212) connected to the tube (211) to form a heat transfer surface with respect to the air is defined in claims 1 to 2. It is formed by the water-repellent substrate (100) according to any one of Items 4.

  In the heat exchanger for heat absorption (200), when the air temperature is lower than the dew point temperature of the water vapor contained in the air when absorbing heat from the air, the water vapor becomes condensed water and the surface of the heat exchange part (210). Adhere to. If the condensed water adheres, the ventilation resistance of the air passing through the heat exchange section (210) increases, and the heat resistance due to the condensed water increases, so the heat exchange performance in the heat exchanger (200) decreases. To do. Further, the condensed water freezes and becomes frost on the surface of the heat exchanging portion (210) when it becomes below the freezing temperature.

  According to the fifth aspect of the present invention, even if condensed water is generated on the surface of the heat exchanging portion (210) at the time of heat absorption, it gives a good sliding effect on the generated condensed water. Furthermore, the performance fall of the heat exchanger (200) by frost formation can be suppressed.

In invention of Claim 6, it is a manufacturing method of the water-repellent base material provided with the hydrophobic membrane | film | coat (120) on the surface of the base material (110),
A protrusion forming step of forming a large number of needle-like protrusions (111) extending in a needle shape on the surface of the substrate (110);
A large number of fine protrusions (121) finer than the needle-like protrusions (111) are formed on the surface of the needle-like protrusions (111) and on the surface of the base material (111) between the needle-like protrusions (111). And a film forming step of providing a hydrophobic film (120).

  According to this invention, it can provide as a method for manufacturing the water-repellent substrate (100) according to claim 1.

In invention of Claim 7, a base material (110) is a base material (110) made from aluminum,
In the protruding portion forming step, the needle-shaped protruding portion (111) is formed by performing a boehmite treatment on the base material (110).

  According to this invention, a large number of needle-like protrusions (111) can be easily formed due to the etching effect in the boehmite treatment.

  In the invention according to claim 8, in contrast to the invention according to claim 7, in the film forming step, the substrate (110) on which the needle-like protrusions (111) are formed is treated with water containing a hydrophobic functional group. It is characterized in that the fine protrusions (121) are formed by dipping in a saturated solution.

  According to this invention, at the time of immersion, hydrophobic functional groups in the water-saturated solution are formed on the surface of the needle-like protrusion (111) and the surface of the base material (111) between the needle-like protrusions (111). Thus, the fine protrusion (121) can be reliably formed.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows a corresponding relationship with the specific means of embodiment description mentioned later.

It is sectional drawing which shows a water repellent base material. It is an enlarged view which shows the II section in FIG. It is an enlarged view which shows the surface of a base material (magnification 1000 times). It is an enlarged view which shows the surface (acicular projection part) of a base material (magnification 100000 times). It is a perspective view which shows a heat exchanger. It is a model figure which shows a fin cross section and a condensed water droplet diameter. It is a model figure for obtaining a water drop sliding formula. It is a model figure for calculating the surface energy of a slidable film. It is a model figure for calculating a contact angle so that a droplet diameter may slide at 0.4 mm. It is a graph which calculates | requires the contact angle for a water drop not to obstruct | occlude in a fin. It is a graph which shows frost formation time when frost formation and defrosting in a heat exchanger are repeated.

  A plurality of modes for carrying out the present invention will be described below with reference to the drawings. In each embodiment, parts corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals, and redundant description may be omitted. When only a part of the configuration is described in each mode, the other modes described above can be applied to the other parts of the configuration. Not only combinations of parts that clearly indicate that the combination is possible in each embodiment, but also a combination of the embodiments even if they are not clearly specified unless there is a problem with the combination. It is also possible.

(First embodiment)
The water-repellent substrate 100 according to the first embodiment will be described with reference to FIGS. 1 is a cross-sectional view showing the water-repellent substrate 100, FIG. 2 is an enlarged view showing a portion II in FIG. 1, FIG. 3 is an enlarged view showing the surface of the substrate 110 (1000 times magnification), and FIG. It is an enlarged view (magnification 100000 times) which shows the surface (needle-like projection part 111) of 110. FIG. As shown in FIG. 1, the water-repellent substrate 100 is formed by providing a hydrophobic film 120 on the surface of a substrate 110 formed from an aluminum plate material.

