JP2001074384A - Internally grooved tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internally grooved tube in which lowering of heat transfer performance is prevented along with troubles occurring in the process following expansion of a tube by limiting inclination of fins when expanding the tube. SOLUTION: In a tube having a plurality of parallel grooves 2, in the inner surface thereof, extending spirally in a direction inclining against the axial direction of tube, fins 3 are formed between adjacent grooves on the plane orthogonal to the tube axis such that a line dividing an angle ϕ1, defined by a line connecting the center of tube O and the vertex P of the fin 3 (where the distance between the center of tube O and the fins 3, 4 is shortest) and a line connecting the center of tube O and the vertex P of an adjacent fin 4, equally into two intersects the inner surface of tube at point Q between the fins 3, 4 and the angle θ between a line L4, connecting the intersections of the land parts at the opposite ends of the fin and an imaginary circle 5 having a center at the center of tube O and a radius equal to the tube radius R1 represented by the distance between the center of tube O and the point Q, and a line L5 connecting the middle point 7 of the line L4 and the vertex P of the fin 3 is in the range of 70-90 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner grooved pipe made of, for example, copper or copper alloy, which is incorporated in a room air conditioner or the like and is suitable for a heat exchanger which is bent into a U-shape or the like. Field of the Invention The present invention relates to an inner grooved tube in which a fin is prevented from being inclined at the time.

[0002]

2. Description of the Related Art Heat exchangers are used in various fields such as room air conditioners, package air conditioners, freezer showcases, refrigerators, oil coolers and radiators.
In this heat exchanger, an internally grooved tube made of copper or copper alloy having a groove formed on the inner surface of the tube to enhance heat transfer efficiency is assembled as a heat transfer tube. That is, in the heat exchanger, a plurality of aluminum fin plates (hereinafter, referred to as fin plates) manufactured by press working are arranged in parallel at appropriate intervals and provided on each fin plate. By inserting an inner grooved tube bent into a U-shape in a hairpin shape into the hole, and then expanding the inner grooved tube, the fin plate and the inner grooved tube are brought into close contact with each other to be integrally assembled and assembled.
At this time, the inner grooved pipe is usually attached to a tip of a mandrel with a pushing and spreading tool (hereinafter, referred to as a burette) larger than the inner diameter of the inner grooved pipe, and the buret is press-fitted into the inner grooved pipe to thereby form the inner grooved pipe. The pipe is expanded to enhance the adhesion between the inner grooved pipe and the fin plate, thereby mechanically joining the inner grooved pipe and the fin plate.

[0003] As a method of manufacturing such an inner grooved pipe, first, the raw pipe is sequentially reduced in diameter by a holding die and a plurality of compaction balls, and a floating plug and a connecting shaft are connected to the floating plug in the raw pipe. And a grooved plug that is relatively rotatably connected via a pipe, and the floating plug in the pipe is engaged with a holding die outside the pipe via the pipe wall to place the grooved plug in a rolling ball arrangement position. Position. Then, when the rolling ball is planetary-rotated around the groove plug, the raw tube is pressed by the grooved plug, and the groove shape of the grooved plug is transferred to the inner surface of the raw tube. At this time, in a cross section orthogonal to the longitudinal direction of the pipe (a cross section orthogonal to the pipe axis), the fins formed between the grooves transferred to the inner surface of the pipe are inclined without the fins being directed toward the center of the pipe. In particular, in the case of an inner grooved tube with high heat transfer performance by increasing the depth of the groove to form a high fin with a high fin height,
The phenomenon of fin inclination during groove processing is apt to occur remarkably.

FIG. 7 is a schematic view showing the shape of a fin of a conventional inner grooved pipe. As shown in FIG. 7, in the inner grooved pipe 1 in which a plurality of spiral parallel grooves extending in a direction inclined in the longitudinal direction of the pipe are formed on the inner surface of the pipe, a cross section orthogonal to the pipe axis of the pipe 1 is shown in FIG. Thus, the fins 3 formed between adjacent grooves on the inner surface of the pipe 1 are inclined without going toward the pipe center O. That is, assuming that the point at which the distance from the pipe center O to the fin 3 is the shortest is the vertex P of the fin 3, there is a large difference between the direction C in which the vertex P of the fin 3 extends and the radial direction D of the pipe 1. Generally, the angle formed by the direction C in which the vertex P extends and the radial direction D exceeds 20 °.

