JPH073183Y2 - Heat transfer tube for heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a heat transfer tube for a heat exchanger that allows cooling water to pass through the tube, and in particular, has a corrosion-resistant protective film formed on the inner surface to prevent corrosion by the cooling water. The present invention relates to a heat transfer tube made of copper or a copper alloy for a heat exchanger.

[Prior Art] As a heat transfer tube for a heat exchanger that allows sea water, river sea water, or fresh water to pass through as cooling water, a tube material of copper or a copper alloy has been conventionally used. In this case, a protective film is often formed on the inner surface of the pipe in order to prevent corrosion due to cooling water. In this anticorrosion method, a corrosion-resistant protective film containing iron hydroxide as a main component is formed on the inner surface of the heat transfer tube.

As a method of forming a protective film containing iron hydroxide as a main component, ferrous ions are injected into the cooling water flowing through the heat exchanger in operation, and this cooling water is fed into the heat transfer tube. There is a method of forming a protective film on the inner surface of the tube by the method and a method of forming a protective film on the inner surface of the tube in advance at the time of manufacturing the heat transfer tube.

Thus, while the heat transfer tube having the protective film formed by these methods has a significantly improved corrosion resistance, the heat transfer performance as the heat transfer tube for the heat exchanger has to be sacrificed slightly due to the thermal resistance of the protective film. There is a problem that you cannot get it. Therefore, the application of the heat transfer tube with a protective film is restricted.In particular, the heat transfer tube with a protective film formed on the inner surface of the tube in advance is used because the corrosive environment is extremely strict and the anticorrosion measure is better than the heat transfer performance. However, it was limited to the case where the priority was given to the case, or the case where the inner surface including the protective film did not significantly affect the performance of the heat exchanger.

[Problems to be Solved by the Invention] However, there are various forms of corrosion of heat transfer tubes for heat exchangers due to cooling water. That is, the corrosion of the inner surface of the heat transfer tube is often affected by the water quality, the usage conditions, and the like, and often exhibits a unique form for each plant. One of the forms of this corrosion may be linear or strip-shaped corrosion only on the lower side of the pipe body when mounted due to sand erosion or the like. In this way, in the case where only a part of the inner surface of the pipe is corroded, forming a protective coating on the entire inner surface of the pipe as described above is not only an excessive measure in terms of anticorrosion effect but also heat transfer. The loss was large from the viewpoint of performance.

The present invention has been made in view of such problems,
An object of the present invention is to provide a heat transfer tube for a heat exchanger, which has excellent anticorrosion performance and minimizes a decrease in heat transfer performance in an environment such as a lower part of the tube which is locally corroded.

[Means for Solving the Problems] The heat transfer tube for a heat exchanger according to the present invention has a corrosion-resistant protective coating mainly composed of strip-shaped iron hydroxide formed on the inner surface of the tube and extending in the longitudinal direction of the tube. The arc length of the coating on the inner surface of the pipe in the circumferential direction is 5 mm or more and is less than 1/2 of the total inner circumferential length.

[Operation] In the present invention, for example, as shown in the sectional view along the pipe diameter direction of FIG. 1 and the sectional view along the pipe longitudinal direction of FIG. 2, on the inner surface of the tube body 1 of the heat exchanger tube for heat exchanger, A band-shaped corrosion-resistant protective film 2 extending in the longitudinal direction is formed in a partial region in the circumferential direction. Therefore, in the case of a corrosive form in which a partial area of the inner surface of the pipe is selectively corroded by sand erosion or the like, the protective film 2 is applied only to the corroded area.
By providing the above, corrosion can be effectively avoided and excellent heat transfer performance can be secured.

For example, in the case of a steam condensing heat exchanger such as a condenser, the condensed water film on the outer surface of the tube is thinner on the upper side of the tube than on the lower side of the tube due to the influence of gravity. Therefore, the heat transfer on the outer side of the tube is better on the upper side, and therefore, the amount of heat exchange is also higher on the upper side.

