JPS61270393A - Plating method for inside wall of heat transmission pipe - Google Patents

Abstract

PURPOSE:To form a metallic plating layer having adequate dendrite ruggedness on the inside wall of a heat transmission pipe by using the wall surface of said pipe as a cathode side and pouring a plating liquid prepd. by adding an oxyethylene surface active agent and a low concn. of chloride as an additive to said liquid into the heat transmission pipe thereby plating the inside wall thereof. CONSTITUTION:The heat transmission pipe 10 and fins 3 are tentatively fitted to each other in a prescribed position. The pipe 10 and the fins 3 are press welded and fixed by expanding the pipe 10. The pipe 10, a connecting pipe 11 and a circulating pump 12 are then combined and the acidic copper sulfate plating liquid 9 added with the oxyethylene surface active agent and a low concn. of chloride in a plating cell 7 is circulated toward the side A in the pipe 10. Negative electric charge is thereupon applied to a counter electrode 15 of an iron bar from a DC power source and said electrode is used as the cathode side. Positive electric charge is applied to a connecting terminal 16 as the anode side. Since the terminal 16 and the pipe 10 conduct to each other, the pipe 10 has the positive charge and the inside wall of the pipe 10 is plated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of plating the inner wall surface of a heat exchanger tube used in a heat exchanger or a heat pipe, particularly in which a liquid medium flows.

BACKGROUND OF THE INVENTION It is generally well known to form porous layers in heat exchange members to increase surface area and to act as boiling nuclei to promote heat transfer efficiency.

Therefore, it is difficult to form a porous layer inside the heat exchanger tube by sintering or thermal spraying, and the strength of the heat exchanger tube decreases due to heat, so plating is usually used. However, the plating layer conventionally used to increase the surface area and promote boiling heat transfer needs to be processed under conditions different from those for smooth plating, and finished into a plating layer with appropriate porousness and protrusions.

Therefore, as a method for forming such a plating layer, complex salts, button glue, brightening agents, additives for making crystal particles, etc. necessary for obtaining normal smooth plating are added to the plating solution. The plating solution is either not mixed or used in a very small amount, and the plating conditions are, for example,
Either it is carried out at high temperature and high current density as in Publication No. 9, or
It is formed by stirring a plating solution in high-speed fluidization as disclosed in Japanese Patent No. 5-41312.

Problems to be Solved by the Invention However, even if the plating solution is introduced onto the inner wall surface of the heat transfer tube under these conditions, the plating solution will be unstable if carried out at high temperature and high current. Porous plating cannot be achieved uniformly all the way to the inside, such as metal precipitating locally at the entrance and in areas where the spacing between electrodes is relatively small, and unstable plating with few complex salts. Due to the bath composition, it decomposes in a short period of time, making it unsuitable for mass production.In addition, the adhesion between the inner wall surface of the heat transfer tube and the plating layer is insufficient, and it is susceptible to external vibrations and vibrations when the liquid medium flows. There were defects such as the plating layer peeling off due to impact. Furthermore, when plating the inside of a heat transfer tube, when a high current is applied, a large amount of monovalent copper ions, which are more stable on the anode side, are generated, resulting in the precipitation of powdered copper, resulting in poor adhesion and a soft plating layer. There was a problem.

In view of the above problems, the present invention forms an uneven plating layer with uniformity and excellent adhesion, and further controls the uneven shape, thereby increasing the surface area and promoting boiling heat transfer. A heat transfer tube having a heat transfer wall surface is provided.

Means for Solving the Problems In order to solve the above problems, the heat exchanger tube of the present invention has an oxyethylene surfactant and an appropriate concentration of chloride ions interposed in the plating solution to coat the wall surface of the heat exchanger tube. As the cathode side,
Plating is performed by pouring the plating solution into the heat exchanger tube,
A spiral insulator fixed to the counter electrode causes the flow of the plating solution to spiral, thereby forming a metal plating layer with appropriate dendritic irregularities on the wall surface of the heat exchanger tube.

Function According to the present invention, the oxyethylene surfactant in the plating solution forms a complex with metal ions, and the chloride ions work to form an appropriate unevenness. In addition, when the flow of the plating solution becomes constant along the longitudinal direction of the heat transfer tube, the tips of the metal plating with dendritic irregularities align in the flow direction of the plating solution, so when used as a heat exchanger, the refrigerant flow It is not possible to properly alienate and fully exhibit the heat transfer effect. Therefore, by forcibly changing the flow during plating, the streaks of the dendritic uneven metal plating layer are formed in a spiral shape, resulting in an uneven metal plating layer with improved heat transfer efficiency.

In other words, since there is no need for an unstable plating solution containing few complex salts or a plating method under excessively harsh conditions, a uniformly uneven plating layer is formed on the inner wall surface of the heat transfer tube, and the adhesion between the plating layer and the wall surface of the heat transfer tube is improved. Since the oxyethylene surfactant and metal ions form a complex salt, there is little decomposition of the plating solution, and a reentrant dendritic uneven metal plating layer is formed in a stable state, increasing the surface area and preventing boiling. This makes it possible to measure the effect of promoting heat transfer.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 7.

