JPH0312150B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for imparting hydrophilicity to a condensing heat transfer surface (in this specification, the term "heat transfer surface" simply refers to a condensing heat transfer surface) of an aluminum heat exchanger. 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 the condensing heat transfer surface of aluminum heat exchangers,
For example, in order to improve the heat exchange performance with condensation on the inner surface of the medium flow pipe of a heat exchanger used as a condenser, it is necessary to remove energy from uncondensed vapor through a layer of liquid produced by condensation. It is necessary to make the layer of condensate as thin as possible. Therefore, such a condensing surface is required to have good hydrophilicity with the liquid, that is, good wettability. In addition, on other condensation heat transfer surfaces, that is, on the surface of the fins of heat exchangers used as evaporators in air conditioners such as car coolers and room coolers, the surface temperature of the fins is lower than the atmospheric temperature. Water droplets adhere to the surface, and the adhesion of such water droplets increases ventilation resistance and reduces the air volume, resulting in a decrease in heat exchange efficiency. This becomes especially noticeable when the fin pitch is narrowed to improve the performance and downsize the evaporator. Heat exchange efficiency is greatly influenced by the wettability of the fins, that is, their hydrophilicity.If the fins have good wettability, attached water will be less likely to form droplets, which will reduce ventilation resistance and increase the amount of air, which will reduce heat transfer. Exchange efficiency is also improved. From this point of view, efforts have been made to mechanically or chemically roughen the condensation 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 safety, and manufacturing cost.Furthermore, they have problems in terms of corrosion, and heat transfer performance deteriorates due to the generation of hydrogen gas due to reaction with water. Because of this, it has not yet been put into practical use industrially. An object of the present invention is to provide a method that can easily impart excellent hydrophilicity to the condensing heat transfer surface of an aluminum heat exchanger. That is, the method of the present invention is characterized in that a condensation heat transfer surface of an aluminum heat exchanger is subjected to a chemical conversion treatment using an acid-based treatment liquid containing alumina sol or silica sol. This is a method of imparting hydrophilicity to surfaces. The film formed on the surface of the aluminum material by the above treatment constitutes a heat transfer surface. Typical examples of chemical conversion treatment using acid-based treatment liquids include:
Examples include chromate film formation treatment, zirconium film formation treatment, phosphoric acid film formation treatment, and the like. In particular, chromate film formation treatment, i.e. chromic acid,
Treatment with a treatment solution containing chromate and/or dichromate is preferred. As a result of the chemical conversion treatment using this acid-based treatment liquid, a heat transfer surface having good wettability and excellent corrosion resistance can be formed. In the chromate treatment, sodium chromate and potassium chromate are often used as the chromate, and sodium dichromate and potassium dichromate are often used as the dichromate. The concentration of these salts is preferably in the range of 0.001 to 1 mol/mol. The reason is 0.001
If the amount is less than 1 mol/mol, the above effect will not be fully exhibited, and if it exceeds 1 mol/mol, it will be economically disadvantageous and the subsequent waste liquid treatment load of the washing water will be increased. A particularly preferable concentration is 0.01 to 0.5 mol/
It is. The content of alumina sol is _0.0001 ~ as _Al2O3
4.0%, preferably 0.01-20%. The content of the silica sol is 0.0001 to 40%, preferably 0.0001 to 7% as _SiO2 . The reason is that the content of alumina sol and silica sol is 0.0001% each.
This is because if it is less than 40%, the above effect will not be sufficiently exhibited, and if it exceeds 40%, the above effect will not be significantly improved. The prepared bath water used for preparing the treatment liquid may be water containing various ions such as deionized water, distilled water, tap water, and ground water. The pH of the treatment liquid is preferably 2 to 7. Therefore, pH may be adjusted using alkali metal carbonates or hydroxides. The treatment temperature is preferably 20°C or higher. At temperatures below 20°C, the amount of chromate adsorbed or reacted with the film is small, and the above effects are not sufficient. Preferably the temperature is 80°C or higher. Further, the processing time is related to the concentration and temperature of the processing liquid, but is usually from several seconds to one hour. Note that the method for forming a heat transfer surface according to the present invention is more effective when performed after roughening the aluminum surface by chemical or mechanical treatment such as etching or blasting, or after groove forming processing 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 this way, an oxide or hydrated oxide layer that is dense and has good wettability with liquid can be formed.
Furthermore, according to the present invention, it is possible to easily treat the inner surface of the tube, which has traditionally been difficult to treat, and therefore the inner and outer surfaces of the tube can be treated simultaneously, resulting in extremely high workability. . Furthermore, the method according to the present invention can be applied to brazed products to which boehmite films are generally difficult to adhere, and can form a heat transfer surface with good corrosion resistance. Furthermore, by applying the method of the present invention to the outer surface of a heat exchanger, particularly an evaporator, its wettability can be improved and water droplets between the fins can be smoothly removed. Therefore,
It is possible to avoid troubles such as water droplets accumulating in a cross-linked manner between the fins, increasing air flow resistance, and noise caused by the fins vibrating due to inflowing air, and it is possible to sandwich the fin pitch. ,
The heat exchanger can be made more compact. Example: Aluminum material for condensation heat transfer surface of heat exchanger:
JISA1100−H24

[Table] The relationship between the number of days elapsed and the contact angle was determined for the heat transfer surfaces formed in Examples and Comparative Examples. The results are shown in the attached drawings. As can be seen from the figure, the heat transfer surface formed according to the example has a smaller contact angle than that of the comparative example, in other words, it has excellent wetting properties. Moreover, this wettability does not deteriorate over a long period of time. Corrosion resistance and wettability tests were also conducted on each heat transfer surface. The results are shown in Table 1 below. The corrosion resistance test was conducted using a salt spray test (JIS, Z2371).

【table】

[Table] × Poor As can be seen from the table, the heat transfer surface formed according to the example has good corrosion resistance and wettability.

[Brief explanation of drawings]

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

Claims (1)

[Claims] 1. A method for imparting hydrophilicity to a condensing heat transfer surface of an aluminum heat exchanger, the method comprising chemically treating the condensing heat transfer surface of the aluminum heat exchanger using an acid-based treatment liquid containing alumina sol or silica sol.