JPH11201680A - Internally grooved tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a single weight without deteriorating the performance of heat transfer. SOLUTION: When Di indicates the maximum internal diameter of an internally grooved tube, with Hf indicating the height of a fin that is formed between grooves, Wf indicating the width of the base of this fin, θ indicating the angle of torsion, which is formed by the direction in that the grooves are formed and the direction of the tube axis, and P indicating the pitch of the grooves in the direction of the tube periphery, Hf/Di ranges from 0.01 to 0.02, θ/Di ranges from 2.0 to 4.5, Hf/Wf is less than 1.6, and P ranges from 0.35 to 0.45 (mm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner grooved tube made of, for example, copper or a copper alloy, which is suitable for a heat exchanger of a room air conditioner or the like, and more particularly to an inner grooved tube having a reduced weight.

[0002]

2. Description of the Related Art In recent years, a heat pump type air conditioner which is used for both cooling and heating has become mainstream as a room air conditioner. The heat transfer tube made of copper or copper alloy used in the heat pump type air conditioner or the like is required to have excellent evaporation performance and condensation performance. In order to enhance the evaporation performance of the heat transfer tube, a structure is required in which the refrigerant liquid is spread over the entire inner surface of the tube, which is a heat transfer surface, so that the refrigerant evaporates over the entire inner surface of the tube. On the other hand, in order to increase the condensation performance of the heat transfer tube, a structure that prevents the refrigerant liquid from spreading over the entire tube inner surface is required to prevent the inner surface of the tube from being covered with the condensed refrigerant liquid. . Therefore, in order to obtain a heat transfer tube having excellent evaporation performance and condensation performance, a structure that satisfies the aforementioned contradictory characteristics is required.

[0003] Therefore, as such a heat transfer tube, a tube with an inner surface groove having improved heat transfer efficiency by forming a plurality of spiral parallel grooves on the inner surface of the tube is used. And, the weight per unit length (hereinafter, referred to as single weight) of the inner grooved pipe in the pipe axis direction is reduced to reduce the cost of the heat exchanger. For example, Japanese Patent Application Laid-Open Nos. 5-18991 and 5-79783 have proposed a grooved tube having an inner surface with a reduced weight. In the inner grooved pipe described in JP-A-5-1891, the ratio of the groove depth to the pipe inner diameter, the torsion angle of the groove with respect to the pipe axis, the groove cross-sectional area with respect to the groove depth, and the peak angle of the fin are defined. By doing so, the performance and weight of the inner grooved pipe are improved.

On the other hand, in the case of an inner grooved pipe described in Japanese Patent Application Laid-Open No. 5-79783, the outer diameter of the pipe, the twist angle of the groove with respect to the pipe axis, the ratio of the groove depth to the pipe inner diameter, the wall thickness of the pipe, the groove By defining the width of the groove bottom with respect to the depth and the peak angle of the fin, the performance and weight of the inner grooved tube are improved.

[0005] Further, there has been proposed an inner grooved pipe in which a plurality of parallel grooves which cross each other are formed on the inner surface of the pipe (Japanese Utility Model Application Laid-Open No. H06-163).
3-148078). In the tube with an inner surface groove described in this publication, since grooves intersecting each other are formed on the inner surface of the tube, a plurality of quadrangular pyramid-shaped protrusions are formed on the inner surface of the tube. By adopting such a shape, the heat transfer performance is improved as compared with the existing inner grooved tube.

[0006]

However, there is a problem that the reduction of the single weight and the maintenance of the heat transfer performance by the above-mentioned conventional inner grooved tube are not sufficient.

[0007] In the case of a tube with an inner surface groove described in Japanese Patent Application Laid-Open No. Hei 5-1891, the ratio of the groove depth to the inner diameter of the tube is set to 0.1.
The fin is so high that the reduction of the unit weight is not sufficient.

Further, in the tube with an inner surface groove described in Japanese Patent Application Laid-Open No. Hei 5-79783, the ratio of the groove depth to the inner diameter of the tube is specified to be 0.023 to 0.025. Is not enough.

On the other hand, if the ratio of the groove depth to the inner diameter of the tube is simply set to be small, the fins become low and the heat transfer performance deteriorates.

Further, even in the tube with an inner surface groove described in Japanese Utility Model Application Laid-Open No. 63-148078, the reduction of the single weight is not sufficient.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an inner grooved tube capable of reducing a single weight without deteriorating heat transfer performance.

