JP2003236639A - Method for manufacturing boiling heat transfer pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a boiling heat transfer pipe for stably and accurately manufacturing the boiling heat transfer pipe having high heat transfer capacity with the small number of tools even in the case that a cooling medium which is less dense is used. <P>SOLUTION: A fin 2 is helically formed by bringing a disk 11 into rotative contact with the outer surface of a copper pipe stock 15. Next, the top part of the fin 2 is pressed in the diameter direction of the pipe by bringing rolling rolls 12, 13 into rotative contact with the top part of the fin 2. In this way, the point part of the fin 2 is deformed into flat and wide. At this time, flattening is performed so that the value of the ratio (he/hs) of the height he of the fin after flattening to the height hs of the fine before flattening is 0.47 to 0.67. Next, the top of the fin 2 is pressed in intermittent positions with a gear disk 14. In this way, the upper part of the fin 2 is parted and trapezoidal recessed parts 5 are formed intermittently along the direction where the fin 2 is extended. A part between the recessed parts 5 is made into a projecting part 4. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is incorporated in a liquid-filled evaporator such as a vapor compression refrigerator such as a turbo refrigerator and a screw refrigerator, and is immersed in a liquid refrigerant such as CFC or liquid nitrogen. The present invention relates to a method for manufacturing a boiling heat transfer tube used for heating and boiling this liquid refrigerant, and more particularly to a method for manufacturing a boiling heat transfer tube with improved heat transfer performance when a low density refrigerant is used.

[0002]

2. Description of the Related Art Conventionally, boiling type heat transfer tubes having several kinds of heat transfer surface shapes have been proposed as the above boiling type heat transfer tubes. For example, in Japanese Patent Publication No. 53-25379 and Japanese Patent Publication No. 4-78917, a heat exchange wall (heat transfer wall).
Discloses a technique in which a hollow portion is formed on the surface and a hole portion that communicates the hollow portion with the outside is provided. This causes the liquid refrigerant to boil in the cavity and generate bubbles,
It is described that when the generated bubbles are released to the outside through the holes, the bubbles can be continuously grown in the cavity and the heat transfer property is improved.

Further, in Japanese Patent Publication No. 64-2878, after forming a spiral fin on the outer surface of the pipe, the tip of the fin is compressed and deformed to provide a cavity extending along the pipe circumferential direction and the pipe axial direction. There is disclosed a heat transfer tube provided with a gap portion having a width of 0.13 mm or less, which communicates between the hollow portion and the outside. Since the cavity is formed along the tube circumferential direction and the tube axis direction in this heat transfer tube, it is possible to improve the heat transfer performance without making the space between the cavities excessively small. Is described as easy.

Further, in Japanese Patent Laid-Open No. 236097/1992, a cavity is provided on the outer surface of the heat transfer tube, and the shape of the cavity is devised to suppress the movement of the coolant in the cavity to locally cool the coolant. There is disclosed a technique for facilitating various heating and promoting boiling of the refrigerant.

Further, in JP-A-7-151485, a hollow portion extending in the pipe circumferential direction or a direction inclined in the pipe circumferential direction is provided on the surface of the pipe, and a groove portion intersecting the hollow portion is provided. A heat transfer tube is disclosed in which a hole portion that communicates the hollow portion and the outside is provided, and the area of the hole portion is 2 to 40% of the surface area when the tube is regarded as a smooth tube. This heat transfer tube promotes heating of the liquid refrigerant and bubbles, and promotes convection of the liquid refrigerant and disturbance of the liquid refrigerant and bubbles at the time of bubble generation, so that heat transfer performance can be improved.

However, in these heat transfer tubes, when a refrigerant having a relatively high density such as trichlorofluoromethane, chlorodifluoromethane and 1,1-dichloro-2,2,2-trifluoroethane is used, the heat transfer tube Although the thermal performance is improved, for a refrigerant having a low density such as 1,1,1,2-tetrafluoroethane, the opening (gap) for communicating the cavity with the outside is small, and the liquid in the cavity is small. There is a problem in that the inside of the cavity is dried due to the resistance when the refrigerant flows in, and the heat transfer performance deteriorates.

In order to avoid this problem, there is also a method of dealing with the problem by increasing the amount of the liquid refrigerant to be filled in the evaporator, but the cost of the refrigerant is increased and the volume of the heat exchanger must be increased. Therefore, there is a problem that the cost and volume of the heat exchanger increase.

Therefore, the present inventors have developed a boiling type heat transfer tube capable of improving the heat transfer performance even when using a refrigerant having a low density, and disclosed it in Japanese Patent Laid-Open No. 11-316096. In this boiling type heat transfer tube, fins extending in a direction inclined in the tube circumferential direction or the tube axis direction are provided on the outer surface of the heat transfer tube body at a predetermined pitch with respect to the tube axis direction, and the fins are arranged along the longitudinal direction of the fin. Thus, the recesses and the protrusions are provided by pressing in the pipe diameter direction at intermittent positions.
In this boiling type heat transfer tube, the liquid refrigerant boils in the cavity formed between the fins to generate bubbles, and the bubbles are discharged from the cavity through the protrusions in the upper part of the cavity, The liquid refrigerant flows into the hollow portion through the space between the recesses in the upper part of the portion, whereby boiling of the liquid refrigerant is promoted and heat transfer performance is improved.

[0009]

However, the above-mentioned conventional technique has the following problems.
That is, the boiling type heat transfer tube described in Japanese Patent Application Laid-Open No. 11-316096 has a problem that it is difficult to manufacture by the conventionally known method. In the conventionally known method, for example, as described in JP-A-4-236097, a fin-forming disk is pressed against the outer surface of the tube and rotated, whereby the fin is formed on the outer surface of the tube. To form a notch in the fin by rotating the gear disk by pressing the gear disk to the fin, and then performing a several-step pressing process on the fin to form a cavity formed between the fins adjacent to each other. There is a method of forming a narrowed portion, that is, a narrow opening between the hollow portion and the outside in the upper part of the portion, and also forming the hollow portion in the tube axis direction.

