JPH11118382A - Heat transfer pipe for evaporator and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance heat transfer pipe suitable for an evaporator of an absorption refrigerator wherein dryness of fins is hardly induced and heat transfer area extension effect by fins can be demonstrated to the maximum. SOLUTION: A heat transfer pipe used in an evaporator of an absorption refrigerator is provided on an outer face of the pipe with helical-formed fins l having a height of 0.2-0.6 mm in an axial direction of the pipe at a pitch of 35-50 pieces per inch and each of the fins 1 is provided at an interval of 0.5-0.9 mm in a circumferencial direction of the pipe with pressing parts 2 having a width of 0.3 mm or less, a depth of 0.1-0.45 mm and a height of less than the height of the fin 1. By such a construction, because a large number of the fins having a short height and provided with the pressing parts are formed, a refrigerant liquid film extends thinly and uniformly on a whole outer surface of the pipe so that a superior heat transfer performance is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube used for an evaporator such as an absorption refrigerator for producing cold water and an absorption heat pump for air conditioning.

[0002]

2. Description of the Related Art An evaporator of an absorption refrigerator or an air conditioning absorption heat pump, for example, flows water into a horizontally arranged heat transfer tube, and drops or sprays refrigerant water on the outer surface of the heat transfer tube under reduced pressure. (Spray) to evaporate, and the flowing water in the heat transfer tube is cooled by the latent heat of evaporation at this time. Meanwhile, in recent years, from the viewpoint of global environmental conservation, reduction of the use of CFC refrigerant has been required, and instead of a centrifugal chiller using CFC refrigerant, an absorption chiller using a natural refrigerant such as water has attracted attention. However, particularly, the coefficient of performance of an absorption refrigerator using water as a refrigerant is only about 1.0, and the coefficient of performance of a turbo refrigerator using Freon as a refrigerant (generally 3.0).
Above). To compensate for this lack of performance, absorption chillers require larger equipment than turbo chillers. For this reason, there is a strong demand for improved performance of heat transfer tubes in absorption chillers. By the way, in various heat exchangers such as a centrifugal chiller, a heat transfer tube with a spiral fin having a larger heat transfer area by forming a spiral fin on the outer surface has been used,
Recently, this heat transfer tube with spiral fins has come to be used also in an evaporator of an absorption refrigerator.

[0003]

Conventionally, regarding the size and shape of a heat transfer tube with spiral fins, see JP-A-61-26549.
No. 9 only roughly discloses the fin height of 0.1 to 8 mm, the fin pitch of 0.5 to 8 mm, and the number of fins of 50 to 3 / inch. For this reason,
The dimensions and shape of the spiral finned tube are individually designed according to the application. In an evaporator of an absorption refrigerator, the fin height is generally as high as about 1.0 to 1.5 mm, The number of fins is designed to be as small as 15 to 30 per inch so as not to hinder the evaporation of the refrigerant. But,
In the heat transfer tube of this design, since the height of the fins is high, as shown in FIG.
21 has a problem that it is difficult to spread in the axial direction of the tube, the dry surface not wetted by the coolant water 21 increases, and the effect of the fin 1 is not sufficiently obtained, but the heat transfer performance is rather deteriorated.

In Japanese Patent Publication No. 58-13837, as shown in FIG. 7, a fin 1 of a spiral finned tube is divided into a plurality of tubes in a tube axis direction so that a refrigerant liquid film passes through a divided portion and is connected to a tube shaft. A condensing heat transfer tube that is easy to spread in a direction is disclosed.
This heat transfer tube has a structure in which the tip of the divided fin 1 is formed in an acute angle to promote the drainage of the condensed liquid film.
Therefore, a dry surface tends to occur at the tip of the fin, and sufficient heat transfer performance cannot be expected.

Japanese Patent Application Laid-Open No. 62-206356 discloses a heat transfer tube for an evaporator in which a fin 1 of a heat transfer tube with spiral fins is divided into a plurality of tubes in the tube axis direction. Since there are many notches, the effect of expanding the heat transfer area of the fin cannot be sufficiently obtained, and the heat transfer performance is still insufficient.

