JP5687182B2 - Heat transfer tube with leak detection function and outer tube used for it - Google Patents

Description

  The present invention relates to a heat transfer tube having a leak detection function of a double tube structure, and more particularly to a heat transfer tube having a leak detection function suitably used for a heat exchanger and an outer tube used therefor.

In a heat pump type water heater or the like, an outer heat transfer tube and an inner heat transfer tube disposed inside the outer heat transfer tube are provided, and CO ₂ refrigerant or water is passed through the inner heat transfer tube so that the outer heat transfer tube and the inner heat transfer tube are flown. A heat exchanger is used in which water or CO ₂ refrigerant flows between the heat pipes and heat exchange between the CO ₂ refrigerant and water is performed through the tube wall of the inner heat transfer pipe. In this case, a heat transfer tube having a leakage detection function is often used as the inner heat transfer tube that separates the CO ₂ refrigerant and water and provides a heat transfer effect between them. This heat transfer tube having a leakage function is composed of an outer tube and an inner tube provided so as to be in contact with the outer tube while leaving a part of the outer tube. A leakage detector is provided as a fine gap with the tube. A copper or copper alloy tube is used for the outer tube and / or the inner tube. When the outer tube of the inner heat transfer tube with this leakage detection function is in contact with water, a hole may be formed through the outer tube due to corrosion. It reaches the leak detection part which is a minute gap between the pipes, leaks through the leak detection part to the end of the inner heat transfer tube, and can know that corrosion has occurred in the inner heat transfer pipe. Further, when this water further corrodes the inner pipe, the CO ₂ refrigerant flowing inside the inner pipe leaks to the leakage detection part outside the inner pipe through the hole formed in the inner pipe. CO In this case, the flow since CO ₂ refrigerant is a high pressure, CO ₂ refrigerant is leaked to an end of the inner heat transfer pipe through the leak detection unit provided between the inner tube and the outer tube, further heat exchanger _{2 Since} the pressure drop of the refrigerant occurs, it is possible to detect the leakage, and it is possible to stop the operation of the heat pump water heater or the like by this leakage detection. This means that if a crack in the inner tube is generated by the pressure of the CO ₂ refrigerant flowing through the inside inner heat transfer tube, or CO ₂ refrigerant flows between the outer heat transfer pipe and the inner heat transfer tube, the water inside the inner heat transfer tube The same applies to the case where the current flows. In this way, if a heat transfer tube made of copper or a copper alloy having a leakage detection function is used for the inner heat transfer tube, the occurrence of holes or cracks can be quickly detected.

Thus, as described in Patent Documents 1 and 2, a conventional heat transfer tube having a leakage function is composed of an outer tube and an inner tube inserted into the outer tube. In this configuration, a plurality of rectangular or triangular grooves extending in the axial direction are used, and the inner surface of the outer tube and the outer surface of the inner tube are brought into close contact with each other. Through internal CO ₂ refrigerant of the inner tube of the heat exchanger tube, by passing the water in the space between the outside of the outer heat transfer tube of the outer tube, through a heat transfer tube having a leakage function, CO ₂ refrigerant and water Heat exchange with the At this time, if the holes or cracks occurred in the heat transfer tube, the groove formed on the inner surface of the outer tube of the heat transfer tube, CO ₂ refrigerant or water to penetrate, CO ₂ refrigerant flowing through the heat exchanger It is possible to detect that a hole or crack has occurred in the heat transfer tube due to a decrease in pressure or a decrease in water pressure.

JP 2005-69620 A JP 2005-147469 A

  However, the conventional heat transfer tube having a leakage function uses an internally grooved tube in which a large number of grooves extending in the axial direction are formed on the inner surface of the outer tube, and there is a problem that the productivity is low and the manufacturing cost is high. . Moreover, although the groove itself is surrounded by the outer surface of the inner tube, the outer surface of the inner tube that covers the upper portion of the groove is not in contact with the outer tube. For this reason, the contact area between the inner surface of the outer tube and the outer surface of the inner tube is small. For example, when the groove is formed by matching the width of the groove with the interval between the grooves, the contact area between the inner surface of the outer tube and the outer surface of the inner tube Is only 50%. Therefore, the heat transfer performance is also lowered accordingly.

