JP3494625B2 - Internal grooved heat transfer tube - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat transfer tube with an inner groove for use in heat exchangers such as refrigeration equipment and air conditioners which use difluoromethane or a mixture containing difluoromethane as a refrigerant, and more particularly to a condensation heat transfer coefficient. And a seamless inner grooved heat transfer tube excellent in both evaporation heat transfer rate.

[0002]

2. Description of the Related Art Conventionally, chlorodifluoromethane (R) has been used for air conditioning equipment such as room air conditioners and refrigeration equipment.
22) etc., a refrigerant (HCF) containing chlorine in its molecular structure.
C) has been widely used. However, since these refrigerants (HCFCs) are substances that destroy the ozone layer, the conversion to chlorine-free refrigerants (HFCs) has recently been in progress. Further, in order to suppress global warming, refrigeration equipment and air conditioning equipment are required to reduce power consumption. This is because the amount of carbon dioxide gas discharged from the thermal power plant can be reduced by reducing the power consumption of the refrigeration equipment and the air conditioning equipment.

As an alternative to R22, HFC 1,
1,1,2-Tetrafluoroethane (R134a) was adopted for some large air conditioners, but R134a is R22
Since the liquid thermal conductivity is lower than
Since it causes an increase in heat exchanger volume and power consumption, it is rarely used in room air conditioners and package air conditioners.

A mixed refrigerant containing difluoromethane (R32) has begun to be used in room air conditioners and package air conditioners. R32 has an advantage that it has larger latent heat, vapor thermal conductivity and liquid thermal conductivity than R22. In addition, since R32 is flammable and the operating pressure is 1.6 times that of R22, R125 has R125 or R13.
4a mixed refrigerant, ie R410A and R407C
Non-azeotropic mixed refrigerants such as However, since R32 has a relatively low flammability and is close to nonflammability, it is possible to use R32 alone as a refrigerant.

On the other hand, an inner grooved tube is widely used as a heat transfer tube of an air-cooling type heat exchanger of an air conditioner, and the groove shape of the inner surface is optimized as follows.

Japanese Unexamined Patent Publication (Kokai) No. 8-105699 discloses a technique for defining the groove shape on the inner surface for the purpose of improving the evaporation and condensation heat transfer coefficients. Specifically, the fin crest angle is 10 to 20 ° and the groove depth is 0.15.
To 0.23 mm, groove bottom width 0.1 to 0.3 mm, and groove lead angle (torsion angle) to the tube axis of 10 to 30 °
It is described that the above can improve the evaporation heat transfer coefficient and the condensation heat transfer coefficient of the heat transfer tube.

Further, Japanese Patent Laid-Open No. 8-145585 discloses a groove shape devised for a non-azeotropic mixed refrigerant. This technique has an extremely large lead angle (twist angle) of 45 ° or more for the purpose of improving the condensation heat transfer coefficient.

Further, Japanese Patent No. 2997189 also discloses a groove shape devised for a non-azeotropic mixed refrigerant.
In this technique, the lead angle of the inner surface groove is set to 25 ° or more and the groove depth is set to 0.
It is specified to be 15 to 0.35 mm.

[0009]

However, the conventional techniques have the following problems. JP-A-8-105
The inner grooved tube disclosed in Japanese Patent No. 699 is suitable for a conventional refrigerant such as chlorodifluoromethane (R22) and 1,1,1,2-tetrafluoroethane (R134a), and is difluoromethane ( R32) and R41
There is a problem that it is not suitable for a mixed refrigerant containing difluoromethane such as 0A and R407C.

The inner grooved tube disclosed in Japanese Unexamined Patent Publication No. 8-145585 has an extremely large lead angle, so that the condensation heat transfer coefficient is improved but the evaporation heat transfer coefficient is significantly reduced. To do. Also, it is extremely difficult to provide a seamless copper tube with a lead angle of 45 ° or more.

Further, the inner grooved tube disclosed in Japanese Patent No. 2997189 also has a condensing heat by limiting the lead angle similarly to the inner grooved tube disclosed in Japanese Patent Laid-Open No. 8-145585. Although the transfer rate is improved, there is a problem that the evaporation heat transfer rate is decreased.

The present invention has been made in view of the above problems, and is an internal grooved heat transfer tube suitable for difluoromethane and a mixed refrigerant containing difluoromethane, and the condensation heat transfer is achieved by limiting the inner surface shape. It is an object of the present invention to provide a lightweight seamless heat transfer tube with inner surface groove, which improves not only the heat transfer coefficient but also the heat transfer rate of evaporation.

[0013]

A heat transfer tube with an inner groove according to the present invention is used in a heat exchanger that uses difluoromethane or a mixture containing difluoromethane as a refrigerant, and an inner groove having a groove formed on the inner surface of the tube. In the heat transfer tube with a pipe, the lead angle of the groove on the inner surface of the tube is 25 ° or more, the groove pitch is 0.25 mm or more, and in the development view of the inner surface of the tube, the outer surface of the tube is pressed by a rolling ball or a rolling roll. The trace of the indentation appearing on the surface is 0 in the same direction as the groove with respect to the direction orthogonal to the tube axis.
It is characterized in that it is inclined at an angle of more than ° and less than 10 °.

In the present invention, by setting the lead angle to 25 ° or more, it is possible to suppress the refrigerant liquid from rising along the groove at the time of condensation, and it is possible to keep the vicinity of the pipe top dry during the condensation. . As a result, on the inner surface of the heat transfer tube with internal groove, the refrigerant gas can be condensed on the dry surface which is not wet with the refrigerant liquid, and the condensed refrigerant liquid can be quickly discharged, so that the condensation heat transfer rate is improved. Can be made. The lead angle refers to the smaller one of the angles formed by the groove formed on the inner surface of the tube and the tube axis.