[0005]

However, the increase in the inclination of the fins not only hinders the flow of the refrigerant due to the inclination of the fins, but also lowers the fins due to the inclination of the fins. There is a problem that the heat transfer performance is reduced.

[0006] Further, the inner grooved pipe having the increased fin inclination as described above has a pipe expansion ratio and a pipe expansion ratio indicating the rate at which the inner diameter of the inner grooved pipe increases in comparison with the inner grooved pipe having no increased fin inclination. The tube shrinkage, which indicates the rate at which the longitudinal length of the inner surface grooved tube shrinks due to the expansion, decreases.

[0007] The decrease in the pipe expansion rate reduces the adhesion between the inner grooved pipe and the fin plate, and as a result, a gap is formed between the inner grooved pipe and the fin plate, and an air layer is formed in the gap. Therefore, there is a problem that heat transfer performance is reduced.

In addition, a decrease in the shrinkage ratio of the tube causes a problem in the process after the expansion of the tube, such as making the length of the inner grooved tube nonuniform, reducing the return bend insertion property and the brazing property.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and by suppressing the inclination of the fin at the time of expanding the pipe, it is possible to prevent a decrease in heat transfer performance and a problem that occurs in a process after expanding the pipe. It is an object to provide an internally grooved tube.

[0010]

According to the present invention, there is provided an inner grooved pipe having a plurality of spiral parallel grooves extending in a direction inclined in the pipe axis direction on an inner surface of the pipe. In a cross section orthogonal to the above, the shape of the fin formed between adjacent grooves on the inner surface of the pipe is such that the point P where the distance from the pipe center O to the fin is the shortest is the apex of the fin, and The straight line bisecting the angle formed by the line connecting the apex of the first fin and the line connecting the apex of the second fin adjacent to the first fin from the pipe center O is the first fin and the second fin. Assuming that points intersecting with the inner surface and the outer surface of the pipe between the two fins are Q and R, respectively,
When a distance between the point Q and the point R is defined as a pipe wall thickness, and a distance between the point Q and the point R is defined as a pipe wall thickness, an imaginary circle centered on the pipe center O and having a radius equal to the pipe inner diameter and both ends of the first fin. An angle θ formed by a line segment connecting a point where the land portion intersects and a line segment connecting the midpoint of the line segment and the vertex of the first fin is 70 to 90 °. .

In the present invention, a straight line segment connecting a point where an imaginary circle having the same radius as the inner diameter of the pipe and the land portions at both ends of the fin intersects, and a midpoint of the line segment and a vertex P of the fin are connected. The angle θ formed by the line segment is as large as 70 to 90 °, and the fin formed on the inner surface of the tube is formed almost perpendicular to the inner surface of the tube. For this reason, when assembling the heat exchanger, the inner grooved tube is bent into a hairpin shape, inserted into the holes provided in each fin plate, expanded, and brought into close contact with the fin plate. Because of the difference, the inclination direction of the fins is apparently reversed depending on the expansion direction, and the fins fall when expanded from one side, and the fins occur when expanded from the other side, and even in the same pipe, the expansion direction depends on the expansion direction. The rate changes.
However, when the angle θ is as large as 70 to 90 °, the fins do not fall down depending on the expanding direction to reduce the angle θ, or the fins do not occur to increase the angle θ. As a result, a tube with an inner groove having a fin shape on the inner surface of the tube which is substantially symmetrical about the apex P of the fin after expansion is obtained, and the flow of the refrigerant is not hindered and the high heat transfer performance as a high fin effect is maintained. . In addition, since the angle θ is close to 90 °, the shape of the fin with respect to the longitudinal direction of the pipe does not change depending on the direction in which the pipe is expanded, so that the expansion rate and the contraction rate after expansion are constant. When the expansion rate is uniform, the contraction rate in the longitudinal direction of the inner grooved pipe caused by expanding the pipe becomes uniform, so that good adhesion between the fin plate and the inner grooved pipe can be obtained.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present application have conducted extensive experimental studies on the shape of a fin of an internally grooved tube for preventing the fin from being inclined when the tube is expanded. As a result, the top of the fin formed on the inner surface of the tube has a pipe top. In the cross section perpendicular to the axis, it has been found that when the inner grooved pipe formed to be inclined from the direction toward the pipe center O is expanded, the inclination angle of the fin increases due to the difference in the expansion direction. In addition, it has been found that when the inclination angle of the fin increases, the expansion ratio and the contraction ratio differ depending on the expansion direction, so that the adhesion between the inner grooved tube and the fin plate is reduced.

