JP2012002453A - Heat transfer tube with inner face groove, and heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer tube with inner face grooves, which is configured to minimize the collapse or tilting of a fin tip in tube expanding processing, and to provide a heat exchanger excellent in heat-exchange performance.SOLUTION: In the heat transfer tube with inner surface grooves 1, the ratio of the height (Hf) of the highest one of first fins 4 to the height (Hf) of the lowest one of second fins 5 (Hf/Hf) is set to 1.15 or less. The height difference between the height (Hf) of the highest first fin 4 and the height (Hf) of the lowest second fin 5 is set to 0.02 mm or less.

Description

  The present invention relates to an internally grooved heat transfer tube that is preferably used when a refrigerant flows in a tube to exchange heat with an external fluid, and a heat exchanger excellent in heat exchange performance.

  As an example of a heat exchanger applied to an air conditioner, a refrigerator, etc., a plate fin that exchanges heat with an external fluid by causing the refrigerant to flow in the pipe and causing the refrigerant to evaporate or condense. There is a tube-type heat exchanger.

  This plate fin tube type heat exchanger includes a plurality of plate-like fins arranged in parallel with a constant interval, and inserts and expands a heat transfer tube into a through-hole formed through each plate-like fin. It is formed by that. With the heat exchanger having such a configuration, heat exchange is performed between the fluid flowing between the plurality of plate-like fins and the chlorofluorocarbon refrigerant, alternative chlorofluorocarbon refrigerant, or carbon dioxide refrigerant flowing inside the heat transfer tube.

  This heat exchanger is required to have good heat exchange performance and light weight. The heat transfer tube used for it has good heat transfer performance with the refrigerant flowing in the tube, good heat transfer performance with the other plate-like fin, and the weight of the tube is small. Desired.

  As an example of this type of heat transfer tube, a plurality of spiral fins extending in the longitudinal direction of the tube are formed with a certain height, and an internally grooved heat transfer tube in which a spiral groove is formed between each spiral fin is provided. It has been proposed (see, for example, Patent Document 1). According to the inner surface grooved heat transfer tube, the inner surface area of the tube is increased as compared with a smooth tube having no spiral fin or spiral groove on the inner surface, so that the heat transfer efficiency in the tube can be improved.

  As another example of this heat transfer tube, an internally grooved heat transfer tube in which a height difference is provided in the fin height of a plurality of spiral fins has been proposed (for example, see Patent Document 2). According to the heat transfer tube with an inner surface groove, since the material required per unit length can be reduced by the amount of the helical fin formed with a low fin height, the inner surface groove described in Patent Document 1 is used. Compared to the attached heat transfer tube, the weight of the heat transfer tube can be reduced.

JP-A-8-327272 JP 2002-350080 JP

  By the way, when manufacturing a plate fin tube type heat exchanger using an internally grooved heat transfer tube, an internally grooved transfer is formed in through holes formed through a plurality of plate fins arranged in parallel at regular intervals. After inserting the heat pipe, a tube expansion jig slightly larger than the minimum inner diameter determined by the tip of the spiral fin is inserted into the heat transfer pipe. The heat transfer tube is expanded by the insertion force of the tube expansion jig, and the outer surface of the heat transfer tube and the plate fins are fixed in close contact with each other.

  In the heat transfer tube with an inner surface groove described in Patent Document 2, a good heat transfer performance can be obtained in a test for a heat transfer tube or a single unit. However, when a heat exchanger subjected to the above-described tube expansion processing is created, a good heat transfer performance is obtained. Heat transfer performance cannot be obtained. That is, if a spiral fin having a fin height lower than that of the spiral fin formed at a certain height as in the above-mentioned Patent Document 1 is manufactured, compared with the spiral fin described in the above-mentioned Patent Document 1. In addition, there is a problem that the heat exchange performance of the heat exchanger is lowered.

  Therefore, the present invention has been made to solve the above-described conventional problems, and a specific object thereof is an internally grooved heat transfer tube that exhibits good heat transfer performance even after tube expansion processing, and The object is to provide a heat exchanger with excellent heat exchange performance.

