JPH0712482A - Heat transfer tube with inner surface groove and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a heat transfer tube with an inner surface groove and a method for manufacturing the same in which performance is further improved without increasing a pressure loss and without increasing a processing load at the time of manufacturing. CONSTITUTION:A heat transfer tube with an inner surface groove comprises a plurality of fins 3 of substantially a triangular section formed of a secondary groove of an inverted trapezoidal shape on an inner surface of the tube, and a plurality of cavities 5 provided at a suitable interval at a top of the fins 3. A height of the cavity 5 is 0.25 to 1.0 times as large as a depth of the secondary groove. The tube is manufactured by the steps of providing a primary groove having a rectangular shape and a ratio of groove widths of 1.2 to 2.0 on the inner surface of the tube, and then providing the secondary groove of an inverted trapezoidal shape in section crossed with the primary groove on the inner surface of the tube. A depth of the primary groove is 0.25 to 1.0 times as large as a depth of the secondary groove, and the secondary groove is crossed at an angle of 10 to 45 deg. to a lead of the primary groove.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner grooved heat transfer tube incorporated in a heat exchanger such as a room air conditioner and a method for manufacturing the same, and particularly to an inner grooved heat transfer tube which contributes to high performance and downsizing. Regarding the method.

[0002]

2. Description of the Related Art As a heat transfer tube for a room air conditioner, an inner grooved tube having a plurality of spirally continuous fins and grooves formed on the inner surface of the tube is used (JP-A-60-142).
195). In order to improve the heat transfer performance of the inner grooved tube, it is known that it is effective to elevate the fins, increase the number of grooves, or sharpen the tip angle of the fins.

Further, there has been proposed an inner surface grooved heat transfer tube in which two grooves are provided so as to intersect each other in an inverted trapezoidal shape on the inner surface of the tube to further improve heat transfer performance (Japanese Patent Laid-Open No. 1-317637).
Etc.).

[0004]

However, in these conventional heat transfer tubes with inner groove, although heat transfer performance can be improved by providing high fins on the inner surface of the tube, the heat transfer performance can be improved by providing high fins. There is a drawback that the pressure loss increases, the load of the compressor increases, and the energy efficiency decreases.

Further, in the manufacture of the heat transfer tube with the inner groove,
There is a drawback that the manufacturing cost increases because the processing load increases due to the formation of the high fins, the processing speed decreases, and the tool consumption increases.

As described above, the heat transfer tube with groove on the inner surface in which the high fins are formed on the inner surface of the tube has the disadvantages of high pressure loss and high manufacturing cost. The improvement is not sufficient, and it has been desired to manufacture a heat transfer tube having further improved heat transfer performance.

The present invention has been made in view of the above problems, and pressure loss does not increase, processing load during manufacturing does not increase, and a heat transfer tube with an inner groove having further improved performance and its manufacture. The purpose is to provide a method.

[0008]

DISCLOSURE OF THE INVENTION In a heat transfer tube with an inner groove according to the present invention, a plurality of fin portions each having an inverted trapezoidal groove formed on the inner surface of the tube and having a substantially triangular cross section, and the fin portions are provided. Has a plurality of cavities provided at appropriate intervals on the top of,
The height of the cavity is 0.25 to 1.0 times the depth of the groove.

A method of manufacturing a heat transfer tube with an inner groove according to the present invention comprises a step of providing rectangular primary grooves on the inner surface of the tube at a groove width ratio of 1.2 to 2.0, and a step of forming the primary groove on the inner surface of the tube. And a step of providing a secondary groove having an inverted trapezoidal cross section. The depth of the primary groove is 0.25 to 1.0 times the depth of the secondary groove. In this case, it is preferable that the secondary groove is provided so as to intersect the lead of the primary groove at an angle of 10 to 45 °.

[0010]

In the present invention, first, as the primary groove, for example, as shown in FIG. 2, a groove having a rectangular cross section is formed on the inner surface of the pipe. The groove width ratio of this groove is a ratio a of the circumferential length a of the convex portion 1 of the groove and the circumferential length b of the concave portion 2 of the groove of FIG.
/ B. In the present invention, since the groove width ratio a / b is 1.2 to 2.0, the groove length ratio in the circumferential direction is groove recess width: groove projection width = 1: 1.2 to 1. : 2.0
Is. Further, the depth of the primary groove is 0.25 to 1.0 times the depth of the secondary groove formed in the next step.

Next, as a secondary groove, for example, as shown in FIG. 3, a groove having an inverted trapezoidal cross section is formed so as to intersect the lead angle of the primary groove at an angle of 10 ° to 40 °. With the secondary groove shown in FIG. 3, a groove bottom 4 is formed on the inner peripheral surface of the pipe,
A fin 3 having a triangular cross section, which is erected from the groove bottom portion 4, is formed.