On the other hand, a rolling ball or rolling roll presses the outer surface of the heat transfer tube with inner groove to form a locus of an indentation on the inner surface of the tube. The locus of the indentation is a developed view of the inner surface of the tube. With respect to the direction orthogonal to the tube axis direction (tube orthogonal direction), the groove is inclined at an angle of more than 0 ° and 10 ° or less in the same direction as the groove. This indentation can cause a flow of the refrigerant liquid along the trajectory of the indentation during evaporation. As a result, the tube side portion can be wetted during evaporation, and the evaporation heat transfer coefficient can be improved. Since the temperature of the refrigerant liquid is high at the time of condensation, the surface tension of the refrigerant liquid is reduced to about 30% of that at the time of evaporation and the viscosity is reduced to about 60%, so that the flow along the indentation cannot exist. Therefore, at the time of condensation, the area of the wet region on the inner surface of the tube is not increased and the condensation heat transfer coefficient is not reduced. Further, in the present invention, the pipe side portion means the vicinity of the central portion of the pipe top portion and the pipe bottom portion on the inner surface of the pipe.

Further, by setting the groove pitch of the inner surface grooved heat transfer tube to 0.25 mm or more, it is possible to suppress the formation of a continuous liquid film at the groove bottom at the time of condensation, so that the refrigerant liquid is condensed at the groove at the time of condensation. It is possible to suppress the rise along and to keep the vicinity of the pipe top in a dry state at the time of condensation.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.
A detailed description will be given with reference to the accompanying drawings. 1A to 1D are schematic diagrams showing the relationship between the lead angle and the behavior of the refrigerant liquid. 1A and 1B show a heat transfer tube with an inner groove having a large lead angle, FIG. 1A is a schematic development view of the inner surface of the tube, and FIG. 1B is a sectional view perpendicular to the tube axis direction. Is.
On the other hand, FIGS. 1 (c) and 1 (d) show a heat transfer tube with an inner groove having a small lead angle, FIG. 1 (c) is a schematic development view of the inner surface of the tube, and FIG. 1 (d) is a view perpendicular to the tube axis direction. FIG. Also,
2A to 2C are development views showing a flow along the locus of the indentation, FIG. 2A shows the position of the locus of the indentation on the inner surface of the pipe, and FIG. 10 shows a case in which the groove 3 is tilted in the opposite direction to the groove 3, and FIG. 10C shows a case in which the locus 4 of the indentation is tilted in the same direction as the groove 3 with respect to the line 10.

The inner grooved heat transfer tube according to the present invention is used for a heat exchanger using difluoromethane (R32) or a mixed refrigerant containing difluoromethane as a refrigerant, for example, a non-azeotropic mixed refrigerant such as R410A and R407C. It is what is done. Difluoromethane (R32) has a higher vapor density than chlorodifluoromethane (R22) that is a conventional refrigerant, and even if the same mass flow rate as R22 is flown into the pipe, the volume flow rate is small and the pressure loss is small. There is a feature called. The surface tension of R32 is smaller than that of R22 by 7 to 30%.

For the heat transfer tube with groove on the inner surface of this embodiment, a seamless copper tube having no groove is prepared as a raw material, a plug with groove is inserted into the inside of the tube, and a rolling ball is placed on the outer surface of the tube. It is manufactured by rolling by pressing and rotating the grooved plug and the rolling ball. As a result, a spiral groove is formed on the inner surface of the pipe by the grooved plug, and by pressing the outer surface of the pipe with the rolling ball, the locus of the indentation of the rolling ball appears on the inner surface of the pipe. Normally, since the rolling ball rotates in the opposite direction to the grooved plug, the indentation locus is formed in the direction opposite to the groove relative to the tube axis orthogonal direction. Indicates that the rolling direction of the rolling ball is the same as that of the grooved plug,
That is, by making the direction forward, the locus of the indentation of the rolled ball is formed in the same direction as the groove with respect to the direction orthogonal to the tube axis. After this, the tube is reduced in diameter to manufacture the heat transfer tube with inner groove 1c. As shown in Fig. 2 (a), the heat transfer tube 1c with an inner groove
On the inner surface of the tube, a spiral groove 3 and a locus 4 of the indentation of the rolling ball are formed. The angle formed by the spiral groove 3 and the line 5 parallel to the tube axis direction on the inner surface of the tube is 25 ° or more,
The locus 4 of the indentation of the rolling ball is the groove 3 in the direction orthogonal to the tube axis.
It is inclined at an angle of more than 0 ° and 10 ° or less in the same direction as.

The reasons for limiting the numerical values of the respective constituents of the present invention will be described below.

Lead angle: 25 ° or more In an inner grooved heat transfer tube used in a heat exchanger, the refrigerant gas is condensed on a dry surface which is not wet with the refrigerant liquid during condensation, and the condensed refrigerant liquid is quickly discharged. Preferably. As shown in FIGS. 1A and 1B, the angle formed by the groove 3 formed on the inner surface of the inner grooved heat transfer tube 1a and the line 5 parallel to the tube axis direction on the inner surface of the tube, that is, the lead angle θ. Is large, it is difficult for the refrigerant liquid 2 to rise along the groove 3, so that the vicinity of the pipe top 8 is dry. Further, the refrigerant liquid 2 condensed near the pipe top 8 is promptly discharged from the pipe top 8. In addition,
Refrigerant gas 9 exists in the space not occupied by the refrigerant liquid 2 in the inner grooved heat transfer tubes 1a and 1b.