  The inventors of the present invention have repeatedly examined the fin heat transfer tubes having a plurality of heights, and confirmed the following phenomenon. That is, the tube expansion jig contacts only the spiral fin having a high fin height, and the tip of the spiral fin having a high fin height contracts and deforms when crushed by the contact with the tube expansion jig. . The tip of a spiral fin having a low fin height is less susceptible to deformation than a spiral fin having a high fin height. Furthermore, since the pipe expansion jig does not come into contact with the fin with a low fin height, the pressure to the fin with a high fin height is excessive as compared with the internally grooved heat transfer tube with a constant fin height. It turned out that it is easy to receive the shape change which the tip of a fin crushes excessively or tilts.

  In pipe expansion processing of internally-grooved heat transfer tubes with different heights in the fin height, we have intensively studied to solve the above problems based on the phenomenon that the tip of the fin is excessively crushed or tilted locally. However, if the fin height ratio and / or fin height difference is set to a predetermined value, the inner grooved heat transfer tube can be expanded while suppressing the collapse and tilting of the fin tip in the tube expansion process. I found out that I was able to achieve unexpected results and that I could form an excellent product that would not cause any practical problems.

That is, in order to achieve the above-mentioned object, the present invention has a plurality of fins in which concave and convex grooves are formed on the inner surface of the tube in the longitudinal direction of the tube, and the plurality of fins include the first fin and the first fin. The second fin is lower than the height, and the ratio (Hf ₁ / Hf ₂ ) between the highest height (Hf ₁ ) of the first fin and the lowest height (Hf ₂ ) of the second fin is defined. An internally grooved heat transfer tube characterized by being set to 1.15 or less is provided.

In the internally grooved heat transfer tube according to the present invention, in addition to the above configuration, the height difference between the highest first fin height (Hf ₁ ) and the lowest second fin height (Hf ₂ ) is 0.02 mm. It is preferable to set the following.

  In the internally grooved heat transfer tube according to the present invention, it is preferable to set the number of fins of the lowest second fin to the same number as the highest first fin. In addition, it is more preferable to alternately arrange the lowest second fin and the highest first fin.

  In the internally grooved heat transfer tube according to the present invention, the number of fins of the lowest second fin may be set smaller than the number of highest first fins, or the number of fins of the lowest second fin may be the largest. The number may be set higher than that of the high first fin.

  Furthermore, in the present invention, in order to achieve the above object, there is provided a heat exchanger characterized by including a tube heat transfer tube obtained by expanding the inner surface grooved heat transfer tube.

  According to the present invention, fin crushing and fin tilt in tube expansion processing are reduced, and stable heat exchange performance can be sufficiently ensured.

(A) is sectional drawing which shows typically the heat transfer tube with an inner surface groove | channel which is 1st Embodiment suitable for this invention, (b) is a part which shows the part enclosed by the dotted line of (a) It is a cross-sectional enlarged view. It is the fragmentary sectional view which notched the heat transfer tube with an inner surface groove | channel which is 1st Embodiment along the pipe longitudinal direction. It is a figure for demonstrating the assembly of the heat exchanger which concerns on 2nd Embodiment to which the inner surface grooved heat exchanger tube which is 1st Embodiment is applied. The partial cross section of the inner surface grooved heat exchanger tube before pipe expansion processing is shown, (a) is a fin partial cross section according to Example 1, (b) is a partial cross section according to Example 2, and (c) is Comparative Example 1. It is a fin partial cross section, (d) is a fin partial cross section of Comparative Example 2. The partial cross section of the inner surface grooved heat exchanger tube after pipe expansion processing is shown, (a) is a fin partial cross section according to Example 1, (b) is a partial cross section according to Example 2, and (c) is Comparative Example 1. It is a fin partial cross section, (d) is a fin partial cross section of Comparative Example 2. It is a figure for demonstrating the heat exchanger tube performance measuring apparatus which assembled | attached the inner surface grooved heat exchanger tube which concerns on this invention.

  Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings.

[First Embodiment]
(Overall structure of heat transfer tube)
1 and 2, reference numeral 1 indicating the whole schematically illustrates a typical heat transfer tube with an inner groove according to the first embodiment. The heat transfer tube 1 is made of a copper-based material such as copper or copper alloy, or an aluminum-based material such as aluminum or aluminum alloy, and has a tube body 2 formed by a round tube.

  As shown in FIGS. 1 and 2, a plurality of fins 3,..., 3 processed spirally in the tube axis O direction (tube longitudinal direction) are formed on the inner surface of the tube body 2. The pipe body 2 according to the illustrated example has an outer diameter do of 6.35 mm and a minimum inner diameter di of 5.61 mm. The groove bottom thickness Tw of the tube body 2 in the portion where the fins 3 are not present is set to 0.22 mm.