  The base material 110 is a plate member made of metal such as aluminum, iron, copper, or resin, and a large number of needle-like protrusions 111 extending in a needle shape are formed on the surface of the base material 110. When the dimension between the protrusions of the needle-like protrusions 111 is defined as a period, the period of the needle-like protrusions 111 is about 700 nm to 500 μm. The period of the acicular protrusion 111 is preferably about 1 μm to 10 μm. Thus, the needle-like protrusion 111 is a protrusion on the order of microns.

  The hydrophobic film 120 is formed by a large number of fine protrusions 121. That is, the hydrophobic film 120 is formed as an aggregate of a large number of fine protrusions 121. The fine protrusions 121 are a large number of protrusions formed more finely than the needle-like protrusions 111 on the surface of the needle-like protrusions 111 and the surface of the base 111 between the needle-like protrusions 111. The period of the fine protrusions 121 is about 1 nm to 500 nm. The period of the fine protrusions 121 is preferably about 1 nm to 10 nm. Thus, the fine protrusion 121 is a nano-order protrusion.

  The water repellent substrate 110 is manufactured as follows.

1. First step (previous step)
First, a 4 cm ² (2 cm square) aluminum plate material is manufactured as the base material 110. And the uneven | corrugated | grooved part 112 is formed in the surface of the base material 110 by grinding | polishing. This uneven | corrugated | grooved part 112 is made into the uneven | corrugated state equivalent to the surface in the material step of the tube and fin which comprise a heat exchanger, for example.

  In actual polishing, for example, # 100 water-resistant sandpaper (Fuji Star manufactured by Sankyo Rikagaku) was used. By measuring the surface roughness of the substrate 110 after polishing using a surface roughness measuring instrument (Dektak 6M, manufactured by Digital Instruments), the period of the irregularities 112 (the dimension between the peaks) is measured. can do. It was confirmed that the obtained period (average length RSm of contour curve element: JIS B0601-2001) was 10 μm. At this time, the arithmetic average height Ra of the uneven portion 112 was 0.5 μm. The surface shape observation image by the scanning electron microscope (SEM) at this time is shown in FIG. Note that (a) and (b) in FIG. 3 are observation results at two representative positions on the surface of the substrate 110.

2. Second step (projection forming step)
In the first step, the substrate 110 on which the irregularities 112 were formed was immersed in acetone to clean the surface, and the boehmite treatment was performed by immersing in boiling pure water for 5 minutes. Next, the substrate 110 taken out was cooled, washed by blowing ultrapure water, and dried by blowing nitrogen gas. Thereby, a hydroxyl group was generated on the surface of the substrate 110. In addition, a needle-like protrusion 111 was formed on the surface of the substrate 110. An amine such as diethanolamine may be added to boiling water.

  As described above, there are two purposes for boehmite treatment of the substrate 110. One is to form a hydroxyl group on the surface of the substrate 110 by performing boehmite treatment, and in the subsequent third step, the monomolecular film forming reagent and the hydroxyl group react to form a strong bond.

  The second purpose of the boehmite treatment is to etch the surface of the substrate 110 in the course of the boehmite treatment, thereby forming the needle-like protrusions 111 having a very fine needle-like structure on the surface of the concavo-convex portion 112. FIG. 4 shows an image obtained by observing the substrate 110 after the boehmite treatment with a scanning electron microscope (SEM). 4A and 4B are observation results at two representative positions on the surface of the substrate 110. FIG. When the roughness was analyzed from the analysis result from the SEM image, the needle-like protrusion 111 was confirmed. At this time, the arithmetic average height Ra of the needle-like protrusion 111 was 20 nm.

3. Third step (film formation step)
In the film-forming step, after the first and second steps, the substrate 110 is immersed in a water-saturated solution of the hydrophobic film, whereby the hydrophobic film 120 (many fine protrusions are formed on the surface of the needle-shaped protrusion 111. Part 121).