FIG. 1 is a schematic cross-sectional view illustrating the structure of a fin of an internally grooved tube according to an embodiment of the present invention. This figure 1
Is a cross section orthogonal to the tube axis. On the inner surface of the inner grooved tube 1, a plurality of spirally arranged grooves 2 extending in a direction inclined in the longitudinal direction of the tube are formed. Fins 3 are formed between adjacent grooves 2 on the inner surface of the inner grooved tube 1. In FIG. 1, a point P at which the distance from the pipe center O to the fin 3 is the shortest is defined as the top of the fin.
L ₁ a straight line connecting the straight line connecting the vertex P of the fins 4 adjacent the tube center O to the fin 3 and L _2, and L ₁ and L ₂ and L ₃ the straight line that the angle phi ₁ 2 bisects formed by I do. The straight line L ₃
When the points of intersection between the fins 3 and 4 intersect the inner and outer surfaces of the pipe are Q and R, respectively, the distance from the pipe center O to the point Q is the pipe inner diameter R ₁ , and the distance from the pipe center O to the point R is Is the pipe outer diameter R ₂ , and the distance between the point Q and the point R is the pipe wall thickness R ₃ . In such a pipe 1, points where the imaginary circle 5 whose radius is the pipe inner diameter R ₁ intersects with the land of the fin 3 are defined as a land 6 a and a land 6 b, respectively. The land portion 6a and the land part of a line segment of a straight line connecting the 6b and L _4, the midpoint 7 and the vertex P of the land portion 6a and the land portion 6b along the line L ₄
The line segment connecting the bets when the L _5, line L ₄ and the line segment L ₅ and the angle θ is 70 to 90 °.

Hereinafter, the angle θ formed by the line segment L ₄ and the line segment L ₅ is 7
The reason for setting the angle to 0 to 90 ° will be described. The inner grooved tube is inserted into the hole of the fin plate after being bent into a hairpin shape. By inserting an expansion burette into both ends of the pipe, and expanding the pipe with the buret, the pipe and the fin plate are brought into close contact with each other. 2A and 2B are views showing a state before the expansion of the inner grooved pipe, in which FIG. 2A is a schematic view showing an inner grooved pipe bent into a hairpin shape, and FIG. 2B is a view from the end A shown in FIG. Schematic diagram showing the shape of the fin in the tube seen,
(C) is a schematic diagram showing the shape of the fin in the tube viewed from the end B shown in (a). 2A, a plurality of grooves extending spirally in a direction inclined in the longitudinal direction of the pipe shown in FIG. 2A and extending counterclockwise with respect to the pipe center O are formed on the inner surface of the pipe. The fins 3 are arranged in parallel between these grooves.
0 is formed.

In this case, as will be described later, when the grooves are formed on the inner surface of the tube, the fins are inclined without being upright.
That is, rather than the line segment L ₄ and the line segment L ₅ represents a angle formed theta 90 ° defined in Fig. 1, the fins 30 in the tube surface is inclined in one direction. For this reason, as shown in FIG. 2B, at one tube end A, the angle θ ₁ (FIG. 1) formed by the line segment L ₄ and the line segment L ₅ of the fin 30 in the cross section orthogonal to the tube axis is formed. It is sharp.