[0006] Japanese Patent Application Laid-Open No. 7-71889 discloses that
As shown in FIG. 8, there is disclosed a heat transfer tube for an evaporator in which a fin 1 is divided into a plurality in the tube axis direction and a groove 22 is provided along a tip of the fin 1. The fins 1 are thickened to provide grooves, so the number of fins is reduced to 19 to 26 per inch,
Therefore, the heat transfer area decreases, and sufficient heat transfer performance cannot be obtained. SUMMARY OF THE INVENTION An object of the present invention is to provide a high-performance heat transfer tube suitable for an evaporator of an absorption refrigerator in which fins are unlikely to dry and maximize the heat transfer area expansion effect of the fins, and a method for manufacturing the same.

[0007]

According to the first aspect of the present invention,
In a heat transfer tube used for an evaporator of an absorption refrigerator, fins having a height of 0.2 to 0.6 mm are spirally formed on an outer surface of the heat transfer tube, and 35 to 50 fins are formed per inch in a tube axis direction. The fin has a width of 0.3 mm or less and a depth of 0.3 mm.
A heat transfer tube for an evaporator, wherein the pressing portions having a height of 1 to 0.45 mm and less than the height of the fin are formed at intervals of 0.5 to 0.9 mm in a circumferential direction of the heat transfer tube.

The invention according to claim 2 is the heat transfer tube for an evaporator according to claim 1, wherein the height of the fin on the outer surface of the heat transfer tube is 0.2 mm or more and less than 0.5 mm.

The invention according to claim 3 is the heat transfer tube for an evaporator according to any one of claims 1 and 2, wherein a plurality of convex ridges are spirally provided on the inner surface of the heat transfer tube. .

According to a fourth aspect of the present invention, a fin is formed on the outer surface of the heat transfer tube in a spiral shape by a group of fin forming disk tools, and then a pressing portion is pressed on the fin and a gear-shaped disk tool is pressed. The method for manufacturing a heat transfer tube for an evaporator according to any one of claims 1 and 2, wherein the heat transfer tube is formed in a circumferential direction of the tube.

According to a fifth aspect of the present invention, fins are spirally formed on the outer surface of a heat transfer tube in which a plurality of convex ridges are spirally provided on the inner surface of the heat transfer tube by a group of fin forming disk tools.
4. The method according to claim 3, wherein the pressing portion is formed on the fin in a circumferential direction of the tube by pressing a gear-shaped disk tool.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A heat transfer tube according to the present invention is shown in FIGS.
As shown in (c), the height of the fins 1 is reduced to prevent a dry surface from being formed on the fins 1, and the reduced surface area of the fins 1 due to the reduced height is complemented by increasing the number of the fins 1. Further, the pressing portion 2 is formed on the fin 1 to facilitate the spreading of the refrigerant liquid film in the tube axis direction, thereby improving the heat transfer performance. Since the height of the fins 1 of this heat transfer tube is low, the heat transfer tube before drawing can be made thinner, which is advantageous in terms of cost. In the present invention, the reason for defining the fin height to be 0.2 to 0.6 mm is that if the fin height is less than 0.2 mm, the effect of expanding the heat transfer area by the fin is not sufficiently obtained,
If it exceeds 0.6 mm, it becomes difficult for the refrigerant to climb over the fins and spread in the tube axis direction, and a dry surface occurs at the fin tip,
This is because sufficient heat transfer performance cannot be obtained. In the present invention, the number of fins is 35 to 1 per inch in the tube axis direction.
The reason why the number of fins is set to 50 is that if the number of fins is less than 35, the effect of expanding the heat transfer area by the fins cannot be sufficiently obtained.