  The present invention has been made in view of such problems, and an object thereof is to provide a heat transfer tube and an outer tube having a leakage function with excellent productivity, low manufacturing cost, and excellent heat transfer performance. .

The heat transfer tube having a leakage function according to the present invention is a heat transfer tube having a leakage detection function of a double-pipe structure composed of an outer tube and an inner tube arranged inside the outer tube.
The outer tube has a cross-sectional shape orthogonal to the tube axis, the outer surface is circular, the inner surface is polygonal, the outer surface of the inner tube is circular and has a circular shape orthogonal to the tube axis , and the inner tube is disposed in the outer tube. In the inserted state, by reducing the diameter of the outer tube or expanding the diameter of the inner tube, the central part of the polygonal side of the outer tube is aligned with the circular circumference of the inner tube. A space exists between the polygonal corner portion of the outer tube and the circular circumferential portion of the inner tube.

In the heat transfer tube with this leakage detection function,
In the cross section perpendicular to the tube axis, Di is the outer diameter of the inner tube, N is the polygonal angle of the inner surface of the outer tube, and a contact length per location between the inner surface of the outer tube and the outer surface of the inner tube is a. The adhesion rate A represented by (a × N) / (Di × π) × 100 is preferably 5 to 95%.

In this case,
In the cross section perpendicular to the tube axis, the polygon of the inner surface of the outer tube has an angle of 5 to 16, the outer diameter of the outer tube before the diameter reduction is Do, and the outer diameter of the outer tube after the diameter reduction is Ds, The outer tube diameter reduction ratio ΔD represented by {(Do−Ds) / Do} × 100 is 3 to 25%, and the minimum distance Cl between the inner surface of the outer tube and the outer surface of the inner tube before the diameter reduction. Is preferably 0.02 to 0.8 mm.

  The outer tube has a plug having a polygonal cross section perpendicular to the tube axis arranged at the center of the outer tube, the outer tube is passed through a die having an annular inner surface, and the outer tube is plugged into the plug by the die. The polygon can be formed by a drawing process in which the outer tube is pulled out while pressing toward the center.

  The outer tube according to the present invention is used for manufacturing a heat transfer tube having the leakage detection function described above.

According to the present invention, the inner surface of the outer tube, forming a polygonal shape in cross section perpendicular to the tube axis, only reduced in diameter or diameter machining, it is possible to provide a leak function double tube structure Therefore, it is easy to manufacture and can be manufactured at low cost. Further, the contact area between the outer tube and the inner tube can be arbitrarily adjusted within a range of, for example, 5 to 95% by adjusting the degree of pressing between the outer tube and the inner tube, and is about 95%. If the contact area is high, the heat transfer performance can be remarkably improved.

It is a cross-sectional view showing a heat transfer tube having a leakage detection function according to an embodiment of the present invention. It is a figure which shows the method of manufacturing the outer tube | pipe of this heat exchanger tube. It is a cross-sectional view which shows the method of manufacturing this heat exchanger tube.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view orthogonal to the tube axis of a heat transfer tube having a leakage function according to an embodiment of the present invention. The outer tube 1 and the inner tube 2 inserted into the outer tube 1 are arranged in close contact with each other. As shown in FIG. 3B, the double pipe structure of the outer pipe 1 and the inner pipe 2 includes, for example, an inner pipe in the outer pipe 1 having a large inner space with respect to the outer diameter of the inner pipe 2. By inserting 2 and reducing the diameter of the outer tube 1 as shown in FIG. 3A, both can be manufactured in close contact with each other. In the present embodiment, the inner surface of the outer tube 1 forms a regular octagon in the cross-sectional shape orthogonal to the tube axis. Then, by reducing the diameter of the outer tube 1 and bringing the outer tube 1 and the inner tube 2 into close contact with each other, a regular octagonal side on the inner surface of the outer tube 1 is obtained as shown in FIGS. The central portion of the inner tube 2 comes into contact with the outer surface of the inner tube 2, and the contact portion 3 deforms the outer surface of the inner tube 2 to be substantially flat (a straight line in the cross section perpendicular to the tube axis). However, the regular octagonal corner portion on the inner surface of the outer tube 1 remains without contacting the outer surface of the inner tube 2, and the corner shape of the inner surface of the outer tube and the arc shape of the outer surface of the inner tube remain. This corner portion is left in the space without the outer tube 1 and the inner tube 2 being in contact with each other, and serves as a gap 4 as a leakage detector.

