JPS5947032B2 - Method for imparting hydrophilicity to the condensing surface of an aluminum heat exchanger - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for imparting hydrophilicity to the condensing surface of an aluminum heat exchanger.

In this specification, the term "aluminum" means
It is intended to include pure aluminum, commercially available aluminum with small amounts of impurities, and aluminum alloys in which aluminum predominates.

In general, on the condensing surface of an aluminum heat exchanger, for example on the inner surface of the medium flow pipe of a heat exchanger used as a condenser, in order to improve the heat exchange performance with condensation, it is necessary to pass through a layer of liquid produced by condensation. Since it is necessary to take away the energy of the condensed steam, it is necessary to make the layer of condensed liquid 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 condensing surfaces, that is, on the fin surfaces 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 fin surface has good wettability, attached water will be less likely to form droplets.
This reduces ventilation resistance, increases the amount of air, and improves heat exchange efficiency. From this point of view, efforts have been made to mechanically or chemically roughen the condensation surface, process it into various shapes, and even form a sintered alloy layer. All of them have drawbacks in terms of heat exchange performance, quality stability, and manufacturing cost, and are also problematic 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 surface of an aluminum heat exchanger.

That is, the method of the present invention involves the use of a 40° C.
This method is characterized by comprising a first step of treating the condensing surface of an aluminum heat exchanger with the above treatment liquid, and a second step of treating the condensing surface with a treatment liquid containing silica sol.

In the first step, a chemical conversion film is formed on the condensation surface by treatment with an alkali metal or alkaline earth metal.

The alkali metal or alkaline earth metal can 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 usually chlorides, iodides, etc., rogens, sulfates, nitrates, carbonates, oxalates, etc. are often used. The above salt is an essential component 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 salt in the treatment liquid is in the range of 0.005 to 2 mol/t. The reason for this is that if the concentration is less than 0.005 mol/t, film formation will not proceed sufficiently, and even if the concentration exceeds 2 mol/t, the film-forming ability will remain almost constant and there will be no further effect. On the contrary, the metal hydroxide will precipitate in the treatment solution, which will worsen the stability of the solution. When treating a condensation surface, the thinner the film, the better, and therefore the concentration is preferably 0.01 to 0.2 mol/t. An amine such as triethanolamine may be added to the treatment solution in the first step. Amines have the effect of improving the stability of the treatment solution and preventing precipitation of metal hydroxides. The temperature of the treatment liquid in the first step is preferably 40° C. or higher. If the temperature is less than 40°C, sufficient film formation will not occur. The pH of the treatment liquid is preferably 6 to 13. When the pH is less than 6, the dissolution of aluminum progresses more than the formation of a film, making it difficult to form a film. In the second step, the silica sol serves to increase the corrosion resistance of the condensation surface treated in the first step and improve the stability of the film. The concentration of the silica sol is preferably within the range of 0.0001 to 40Cf6 as SiO2.

The reason for this is that if it is less than 0.0001%, the above effect will not be fully exhibited, and if it exceeds 40%, SiO2 will precipitate in the treatment solution.
is preferred. Further, the temperature of the aqueous solution containing silica sol is preferably room temperature or higher, and the pH thereof is preferably 2 to 11. In each step, the bath water used to prepare the treatment liquid may be water containing various ions such as deionized water, distilled water, or tap water. The immersion time in each step is usually 1 to 60 minutes, although it is related to the concentration of the treatment liquid. To treat condensation surfaces, a relatively short immersion is performed using a low concentration treatment solution. The method according to the present invention is more effective when carried out 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.

As described above, according to the present invention, it is possible to form a dense oxide or hydroxide layer on the condensing surface of an aluminum heat exchanger used as a condenser and with good wettability with liquid. A heat exchanger having excellent heat exchange performance can be obtained. Furthermore, the wettability, ie, hydrophilicity, of the surface of the fins of the evaporator can be improved, allowing water droplets between the fins to be smoothly removed. Therefore, it is possible to avoid troubles such as when water droplets accumulate in a cross-linked manner between the fins and increase air flow resistance, or when the fins vibrate due to floating air and cause noise, and improve heat exchange efficiency. In addition,
The fin pitch can be narrowed and the heat exchanger can be made more compact. Further, since the present invention consists of two steps, it is easy to select the concentration of the treatment liquid and other conditions, and the treatment can be carried out under optimal conditions. Moreover, the stability of the processing liquid is excellent, the amount of precipitation in the processing liquid is reduced, and the life of the processing liquid is extended. Examples 1 and 2 JISAIIOO-H24 was used as the aluminum material and treated under the conditions shown in the table below.

Next, for the hydrophilic surfaces formed in Examples 1 and 2, the relationship between the contact angle and the number of days elapsed was determined. The results are shown in the drawing. For comparison, the same material as the aluminum material above was treated with chromate at 30°C for 2 minutes (Comparative Example 1)
, the same aluminum material was treated with 5% NaOH solution at 50°C.
The above relationship was also determined for the aluminum material treated for 3001 minutes and degreased with 3001) HNO3 (Comparative Example 2), and the same aluminum material anodized and steam treated (Comparative Example 3). These results are shown in the same drawing. As can be seen from the figure, the hydrophilic surface formed according to the example has a smaller contact angle than that formed according to the comparative example, and therefore has superior wettability. Moreover, this wettability does not deteriorate over a long period of time. Furthermore, when the surface of the JISA AllOO-H24 material was treated under the same conditions as the second step conditions in Examples 1 and 2 above, the wettability of the obtained hydrophilic surface was almost the same as in Examples 1 and 2 above. However,
There was a problem with the stability of the film.

[Brief explanation of the drawing] The drawing is a graph showing the relationship between elapsed days and contact angle.

Claims (1)

[Claims] 1 Treat the condensing surface of an aluminum heat exchanger with a treatment liquid at 40°C or higher containing one or more salts of alkali metals or alkaline earth metals, and then treat the condensation surface with a treatment liquid containing silica sol. A method for imparting hydrophilicity to a condensing surface of an aluminum heat exchanger.