As shown in FIGS. 1 (c) and 1 (d), in the inner grooved heat transfer tube 1b having a small lead angle θ, the refrigerant liquid 2 flows along the groove 3 and a large amount of the refrigerant near the tube top 8 is formed. Liquid 2
Is supplied, the condensation of the gas refrigerant is hindered by the thermal resistance of the refrigerant liquid film.

As described above, in both the single refrigerant and the mixed refrigerant, the condensing heat transfer coefficient is improved by increasing the lead, that is, by increasing the lead angle θ. As described above, since the pressure loss of difluoromethane (R32) is smaller than that of chlorodifluoromethane (R22) which is a conventional refrigerant, the inner grooved heat transfer tube using difluoromethane (R32) is chlorodifluoromethane (R32). R22) can be used to increase the lead angle and improve the heat transfer coefficient during condensation, as compared with an inner grooved heat transfer tube. If the lead angle is 25 ° or more, the above effect is remarkably observed. Therefore, in the present invention, the lead angle is 25 ° or more.
On the other hand, the improvement of the condensing heat transfer coefficient by increasing the lead also has an advantage that the unit weight of the tube hardly increases.

FIG. 3 is a sectional view showing the structure of a test apparatus for measuring the surface temperature distribution of the heat transfer tube with internal groove. Figure 3
The test apparatus shown in (1) includes a test section 11 and piping sections 12 provided on both sides of the test section 11. Test section 11
Has a length of 500 mm, and the total length of the test equipment is 83 mm.
It is 0 mm. The test section 11 is for performing heat exchange between the refrigerant and water by using the heat transfer tube with inner groove to be tested, and the heat transfer tube with inner groove to be tested is the test tube 13
The test tube 13 is inserted into another tube 14 to form a double tube structure, and the circumference of the tube 14 is covered with a heat insulating material 15. The portion of the test tube 13 included in the test section 11 is the test section 1
3a. In the test section 11, water is caused to flow in an annular portion between the test section 13a and the tube 14, and a refrigerant is caused to flow in the test tube 13 for heat exchange. A sheath thermocouple 16 having a diameter of 0.2 mm is provided at an intermediate position in the longitudinal direction of the test portion 13a.
It is evenly attached at eight locations along the circumferential direction, and the temperature distribution in the circumferential direction of the test portion 13a can be measured. The pipe section 12 is for supplying the refrigerant and water to the test section 11, and is provided on both sides of the test section 11.
Each of the piping portions 12 is provided with a water inlet / outlet 17 for letting in / out water and a refrigerant inlet / outlet 18 for letting in / out refrigerant.
The refrigerant is circulated by a pump 19 provided outside the test device.

Further, FIG. 4 shows the shape of the heat transfer tube with inner groove 1d to be tested, that is, the minimum inner diameter (Di) and the bottom wall thickness (t).
w), fin height (Hf), fin root arc radius (R), tip arc radius (R0), fin peak angle (α) and groove bottom width (Wg). is there.
In FIG. 4, the peak angle α indicates the angle formed by the side walls on both sides of the fin 6c in the inner surface grooved heat transfer tube 1d.

5 (a) to 5 (d) respectively show the lead angle θ.
FIG. 6 is a graph showing a surface temperature distribution in the tube circumferential direction at the time of condensation in a heat transfer tube with inner groove having angles of 10 °, 20 °, 25 ° and 30 °. This surface temperature distribution is measured by the test device shown in FIG. The test conditions are such that the dryness of the refrigerant at the inlet of the test portion 13a is 0.6, the dryness at the outlet is 0.4, and the condensation temperature is about 45 ° C. at the longitudinal intermediate position of the test portion. The dryness of the refrigerant is a mass ratio of the amount of the refrigerant of the vapor to the total amount of the refrigerant of the liquid and the refrigerant of the vapor. The heat transfer tube with inner groove to be tested has an outer diameter (D0) of 7.9.
4 mm, number of grooves (N) is 70, bottom wall thickness (tw) is 0.26
The inner surface shape of these heat transfer tubes with inner grooves is such that the angle (η) formed by the locus of the indentation and the direction orthogonal to the tube axis is + 3 °, the groove pitch (Pg) is 0.333 mm, and the fin height ( H
f) is 0.15 mm, the arc radius (R) of the base of the fin is 0.05 mm, and the arc radius (R0) of the tip of the fin is 0.
04 mm, fin crest angle (α) is 20 °. Figure 5
In (a) to (d), the numbers written along the vertical axis of each figure indicate the temperature, the numbers 1 to 8 written on the outside of each figure indicate the measurement position, and 1 is the pipe top. Reference numerals 3 and 7 denote side portions of the tube, and 5 denotes a bottom portion of the tube. The description method is the same in FIGS. 6 to 9 below. The octagon drawn with a thick solid line shows the measurement result of each test tube, and the octagon drawn with a thick broken line shows a line at a temperature of 45 ° C, that is, a gas-liquid boundary. A portion where the temperature is higher than 45 ° C. indicates that the state of the refrigerant in the portion is vapor, and a portion where the temperature is 45 ° C. or lower indicates the liquid.

As shown in FIGS. 5 (a) and 5 (b), in the heat transfer tube with inner groove having the lead angles (θ) of 10 ° and 20 °, the liquid refrigerant reaches the top of the tube. On the other hand, FIG.
As shown in (c) and (d), the lead angle (θ) is 25
In the heat transfer tubes with grooved inner surfaces of 30 ° and 30 °, there is no liquid refrigerant at the top of the tubes and they are dry, indicating that the condensation performance is excellent.