[0012]

An inner grooved pipe according to the present invention has a maximum inner diameter in an inner grooved pipe in which a plurality of spiral parallel grooves extending in a direction inclined in the pipe axis direction are formed on the inner surface of the pipe. Di, the height of the fins formed between the grooves is Hf, the width of the base of the fins is Wf, the torsion angle between the direction in which the grooves are formed and the tube axis direction is θ, the circumferential direction of the grooves. Where Hf / Di is 0.01 to 0.02, θ / Di is 2.0 to 4.5, and Hf / Wf
Is less than 1.6, and P is 0.35 to 0.45 (mm).

In the present invention, since the shape of the groove formed on the inner surface of the tube is specified appropriately, the single weight can be reduced without lowering the evaporation performance and the condensation performance as compared with the conventional product. be able to.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive experiments and research conducted by the present inventors to solve the above problems, the maximum inner diameter Di
Ratio Hf / Di of fin height Hf to maximum diameter D
ratio of the helix angle θ of the spiral groove to the pipe axis with respect to i / θ / D
i, the ratio H of the height of the fin to the width Wf of the base of the fin, H
By defining f / Wf and the groove pitch P to appropriate values, it has been found that the single weight of the inner grooved pipe made of copper or copper alloy can be reduced without lowering the heat transfer performance.

The reason for limiting the numerical value of the inner grooved pipe according to the present invention will be described below. FIG. 1 is a schematic sectional view illustrating a position corresponding to the maximum inner diameter Di of the inner grooved pipe, the height Hf of the fin, the width Wf of the base of the fin, and the groove pitch P. On the inner surface of the inner grooved tube 1, spiral grooves 2 extending in a direction inclined with respect to the tube axis direction are formed at regular intervals. As a result, between the adjacent grooves 2, fins 3 having a mountain shape are formed. Here, the maximum inner diameter Di is
The distance from the bottom 4 of the groove 2 to the tube axis (not shown) is doubled. The fin height Hf is defined as fin 3
From the top 5 to the cylindrical surface having a radius of (Di / 2) about the tube axis. The width of the base of the fin is the distance between the side surfaces 6 at the base of the fin 3. The groove pitch P is the interval between the adjacent fins 3 on the cylindrical surface, and when the number of grooves in the pipe circumferential direction is m, (π ×
Di / m).

FIG. 2A is a schematic perspective view for explaining the position corresponding to the torsion angle θ of the inner grooved pipe, and FIG. 2B is a schematic sectional view of the same. The torsion angle θ of the spiral groove with respect to the tube axis is the angle between the tube axis direction and the direction in which the groove 2 extends when the inner grooved tube 1 is cut open along the cut portion 7 parallel to the tube axis. .

The height Hf of the fin with respect to the maximum inner diameter Di
Ratio Hf / Di: 0.01 to 0.02 The inventors of the present invention have determined that the height H of the fin with respect to the maximum inner diameter Di.
The relationship between the ratio ff / Di of f and the heat transfer coefficient of evaporation was investigated.
The result is shown in FIG. FIG. 3 is a graph showing the relationship between the ratio Hf / Di on the horizontal axis and the heat transfer coefficient in the pipe during evaporation on the vertical axis. In the measurement of the heat transfer coefficient in the pipe,
Two types of inner grooved tubes having an outer diameter of 7 mm or 9.52 mm were used, and R22 was used as a refrigerant. R22 is a name in the American Society for Heating, Refrigeration and Air Conditioning (ASHHRAE) and is a CFC-based refrigerant represented by the chemical formula CHF ₂ Cl. The length of the inner grooved tube is 3m with an outer diameter of 7mm,
It is 4 m with an outer diameter of 9.52 mm. The refrigerant flow rate when using an inner grooved pipe having an outer diameter of 7 mm is 30 k.
g / h, and the refrigerant flow rate when using an inner grooved tube having an outer diameter of 9.52 mm is 40 kg / h.
Further, the evaporation temperature is 7.5 ° C., the temperature before the expansion valve is 40 ° C., and the superheat degree at the outlet is 5 ° C. In FIG. 3, the solid line indicates that the outer diameter is 7
The results are shown for an internally grooved tube with an outer diameter of 9.52 mm.
4 shows the results for an internally grooved tube of mm.

