JPH0312152B2 - - 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, "heat transfer surface" simply refers to a condensation heat transfer surface) of an aluminum heat exchanger. In this specification, the term "aluminum" shall include pure aluminum, commercially available aluminum with small amounts of 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 air condensate as thin as possible. Therefore, such a condensing surface is required to have good aqueous properties 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, room coolers, etc., the surface temperature of the fins is lower than the open air 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. The heat exchange efficiency is greatly influenced by the wettability of the fins, that is, the freshness of water.If the fins have good wettability, attached water will be less likely to form droplets, which will reduce ventilation resistance and increase the airflow, which will reduce 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 stability, 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, in the method of the present invention, the condensing heat transfer surface of an aluminum heat exchanger is subjected to anodic oxidation treatment or a chemical conversion treatment using a treatment liquid other than an acid-based treatment liquid to form an oxide film on the surface, and then acid-based treatment is performed. This is a method for imparting hydrophilicity to the condensation heat transfer surface of an aluminum heat exchanger, which is characterized by applying a chemical conversion treatment to the upper air condensation heat transfer surface using a liquid. A film formed on the surface of the aluminum material by upper air treatment constitutes a heat transfer surface. First, the process of forming an oxide film will be explained.
The anodizing treatment in this step is carried out by a conventional method using an aqueous solution containing a required amount of sulfuric acid, oxalic acid, phosphoric acid, etc. as a treatment liquid. Silicic acid, silicate or silica sol may also be added to the treatment liquid. These substances serve to increase the corrosion resistance of the formed heat transfer surface and improve the safety of the coating. 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 for this is that the above effect is not fully exhibited at a concentration of less than 0.0005 mol/0.5 mol/
This is because, if it exceeds this amount, 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 0.0001-5% as _SiO2
within the range of The reason for this is also the same as in the case of the silicic acid and its salts. In addition, chemical conversion treatment methods in the oxide film forming step include (a) a method using a treatment solution consisting of deionized water or distilled water, and (b) a method using a treatment solution containing alkali metal and/or alkaline earth metal salts. (c) A method using a treatment liquid containing silicic acid or its salt, tannic acid or its salt, and/or silica sol. However, the method using an acid-based treatment liquid, which will be described later, cannot be applied. In the chemical conversion treatment (b), the alkali metal or 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 either, but halides such as chlorides and iodides, sulfates, nitrates, carbonates, oxalates, and the like are commonly used.
Salts may be used alone or in combination.
In the latter case, a particularly uniform and thick film can be formed. The concentration of salt in the processing solution is
It is in the range of 0.005 to 2 mol/. The reason is,
If the concentration is less than 0.005 mol/l, film formation will not proceed sufficiently, and even if the concentration exceeds 2 mol/l,
This is because the film formation ability is not improved, and instead, metal hydroxides are precipitated in the treatment solution, resulting in poor stability of the solution. The concentration of the above salt is preferably 0.01 to 0.2 mol/. In the chemical conversion treatment (c), sodium silicate, potassium silicate, etc. are used as the silicate, and sodium tannate, potassium tannate, tannic acid amide, etc. are used as the tannate. These substances serve to increase the corrosion resistance of the formed heat transfer surface and improve the stability of the film. The concentration of silicate is 0.005-1.0 mol/
within the range of The reason is that the concentration is 0.0005 mol/
If the amount is less than 1.0 mol/mol, the above effect will not be sufficiently exhibited, and if it exceeds 1.0 mol/min, a precipitate will be formed in the treatment liquid. A particularly preferable concentration is 0.003 to 0.3 mol/
It is. The concentration of tannic acid or its salts is 0.001
It is in the range of ~1.0 mol/. The reason is that the concentration
This is because if the amount is less than 0.001 mol/mol, the above effect will not be sufficiently exhibited, and if it exceeds 1.0 mol//, a precipitate will still be formed. The water used for preparing the treatment liquids (b) and (c) may be water containing various ions, such as deionized water, distilled water, tap water, or ground water. Furthermore, an aluminate salt such as sodium aluminate or potassium aluminate may be added to the treatment solutions (a), (b), and (c), respectively. Aluminate promotes film formation and improves the cohesive force of the film, contributing to obtaining a uniform film.
The concentration of aluminate is in the range 0.001-1.0 mol/. The reason is that when the concentration is less than 0.001 mol/aluminate, the above effects are not exhibited.
This is because if the amount exceeds 1.0 mol, a precipitate will be formed.
A particularly preferred concentration is 0.01 to 0.3 mol/. Furthermore, amines such as triethanolamine may be added to the treatment solutions (a), (b), and (c), respectively. Amines serve to improve the stability of the treatment solution and prevent precipitation of metal hydroxides. The treatment temperature in the oxide film forming step is preferably 4° C. or higher. If the temperature is less than 40°C, film formation will not be sufficient. 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. Although the processing time is related to the concentration of the processing solution, it is usually 1 to 60 minutes. The treatment liquids (a), (b) and (c) may be used alone or in combination. Further, the chemical conversion treatment (c) may be performed subsequent to the chemical conversion treatment (a), the chemical conversion treatment (b), and/or the anodic oxidation treatment. The formation of this oxide film imparts good wettability to the heat transfer surface. Next, chemical conversion treatment using an acid-based treatment liquid will be explained. This chemical conversion treatment is performed by a method using an acid-containing treatment solution, and typical examples include chromate film formation treatment, zirconium film formation treatment, phosphoric acid film formation treatment, and the like. Particularly preferred is chromate film forming treatment, that is, treatment with a treatment solution containing chromic acid, chromate and/or dichromate. This chemical conversion treatment improves the corrosion resistance of the heat transfer surface while maintaining good wettability. 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. In this case, the pH of the treatment liquid is preferably 5 to 8. Therefore, the pH may be adjusted using alkali metal carbonates or hydroxides. The treatment temperature for chromate treatment is preferably 20°C or higher. If it is 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. Processing time is also related to the concentration and temperature of the processing solution, but usually
It is 0.5-30 minutes. Note that, if necessary, after the chemical conversion treatment using the acid-based treatment liquid, an additional chemical conversion treatment is performed using a treatment liquid containing silicic acid or its salt, tannic acid or its salt, or silica sol. This additional treatment improves the wettability of the heat transfer surface. Further, the method for forming a heat transfer surface according to the present invention is performed after roughening the aluminum surface by chemical or mechanical treatment such as etching or blasting, or after forming grooves such as knurling or cutting.
Even more effective. 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 was difficult to treat in the past, 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. Furthermore, since the present invention consists of two steps, the concentration of the treatment liquid and other conditions can be easily selected, and the treatment can be carried out under optimal conditions. Example: Aluminum material for condensation heat transfer surface of heat exchanger:
JISA1100−H24

【table】

【table】

[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 The condensation heat transfer surface of an aluminum heat exchanger is anodized or chemically treated with a treatment liquid other than an acid-based treatment liquid to form an oxide film on the surface, and then the condensation heat transfer surface is treated with an acid-based treatment liquid. A method for imparting hydrophilicity to a condensing heat transfer surface of an aluminum heat exchanger, the method comprising applying a chemical conversion treatment to the heat surface.