JPH0230696Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a cross-fin type heat exchanger in which fins are fitted into heat transfer tubes.

If the above type of heat exchanger is used as an outdoor heat exchanger in a heat pump air conditioner, for example, when the outside temperature is low during heating operation, the fin surface temperature will drop below 0°C, causing frost formation, but the frost formation will increase. If this occurs, the spaces between the fins become clogged, creating resistance to the airflow flowing between the fins and inhibiting heat transfer between the air and the fins, and heating operation must be interrupted for defrosting. There was a problem that it disappeared.

Frost formation on the fin surface occurs when moisture in the air freezes and adheres to the fin surface, but it is already known that this frost formation phenomenon differs depending on the method of treating the fin surface.

Figure 1 shows the state of frosting and frosting on the fins with hydrophilic surface treatment (indicated by the symbol X) and the state of frosting and frosting on the fins with the hydrophobic surface treatment (indicated by the symbol Y). A graph is shown in which time t is plotted on the horizontal axis and ventilation resistance ΔPa is plotted on the vertical axis.

Here, hydrophilic refers to a substance with a relatively large surface tension, and the contact angle when water is attached is 40° or less, and hydrophobic refers to a substance with a relatively small surface tension. The contact angle when water is attached is approximately
100°.

According to this, frost growth is slower on the fin surface with hydrophobic surface treatment than on the fin surface with hydrophilic surface treatment, but when defrosting, water becomes droplets and is less likely to fall between the fins. The disadvantage is that the recovery rate of ventilation resistance is poor. Therefore,
During heating operation after defrosting, accumulated water droplets become nuclei, and frost grows between the fins, resulting in an increase in ventilation resistance.

On the other hand, on the fin surface that has been subjected to hydrophilic surface treatment, frost growth is rapid during frost formation, but water drainage is rapid during defrosting, and the recovery rate of ventilation resistance is also good.

On the other hand, if defrosting operation is performed using a reverse cycle or the like, it causes a decrease in heating capacity, discomfort due to cold drafts, and a decrease in energy efficiency, so it is desirable to reduce the number and time of defrosting operations as much as possible. To this end, it is desirable to use fins fitted to the heat transfer tubes that are resistant to frost formation and have good drainage (that is, are easy to defrost).

The present invention was developed based on the above-mentioned observations regarding frost formation and defrost in heat exchangers. The purpose of this is to delay the growth of frost during frost formation on the surface and improve drainage during defrosting, and in order to achieve this purpose, one surface of the opposing surfaces of adjacent fins is A hydrophobic part is formed on one side, and a hydrophilic part is formed on the other side entirely or partially, so that water droplets generated on the hydrophobic part during defrosting are attracted to the hydrophilic part and quickly fall. and action.

The heat exchanger of the present invention will be explained below based on the embodiments shown in FIGS. 2 to 4. In FIGS. A heat exchanger tube is shown, and the symbol A attached to the surface of the fin 1 indicates a hydrophobic portion, and the symbol B indicates a hydrophilic portion.

The heat exchanger of this embodiment is used, for example, as an outdoor heat exchanger in a heat pump air conditioner, and exchanges heat with air (that is, cools or heats the air).

FIG. 2 shows a first embodiment of the present invention, in which each fin 1 has a hydrophobic portion A on one side and a hydrophilic portion B on the other side over the entire surface. These fins 1a, 1a... are arranged in parallel so that the hydrophobic part A and the hydrophilic part B face each other.

FIG. 3 shows a second embodiment of the present invention, which includes a fin 1b with hydrophobic parts A formed on both sides, and a fin 1b with hydrophilic parts B formed on both sides.
c are arranged alternately in parallel.

FIG. 4 shows a third embodiment of the present invention, in which vertically continuous band-shaped hydrophobic parts A and hydrophilic parts B are alternately formed on both sides of each fin. When these fins 1d, 1d, .

A method of imparting hydrophilicity to the fin surface is, for example, a method of applying a water-based paint containing synthetic silica, while a method of imparting hydrophobicity to the fin surface is, for example, applying a water-based paint containing synthetic silica. There is a method of coating with fluorocarbon resin such as chlorofluorocarbon resin.

Furthermore, it goes without saying that either the hydrophobic or hydrophilic surface may be replaced with an untreated surface.