On the other hand, as shown in FIG. 2C, at the other end B, the angle θ ₂ formed by the line segment L ₄ and the line segment L ₅ of the fin 30 in the cross section orthogonal to the tube axis is θ ₂ = it is an obtuse angle 180 ° -θ _1. For this reason, when a burette is inserted from ends A and B for pipe expansion, at end A, FIG.
As shown in (b), since the fin 30 is inclined so as to face the traveling direction of the burette, the burette presses the fin 30 in the direction in which the fin 30 is raised by pushing the burette. 30 will not fall. Therefore, the expansion efficiency is high. On the other hand, at the end B, when the burette is pushed into the pipe, the buret advances in the opposite direction to the case of the end A, and the fin 30 escapes from the buret inserted from the end B. When the burette is pushed in, the burette presses the fin 30 in the direction in which the fin 30 is laid down. For this reason, the fin 30 falls down further in this tube expansion process.

As described above, since the fin shape of the inner grooved pipe after the rolling is inclined in one direction, the fin inclined at an obtuse angle to the traveling direction of the buret in the expanding process (FIG. 2 (c)) is greatly inclined, and the fin is inclined at an acute angle with respect to the traveling direction of the burette (FIG. 2).
(B)) stands upright without falling down. In the process of assembling the heat exchanger, the pipe is bent into a U-shape and then expanded, so that the burette cannot always be passed only unilaterally as shown in FIG. It is necessary to pass the burette also in the direction shown in FIG. Therefore, conventionally, in the tube expanding step, the fin has fallen in a half portion of the tube.

FIGS. 3 (a) to 3 (c) are views showing an inner grooved pipe after expansion, and FIG. 3 (a) is a cross-sectional photograph showing a cross section orthogonal to the pipe axis expanded from the end B shown in FIG. 3 (c). (B) is a cross-sectional photograph showing a cross section orthogonal to the pipe axis after pipe expansion expanded from the end A shown in (c), and (c) is a cross-sectional view in the pipe longitudinal direction. is there. The inner grooved tube shown in FIG. 3 is obtained by observing a fin having a fin height of 0.20 mm or more and a peak angle of 40 ° or less.

As shown in FIG. 3 (c), on the inner surface of the inner grooved tube after rolling parallel to each other, a groove lead angle phi ₂ is formed with respect to the longitudinal direction of the tube, next to The fins formed between the mating grooves are inclined. As described above, since such an internally grooved pipe is expanded after being bent into a hairpin shape, the inclination direction of the fin is different between the case of expanding from the end A and the case of expanding from the end B.

As shown in FIG. 3 (b), when the pipe is expanded from the end A, the fin becomes less inclined after the expansion, and the fin stands up. On the other hand, as shown in FIG. 3A, when the tube is expanded from the end B, the inclination of the fin becomes larger after the tube is expanded. As described above, when the inner grooved pipe having the inclined fins is expanded, the inclination direction of the fins differs depending on the expansion direction.

When expanded from the A end shown in FIGS. 2 and 3,
While the pipe is expanded normally, expanding the pipe from the end B not only increases the inclination of the fin, but also consumes energy at the time of expanding the pipe to tilt the fin. I will. Therefore, the inclination of the fin becomes large and the high fin effect is lost, so that not only the heat transfer performance of the internally grooved tube is reduced, but also the pipe expansion rate is reduced. As a result, the adhesion between the tube and the fin plate is reduced, and the heat transfer performance is further reduced. When the tube is expanded, its length contracts,
Due to the decrease in the expansion rate, the contraction rate of the pipe length also decreases.
The length of the inner grooved pipe becomes uneven at the end and the end. This makes it difficult to connect the pipe end to the pipe of the heat exchanger after assembling the pipe and the fin. The present inventors have not changed, but the expansion ratio by the tube expanding direction, as a condition that can maintain high even after tube expansion heat transfer performance, and the line segment L ₄ and the line segment L ₅ of inner grooved tube before the tube expansion Make an angle θ of 70 to 9
I found that it was good to make it 0 °.

