JP2005257160A - Heat transfer pipe with grooved inner surface and heat exchanger using the heat transfer tube with grooved inner surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat transfer tube with grooved inner surface, in which an inner surface fin does not fall down during expanding the tube, and which is suitable for a heat exchanger using carbon dioxide as a refrigerant. <P>SOLUTION: A heat transfer tube with grooved inner surface for use in an heat exchanger, comprising fins formed on the tube inner surface, wherein a first fin has a height of 0.10 mm to 0.22 mm, an apex angle of 20° to 60° and a ratio of the curvature radius to height of the top part of 5 or more, or a ratio of the width of a plane part to fin height of the top part of 0.3 to 1.0; a second fin has an apex angle of 20° to 60° and a height ratio of the first to second fins of 0.5 to 0.9; the thickness "t" of the pipe is 0.4 mm or more, and the ratio t/D of the thickness "t" to an outer diameter "D" ranges from 0.04 to 0.25. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat exchanger tube used in a water heater or an air conditioner, and more particularly to an internally grooved heat transfer tube used as a heat transfer tube of a heat exchanger using carbon dioxide as a refrigerant.

  Conventionally, evaporators and condensers, which are heat exchangers of air conditioners such as air conditioners, have a rolling process step in which a spiral inner fin is provided on the inner surface of a heat transfer tube, and an inner grooved transmission obtained by the rolling process. The heat pipe is press-fitted into a heat radiating plate fin, and is manufactured by a pipe expanding process for expanding the heat transfer pipe.

  The heat transfer tube usually has an inner fin formed inside the tube by inserting a grooved plug into the tube and pressing the tube against the plug with a ball rotating from the periphery. The plate fin is plate-shaped and has a hole larger than the outer diameter of the heat transfer tube. The heat transfer tube is inserted into the plate fin and then expanded. That is, an operation of bringing the tube and the plate fin into close contact is performed by inserting a tube expansion plug into the heat transfer tube and enlarging the diameter of the heat transfer tube.

  At this time, since the inner fins of the heat transfer tubes are pressed by the tube expansion plug, the inner fin tops are crushed and deformed, and fin collapse occurs. Further, the distribution of the pressing force causes an excessive stress to be applied to the plate fins, resulting in cracks. As a result, there arises a problem that the heat exchange efficiency is lowered. In order to solve this problem, there is an example of an internally grooved tube provided with an internal fin having a flat top surface and a trapezoidal cross section on the inner surface of the tube (for example, see Patent Document 1).

  However, since the inner fin is larger than the conventional fin, there is a problem that the weight of the heat transfer tube is increased and the cost is increased accordingly. If the number of internal fins is reduced to suppress the increase in weight, the heat transfer performance is reduced.

  There is an example in which the weight is reduced without reducing the heat transfer performance by defining the shape of the inner fin (see, for example, Patent Document 2). In addition, there is an example in which heat transfer performance is improved by forming inner fins of two or more heights (see, for example, Patent Documents 3, 4, and 5).

Japanese Patent Laid-Open No. 4-327792 Japanese Patent Laid-Open No. 11-201680 Japanese Patent Laid-Open No. 7-4884 JP-A-8-233480 JP-A-8-145583

  By the way, recently, due to environmental problems, the development of a heat cycle apparatus using chlorofluorocarbons, particularly carbon dioxide, has been carried out. In order to use the carbon dioxide as a refrigerant, it is necessary to increase the operating pressure of the refrigerant. For this reason, the heat transfer tube requires strength, and a heat transfer tube having a thicker wall thickness than that for an air conditioner is used. At this time, if there are two or more types of inner fin heights, the distribution of the pressing force occurs during tube expansion, and the pressing force exceeding the strength of the grooved plug material is generated depending on the site, causing damage to the plug and collapse of the inner fin. .