If the ratio Hf / Di of the fin height Hf to the maximum inner diameter Di is less than 0.01, the heat transfer coefficient of evaporation is extremely low as shown in FIG. This is because when the height of the fins is extremely low, the capillary effect does not occur, the diffusion effect of the refrigerant liquid is almost eliminated, and the refrigerant liquid does not spread to the upper part of the tube. On the other hand, when the ratio Hf / Di exceeds 0.02, the single weight cannot be reduced as compared with the conventional product. Therefore, the ratio Hf / Di of the fin height Hf to the maximum inner diameter Di is set to 0.01 to 0.02.

With respect to the tube axis of the spiral groove with respect to the maximum inner diameter Di
Ratio of the torsion angle θ / Di: 2.0 to 4.5 The present inventors have determined the ratio of the torsion angle θ to the tube axis of the spiral groove with respect to the maximum inner diameter Di, θ / Di, the evaporation heat transfer rate, and the condensation heat transfer. The relationship between rate and pressure drop was investigated. The results are shown in FIGS. 4A and 4B and FIG. 4A and 4B are diagrams in which the horizontal axis indicates the ratio θ / Di and the vertical axis indicates the in-tube heat transfer coefficient. FIG. 4A shows the ratio θ / Di and the in-tube heat transfer during evaporation. FIG. 4B is a graph showing the relationship with the ratio, and FIG.
It is a graph which shows the relationship between i and the heat transfer coefficient in a pipe at the time of condensation. The measurement conditions for the heat transfer coefficient in the tube during evaporation are the same as those described above. In the measurement of the heat transfer coefficient in the pipe during condensation, the same inner grooved pipe and refrigerant as described above were used, and the condensing temperature was set at 4%.
5 ° C., the inlet temperature was 70 ° C., and the outlet subcooling degree was 5 ° C.
4 (a) and 4 (b), the solid line indicates that the outer diameter is 7 mm.
mm shows the result for an internally grooved tube, and the dashed line shows the result for a 9.52 mm internally grooved tube.

As shown in FIG. 4 (a), when the ratio θ / Di is about 2.0, the heat transfer coefficient of evaporation becomes maximum.
The groove is formed in a spiral shape so as to extend in a direction inclined with respect to the tube axis direction in order to easily spread the refrigerant on the entire inner surface of the tube. However, if the twist angle θ becomes excessively large,
The gravitational component of the force acting on the refrigerant increases, so that the refrigerant hardly spreads on the upper part of the pipe, and on the contrary, the heat transfer coefficient of evaporation decreases.

As shown in FIG. 4B, the ratio θ / D
Although the condensed heat transfer coefficient increases with increasing i, the ratio θ / D
Almost saturated when i reaches around 4.5. In order to improve the heat transfer coefficient of condensation, it is necessary to reduce the wetting and spreading property of the refrigerant, contrary to the case of the heat transfer coefficient of evaporation. The gaseous refrigerant flowing into the inner grooved tube is deprived of heat by the inner wall of the tube and is condensed to become a liquid. However, when the wet refrigerant has high spreading property, the liquefied refrigerant covers the inner surface of the tube. And
The refrigerant itself acts as thermal resistance, and condensed heat transfer coefficient is reduced. For this reason, it is desirable that the upper part of the tube is always in a dry state, condensing the gaseous refrigerant, and the liquefied refrigerant is flowing in the lower part of the tube.

As described above, when the torsion angle θ increases, the refrigerant hardly spreads over the upper part of the pipe, so that a dry region can be formed on the upper part of the pipe. But,
Even if the torsion angle θ is increased, the area of the region through which the refrigerant can flow in the cross section perpendicular to the tube axis does not increase, and therefore, the area of the dry region has an upper limit. Therefore, as shown in FIG. 4B, there is a twist angle θ at which the improvement of the ratio θ / Di is saturated.

FIG. 5 is a graph showing the relationship between the ratio θ / Di on the horizontal axis and the pressure loss during evaporation on the vertical axis. The measurement conditions are the same as those described above. In FIG. 5, the solid line shows the result for an inner grooved tube with an outer diameter of 7 mm, and the broken line shows the result for a 9.52 mm inner grooved tube. When the torsion angle θ is increased in the inner grooved pipe,
As shown in FIG. 5, the pressure loss increases accordingly.
When the pressure loss increases, the heat exchanger inlet temperature increases during evaporation, and the temperature difference between the air and the refrigerant decreases. For this reason,
The heat transfer coefficient of evaporation decreases.