1 is a heat exchanger consisting of a heat exchanger tube 2 made of a copper pipe and a heat dissipation fin 3 made of a thin piece of aluminum.A copper plating layer 6 having dendritic irregularities is formed in a spiral shape on the inner wall surface 4 of the heat exchanger tube 2. has been done. Further, both ends ea and eb of this heat transfer tube 2 are completely sealed by caulking and welding, and a refrigerant such as fluorocarbon is sealed inside.

7 is a plating tank whose temperature can be controlled by a heater 8, into which a plating solution 9 is placed. This plating solution 9 is 15
0 y/gcuso4-5H20 and 60g/gH2S
An acidic copper sulfate plating solution with O4, o = osg/cl polyoxyethylene oleyl ether and 0.3 mmol of hydrochloric acid is used.

Further, reference numeral 10 denotes a heat transfer tube made of a copper pipe before both ends 6a and 6b are sealed. By combining a connecting tube 11 and a circulation pump 12, the plating solution 9 is circulated inside the heat transfer tube 10. . Note that the heat radiation fins 3 have already been fixed to the outer periphery of the heat exchanger tube 10 (by expanding the heat exchanger tube 10). In addition, the connecting pipe 11 has a counter electrode 16 of a copper rod that is directly connected to the DC power source 14 via the changeover switch 13.
, 5 Connection terminal 1 that is given an opposite charge to the counter electrode 16
6 is fixed. The counter electrode 16 is fixed to the connecting tube 14 by tightening a dice-shaped ring 17 with a nut so that the center of the counter electrode 15 is the center of the heat exchanger tube 1o for sealing and fixing. Also, heat exchanger tube 1o
When the connecting tube 11 is connected to the connecting terminal 1e, the connecting terminal 16 and the heat exchanger tube become electrically conductive. Furthermore, the opposite pole 16
is provided with a certain gap 18 to prevent contact with the heat exchanger tube 10.
In order to maintain the flow of the plating solution 9 in a spiral shape, a non-conductive spacer 19 made of spiral polypropylene is used.
is inserted.

Furthermore, 2o is an air pump for blowing air into the plating solution 9.

Next, a method for manufacturing a heat exchanger with such a configuration will be described.

First, the heat exchanger tube 1o and the heat radiation fin 3 are temporarily fitted at a predetermined position, the heat exchanger tube 10 is expanded using a predetermined tube expander, and the heat exchanger tube 10 and the heat radiation fin 3 are crimped and fixed. Next, the heat exchanger tube 10, the connecting tube 11, and the circulation pump 12 are combined, and the plating solution 9 in the plating bath 7 is circulated inside the heat exchanger tube 10 from above (in the direction into the figure). At this time, the plating solution was 150 g/ll CuS041I6H2o, 60
g/1H2S04° An acidic copper sulfate plating solution containing 0.05 g/l polyoxyethylene oleyl ether and 0.3 mmol of hydrochloric acid is used.

Therefore, first, a negative charge is applied to the counter electrode 16 of the copper rod of the DC power source to make it the cathode side, and a positive charge is applied to the other end or the connecting terminal 1e to make it the anode side. The current value at this time is approximately 1 o
Turn on the current at mA/crti for about 1 minute.

That is, since the connection terminal 16 and the heat exchanger tube 1o are electrically connected, the heat exchanger tube 10 has a positive charge, and the heat exchanger tube 10
Copper on the surface layer of the inner wall surface of the plate is electrolytically eluted and electrolytically polished to improve adhesion to the plating layer that is subsequently plated.

Next, the changeover switch 13 is used to reverse the positive and negative charges. That is, the counter electrode 16 side is made into an anode side, and the connection terminal 16 and heat exchanger tube 1o side are made into a cathode side.

Therefore, contrary to the above process, copper is dissolved in the plating solution 9 from the copper rod of the counter electrode 15, and the plating solution e is applied to the inner wall surface of the heat exchanger tube 1o.
The copper ions inside will precipitate as copper. The current value at this time was also about 100 mA/cni, and the time was about 10 minutes. Further, the temperature of the plating solution 9 was heated to about 60° C. by the heater 8 of the plating tank 7.