When the heat exchanger shown in each of the above embodiments is used as an outdoor heat exchanger of a heat pump type air conditioner, each fin functions as follows.

When the outside temperature drops during heating operation and the surface temperature of the fins 1 becomes 0°C or less, frost begins to form on the surface of the fins 1, but the growth rate of frost is slow on the hydrophobic part A, and on the hydrophilic part. There are differences in frost growth speed, with B being faster.

Here, in the adjacent fins 1, 1, the hydrophobic part A and the hydrophilic part B face each other, and since the growth rate of frost is slow in the hydrophobic part A, the wind that flows between the fins As a result of suppressing the increase in resistance, the duration of heating operation becomes longer (that is, the number of times of defrosting operation decreases).

Next, during defrosting operation, the frost melting in the hydrophilic part B precedes the hydrophobic part A, and the melting frost becomes drain and flows down. On the other hand, in the hydrophobic part A, droplet-like water ω (shown in Fig. 5 A) adhering to the surface during frost melting grows due to static and dynamic coalescence, and its height h becomes the fin pitch.
When it becomes equal to Fp (shown in Figure 5), the hydrophobic part A
It comes into contact with the hydrophilic part B facing the hydrophilic part B, and is instantly attracted to the hydrophilic part B side due to the difference in surface tension (as shown in Figure 5, C), and then quickly moves along the hydrophilic part B. (as shown in Figure 5 D). That is,
The phenomenon of ``water droplets straddling the fins'', which is a major cause of water droplet retention, cannot occur. Therefore, drainage properties during defrosting are improved, and the rate of recovery of ventilation resistance is also significantly improved.

In addition, as in the third embodiment, in the case where vertically continuous band-shaped hydrophobic portions A and hydrophilic portions B are alternately formed on the same surface, the hydrophobic portion A is more hydrophilic than the hydrophilic portion A even within the same surface. Water droplets are attracted to genital area B, further improving drainage.

Furthermore, if a part of the fin 1 is cut and raised to form a slit 3 as shown in FIG. 6, water droplets may be attracted from the hydrophobic part A to the hydrophilic part B on the back surface of the fin through the slit 3. Such a structure is limited to one in which the hydrophobic part A and the hydrophilic part B are formed on both surfaces of the fin 1, respectively, as in the first and third embodiments.

Next, the effects of the heat exchanger of the present invention will be listed below.

That is, according to the present invention, (1) In the opposing surfaces of the adjacent fins 1, 1, the hydrophobic portion A is formed on one surface and the hydrophilic portion B is formed on the other surface, either entirely or partially. So,
The increase in ventilation resistance during frosting is suppressed, and the number of defrosting operations can be reduced, and an increase in fan power and a decrease in heating capacity during frosting can be suppressed as much as possible.

(2) During defrosting, droplets of water ω in the hydrophobic part A are attracted to the opposing hydrophilic part B, preventing water droplets from straddling the fins, improving drainage, and defrosting. As a result of the shortened time and improved recovery rate of draft resistance, there are practical effects such as improved energy efficiency and reduced discomfort due to cold drafts.

[Brief explanation of the drawing]

Figure 1 shows the state of frosting and frosting on the fins with hydrophilic surface treatment (indicated by the symbol X) and the state of frosting and frosting on the fins with the hydrophobic surface treatment (indicated by the symbol Y). ) is plotted with time t on the horizontal axis and ventilation resistance △Pa on the vertical axis.
4 to 4 are cross-sectional plan views and fifth embodiments of heat exchangers according to the first to third embodiments of the present invention, respectively.
Figures A to D are schematic diagrams for explaining the state of water droplets during defrosting of the heat exchanger according to each of the above embodiments, and Figure 6 is a modification of the fins of the heat exchanger according to the first and third embodiments. FIG. 1... Fin, 2... Heat exchanger tube, A... Hydrophobic part, B... Hydrophilic part.

Claims (1)

[Scope of utility model registration request] A heat exchanger that exchanges heat with air, in which a large number of fins 1, 1... are fitted into heat transfer tubes 2, 2..., and one side is attached to the opposing surfaces of adjacent fins 1, 1. A heat exchanger characterized in that a hydrophobic part A is formed on one surface and a hydrophilic part B is formed entirely or partially on the other surface.