  An object of the present invention is to reduce the increase in weight of a thick inner surface grooved heat transfer tube that uses a refrigerant having a high operating pressure typified by carbon dioxide, even if the tube is expanded, and the inner fin does not collapse. The object is to provide an internally grooved heat transfer tube.

The present inventors have researched heat transfer tubes with internal grooves suitable for heat exchanger applications, especially heat exchangers that use carbon dioxide as a refrigerant, and found the relationship between the shape of the internal fins and the collapse of the internal fins during the tube expansion process. As a result, the inventors have completed the invention of an internally grooved heat transfer tube suitable for a carbon dioxide refrigerant. That is, the present invention
(1) In an internally grooved tube in which fins are formed on the tube inner surface, the first fin has a height of 0.10 to 0.22 mm, the apex angle is 20 to 60 degrees, and the ratio of the radius of curvature and the height of the apex portion 5 or more, the apex angle of the second fin is 20 to 60 degrees, the ratio of the height of the second fin to the height of the first fin is 0.5 to 0.9, The wall thickness t is 0.4 mm or more, and the ratio t / D with the outer diameter D of the tube is in the range of 0.04 to 0.25. ) In an internally grooved tube in which fins are formed on the inner surface of the tube, at least a part of the top of the first fin has a flat surface, and the ratio of the width of the flat surface of the top to the height of the fin is 0.3 to 1. Heat exchange using the internally grooved heat transfer tube for the heat exchanger according to (1) (3) (1) or (2), characterized by being 0.0 In vessel (4) (3) A heat exchanger according, there is provided a heat exchanger wherein the refrigerant is carbon dioxide.

  The inner surface grooved heat transfer tube of the present invention is particularly intended for a thick inner surface grooved heat transfer tube that uses a refrigerant having a high operating pressure such as carbon dioxide. Since a fall or the like does not occur and an increase in weight can be suppressed, a heat transfer tube suitable for a carbon dioxide refrigerant can be provided.

  Hereinafter, the reason for numerical limitation regarding the internally grooved pipe according to the present invention will be described. 1 and 2 show the outer diameter D of the internally grooved tube, the wall thickness t, the height h1 of the first fin, the radius of curvature R1 of the top of the first fin, and the top flat portion of the first fin. Schematic cross-sectional view for explaining the width wf1, the apex angle γ1 of the first fin, the height h2 of the second fin, the apex angle γ2 of the second fin, and the curvature radius R2 of the apex of the second fin It is.

  FIG. 1 is an example of the internally grooved tube of the present invention. The internally grooved heat transfer tube according to the present invention has a wall thickness t of at least 0.4 mm and a ratio t / D of the outer diameter D to the wall thickness t of 0.04 to 0.25. Thereby, even if the refrigerant | coolant which uses supercritical cycles, such as a carbon dioxide, is high pressure, it can be used. If t / D is less than 0.04, the strength of the tube is low, so that it cannot withstand the pressure of the refrigerant and is destroyed. If it exceeds 0.25, the strength of the tube will be high, but rolling will not be possible. Preferably the value of t / D is 0.05-0.20, more preferably 0.06-0.10. However, the wall thickness t needs to be at least 0.4 mm. Generally, the smaller the outer diameter of the tube, the higher the pressure resistance of the tube, but if it is less than 0.4 mm, the strength of the bent portion is insufficient and cracks occur. Considering bending of the tube, the outer diameter D is preferably 4.0 to 10.0 mm. Further, the wall thickness t is preferably 0.4 to 1.0 mm from the viewpoint of the rolling process on the inner surface of the pipe.

  The internally grooved heat transfer tube of the present invention has two types of internal fins with different fin heights, and the higher fin height is the first fin and the lower fin is the second fin. Here, the fin height means the difference between the distance from the tube center to the groove portion on the inner surface of the tube and the distance from the tube center to the top of the inner surface fin. The apex angle of the fin means an angle formed by one side surface of the inner fin and the other side surface. The width of the fin plane portion means a distance between two tangent lines, that is, a tangent line formed by one side surface of the top surface of the inner fin and a tangent line formed by the other side surface. The torsion angle of the fin refers to an angle formed by the tube axis direction and the direction in which the inner surface fin extends when the inner grooved tube is cut in parallel with the tube axis and deployed.