  In the present embodiment, the inner surface of the outer tube 1 has a polygonal shape (in the illustrated example, a regular octagon) in a cross section perpendicular to the tube axis. The outer tube 1 can be manufactured as shown in FIG. As shown in FIG. 2 (b), a plug 11 having a polygonal (for example, regular octagonal) machining surface whose outer surface is a cross section perpendicular to the tube axis is inserted into a die 10 having an annular inner surface, and a cylindrical tube. The outer tube 1 shown in FIG. 3A is manufactured by passing the raw tube 1a between the die 10 and the plug 11 and drawing the raw tube 1a. The end surface 12 at the processed rear end of the plug 1 has a polygonal shape (regular octagon), and the processed surface 14 on the inner surface of the raw tube 1a has an opening angle of 22 °, for example. The opening angle of the processing surface 13 on the inner surface of the die 10 is, for example, 27 °. In this way, the outer tube 1 having the cross-sectional shape shown in FIG. 2A can be manufactured by drawing.

And this outer tube | pipe 1 is a thing before diameter reduction processing, and has a larger internal space than the inner tube | pipe 2, as shown in FIG.3 (b). In other words, the outer tube 1 before the diameter reduction processing is provided with a clearance Cl between the regular octagonal flat portion and the arc outer surface of the inner tube 2. Note that the thickness of the corner of the inner surface of the outer tube 1 is Ts. Then, as shown in FIG. 3B, by inserting the inner tube 2 into the outer tube 1 and reducing the diameter of the outer tube 1, the inner surface of the outer tube 1 as shown in FIG. Is pressed into the outer surface of the inner tube 2 to form a flat contact portion 3 between the outer surface of the inner tube 2 and the inner surface of the outer tube 1. The length of the contact portion 3 in the cross section perpendicular to the tube axis is a, and the outer surface of the inner tube 2 is recessed at the center of the contact portion 3, that is, the outer surface of the inner tube 2 before the outer tube 1 is reduced in diameter. The interval between the outer tube 1 and the flat surface of the inner tube 2 after the diameter reduction processing is defined as γ. By reducing the diameter of the outer tube 1, a contact portion 3 is formed between the outer tube 1 and the inner tube 2, and a gap 4 is formed at a corner of the inner surface of the outer tube 1 to transmit the double tube structure. The heat pipe is completed. In this heat transfer tube, the heat transfer action as a heat transfer tube is performed in the contact portion 3. Further, in the gap 4, as a leak detection unit, when a hole or a crack occurs in the heat transfer tube, CO ₂ refrigerant or water leaks into the gap 4, and the flow pressure of these refrigerant or water decreases. , Has a function to detect the leakage.

  In addition, this invention is not restricted to the said embodiment, A various deformation | transformation is possible. First, in the above-described embodiment, the outer tube 1 is reduced in diameter to achieve close contact between the outer tube 1 and the inner tube 2, but conversely, the inner tube 2 is increased in diameter to increase the outer tube 1. The inner tube 2 may be closely attached. Moreover, in the said embodiment, although the polygonal shape in a tube-axis orthogonal cross section is formed in the inner surface of the outer tube 1, the polygonal shape in a tube-axis orthogonal cross section can also be formed in the outer surface of the inner tube 2.

Next, the configuration of the embodiment of the present invention will be described in more detail. Both the outer tube 1 and the inner tube 2 are preferably made of copper or a copper alloy tube. Among them, the outer tube 1 is made of CO ₂ refrigerant flowing inside the inner tube 2 and water flowing outside the outer tube 1. In order to exchange heat between the two, it is desirable to use a variety having excellent thermal conductivity and corrosion resistance. In addition, the material of the inner tube 2 may be of a type that has a strength equal to or higher than that of the outer tube 1 and has excellent thermal conductivity because the CO ₂ refrigerant flowing inside the inner tube 2 may be at a high pressure. It is desirable.

