JPH02280933A - Heat transfer tube and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the heat transfer performance by providing >=2 kinds of continuous or discontinuous projections intersecting on the inside surface of a tube. CONSTITUTION:Two kinds of spiral grooves 4, 5 are provided on a grooved roll 2 and they twist to a roll axis and intersect each other at a prescribed intersection angle. A metal bar 1 is rolled by this grooved roll 2 and a smooth roll and the groove shape of the grooved roll 2 is transferred on the surface of one side of the metal bar 1 to provide intersecting oblique projections 6, 7 on the surface of one side of the metal bar 1. Consequently, heat transfer performance can greatly be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat exchanger tube used in a heat exchanger for a refrigerator or an air conditioner, and a method for manufacturing the same.

[Conventional technology]

Heat exchanger tubes used in heat exchangers for refrigerators and air conditioners are generally internally grooved tubes due to their high heat exchange efficiency. This is a pipe in which triangular or trapezoidal protrusions or grooves are continuously formed on the inner surface of the pipe, either parallel to the pipe axis or spirally.
Heat transfer performance is improved compared to smooth tubes. This heat exchanger tube is the first
As shown in Figure 0 (a) and (b), a protrusion (13) is formed on the inner surface of a tube (12), and in a heat exchanger using this, the refrigerant undergoes a phase change of evaporation or condensation within the tube. It is something to be flowed while doing so.

The reason why the heat transfer performance of such an internally grooved tube is improved compared to that of a smooth tube is that the fine grooves on the inner surface cause flow turbulence and the heat transfer area increases. However, when the phase changes on the inner surface in this way, in the high dryness region at the tip of the protrusion,
As shown in Fig. 11, the liquid film (15) is maintained in the groove (14), and even in the tube axis direction, the capillary force in the groove (14) is used to thin the liquid film (15) even to highly dry areas such as the protrusions (13). forms a liquid film,
This works effectively.

This type of heat exchanger tube is a smooth tube (16
) is held in place in the pipe by a die (18) and a floating plug (17) with a grooved plug (19).
and rolling with a rolling roll (2G) provided on the outer periphery of the tube (I6) to form a protrusion (13) on the inner surface of the tube (16), and finally through a finishing die (21), or As shown in FIGS. 13(a) and 1(b), the metal strip (1) is rolled with a grooved roll (2) and a smooth roll (3),
A protrusion is formed on one surface of the metal strip (1), and then the forming roll (8-1), (8-n
) is formed into a tubular shape and its edges are joined together.

[Problem to be solved by the invention]

Internally grooved tubes have been improved by changing the shape of the grooves (protrusions) to obtain higher performance heat transfer tubes, but there is a limit to the shape of the grooves (protrusions) that can be obtained with conventional processing methods. However, there were limits to the performance of the processed heat exchanger tubes.

In addition, a high-performance heat transfer tube has been proposed in which the tube is subjected to rolling or rolling twice or more to form protrusions (grooves) with a complex shape on the inner surface of the tube to improve heat transfer performance. However, when machining is performed more than once, the equipment becomes complicated, equipment costs are high, and it is difficult to adjust the equipment, which not only makes it impossible to stably process long lengths, but also makes it impossible to increase the machining speed. was there.

[Means to solve the problem]

In view of this, as a result of various studies, the present invention has been developed to create protrusions (grooves) with a more complex shape than conventional heat exchanger tubes on the inner surface of the tube in one process.
We have developed a heat exchanger tube with improved heat transfer characteristics and a method for manufacturing it.

That is, the heat exchanger tube of the present invention is characterized by having two or more types of continuous or discontinuous protrusions that intersect on the inner surface of the tube, and the height of the secondary protrusions that intersect with the main protrusion is determined by the main protrusion. The height of the sub-protrusions is 374 or less, and the height of the sub-protrusions is 0.
It is desirable that it be less than 2 mm.

In addition, the manufacturing method of the present invention allows the metal strip to be continuously supplied to
Heat exchanger tubes are produced by applying pressure with grooved rolls and smooth rolls to form protrusions on one side of the metal strip, then forming the protrusions into a tube with the protrusions inside, and joining both edges to form protrusions on the inner surface of the tube. In manufacturing, two or more types of continuous or discontinuous grooves are formed intersecting the circumferential surface of the grooved roll, and the metal strip is pressurized.

[Effect]

A heat exchanger tube with intersecting ribs on the inner wall surface was developed in 1988.
This is proposed in Japanese Patent No. 53476. This heat exchange is performed by flowing a single-phase flow inside the tube and changing the phase of the refrigerant outside the tube using fins outside the tube, and its application is different from that of the heat exchanger tube of the present invention. In the case of this heat transfer tube, in order to improve the heat transfer performance inside the tube, only a disturbance action on the inner wall surface is required, and therefore the height of the ribs is set to 0.2 to 1. The numerical value is limited to 0.0 mm, and if it is smaller than 0.2 mm, it is said that no effective disturbance effect can be expected.