From the above, when the evaporation performance is important,
When the ratio θ / Di is set to about 2.0 and the condensation performance is emphasized, the optimum performance can be obtained by setting the ratio θ / Di to about 4.5. However, in the recent room air conditioners, the cooling / heating type is mainly used, so that the inner grooved pipe is required to have high evaporation performance and high condensation performance.
Therefore, the ratio θ / Di of the torsion angle θ of the spiral groove to the tube axis with respect to the maximum inner diameter Di is set to 2.0 to 4.5.

Fin height relative to fin base width Wf
The ratio Hf / Wf of the height Hf is less than 1.6 The present inventors investigated the relationship between the ratio Hf / Wf of the height Hf of the fin to the width Wf of the base of the fin and the inclination angle of the fin after expansion. The result is shown in FIG. FIG. 8 is a graph showing the relationship between the ratio Hf / Wf on the horizontal axis and the inclination angle of the fin after expansion on the vertical axis. FIG.
FIG. 4 is a schematic cross-sectional view illustrating a fin inclination angle の. In the measurement of the fin inclination angle after the expansion, first, the expansion blit attached to the tip of the mandrel is inserted into the inner grooved tube, and the inner grooved tube is expanded by pushing the inner grooved tube into close contact with the fin material. I let it. Next, as shown in FIG. 9, the angle between the direction 8 in which the fins inclined by the expansion and the radial direction 9 formed was measured as the inclination angle ξ.

When the ratio Hf / Wf of the height Hf of the fin to the width Wf of the base of the fin is 1.6 or more, the inclination angle ξ becomes extremely high as shown in FIG. Further, the fins are easily collapsed by the expansion. As described above, when the inclination angle 高 く is increased or the fins are crushed, the heat transfer performance of the inner grooved tube may not be exhibited. Therefore, the width W of the base of the fin
The ratio Hf / Wf of the fin height Hf to f is less than 1.6.

Groove pitch P: 0.35 to 0.45 (m
m) The present inventors investigated the relationship between the groove pitch P and the evaporation heat transfer coefficient, the condensation heat transfer coefficient, and the unit weight. The result is shown in FIG.
(A) and (b) and FIG. 6A and 6B are diagrams in which the horizontal axis indicates the groove pitch P and the vertical axis indicates the heat transfer coefficient in the pipe. FIG. 6A shows the groove pitch P and the heat transfer coefficient in the pipe at the time of evaporation. (B) is a graph showing the relationship between the groove pitch P and the heat transfer coefficient in the pipe during condensation. The measurement conditions for the heat transfer coefficient in the tube are the same as those described above. FIG. 7 is a graph showing the relationship between the groove pitch P on the horizontal axis and the unit weight on the vertical axis. 6 (a) and 6 (b) and FIG. 7, the solid line shows the results for an inner grooved tube having an outer diameter of 7 mm, and the broken line shows 9.52 mm.
3 shows the result of the inner grooved tube.

When the groove pitch P is less than 0.35 mm,
Since the width of the groove is extremely narrow, the heat transfer coefficient of evaporation is extremely low as shown in FIG. Further, as shown in FIG. 7, the single weight increases. On the other hand, the groove pitch is 0.45 mm
When the pressure exceeds the surface area, the surface area of the inner surface of the pipe is reduced.
As shown in (b), the condensation heat transfer coefficient becomes extremely low.
Therefore, the groove pitch P is set to 0.35 to 0.45 (mm).

The material of the inner grooved pipe is not limited to copper or copper alloy. For example, an inner grooved tube made of aluminum or an aluminum alloy may be used.

[0030]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples.

First, an inner grooved tube having grooves having the shapes shown in Tables 1 and 2 below was prepared. In addition, the wall thickness of the groove portion of each inner surface grooved tube is 0.28 mm, the outer diameter is 9.52 mm, and the length is 4 m.

[0032]

[Table 1]

[0033]

[Table 2]

Next, in each of Examples and Comparative Examples, R22 was used as a refrigerant, and the flow rate of the refrigerant was 40 kg / h.
The heat transfer coefficient of evaporation and the heat transfer coefficient of condensation were measured. In addition, the single weight and the inclination angle の of the fin after expansion were measured.
The test material for measurement was expanded at a pipe expansion ratio of 105%. The expansion ratio is (outer diameter after expansion) /
(Outer diameter before expansion) × 100. The results are shown in Table 3 below.