In the development view of the inner surface of the pipe, a rolling ball or rolling
Formed on the inner surface of the inner surface grooved heat transfer tube by a forming roll
Direction of indentation locus: same direction as groove with respect to tube axis orthogonal direction
Inclining at an angle of more than 0 ° and not more than 10 ° as described above, with the increase in the lead of the inner grooved heat transfer tube, the refrigerant liquid is suppressed from rising in the tube along the groove,
The condensation heat transfer coefficient of the tube is improved, but the evaporation heat transfer coefficient is decreased because the wetting area is reduced. Therefore, in the present invention, this problem is solved by defining the angle formed by the trajectory of the indentation of the rolling ball or rolling roll and the tube axis. In the manufacturing process of the inner grooved heat transfer tube, the rolling balls or the rolling rolls form a trace of an indentation on the outer surface of the tube, and this trace also appears on the inner surface of the tube. The locus of the indentation defined in the present invention refers to the locus of the indentation appearing on the inner surface of the tube.

A slight amount of flow is generated on the surface of the tube wall along the trajectory of the above-mentioned indentation. This occurs because the refrigerant liquid wets and spreads the unevenness of the indentation surface due to the surface tension. As shown in FIG. 2A, the angle formed by the locus 4 of the indentation and the line 10 on the inner surface of the pipe orthogonal to the axial direction of the pipe is an angle η. The lead angle θ is the smaller of the angles formed by the groove 3 and the line 5 parallel to the tube axis direction on the inner surface of the tube. The locus 4 of the indentation is inclined with respect to the line 10 in the same direction as the groove 3.

As shown in FIG. 2B, when the locus 4 of the indentation is inclined with respect to the line 10 in the direction opposite to the groove 3, or when the locus 4 of the indentation is parallel to the line 10, that is, When the angle η is 0 ° or less, the flow of the refrigerant liquid that is going to rise to the pipe top along the locus 4 of the indentation cannot exist because it is not in the forward direction with respect to the flow of the refrigerant gas. Even when the flow direction of the coolant is opposite to the flow direction of the coolant shown in FIG. 2B, the flow direction of the coolant along the groove 3 and the flow of the coolant along the locus 4 of the indentation Since the angle formed with the flow direction is an obtuse angle, the flow of the refrigerant along the locus 4 of the indentation does not occur.

On the other hand, as shown in FIG. 2 (c), when the locus 4 of the indentation is inclined with respect to the line 10 in the same direction as the groove 3, that is, when the angle η exceeds 0 °, The flow of the refrigerant liquid along the locus 4 of the indentation is a flow in the forward direction with respect to the flow of the refrigerant gas, and the direction of the flow of the refrigerant along the groove 3 and the direction of the flow of the refrigerant along the locus 4 of the indentation are formed. Since the angle becomes acute, there can be a flow of the refrigerant along the locus 4 of the indentation toward the top of the tube, the refrigerant liquid can spread to the side of the tube, and the evaporation heat transfer coefficient can be improved. Further, in the case where the direction of the flow of the refrigerant is opposite to the direction of the flow of the refrigerant shown in FIG. 2C, the flow of the refrigerant along the locus 4 of the indentation is once directed to the pipe bottom and then the pipe bottom. After passing through, the flow goes to the pipe top.

On the other hand, from the manufacturing limit, η needs to be 10 ° or less. Since the temperature of the refrigerant liquid is high during condensation, the surface tension of the refrigerant liquid is about 30% of that during evaporation,
The viscosity drops to about 60% and no flow along the indentation trajectory occurs. Therefore, this flow does not reduce the condensation heat transfer coefficient.

In FIGS. 6A to 6D, the angle η is-.
It is a graph figure which shows the circumferential surface temperature distribution at the time of evaporation in a smooth tube of 8 degrees, -3 degrees, +3 degrees, and +8 degrees. The smooth tube is a tube manufactured without inserting a grooved plug into the inner surface in the process of manufacturing the inner surface grooved heat transfer tube. That is,
Only the indentations due to the rolling balls are formed on the inner and outer surfaces of these smooth tubes, and no grooves are formed. The surface temperature distribution in the circumferential direction of such a smooth tube is measured using the test apparatus shown in FIG. The test conditions are as follows:
The dryness of the refrigerant at the inlet of a is 0.4, the dryness at the outlet is 0.6, and the evaporation temperature is controlled to be 5 ° C. at the central position in the longitudinal direction of the test portion. The inner grooved heat transfer tube to be tested has an outer diameter (D0) of 7.94 mm and a bottom wall thickness (tw) of 0.26 mm. 6 (a) to 6 (d),
An octagon drawn with a thick solid line shows the measurement result of each test tube, and an octagon drawn with a thick broken line shows a line at a temperature of 5 ° C, that is, a gas-liquid boundary. A location where the temperature is higher than 5 ° C indicates that the state of the refrigerant at that location is vapor, and a location where the temperature is 5 ° C or lower is a liquid.

As shown in FIGS. 6 (a) and 6 (b), in the test tubes having η of -8 ° and -3 °, the refrigerant liquid is at the bottom of the tube and does not reach the side surface and the top of the tube. On the other hand, as shown in FIGS. 6C and 6D, η is + 3 ° and +8.
In the test tube of °, the liquid refrigerant spreads to the side surface of the tube, and the evaporation performance is excellent.

Groove pitch: 0.25 mm or more As described above, the surface tension and viscosity of the refrigerant liquid at the time of condensation are smaller than those at the time of evaporation, so if the lead angle is 25 ° or more,
The refrigerant does not spread to the top of the pipe during condensation. However, if the groove pitch is made too narrow, a continuous liquid film is formed at the groove bottom, and the refrigerant liquid reaches the vicinity of the pipe top, reducing the condensation heat transfer coefficient. If the groove pitch is 0.25 mm or more, the above problem does not occur, so the lower limit of the groove pitch is set to 0.2.
5 mm.