As a result, as shown in FIG. 1, the fin 3 formed by the inverted trapezoidal groove has a substantially triangular cross section, and after the secondary groove is formed, the appearance of the inner peripheral surface of the pipe is substantially improved. The shape has a bottom 4 of the secondary groove and a fin 3 having a triangular cross section, and a cavity 5 formed by crushing the primary groove at the top of the fin 3 remains.

That is, at the top of the fin portion formed by the secondary groove, a cavity 5 is formed by pressing the concave portion of the primary groove in the molding step of the secondary groove and connecting the opening thereof. Further, the cavities 5 are continuous in a crack shape up to the outer surface of the mountain, and form an opening 6 in the outer surface layer portion. This cavity 5
The shapes of the openings 6 and 6 are schematically shown in FIG. The cavity 5 formed by collapsing the primary groove has a depth of hi and the secondary groove has a depth of ho. And the groove depth ratio of the cavity is hi / h
o.

The cavity thus formed serves as a boiling nucleus and promotes in-liquid boiling when the heat transfer surface is filled with the liquid. As a result, the heat transfer tube with inner groove of the present invention has improved evaporation performance. Further, since the inner surface area is increased due to the opening of the mountain on the outer surface layer, the condensation performance is also improved. On the other hand, the internal pressure loss of the pipe is slightly increased because the external shape of the internal surface of the product is the same as that of the conventional internal grooved pipe. It can be suppressed small.

Next, the numerical conditions specified in the present invention will be described. Shape of primary groove In the present invention, the groove width ratio a / b of the primary groove in the inner circumferential direction of the pipe.
Is 1.2 to 2.0. FIG. 5 is a graph showing the relationship between the groove width ratio of the primary grooves on the horizontal axis and the evaporation performance ratio on the vertical axis. Note that the fin height ratio is also shown in FIG. In FIG. 5, the evaporation performance ratio is a performance ratio when the performance of the single groove having the same shape as the secondary groove shape is 1.

The fin height ratio is the fin height of the actually formed secondary groove when the fin height of the predetermined secondary groove is 1. When the groove width ratio of the primary groove becomes small, that is,
When the width of the groove convex portion is smaller than the width of the groove bottom portion of the primary groove, the tube wall portion that enters the groove of the plug during molding of the secondary groove is reduced, and the fin height of the obtained secondary groove is reduced. Is smaller than 1.

The tube diameter is 7.0 mm, the secondary groove has a groove number of 50 fins in a cross section perpendicular to the tube axis, the lead angle is 18 °, and the groove depth is 0.21 mm. The number of single grooves to be compared is 5
The fin is 0, the lead angle is 18 °, and the groove depth is 0.21 mm.

As is apparent from FIG. 5, in the region where the groove width ratio is less than 1.2 times, it is difficult to obtain high ridges because the pressure amount of the material is insufficient at the time of forming the secondary groove, and the evaporation performance is deteriorated. To do. On the other hand, in the region of more than 2.0 times, the amount of compression of the material becomes excessive at the time of forming the secondary groove, so that the concave portion of the primary groove is closed, and it becomes difficult to form a cavity effective for boiling, as in the above case. Evaporation performance deteriorates. The heat transfer performance tends to improve as the groove depth of the primary groove increases, but 1.0
The pressure resistance strength of the pipe tends to decrease in a region exceeding twice, which may cause a problem in practical use. This is because when the depth of the primary groove is deeper than that of the secondary groove, a cavity is formed at the bottom of the secondary groove in the final cross-sectional shape, so that the wall thickness required for strength cannot be secured.

Depth Ratio of Primary Grooves FIG. 6 shows the groove depth ratio hi / ho (see FIG. 4) on the horizontal axis and the evaporation performance ratio and pressure resistance strength ratio on the vertical axis, showing the relationship between the two. It is a graph figure. The evaporation performance ratio is a performance ratio when the performance of a single groove having the same shape as the secondary groove shape is 1. The pressure resistance strength ratio is a strength ratio when the pressure resistance of a single groove having a shape similar to the shape of the secondary groove is 1.

The depth h i of the primary groove is 0.
The reason for setting it to 25 to 1.0 times is that if it is less than 0.25 times, the concave portion of the primary groove is closed at the time of forming the secondary groove, and it becomes impossible to form a cavity. As a result, the evaporation performance is lowered, as can be seen from FIG. On the other hand, the depth of the primary groove is set to 1.0 of the depth of the secondary groove.
The reason why it is set to not more than twice is that, if it exceeds this, a cavity is formed in the groove bottom of the secondary groove, and as is clear from FIG. 6, the strength of the pipe is significantly reduced.

Crossing Angle FIG. 7 is a graph showing the relationship between the primary groove and the secondary groove on the horizontal axis and the evaporation performance ratio and the pressure loss ratio on the vertical axis. The evaporation performance ratio is the performance ratio when the performance of the single groove of the same shape as the secondary groove shape is 1, and the pressure loss ratio is the pressure loss when the pressure loss of the single groove of the same shape as the secondary groove shape is 1. Is a ratio.