(Internal structure of heat transfer tube)
As shown in FIGS. 1 and 2, the fin 3 of the heat transfer tube 1 has a corrugated shape in which peaks and valleys are repeatedly formed as viewed from the direction of the tube axis O, as shown in FIGS. It consists of two types of fins of different sizes (high and low). The fin 3 according to the illustrated example is a first fin 4 (hereinafter also referred to as “high fin 4”) and a second fin 5 (hereinafter also referred to as “low fin 5”) having a height lower than that of the first fin 4. .) The high fins 4 and the low fins 5 are formed by processing a plurality of grooves 6,..., 6 spirally in the direction of the tube axis O, and alternately on the inner surface of the tube body 2 with the same pitch P. It is arranged. In the illustrated example, the twist angle β of the high fin 4, the low fin 5, and the groove 6 is set to 30 degrees.

As shown in FIGS. 1 and 2, the high fin 4 is formed by 24 band-like protrusions having a substantially trapezoidal shape in a front view as viewed from the tube axis O direction. The apex angle α of the high fin 4 according to the illustrated example is set within a range of 0 <α <90 degrees, and the height Hf ₁ is set to 0.15 mm.

As shown in FIG. 1 and FIG. 2, one low fin 5 is composed of a belt-like protrusion having the same shape as the high fin 4. The low fins 5 are arranged between two high fins 4 adjacent to each other, and are formed in the same number as the high fins 4. The height Hf ₂ of the low fin 5 according to the illustrated example is set to 0.13 mm lower than the high fin 4 by about 0.02 mm.

Inner surface grooved heat transfer tube 1 constructed as described above, before pipe expanding, the fin height ratio between the height Hf ₁ high fin 4 the height Hf ₂ low fin 5 (Hf 1 / _{Hf 2)} The main feature is to set it to 1.15 or less. As the inner surface grooved heat transfer tube 1, further be configured fin height difference between the height Hf ₁ high fin 4 the height Hf ₂ low fin 5 _(Hf 1 -Hf ₂₎ below 0.02mm desirable.

In addition, it is important for the inner surface grooved heat transfer tube 1 to keep the crushing amount ratio of the height Hf ₁ of the high fin 4 within 15%. In this first embodiment, the “crushing amount ratio” means “the amount of change between the fin height Hf ₁ before tube expansion and the fin height Hf _1-1 after tube expansion” is “fins before tube expansion”. A value {(Hf ₁ −Hf _1-1 ) / Hf ₁ } divided by “height Hf ₁ ”.

  By setting the fin height ratio before tube expansion processing to 1.15 or less and / or the fin height difference before tube expansion processing to 0.02 mm or less, the crushing amount ratio of the high fin 4 after tube expansion processing is within 15%. Can be fastened. Thereby, while being able to form the several fin 3 in the range which does not inhibit the fin processing property made into the initial objective, the heat transfer efficiency of the heat transfer tube 1 with an inner surface groove is not reduced. On the other hand, if the fin height ratio before tube expansion processing exceeds 1.15, or the fin height difference before tube expansion processing exceeds 0.02 mm, the crushing amount ratio of the high fin 4 after tube expansion processing is greater than 15%. This is not preferable because the heat transfer efficiency, processing accuracy, and productivity of the internally grooved heat transfer tube 1 cannot be improved.

(Modification of heat transfer tube)
According to the heat transfer tube 1 with the inner surface groove in the illustrated example, the high fin 4, the low fin 5, and the groove 6 are formed in a spiral shape on the inner surface of the tube body 2, but are not limited thereto. . Maximum fin height Hf ₁ and a minimum fin height fin height ratio of the Hf _{2 (Hf} 1 / Hf ₂₎ is a fin and 1.15 or less, and / or the maximum fin height Hf ₁ and a minimum fin height Hf ₂ If the height difference (Hf ₁ −Hf ₂ ) is set to 0.02 mm or less, for example, the fins 4 and 5 and the grooves 6 extending linearly or curvedly in the direction of the tube axis O may be formed in a strip shape. Of course.