In FIGS. 7A to 7D, the groove pitch (Pg) is 0.333 mm, 0.274 mm and 0.24, respectively.
FIG. 5 is a graph showing a surface temperature distribution in the tube circumferential direction during condensation in the heat transfer tube with inner groove having a size of 5 mm and 0.222 mm. This temperature distribution is measured using the test device shown in FIG. The test conditions are controlled so that the dryness of the refrigerant at the inlet of the test part 13a is 0.6, the dryness at the outlet is 0.4, and the condensation temperature is 45 ° C. at the intermediate position in the test part longitudinal direction. The heat transfer tube with inner groove to be tested has an outer diameter (D
0) is 7.94 mm and the bottom wall thickness (tw) is 0.26 mm. The inner surface shape of these heat transfer tubes with inner grooves has a lead angle (θ) of 30 °, an indentation locus and a tube axis orthogonal direction. Angle (η) is + 3 °, fin height (Hf) is 0.15m
m, the arc radius (R) of the base of the fin is 0.05 mm, the arc radius (R0) of the tip of the fin is 0.04 mm, and the crest angle (α) of the fin is 20 °. 7 (a) to 7 (d)
In, the octagon drawn with a thick solid line shows the measurement result of each test tube, and the octagon drawn with a thick broken line has a temperature of 45 ° C.
Line, that is, the gas-liquid boundary. A location where the temperature is higher than 45 ° C indicates that the state of the refrigerant at that location is vapor, and a location where the temperature is 45 ° C or lower is liquid.

As shown in FIGS. 7 (a) and 7 (b), in the inner grooved heat transfer tubes having groove pitches (Pg) of 0.333 mm and 0.274 mm, the tube tops are dry. on the other hand,
As shown in FIGS. 7C and 7D, the groove pitch (Pg)
In the heat transfer tubes with inner grooves of 0.245 mm and 0.222 mm, the condensing performance is poor because the liquid refrigerant reaches the top of the tubes.

Fin height: 0.10 mm or more In the inner grooved heat transfer tube of the present invention, since the condensing heat transfer coefficient is improved by increasing the lead, the fin height is higher than that of the conventional inner grooved heat transfer tube. Can be lowered, and unit weight can be reduced. However, at the time of evaporation, if the height of the fin is less than 0.10 mm, the fin is completely buried in the liquid film, so that the effect of wetting and spreading the refrigerant liquid film is reduced.
On the other hand, if the height of the fins is set to 0.10 mm or more, the fins can be prevented from being buried in the liquid film, so that the liquid film of the refrigerant can be made wet and spread, and the evaporation heat transfer coefficient is further improved. Therefore, the height of the fin is preferably 0.10 mm or more.

FIGS. 8 (a) to 8 (d) show inner circumferential groove heat transfer tubes with fins of 0.05 mm, 0.08 mm, 0.10 mm and 0.15 mm in height, respectively. It is a graph which shows temperature distribution. The surface temperature distribution in the circumferential direction is measured using the test device shown in FIG.
The test conditions are such that the dryness of the refrigerant at the inlet of the test portion 13a is 0.4, the dryness at the outlet is 0.6, and the evaporation temperature is 5 ° C. at the middle position in the longitudinal direction of the test portion. The heat transfer tube with inner groove to be tested has an outer diameter (D0) of 7.94 m.
m, the number of grooves (N) is 70, and the bottom wall thickness (tw) is 0.26 mm
The inner surface shape of these inner grooved heat transfer tubes has a lead angle (θ) of 30 °, an angle (η) formed by the track of the indentation and the direction orthogonal to the tube axis is + 3 °, and a groove pitch (Pg) of 0. .333 m
m, the arc radius (R) of the base of the fin is 0.05 mm, the arc radius (R0) of the tip of the fin is 0.04 mm, and the crest angle (α) of the fin is 20 °. 8 (a) to 8 (d)
In, the octagon drawn with a thick solid line shows the measurement result of each test tube, and the octagon drawn with a thick broken line shows a line at a temperature of 5 ° C, that is, a gas-liquid boundary. A location where the temperature is higher than 5 ° C indicates that the state of the refrigerant at that location is vapor, and a location where the temperature is 5 ° C or lower is a liquid.

As shown in FIGS. 8 (a) and 8 (b), in the inner grooved heat transfer tube having fin heights (Hf) of 0.05 mm and 0.08 mm, the position of the refrigerant liquid is on the tube side. It remains, and the effect more than the effect by the trace of the indentation is not obtained. On the other hand, as shown in FIGS. 8 (c) and 8 (d), in the heat transfer tube with inner groove having fin heights of 0.10 mm and 0.15 mm, the refrigerant liquid spreads to the top of the tube, and the evaporation performance is It can be seen that it is improving.

Groove pitch: 0.40 mm or less Difluoromethane (R32) has a smaller surface tension than conventional refrigerant chlorodifluoromethane (R22), so that the liquid film in the groove is difficult to spread and the evaporation heat transfer coefficient is increased. It causes to decrease. For this reason, it is preferable that the refrigerant liquid be wet and spread by narrowing the groove pitch and forming a continuous liquid film on the groove bottom. When the groove pitch is 0.40 mm or less, the effect of improving the evaporation heat transfer coefficient is remarkably observed. Therefore, the groove pitch is preferably 0.40 mm or less.