Next, a description will be given of a phenomenon in which the fins of the inner grooved tube are inclined during rolling. The inclination of the fins formed on the inner surface of the pipe as in the above-described inner grooved pipe is such that when transferring the groove shape of the groove plug to the pipe, the fins are hard to separate from the groove plug (hard to come off), and This is because the groove plug pushes the side surface or the formed fin pushes the groove side surface to cause an inclination in a cross section orthogonal to the direction of the groove.

FIG. 4 is a schematic view for explaining the principle that the fins formed between the grooves are inclined when the inner surface grooved tube is formed. In FIG. 4, a thin line indicates a formed inner grooved pipe immediately after rolling, and a thick line indicates a groove plug for forming the inner grooved pipe. This shows a state of the fins and the groove plugs in a cross section orthogonal to the pipe axis of the inner grooved pipe whose outer diameter is increased by springback. The direction from the back of the paper to the front is the drawing direction when the pipe is rolled.

As shown in FIG. 4, the inner surface of the pipe 11
The fin 12 is formed by the groove plug 13 inserted into the groove plug 13, and the fin 12 and the groove 14 of the groove plug 13 overlap. Here, for example, if the groove plug 13 rotates clockwise, the pipe 11 rotates counterclockwise. Immediately after rolling, the material forming the pipe 11 has a larger pipe inner diameter and pipe outer diameter due to springback due to pressing of a rolling ball during rolling, and has a larger cross-sectional area in a cross section orthogonal to the pipe axis.

On the other hand, in the longitudinal direction of the tube, the passage length of the tube that passes because it is rolled per unit time is always constant. However, since the material of the pipe 11 immediately after rolling is expanded in the direction perpendicular to the pipe axis due to springback, the length of the pipe per unit time immediately after rolling is shorter than that immediately below the rolling. That is, the drawing speed of the pipe 11 immediately after rolling converted into the longitudinal direction becomes slow. In other words, the drawing speed of the pipe immediately below the rolling is slightly higher than the drawing speed immediately after the rolling, in which the pipe inner diameter and the pipe outer diameter are increased by springback.

If the speed of the groove plug 13 and that of the tube 11 after rolling are equal, the tube 11 is pulled out while the phase of the groove 14 of the groove plug 13 and the fin 12 formed on the inner surface of the tube 11 are in phase. However, since the speed after the fin 12 is formed, that is, the speed of the tube 11 after rolling is lower than the speed of the groove plug 13, the phase between the groove 14 of the groove plug 13 and the formed fin 12 is shifted. The left oblique side 14a of the groove 14 of the groove plug 13 is pressed by the left oblique side 12a of the fin 12 formed on the inner surface of the pipe. That is, the groove plug 13
Since the speed of the tube 11 is lower than the speed of the groove 11, the left oblique side 12a of the fin 12 presses the left oblique side 14a of the groove 14 to prevent the movement of the groove plug 13 and the fin 12 is inclined.

From the above, the groove plug 14 that rotates clockwise is
Left hypotenuse 1 of fin 12 for rolling internal grooved pipe
The fin 12 tilts rightward because 2a presses the left oblique side 14a of the groove plug 14. Therefore, in order to roll an inner grooved tube in which the fin angle θ is large, that is, the fins are not inclined by the right-handed groove plug, a groove plug having a groove inclined to the left is used to form an inner grooved tube. Tubes can be molded.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the embodiments of the present invention will be specifically described below in comparison with comparative examples that depart from the scope of the claims. First, using a groove plug having a groove 55 having the shape shown in Table 1 and a tube having a tube outer diameter of 7 mm and a tube wall thickness of 0.25 mm, the angle θ of the fin formed on the inner surface is 60 to 90 °. An inner grooved tube was formed. FIG. 5 is a schematic sectional view illustrating the groove shape of the groove plug. As shown in FIG. 5, a straight line L connecting the groove bottom 24 of the groove 23 between the left protrusion 21 of the groove plug 20 and the right protrusion 22 on the side thereof to the top of the left protrusion 21 and the right protrusion 22. The distance up to _{6 is} defined as the groove depth h of the groove plug 20, and the radius of the deepest portion at the bottom of the groove 23 is defined as the groove bottom radius r. Further, the left slope angle is the angle and extension of the left oblique side 23a of the groove center line L ₇ and grooves 23 is a perpendicular drawn from the groove bottom 24 of the groove 23 to the straight line L ₆ .phi.L, the groove center line L ₇ and grooves 2
3 is defined as the right slope angle φR.
And the peak angle φ ₃ of the groove 23 is φ ₃ = φL + φR.