In the first embodiment, the same number of the low fins 5 of the heat transfer tube 1 with the inner groove are formed between the two high fins 4 adjacent to each other, but the present invention is not limited to this. Is not to be done. Maximum fin height Hf ₁ and a minimum fin height fin height ratio of the Hf _{2 (Hf} 1 / Hf ₂₎ is a fin and 1.15 or less, and / or the maximum fin height Hf ₁ and a minimum fin height Hf ₂ If the height difference (Hf ₁ −Hf ₂ ) satisfies 0.02 mm or less, for example, the number of fins of the low fins 5 may be set to be smaller than that of the high fins 4. Of course, the number of fins of 5 may be set larger than that of the high fins 4.

In the first embodiment, the fins of the internally grooved heat transfer tube 1 are composed of two types of fins 4 and 5 which are different from each other. For example, the fin heights are different according to a certain rule. It may be composed of three or more types of fins, and is not limited to the illustrated example. If the fin height ratio (Hf ₁ / Hf ₂ ) is set to 1.15 or less and / or the fin height difference (Hf ₁ −Hf ₂ ) is set to satisfy 0.02 mm or less, the heat transfer tube with an inner groove 1 inner / outer diameter, bottom wall thickness, number of grooves, fin apex angle, twist angle, fin tip width, fin root width, groove bottom width, fin root radius, pitch between multiple fins, cross-sectional form, arrangement position, number of arrangement Etc. can be set appropriately.

(Effects of the first embodiment)
According to the first embodiment and the inner surface grooved heat transfer tube 1 which is a modified example, the following effects can be obtained.
(1) By setting each of the fin height ratio and / or fin height difference of the internally grooved heat transfer tube 1 to a predetermined value, it is possible to minimize the collapse and tilt of the fin tip during tube expansion processing. it can.
(2) The tube mass per unit length can be reduced while suppressing the crushing and tilting of the fin tip in the tube expansion processing of the inner surface grooved heat transfer tube 1.
(3) Since there is little fin crushing or fin collapse in the expansion processing of the inner surface grooved heat transfer tube 1, the inner surface grooved heat transfer tube of the heat exchanger used as a freon refrigerant, alternative freon refrigerant, carbon dioxide refrigerant or the like flowing in the tube As a result, excellent heat transfer performance can be maintained.

[Second Embodiment]
(Heat exchanger)
Referring to FIG. 3, FIG. 3 illustrates an outline of manufacturing a heat exchanger using the heat transfer tube 1 formed as described above. According to the figure, aluminum thin plate-like fins 10 obtained by press punching through holes 11 having a diameter larger than the outer diameter of the heat transfer tube 1 are arranged in parallel, and through the through holes 11, according to a conventional method. The heat transfer tube 1 which is formed into a U-shape by rolling the inner surface of the tube is inserted. At this time, a gap 12 is formed between the outer surface of the heat transfer tube 1 and the through hole 11 of the thin plate fin 10.

  A tube expansion heat transfer tube 1a is formed by inserting a tube expansion mandrel 20 into the heat transfer tube 1 along the longitudinal direction of the tube of the heat transfer tube 1 via a pressing rod 21 to expand the heat transfer tube 1, and this tube expansion heat transfer tube The outer surface of 1a and the thin plate-like fin 10 are closely fixed and integrated. A short tube (not shown) bent in a U-shape is used, the open ends of the adjacent expanded heat transfer tubes 1a are connected, and the expanded heat transfer tube 1a and the short tube are brazed and joined using, for example, a burner.

  Through the above assembling operation, a plate fin tube type heat exchanger including the expanded heat transfer tube 1a in which the heat transfer tube 1 is expanded and the thin plate-like fins 10 in close contact with the outer surface of the expanded heat transfer tube 1a can be manufactured at low cost. . This heat exchanger is used as an evaporator or a condenser.

(Effect of the second embodiment)
According to the heat exchanger which is the said 2nd Embodiment, there can exist the following effects.
(1) Even when a heat exchanger is manufactured by mounting thin plate fins on the tube outer surface by tube expansion processing, the outer surface of the heat transfer tube and the thin plate are suppressed while minimizing crushing and tilting of the fin tip during tube expansion processing. The fins can be tightly fixed.
(2) Since the fin collapse amount can be suppressed to be small and the fin can be prevented from falling down obliquely, a decrease in condensation / evaporation heat transfer coefficient can be prevented.
(3) By setting the fin height ratio and / or fin height difference to the fin height of the heat transfer tube, the tube mass per unit length can be reduced, so the heat exchanger can be reduced in weight. Become.

