JPS588957B2 - NetsukoukankiyoudennetskannoSeizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a heat exchanger tube for a heat exchanger, and particularly to a method of manufacturing a heat exchanger tube with excellent nucleate boiling characteristics.

Heat exchangers, such as heat transfer tubes in refrigerators, are equipped with fins to increase the surface area in order to improve the heat transfer effect.

Although the heat exchange efficiency can be improved to some extent by adding fins, it is still not sufficient.

On the other hand, it is also known that heat transfer efficiency can be significantly increased if a nucleate boiling transfer method is applied to heat transfer tubes.

By the way, the nucleate boiling phenomenon is a phenomenon in which heat is transferred from the surface of the heat exchanger tubes into the liquid under conditions where the temperature at or near the surface of the heat exchanger tubes is sufficient to form a vapor phase. It can also happen below.

Moreover, in this nucleate boiling phenomenon, the liquid is disturbed by the generation of bubbles, so the heat transfer coefficient increases significantly and the heat load on the heat transfer surface also increases rapidly.

FIG. 1 shows this state by showing the boiling characteristic curve of water under atmospheric pressure.

In heat exchanger tubes for heat exchangers that utilize the nucleate boiling phenomenon as described above, the tube surface is usually coated with a porous layer made of metal powder to provide desired characteristics.

However, in the case of this heat exchanger tube, there is an inconvenience in that the heat exchanger tube cannot be subjected to bending work because the covering porous material has poor flexibility.

The present invention aims to provide a method for manufacturing a heat exchanger tube that has reduced liquid flow resistance, can be bent, and has greatly improved boiling heat transfer efficiency, and can be easily scaled.

To explain the present invention in detail below, the surface of the heat exchanger tube body is coated with steel or copper alloy fibers having a diameter of 100μ or less, and heat treatment is performed in a non-oxidizing atmosphere to diffusely bond the coated fibers to the tube surface. This is a method for manufacturing a heat exchanger tube for a heat exchanger, and is generally carried out as follows.

For example, it is formed into a copper fiber having a diameter of about 50 μm manufactured by a wire drawing method.

Then, the copper fibers are cut into short fibers having a length of 10 to 20 cm, and a large number of these fibers are made into a cotton-like aggregate by an operation similar to a paper-making method.

Next, this assembly is applied to the circumferential surface of the heat exchanger tube body to a thickness of 1 to 5 mm.
For example, in a N2 gas flow at 850°C,
When heat-treated for about 3 hours, the covering fibers and copper fibers of the aggregate and the circumferential surface of the heat exchanger tube are appropriately diffused bonded and integrated, and the heat exchanger tube has sufficient mechanical strength.

Although the above example shows an example in which short copper fibers are aggregated, coated, and diffusion bonded, the present invention is not limited to this embodiment, and gold layer particles or powder of the same material as the fibers may be included in the coated fibers. It may be dispersed and baked.

Further, the constituent group of the fiber is not limited to copper, but may be a copper alloy such as copper-tin or copper-zinc.

In the present invention, copper or copper alloy is selected as the metal fiber for forming the diffusion layer provided in the heat exchanger tube in consideration of thermal conductivity.

Furthermore, the fiber diameter is selected to be 100μ or less.
This is because when it exceeds 00μ, a significant decrease in the boiling heat transfer coefficient is observed.

For example, when the present inventors determined the heat transfer efficiency of heat transfer tubes obtained by changing the diameter of the individual fibers while keeping the amount of coverage of the aggregate constant, the average diameter of the fibers became larger as shown in Figure 2. A decrease in efficiency is observed as the fiber diameter exceeds 100μ, and the heat transfer coefficient decreases rapidly.

This is thought to lead to a relative decrease in properties because the specific surface area of the fibers decreases and the degree of bonding with the heat exchanger tube body also decreases.

Furthermore, when coating copper fibers and the like to heat-treat and bond them by diffusion, a non-oxidizing gas is selected as the atmosphere in order to prevent oxidation of the metal fibers and to more easily cause mutual diffusion reactions.

According to the method of the present invention as described above, a heat exchanger tube with excellent heat conduction characteristics can be easily obtained.