The peak angle φ of the groove plug having such a shape
₃ (= φL + φR), as shown in Table 2, is based on the assumption that the right and left slope angles φL and φR are symmetrical.
Six types of shapes were used. Category A is the groove center line L ₇ and the groove 2
3 of the form left slope angle φL the left oblique side 23a fixed 10 °, forming the right slope angle φR of a right oblique side 23b of the groove center line L ₇ and the groove 23 is greater 5 ° or 10 ° from the left slope angle φL 15 ° or 20 °. Conversely, for category B, the right slope angle φR is fixed to 10 °, and the left slope angle φL is set to 15 ° or 20 °, which is 5 ° or 10 ° larger than the right slope angle φR. Category C is the summit angle φ ₃ fixed 20 °, φL-
φR was set to ± 6 °.

[0030]

[Table 1]

[0031]

[Table 2]

Next, the inner grooved pipe formed by using the groove plug having the above-described shape was expanded, and the inner grooved pipe after the expansion was evaluated. The evaluation method is as follows.
Was used to measure the heat transfer performance in the heat exchanger. FIG.
FIG. 2 is a schematic diagram showing a heat exchanger. As shown in FIG.
A plurality of aluminum fin plates 41 manufactured by press working are arranged in parallel with a suitable interval between each other, and U-shaped fin plates 41 are formed in holes formed in each fin plate 41 in a hairpin shape.
The fin plate 41 and the inner grooved tube 42 were brought into close contact with each other by assembling them by inserting the inner grooved tube 42 bent in the shape of a letter, and thereafter expanding the inner grooved tube 42 to assemble them. Table 3 shows the measurement conditions, and Table 4 shows the heat exchanger conditions. The measurement results were compared and evaluated based on the heat transfer performance of the internally grooved tube having no fin inclination of 100, and 95 or more was evaluated as good. Next, the secondary processing defect occurrence rate was examined. The secondary processing defect occurrence rate is defined as the incidence rate of failure of insertion and brazing of return bend after pipe expansion per 100 hairpins, and the incidence rate is 5%.
The following were regarded as good. The inner grooved pipe was evaluated as good only when both of these evaluations were good. Table 5 shows the results.

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

[Table 5]

In the first to fourth embodiments, the angle θ of the fin before expansion is
Was within the range of the present invention, so that the heat transfer performance was excellent, the secondary processing occurrence rate was low, and the judgment was good.

In Comparative Examples 1 to 3, the fin angle θ before expansion was used.
Was out of the range of the present invention, so that the heat transfer performance in the heat exchanger was poor. Further, in Comparative Examples 1 and 2, the heat transfer performance and the rate of occurrence of secondary processing defects were lower than those of Example 1 even though the crest angle of the groove plug used for forming the inner grooved tube was small. It is extremely inferior to Example 1. Therefore, it is understood that the magnitude of the angle θ of the fin before the expansion is more affected by the performance of the inner grooved pipe than the angle of the peak angle of the groove plug.