However, in this method, since the press working is performed after the notch is formed at the tip of the fin by the gear disk, a load is applied to the convex portion of the fin during the press working. Alternatively, the fins are likely to fall down in the longitudinal direction, the shapes of the narrowed portion and the hollow portion formed are changed, or the hollow portion is crushed, so that the heat transfer performance of the tube is easily deteriorated. Further, in such a method, the number of tools to be used increases, and the tool adjustment time increases. As a result, there is a problem that the manufacturing cost of the heat transfer tube increases. Even in the boiling heat transfer tube described in Japanese Patent Laid-Open No. 11-316096, if at least a part of the cavity is crushed during manufacturing, the above-mentioned density is high when a low density refrigerant is used. Although the heat transfer performance is improved as compared with the conventional heat transfer tube suitable for the refrigerant, the heat transfer performance is lower than that in the case where the cavity is not crushed at all.

On the other hand, there is known a method of forming ribs on the inner surface of a boiling type heat transfer tube by using the rolling device disclosed in Japanese Patent Publication No. 52-11670. By forming the ribs on the inner surface of the boiling heat transfer tube, the liquid flowing inside the tube can be agitated and the heat transfer performance of the boiling heat transfer tube can be improved. However, the rolling device disclosed in Japanese Patent Publication No. 52-11670 cannot form ribs having a sufficient height on the inner surface of the pipe.

The present invention has been made in view of the above problems, and it is possible to stably and accurately manufacture a boiling heat transfer tube having a high heat transfer performance with a small number of tools even when a refrigerant having a low density is used. An object of the present invention is to provide a method for manufacturing a boiling heat transfer tube capable of achieving the above.

[0013]

A method for manufacturing a boiling heat transfer tube according to the present invention comprises a fin having a predetermined pitch, the top of which is narrower than the bottom and extends in the tube circumferential direction or in a direction inclined to the outer surface of the tube. A step of forming, and a step of rolling one or a plurality of rolls to the top of the fin, and flattening the top of the fin by simultaneously pressing three or more fins in the pipe diameter direction by each roll. Pressing the fins in the pipe diametrical direction at intermittent positions along the longitudinal direction of the fins to intermittently form recesses in the upper portions of the fins.

In the present invention, the fin whose top is narrower than the bottom is pressed in the pipe diameter direction to flatten the top,
Since the fins are pressed in the pipe diametrical direction along the lengthwise direction at intermittent positions to form recesses in the upper part of the fins intermittently, the protrusions of the fins are pressed and seated as in the conventional case. It is possible to prevent the narrowed portion and the hollow portion from being deformed due to the bending so that their shapes are not uniform. Therefore, the boiling type heat transfer tube can be stably and accurately manufactured. Further, since no special tool is required to prevent the fins from collapsing, the boiling heat transfer tube can be manufactured with a small number of tools. In addition, by intermittently forming the concave portions on the upper portions of the fins, the portions where the concave portions are not formed on the upper portions of the fins are relatively convex portions, and the concave portions and the convex portions are alternately formed on the upper portions of the fins. Obtainable.

Further, one or a plurality of rolls are brought into rolling contact with the tops of the fins along the longitudinal direction of the fins, and each roll simultaneously presses three or more fins so that the rolls add to the fins. The pressing force is dispersed, and the fluctuation of the pressing force can be suppressed. As a result, it is possible to prevent the fins from buckling when the pressing force changes in the increasing direction. The rolling contact of the roll with the top of the fin means that the roll rotates while contacting the top of the fin, and the roll does not slip on the top of the fin.

Further, in the step of pressing the fins in the pipe diameter direction to flatten the tops of the fins, one or a plurality of roll sets in which two or more kinds of rolls having different outer diameters are coaxially arranged are provided. Using a set to press the fins with a roll having a smaller outer diameter to flatten the tops of the fins, and then pressing the fins with a roll having a larger outer diameter to further flatten the tops of the fins. Therefore, it is preferable to flatten the fins stepwise. As a result, the pressing force for flattening the fins is dispersed, and buckling of the fins can be prevented more reliably.

Furthermore, in the step of pressing the fins in the pipe diameter direction to flatten the tops of the fins, the height of the fins before flattening is hs, and the height of the fins after flattening is he. In this case, the value of the ratio (he / hs) is preferably 0.47 to 0.67. This more reliably prevents buckling of the fins, and reduces the distance between the tips of the fins adjacent to each other, that is, the width of the opening of the cavity formed between the fins adjacent to each other. In addition to the prevention, it is possible to promote the boiling of the liquid refrigerant by ensuring the height difference between the concave portion and the portion other than the concave portion in the upper part of the fin.

Furthermore, in the step of intermittently forming recesses in the upper portion of the fins by pressing the fins in the pipe diametrical direction at intermittent positions along the longitudinal direction, a tool having a trapezoidal cutting edge is used. It is preferable to press the fins. As a result, the shape of the concave portions formed on the upper portions of the fins and the convex portions that appear between the concave portions can be trapezoidal. As a result, air bubbles are more likely to escape between the upper side (the shorter side of the tip) of the convex part in the opening of the cavity, and the lower side of the concave part (the shorter side of the root near the cavity) in the opening of the cavity. Since the liquid refrigerant easily flows in, the efficiency of bubble separation from the cavity and the inflow of the liquid refrigerant is improved, and boiling of the liquid refrigerant can be promoted.

Furthermore, in the step of flattening the top of the fin, a groove is formed on the outer surface of the fin, and the inner surface of the tube is pressed in the tube diametrical direction by a grooved mandrel inserted inside the tube. It is preferable to form ribs on the inner surface of the tube. As a result, the roll presses the outer surface of the pipe in the pipe diametrical direction, and the grooved mandrel presses the inner surface of the pipe in the pipe diametrical direction. Ribs with a high height can be formed on the inner surface. Thereby, the liquid flowing inside the tube can be sufficiently stirred, and the heat transfer performance of the boiling heat transfer tube can be improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for manufacturing a boiling type heat transfer tube according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 1 is a perspective view showing a boiling heat transfer tube manufactured by a method for manufacturing a boiling heat transfer tube according to an embodiment of the present invention, and FIG. 2 is a sectional view including a tube axis of the boiling heat transfer tube shown in FIG. 3 is a cross-sectional view taken along the line AA shown in FIG.

