JPH11211378A - Heat transfer pipe for heat-exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat transfer pipe for a heat-exchanger having a thin section and a sufficiently high pressure resisting strength even when a refrigerant having a working pressure higher than that of R22 is used. SOLUTION: A refrigerant the phase of which is changed is caused to flow through a pipe and heat-exchange with fluid outside a pipe to cause the occurrence of vaporization or condensation of a refrigerant. In such a heat transfer pipe for a heat-exchanger, the number of cycle to break available when a repeated pressure being 1.5 times a working pressure is exerted is 326, 500 times or more and a ratio of a minimum thickness T of a pipe to the outside diameter thereof is 0.04-0.056.

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 used for a heat exchanger such as an air conditioner and a refrigerator.

[0002]

2. Description of the Related Art R22 is a conventional refrigerant used in air conditioners such as room air conditioners and package air conditioners.
However, since R22 has a high ozone layer depletion potential, it has been switched to R410A from the viewpoint of environmental protection.

The condensing pressure of R410A (hereinafter referred to as operating pressure) is the operating pressure of R22 (about 18 kgf / cm).
² (1.76 × 10 ⁶ Pa)), the refrigerant is changed to R410A and the condensation temperature is changed to R2.
2 When the temperature is about 50 ° C, which is the same as when using, R410A
Operating pressure is about 30 kgf / cm ² (2.94 × 10 ⁶
Pa). Therefore, when R410A is used as the refrigerant, it is necessary to improve the pressure resistance of the equipment used, and also to improve the pressure resistance of the heat exchanger tubes for the heat exchanger.
Here, as a heat exchanger tube for a heat exchanger, an inner surface grooved tube is often used.

FIG. 6 shows a cross sectional view of an inner grooved tube.

As shown in FIG. 6, a plurality of continuous fins 32 are formed on the inner surface of an inner grooved tube 31, and an inner groove 33 is formed between adjacent continuous fins 32.
Thickness T of inner grooved tube 31 at the base of continuous fin 32
Is, for example, an inner grooved copper pipe having an outer diameter D of φ7.0 mm, which is 0.25 to 0.27 mm.

[0006]

However, since the evaluation pressure for measuring the pressure resistance of the heat exchanger tube for a heat exchanger is 1.5 times the working pressure, the evaluation pressure of R22 is about 2 times.
8 kgf / cm ² (2.74 × 10 ⁶ Pa), R410
The evaluation pressure of A is about 45 kgf / cm ² (4.41 × 10
⁶ Pa).

In the conventional case where R22 is used as the refrigerant, no problem has occurred in the durability of the heat exchanger tubes for the heat exchanger. Therefore, when R410A is used as the refrigerant, when the stress of the heat exchanger tubes for the heat exchanger is R22. If they are equal, there is no problem in durability.

Accordingly, a thin cylinder formula σ = p (b ₀ / t−1) (where σ: stress, b ₀ : initial outer diameter, t = b ₀ −a ₀ ,
a _0: initial inner diameter, p: pressure (Mechanical Engineering Handbook Japan Society of Mechanical Engineers ed. 1987 Chapter 6 A4-72)) using a, p =
28 kgf / cm ² , t = 0.25 mm, b ₀ = 7.0
mm, the stress σ ₂₂ of the heat transfer copper tube for a heat exchanger when R22 is used as the refrigerant is σ ₂₂ = 756 kgf / cm
It becomes ² . Next, when the stress of the heat transfer copper pipe for a heat exchanger when p = 45 kgf / cm ² and R410A is used as the refrigerant is σ ₂₂ , and the thickness t when b ₀ = 7.0 mm is obtained from the equation, , T = 0.39 mm.

Therefore, in the current technology, the refrigerant is R
22 to R410A, and the condensation temperature to R2
2 When the temperature is the same as when using 50 ° C, φ7.0m
The minimum thickness of the heat transfer copper tube for heat exchangers is 0.39mm
Required (thickness / outer diameter ratio ≧ 0.056).

That is, the heat transfer copper pipe for the heat exchanger when using R410A is about 0.14 mm thicker than the conventional heat transfer copper pipe for heat exchanger when using R22. As the weight per unit length of the hot copper tube increases,
Since the inner diameter is reduced by about 0.28 mm, problems such as an increase in pressure loss of the heat transfer copper tube for a heat exchanger occur.