The crossing angle between the leads of the primary groove and the secondary groove is 1
The reason for setting 0 ° to 45 ° is that in the region of less than 10 °, two types of grooves interfere with each other when the secondary groove intersects with the primary groove and is formed, and thus a groove having a desired shape cannot be formed. is there. On the other hand, the heat transfer performance tends to improve as the crossing angle increases, but the pressure loss also increases. Then, in the region where the intersection angle exceeds 45 °, as can be seen from FIG.
The pressure loss is 1.4 times or more compared to a heat transfer tube with a single groove of the same shape, and it is necessary to make an improved design such as increasing the number of refrigerant circuits in the heat exchanger in actual use. The manufacturing cost of the container increases. Therefore, the intersection angle is 1
The angle is 0 to 45 °.

[0023]

EXAMPLE Next, an example in which the present invention is applied to a heat transfer tube having an outer diameter of 7 mm will be described. First, as the primary grooves, the number of grooves in the cross section orthogonal to the tube axis is 5.0 and the lead angle is 0.
°, groove depth 0.15 mm, concave to convex ratio 1: 1.
A rectangular groove having a groove width ratio of 5 (groove width ratio a / b = 1.5) was formed.

Next, as secondary grooves, the number of grooves in the cross section orthogonal to the tube axis is 50, the lead angle is 18 °, and the groove depth is 0.22 m.
The reverse trapezoidal groove of m was formed by intersecting the primary groove.
The fin portion formed by the inverted trapezoidal groove has a triangular cross section with a peak angle of 40 °.

The heat transfer tube was used in a double tube heat exchanger to measure the single tube performance. FIG. 8 is a graph showing the tube inner membrane heat transfer coefficient during condensation and during evaporation, with the horizontal axis representing the condensation performance and the vertical axis representing the evaporation performance. The condensation and evaporation performances are both measured values when the refrigerant flow rate is 30 kg / hour. In the figure, (1) shows the heat transfer performance of a conventional inverted trapezoidal inner grooved tube (primary groove only). This heat transfer tube has 50 grooves, a lead angle of 18 °, and a groove depth of 0.22 mm. The groove is provided. Further, (2) is a data group of the embodiment of the present invention. As shown in FIG. 8, the inner grooved tube of the embodiment of the present invention has improved the evaporation and condensation performances by 110% or more as compared with the conventional inner grooved tube of the same shape. On the other hand, the pressure loss only increased by 103 to 105%.

[0026]

As described above, since the heat transfer tube with the inner surface groove according to the present invention is provided with the fin portion having the cavity, the heat transfer characteristics at the time of evaporation and condensation are remarkably suppressed while suppressing the pressure loss and the like. Can be improved. Thus, the present invention
High-performance heat transfer tubes can be supplied, contributing to the miniaturization and high performance of heat exchangers such as room air conditioners.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an appearance of a heat transfer surface of the present invention.

FIG. 2 is a schematic perspective view showing a groove shape of a primary groove.

FIG. 3 is a schematic perspective view showing a groove shape of a secondary groove.

FIG. 4 is a schematic diagram illustrating the shapes of a cavity 3 and an opening 6.

FIG. 5 is a graph showing the relationship between the groove width ratio of the primary groove on the horizontal axis and the evaporation performance ratio and the fin height ratio on the vertical axis.

FIG. 6 is a graph showing the relationship between the groove depth ratio on the horizontal axis and the evaporation performance ratio and pressure resistance strength ratio on the vertical axis.

FIG. 7 is a graph showing the relationship between the two, with the horizontal axis representing the groove intersection angle and the vertical axis representing the evaporation performance ratio and the pressure loss ratio.

FIG. 8 is a graph showing the results of single tube performance measurement of the heat transfer tubes of the examples of the present invention.

[Explanation of symbols]

 1; convex part 2; concave part 3; fin 4; groove bottom part 5; cavity 6; opening

Claims (3)

[Claims] 1. A plurality of fins each having a substantially triangular cross section formed by an inverted trapezoidal groove on the inner surface of the pipe, and a plurality of cavities provided at appropriate intervals on the tops of the fins. An inner grooved heat transfer tube, wherein the height of the cavity is 0.25 to 1.0 times the depth of the groove. 2. A step of providing a rectangular primary groove on the inner surface of the pipe at a groove width ratio of 1.2 to 2.0, and a secondary groove having an inverted trapezoidal cross section intersecting with the primary groove on the inner surface of the pipe. And the step of providing, the depth of the primary groove is 0.25 of the depth of the secondary groove.
To 1.0 times the inner surface grooved heat transfer tube manufacturing method. 3. The method of claim 2, wherein the secondary groove intersects with the lead of the primary groove at an angle of 10 to 45 °.