In the present invention, the width of the pressing portion is 0.3 mm
The reason specified below is to minimize the decrease in the fin surface area due to the formation of the pressing portion. The reason why the depth of the pressing portion is defined to be 0.1 to 0.45 mm is that if the depth is less than 0.1 mm, the refrigerant liquid film does not sufficiently spread in the tube axis direction, and
This is because if the diameter exceeds 2,000 mm, the surface area of the fins decreases, and a sufficient effect of expanding the heat transfer area cannot be obtained. The reason for defining the depth of the pressing part to be less than the height of the fin is that if the depth of the pressing part is greater than the fin height, the thickness of the refrigerant liquid film at the pressing part becomes too thick, and the heat transfer performance decreases. To do that. A desirable depth of the pressing portion is a depth smaller by about 0.1 to 0.3 mm than the fin height. The interval between the pressing parts in the pipe circumferential direction is 0.5
The reason for defining the thickness to be 0.9 mm is that if it is less than 0.5 mm, the surface area of the fin becomes small and the effect of expanding the heat transfer area cannot be sufficiently obtained. Is not sufficiently obtained.

In the heat transfer tube of the present invention, the excess refrigerant is separated from the heat transfer tube by the fins, and only the required refrigerant passes through the pressing portions formed on the fins to form a thin liquid film on the entire surface of the fins. Spread out. Therefore, the increase in the actual surface area of the outer surface of the tube due to the formation of the fins can effectively act as a heat transfer surface.

In the heat transfer tube according to the first aspect, as shown in FIG. 2, fins are spirally formed on the outer surface of a heat transfer tube 4 manufactured by a conventional method using a fin forming disk tool group 5. It is manufactured by pressing the gear-shaped disk tool 6 against the outer surface of the heat transfer element tube 4 on which the fin is formed to form a pressing portion on the fin. By forming the fins and the pressing portions continuously, extremely high productivity can be obtained.

In the heat transfer tube according to the second aspect, as shown in FIG. 3, a plurality of convex ridges (linear projections) 3 are spirally provided on the inner surface. In the heat transfer tube 3, turbulence is generated in the cold water in the tube by the convex ridge 3, and the heat transfer area on the inner surface is increased, so that the heat transfer rate is improved. This heat transfer tube uses a heat transfer tube in which a convex ridge is provided on the inner surface,
It can be manufactured by the same method as shown in FIG. The heat transfer pipe provided with the convex ridge on the inner surface can be easily manufactured by a normal drawing method, an electric resistance welding method, or the like.

In the present invention, the material of the heat transfer tube is preferably a phosphorous deoxidized copper tube that is frequently used for air conditioning and the like. Other materials, such as a steel pipe, can also be used according to use conditions.

[0018]

The present invention will be described below in detail with reference to examples. (Example 1) Spiral fins were formed on a phosphorous deoxidized copper raw tube having an outer diameter of 15.88 mm and a wall thickness of 0.8 mm by the method shown in FIG. A heat transfer tube with a spiral fin having a pressing portion was manufactured. The height, the number of fins, the pitch, the depth, and the width of the pressing portion were variously changed within the specified values of the present invention. Note that the heat transfer tube could be easily manufactured at a high yield.

(Comparative Example 1) A heat transfer tube with a spiral fin having a pressing portion was manufactured in the same manner as in Example 1, except that the dimensions of the heat transfer tube were outside the specified values of the present invention. (Conventional example 1) Three types of conventional heat transfer tubes disclosed in the above-mentioned patent publication were prepared.

The heat transfer coefficient outside the tube was measured for each of the obtained heat transfer tubes. The measurement of the heat transfer coefficient outside the tube was performed using the test device shown in FIG. The test conditions are shown in Table 1, and the obtained results are shown in Table 2. Table 2 also shows the dimensions of the fins and the pressing parts. The heat transfer coefficient outside the tube was expressed as a ratio when the heat transfer coefficient outside the tube of the conventional product (No. 10) was set to 100.

