JPH0312151B2 - - 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 below the dew point of the atmosphere. 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 wettability of the fins is good, the adhering water will be less likely to form droplets, which will reduce ventilation resistance and increase the amount of air, which will increase the heat transfer efficiency. 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.
1 or 2 alkaline earth metals or their salts
This is 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 an aluminum heat exchanger with a treatment liquid containing a silica sol and a silica sol. A chemical conversion film formed on the surface of the aluminum material by the above chemical conversion treatment constitutes a heat transfer surface. The alkali metal and alkaline earth metal may be any metal in the periodic table. Particularly preferred are lithium, sodium, potassium, magnesium, calcium, and strontium. The form of the salt is not particularly limited, but it usually includes halides such as chlorides and iodides, sulfates, nitrates, carbonates,
Oxalates are often used. The above metals and their salts are essential components for forming a chemical conversion film on the aluminum surface. These can be used alone or in combination. In the latter case, a particularly uniform and thick film can be formed. The concentration of the above-mentioned metals or their salts in the treatment liquid is in the range of 0.005 to 2 mol/mole.
The reason for this is that if the concentration is less than 0.005 mol/mol, the film formation will not proceed sufficiently, and if the concentration is less than 2 mol/mol/
This is because, even if the amount exceeds 1, the film-forming ability is not particularly improved, and on the contrary, metal hydroxides are precipitated in the treatment solution, resulting in worsening of the stability of the solution. When forming an evaporative heat transfer surface, it is necessary to roughen the surface, so it is better to have a relatively high salt concentration, especially 0.1
~1 mol/ is preferred. Furthermore, when forming a condensing heat transfer surface, it is better for the film to be thinner than in the case of an evaporative heat transfer surface, and therefore the concentration is preferably 0.01 to 0.2 mol/. The silica sol functions to improve the corrosion resistance of the formed heat transfer surface. The concentration of silica sol is in the range of 0.0001-0.5% as _SiO2 . The reason for this is that if the concentration is less than 0.0001%, corrosion resistance is poor, and if it exceeds 0.5%, film formation is inhibited. A particularly preferred concentration is 0.003 to 0.3 mol/. Further, an aluminate salt such as sodium aluminate or potassium aluminate may be added to the treatment liquid. Aluminate promotes film formation and improves the cohesive force of the film, contributing to obtaining a uniform film. The concentration of aluminate is 0.001
It is in the range of ~1.0 mol/. The reason for this is that if the concentration is less than 0.001 mol/mol, the above effect of the aluminate will not be exhibited, and if it exceeds 1.0 mol/mol, a precipitate will form. Particularly preferred concentration is 0.01~
It is 0.3 mol/. Furthermore, amines such as triethanolamine may be added to the treatment liquid. The amines serve to improve the stability of the treatment solution and prevent precipitation of metal hydroxides. The temperature of the treatment liquid is preferably 40°C or higher. temperature is 40
If the temperature is lower than ℃, sufficient film formation will not occur. The pH of the treatment liquid is preferably 6 to 13. If the pH is less than 6, the dissolution of aluminum will proceed faster than the formation of a film, making it difficult to form a film. 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 treatment time is related to the concentration of the treatment liquid, but is usually 1 to 60 minutes. Even if the length is longer than this, the film forming effect will not be particularly improved. 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. 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.
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. Moreover, since the processing is performed in one step, workability is also good in this respect. Examples 1 to 5 As an aluminum material for the condensing heat transfer surface of a heat exchanger
Made of JISA1100-H24 (size 1mm x 50mm x
100 mm) and was immersed in the treatment solution under the following conditions.

【table】

[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 drawings]

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

Claims (1)

[Scope of Claims] 1. A process for chemically treating the condensing heat transfer surface of an aluminum heat exchanger with a treatment liquid containing one or more alkali metals, alkaline earth metals, or their salts and silica sol. A method for imparting hydrophilicity to the condensing heat transfer surface of an aluminum heat exchanger. 2. The method according to claim 1, wherein the treatment liquid further contains an aluminate. 3. The method according to claim 1 or 2, wherein the treatment liquid further contains an amine.