In the present invention, since the arc length of the protective coating 2 in the circumferential direction of the pipe body 1 is 1/2 or less of the total inner circumferential length, the protective coating 2
When the tube body 1 is mounted so that the center of the tube body is at the lower end, the non-formed area where the protective film 2 does not exist over the upper half or more of the inner peripheral surface of the tube body 1. As described above, the upper half portion of the tube body 1 is a portion that has good heat transfer and a large amount of heat exchange. Therefore, by making this portion a non-formation region of the protective film 2, the heat transfer as a whole is improved. The performance is improved more than a ratio determined in proportion to the area ratio of the non-formed region.

Further, in the present invention, the arc length of the protective film 2 is 5 mm or more and is 1/2 or less of the total inner peripheral length. This is because when only the lower side of the pipe body is corroded by sand erosion or the like, corrosion by sand erosion cannot be prevented if the arc length of the protective film 2 is less than 5 mm.
If the arc length of the protective film 2 exceeds 1/2 of the total inner circumference,
The heat transfer performance of the heat transfer tube is remarkably reduced, the effect of improving the anticorrosion performance is slowed down, and the protective film 2 is extended over the arc length.
It is useless to form.

For the reason described above, the band-shaped protective coating 2 has an arc length of 5 mm or more along the circumferential direction of the inner surface of the pipe, and has a total inner circumferential length of 1 mm.
It should be less than / 2.

[Embodiment] Next, an embodiment of the present invention will be described.

Aluminum brass tube with an outer diameter of 25.4 mm and a wall thickness of 1.24 mm (JI
SH 3300 C6872T) was coated with a protective film mainly composed of iron hydroxide with a predetermined width so as to form a strip extending in the tube axis direction. The protective film was formed by applying an acidic iron powder suspension on the inner surface of the tube and then blowing air containing steam into the tube to oxidize the iron powder.

Then, the heat transfer performance of the test tube under the steam condensing condition and the corrosion test by the passage of seawater were performed. The heat transfer performance is measured by measuring the overall heat transfer coefficient under the condition that 100 ° C saturated steam outside the tube is condensed by room temperature industrial water flowing at a flow rate of 2 m / sec. It was evaluated by the rate of decrease with respect to the overall heat transfer coefficient. Also,
The corrosion test was carried out by passing seawater containing 300 ppm of sand drift in the pipe at 2.5 m / sec for 4 months and observing the corrosion state. The corrosion resistance was evaluated by this corrosion depth.

In each of Examples 1 to 3 and Comparative Example 1, the heat transfer tube was mounted and tested so that the protective film forming portion was located at the lower end. However, for comparison of heat transfer performance, the heat transfer tube of Comparative Example 2 was formed with a protective film. The part was mounted on the upper side. Table 1 below shows the conditions for forming and disposing the protective film and the test results of heat transfer performance and corrosion resistance in each of Examples 1 to 3 and Comparative Examples 1 to 4.

As is clear from Table 1, the protective film forming pipes of Examples 1 to 3 have a smaller reduction rate of the overall heat transfer coefficient as compared with the pipe (Comparative Example 3) in which the protective film is formed all around. Excellent heat transfer performance. Further, as is clear from the comparison between Example 3 and Comparative Example 2, even if the width, that is, the area of the protective film is the same, the effect on the heat transfer performance when the heat transfer tube is mounted with the protective film on the lower surface side. Is smaller, the decrease rate of the overall heat transfer coefficient is small. Further, regarding the anticorrosion effect, the heat transfer tubes of Examples 1 to 3 exhibit the same excellent anticorrosion effect as the tube having the protective film formed on the entire circumference (Comparative Example 3).

[Effects of the Invention] The heat transfer tube for a heat exchanger according to the present invention has an excellent anticorrosion effect and less deterioration in heat transfer performance, and is extremely useful as a heat transfer tube for a heat exchanger exposed to sand erosion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in the pipe diameter direction showing an example of the heat transfer pipe for a heat exchanger of the present invention, and FIG. 2 is a cross-sectional view in the pipe longitudinal direction. 1: Tube body, 2: Protective film

Claims (1)

[Scope of utility model registration request] 1. A corrosion-resistant protective coating, which is formed on the inner surface of the pipe and extends in the longitudinal direction of the pipe, and whose main component is iron hydroxide, and the arc length of the protective coating on the inner surface of the pipe is 5 mm or more. The heat transfer tube for heat exchangers has a total inner circumference of less than 1/2.