First, the structure of the boiling type heat transfer tube manufactured by the method of this embodiment will be described. As shown in FIGS. 1 to 3, in the boiling heat transfer tube of the present embodiment, a tube body 1 made of, for example, copper or a copper alloy is provided, and the outer surface of the tube body 1 is inclined in the tube axis direction. Spiral fins 2 extending along are provided at a predetermined pitch in the tube axis direction. The fin 2 is provided with, for example, three rows. Fin 2
The recesses 5 are intermittently formed in the upper part of the fins, and the spaces between the recesses 5 in the upper part of the fin 2 are the convex parts 4. As a result, the convex portions 4 and the concave portions 5 alternately appear on the upper portion of the fin 2. The shape of the convex portion 4 and the concave portion 5 when viewed from the direction orthogonal to the direction in which the fin 2 extends is a trapezoid, and the convex portion 4 has an upper side shorter than the lower side and a concave portion 5 a lower side shorter than the upper side.

A cavity 3 extending in the same direction as the fin 2 is provided between the fins 2 adjacent to each other, and an opening 6 for communicating the cavity 3 with the outside is provided in an upper portion of the cavity 3. Has been. That is, the openings 6 are located between the tips of the fins 2 adjacent to each other. In the opening 6, the recesses 5 of the fins 2 adjacent to each other project so as to approach each other. However, these recesses 5 are not in contact with each other. Further, in the opening 6, the convex portions 4 of the fins 2 adjacent to each other are inclined so as to be away from each other. That is, the openings 6 between the protrusions 4 widen in the tube axial direction toward the tube outer peripheral direction. Hereinafter, the area between the protrusions 4 in the opening 6 will be referred to as an opening 6a, and the area between the recesses 5 will be referred to as an opening 6b.

As shown in FIG. 2, the width of the opening 6a in the tube axis direction is W. The width W is, for example, 0.13 <W ≦
It is 0.4 mm. Further, the pitch of the fins 2 in the tube axis direction, that is, the pitch of the hollow portions 3 is P ₂ . The pitch P ₂ is, for example, 0.50 ≦ P ₂ ≦ 0.90 mm.

As shown in FIG. 3, the pitch of the convex portions 4 in the pipe circumferential direction, that is, the pitch of the concave portions 5 is P ₁ . The pitch P ₁ is, for example, 0.28 ≦ P ₁ ≦ 0.55 mm.
Further, the angle formed by the sidewalls of the adjacent convex portions 4 in the pipe circumferential direction is θ. θ is, for example, 55 ° or less.

On the other hand, as shown in FIG. 2, the inner surface of the tube body 1
There is a rib 7 extending spirally in the direction inclined to the pipe axis direction.
Has been formed. Lead of this rib 7 in the tube axis direction
The angle is α, and the pitch of the ribs 7 in the pipe axis direction is P_ThreeWhen
Then, the height of the rib 7 is set to h. In this embodiment,
The angle α is, for example, 41 ≦ α ≦ 50 °, and the pitch P is _Three
Is, for example, 2.6 ≦ P_Three≦ 6.5 mm, height h is an example
For example, 0.22 ≦ h ≦ 0.45 mm.

The reasons for limiting the numerical values in the boiling type heat transfer tube of this embodiment will be described below.

The width W of the opening 6a in the tube axis direction is W: 0.
If the width W is greater than 13 mm and 0.4 mm or less and the width W is 0.13 mm or less, bubbles in the hollow portion 3 are less likely to be discharged to the outside, the inside of the hollow portion 3 is dried, and the heat transfer performance of the heat transfer tube is deteriorated. On the other hand, when the width W is larger than 0.4 mm, the bubbles in the cavity 3 are likely to be excessively discharged, and the liquid refrigerant is likely to be excessively flown into the cavity 3, so that the heat transfer performance is deteriorated. Therefore, the width W of the opening 6a in the tube axis direction is larger than 0.13 mm and 0.4 m.
It is preferably m or less.

Pitch P ₂ of the cavities 3 in the tube axis direction:
If the pitch P ₂ of 0.50 to 0.90 mm is smaller than 0.50 mm, the cavity 3 becomes small, and it becomes difficult for the liquid refrigerant to flow into the cavity 3, and the heat transfer performance of the heat transfer tube deteriorates. On the other hand, the pitch P ₂ is 0.90 m
When it is larger than m, the number of cavities per unit length of the heat transfer tube decreases, and the heat transfer performance deteriorates. Therefore, the pitch P ₂ of the hollow portions 3 in the tube axis direction is preferably 0.50 to 0.90 mm.

Pitch P ₁ of the recesses 5 in the pipe circumferential direction:
When the pitch P _{1 of} 0.28 to 0.55 mm is smaller than 0.28 mm, it becomes difficult for the liquid refrigerant to flow into the cavity 3, the inside of the cavity 3 is dried, and the heat transfer performance deteriorates. On the other hand, the pitch P ₁ is 0.55
If it is larger than mm, the liquid refrigerant tends to excessively flow into the cavity, and the heat transfer performance also deteriorates. Therefore, the pitch P ₁ of the recesses 5 in the pipe circumferential direction is 0.28 to 0.55 m.
It is preferably m.

The side walls of the protrusions 4 adjacent to each other in the pipe circumferential direction are
Formed angle θ: 55 ° or less When the angle θ is larger than 55 °, the liquid refrigerant easily flows into the cavity 3 excessively, and the heat transfer performance is deteriorated. Therefore, it is preferable that the angle θ formed by the side walls of the adjacent protrusions 4 in the pipe circumferential direction is 55 ° or less.

