JPH0213038B2 - - 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) Makes nucleate boiling more likely. (3) Facilitates 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 that satisfies (2), a method is known in which a porous layer is formed 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 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 it is difficult to make use of the nucleate boiling phenomenon, which is the most effective method for increasing heat transfer efficiency. , due to the limitations on the number of spiral grooves and the angle of twist,
The thermal characteristics were only about 1.2 to 1.5 times higher than ordinary grooveless tubes, 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. In view of the above-mentioned problems, the present invention provides a heat transfer body with excellent heat transfer properties by easily forming a porous layer on the inner surface of a tubular body that improves heat transfer properties by causing nucleate boiling. It is an object of the present invention to provide a method for forming a porous layer that is useful for manufacturing at low cost. [Means for Solving the Problems] The present invention uses a metal substrate with a hydrophobic thin film formed on the surface thereof as a cathode, performs electroplating using an insoluble anode, and electrolytizes the substrate. on the surface,
A plating layer having pores with narrow openings (hereinafter referred to as narrow pores) is formed. [Operation] The mechanism by which narrow pores are formed on the substrate surface in this method is thought to be as follows. First, by performing plating using an insoluble anode, water in the plating solution is electrolyzed and oxygen gas is generated at the anode. A part of this oxygen gas is transported to the surface of the cathode substrate as the plating solution moves.
The hydrophobic thin film formed on the surface reduces the wettability of the substrate to the plating solution, and the carried gas adheres to the surface of the substrate as bubbles. Therefore,
The deposited metal grows to envelop these air bubbles, forming uniform and fine narrow pores. Therefore, the number of bubbles attached to the substrate can be controlled by changing the anode current density or the relative moving speed of the plating solution with respect to the substrate. Note that an anode current density of 20 A/dm ² or less is not preferable because oxygen gas is insufficiently generated. [Example] Hereinafter, an example in which the method of the present invention is applied to a heat transfer body will be specifically described. To form a hydrophobic thin film on the surface of the tube,
A solution in which a hydrophobic substance such as oil or paint is dispersed or dissolved in a solvent is applied with a brush or spray to adhere to the surface of the tube. Alternatively, various methods can be considered, such as immersing the tubular body in this solution and then pulling it out to evaporate the solvent to leave a hydrophobic thin film. The preferred thickness of this thin film varies depending on the type of hydrophobic substance, but 0.1 to 5 μm is appropriate;
If it is less than this, the generation rate of narrow pores will decrease, and if it is more than this, the insulation will become too high and a uniform plating layer will not be obtained. When plating the inner surface of a tube in this way, especially if the tube is long and slender, the anode wire is stretched along the axis of the tube under tension, and an insulating layer is placed around the wire. It is preferable to provide spacers at appropriate intervals to prevent short circuits due to contact between the tube and the wire. As the current for plating, a pulse current such as an intermittent current, a normal pulse current, or a PR current is used as appropriate. Such pulsed current facilitates the transport of metal ions into the pores compared to direct current, so
It is possible to increase the electrodeposition rate, suppress local whisker-like deposition that occurs in the case of direct current, and prevent short circuits due to deposited metal. Furthermore, in the PR current, since positive and reverse currents are passed periodically and alternately, the growth of the deposited film can be made uniform. Furthermore, since an insoluble anode is used in this method, it is necessary to appropriately replenish the ions of the deposited metal to maintain its concentration at an appropriate value. Example 1 As shown in Figure 1, the outer diameter is 9.35 mm and the wall thickness is 0.35 mm.
A copper tube 1 was formed by drawing and cut to a length of 1000 mm. The inner surface of the copper tube 1 was cleaned by trichlene cleaning, and a solution of silicone oil diluted 3 times with ethanol was passed through the inside. The ethanol was removed by evaporation to form a coating 2 on the inner surface. A Ti-Pt wire with resin spacers 3 attached at regular intervals is inserted into this copper tube 1, and tension is applied to both ends to form an insoluble anode 4, while the copper tube 1 is used as a cathode. did. Then, copper sulfate plating solution (copper sulfate 200g/, sulfuric acid
A storage tank 5 for storing 50 g/) and a chemical pump 6 for flowing this plating solution into the copper pipe 1 are provided, and basic copper carbonate is replenished in an amount corresponding to the copper ions reduced by plating in this storage tank 5, and the circulation is started. configured for use. With the above equipment, the temperature of the plating solution is 30℃,
Plating was performed for 10 minutes under the conditions of a cathode current density of 33 A/dm ² and a flow rate of the plating solution of 2 m/s to form a homogeneous narrow hole of 250 μm on the inner surface of the copper tube 1 as shown in Figures 2 and 3. An electrodeposited metal layer having a thickness of 50 μm and having pores with a porosity of 18% was obtained. 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 pressed in a vice, and the copper tube 1 was annealed at 530°C for 20 minutes, and expansion using a mandrel was attempted. However, in all cases, no peeling or falling off of the electrodeposited metal layer was observed, indicating 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. 4 under the conditions shown in the table on the next page. 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. 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.

[Table] 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 as shown in FIG. niD
It was found that the thermal properties were 7 to 8 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 of Example 1 by rolling, and then, by the method of Example 1, plating with narrow holes was formed on the inclined wall of the spiral groove. formed a layer. The heat transfer properties were measured using the same method, and the results showed that the heat transfer properties were approximately 10 times higher than those of ordinary copper tubes. Example 3 After applying lubricating oil to a 200 x 100 x 1 (t) mm copper plate using a roll coater method to form a hydrophobic oil film on the copper plate surface, the cathode current density was 25 A/dm ² and the flow rate of the plating solution was 2 m. Plating was performed for 10 minutes with /s. When this copper plate was placed in hot water and the hot water was heated from the bottom, nucleate boiling was observed to occur from the pores. In each of the above examples, copper was used as the metal of the base, but the implementation of the present invention is of course not limited to this. Furthermore, the application of the present invention is not limited to heat transfer bodies. [Effects of the Invention] As detailed above, the present invention uses a metal substrate on which a hydrophobic thin film is formed on the surface as a cathode, performs electroplating using an insoluble anode, and coats the surface of the substrate with electroplating. Since the plating layer has pores with narrow openings, it is possible to form a plating layer with uniform narrow pores on the inner surface of the tubular metal.
The size and number of pores can be controlled and formed, and therefore, it is possible to efficiently manufacture a heat transfer body with good heat transfer characteristics using nucleate boiling, and it is also possible to use it as a material or device for this purpose. It has advantages such as low manufacturing cost because it does not require anything complicated or large-scale.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the method of the present invention;
Figure 2 is a diagram showing the cross-sectional shape of a porous layer formed by the method of the present invention, Figure 3 is a diagram showing the surface shape of the porous layer, and Figure 4 is a diagram showing the shape of the surface of the porous layer. FIG. 5 is a graph showing the heat transfer characteristics of a heat transfer body manufactured by applying the method of the present invention. 1...Substrate, 2...Hydrophobic thin film, 4...Insoluble anode.

Claims (1)

[Claims] 1. A metal substrate with a hydrophobic thin film formed on its surface is used as a cathode, electroplating is performed using an insoluble anode, and an opening is relatively narrowed on the surface of the substrate. A method for forming a porous layer, the method comprising forming pores. 2. The method for forming a porous layer according to claim 1, wherein the plating is performed using a pulsed current. 3. The method of 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. 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 of the above substrate and plating solution is 0.5~
5. The method for 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 3, wherein the cathode current density is 15 A/dm ² or more. 8. The method for forming a porous layer according to claim 3, wherein the anode current density is 20 A/dm ² or more.