Hereinafter, the test apparatus will be described with reference to FIG. Inside the evaporator 7 which has been decompressed, evaporator heat transfer tubes 8 are arranged in two rows in one row and five stages. Heat transfer tubes 8 in each row
Are communicated with each other. Refrigerant water (pure water) is dropped from a coolant water drop tray 9 disposed above the heat transfer tube 8, and the water in the heat transfer tube 8 is cooled by the latent heat of evaporation of the coolant water.
On the other hand, the heat transfer tubes 12 for the absorber are arranged in one row in five rows in the absorber 11 in which the pressure is reduced. Each heat transfer tube 12 is communicated with each other. Absorbing liquid (aqueous lithium bromide solution) is sprayed on the surface of the heat transfer tube 12 from the spraying pipe 13, and the vapor generated in the evaporator 7 is absorbed by the absorbing liquid. Cooling water is allowed to flow inside the absorber heat transfer tube 12 to cool the absorbing liquid, thereby increasing the vapor absorption efficiency. The absorbing liquid diluted by absorbing the vapor is transferred from the absorbing liquid storage tank 14 to the absorbing liquid adjusting tank 15, where the concentration is adjusted, and then circulated to the spray pipe 13 by the pump 16.

[0022]

[Table 1] (Note) Only one row on the absorber side of the heat transfer tube in the evaporator in Fig. 2 is used.

[0023]

[Table 2] (Note) * Refrigerant water flow rate 1.5 liter / m · min.

As is clear from Table 2, No. 1 of the present invention example
In each of Nos. 5 to 5, the ratio of the heat transfer coefficient outside the tube was high, and the heat transfer performance was superior to the conventional product. This is because low fins are formed with a large number of pressing parts,
This is because the refrigerant liquid film spread thinly and uniformly over the entire outer surface of the tube. In particular, fins with a height of 0.45 mm or less (No.
1 to 3) showed excellent heat transfer coefficient outside the tube. In contrast, No. 6 of the comparative example had a low fin height, No. 7 had a small number of fins, No. 8 had a small pitch of the pressing portion, and No. 9 had a low fin depth. Since the depth was higher than the height, the heat transfer coefficient outside the tube decreased in all cases.

With respect to No. 2 of the present invention, No. 11 of the conventional product, and the smoothing tube, the refrigerant flow rate was 0.6 to 2.4 liter / m · m.
in. The heat transfer coefficient outside the tube when variously changed in the range of was obtained. FIG. 5 shows the results. As is clear from FIG.
No. 2 of the present invention example showed a higher heat transfer coefficient outside the pipe at all refrigerant water flow rates than No. 11 of the conventional product and the smooth pipe.

(Example 2) A heat transfer tube with a spiral fin having a pressing portion on the outer surface of a heat transfer tube having a convex ridge formed on the inner surface by a drawing method was manufactured. The shape and dimensions of the spiral fin were the same as No. 2 of Example 1. The number of the ridges in the cross section was 24, the twist angle was 40 °, and the ridge height was 0.20 mm (see FIGS. 3A and 3B). For this heat transfer tube (No. 13) and No. 2 of Example 1, the heat transfer coefficient (overall heat transfer coefficient) was determined using the apparatus of FIG. Table 3 shows the results. The heat transmission rate was represented by a ratio when the heat transmission rate of No. 2 was set to 100.

[0027]

[Table 3]

As is clear from Table 3, No. 13 having a convex ridge on the inner surface was No. 2 having no convex ridge on the inner surface.
The heat transmission rate was 25% higher than that of. No. 13 is due to the turbulence effect of cold water flowing in the pipe due to the convex ridge on the inner surface of the pipe.

In the evaporator of the absorption refrigerator, the dropping type and the spray type are mainly used for dispersing the refrigerant water. In the spray type, since the coolant water is sprayed in a shower state, the coolant water is sprayed on the entire surface of the heat transfer tube group, and a dry surface hardly occurs on the heat transfer tubes. The dripping method is a method in which the coolant water is dropped for each row of the heat transfer tube group, and the dry surface is more likely to occur than the spray method,
There is no need to apply water pressure, the structure is simple and the cost is low. Since the heat transfer tube of the present invention is one in which the refrigerant easily spreads,
A dry surface is unlikely to occur even with a dropping method. Therefore, it is more effective to adopt a low-cost dropping type.