  The adhesion rate A is expressed as A = (a × N) / (Di × π) × 100 when a polygon is formed on the inner surface of the outer tube 1 in a cross section orthogonal to the tube axis. However, a is the length of the contact part 3 in a cross section orthogonal to the tube axis, as shown in FIG. N is the number of polygons on the inner surface of the outer tube. Di is the outer diameter of the inner tube 2. The length a of the contact portion 3 can be obtained by actual measurement from cross-sectional observation of the heat transfer tube after the diameter reduction processing. The adhesion rate A is preferably 5 to 95% in consideration of the heat exchange performance and the leakage detection performance. More preferably, the adhesion rate A is 10 to 80%.

The length a of the contact portion 3 may be obtained from an actually measured value of cross-sectional observation. However, by design, the outer tube 1 at the time of diameter reduction defines a crushing margin γ where the inner tube 2 is crushed, and a = √ [ Di ^2- (Di-γ) ² ] can also be obtained. That is, if the crushing allowance γ is defined in design, a can be obtained from the above equation, and the adhesion rate A can be calculated.

  Further, in the case where a polygon is formed on the outer surface of the inner tube 2 in a cross section perpendicular to the tube axis instead of a polygon on the inner surface of the outer tube 1, the adhesion rate A is assumed in the same manner. can do. Also in this case, the adhesion rate A is preferably 5 to 95%. Eventually, the inner surface of the outer tube 1 and the inner tube 2 both in the case where a polygon is formed on the inner surface of the outer tube 1 with a cross section orthogonal to the tube axis and in the case where a polygon is formed on the outer surface of the inner tube 2 with a cross section orthogonal to the tube axis. When the length of the contact portion between the outer surface and the outer surface of the outer tube 1 or the outer surface of the inner tube 2 is b is the circumferential length of the circular surface before processing, the adhesion rate A can be represented by A = (a / b) × 100, and the adhesion rate A is preferably 5 to 95%.

  The number N of corners of the outer tube 1 is preferably 5 to 16 from the viewpoint of adhesion between the outer tube 1 and the inner tube 2. A more desirable range of N is 5-12.

  The diameter reduction ratio ΔD of the outer tube 1 is preferably 3 to 25% from the viewpoint of workability, such as variations in elongation of the outer tube 1 during diameter reduction. A more preferable range of the diameter reduction rate ΔD is 5 to 15%.

  The outer diameter Do of the outer tube 1 depends on the overall design of the heat exchanger, but is preferably 3 to 10 mm as a practical range. The outer diameter Di of the inner tube 2 is naturally smaller than that of the outer tube 1, but the range is desirably 2 to 8 mm.

  In this case, the minimum clearance Cl between the outer tube 1 and the inner tube 2 before the diameter reduction, that is, the clearance Cl that is the minimum value of the distance between the flat portion of the outer tube 1 and the arc of the inner tube 2 is From the viewpoint of insertability of the tube 2 into the outer tube 2 and workability such as diameter reduction, it is preferably 0.02 to 0.8 mm. Further, the minimum wall thickness Ts of the outer tube 1 before the diameter reduction, that is, the wall thickness Ts of the corner portion of the outer tube 1 before the diameter reduction is 0.2 to 0. It is preferably 8 mm.

Test example 1
Hereinafter, in the numerical limitation of the present invention, the effect of the embodiment that falls within the numerical limitation range will be described in comparison with a comparative example that deviates from the numerical limitation range. In the present invention, it is needless to say that this numerical limitation is not an essential component, and the present invention is defined by the technical scope of claim 1.

  Using the heat transfer tubes of the five types shown in Table 1 below and the heat transfer tubes of the three types of comparative examples, the productivity and leakage detection performance of the heat transfer tubes were determined.

  Examples 1 to 5 were excellent in adhesion and excellent in leakage detection function. On the other hand, in Comparative Example 1, Do was 5.66 mm and Ds was 5.30 mm as in Example 1, but γ was negative and did not adhere to the inner tube. In Comparative Example 2, since N is large and the adhesion rate A exceeds 100% (because adhesion is made in all regions, the actual adhesion rate is 100%, but the calculation of A exceeds 100%. ) Leakage detection performance is extremely reduced. In Comparative Example 3, the clearance Cl is small, and the insertability of the inner tube is extremely deteriorated. Still, when a leak detection tube is manufactured, γ becomes large, the adhesion rate A becomes 97%, and the leak detection performance is extremely lowered. In addition, the inner tube has also been deformed into a square cross section.

