JPH0238676B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for forming a porous layer suitable for forming, for example, a heat transfer surface of an evaporation tube or a condensation tube of an air conditioning heat exchanger, or a heat pipe wick, etc. In particular, the present invention relates to a method of forming a porous layer that is inexpensive to form and can improve heat transfer properties. [Prior Art] In order to increase the heat transfer efficiency of a heat transfer tube for exchanging heat between an internal medium and an external medium, (1) the heat transfer area must be increased; (2) Make nucleate boiling more likely. (3) Facilitate capillary action. (4) Make turbulence more likely. It is said that this is effective. As a method that satisfies (1) and (4), a method is used in which a spiral groove is formed on the inner surface of a copper tube by a rolling method or the like. In addition, as a method to satisfy (2), there is a known method of forming a porous layer on the surface of the heat transfer body, which becomes the core of nucleate boiling. Such a porous layer is formed by a deposition method. [Problems to be Solved by the Invention] However, the above conventional methods have the following problems. In other words, when forming spiral grooves, the nucleate boiling phenomenon, which is the most effective of the above methods for increasing heat transfer efficiency, is not used, and there are also Therefore, due to the limitations on the number of spiral grooves and the angle of twist, the thermal characteristic value is 1.2~1.2 compared to ordinary grooveless pipes.
The increase was only about 1.5 times, and the performance was insufficient.
In addition, during manufacturing, the frictional force between the rolling tool and the inner surface of the tube is large, so a large pressing force is required, which in turn requires large-scale equipment, shortens the life of the tool, and increases production costs. There was a problem. On the other hand, in the method of forming a porous layer, it is difficult to form a porous layer on the inner surface of a tubular structure such as a heat exchanger tube by sintering, brazing, etc. Additionally, it is possible to form a porous layer by applying pattern masking to the metal surface by screen printing, etc., and then electroplating, but it is difficult to form a porous layer on the inner surface of the tube using this method. Moreover, there was a problem in that it required complicated processes such as printing and baking, resulting in high manufacturing costs. [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention forms an insulating thin film on the surface of a metal base, uses the base as a cathode, and uses a soluble Using an anode,
Electroplating is performed in the anode current density region where anode slime is generated, and dendritic,
It is designed to precipitate granular metal. [Operation] The mechanism by which a porous layer is formed on the surface of the substrate in this method is thought to be as follows. When plating is performed at a high current density using a soluble anode, initial electrodeposition occurs in particularly thin or broken parts of the insulating thin film formed on the surface of the substrate, which is the cathode, and countless plating needle-like nuclei are formed. formed, forming the basis of a porous electrodeposited layer. Next, the anode is melted and a powdered anode metal (slime) is generated on its surface, and this anode slime is carried to the cathode substrate surface with the movement of the plating solution, and the initial stage is growing in the thickness direction. It is taken into the plating needle-like core of the electrodeposited area.
Since this slime has conductivity, further growth of the next deposited metal occurs using this slime as a nucleus, and the flow of the plating solution is accompanied by acicular growth in multiple directions and an intertwined cross-linked structure. Alternatively, a porous layer made of dendritic metal or granular metal can be easily formed depending on conditions such as current density. Although the anode current density varies depending on the type of material of the soluble anode, it is preferably 20 A/dm ² or more, since sufficient anode slime is not generated at 20 A/dm ² or less. As the substance constituting the insulating thin film, it is required that a thin film layer can be easily obtained and that the thin film has appropriate insulation properties, that is, appropriate insulation defects, and therefore oil that is difficult to dissolve in the plating solution is preferred. Particularly, when the oil is a lubricating oil used to prevent friction between the tool and the base during drawing, there is an advantage that an insulating thin film can be formed at the same time as the metal base is drawn. The relative movement speed between the substrate and the plating solution is 0.5 to 5.
m/sec is preferable; if it is less than this, the movement of metal ions to the substrate surface will be hindered and only a brittle deposited film will be obtained, and if it is more than this, the energy cost will only increase and no particular effect will be observed. I can't. [Example] Hereinafter, an example in which the method of the present invention is applied to a heat transfer body will be specifically described. Example 1 As shown in Figure 1, the outer diameter is 9.52 mm and the wall thickness is 0.35 mm.
Copper tube 1 is cut to a length of 1000 mm, its inner surface is cleaned by trichlene cleaning, silicone oil is applied through a solution diluted 3 times with ethanol, the ethanol is removed by evaporation, and the inner surface is coated with silicone. An oil film 2 was formed. A copper wire 4 having an outer diameter of 4 mm and having a resin spacer 3 wound therein in a spiral was inserted into the copper tube 1, and tension was applied to both ends to correct the deflection. Then, put copper sulfate plating solution (copper sulfate 200
While circulating sulfuric acid (g/g/, sulfuric acid 50 g/) from the storage tank 5 with the chemical pump 6, the copper tube 1 is used as the cathode,
Wire 4 is used as an anode, plating solution temperature is 30°C, cathode current density is 17A/dm ² , anode current density is 310A/dm ² ,
Plating was performed for 15 minutes at a plating solution flow rate of 1.5 m/s to obtain a 50μ thick electrodeposited metal layer consisting of a granular porous layer as shown in Figure 2 on the inner surface of the copper tube 1. Ta. In addition, after washing the inner surface of the copper tube 1 with water and drying it, a test was conducted in which the copper tube 1 was crushed in a vise.
No peeling or falling off of the electrodeposited metal layer was observed, demonstrating excellent adhesion and strength. The thermal characteristics of the copper tubes manufactured as described above were measured using a thermal characteristics testing apparatus as shown in FIG. 3 under the conditions shown in the following table. In this device, T is a temperature sensor, P is a pressure gauge,
PD is a differential pressure gauge, 10 is a pump, 11 is a valve, 1
2 is a flow meter, 13 is an expansion valve, 14 is a compressor, 15 is a sub-condenser, 16 is a sub-evaporator, 17 is a constant temperature water tank, and 18 is a copper tube as a test tube. In this thermal property testing apparatus, a refrigerant supplied from a compressor 14 is flowed inside the test tube 18, and hot water from a constant temperature water tank 17 is flowed outside against the refrigerant. The temperature of the constant temperature water was controlled in accordance with each refrigerant flow rate so that the refrigerant system was stabilized.