  Note that the present invention is not limited to the above-described embodiments, modifications, and illustrated examples, and the technical scope that can be easily changed by those skilled in the art from these embodiments, modifications, and illustrated examples. Naturally, it is included.

  Hereinafter, examples and comparative examples will be given as more specific embodiments of the present invention, and the inner surface grooved heat transfer tubes will be described in detail with reference to FIGS. 4 to 6 and Tables 1 to 6. . In addition, in this Example, the typical example of the heat transfer tube with an inner surface groove | channel is given, and of course, this invention is not limited to these Examples.

(Dimension of heat transfer tube with inner groove)
By rolling the inner surface of the pipe using a copper original pipe in accordance with a standard method, there are four types of fin height difference 0.01 mm, fin height difference 0.02 mm, fin height difference 0.03 mm, and constant fin height. Each of the heat transfer tubes was prototyped under the dimensional conditions shown in Table 1 below. As shown in Table 1 below, the average outer diameter, minimum inner diameter, bottom wall thickness, number of grooves, fin apex angle, helix angle, fin tip width, fin base width, groove bottom other than the fin height dimension in these heat transfer tubes The width and the fin base radius were prototyped with the same dimensions.

  The cross-sectional shape of the heat transfer tube manufactured as described above before the tube expansion processing is as shown in FIG. 4A shows a heat transfer tube according to Example 1 having a fin height ratio of 1.07 and a fin height difference of 0.01 mm, and FIG. 4B shows a fin height ratio of 1.14 and a fin height difference of 0.02 mm. FIG. 4C shows a heat transfer tube according to Example 2, and FIG. 4C shows a heat transfer tube according to Comparative Example 1 in which the fin height is constant. FIG. 4D shows a fin height ratio of 1.24 and a fin height difference of 0. .03 mm is a heat transfer tube according to Comparative Example 2.

(Evaluation results of internally grooved heat transfer tubes)
The shape of the inner surface of the heat transfer tube of Examples 1 and 2 and the heat transfer tube of Comparative Examples 1 and 2 after tube expansion processing was investigated, and the presence or absence of fin collapse or fin collapse was confirmed. The results are summarized in Table 2 below.

  The fin cross-sectional shape of the heat transfer tube after the pipe expansion process is as shown in FIG. FIG. 5A is a heat transfer tube of Example 1, FIG. 5B is a heat transfer tube of Example 2, FIG. 5C is a heat transfer tube of Comparative Example 1, and FIG. These are the heat transfer tubes of Comparative Example 2.

  As is clear from FIGS. 4 and 5, when the fin cross-sectional shape before tube expansion shown in FIG. 4 is compared with the fin cross-sectional shape after tube expansion shown in FIG. 5, Example 1 shown in FIG. The fins 4 and 5 of Example 2, the fins 4 and 5 of Example 2 shown in FIG. 5B, and the fins 4 and 5 of Comparative Example 1 shown in FIG. 5C are not inclined, but are shown in FIG. The fin 4 of the comparative example 2 shown in FIG.

  Here, referring to Table 2 below, as is clear from Table 2, the fin height difference before tube expansion processing is 0.02 mm or less as in Examples 1 and 2, and the fin height ratio before tube expansion processing is 1. If it is 15 or less, the dimensional change of the high (main) fin before the pipe expansion process and the high (main) fin after the pipe expansion process, the low (sub) fin before the pipe expansion process, and the low (sub) fin after the pipe expansion process The dimensional change of each remains within 0.02 mm, and even within those fin crushing ratios, it is within 15%.

  On the other hand, when the fin height difference is 0.03 mm or more as in Comparative Example 2 and the fin height ratio before the tube expansion process exceeds 1.15, the dimensional change and the amount of collapse of the low (sub) fin after the tube expansion process The ratio is almost the same as that of the low (secondary) fin of Example 2, but the dimensional change of the high (main) fin after the pipe expansion processing exceeds 0.02 mm, and even in the crushing amount ratio. Over 15%. The size and crushing ratio of the high (main) fins changed more greatly than the fins of Examples 1 and 2.