Test example 2
Next, with respect to the heat transfer tube of Example 1 and Example 2 above and the heat transfer tube manufactured by using an inner grooved tube having an outer diameter of 5.3 mm as in the conventional case, the heat transfer performance, leakage detection performance, and Productivity was compared. The results are shown in Table 2 below.

As for the heat transfer performance, the outer heat transfer tube having an outer diameter of 8 mm, the wall thickness of 0.6 mm, and the length of 3 m is used as the inner heat transfer tube. Is inserted, water is caused to flow in the annular space between the outer heat transfer tube and the inner heat transfer tube, and the CO ₂ refrigerant that has been pressurized and brought into a supercritical state is caused to flow into the inner heat transfer tube in a countercurrent flow. The temperature difference between the inlet and outlet of water flowing through the space was measured to evaluate the heat transfer performance and leakage detection performance.

  The leak detection performance is that a minute hole is artificially formed in the longitudinal center of the heat transfer tube as the inner heat transfer tube, air is poured into the heat transfer tube at a constant pressure, and a leak consisting of a gap is made within one minute. It was confirmed whether air could be detected from the detection part.

  Regarding productivity, in order to manufacture the outer tube of the heat transfer tube of Example 1 and Example 2, the raw tube (outer diameter: about 8.6 mm) was drawn. In the conventional example, the inner pipe was subjected to a grooved rolling process through an annealing process to obtain an internally grooved pipe. When the outer tube of the heat transfer tube is manufactured by drawing using a 300 kg base tube (Examples 1 and 2), and the outer tube of the heat transfer tube is manufactured by annealing and grooved rolling The overall apparatus operating time (conventional example) was compared.

  As shown in Table 2, the heat transfer performance of Example 1 of the present invention is 3% higher than that of the conventional example, and the heat transfer performance of Example 2 of the present invention is equivalent to that of the conventional example. However, the productivity of Examples 1 and 2 of the present invention was four times that of the conventional example, and the manufacturing time could be shortened to ¼ the time of the conventional example.

1: Outer tube 2: Inner tube 3: Contact part 4: Gap

Claims (5)

In a heat transfer tube having a leak detection function of a double tube structure composed of an outer tube and an inner tube arranged inside the outer tube,
The outer tube has a cross-sectional shape orthogonal to the tube axis, the outer surface is circular, the inner surface is polygonal, the outer surface of the inner tube is circular and has a circular shape orthogonal to the tube axis , and the inner tube is disposed in the outer tube. In the inserted state, by reducing the diameter of the outer tube or expanding the diameter of the inner tube, the central part of the polygonal side of the outer tube is aligned with the circular circumference of the inner tube. A heat transfer tube having a leakage detection function, wherein a space exists between the polygonal corner portion of the outer tube and the circular circumferential portion of the inner tube. In the cross section perpendicular to the tube axis, Di is the outer diameter of the inner tube, N is the polygonal angle of the inner surface of the outer tube, and a contact length per location between the inner surface of the outer tube and the outer surface of the inner tube is a. 2. The heat transfer tube having a leakage detection function according to claim 1, wherein an adhesion rate A represented by (a × N) / (Di × π) × 100 is 5 to 95%. In the cross section perpendicular to the tube axis, the polygon of the inner surface of the outer tube has an angle of 5 to 16, the outer diameter of the outer tube before the diameter reduction is Do, and the outer diameter of the outer tube after the diameter reduction is Ds, The outer tube diameter reduction ratio ΔD represented by {(Do−Ds) / Do} × 100 is 3 to 25%, and the minimum distance Cl between the inner surface of the outer tube and the outer surface of the inner tube before the diameter reduction. The heat transfer tube having a leakage detection function according to claim 2, wherein is 0.02 to 0.8 mm. The outer tube has a plug having a polygonal cross section arranged at the center of the outer tube, the outer tube is passed through a die having an annular inner surface, and the outer tube is pressed toward the plug by the die. 4. The heat transfer tube having a leakage detection function according to claim 1, wherein the polygon is formed by drawing the outer tube. An outer tube used for manufacturing a heat transfer tube having a leakage detection function according to any one of claims 1 to 4.

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