In FIGS. 9A to 9D, the groove pitch (Pg) is 0.466 mm, 0.424 mm and 0.38, respectively.
It is a graph figure which shows the tube peripheral direction surface temperature distribution at the time of evaporation in the heat transfer tube with an inner surface groove which is 9 mm and 0.333 mm. The surface temperature distribution in the circumferential direction is measured using the test device shown in FIG. The test conditions are such that the dryness of the refrigerant at the inlet of the test part is 0.4, the dryness at the outlet is 0.6, and the evaporation temperature is 5 ° C. at the middle position in the test part longitudinal direction. The inner grooved heat transfer tube to be tested had an outer diameter (D0) of 7.94 mm and a bottom wall thickness (tw) of 0.26 mm,
The shape of the inner surface of these heat transfer tubes with internal grooves is the lead angle (θ)
Is 30 °, the angle between the indentation locus and the direction orthogonal to the tube axis (η)
Is + 3 °, the height (Hf) of the fin is 0.15 mm, the arc radius (R) of the base of the fin is 0.05 mm, the arc radius (R0) of the tip of the fin is 0.04 mm, and the peak angle of the fin (α ) Is 20 °. In FIGS. 9A to 9D, the octagons drawn with thick solid lines show the measurement results of each test tube, and the octagons drawn with thick broken lines are lines at a temperature of 5 ° C., that is, the gas-liquid boundary. Indicates. A location where the temperature is higher than 5 ° C indicates that the state of the refrigerant at that location is vapor, and a location where the temperature is 5 ° C or lower is a liquid.

As shown in FIGS. 9A and 9B, in the tubes having the groove pitches (Pg) of 0.466 mm and 0.424 mm, the refrigerant liquid does not reach the top of the tubes. On the other hand, as shown in FIGS. 9C and 9D, the groove pitch (P
In the tubes having g) of 0.389 mm and 0.333 mm, the refrigerant liquid is wet and spread, so that the evaporation performance is excellent.

Ratio of arc radius of fin base to fin height:
By processing the base of the fin of 0.15 to 0.45 into a curved surface, the liquid film at the base of the fin can be thinned. As a result, the thermal resistance of the liquid film is reduced, and the evaporation heat transfer coefficient can be improved. 10A and 10B are schematic cross-sectional views showing the relationship between the root shape of the fin and the thickness of the liquid film. As shown in FIG. 10A, the base 7a of the fin 6a
Is not processed into a curved surface, the liquid film of the refrigerant liquid 2 becomes thick in the vicinity of the root 7a. On the other hand, as shown in FIG. 10B, when the root 7b of the fin 6b is provided with a curved surface having an appropriate arc radius, the liquid film of the refrigerant liquid 2 is larger than that in the case where the curved surface is not provided. Becomes thin. When the radius of the arc of the fin is R and the height of the fin is Hf, if the value of R / Hf is 0.15 to 0.45, the liquid film at the base of the fin becomes thin, and the heat of vaporization is transferred. The rate is improved.

FIG. 11 is a schematic diagram showing the structure of a test apparatus for measuring the evaporation heat transfer coefficient and the condensation heat transfer coefficient of the inner grooved heat transfer tube. As shown in FIG. 11, this test apparatus is provided with a test section 20 and a bypass section 21. Test section 20
Is for measuring the evaporation heat transfer coefficient and the condensation heat transfer coefficient of the inner grooved heat transfer tube, and the bypass section 21 is for adjusting the refrigerant supplied to the test section 20 to a predetermined condition. Test section 2
0 and the bypass unit 21 are connected in parallel. The test section 20 has a double-tube structure and is provided with an inner tube 22 and an outer tube 23. The inner tube 22 is a heat transfer tube with an inner groove, which is a sample tube, and the outer tube 23 is a smooth copper tube. Heaters 24 are provided on both sides of the test section 20, and an expansion valve 25 is connected between one heater 24 and the test section 20. Further, a water tank 26 for supplying water to the test section 20 is connected to the test section 20. On the other hand, the bypass section 21, the bypass condenser 27, the expansion valve 28, the bypass evaporator 29, and the compressor 30 are annularly connected in this order to form an independent refrigeration cycle.

In the test apparatus shown in FIG. 11, the compressor 30 is driven to drive the bypass condenser 2
Refrigerant is made to flow through a refrigeration cycle composed of 7, an expansion valve 28, a bypass evaporator 29, and a compressor 30 to adjust the refrigerant to a predetermined condition. Then, the refrigerant whose conditions are adjusted is flown into the inner tube 22 of the test section 20. On the other hand, water is supplied from the water tank 26 to the annular portion between the inner pipe 22 and the outer pipe 23, heat is exchanged between the water and the refrigerant, and the amount of heat transfer is measured from the temperature difference between the inlet and outlet of the water. Further, the pressure difference between the refrigerant inlet and outlet of the inner pipe 22 is also measured. At this time, the bypass condenser 2 is adjusted so that the conditions such as the pressure of the refrigerant and the flow rate of the refrigerant have the values shown in Table 1.
7, the flow rate of water flowing to the bypass evaporator 29 and the bypass evaporator 29, the openings of the expansion valves 25 and 28, and the output of the heater 24 are adjusted.

The heat transfer coefficient in the tube is as follows: the heat transfer coefficient in the tube is αi, the overall heat transfer coefficient is Ko, the heat transfer coefficient outside the tube is αo, the heat resistance of the tube wall is R, the inner diameter of the test tube is Di, and the outer diameter of the test tube is Where Do is represented by the following mathematical formula 1.

[0048]

## EQU1 ## αi = 1 / (1 / Ko-1 / αo-R) / (D
i / Do)

The external heat transfer coefficient αo is Monrad-
It can be obtained by the Pelton formula. Further, the overall heat transfer coefficient Ko is represented by the following mathematical formula 2 where Q is the amount of heat transfer, Ao is the outer surface of the tube, and ΔTm is the logarithmic average temperature difference between the refrigerant and water.