When a heat transfer copper tube for a heat exchanger is incorporated into a heat exchanger, an expansion plug is inserted into the copper tube to increase the adhesion between the outer surface of the copper tube and the plate fin. The outer diameter of has been expanded. At this time, as the thickness of the heat transfer copper tube for a heat exchanger increases, the load required for expanding the copper tube also increases. For this reason, in the copper pipe with an inner surface groove in which a groove is formed on the inner surface of the copper tube, a large force acts to crush the fins on the inner surface of the copper tube during expansion.
Fin collapse at the time of tube expansion is greater than in the case of using R22. As a result, there is a problem that the heat transfer coefficient of the inner grooved pipe is greatly reduced, and the performance of the air conditioner itself is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a heat exchanger tube for a heat exchanger which is thin and has a sufficient pressure resistance even when a refrigerant having a higher working pressure than R22 is used. .

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the invention of claim 1 circulates a phase-change refrigerant in a pipe and causes heat exchange with a fluid outside the pipe to cause evaporation or condensation of the refrigerant. In the heat exchanger tube for a heat exchanger, the number of repetitions of destruction when a repetitive pressure 1.5 times the working pressure is applied is 326,500 or more, and the ratio of the minimum wall thickness to the outer diameter of the tube is 0. 04 to 0.056.

According to a second aspect of the present invention, the repetition pressure is 4
The heat exchanger tube for a heat exchanger according to claim 1, wherein the heat transfer tube has a pressure of 5 kgf / cm ² (about 4.41 × 10 ⁶ Pa) or more.

According to a third aspect of the present invention, the refrigerant is R410A
The heat exchanger tube for a heat exchanger according to claim 1, wherein

According to the above-described structure, in the heat exchanger tube for a heat exchanger in which the phase-changing refrigerant is circulated in the pipe and exchanges heat with the fluid outside the pipe to cause the refrigerant to evaporate or condense, the operating pressure of 1.5. Since the number of times of destruction repetition when a double pressure is applied is 326,500 times or more, and the ratio of the minimum wall thickness to the outer diameter of the pipe is 0.04 to 0.056, it is thin and Even when a refrigerant having a higher working pressure than R22 is used, a heat exchanger tube for a heat exchanger having a sufficient pressure resistance can be obtained.

[0017]

Embodiments of the present invention will be described below.

In the heat exchanger tube for a heat exchanger of the present invention, the number of times of destruction repetition when a repetitive pressure 1.5 times the working pressure is applied is 326,500 times or more, and the minimum wall thickness and outer diameter of the tube. Is 0.04 to 0.056.

Although the heat transfer tube for the heat exchanger is not particularly limited, an inner grooved tube is particularly preferable in consideration of heat exchange efficiency.

The material of the heat exchanger tube is not particularly limited, but copper or a copper alloy is particularly preferred.

Next, the operation of the present invention will be described.

R22 whose working pressure is about 18 kgf / cm ²
Heat exchanger tube for heat exchanger, for example, the outer diameter is 7.0m
m, when using a grooved tube with an inner surface with a minimum thickness of 0.25 mm, if the refrigerant is changed from the current R22 to R410A while keeping the condensing temperature substantially equal, the working pressure becomes about 30 kgf / c.
m ² , the pressure resistance must be improved. In the case where the outer diameter of the pipe is the same, the calculated dimension of the inner grooved pipe for R410A is 0.39 from the above equation.
mm.

However, in the heat exchanger tube for a heat exchanger of the present invention, the number of times of destruction when applying a repetitive pressure 1.5 times the working pressure is 326,500 or more, and
Since the ratio between the minimum wall thickness and the outer diameter of the pipe is defined as 0.04 to 0.056, the outer diameter is actually 7.0 mm and the minimum wall thickness is 0.28 to 0.392 mm. .

That is, according to the heat exchanger tube for a heat exchanger of the present invention, the number of repetitions of breakage when a repetitive pressure 1.5 times the working pressure is applied and the ratio of the minimum wall thickness to the outer diameter of the tube are specified. Therefore, when using a refrigerant having a higher working pressure than R22, which is the current refrigerant, while maintaining sufficient durability, the minimum wall thickness obtained from the working pressure of R22 by using the thin cylinder formula is used. Further, a heat exchanger tube for a heat exchanger having a small thickness can be obtained.

In addition, since the minimum thickness of the heat exchanger tube for a heat exchanger is reduced, the cross-sectional area in which the refrigerant flows in the tube increases, and the pressure loss of the refrigerant can be reduced. Further, since the thickness can be further reduced from the minimum thickness estimated from the calculation, the weight per unit length of the heat exchanger tube for a heat exchanger can be reduced. That is, it is effective in reducing the weight of the heat exchanger and improving the efficiency of the entire air conditioner.

Next, another embodiment of the present invention will be described.