[Table] In this figure, arrows A and A' indicate the flow directions of refrigerant and water, respectively, in the case of the evaporation test.
Arrows B and B' indicate the flow directions of refrigerant and water, respectively, in the case of the condensation test. As a result of this test, the copper tube 1 of Example 1 obtained by the method of the present invention showed a film heat transfer coefficient on the inside thereof as shown as C in FIG. It was found that the thermal properties were approximately 10 times better than that of ordinary copper tubes. Example 2 A spiral groove was formed on the inner surface of a copper tube having the same shape as the material in Example 1 by rolling, and then the same pretreatment and plating as in Example 1 were performed to obtain a material as shown in FIG. A porous layer was formed. The heat transfer characteristics were measured using the same method, and as a result, excellent heat transfer characteristics were shown as E in FIG. Example 3 The same material as in Example 1 was subjected to the same pretreatment, and the plating conditions were as follows: plating solution temperature: 30°C, cathode current density: 27A/dm ² , anode current density: 500A/dm ² ,
Plating was carried out for 10 minutes at a moving speed of the plating solution of 1.5 m/s to obtain a dendritic porous layer as shown in FIG.
The heat transfer characteristics were measured in the same manner as in the previous example, and the characteristic values shown as F in FIG. 4 were obtained. In these Examples, a copper tube was used as the base, but the present invention is not limited thereto, and may be applied to metals other than copper or flat members. It is not necessary to form an insulating thin film on the surface, and instead of using the same metal as the base as the soluble anode, a different metal may be electrolytically deposited to form a porous layer. Further, the present invention is not limited to implementation on heat transfer bodies. [Effects of the Invention] As detailed above, the present invention forms an insulating thin film on the surface of a metal base, uses the metal base as a cathode, uses a soluble anode, and produces an anode slime. Electroplating is performed in the generated anode current density region to deposit dendritic and granular metal on the surface of the substrate, making it easy to form a porous layer even on the inner surface of a thin tube. Therefore, it is possible to efficiently manufacture a heat transfer body with good heat transfer characteristics using nucleate boiling, and it does not require complicated or large-scale materials or equipment. It has advantages such as low manufacturing cost. Furthermore, by changing the moving speed of the plating solution and the plating conditions, excellent effects such as the ability to form porous layers of various shapes suited to the purpose can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention;
FIG. 2 is a diagram showing the surface shape of the porous layer of the first example formed by the method of the present invention, FIG. 3 is a schematic diagram of an apparatus for testing heat transfer characteristics, and FIG. 4 is a diagram of the present invention. A graph showing the heat transfer characteristics of the heat transfer body manufactured by applying the method of the invention, FIG. 5 is a diagram of the porous layer of the second embodiment of the present invention, and FIG. 6 is a diagram of the porous layer of the third embodiment. FIG. 1...Substrate, 2...Insulating thin film, 4...Soluble anode.

Claims (1)

[Claims] 1. After forming an insulating thin film on the surface of a metal substrate, using the substrate as a cathode and a soluble anode,
A method for forming a porous layer, which comprises performing electroplating in an anode current density region where anode slime is generated, and depositing dendritic or granular metal on the surface of the substrate. 2. The method for forming a porous layer according to claim 1, wherein the substrate is made of copper and the plating solution is a copper sulfate plating solution. 3. The method for forming a porous layer according to claim 2, wherein the substrate is tubular. 4. The method of forming a porous layer according to claim 3, characterized in that the substrate and the plating solution are moved relative to each other. 5 The relative movement speed of the above substrate and plating solution is 0.5~
5. The method for forming a porous layer according to claim 4, wherein the rate is 5 m/sec. 6. The method for forming a porous layer according to claim 3, wherein the anode current density is 20 A/dm ² or more.