When measuring the heat transfer coefficient of evaporation, the evaporation temperature was 7.5 ° C., the temperature before the expansion valve was 40 ° C., and the superheat degree at the outlet was 5 ° C.
And

On the other hand, when measuring the condensation heat transfer coefficient, the condensation temperature was set at 45.degree. C., the inlet temperature was set at 70.degree.
° C. The results are shown in Table 3 below. Table 3
, The heat transfer coefficient of evaporation and the heat transfer coefficient of condensation are values obtained by converting the value of Comparative Example 3, which is a conventional product, to a reference value of 1.00.

[0037]

[Table 3]

As shown in Table 3 above, in Example 1, since the groove shape of the inner grooved pipe is appropriate, it is possible to significantly reduce the unit weight while maintaining the same performance as the conventional product. did it. Further, in Example 2, since the groove shape of the inner grooved tube was appropriate, the single weight could be reduced, and the evaporation heat transfer coefficient and the condensation heat transfer coefficient could be significantly improved. .

On the other hand, in Comparative Example 4, since the groove pitch P was less than the lower limit of the range of the present invention, the heat transfer coefficient of evaporation was low.

In Comparative Example 5, since the groove pitch P exceeded the upper limit of the range of the present invention, the heat transfer coefficient, particularly the condensation heat transfer coefficient, was low.

In Comparative Example 6, since the ratio Hf / Di was less than the lower limit of the range of the present invention, although the unit weight was reduced, the heat transfer coefficient of evaporation and the heat transfer of condensation were remarkably low.

In Comparative Example 7, since the ratio θ / Di was less than the lower limit of the range of the present invention, the condensed heat transfer coefficient was low.

In Comparative Example 8, since the ratio Hf / Wf exceeded the upper limit of the range of the present invention, the fin inclination angle ξ after the expansion was significantly increased. For this reason, the heat transfer coefficient, especially the evaporation heat transfer coefficient, was low.

[0044]

As described in detail above, according to the present invention,
Since the shape of the groove formed on the inner surface of the tube is specified to be appropriate, it is possible to reduce the unit weight without lowering the heat transfer performance as compared with the conventional product. Thereby, the cost of the heat exchanger can be reduced.

[Brief description of the drawings]

FIG. 1 shows the maximum inner diameter Di of the inner grooved pipe and the height H of the fin.
FIG. 4 is a schematic cross-sectional view illustrating a position corresponding to f, a peak angle α of a fin, and a groove pitch P.

FIG. 2A is a schematic perspective view illustrating a position corresponding to a twist angle θ of an inner grooved pipe, and FIG. 2B is a schematic cross-sectional view of the same.

FIG. 3 is a graph showing the relationship between the ratio Hf / Di on the horizontal axis and the heat transfer coefficient in the pipe during evaporation on the vertical axis.

FIG. 4 (a) is a graph showing the relationship between the ratio θ / Di and the heat transfer coefficient in the pipe during evaporation, and FIG. 4 (b) is a graph showing the relation between the ratio θ / Di and the heat transfer coefficient in the pipe during condensation. FIG.

FIG. 5 is a graph showing a relationship between a ratio θ / Di and a pressure loss during evaporation.

6A is a graph showing a relationship between a groove pitch P and a heat transfer coefficient in a pipe during evaporation, and FIG. 6B is a graph showing a relation between the groove pitch P and a heat transfer coefficient in a pipe during condensation. is there.

FIG. 7 is a graph showing the relationship between the groove pitch P on the horizontal axis and the simple weight on the vertical axis.

FIG. 8 is a graph showing the relationship between the ratio Hf / Wf and the inclination angle の of the fin after expansion.

FIG. 9 is a schematic cross-sectional view illustrating a fin inclination angle フ ィ ン.

[Explanation of symbols]

 1; inner surface grooved pipe 2; groove 3; fin 4; bottom 5; top 6; side 7;

Claims (1)

[Claims] An inner grooved pipe having a plurality of spiral parallel grooves extending in a direction inclined in the pipe axis direction on an inner surface of the pipe, wherein a maximum inner diameter is Di, and a height of a fin formed between the grooves is Di. Hf / Di, when the width of the base of the fin is Wf, the torsion angle between the direction in which the groove is formed and the tube axis direction is θ, and the groove pitch of the groove in the circumferential direction of the groove is P, Hf / Di
Is 0.01 to 0.02, and θ / Di is 2.0 to 4.
5, Hf / Wf is less than 1.6, P is 0.35 to 0.4
An inner grooved pipe having a diameter of 5 (mm).