FIG. 2 is a schematic view of a part of the inner surface of the heat exchanger tube for a heat exchanger according to the first embodiment.

As shown in FIG. 2, the heat exchanger tube (tube with an inner surface groove) 1 for a heat exchanger of the present embodiment has an inner surface groove 3 and a second groove 4 intersecting with the inner surface groove 3 on the inner surface of the tube. A large number of projections (fins) 2 having a substantially triangular cross section are formed on the inner surface of the tube. In the figure, the portion of the second groove 4 has the minimum thickness T, but it goes without saying that the groove depth of the inner surface groove 3 may be deeper than the second groove 4. Further, the intersection angle between the inner surface groove 3 and the second groove 4 is not particularly limited.

FIG. 3 is a schematic view of a part of the inner surface of the heat exchanger tube for a heat exchanger according to the second embodiment.

As shown in FIG. 3, a heat exchanger tube (inner grooved tube) 11 for a heat exchanger of the present embodiment has an inner surface groove 13 having a step portion 14 on the inner surface of the tube to form a large number of grooves on the inner surface of the tube. The continuous fins 12 are formed. In the figure, the inner surface groove 1
The cross-sectional shape of the three bottoms is concave, but it goes without saying that it may be convex. Needless to say, the number of steps 14 at the bottom of the inner groove 13 may be plural.

Here, when the heat exchanger tubes (inner grooved tubes) 1 and 11 of the first and second embodiments are actually welded to the heat exchanger, no weld bead portion is included. The thickness of the portion of the second groove 4 and the step portion 14 is defined as a minimum thickness (bottom thickness) T. This is because the weld bead portion is thicker than the portion of the second groove 4 and the step portion 14.

The durability of the heat exchanger tubes (inner grooved tubes) 1 and 11 of the first and second embodiments against internal pressure depends on the number and shape of the fins 2 and 12 formed on the inner surfaces of the tubes. , And not due to the tip processing state,
It is clear that this is due to the minimum wall thickness of the tube. Therefore, the number, shape, and processing state of the end portions of the fins 2 and 12 are not particularly limited, and are appropriately selected.

Further, the boundaries between the fins 2, 12 and the inner grooves 3, 13 in the heat exchanger tubes (inner grooved tubes) 1, 11 of the first and second embodiments are caused by stress concentration. In order to avoid cracks in the pipe, it is preferable to carry out R processing.

It is needless to say that the heat transfer tubes for heat exchangers of the first and second embodiments also have the same operational effects as the present invention.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, R22 having a minimum thickness of 0.25 mm
For the inner grooved tube for use, the same expansion tube and hairpin bending process as in the heat exchanger assembly was used as the evaluation sample.
An internal pressure repetition test was performed by applying a repetition pressure (evaluation pressure; 30 kgf / cm ² ) 1.5 times the operating pressure of the current room air conditioner, and the number of repetitions up to destruction was evaluated. At this time, the variation of the pressure on the air-conditioning heat exchanger, since the time of operation from the air conditioner stop state operating state and vice versa is maximum, 1.0~30kgf / cm ² (about 0.098 × 10 ⁶ ~ The pressure is repeatedly increased and reduced in the range of 2.94 × 10 ⁶ Pa).

As a result, the inner grooved pipe for R22 is 32
At 6,500 times, structural destruction occurred. The heat exchanger using the current refrigerant R22 has sufficient durability (pressure resistance)
Therefore, the repetition number 326,500 times is a criterion for determining durability. That is, the working pressure is
Even if the operating pressure of the current air conditioner heat exchanger is higher than that of the current air conditioner, the durability of the heat exchanger of the current air conditioner is equal to or higher than that of the current air conditioner in the repetition test at the evaluated pressure.
(326,500 times or more), it is considered that sufficient durability can be ensured even in a use environment similar to that of a heat exchanger of a current air conditioner.

FIG. 4 shows a hydraulic system diagram of the internal pressure repetition tester used for the durability test.

As shown in FIG.
1 is an oil tank 22 for storing hydraulic oil 23
, A hydraulic pump 24 for drawing up the hydraulic oil 23, a motor 25 for driving the hydraulic pump 24, and a part of the hydraulic oil 23 discharged from the hydraulic pump 24 Relief valve 26 for returning pressure and pressure gauge 2 for measuring generated pressure
7 and the pressurized hydraulic oil 23 are supplied to the flexible hose 2
Internal grooved tube (test sample) 21 connected via 9
And a return pipe 30 to the oil tank 22.