  The height h1 of the first fin is 0.10 to 0.22 mm. If it is less than 0.10 mm, the heat transfer characteristics are inferior, and if it exceeds 0.22 mm, rolling cannot be performed. Preferably it is 0.13-0.20 mm. The apex angle γ1 of the first fin is 20 to 60 degrees. If it is less than 20 degree | times, the fall of an internal fin will arise in a pipe expansion process. If it exceeds 60 degrees, the contact area with the refrigerant decreases and the heat transfer performance deteriorates. Preferably it is 25-40 degrees. The top of the first fin is a curved surface having a radius of curvature R1 toward the center of the tube, and may be convex or flat. Even if the top portion is concave toward the center of the pipe, the heat transfer performance is not improved, and the cost is increased in the rolling process. The ratio R1 / h1 between the curvature radius R1 of the fin top and the height h1 of the fin is 5 or more. If it is less than 5, the fins on the inner surface will fall during the tube expansion process. Preferably it is 15 or more. The radius of curvature R1 is preferably 0.03 mm or more, and it is more preferable as it is larger.

  FIG. 2 is an example of the internally grooved tube of the present invention having a flat surface at least at a part of the top of the first fin. In the shape of the first fin, it is sufficient that the R1 / h1 ratio is approximately 5 as in the case where the ratio is 5 or more, but it is more preferable that the top is a plane. In the inner fin, the ratio wf1 / h1 between the width wf1 of the planar portion and the fin height h1 is set to 0.3 to 1.0. If it is less than 0.3, the fins on the inner surface will fall in the tube expansion process. If it exceeds 1.0, the contact area between the refrigerant and the tube will decrease and the heat transfer performance will deteriorate, and the weight of the tube will increase. Preferably it is 0.35-0.5.

  Next, the second fin will be described. The ratio h2 / h1 between the height h2 of the second fin and the height h1 of the first fin is 0.5 to 0.9. If it is less than 0.5, the pressing force applied to the part where the grooved plug and the first fin are in contact with each other in the rolling process is increased, and the grooved plug is damaged. If it exceeds 0.9, the contact area between the refrigerant and the tube decreases, and the desired heat transfer performance cannot be obtained. Preferably it is 0.5-0.8. The apex angle γ2 of the second fin is 20 to 60 degrees. If it is less than 20 degrees, the inner fins cannot be formed with high accuracy in the rolling process, and the heat transfer performance is degraded. If it exceeds 60 degrees, the contact area between the refrigerant and the tube will decrease, and the heat transfer performance will deteriorate. Preferably it is 25-40 degrees. The radius of curvature R2 of the top of the second fin is 0.02 mm or more. If it is smaller than 0.02 mm, the rolling process cannot be performed. Preferably it is 0.035 mm or more.

  The twist angles of the first fin and the second fin are the same. If the angle is different, the rolling process becomes complicated and the cost increases. The twist angle is 5 to 80 degrees. If it is less than 5 degrees, the heat transfer performance is lowered because the stirring effect of the refrigerant is small. If it exceeds 80 degrees, not only the stirring effect of the refrigerant is saturated, but also the pressing force applied to the grooved plug in the rolling process increases and breaks. Considering the fact that it can be stably processed for manufacturing and the manufacturing cost is suppressed, it is preferably 5 to 30 degrees. The ratio of the number of first fins to the number of second fins is 0.7 to 1.5. If it is less than 0.7 or exceeds 1.5, the area where the refrigerant and the pipe come into contact with each other is reduced, and the heat transfer performance is poor. The number of first fins and second fins is preferably the same.