In the boiling type heat transfer tube of this embodiment, the cavity 3 is provided between the adjacent fins 2 and the convex portions 4 and the concave portions 5 are alternately provided at the tips of the fins 2. The refrigerant is heated and boiled in the cavity 3, the generated bubbles are appropriately discharged through the openings 6a between the convex portions 4, and a necessary amount of the liquid refrigerant is discharged through the openings 6b between the concave portions 5. Flow into the cavity 3. As a result, boiling of the liquid refrigerant is promoted in the hollow portion 3, so that the heat transfer performance is high.

Further, the convex portion 4 and the concave portion 5 when viewed from the tube axis direction.
Since the trapezoidal shape is trapezoidal, air bubbles are easily discharged from the cavity 3 through the upper side (shorter side of the tip) of the convex section 4 (opening 6a), and the lower side of the concave section 5 (root near the cavity) Since the liquid refrigerant easily flows into the cavity 3 through the space (the shorter side) (the opening 6b), the efficiency of discharging the bubbles from the cavity 3 and the flow of the liquid refrigerant into the cavity 3 is high, and The boiling of the refrigerant can be promoted. Therefore, the heat transfer performance is high.

Further, in the opening 6, since the recesses 5 of the fins 2 adjacent to each other project so as to approach each other, the bubbles in the cavity 3 are disturbed when being discharged through the opening 6. , This further promotes boiling.
Further, in the openings 6, the protrusions 4 of the fins 2 adjacent to each other are inclined so as to be distant from each other, and the openings 6 between the protrusions 4 expand in the pipe axial direction toward the pipe outer peripheral direction. As a result, when the bubbles generated in the cavity 3 are discharged, the convex portions 4 promote the bubbles, and the resistance when the bubbles are discharged is reduced.

Next, a method for manufacturing the boiling type heat transfer tube according to this embodiment will be described. FIG. 4 is a cross-sectional view parallel to the tube axis showing a method for continuously performing fin forming and fin deformation processing in the method for manufacturing a boiling heat transfer tube according to this embodiment. As shown in FIG. 4, first, as a material, a copper base pipe 15 which is a smooth pipe made of, for example, copper or a copper alloy is prepared. Disc 11, rolling rolls 12 and 13, gear disc 14
Are attached to the arbor 16 in this order along the moving direction of the copper pipe 15 to be processed. Disk 1
1, the rolling rolls 12 and 13, and the gear disc 14 are rotatable together with the arbor 16. The disk 11 forms the fin 2 on the outer surface of the copper tube 15, and the rolling rolls 12 and 13 press the tip of the fin 2 to flatten the top of the fin 2, and the gear disk 14 Is a disc-shaped tool in which trapezoidal concave portions and convex portions are alternately formed on the outer peripheral surface when viewed from the axial direction of the gear disk 14, and the concave portions are intermittently formed on the tops of the flattened fins 2. To form. When the number of fins formed on the outer surface of the copper tube 15 is n, n arbores are formed on a virtual cylinder around the copper tube 15 with the tube axis of the copper tube 15 as the central axis. , Are provided at equal intervals so that their axes are parallel to the tube axis of the copper tube 15. That is, the n arbores are arranged at intervals of (360 / n) ° when viewed from the tube axis of the copper tube 15. For example, when three fins 2 are formed, three arbores are arranged at intervals of 120 ° about the tube axis of the copper tube 15 in a cross section orthogonal to the tube axis of the copper tube 15. Further, the disk 11, the rolling rolls 12 and 1
3. The gear disk 14 is in rolling contact with the copper tube 15. In addition, in order to improve productivity, a plurality of discs 11, rolling rolls 12 and 13, and gear discs 14 may be attached to each arbor 16. On the other hand, the copper tube 15
A grooved mandrel 17 is inserted into the inside of the core as a core. The outer surface of the grooved mandrel 17 has a spiral groove 18
Are formed.

In such a processing apparatus, the disk 1
1, by rotating the rolling rolls 12 and 13, and the gear disk 14, the copper tube 15 is rotated, and the copper tube 15 is rotated.
The fins 2 are formed in a spiral shape on the outer surface of the fin along the direction inclined in the pipe circumferential direction. On the other hand, by transferring the groove 18 of the grooved mandrel 17 to the inner surface of the copper tube 15, the copper tube 1
Ribs 7 extending spirally are formed on the inner surface of 5. In the present embodiment, the fin 2 has, for example, three rows. Fin 2
As shown in FIG. 4, the cross-sectional shape of is a shape in which the top is narrower than the bottom.

Next, the rolling roll 12 is applied to the tip of the fin 2.
And the rolling roll 12 presses the tip of the fin 2 in the pipe diameter direction. As described above, the rolling roll 12
A plurality of sets may be provided, for example, three rolling rolls 12
May be arranged at equal intervals viewed from the tube axis at 120 ° intervals. At this time, each rolling roll 12 simultaneously presses the three fins 2. As a result, the fin 2 is deformed, and the upper portion of the fin 2 is made flat and wide.

Next, the rolling roll 13 is brought into contact with the upper part of the fin 2, and the fin 2 is pressed in the pipe diameter direction by the rolling roll 13 so that the fin 2 is further flattened and widened. At this time, the rolling roll 13 having a diameter larger than that of the rolling roll 12 is used.
And the rolling roll 13 are arranged coaxially.

When the tip portions of the fins 2 are flattened by the rolling rolls 12 and 13, the ratio of the fin heights he after flattening to the fin heights hs before flattening (he
The value of / hs) should be 0.47 to 0.67.

Next, the tip of the fin 2 is intermittently pressed by the gear disk 14 in the pipe diameter direction. This allows
The upper portion of the fin 2 is divided, and trapezoidal recesses 5 are formed intermittently along the direction in which the fin 2 extends. Further, the position between the concave portions 5 on the upper portion of the fin 2 is a trapezoidal convex portion 4
become.