Hydraulic oil 23 discharged from hydraulic pump 24
By adjusting the amount of oil returning to the oil tank 22 by the relief valve 26, the pressure applied to the inner grooved pipe 21 is adjusted. This pressure adjustment is performed while measuring the pressure with the pressure gauge 27.

The pressurization and depressurization of the inner grooved pipe 21 is performed by switching the hydraulic path by the ON / OFF operation of the solenoid valve 28. The ON and OFF holding times of the solenoid valve 28 can be set by individual timers (not shown).

Next, as a heat exchanger tube for a heat exchanger for R410A, tubes each having an inner diameter of 7 mm with a different wall thickness and subjected to the same expansion and hairpin bending as in the assembly of the heat exchanger were used. Pressure of 1.6 to 45 kgf / cm ² (approximately 0.157 × 10 ^{6 to} 4.41 × 10 ⁶ Pa), and the relationship between the number of repetitions up to the destruction of each inner grooved tube and the wall thickness. The minimum wall thickness of the inner grooved pipe for R410A having the durability equal to or more than that of the inner grooved pipe for R22 is determined.

FIG. 5 shows a chart of the pressure gradient in the internal pressure repetition test. In the figure, the horizontal axis represents time, and the vertical axis represents pressure (kgf / cm ² ).

As shown in FIG. 5, the internal pressure repetition test
The holding time of ON and OFF of the solenoid valve is set to 5 sec and 1.5 sec, respectively, and 1.6 to 4 sec.
The pressure is repeatedly increased and reduced in the range of 5 kgf / cm ² continuously.

FIG. 1 shows the relationship between the number of repetitions up to the destruction of the heat exchanger tube for a heat exchanger of the present invention and the wall thickness. The abscissa in the figure indicates the number of repetitions of fracture (× 10 ⁵ times) when the internal pressure repetition test shown in FIG. 5 was performed, and the ordinate indicates the inner grooved tube (for heat exchanger) before being assembled into the heat exchanger. Minimum wall thickness of heat transfer tube (m)
m), and the dotted line in the figure indicates 336,500 lines.

As shown in FIG. 1, the minimum thickness of the inner grooved pipe having the number of times of destruction repeated at the evaluation pressure exceeding 336,500 is 0.28 mm or more. This is at least 0.04 times the outer diameter of the inner grooved tube. Here, the upper limit of the minimum thickness is 0.056 or less, which is the thickness / outer diameter ratio obtained from the above-described equation.

Needless to say, the heat exchanger tube for a heat exchanger of the present invention can be applied not only to air conditioners but also to general heat exchangers, and the refrigerant used is not limited to R410A, and the operating pressure is not limited to R410A. May be a refrigerant larger than 30 kgf / cm ² .

[0047]

In summary, according to the present invention, the number of repetitions of breakage and the ratio of the minimum wall thickness to the outer diameter of a pipe when a repetitive pressure 1.5 times the working pressure is applied are defined. When using a refrigerant having a higher operating pressure than R22, which is a refrigerant, the wall thickness is thinner than the minimum thickness obtained by using the thin-walled cylindrical formula from the operating pressure of R22 while maintaining sufficient durability. An excellent effect that a heat exchanger tube for a heat exchanger can be obtained is exhibited.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of repetitions up to destruction and the wall thickness of a heat exchanger tube for a heat exchanger of the present invention.

FIG. 2 is a schematic diagram of a part of the inner surface of the heat exchanger tube for a heat exchanger according to the first embodiment.

FIG. 3 is a schematic view of a part of an inner surface of a heat exchanger tube for a heat exchanger according to a second embodiment.

FIG. 4 is a hydraulic system diagram of an internal pressure repetition tester used for a durability test.

FIG. 5 is a chart of a pressure gradient in an internal pressure repetition test.

FIG. 6 is a cross-sectional view of the inner grooved pipe.

[Explanation of symbols]

 T Minimum thickness

Claims (3)

[Claims] 1. A heat exchanger tube for a heat exchanger, in which a phase-changing refrigerant flows through a pipe and exchanges heat with an extrapipe fluid to cause the refrigerant to evaporate or condense.
The number of repetition of destruction when applying double pressure is 32
A heat exchanger tube for a heat exchanger, wherein the ratio is a minimum of 6,500 times and the ratio of the minimum wall thickness to the outer diameter is 0.04 to 0.056. 2. The method according to claim 1, wherein the repetition pressure is 45 kgf / cm ^2.
The heat transfer tube for a heat exchanger according to claim 1, wherein the heat transfer tube is at least about 4.41 x 10 ⁶ Pa. 3. The heat exchanger tube for a heat exchanger according to claim 1, wherein the refrigerant is R410A.