  The internally grooved heat transfer tube and the heat exchanger of the present invention are manufactured by an ordinary method. That is, a rolling process is performed in which fins are formed on the inner surface of a pipe by inserting a grooved plug into the pipe and pressing the pipe against the plug with a ball rotating from the periphery. Further, a heat transfer tube is inserted into a plate fin having a hole larger than the outer diameter of the heat transfer tube, and then a tube expansion plug is inserted into the heat transfer tube to enlarge the diameter of the heat transfer tube, thereby bringing the tube and the plate fin into close contact with each other. A pipe expansion process is performed to manufacture a heat exchanger. The plate fin is formed of a metal material such as aluminum or an aluminum alloy.

  The material of the internally grooved heat transfer tube of the present invention may be any material that is excellent in heat conduction. For example, metals such as copper, copper alloy, aluminum, aluminum alloy, iron and the like can be mentioned. Among them, copper is preferably 99.0% or more and other unavoidable impurities. More preferably, it consists of JIS C 1020 (oxygen-free copper), JIS C 1100 (tough pitch copper), and JIS C 1200 (phosphorus deoxidized copper).

Next, the present invention will be described in more detail based on examples.
A heat transfer tube shown in Table 1 was manufactured by rolling a tube made of phosphorous deoxidized copper (JIS C 1200), and the heat transfer rate was measured as the heat transfer performance before tube expansion. Next, the heat transfer tube was expanded with a tube expansion plug and attached to an aluminum fin, and the presence or absence of an internal fin collapsed and the presence or absence of cracking of the aluminum fin were evaluated. Further, the heat transfer tube was removed from the aluminum fin, and the heat transfer coefficient was measured as the heat transfer performance after the tube expansion. Except for Comparative Example 6, the outer diameter D was 7 mm, the wall thickness t was 0.6 mm, the total number of inner fins was 60, the twist angle was 10 degrees, and the apex angle γ2 of the second fin was 25 degrees. Comparative Example 6 is a smooth tube, and there is no groove on the tube inner surface.

In addition, the measuring method of each evaluation item is as follows. Regarding the measurement of the inner surface of the tube, the tube was cut and polished with # 1000 polishing paper, and then photographed with an optical microscope at a magnification of 100 to measure the cross-sectional shape. For the heat transfer performance evaluation, a sample was inserted as an inner tube of a horizontally installed double tube heat exchanger, and a pressure of 3 MPa was introduced at the inlet side of the internally grooved heat transfer tube for measuring carbon dioxide as a refrigerant in the sample. with flowing in the refrigerant flow rate of 400 kg / m 2 ^sec in the the double tube portion between the outer tube and the inner tube flowing in opposite the cooled water against refrigerant, by heat exchange the coolant CO Evaporate. In addition, the degree of superheat of 1 ° C. was set on the carbon dioxide outlet side of the internally grooved heat transfer tube, the exchange heat quantity was measured, and the evaporation heat transfer coefficient in the tube was calculated. However, the evaporation heat transfer coefficient in the tube is based on the outer surface of the tube, and the evaluation includes a value including the heat conductivity of the tube itself. In addition, when the fin collapsed in the axial direction of the heat transfer tube, the refrigerant was flowed in the same direction as the direction in which the fin fell.