That is, the heat exchanger tube according to the present invention is provided with a fibrous copper-based coating layer, and the coating layer made of this fiber has significantly better heat transfer efficiency than, for example, a porous layer made of metal powder and provided by thermal spraying.

However, since the diffusion layer formed using the covering layer made of fibers is flexible, it not only withstands bending, etc., but also has a low flow resistance against forced convection liquid, so it can be used as a heat exchanger tube in a heat exchanger. Always exhibits excellent performance.

Furthermore, since the manufacturing process is not complicated as it only involves heating the fibrous material, it can be said to be a practically excellent manufacturing method in that it can exhibit the above-mentioned good functions.

Next, examples of the present invention will be described.

Example 1 Average diameter of about 30 mm made from copper manufactured by wire drawing method
The μ-sized fibers are cut into lengths of 10 to 20 cm, and a large number of these fibers are made into a cotton-like aggregate by an operation similar to a paper-making method.

The outer diameter of this aggregate is 25.4 m so that the thickness is about 5 mm.
The coating was maintained on the surface of a steel pipe with a wall thickness of 2 mm.

Next, by heating at 850° C. for 3 hours in a high-purity N2 gas stream, the fibers and the fiber-copper tube are bonded together by diffusion,
A heat exchanger tube with a diffusion layer for use in a heat exchanger with sufficient strength was formed.

In order to evaluate the boiling heat transfer characteristics of the heat transfer tube thus obtained, R-11, which is used as a refrigerant for refrigerators, was used as the flow medium, and the temperature difference v. When the relationship with the S boiling heat transfer coefficient was determined, the boiling heat transfer efficiency was extremely excellent as shown by curve 1 of the example in FIG.

For comparison, the same figure shows a heat transfer tube with a coating layer formed from the same kind of powder of about 100 mesh, which was evaluated on the same strip, and the heat transfer efficiency was 1.
/2 or less.

From this comparison, it can be seen that the characteristics of the heat exchanger tube according to the present invention are significantly improved.

Example 2 Average diameter of 78μ made from copper manufactured by wire drawing method
The fibers having a diameter of 25.4 cm were cut into lengths of 10 to 20 cm, and the fibers were made into aggregates (cotton-like) using an operation similar to the paper-making method. Approximately 7m thick on the surface of a steel pipe with mmφ wall thickness of 2mm
The coating was maintained so that it became m.

Next, electrolytic copper powder 78 with a particle size of -250+325 mesh
A slurry liquid consisting of 2 parts of ammonium alginate and 20 parts of pure water as a binder was passed through the copper fiber coating and deposited on the whole or a part of the surface of the copper fiber, and then left in the atmosphere at room temperature. A drying process was performed for about 10 hours.

Next, heat treatment was performed at 900° C. for 4 hours in a stream of high-purity N2 gas to produce a diffusion layer with sufficient bonding strength between the fibers, the fibers/powder, and the copper tube body to produce a heat exchanger tube.

Thereafter, the heat transfer characteristics were evaluated in accordance with Example 1, and the results are shown by curve 2 in FIG.

As described above, the boiling heat transfer coefficient of the heat exchanger tube formed by the method of the present invention is extremely high.

As is clear from the above, the heat exchanger tubes formed by the method of the present invention are effective for use in heat exchangers.

Furthermore, since it is formed as a diffusion layer on the surface of the tube, it has sufficient mechanical strength to withstand the bending stress of the heat exchanger tube.

Further, as described above, the method of the present invention can be easily produced by forming a copper metal into a fiber, covering a tube with the fiber, and heating it, thereby eliminating the need for special equipment.

[Brief explanation of the drawing]

FIG. 1 is a relationship curve diagram between the boiling heat transfer coefficient and temperature difference of a heat exchanger tube, FIG. The figure is a curve diagram showing the relationship between the heat transfer coefficient and temperature difference of a heat exchanger tube manufactured by the method of the present invention in comparison with a heat exchanger tube not related to the present invention.

Claims (1)

[Claims] 1. A heat exchanger characterized in that the surface of the heat exchanger tube body is coated with copper or copper alloy fibers with a diameter of 100μ or less, heat treated in a non-oxidizing atmosphere, and the coated fibers are diffusion bonded to the tube surface. A method for manufacturing dexterous heat exchanger tubes.