[0050]

[Formula 2] Ko = Q / (Ao × ΔTm)

FIG. 12 shows that the fin height is 0.15 mm,
The evaporation heat transfer rate ratio when the arc radius R of the root of the fin in the heat transfer tube with inner groove of 0.20 mm and 0.25 mm is changed is shown. The measurement was performed by the test device shown in FIG. Table 1 shows the measurement conditions at this time. An inner grooved heat transfer tube with no R at the root of the fin, that is, R = 0
The heat transfer tube with inner groove having R / Hf in the range of 0.15 to 0.45 has a higher evaporation heat transfer rate by 5 to 8% than the heat transfer tube with inner groove of No.

[0052]

[Table 1]

Regarding the heat transfer tube with internal groove, in order to further improve the heat transfer performance and reduce the weight, the crest angle (α) of the fin is 25 ° or less, and the arc radius (R
0) is preferably 0.05 mm or less.

Since the pressure during operation of difluoromethane is higher than that of the conventional refrigerant, the bottom wall thickness of the heat transfer tube with inner groove is as follows, where tw is the bottom wall thickness and D0 is the outer diameter of the tube. It is desirable to satisfy the relationship of Expression 3.

[0055]

## EQU3 ## D0 / tw ≦ 31.7

[0056]

EXAMPLES The heat transfer tubes with internal grooves according to the examples of the present invention will be specifically described below in comparison with comparative examples outside the scope of the present invention. Table 2 shows the inner surface shapes of the heat transfer tubes with inner groove in Examples and Comparative Examples of the present invention.

[0057]

[Table 2]

The heat transfer tubes with internal grooves shown in Table 2 are all J
It is made of a copper alloy of alloy number C1220 described in ISH3300. In Table 2, the number of grooves means the number of grooves crossing a cross section perpendicular to the tube axis direction of the tube. Bottom wall thickness refers to the thickness of the tube at the bottom of the groove, as shown in FIG. The angle η refers to an angle formed by a trajectory of an indentation formed on the inner surface of the heat transfer tube with the inner groove by a rolling ball or a rolling roll in a developed view of the inner surface of the tube and a direction orthogonal to the tube axis,
The case where the direction is the same as that of the groove is positive. Further, the groove pitch refers to the groove interval in the circumferential direction of the pipe, and is calculated by the following formula 4 where Pg is the groove pitch, Di is the minimum inner diameter of the pipe, Pi is π, and N is the number of grooves.

[0059]

(4) Pg = Di × π / N

No. in Table 2 1 to 3 are embodiments of the present invention. Example No. The lead angle and the angle η are all within the scope of the present invention. Further, the fin height, groove pitch, and the ratio of the fin radius H of the circular arc radius R to the fin height Hf are also within the preferred range of the present invention. On the other hand, N
o. 4 to 6 are comparative examples. Comparative Example No. 4 to 6
Has a lead angle and angle η outside the scope of the present invention.

The heat transfer tubes with internal grooves shown in Table 2 are shown in FIG.
The evaporation heat transfer coefficient and the condensation heat transfer coefficient were evaluated using the test apparatus shown in FIG. As for the evaluation method, for the examples and comparative examples having the same tube diameter, the refrigerant mass velocity was changed to measure the in-tube heat transfer coefficient during evaporation and condensation, and the results were compared. The test conditions other than the refrigerant mass velocity were the conditions shown in Table 1. The test results are shown in FIGS. 13 (a) and (b), FIG. 14 (a).
And (b) and FIGS. 15 (a) and 15 (b).

13 (a) and 13 (b), the outer diameter is 7.0.
Example No. using a 0 mm tube. 1 and Comparative Example N
o. 4 shows the test results of (4), (a) shows the heat transfer coefficient in the tube at the time of evaporation, and (b) shows the heat transfer coefficient in the tube at the time of condensation. FIG.
As shown in (a) and (b), Example No. 2 was used in both cases of evaporation and condensation. The heat transfer coefficient in the tube of No. 1 is Comparative Example No. It was larger than the in-tube heat transfer coefficient of 4.

14 (a) and 14 (b), the outer diameter is 7.9.
Example No. using a 4 mm tube. 2 and Comparative Example N
o. 5 shows the test results of FIG. 5, (a) shows the heat transfer coefficient in the tube at the time of evaporation, and (b) shows the heat transfer coefficient in the tube at the time of condensation. As shown in FIGS. 14A and 14B, in each of the cases of evaporation and condensation, Example No. The heat transfer coefficient in the tube of No. 2 is Comparative Example No. It was larger than the heat transfer coefficient in the tube of No. 5.

15 (a) and 15 (b) show Example No. Three
And Comparative Example No. 6 shows the test results of 6. The outer diameters of these tubes are both 9.52 mm. FIG. 15A shows the heat transfer coefficient in the tube during evaporation, and FIG. 15B shows the heat transfer coefficient in the tube during condensation. In both cases of evaporation and condensation, Example No. The heat transfer coefficient in the tube of Comparative Example No. 3 was It was larger than the in-tube heat transfer coefficient of 6.

As described above, in Example No. The heat transfer tubes with inner groove Nos. 1 to 3 are each of Comparative Example No. Although the condensing heat transfer coefficient and the evaporation heat transfer coefficient were superior to those of the inner grooved heat transfer tubes Nos. 4 to 6, the mass per unit length was the same as shown in Table 2. If the groove shape is designed so that the condensation heat transfer coefficient and the evaporation heat transfer coefficient are equal, the embodiment No. In the heat transfer tubes with inner groove Nos. 1 to 3, the heights of the fins were set to Comparative Example Nos. It can be made lower than the heat transfer tubes with inner grooves 4 to 6 and can be made lighter.

