JPS62127494A - Formation of porous layer - Google Patents

Abstract

PURPOSE:To form a porous layer even in the inside surface of a small metallic tube by making a base body made of metal a cathode and using a soluble anode and performing electroplating in an anode current density region wherein anode slime is formed. CONSTITUTION:A wire 4 made of copper where on a spacer 3 made of resin is spirally wound is inserted into the inside of a copper tube 1 formed with a coated film 2 of silicon oil on the inside surface, and deflection is corrected by imparting tension to both ends. While circulating copper sulfate plating liquid into the inside of the copper tube 1 from a storage tank 5 by a chemical pump 6, electroplating is performed in an anode current density region wherein anode slime is formed by making the copper tube 1 a cathode and making the wire 4 an anode. Dendritic or granular copper is deposited on the inside surface of the copper tube 1 and a porous layer is formed.

Description

[Detailed Description of the Invention] Industrial Field of Application] The present invention is suitable for configuring, for example, the evaporator of a heat exchanger for air conditioning, the heat transfer surface of a condensing pipe, or the wick of a heat pipe. The present invention relates to a method of forming a porous layer, and particularly relates to a method of forming a porous layer that is inexpensive to form and can improve heat transfer characteristics.

[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 it easier to cause nucleate boiling.

(3) Facilitate capillary action.

(4) Make turbulence more likely.

What are the benefits of this?

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 steel pipe by a rolling method or the like.

In addition, as a method that satisfies (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. Formation of such a porous layer is carried out by a method.

"Problems to be Solved by the Invention" However, the above conventional methods have the following problems.

In other words, when forming a spiral groove, the nucleate boiling phenomenon, which is the most effective of the above methods for increasing heat transfer efficiency, is not used, and the manufacturing technology of the rolling tool, the technology of skin rolling, is not used. Due to reasons such as restrictions on the number of helical grooves and the angle of helix; the thermal properties are only 12 to 15 times different compared to regular grooveless pipes, resulting in poor performance. is 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 requires large-scale equipment, shortens the life of the tool, and reduces manufacturing costs. There was a problem with getting expensive.

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, finishing, 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. In addition, there was a problem in that complicated processes such as printing and burning were required, resulting in high manufacturing costs.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses a metal substrate as a cathode, a soluble anode, and an anode current density range in which anode slime is generated. Electroplating is performed to deposit dendritic and granular metal on the surface of the substrate.

1 Effect] 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 high current density using a soluble anode, the anode will melt and a powdered anode metal (slime) will be produced on its surface. As the plating solution moves, this anode slime is carried to the surface of the cathode substrate and incorporated into the plating film. This slime develops electrical conductivity, so ri-origin metal growth occurs using this as a core.
Depending on conditions such as flow of the plating solution or current density, a porous layer made of dendritic metal or ridge-like metal is formed.

The anode current density varies depending on the type of material of the soluble anode, but if it is less than 2OA/d+n'', sufficient anode slime will not be generated, so it is preferably 2OA/dm' or more.

When an insulating thin film is formed on the surface of the substrate, which is the cathode, the initial electrodeposition occurs in particularly thin or broken parts of the thin film, so that dendritic or granular metal deposition occurs more easily.

The relative movement speed between the substrate and the plating solution is preferably 0.5 to 5 m/sec; 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; , the energy cost increases and no particular effect is observed.

5 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 Fig. 1, the outer diameter is 9.52+n+n and the wall thickness is 0.
A 35 mm copper tube was cut to a length of 1000 mm, its inner surface was cleaned by trichlene cleaning, silicone oil was applied through a solution diluted 3 times with ethanol, the ethanol was removed by evaporation, and the inner surface was cleaned. A wave film 2 of silicone oil was formed. Inside this copper tube l, a resin spacer 3 is spirally wound, and the outer diameter is 4 mmφ.
The wire 4 was inserted and tension was applied to both ends to correct the problem.