On the other hand, the disk 11, the rolling rolls 12 and 13, and the gear disk 14 press the outer surface of the copper tube 15, and at the same time, the grooved mandrel 17 presses the inner surface of the copper tube 15. As a result, the rib 7 is formed on the inner surface of the copper tube 15. At this time, since the outer surface and the inner surface of the copper base pipe 15 are pressed at the same time, the rib 7 having a sufficient height can be formed without the material forming the copper base pipe 15 escaping. The method other than the above in the method of forming the rib 7 may be the same as the method described in Japanese Patent Publication No. 52-11670. Thereby, the fins 2 having the convex portions 4 and the concave portions 5 can be formed on the outer surface of the smooth tube 15, and at the same time, the ribs 7 can be formed on the inner surface of the smooth tube 15. As a result, a boiling heat transfer tube as shown in FIG. 1 is manufactured.

The reasons for limiting the numerical values in the method for manufacturing a boiling heat transfer tube of the present invention will be described below.

Number of fins pressed simultaneously by each roll: 3
If the number of fins 2 that each roll simultaneously presses is less than three, the pressing force applied to the fins 2 by the rolling rolls 12 and 13 is not dispersed, and the fluctuation of this pressing force makes the fins 2 buckle easily. . When the fin 2 buckles, the cavity 3 is not formed in that portion, and the heat transfer performance deteriorates. On the other hand, if the number of the fins 2 is 3 or more, the pressing force applied to the fins 2 by the rolling rolls 12 and 13 is dispersed, and therefore,
The fluctuation of the pressing force is also dispersed, and the fluctuation of the pressing force applied to a specific portion of the fin 2 can be suppressed. As a result, it is possible to reliably prevent the fins 2 from buckling when the pressing force changes in the increasing direction. Therefore,
The number of fins that each roll deforms at the same time must be three or more.

Flattening for fin height hs before flattening
Rear fin height he ratio (he / hs): 0.47
If the ratio (he / hs) of 0.67 is smaller than 0.47, the tips of the fins 2 become excessively wide, and in the boiling heat transfer tube to be manufactured, the width of the openings 6a between the protrusions 4 is increased. (W) is 0.1
It is smaller than 3 mm. Further, the fin 2 is likely to buckle during the deformation process of the fin 2. On the other hand, the ratio (he
When / hs) is larger than 0.67, the recess 5 is shallowly formed in the manufactured boiling heat transfer tube, the overhang on the cavity 3 is reduced, and the boiling of the liquid refrigerant is hard to be promoted. Therefore, the ratio (he / hs) is preferably 0.47 to 0.67.

In the present embodiment, the fins 2 are formed on the tube body 1, and then the fins 2 are pressed in the diametrical direction to flatten the tops of the fins 2 and then the tops of the fins 2 are intermittently cut. By pressing and dividing the fin 2, the fin 2 is not collapsed or buckled in the manufacturing process,
The above-mentioned boiling heat transfer tube (see FIG. 1) can be manufactured accurately and stably. As a result, the shapes of the convex portion 4 and the concave portion 5 and the openings 6a and 6b are also stable, so that the bubbles generated in the cavity 3 are stably discharged from the openings 6a located between the convex portions 4, while Recess 5 in cavity 3
A required amount of liquid refrigerant stably flows in from the opening 6b located between them. In this way, it is possible to stably manufacture a boiling heat transfer tube having good heat transfer performance.

In this embodiment, in the step of pressing the fins 2 to flatten them, the outer diameters of the fins 2 are different from each other.
The type of rolling rolls 12 and 13 is used to flatten the fin 2 in stages. This makes it possible to further disperse the pressing force applied to the fins 2 and form the cavity 3 and the opening 6 more stably.

Furthermore, since the fin 2 is divided by using a tool (gear disk 14) having a trapezoidal cutting edge, the projections 4 and the recesses 5 can be trapezoidal. The effect of this is as described above.

In this embodiment, the fin 2 is
Although the example of forming by the rolling method using the disk 11 is shown, the fin forming method is not limited to the rolling method in the present invention, and other methods such as a cutting method may be used.
Further, in the present embodiment, an example in which the fin 2 is formed in three rows is shown, but the number of the fins may be other than three,
Considering mass productivity, for example, the number of articles may be four or more. Furthermore, in the present embodiment, an example in which the fin forming, the fin flattening, and the fin dividing are continuously performed is shown, but these may be performed in separate steps. Furthermore, the material is not limited to copper and copper alloys, and other materials may be used.

[0048]

EXAMPLES The effects of the method for manufacturing a boiling type heat transfer tube according to the examples of the present invention will be specifically described below in comparison with comparative examples outside the scope of the claims. First, common manufacturing conditions in each example and comparative example will be described. The material is phosphorus deoxidized copper (JIS H3300 C1220T
s), with a diameter of 19.05 mm and a wall thickness of 1.19.
A smooth tube having a size of mm was used. The discs are arranged at three positions that are equidistant from the axis of the smooth pipe and spaced 120 ° apart, and these discs are brought into rolling contact with the outer surface of the smooth pipe so that they are attached to the outer surface of the smooth pipe. Three helical fins having a pitch of 34 fins / inch in the tube axis direction were formed. The diameter of the fin forming disk used for final forming of the fin was 53.08 mm. The height of the fins was different in each example and comparative example. The individual conditions of each example and comparative example will be described below.

Example 1 A fin having a height of 1.0 mm was formed by the above-described fin forming method. Next, the fin was deformed (flattened). The transformation process was one stage. A flat roll disk for pressing and deforming the tip of the fin is equidistant from the tube axis and
Three places were arranged at 0 ° intervals. The flat roll disc for pressing and deforming the fin tip portion had a diameter of 51.68 mm and a disc width of 2.5 mm. By rolling this flat roll disk to the tip of the fin on the outer surface of the tube, the tip of the fin was deformed to be flat and wide. The three fins were simultaneously pressed and deformed by the flat roll disk.

Next, three gear discs having trapezoidal blade edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after flattening is 0.70
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. In addition, there was no crush in the concave portion. That is, the side of the recess is curved, and the width of the bottom of the recess does not become wider than the width of the opening of the recess in the direction in which the fin extends, and the recess is formed in a trapezoidal shape.

