JPS6259198B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of forming a heat transfer surface on an aluminum material. In this specification, the term "aluminum" is intended to include pure aluminum, commercially available aluminum with minor impurities, and aluminum alloys in which aluminum predominates. Generally, in the evaporative heat transfer side of a heat exchanger, heat exchange is mainly performed by boiling heat transfer. Therefore, in order to improve heat exchange performance, it is important to expand the area of the heat transfer surface as much as possible, and also to increase the density of the generation nuclei of fluid vapor bubbles on the heat transfer surface, thereby stirring the fluid sufficiently. I'm getting old. On the other hand, in order to improve heat exchange performance on the condensation heat transfer surface, in addition to expanding the area of the heat transfer surface as described above, it is also necessary to take energy from uncondensed vapor through a layer of liquid produced by condensation. For this reason, it is necessary to make the layer of the condensate as thin as possible. Therefore, the heat transfer surface is required to have good wettability. From this point of view, efforts have been made to mechanically or chemically roughen the heat transfer surface, process it into various shapes, and even form a sintered alloy layer. All of these have drawbacks in terms of heat exchange performance, quality stability, and manufacturing cost, and also have problems in terms of corrosion, so they have not yet been put into practical use industrially. In view of the above-mentioned circumstances, it is an object of the present invention to provide a method for forming a heat transfer surface of an aluminum heat exchange tube, which is applicable to both the evaporative heat transfer surface and the condensation heat transfer surface. That is, the present invention provides a method for forming a heat transfer surface on an aluminum material by anodizing the aluminum material using a solution obtained by adding silicic acid, silicate, or silica sol to a normal anodizing solution. This is the way to do it. The anodic oxide film formed on the surface of the aluminum material by the above treatment constitutes a heat transfer surface. A typical anodizing solution is an aqueous solution containing a required amount of sulfuric acid, oxalic acid, phosphoric acid, etc. Silicic acid, silicates, and silica sol serve to increase the corrosion resistance of the formed heat transfer surface and improve the stability of the film. As silicates, sodium silicate, potassium silicate, water glass, etc. are often used. The concentration of silicic acid and silicates is in the range 0.0005-0.5 mol/. The reason is that the concentration is 0.0005
If the amount is less than mol/mol, the above effects will not be fully exhibited,
This is because if the amount exceeds 0.5 mol/min, a precipitate will form in the treatment solution. A particularly preferred concentration is 0.003 to 0.3 mol/. The concentration of silica sol is as _SiO2
It is in the range of 0.0001 to 5%. The reason for this is also the same as in the case of the silicic acid and its salts. The prepared bath water used for preparing the treatment liquid may be water containing various ions such as deionized water, distilled water, hydrostatic water, and ground water. The treatment conditions for anodic oxidation are according to conventional methods. The processing time is related to the concentration of the processing solution, but is usually 1 to 120
It's a minute. To form the evaporative heat transfer surface, a highly concentrated treatment liquid is used and the treatment is performed for a relatively long time. On the other hand, in order to form a condensing heat transfer surface, a treatment is performed for a relatively short time using a treatment liquid of low concentration. After the treatment, a sealing treatment is preferably performed using pressurized steam or boiling water. The method for forming a heat transfer surface according to the present invention will be more effective if it is performed after roughening the aluminum surface by chemical or mechanical treatment such as etching or plasting, or after forming grooves such as knurling or cutting. It is true. As described above, according to the present invention, a heat transfer surface having a large heat transfer area and excellent corrosion resistance can be formed by roughening the surface of the aluminum material. In addition, to form an evaporative heat transfer surface, a relatively coarse porous oxide or hydrated oxide layer can be formed, which serves as a nucleus for generating vapor bubbles, and on the other hand, to form a condensation heat transfer surface, It is possible to form an oxide or hydrated oxide layer that is dense and has good wettability with liquid. Further, according to the present invention, it is possible to easily treat the inner surface of the tube, which has conventionally been difficult to treat, and therefore the inner and outer surfaces of the tube can be treated simultaneously, resulting in extremely high workability. Furthermore, since the processing is performed in one step, workability is also good in this respect. Examples 1 to 6 An aluminum material made of JISA1100-H24 (size: 1 mm x 50 mm x 100 mm) was anodized under the following conditions.

[Table] Regarding the heat transfer surface thus formed, the relationship between the number of days elapsed and the contact angle was determined. The results are shown in the drawing. For comparison, the same material as the aluminum material above was used.
Chromate treated at 30℃ for 2 minutes (Comparative Example 1), same aluminum material treated with 5% NaOH solution at 50℃
The above relationship was also determined for the aluminum material treated for 3 minutes and degreased with 30% HNO ₃ (Comparative Example 2), and the same aluminum material anodized and steam treated (Comparative Example 3). These results are shown in the figure. As can be seen from the figure, the heat transfer surface formed according to the example has a smaller contact angle than that formed according to the comparative example, and therefore has excellent wetting properties. Moreover, this wettability does not deteriorate over a long period of time.

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between elapsed days and contact angle.

Claims (1)

[Claims] 1. A method for forming a heat transfer surface on an aluminum material, which comprises anodizing the aluminum material using a solution obtained by adding silicic acid, silicate, or silica sol to a normal anodizing solution.