Then, put copper sulfate plating solution (copper sulfate 200g#!
While circulating sulfuric acid (50g #) from the storage tank 5 with the chemical pump 6, the copper tube 1 was used as a cathode and the wire 4 was used as an anode, the plating solution temperature was 30°C, and the cathode current density was +7A/d.
, anode current density 31OA/dm', plating solution flow rate 1.5
Plating is carried out for 15 minutes under conditions of
An electrodeposited metal layer of 0μ was obtained.

In addition, after washing the inner surface of this copper pipe l with water and drying it,
A test was conducted in which the electrodeposited metal layer was crushed in a vise, but no peeling or falling off of the electrodeposited metal layer was observed, indicating excellent adhesion and strength.

Thermal properties of the steel pipes manufactured as described above were measured using a thermal property 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, IO is a pump, 11 is a valve, 12 is a flow meter, 13
14 is an expansion valve, 14 is a compressor, 15 is a sub-condenser, 16 is a sub-evaporator, 17 is a constant temperature water conveyor, 1
8 is a steel pipe as a test pipe. In this thermal property testing apparatus, a refrigerant supplied from a compressor 14 is flowed into the inside of 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 corresponding to each refrigerant flow 1 so that the refrigerant system was stabilized.

In this figure, arrows A and A' indicate the flow directions of refrigerant and water, respectively, in the case of the evaporation test, and arrows B, B' indicate the flow directions of the refrigerant and water, respectively, in the case of the condensation test. .

As a result of this test, the copper tube l 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. 4, and a value shown as D in the same figure. It was found that this material has thermal properties that are about 10 times better than ordinary steel pipes.

(Example 2) A spiral groove was formed on the inner surface of a steel pipe 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, as shown in Fig. 5. 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. 4.

(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: 27°C.
Plating was performed for 10 minutes at an anode current density of 500 A/dm" and a moving speed of the plating solution of 1.5 m/s.
A dendritic porous layer as shown in the figure was obtained. 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 steel pipe was used as the base, but the present invention is not limited to this, 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 substrate as the soluble anode, a different metal may be electrodeposited as 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 uses a metal substrate as a cathode, uses a soluble positive bottle, and performs electroplating in the anode 7 [I flow density region] where positive bottle slime is generated. By depositing dendritic or granular metal on the surface of the substrate, a porous layer can be formed even on the inner surface of a thin tube, and therefore heat transfer using nucleate boiling is possible. In addition to being able to efficiently manufacture heat transfer bodies with good characteristics,
It does not require complicated or large-scale materials or equipment, so it has advantages such as low manufacturing costs. Further, by changing the moving speed of the plating solution and the plating conditions, excellent effects such as forming a porous layer in a seed-shaped shape suitable for the purpose can be achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the method of the present invention, FIG. 2 is a micrograph showing the surface shape of the porous layer of the first example formed by the method of the present invention, and FIG. A schematic diagram of an apparatus for testing thermal characteristics, FIG. 4 is a graph showing the heat transfer characteristics of a heat transfer body manufactured by applying the method of the present invention, and FIG. Microscopic photograph of porous layer. FIG. 6 is a microscopic photograph of the porous layer of the third example. l...Weir body, 2...Insulating thin film, 4. Soluble anode.

Claims (7)

[Claims] (1) Using a metal substrate as a cathode and a soluble anode, electroplating is performed in an anode current density region where anode slime is generated, and dendritic or granular metal is deposited on the surface of the substrate. A method for forming a porous layer characterized by: (2) The method for forming a porous layer according to claim 1, characterized in that electroplating is performed after forming an insulating thin film in a porous state on the surface of the substrate. (3) The method for forming a porous layer according to claim 1 or 2, wherein the substrate is made of copper and the plating solution is a copper sulfate plating solution. (4) The method for forming a porous layer according to claim 3, wherein the substrate is tubular. (5) The method for forming a porous layer according to claim 4, characterized in that the substrate and the plating solution are moved relative to each other. (6) The relative movement speed between the substrate and the plating solution is 0.5~
6. The method of forming a porous layer according to claim 5, wherein the rate is 5 m/sec. (7) The method for forming a porous layer according to claim 4, wherein the anode current density is 20 A/dm^2 or more.