  Specifically, the base material 110 whose surface was boehmite-treated in the second step was immersed in a 25 mM water-saturated xylene solution of ODS (okudedecyltrimethylsilane) at room temperature (20 ° C.) for 2 days.

4). Fourth step (post-treatment of film forming process)
The substrate 110 subjected to the film forming process in the third step was washed with acetone and then dried at 80 ° C. for 1 hour.

Through the above steps, a monomolecular film (alkyl monomolecular film) of C ₁₈ H ₃₇ Si (O ⁻ ) ₃ having an alkyl group on the surface of the needle-like protrusions 111 and the surface of the base 110 between the needle-like protrusions 111. A water-repellent substrate 100 having a hydrophobic film (water-repellent film) 120 made of The fourth step can be omitted.

  The water-repellent substrate 100 configured as described above has a structure schematically shown in FIGS. In this water-repellent substrate 100, the needle-like protrusion 111 is formed by the second step, and the fine protrusion 121, that is, the hydrophobic film 120 (ODS monomolecular film) is formed by the third step. It has become.

  The water repellent substrate 100 thus formed has high water repellency (contact angle = 160 °), and when condensed water is generated on the water repellent substrate 100 arranged at 3 °, the water droplet diameter is 1 mm. When it became, it slipped down.

  In this embodiment, under the condition that condensed water is generated on the surface of the substrate 110, the condensed water grows in combination with each other even if condensed water is generated from the bottom surface between the needle-like protrusions 111. Since the fine projections 121 are pushed from the bottom side between the needle-like projections 111 toward the tip side by the fine projections 121, the needle-like projections 111 do not stagnate. Therefore, the condensed water accumulates in the concave portions as in the prior art, and the condensed water in the concave portions is connected to each other outside the concave portions to form a large water film, so that the water is repelled as water droplets of condensed water. You can slide down.

  In addition, the water-repellent substrate 100 of the present embodiment exhibits high sliding performance as described above even under conditions where frost can be generated on the surface at low temperatures. It was possible to delay the time of occurrence.

(Second Embodiment)
In the second embodiment, the water-repellent substrate 100 was created by changing the film-forming material in the third step with respect to the first embodiment.

  That is, first, the substrate 110 that has undergone the same steps as those of the first embodiment was prepared until the first step and the second step. Then, as a third step (film formation step), FAS17 (perfluorodeoxymethylsilane) 25 mM water-saturated 1,3-bis (trifluoromethyl) benzene (F6xy) solution was subjected to a boehmite treatment on the surface 110 in the second step. Was immersed at room temperature (20 ° C.) for 2 days.

After the third step, the same process as in the fourth step of the first embodiment was performed. Through the above steps, from the monomolecular film (fluorinated alkyl monomolecular film) of C ₈ F ₁₇ C ₂ H ₄ Si (O ⁻ ) ₃ having a fluoroalkyl group on the surface of the needle-like protrusion 111 of the substrate 110. A water-repellent substrate 100 having a hydrophobic film 120 (many fine protrusions 121) formed thereon was produced. Note that the fourth step can be omitted.

  The water-repellent substrate 100 created in this way showed the same water repellency as the water-repellent substrate 100 created in the first embodiment.

(Third embodiment)
In the third embodiment, the water-repellent substrate 100 was created by changing the film-forming material in the third step with respect to the first and second embodiments.

That is, first, the substrate 110 that has undergone the same steps as those of the first and second embodiments was prepared until the first step and the second step. Then, as a third step (film formation step), a surface of the reaction vessel is sealed in the second step in a sealed and pressurizable container having a capacity of 20 ml in which 0.5 g of C ₈ F ₁₇ C ₂ H ₄ NCO (perfluorodeoxycynate) is enclosed. Boehmite-treated substrate 110 was inserted and sealed, and a gas phase reaction was performed at 150 ° C. for 72 hours.

After the third step, the same process as in the fourth step of the first and second embodiments was performed. Through the above steps, a hydrophobic film made of a monomolecular film (fluorinated alkyl monomolecular film) of C ₈ F ₁₇ C ₂ H ₄ NHCOO ⁻ having a fluoroalkyl group on the surface of the needle-like protrusion 111 of the substrate 110. A water-repellent substrate 100 having 120 (many fine protrusions 121) formed thereon was produced. Note that the fourth step can be omitted.