Example 2 A fin having a height of 1.0 mm was formed by the fin forming method described above. Next, the fin was deformed. The transformation process has two stages. First, the first-stage fin was deformed. A flat roll disc for pressing and deforming the tip of the fin,
They were arranged at three locations equidistant from the tube axis and at 120 ° intervals. The flat roll disc for pressing and deforming the tip of the fin had a diameter of 51.38 mm and a disc width of 2.5 mm. By rolling this flat roll disk to the tip of the fin on the outer surface of the tube, the tip of the fin was deformed to be flat and wide. The three fins were simultaneously pressed and deformed by the flat roll disk.

Next, the second-stage fin was deformed. The flat roll disks for pressing and deforming the fin tips were arranged at three positions equidistant from the tube axis and at 120 ° intervals. The flat roll disk for pressing and deforming the tip of the fin has a diameter of 5
The one having a disk width of 1.68 mm and a disk width of 2.5 mm was used. The flat roll disk was brought into rolling contact with the tip of the fin on the outer surface of the tube to further flatten the fin. In addition, the flat roll disk flattened by simultaneously pressing the three fins.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after flattening is 0.55
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. The recess was not crushed and was formed in a trapezoidal shape.

Example 3 A fin having a height of 1.0 mm was formed by the fin forming method described above. Next, the fin was deformed (flattened). The transformation process was one stage. A flat roll disk for pressing and deforming the tip of the fin is equidistant from the tube axis and
Three places were arranged at 0 ° intervals. The flat roll disc for pressing and deforming the fin tip portion had a diameter of 51.68 mm and a disc width of 2.5 mm. By rolling this flat roll disk to the tip of the fin on the outer surface of the tube, the tip of the fin was deformed to be flat and wide. The three fins were simultaneously pressed and deformed by the flat roll disk. In addition, a grooved mandrel was inserted inside the tube to form ribs on the inner surface of the tube.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after flattening is 0.70
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. The recess was not crushed and was formed in a trapezoidal shape. Further, a rib was formed on the inner surface of the tube, and the height of this rib was 0.35 mm.

Comparative Example 1 A fin having a height of 1.0 mm was formed by the above-described fin forming method. Next, the fin was deformed. The transformation process was one stage. The flat roll disks for pressing and deforming the fin tips were arranged at three positions equidistant from the tube axis and at 120 ° intervals. The flat roll disc for pressing and deforming the fin tip portion had a diameter of 51.68 mm and a disc width of 1.5 mm. By rolling this flat roll disk to the tip of the fin on the outer surface of the tube, the fin was deformed so that the tip of the fin was flat and wide. Two flat fins were simultaneously pressed and deformed by the flat roll disk.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after flattening is 0.55
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. However, part of the fin buckled and the cavity was blocked.

Comparative Example 2 A fin having a height of 1.2 mm was formed by the above-mentioned fin forming method. Next, the fin was deformed. The transformation process has two stages. First, the first-stage fin was deformed. A flat roll disc for pressing and deforming the tip of the fin,
They were arranged at three locations equidistant from the tube axis and at 120 ° intervals. The flat roll disc for pressing and deforming the tip of the fin had a diameter of 51.38 mm and a disc width of 1.5 mm. The flat roll disk was rolled on the tip of the fin on the outer surface of the tube to deform the fin so that the top was flat. Two flat fins were simultaneously pressed and deformed by the flat roll disk.

Next, the second-stage fin was deformed. The flat roll disks for pressing and deforming the fin tips were arranged at three positions equidistant from the tube axis and at 120 ° intervals. The flat roll disk for pressing and deforming the tip of the fin has a diameter of 5
The one having a disk width of 1.68 mm and a disk width of 2.5 mm was used. The flat roll disk was brought into rolling contact with the tip of the fin on the outer surface of the tube to deform the fin. In addition, the flat roll disk flattened by simultaneously pressing the three fins.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the tube axis direction is 34
Fins / inch, fin height after flattening is 0.55
mm, the pitch of the recesses in the extending direction of the fin is 0.
A boiling heat transfer surface of 4 mm could be formed on the outer surface. In addition,
The recess had no crushing and was formed in a trapezoidal shape. However, the width of the opening was 0.12 mm, part of the fin buckled, and the cavity was closed.

Comparative Example 3 A fin having a height of 0.8 mm was formed by the fin forming method described above. Next, the fin was deformed. The transformation process has two stages. First, the first-stage fin was deformed. A flat roll disc for pressing and deforming the tip of the fin,
They were arranged at three locations equidistant from the tube axis and at 120 ° intervals. The flat roll disc for pressing and deforming the tip of the fin had a diameter of 51.38 mm and a disc width of 1.5 mm. The flat roll disk was brought into rolling contact with the tip of the fin on the outer surface of the tube to deform the fin. It should be noted that the flat roll disc 2
The fins of the strip were pressed simultaneously and deformed.

Next, the second-stage fin was deformed. The flat roll disks for pressing and deforming the fin tips were arranged at three positions equidistant from the tube axis and at 120 ° intervals. The flat roll disk for pressing and deforming the tip of the fin has a diameter of 5
The one having a disk width of 1.68 mm and a disk width of 2.5 mm was used. The flat roll disk was brought into rolling contact with the tip of the fin on the outer surface of the tube to deform the fin. The three fins were simultaneously pressed and deformed by the flat roll disk.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after deformation is 0.55m
m, the width of the opening was 0.3 mm, and the pitch of the recesses in the extending direction of the fin was 0.4 mm. The recess was not crushed and was formed in a trapezoidal shape. However, the depth of the recess was shallow, no protrusion in the tube axis direction was observed, and some of the fins buckled to close the cavity.

Comparative Example 4 A fin having a height of 1.0 mm was formed by the fin forming method described above. Next, the fin was deformed. The transformation process has two stages. First, the first-stage fin was deformed. A flat roll disc for pressing and deforming the tip of the fin,
They were arranged at three locations equidistant from the tube axis and at 120 ° intervals. The flat roll disc for pressing and deforming the tip of the fin had a diameter of 51.38 mm and a disc width of 1.5 mm. By rolling this flat roll disk to the tip of the fin on the outer surface of the tube, the fin was deformed so that the top of the fin was flattened. Two flat fins were simultaneously pressed and deformed by the flat roll disk.

