JPS58213196A - Heat exchanger - Google Patents

Abstract

PURPOSE:To suppress corrosion in a water environment, by providing a coated layer of an epoxy ester resin on the surface of a heat-transmitting member brought into contact with a heat-transmitting medium. CONSTITUTION:The coated layer 3 of an epoxy ester resin is provided on the surface of a heat-transmitting medium condensing part 1b on the side for making contact with water stored in a hot water storing tank 2. Accordingly, since the heat-transmitting member formed of copper is coated with the epoxy ester resin which has a good adhesive property for copper, generation of holes due to corrosion of copper and problem of green water can be supressed, and durability is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat exchanger that uses copper as a heat transfer member and is disposed in a heat pipe type solar water heater, a hot water storage tank for oil supply, a water heater, and the like.

Conventionally, copper has often been used as the heat exchanger material because it has good workability and thermal conductivity, and is corrosion resistant to ordinary tap water and seawater. However, free carbonic acid (C02 dissolved in water) exists at pH = 7 or lower, such as in groundwater.
Copper is dissolved in water containing a large amount of copper, and this copper ion reacts with fatty acid salts such as soap to form a copper complex, which may cause blue water. In reality, many households use groundwater, and it is well known that free carbonate can corrode copper heat exchangers such as water heaters, causing holes and producing blue water. .

Various proposals have been made as methods for preventing copper corrosion. First, there is a method in which a rust preventive agent such as a silicate or phosphate polymer is added to water to form a protective film of the rust preventive component on the copper surface. However, as the protective coating deteriorates over time and peels off, it is necessary to periodically add a rust preventive agent, which is difficult to manage in general households, and because the water is used for hot water supply, no rust preventive agent is required. Addition itself has drawbacks such as being unfavorable from a sanitary standpoint. A second method is to form a metal plating layer on the copper surface.

In this case, electroplating or hot-dip plating of nickel, tin, etc. is applied, but these plating layers have many pinholes, and in electroplating, if the shape of the heat exchanger becomes complicated, the current density becomes uneven. In this case, the plating film thickness is uneven, or there are parts that are not coated, corrosion occurs from those parts, the plating layer peels off, and eventually the copper corrodes as well. In fact, although there are heat exchangers in which copper is plated with nickel or tin, in a water environment containing a large amount of free carbonate, not only the plating layer peels off as described above, but the copper also corrodes.

Furthermore, a method of coating copper with an organic or inorganic binder is also considered. Conventionally, there have been many examples of coating zinc-treated steel sheets, aluminum, etc. with organic and inorganic binders to improve their corrosion resistance, but this is an example of practical application of coating on heat exchangers that use copper as a heat transfer material. There isn't. The reason for this is that in the case of heat exchangers, since the coating layer is an insulator, it is necessary to make the film as thin as possible from the standpoint of heat exchange efficiency, but thin films have many pinholes in the coating layer. Therefore, corrosion occurs from that part, and the value of providing a coating layer is lost.Furthermore, copper itself has difficulty adhering to the binder, so the adhesion with the coating layer is poor. The adhesion may be significantly inferior (under certain environmental conditions). Therefore, in general, the coating of the above-mentioned pine goo on copper has been limited to the mere decoration of coloring to maintain the luster of the copper and to hide the fact that it is copper.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to significantly suppress corrosion in an aqueous environment such as groundwater.

In order to achieve the above object, the present inventors believe that a method of coating a non-metallic material such as the binder is desirable from the viewpoint that corrosion is inevitable in the case of metal coating, and that When we investigated a binder that has fewer pinholes, has excellent adhesion to copper, has excellent hot water resistance, and can suppress corrosion, we discovered that epoxy ester resin is useful.

That is, the present invention provides a heat exchanger in which the heat transfer member is made of copper and the heat medium through which heat is transferred from the heat transfer member is water, in which the surface of the heat transfer member that comes into contact with the heat transfer member is coated with epoxy. - By forming a thin film coating layer of ester resin, corrosion of the heat transfer member in water containing a large amount of free carbonate, such as ground water, can be significantly suppressed.

The attached drawing shows a cross-sectional view of the main parts of the heat pipe type solar water heater according to the present invention, centering on the heat exchange part.
1 is a heat pipe composed of a copper pipe, and a heat medium such as fluorinated hydrocarbon is sealed in this heat pipe 1. The heat medium evaporator 12L is heated by sunlight,
When the heat medium evaporates, the heat of the heat medium is transferred to the heat medium condensing section 1.
Heat is exchanged with the water stored in the hot water tank 2 via b. 3
is a coating layer of the epoxy ester resin of the present invention, and this coating layer 3 is formed on the surface of the heat medium condensing section 1b on the side that comes into contact with the water stored in the hot water storage tank 2. Further, the coating layer 3 needs to be a thin film from the viewpoint of heat exchange efficiency, and preferably has a thickness of 1 μm or less. He's talented.
It is also useful for the coating layer 3 to be formed by adding melamine resin or urea resin to epoxy ester resin.

Hereinafter, one embodiment of the present invention will be mainly described.

Example: Using a test piece made of phosphorus deoxidized copper (JI3 01220P) degreased with trichlene and having dimensions of 50 x 100 x 0.4'''m, epoxy ester resin rSK-1024S-15J (trade name: Sakuramiya Chemical Co., Ltd.) was used. ) was adjusted to an appropriate viscosity with a designated solvent, a coating layer was formed by tipping so that the finished film thickness was about 10 μm, and then baked at 160°C for 30 minutes.In this way, Add the prepared test piece to 50pp of free carbonate.
Corrosion tests were carried out by immersion in water containing m at room temperature. For comparison, a phosphorus-deoxidized copper fabric was also tested in the same manner. Next, the presence of copper ions was confirmed by dropping a sodium fat anti-acid solution into the corrosion solution after the corrosion test.

The results are shown in the table below.

(Margins below) Table Discoloration status of contract test liquid As is clear from the above table, the coating layer of the epoxy ester resin of the present invention does not change color even when sodium fatty acid is added dropwise. Excellent results were obtained, indicating that copper ions were not eluted.

Next, the above-mentioned test piece was immersed in boiling water for 10 days, and in order to confirm the adhesion of the coating layer after the test, the following tests were performed:
A falling ball impact test was conducted, but good results were obtained, with no cracking or peeling of the coating layer.

The reason why epoxy ester resin has excellent adhesion with copper and exhibits good corrosion resistance is that it can be baked at a low temperature of 150'C or less, which suppresses oxidation of the copper surface and creates a barrier between the coating layer and the copper. This is thought to be due to the fact that oxidation exposure is not formed, the leveling (wettability) is good when the resin itself is coated, and there are few pinholes even under a thin film. According to the exchanger, it can be expected to significantly improve durability by significantly suppressing the problems of conventional copper corrosion caused by holes and blue water. It can be applied not only to heat exchangers but also to all heat exchangers that come into contact with water and use copper as a heat transfer member, such as water heaters that use gas or electricity as a heat source, and heat exchangers for electric water heaters. , its practical value is extremely significant.

[Brief explanation of the drawing]

The figure is a sectional view of the main parts of the heat pipe type solar water heater according to the present invention, centering on the heat exchange section. 1... Heat pipe, 1b... Heat medium condensing section, 2... Hot water storage tank, 3... Epoxy ester resin coating layer.

Claims (1)

[Claims] In a heat exchanger in which a heat transfer member is made of copper and a heat medium through which heat is transferred from the heat transfer member is water, □
A heat exchanger, wherein a coating layer of epoxy ester resin is formed on the surface of the heat transfer member that comes into contact with the heat medium.