  The water repellent base material thus produced exhibited a water repellency equivalent to that of the water repellent base material 100 prepared in the first and second embodiments.

(Fourth embodiment)
In 4th Embodiment, the film forming material in a 3rd process was changed with respect to 1st-3rd Embodiment, and the water-repellent base material 100 was created.

That is, first, the base material 110 that has undergone the same processes as those in the first to third embodiments until the first process and the second process was prepared. Then, as a third step (film forming step), a surface-boehmite-treated base in the second step is placed in a 100-ml sealed and pressurizable reaction vessel in which 1.4 g of C ₁₈ H ₃₇ NCO (octadecylicocynate) is enclosed. The material 110 was inserted and sealed, and gas phase reaction was performed at 150 ° C. for 72 hours.

The process similar to the 4th process of the said 1st-3rd embodiment was performed after the said 3rd process. Through the above steps, the hydrophobic film 120 (a monomolecular film of C ₁₈ H ₃₇ NHCOO ⁻ having an alkyl group) is formed on the surfaces of the first and second uneven portions 111 and 112 of the substrate 110 ( A water-repellent substrate 100 having a large number of fine protrusions 121) was produced.

  The water-repellent substrate 100 created in this way showed the same water repellency as the water-repellent substrate 100 created in the first to third embodiments.

(Fifth embodiment)
In the fifth embodiment, the water-repellent substrate 100 described in the first to fourth embodiments is applied to a heat exchanger 200.

  The heat exchanger 200 is a heat exchanger for absorbing heat, and as shown in FIG. 5, for example, is an evaporator that cools air for air conditioning in a refrigeration cycle of a vehicle air conditioner. The heat exchanger 200 includes a heat exchange unit 210 and a pair of header tanks 220 connected to the heat exchange unit 210. The heat exchanging unit 210 includes a plurality of laminated tubes 211 having a flat cross section, and corrugated fins 212 interposed between the tubes 211. The tubes 211 are tube members through which a refrigerant as a heat medium flows, and both ends of each tube 211 are connected to communicate with the inside of the pair of header tanks 211, respectively. Further, the fin 212 is a heat transfer member that is formed in a wave shape from a thin strip material and forms a heat transfer surface, and is joined (connected) to the tube 211. As shown in FIG. 6, a plurality of armor-door louvers 212 a are formed on the heat transfer surfaces of the fins 212. In the heat exchanger 200 of the fifth embodiment, the tubes 211 and the fins 212 are formed by the water-repellent substrate 100 described in any one of the first to fourth embodiments.

  In the heat exchanger 200, the refrigerant that has been depressurized in the refrigeration cycle to low temperature and low pressure flows through the plurality of tubes 211, and around the outside of the tubes 211 and around the fins 212 (outside of the heat exchanging unit 210). The air for air conditioning passes through the air and the air for air conditioning is cooled by the refrigerant. When the air-conditioning air is cooled, if the temperature of the air-conditioning air falls below the dew point temperature of the water vapor contained in the air, the water vapor becomes condensed water on the surface of the heat exchange unit 210 (tube 211, fin 212). Adhere to. When this condensed water adheres, the ventilation resistance of the conditioned air passing through the heat exchange unit 210 increases and the thermal resistance due to the condensed water increases, so that the heat exchange performance in the heat exchanger 200 decreases. Furthermore, the condensed water freezes when it becomes below the freezing temperature, and adheres to the surface of the heat exchange unit 210 as frost. Therefore, in the heat exchanger 200 for absorbing heat, first, even if condensed water is generated during operation, it is necessary to quickly slide down the generated condensed water by a water repellent action. Hereinafter, the conditions for promptly sliding down the generated condensed water will be examined.

  First, as shown in FIG. 6, in the fin 212, the distance between the heat transfer surfaces is normally set to about 1.5 mm, and the pitch of the louvers 212a is set to about 0.8 mm. Therefore, even when condensed water is generated, the condensed water droplet diameter is 0.4 mm or less so that the condensed water does not form curtains (water clogging) due to surface tension between the louvers 212a having a narrow gap. It is necessary to suppress it so that it becomes.