Next, the second-stage fin was deformed. The flat roll disks for pressing and deforming the fin tips were arranged at three positions equidistant from the tube axis and at 120 ° intervals. The flat roll disk for pressing and deforming the tip of the fin has a diameter of 5
The one having a disk width of 1.68 mm and a disk width of 2.5 mm was used. The flat roll disk was brought into rolling contact with the tip of the fin on the outer surface of the tube to deform the fin. The three fins were simultaneously pressed and deformed by the flat roll disk.

Next, three gear disks having triangular cutting edges were arranged at equal distances and 120 ° intervals as viewed from the tube axis of the tube. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the tube axis direction is 34
Fins / inch, fin height after flattening is 0.55
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. However, the recess was not crushed but was formed in a triangular shape. In addition, no protrusion was observed in the axial direction of the pipe, and some of the fins buckled to close the cavity.

Comparative Example 5 A fin having a height of 1.0 mm was formed by the fin forming method described above. Next, the fin was deformed (flattened). The transformation process was one stage. A flat roll disk for pressing and deforming the tip of the fin is equidistant from the tube axis and
Three places were arranged at 0 ° intervals. The flat roll disc for pressing and deforming the fin tip portion had a diameter of 51.68 mm and a disc width of 1.5 mm. The flat roll disk was rolled into contact with the tips of the fins on the outer surface of the tube, thereby deforming the tips of the fins to be flat and wide. Two flat fins were simultaneously pressed and deformed by the flat roll disk. In addition, a grooved mandrel was inserted inside the tube to form ribs on the inner surface of the tube.

Next, three gear discs having trapezoidal cutting edges were arranged at equal distances from the pipe axis of the pipe at 120 ° intervals. The gear disc used had a diameter of 51.98 mm and a disc width of 0.75 mm. By rolling this gear disk onto the tops of the fins on the outer surface of the tube, the fins were pressed in intermittent positions, breaking the tops of the fins. At this time, the fins were divided by the respective gear disks.

As a result, the pitch in the pipe axis direction is 34.
Fins / inch, fin height after flattening is 0.55
mm, the width of the opening was 0.3 mm, and the pitch of the recesses in the fin extending direction was 0.4 mm. However, part of the fin buckled and the cavity was blocked. Further, although a rib was formed on the inner surface of the tube, the height of this rib remained at 0.27 mm.

Next, the heat transfer performance of the boiling type heat transfer tubes manufactured in the above Examples 1 to 3 and Comparative Examples 1 to 5 was evaluated. Table 1 shows the heat transfer performance test conditions.

[0078]

[Table 1]

Next, a heat transfer performance test apparatus will be described. FIG. 5 is a schematic diagram showing the configuration of a test apparatus used for evaluation of heat transfer performance. Incidentally, this test device is disclosed in
It is the same as the one used in 316096. The test apparatus is composed of a condenser 20 and an evaporator 30. The condenser 20 is formed by arranging a plurality of heat transfer tubes 21 in a vertical direction with the tube axis direction thereof being horizontal. The heat transfer tubes 21 conduct cooling water inside, and each of the heat transfer tubes 21 is provided with a cooling water inlet 22 at one end and a cooling water outlet 23 at the other end. An inlet 24 for the refrigerant vapor supplied around the heat transfer tube 21 is provided above the heat transfer tube 21, and an outlet 25 for discharging the condensed refrigerant (liquid refrigerant) is provided below the heat transfer tube 21. Has been.

In the evaporator 30, a housing (not shown)
A refrigerant 36 is filled therein, and a test pipe 31 to be tested is immersed in the refrigerant 36 with its pipe axis direction horizontal, and a cold water inlet 34 is provided at one end of the test pipe 31.
A cold water outlet 35 is provided at the other end. Further, an inlet 32 for the liquid refrigerant is provided below the evaporator 30, and an outlet 33 for the evaporated vapor refrigerant is provided above the evaporator 30. The inlet 32 of the evaporator 30 is the outlet 25 of the condenser 20.
The outlet 33 of the evaporator 30 is connected to the condenser 20.
Is connected to the inlet 24 of the.

In this test apparatus, the cooling water is supplied from the inlet 22 to the inside of each heat transfer tube 21, and the cooling water is discharged from the outlet 23. In addition, the inlet 24 above each heat transfer tube 21
From, the refrigerant vapor is supplied to the periphery of the heat transfer tube 21. As a result, the refrigerant vapor gives heat to the cooling water passing through the heat transfer tube 21 via the heat transfer tube 21, and the cooled and condensed liquid refrigerant is discharged from the outlet 25 and supplied to the evaporator 30 via the inlet 32. To be done. The liquid refrigerant 36 supplied to the evaporator 30 is
It is filled around the test tube 31. On the other hand, cold water is supplied into the test tube 31. As a result, the refrigerant 36 becomes the test tube 3
The vaporized refrigerant vapor is heated by cold water via 1 and evaporated, and the vaporized refrigerant vapor is discharged from the upper outlet 33 of the evaporator 30 and supplied to the refrigerant vapor inlet 24 of the condenser 20. On the other hand, the cold water supplied from the inlet 34 into the test tube 31 is cooled by the refrigerant 36 through the test tube 31 and discharged from the outlet 35.

As described above, the above-mentioned test device is a device in which the shell-and-tube type condenser 20 and the evaporator 30 are connected by a pipe, and the refrigerant vapor generated in the evaporator 30 is the upper part of the evaporator 30. Enter the condenser 20 through the pipe of
By passing cooling water through the heat transfer tube 21 in the condenser 20, the refrigerant vapor is condensed on the surface of the heat transfer tube 21, and the condensed refrigerant passes through the pipe below the condenser 20 to the evaporator 30. It has a return structure.