[0030]

As described above, in the heat transfer tube of the present invention, since the low fins are formed with a large number of pressing portions, the refrigerant liquid film is thin and uniform on the entire outer surface of the tube. And excellent heat transfer performance can be obtained. In the case where the convex ridge is formed on the inner surface, the heat transfer performance is further improved due to the turbulence effect of the cold water flowing in the pipe. Further, since the height of the fins is low, the thickness of the processing tube can be reduced, which is advantageous in cost. The heat transfer tube of the present invention can be easily manufactured using a group of fin-formed disk tools and a gear-shaped disk tool, and is excellent in productivity. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are a plan view, a perspective view of a fin portion, and an enlarged perspective view of a fin portion, respectively, showing an example of a heat transfer tube of the present invention.

FIG. 2 is a process explanatory view showing an example of a method for manufacturing a heat transfer tube of the present invention.

FIGS. 3A and 3B are horizontal and vertical cross-sectional views, respectively, showing examples of a convex ridge formed on the inner surface of the heat transfer tube of the present invention.

FIG. 4 is an explanatory view of an apparatus used for measuring the heat transfer performance of the heat transfer tube of the present invention.

FIG. 5 is a diagram illustrating a comparison between an example of the present invention and a conventional product in the heat transfer coefficient outside the tube when the flow rate of the coolant water is changed.

FIG. 6 is an explanatory diagram of a situation where a dry surface occurs on a fin.

FIG. 7 is an explanatory diagram of an outer surface of a conventional heat transfer tube.

FIG. 8 is an explanatory diagram of an outer surface of a conventional heat transfer tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fin 2 Pressing part 3 Convex ridge 4 Heat transfer tube 5 Fin forming disk tool group 6 Gear disk tool 7 Evaporator 8 Heat transfer tube for evaporator 9 Refrigerant water drop tray 11 Absorber 12 Heat transfer tube for absorber 13 Scattering Pipe 14 Absorbent liquid storage tank 15 Absorbent liquid adjustment tank 16 Pump 21 Refrigerant water 22 Groove provided at fin tip

Claims (5)

[Claims] 1. A heat transfer tube used for an evaporator of an absorption refrigerator, wherein a height of the heat transfer tube is 0.2 to 0.6 on an outer surface of the heat transfer tube.
mm fins in a spiral shape, 3 inches per inch in the tube axis direction
5 to 50 sheets are formed, and the fin is provided with a pressing portion having a width of 0.3 mm or less, a depth of 0.1 to 0.45 mm, and a height less than the height of the fin. ~ 0.9
A heat transfer tube for an evaporator, which is formed at an interval of mm. 2. The height of the fin on the outer surface of the heat transfer tube is 0.2 m.
2. The structure according to claim 1, wherein the length is not less than m and less than 0.5 mm.
The heat transfer tube for an evaporator according to the above. 3. The heat transfer tube for an evaporator according to claim 1, wherein a plurality of convex ridges are spirally provided on the inner surface of the heat transfer tube. 4. A fin is formed on the outer surface of the heat transfer tube in a helical shape by a group of fin-formed disk tools, and then a pressing portion is formed on the fin in a circumferential direction of the tube by pressing a gear-shaped disk tool. The method for manufacturing a heat transfer tube for an evaporator according to claim 1, wherein the heat transfer tube is formed. 5. A fin is formed on an outer surface of a heat transfer tube in which a plurality of convex ridges are spirally provided on an inner surface of the heat transfer tube by a group of fin forming disk tools, and then a pressing portion is formed on the fin. 4. The method for manufacturing a heat transfer tube for an evaporator according to claim 3, wherein the heat transfer tube is formed by pressing a gear-shaped disk tool around the tube.