Here, the following mathematical formula 1 is known as a water drop sliding formula. That is,
(Equation 1)
2πrE = mg · sinα
In Expression 1, as shown in FIG. 7, 2πrE represents adhesion force, mg · sin α represents gravity along the sliding direction, r represents condensed water droplet radius (m), and E represents surface energy of the sliding film ( J / m ² ), m is the mass of the water drop (kg), g is the acceleration of gravity (m / s ² ), α is the tilt angle (degree), and θ in FIG. 7 is the contact angle (degree). The condensed water droplet radius r can be expressed as a function of the contact angle θ, and the condensed water droplet radius r = (water droplet diameter d / 2) · cos (θ−90).

Next, the surface energy E is obtained based on the formula 1 and the experimental result. For example, as described in the first embodiment, when the water droplet diameter d is 1 mm, the inclination angle α is 3 degrees, the contact angle θ is 160 degrees, and no wind conditions are used as the experimental conditions, the water droplets slide down. This is confirmed (FIG. 8). Therefore, the surface energy E when the water droplet actually slides is obtained by substituting the above conditions into Equation 1. From Equation 1,
2 ・ π ・ 0.5 ・ cos (160-90) ・ E
^{= 4/3 · π · 0.5} 3 · 9.8 · sin (3)
Thus, E = 2.5 × 10 ⁻⁴ (J / m ² ) was obtained.

Next, when the water droplet diameter d is 0.4 mm that can surely pass through the gap (0.8 mm) of the louver 212a, the slidable contact angle θ is calculated from Equation 2. That is,
(Equation 2)
2πrE = 1/2 · ρ · V ² · A · C _D
In Equation 2, as shown in FIG. 9, 2πrE represents adhesion, 1/2 · ρ · V ² · A · C _D represents drag, r represents condensed water droplet radius (m), and E represents sliding force. The surface energy (J / m ² ) of the water film, ρ is the air density (kg / m 3), V is the relative velocity (m / s), A is the projected cross section (m ² ), and _CD is the drag coefficient.

The air density is calculated by assuming that the condensed water droplet radius r = (water droplet diameter d / 2) · cos (θ−90) and the surface energy E when sliding down is 2.5 × 10 ⁻⁴ (J / m ² ). By substituting ρ = 1000 (kg / m3), relative velocity V = 1 m / s, projected cross-sectional area A = π · 0.2 ² , drag coefficient CD = approximate value, FIG. 10 was obtained by obtaining.

  In order for the condensed water not to be blocked between the louvers 212a, it is necessary that the drag of FIG. 10 is in the range of the contact angle θ that exceeds the adhesive force, and the contact angle θ is found to be 148 degrees or more. .

  The water repellent substrate 100 of the first to fourth embodiments is obtained at a contact angle of 160 degrees. In the heat exchanger 200 using the water repellent substrate 100, the tube 211 and the fin 212 are used. Condensed water could be satisfactorily slid down and removed without any special operation from the surface. Moreover, since the good sliding down of the condensed water was obtained, it was possible to delay the time for generating frost to a predetermined amount on the surface of the heat exchange unit 210.

FIG. 11 is a graph showing the frosting time when frosting and defrosting are repeated in the heat exchanger 200. (A) shows the present invention, and (b) shows a comparative product. The comparative product has a conventional hydrophilic film and does not have the hydrophobic film in this embodiment. Experimental conditions are
・ During frosting operation,
As air-side conditions, dry bulb temperature = 2 ± 0.3 ° C., wet bulb temperature = 1 ± 0.3 ° C.,
Front wind speed = 0.8 ± 0.01m / s,
As refrigerant side conditions, refrigerant inlet temperature = −7.4 ± 0.6 ° C., refrigerant flow rate = 10 ± 0.5 L / MIN,
・ During defrosting operation,
As the air side condition, front wind speed = 0m / s,
As refrigerant side conditions, refrigerant inlet temperature = 13 ± 2 ° C., refrigerant flow rate = 2 ± 0.5 L / MIN,
・ Test cycle It ends when the ventilation resistance of the heat exchanger rises to 100 Pa under frosting conditions, and the defrosting operation is 6 minutes.
The following was repeated.