Next, the test method of the heat transfer performance will be described. A constant flow rate of cold water was caused to flow through the test tube 31 installed in the evaporator 30 within the range shown in Table 1, and the cold water inlet temperature was adjusted to a constant condition (22 ° C.). On the other hand, the evaporation pressure is shown in Table 1.
The flow rate of the cooling water flowing through the heat transfer tube in the condenser was adjusted so that the conditions shown in (4) were satisfied. Cold water flow rate, cold water inlet / outlet temperature,
After the evaporating pressure of the refrigerant became stable under a predetermined condition, the overall heat transfer coefficient was measured.

FIG. 6 is a graph showing the evaluation results of the overall heat transfer coefficient with respect to the water flow velocity in the tube, with the horizontal axis representing the water flow velocity in the test tube 31 and the vertical axis representing the overall heat transfer coefficient of the sample tube 31. is there. As shown in FIG. 6, Examples 1 to 3 had significantly higher heat transfer performance than Comparative Examples 1 to 5. In particular, in Example 3, the ribs were formed on the inner surface of the tube, so the heat transfer performance was better than in Examples 1 and 2.

[0085]

As described in detail above, according to the present invention, even when a refrigerant having a low density is used, boiling heat transfer is promoted and a boiling heat transfer tube having excellent heat transfer performance can be easily manufactured with a small number of tools. It can be stably manufactured. Therefore,
It is possible to improve the performance of the heat exchanger, reduce the size and weight of the heat exchanger, reduce the amount of members used and the amount of refrigerant charged, and further improve the efficiency of the refrigerator.

[Brief description of drawings]

FIG. 1 is a perspective view showing a boiling heat transfer tube manufactured by a method for manufacturing a boiling heat transfer tube according to an embodiment of the present invention.

FIG. 2 is a sectional view including a tube axis of the boiling heat transfer tube shown in FIG.

3 is a cross-sectional view taken along the line AA shown in FIG.

FIG. 4 is a tube axis parallel sectional view showing a method of continuously performing fin forming and fin deformation processing in the method for manufacturing a boiling heat transfer tube according to the present embodiment.

FIG. 5 is a schematic diagram showing a configuration of a test apparatus used for evaluation of heat transfer performance.

FIG. 6 is a graph showing the evaluation results of the overall heat transfer coefficient with respect to the in-tube water flow rate, with the horizontal axis representing the water flow velocity in the test tube and the vertical axis representing the overall heat transfer coefficient of the test tube.

[Explanation of symbols]

1: Tube body 2: Fin 3: Cavity 4: Convex part 5: Recessed part 6: Opening part 7: Rib 11; Discs 12, 13; Rolls 14; Gear disc 15; Copper tube 16; Arbor 17; Groove Mandrel 18; Groove 20: Condenser 21; Heat transfer pipe 22; Cooling water inlet 23; Cooling water outlet 24; Refrigerant vapor inlet 25; Liquid refrigerant outlet 30: Evaporator 31; Test tube 32; Liquid refrigerant inlet 33; Steam refrigerant outlet 34; Cold water inlet 35; Cold water outlet 36; Refrigerant h; Height P _{1 of} rib 7; Pitch P ₂ of the convex portion 4 in the pipe circumferential direction; Pitch W of the fin 2 in the pipe axial direction The width θ of the opening 6a in the tube axis direction; the angle α formed by the sidewalls of the adjacent protrusions 4 in the tube circumferential direction; the lead angle of the rib 7 with respect to the tube axis direction.

Claims (7)

[Claims] 1. A step of forming fins at a predetermined pitch on the outer surface of the tube extending in the tube circumferential direction or in a direction inclined to the tube and having a narrower top portion than the bottom portion, and one or a plurality of rolls on the top portion of the fins. A step of rolling the fins to flatten the tops of the fins by pressing three or more fins simultaneously in the pipe diametrical direction by the rolls, and the fins in the pipe diametrical direction at intermittent positions along the longitudinal direction thereof. And a step of intermittently forming recesses in the upper portions of the fins by pressing to a boiling point of the fins. 2. One or a plurality of roll sets in which two or more types of rolls having different outer diameters are coaxially arranged in the step of pressing the fins in the pipe diameter direction to flatten the tops of the fins. Using a set to press the fins with a roll having a smaller outer diameter to flatten the tops of the fins, and then pressing the fins with a roll having a larger outer diameter to further flatten the tops of the fins. 2. The method for manufacturing a boiling heat transfer tube according to claim 1, wherein the fins are planarized in stages by 3. In the step of pressing the fins in the pipe diameter direction to flatten the tops of the fins, the height of the fins before flattening is hs, and the height of the fins after flattening is he. At this time, the value of the ratio (he / hs) is set to 0.47 to 0.67, The method for manufacturing a boiling heat transfer tube according to claim 1 or 2, wherein 4. In the step of pressing the fin in the pipe diametrical direction at intermittent positions along the longitudinal direction thereof to intermittently form a recess in the upper portion of the fin, the cutting edge is formed by a tool having a trapezoidal shape. The method for manufacturing a boiling heat transfer tube according to claim 1, wherein a fin is pressed. 5. The step of intermittently forming a recess in the upper portion of the fin by pressing the fin in the pipe diametrical direction at intermittent positions along the longitudinal direction of the fin includes forming a gear-shaped tool in the longitudinal direction of the fin. The method according to any one of claims 1 to 4, wherein the step is performed by rollingly contacting the fin along a direction.
Item 6. A method for manufacturing a boiling heat transfer tube as described in the item. 6. A disc-shaped tool is formed on the outer surface of the pipe in the step of forming fins on the outer surface of the pipe extending in the pipe circumferential direction or in a direction inclined to the pipe at a predetermined pitch, the top of which is narrower than the bottom of the fin. The fins are formed between the grooves adjacent to each other by rolling them to form grooves having a predetermined pitch on the outer surface of the pipe and extending in the pipe circumferential direction or in a direction inclined to the pipe. The method for manufacturing a boiling heat transfer tube according to any one of 1 to 5. 7. In the step of flattening the tops of the fins, a groove is formed on the outer surface of the fin and a grooved mandrel inserted inside the tube presses the inner surface of the tube in the tube diametrical direction. The method for manufacturing a boiling heat transfer tube according to any one of claims 1 to 6, wherein a rib is formed on the inner surface of the tube.