Here, if a normal plating solution is used, copper will be deposited with a uniform thickness on the entire inner wall surface of the heat exchanger tube 10, but in the plating solution 9, copper will be deposited with a uniform thickness.
Because it contains polyoxyethylene oleyl ether, an oxyethylene surfactant, and chlorine ions generated by hydrochloric acid at a low concentration of 0.3 μIJmol, the copper plating layer does not have a uniform thickness throughout. A copper plating layer 6 having dendritic irregularities is formed. The reason for this is that polyoxyethylene oleyl ether and monovalent copper ions form a complex and become polycations, and the low concentration of chlorine ions that normally act as brighteners suppresses the cathode reaction in an unstable manner. . Further, such a dendritic uneven plating layer 6 has a characteristic of growing along the flow of the plating solution 9 (the state shown in FIG. 6). In other words, the flow of the plating liquid 9 along the longitudinal direction of the heat exchanger tube 10 is insufficient to form an uneven plating shape that can appropriately restrict the flow of refrigerant when used as the heat exchanger 1. . Therefore, if the spacer 19 made of a spiral polypropylene tree is fixed to the counter electrode 15 as in the present invention, the flow of the plating solution 9 in the heat transfer tube 1o will follow the spiral shape. Become a thing,
The dendritic uneven plating layer 5 formed in the heat exchanger tube 10 has a spiral shape (the state shown in FIG. 7).By making the dendritic uneven plating layer 5 into a spiral shape in this way, the refrigerant Since the forced circulation type heat exchanger appropriately dissipates the refrigerant flowing in the longitudinal direction of the heat transfer tubes 2, it is possible to improve the heat transfer efficiency.The copper plating layer 6 obtained in this way is The difference in height between the unevenness is approximately 100 μm.

Next, the inner wall of the heat exchanger tube 1o is washed with hot water and dried, after which a fluorocarbon gas is sealed inside and both ends 6a and 6b are caulked and welded. Exchanger 1 is completed.

The heat exchanger 1 obtained in this way has the inner wall surface 4 of the heat exchanger tube 2.
The plating layer 6 with dendritic irregularities not only increases the surface area and promotes boiling heat transfer, but also when the fluorocarbon gas liquefies on the inner wall surface 4, the liquid layer 6 Since the droplets leave the inner wall surface 4 faster than the smooth surface, it is difficult to form a liquid layer as a heat insulating layer.
Heat transfer during condensation is also promoted. That is, the heat exchanger 1, which is like a heat pipe in which liquefied fluorocarbon gas is sealed and repeats vaporization and condensation, has a significantly improved heat transfer efficiency.

In the examples of the present invention, an acidic copper sulfate plating solution was used as a means to form a dendritic uneven plating layer, but although copper-based plating solutions are advantageous in terms of thermal conductivity, other metal plating solutions can also be used. However, it is not limited to copper plating. Although polyoxyethylene oleyl ether was used as a surfactant, it includes all oxyethylene surfactants such as polyethylene glycol and polyoxyethylene noryl phenyl ether. In addition to hydrochloric acid, chloride such as sodium chloride can be used as the chloride ion additive, and the additive includes all chlorides that are liberated as chloride ions in the plating solution. However, when the chlorine ion concentration becomes 1 mmol or more, the bond with the complexed copper ion becomes stable, so that copper is deposited with a uniform thickness over the entire surface.

Therefore, the chlorine ion concentration must be kept at a low concentration of 1 mmol or less.

Effects of the Invention As described above, the present invention allows a plating solution containing an oxyethylene surfactant and a low concentration of chloride ions to be poured onto the wall surface of a heat transfer tube, and a spacer fixed to the opposite electrode to direct the flow. By creating a spiral flow, a metal plating layer with dendritic irregularities is formed.It is inexpensive and can be mass-produced by controlling the chlorine ion concentration, plating solution temperature, current density, plating time, and flow cutoff. The shape of the unevenness is stabilized through maintenance such as replacement, and an uneven plating layer with excellent adhesion is formed in a spiral shape inside the heat transfer tube.
It increases the surface area, has the effect of promoting boiling heat transfer, and also has the effect of promoting heat transfer efficiency in condensation, making it possible to easily form a highly efficient heat transfer tube wall surface.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a counter electrode equipped with a spiral insulating spacer according to an embodiment of the present invention, Fig. 2 is a schematic cross-sectional view of the plating equipment, and Fig. 3 is a cross-sectional view of the heat exchanger. Figure 4 is a longitudinal sectional view of the heat exchanger, Figure 6 is a perspective view of the heat exchanger,
FIG. 6 is a perspective view showing an uneven metal plating layer formed without a spiral insulating spacer, and FIG. 7 is a perspective view showing an uneven metal plating layer of the present invention. 2.1o... Heat exchanger tube, 5... Dendritic uneven metal plating layer, 9... Plating solution, 15...
...Counter electrode, 18...... R, 19...
·spacer. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 15... Ri, pole/9
・・・ Sube-°su'-

Claims (1)

[Claims] The heat exchanger tube is used as the cathode side, the counter electrode provided with a certain gap from the heat exchanger tube is used as the anode side, and sulfuric acid containing an oxyethylene surfactant and a low concentration of chloride ions as additives is placed in the gap. A method for plating the inner wall of a heat exchanger tube, which comprises pouring a copper solution plating solution to form an uneven metal plating layer on the inner wall of the heat exchanger tube, the method comprising: attaching a spiral insulating spacer to the counter electrode. .