  In the present invention, since the sliding down of the condensed water can be promoted with respect to the comparative product, the condensed water is less likely to stagnate in the heat exchanging unit 210, and thus frosting occurs, and the ventilation resistance of the heat exchanging unit 210 is a predetermined value (here The time to 100 Pa) can be greatly reduced.

(Other embodiments)
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, as long as it belongs to the technical scope of this invention, without being limited to the said embodiment at all.

For example, in the above embodiments, the hydrophobic coating _{120, ODS, FAS17, C 8} F 17 C 2 H 4 NCO, has formed the monomolecular film by using a _{C 18} H 37 NCO, etc., reagents other than those A monomolecular film may be formed. For example, any structure having a hydrophobic group such as fluorine on one side and a functional group that easily binds to a hydroxyl group such as O—Si—O on the other side is applicable. In addition, when the hydrophobic coating 120 contains a hydrophobic functional group such as an alkyl group or a fluoroalkyl group, high hydrophobicity can be expressed.

  In addition, the method for creating the needle-like protrusion 111 is not limited to the method of each of the above-described embodiments, and besides this, a nanoimprint method or the like can be used.

  Moreover, although the structure which uses an aluminum plate material was illustrated as the base material 110 in each said embodiment, various metals, such as a copper plate and an iron plate, can be used besides an aluminum plate material. Moreover, the base material 110 is not limited to a metal, For example, you may form with resin.

DESCRIPTION OF SYMBOLS 100 Water repellent base material 110 Base material 111 Needle-like protrusion part 120 Hydrophobic film | membrane 121 Fine protrusion part 200 Heat exchanger 210 Heat exchange part 211 Tube 212 Fin

Claims (8)

A substrate (110);
A water-repellent substrate comprising a hydrophobic coating (120) provided on the surface of the substrate (110),
A large number of needle-like protrusions (111) extending in a needle shape are formed on the surface of the base material (110),
The hydrophobic film (120) is formed on the surface of the needle-like protrusion (111) and on the surface of the base material (110) between the needle-like protrusions (111) than the needle-like protrusion (111). A water-repellent substrate characterized by being formed as a large number of fine projections (121).   The water-repellent substrate according to claim 1, wherein the fine protrusion (121) is a monomolecular film having a hydrophobic functional group.   The water-repellent substrate according to claim 2, comprising at least one of an alkyl group and a fluoroalkyl group as the hydrophobic functional group.   The water-repellent substrate according to claim 2 or 3, wherein the substrate (110) is made of metal or metal oxide. A heat exchanger for absorbing heat by absorbing heat from the air flowing outside the heat exchanging part (210) by a heat medium flowing inside the heat exchanging part (210),
At least one of the heat medium distribution tube (211) forming the heat exchange part (210) and the fin (212) connected to the tube (211) to form a heat transfer surface for the air is claimed. A heat exchanger formed of the water repellent substrate (100) according to any one of claims 1 to 4. A method for producing a water-repellent substrate in which a hydrophobic coating (120) is provided on the surface of a substrate (110),
A protrusion forming step of forming a large number of needle-like protrusions (111) extending in a needle shape on the surface of the substrate (110);
A large number of fine protrusions (121) finer than the needle-like protrusions (111) on the surface of the needle-like protrusions (111) and the surface of the base material (111) between the needle-like protrusions (111). And a film forming step of providing the hydrophobic film (120) by forming a water repellent substrate. The substrate (110) is an aluminum substrate (110),
The method for producing a water-repellent substrate according to claim 6, wherein, in the protrusion forming step, the needle-like protrusion (111) is formed by subjecting the base material (110) to a boehmite treatment.   In the film forming step, the fine protrusion (121) is formed by immersing the base material (110) on which the needle protrusion (111) is formed in a water saturated solution containing a hydrophobic functional group. It forms, The manufacturing method of the water-repellent base material of Claim 7 characterized by the above-mentioned.