  From these results, if the fin height difference before the tube expansion process is 0.02 mm or less and the fin height ratio before the tube expansion process is 1.15 or less, the fin collapse of the high fin is suppressed and the fin of the high fin is suppressed. It was possible to stabilize the crushing within 15%, and it was confirmed that an internally grooved heat transfer tube that does not cause a practical problem can be formed.

(Heat exchange test)
Referring to FIG. 6, a heat transfer tube performance measuring device is schematically shown in FIG. In the same figure, the code | symbol 30 which shows the whole has shown the heat exchanger tube performance measuring apparatus. The heat transfer tube performance measuring device 30 includes a compressor 31, a condenser 32, an expansion valve 33, and an evaporator 34.

  In FIG. 6, the compressor 31 compresses refrigerant vapor. The condenser 32 condenses the refrigerant vapor compressed by the compressor 31 to obtain a refrigerant liquid. The expansion valve 33 depressurizes the refrigerant liquid from the condenser 32. The evaporator 34 evaporates the refrigerant decompressed by the expansion valve 33 to obtain refrigerant gas. The specifications of the heat exchanger are as shown in Table 3 below.

  In the evaporation test for measuring the evaporation heat transfer coefficient, the heat transfer tube 1 with an inner groove is incorporated in the evaporator 34. Air is used as a heat exchange fluid in the evaporator 34, and the front wind speeds flowing on the air side between the evaporator 34 and the outer surface of the heat transfer tube 1 are 0.57 m / s, 1.0 m / s, and 1.5 m / s. The refrigerant supplied to the inner surface of the heat transfer tube on the refrigerant side was evaporated by flowing air on the outer surface of the heat transfer tube. As the refrigerant, Freon R410A was used. The evaporation side was tested under the measurement conditions (outdoor conditions) shown in Table 4 below on the air side and the refrigerant side. In this evaporation test, the refrigerant and the heat exchange fluid were flowed in the direction of the arrow indicated by the solid line in FIG.

  On the other hand, the condensation test for measuring the condensation heat transfer coefficient is performed by incorporating the heat transfer tube 1 with an inner groove into the condenser 32. Even in this condensation test, air is used as the heat exchange fluid, and on the air side, the front wind speed is 0.57 m / s, 1.0 m / s, and 1.5 m / s. The refrigerant vapor supplied to the inner surface of the heat transfer tube was condensed by flowing air. The condensation side was subjected to the measurement conditions (outdoor conditions) shown in Table 4 below on the air side and the refrigerant side. In this condensation test, the refrigerant and the heat exchange fluid were flowed in the direction of the arrow indicated by the broken line in FIG.

(Measurement of heat exchange performance)
Using the heat transfer tube performance measuring device 30 thus prepared, the front wind speed is changed in three ways of 0.57 m / s, 1.0 m / s, and 1.5 m / s, and the front wind speeds are changed. In addition, the heat exchange tubes according to Examples 1 and 2 and the heat transfer tubes according to Comparative Examples 1 and 2 were measured for exchange heat, normal fin ratio, refrigerant flow rate, and refrigerant pressure loss, and the quality of condensation performance and evaporation performance was confirmed. . The results are summarized in Table 5 and Table 6 below. In this example, “normal fin ratios” shown in Tables 5 and 6 are “the amount of heat exchange of the heat transfer tube with the inner surface groove according to Examples 1 and 2” and “the amount of heat exchange of the heat transfer tube in Comparative Example 1”. The performance ratio.

(Heat exchange performance measurement results)
As is clear from Table 5 below, the condensation performance of the heat exchanger using the heat transfer tubes of Examples 1 and 2 and the heat transfer tube of Comparative Example 1 is not lowered. The condensation performance is the same when the fin height difference before tube expansion is 0.02 mm or less and the fin height ratio before tube expansion is 1.15 or less. In the heat exchanger using the heat transfer tubes of Examples 1 and 2 with a fin height difference of 0.02 mm or less, the condensation performance of the heat exchanger using the heat transfer tube of Comparative Example 1 in which the fin height is constant is almost the same. Has condensation performance.

  In the heat exchanger using the heat transfer tube of the comparative example 2 in which the fin height difference before the pipe expansion process is 0.03 mm and the fin height ratio before the pipe expansion process exceeds 1.15, the comparative examples 1 and 2 and the comparative example Compared to 1, the condensation performance of the heat exchanger is degraded. The condensing performance of the heat exchanger tends to decrease as the fin height difference before tube expansion increases.