  From the results shown in Table 1, the heat transfer coefficient of the present invention example was high before and after the expansion, and neither the inner fin collapsed nor the aluminum fin cracked due to the expansion. However, in Comparative Example 1, the height of the first fin was 0.25 mm, which was outside the scope of the present invention, so that the inner fin collapsed and the aluminum fin cracked. In Comparative Example 2, since the relationship between the length of the top flat portion of the first fin and the fin height was outside the scope of the present invention, the inner fin collapsed and the aluminum fin cracked. In Comparative Example 3, since the apex angle of the first fin was smaller than 20 degrees and out of the scope of the present invention, the inner fin collapsed and the aluminum fin cracked. In Comparative Example 4, since the relationship between the radius of curvature of the top of the first fin and the fin height was outside the scope of the present invention, the inner fin collapsed and the aluminum fin cracked. In Comparative Examples 1 to 4, the heat transfer coefficient after pipe expansion is significantly reduced due to the fall of the inner fins. In Comparative Example 5, the fin collapse did not occur, but the area where the refrigerant and the pipe contacted was small because the number of the first fins was small, and the heat transfer performance was inferior to that of the present invention example. In Comparative Example 6, the heat transfer coefficient was inferior because there were no tube inner fins.

  The inner grooved heat transfer tube was rolled and manufactured in the same manner as in Example 1. The tube dimensions were as shown in Table 2. However, the total number of inner fins was 60, and the number of first fins was 30. For the second fin, the number of fins was 30, the radius of curvature R2 at the top was 0.04 mm, and the apex angle γ2 was 25 degrees. The evaluation method was the same as in Example 1.

  From the results shown in Table 2, the heat transfer coefficient of the present invention example was high, and neither the inner fin collapsed nor the aluminum fin cracked due to the expansion. However, in Comparative Example 7, since the apex angle of the first fin was smaller than 20 degrees and was outside the scope of the present invention, the inner fin collapsed and the aluminum fin cracked. In Comparative Example 8, the height of the first fin was 0.25 mm, which was outside the scope of the present invention, so that the inner fin collapsed and the aluminum fin cracked. In Comparative Example 9, since the apex angle of the first fin was smaller than 20 degrees and out of the scope of the present invention, the inner fin collapsed and the aluminum fin cracked.

  In the same manner as in Examples 1 and 2, the internally grooved heat transfer tube was rolled to produce a desired outer diameter. The inner fin shape and the state of the grooved plug at the time when the rolling process was performed 4000 m in length were visually confirmed. The tube dimensions were as shown in Table 3. However, the total number of fins was 60. For the second fin, the twist angle was 10 degrees and the curvature radius at the top was 0.04 mm. The evaluation method was the same as in Example 1.

  From the results shown in Table 3, the heat transfer coefficient of the present invention example was high, and neither the inner fin collapsed nor the aluminum fin cracked due to the expansion. However, in Comparative Example 10, since the apex angle of the second fin was smaller than 20 degrees and outside the scope of the present invention, the intended inner fin could not be processed by rolling. In Comparative Example 11, since the relationship between the height of the first fin and the height of the second fin was outside the scope of the present invention, the grooved plug was damaged and the production was stopped midway.

It is a cross-sectional schematic diagram which shows the inner surface grooved heat exchanger tube of this invention. It is a cross-sectional schematic diagram which shows the inner surface grooved heat exchanger tube of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat-transfer tube with inner surface groove 2 Groove part 3 1st fin 4 2nd fin

Claims (4)

In an internally grooved tube in which fins are formed on the tube inner surface, the first fin has a height of 0.10 to 0.22 mm, the apex angle is 20 to 60 degrees, and the ratio of the curvature radius to the height of the apex is 5 or more. The apex angle of the second fin is 20 to 60 degrees, the ratio of the height of the second fin to the height of the first fin is 0.5 to 0.9, and the wall thickness t of the tube Is 0.4 mm or more, and the ratio t / D to the outer diameter D of the tube is 0.04 to 0.25. In the internally grooved tube in which fins are formed on the tube inner surface, at least a part of the top portion of the first fin has a flat surface, and the ratio of the width of the flat portion of the top portion to the fin height is 0.3 to 1. The heat transfer tube with an inner surface groove for a heat exchanger according to claim 1, wherein the heat transfer tube is zero. A heat exchanger using the internally grooved heat transfer tube according to claim 1 or 2. 4. The heat exchanger according to claim 3, wherein the refrigerant is carbon dioxide.

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