[0038]

As described above in detail, according to the present invention, there is provided an inner grooved pipe having a plurality of spiral parallel grooves extending in a direction inclined in the pipe axis direction on the inner surface of the pipe. The angle θ formed by a line segment connecting the land portions at both ends of the fin formed between the grooves to be formed, and a line segment connecting the midpoint of the line segment and the vertex P of the fin is as large as 70 to 90 °. Thus, since the difference in the direction in which the fins face the fins is small, the inclination angles of the fins that hit the burettes are substantially equal.
Therefore, the expansion rate of the inner grooved pipe after expansion is constant. Accordingly, since the shrinkage ratio of the tube in the longitudinal direction becomes uniform, good adhesion between the fin plate and the inner surface grooved tube can be obtained. In addition, since the inclination of the fin does not increase even after the expansion, the shape of the fin becomes substantially axially symmetric, the flow of the refrigerant is not hindered, and the effect of the high fin is obtained, and the heat transfer performance in the heat exchanger is improved.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating the shape of an inner grooved tube according to an embodiment of the present invention.

FIGS. 2A and 2B are views showing a state before expansion of an inner grooved pipe, wherein FIG. 2A is a schematic view showing an inner grooved pipe bent into a hairpin shape, and FIG. (A) is a schematic view showing the shape of the fin in the tube viewed from the end A shown in (a), (c) is (a)
FIG. 4 is a schematic view showing a shape of a fin in a tube viewed from an end B shown in FIG.

3 (a) to 3 (c) are views showing an inner grooved pipe after expansion, and FIG. 3 (b) is a cross section showing a cross section orthogonal to the pipe axis after expansion from the A end shown in FIG. 3 (c). (A) is a cross-sectional photograph showing a cross section orthogonal to the pipe axis expanded from the end B shown in (c),
(C) is a sectional view in the pipe longitudinal direction.

FIG. 4 is a schematic cross-sectional view for explaining the principle that fins between grooves incline when forming an inner surface grooved tube.

FIG. 5 is a schematic cross-sectional view illustrating a groove shape of a groove plug.

FIG. 6 is a schematic diagram showing a heat exchanger.

FIG. 7 is a schematic view showing a conventional inner grooved pipe.

[Explanation of symbols]

1, 11, 42; tubes 2, 14; grooves 3, 4, 12, 30; fins 5; virtual circles 6a, 6b; lands 7; midpoints 13, 20, groove plugs 12a, 14a; protrusions 22; Migitotsubu 23; groove 24; groove bottom 41; fin plate _{L 1, L 2, L 3} , L 6; straight L _4, L _5; line L _7; centerline R _1; tube inner diameter R ₂ ; Pipe outer diameter R ₃ ; Pipe wall thickness h; Groove height φ ₁ ; Angle between L ₁ and L ₂ φ ₂ ; Lead angle φR; Right slope angle φL; Left slope angle φ ₃ ; Peak angle (φL + φR ) O; Pipe center P; Apex

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Mamoru Ishikawa 65, Hirasawa, Hadano City, Kanagawa Prefecture Inside the Hadano Plant, Kobe Steel Co., Ltd. (72) Inventor Kiyonori Koseki 65, Hirasawa, Hadano City, Kanagawa Prefecture Hadano Plant, Kobe Steel Corporation (72) Inventor Taku Nagata 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo F-term in Kobe Steel Research Institute, Kobe Research Institute (reference) 4E096 EA04 EA18 FA23 FA24 GA03

Claims (1)

[Claims] An inner grooved pipe having a plurality of spiral parallel grooves formed in a pipe inner surface extending in a direction inclined in the pipe axis direction, wherein a cross section orthogonal to the longitudinal direction is formed between adjacent grooves on the pipe inner surface. The point P where the distance from the tube center O to the fin is the shortest is defined as the top of the fin, the line connecting the top of the first fin from the center O of the tube, and the center of the tube O The straight line bisecting the angle between the line connecting the vertices of the second fin adjacent to the first fin and the line connecting the vertices of the second fin is the first line.
When the points intersecting the inner surface and outer surface of the pipe between the fin and the second fin are Q and R, respectively, the pipe center O
When the distance from to the point Q is a pipe inner diameter, and the distance between the points Q and R is a pipe wall thickness, an imaginary circle centered on the pipe center O and having the pipe inner diameter as a radius is the first circle. The angle θ formed by a line segment connecting a point where the land portions of both fins intersect with each other and a line segment connecting the midpoint of the line segment and the vertex of the first fin is 70 to 90 °. An inner grooved pipe characterized by the following.