  On the other hand, as is apparent from Table 6 below, the evaporation performance of the second embodiment with the fin height difference of 0.02 mm is almost the same regardless of the fin height difference before the pipe expansion process. The evaporation performance of heat exchangers using heat transfer tubes is the highest. The heat exchanger using the heat transfer tube of Example 1 having a fin height difference of 0.01 mm has substantially the same evaporation performance as the heat exchanger using the heat transfer tube of Comparative Example 1 in which the fin height is constant. . In the heat exchanger using the heat transfer tube of Comparative Example 2 having a fin height difference of 0.03 mm, the amount of heat exchanged (usually fin ratio) is increased as the front wind speed of air increases compared to Example 2 and Comparative Example 1. Tend to decrease.

  From these results, if the fin height difference before tube expansion is 0.02 mm or less and / or the fin height ratio before tube expansion is 1.15 or less, the amount of fin crushing is suppressed and the fins are inclined. It has been confirmed that it is possible to prevent the body from falling down, and it is possible to prevent a decrease in condensation heat transfer coefficient and a decrease in evaporation heat transfer coefficient.

  In Examples 1 and 2 and Comparative Examples 1 and 2, as shown in Table 3 below, the groove bottom width, the number of grooves, and the torsion angle of the internally grooved heat transfer tube were each prototyped. As the groove bottom width increases, the condensation performance increases, and as the number of grooves increases, the condensation performance and evaporation performance increase. Increasing the twist angle increases the condensation performance and evaporation performance, but increases the pressure loss. By appropriately setting the groove bottom width, the number of grooves, the torsion angle, and the like of the internally grooved heat transfer tube, it can be used effectively in an evaporator or a condenser.

  As is clear from the above explanation, if the evaporation performance is important based on the above test results and the set dimensions such as the groove bottom width, the number of grooves, and the torsion angle of the internally grooved heat transfer tube, the evaporation performance It is possible to manufacture a heat exchanger that raises the temperature and a heat transfer tube with an internal groove used in the heat exchanger. When condensing performance is regarded as important, a heat exchanger that improves condensing performance and an internally grooved heat transfer tube used therefor can be manufactured. Even when importance is attached to both evaporation and condensation, it is possible to produce a heat exchanger that improves evaporation performance and condensation performance, and an internally grooved heat transfer tube used for the heat exchanger.

DESCRIPTION OF SYMBOLS 1 Inner surface grooved heat transfer tube 1a Tube expansion heat transfer tube 2 Tube body 3 Fin 4 First fin 5 Second fin 6 Groove 10 Thin plate fin 11 Through hole 12 Gap 20 Expanded mandrel 21 Press rod 30 Heat transfer tube performance measuring device 31 Compression Machine 32 Condenser 33 Expansion valve 34 Evaporator do Outer diameter di Minimum inner diameter Hf ₁ First fin height Hf ₂ Second fin height O Pipe axis P Pitch Yw Groove bottom wall thickness α Fin apex angle β Twist angle

Claims (7)

It has a plurality of fins in which concave and convex grooves are formed on the inner surface of the tube over the longitudinal direction of the tube,
The plurality of fins includes a first fin and a second fin lower than the height of the first fin,
The ratio (Hf ₁ / Hf ₂ ) between the highest height (Hf ₁ ) of the first fin and the lowest height (Hf ₂ ) of the second fin is set to 1.15 or less. Inner grooved heat transfer tube. 2. The inner surface according to claim 1, wherein a difference in height between the height of the highest first fin (Hf ₁ ) and the height of the lowest second fin (Hf ₂ ) is set to 0.02 mm or less. Grooved heat transfer tube.   The heat transfer tube with an inner surface groove according to claim 1 or 2, wherein the number of fins of the lowest second fin is set to be equal to that of the highest first fin.   4. The internally grooved heat transfer tube according to claim 3, wherein the lowest second fin and the highest first fin are alternately arranged.   The inner surface grooved heat transfer tube according to claim 1 or 2, wherein the number of fins of the lowest second fin is set smaller than that of the highest first fin.   The inner surface grooved heat transfer tube according to claim 1 or 2, wherein the number of fins of the lowest second fin is set to be larger than that of the highest first fin.   A heat exchanger comprising an expanded heat transfer tube obtained by expanding the internally grooved heat transfer tube according to any one of claims 1 to 6.