[0066]

As described in detail above, according to the present invention,
An inner grooved heat transfer tube suitable for difluoromethane or a mixed refrigerant containing difluoromethane, which is excellent in both the condensation heat transfer coefficient and the evaporation heat transfer coefficient and is lightweight can be obtained. Further, by configuring a heat exchanger using this inner grooved heat transfer tube, it is possible to manufacture a refrigerating device and an air conditioner that use a chlorine-free refrigerant and consume less power.

[Brief description of drawings]

1A to 1D are diagrams showing a relationship between a lead angle and behavior of a refrigerant liquid, FIG. 1A is a schematic development view of a heat transfer tube with an inner groove having a large lead angle, and FIG. Shows a cross-sectional view of the inner surface grooved heat transfer tube, (c) shows a schematic development view of the inner surface grooved heat transfer tube having a small lead angle, and (d) shows a cross-sectional view of the inner surface grooved heat transfer tube.

2 (a) to 2 (c) are developed views showing the flow along the locus of the indentation, (a) shows the position of the locus of the indentation on the inner surface of the pipe, and (b) shows the locus 4 of the indentation. A case is shown in which the line 10 is inclined in the opposite direction to the groove 3, and (c) shows a case in which the locus 4 of the indentation is inclined in the same direction as the groove 3 with respect to the line 10.

FIG. 3 is a cross-sectional view showing the configuration of a test apparatus for evaluating the performance of a heat transfer tube with an inner groove.

FIG. 4 is a schematic cross-sectional view showing the shape of a heat transfer tube with an inner groove.

5A to 5D are graphs showing surface temperature distributions in the tube circumferential direction during condensation in heat transfer tubes with inner grooves having different lead angles.

6A to 6D are graphs showing circumferential surface temperature distributions during evaporation in smooth tubes having different values of η.

FIGS. 7A to 7D are graphs showing surface temperature distributions in the tube circumferential direction during condensation in heat transfer tubes with inner groove having different groove pitches.

8 (a) to 8 (d) are graphs showing the surface temperature distribution in the tube circumferential direction at the time of evaporation of the inner grooved heat transfer tube having different fin heights.

9A to 9D are graphs showing a surface temperature distribution in the tube circumferential direction at the time of evaporation in an inner grooved heat transfer tube having different groove pitches.

10 (a) and 10 (b) are schematic views showing the relationship between the shape of the fin base and the thickness of the liquid film, and FIG. 10 (a) shows the case where the fin base is not processed into a curved shape. b) shows the case where the root of the fin is processed on a curved surface.

FIG. 11 is a schematic diagram showing the configuration of a test device for measuring the evaporation heat transfer coefficient and the condensation heat transfer coefficient of the heat transfer tube with the inner groove.

FIG. 12 is a graph showing the relationship between the ratio of the arc radius of the root of the fin to the fin height and the evaporation heat transfer coefficient ratio.

13 (a) and (b) show Example No. 3 of the present invention.
1 and Comparative Example No. It is a graph which shows the test result of No. 4, (a) shows the heat transfer coefficient in a pipe at the time of evaporation, (b) shows the heat transfer coefficient in a pipe at the time of condensation.

14 (a) and (b) show Example No. 3 of the present invention.
2 and Comparative Example No. It is a graph which shows the test result of No. 5, (a) shows the heat transfer coefficient in a pipe at the time of evaporation, (b) shows the heat transfer coefficient in a pipe at the time of condensation.

15 (a) and 15 (b) show Example No. 3 of the present invention.
3 and Comparative Example No. It is a graph which shows the test result of No. 6, (a) shows the heat transfer coefficient in a pipe at the time of evaporation, (b) shows the heat transfer coefficient in a pipe at the time of condensation.

[Explanation of symbols] 1a to 1d; heat transfer tube with internal groove 2; Refrigerant liquid 3; groove 4; Trace of indentation 5: Line parallel to the tube axis direction on the inner surface of the tube 6a to 6c; fins 7a, 7b; root of fin 8; pipe top 9; Refrigerant gas 10: Line orthogonal to the tube axis direction on the inner surface of the tube 11; Testing Department 12; Piping section 13; Test tube 13a; test part of test tube 13 14; tube 15; Thermal insulation 16; Thermocouple 17; Water entrance 18: Refrigerant inlet / outlet 19; Pump 20; Testing Department 21; Bypass section 22; Inner tube 23; outer tube 24; heater 25; Expansion valve 26; water tank 27; Bypass condenser 28; Expansion valve 29; Bypass evaporator 30; Compressor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 2002-301514 (JP, A) Patent 2997189 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) F28F 1/40

Claims (4)

(57) [Claims] 1. A heat transfer tube having an inner surface groove having a groove formed on the inner surface of the pipe, which is used in a heat exchanger using difluoromethane or a mixture containing difluoromethane as a refrigerant, and the lead angle of the groove on the inner surface of the pipe is 25 °. Above, the groove pitch is 0.25mm
In addition to the above, in the development view of the inner surface of the pipe, the locus of the indentation appearing on the inner surface of the pipe as a result of pressing the outer surface of the pipe with the rolling ball or the rolling roll is 0 ° in the same direction as the groove with respect to the direction orthogonal to the pipe axis. An inner grooved heat transfer tube, which is inclined at an angle of more than 10 °. 2. The inner grooved heat transfer tube according to claim 1, wherein the height of the fins formed on the inner surface of the tube is 0.10 mm or more. 3. The inner surface grooved heat transfer tube according to claim 1, wherein the groove pitch is 0.40 mm or less. 4. The fin has a base with an arc shape, the radius of the arc is R, and the height of the fin is Hf.
The inner surface grooved heat transfer tube according to any one of claims 1 to 3, wherein R / Hf has a value of 0.15 to 0.45.