In contrast, the heat transfer tube of the present invention is used in a heat exchanger that undergoes phase changes such as evaporation and condensation within the tube, and the factors that improve heat transfer performance include an increase in the heat transfer area and heat transfer due to turbulent flow effects. Performance can be improved, but the increase in the retention of liquid in the grooves and capillary force causes the liquid film to spread in the axial direction through the grooves, making it easier to form liquid films in higher dryness areas. It can be raised.

In the heat exchanger tube of the present invention, the liquid retention force in the groove surrounded by the intersecting protrusions increases, but the height of the main protrusions (
If the ratio (H2/H,) between H+) and the height (H2) of the sub-protrusion that intersects it is too large, for example, H2/H,=
In No. 1, the liquid film does not spread in the axial direction due to capillary force, resulting in a decrease in heat conductivity and an increase in pressure loss.

Therefore, by setting H2/'H+≦374, the liquid retention force is maintained and the liquid film is spread in the axial direction, thereby making it possible to significantly improve heat transfer performance compared to conventional heat transfer tubes. Further, in order to suppress an increase in pressure loss due to secondary protrusions, it is desirable that H2≦0.2M.

In addition, in the manufacturing method of the present invention, the above-mentioned high-performance heat exchanger tube is
Since the process can be performed in one process, conventional equipment can be used, and long length processes can be carried out stably without reducing the process speed.

Examples of the present invention will be described below.

〔Example〕

FIG. 1 shows a series of manufacturing steps in the present invention from rolling a metal strip to tube forming and welding. In the figure, a metal strip (1) is continuously supplied from an uncoiler (not shown). In this example, the copper strip was fed at a speed of 50 i/min, and the protrusions and grooves on the strip (1) were processed using a grooved roll.
2) and a smooth roll (3). As shown in Figure 2, the grooved roll (2) is provided with two types of spiral grooves (4) and (5), which are twisted with respect to the roll axis and intersect at a predetermined intersection angle. are doing. By rolling the metal strip (1) with the grooved roll (2) and the smooth roll (3) and transferring the groove shape of the grooved roll (2) to one side surface of the metal strip (1), the metal strip is rolled as shown in FIG. (A diagonal protrusion (6) that intersects on one side of +1.

Perform (7).

After that, multiple forming rolls (8!, 8b, 8c, ・
A metal strip (1M) with protrusions is formed into a tubular shape with the protrusions f6) and (71 parts facing inside) using a forming device consisting of a metal strip (1M) formed into a tubular shape. ) and join them along the longitudinal direction using a high-frequency induction welder (9).
to), (A heat exchanger tube (12) having an outer diameter of 9.53 mm was manufactured through I+1 or a finishing die (not shown).Here, a high frequency induction welder was used for welding, but the known method is not limited to this. They may be joined using the technique described above.

Since the heat transfer tube of the present invention has a larger heat transfer surface and a more complex shape than a conventional inner grooved tube, it is expected that the pressure loss will be greater than that of a conventional inner grooved tube. If the pressure loss is large, it is necessary to increase the pump power of the heat exchanger, and from the viewpoint of energy saving, the pressure loss must be kept as small as possible. Therefore, the heat transfer coefficient within the tube during evaporation and condensation as well as the pressure loss within the tube were measured for the heat transfer tube.

The heat exchanger tube that was measured had an outer diameter of 9.53m01 and the first protrusion (
The twist angle of the main protrusion with respect to the tube axis is 20°, the protrusion height (H3) is 0.2 degrees, and the second protrusion (secondary protrusion)
The twist angle with respect to the tube axis is 30° in the opposite direction to the first protrusion.
, the protrusion height (H2) was changed from 0 (conventional inner grooved tube) to 0.
Two cylinders, that is, H2/H1 was varied from 0 to 1.

The above heat transfer tube was assembled into a double tube heat exchanger, Freon R-22 was flowed as a refrigerant inside the tube, water to be cooled was flowed orthogonally outside the tube, and performance was evaluated under the measurement conditions shown in Table 1. Ta. The results of measuring the heat transfer coefficient in the tube are shown in FIGS. 4 and 5, and the results of measuring pressure loss are shown in FIGS. 6 and 7.

Table 1 Evaporation in the pipe Refrigerant inlet dryness Refrigerant outlet superheat degree Heat transfer tube effective length Refrigerant flow rate Condensation in the tube 0.21 Refrigerant inlet superheat degree 35°05℃ Refrigerant outlet subcooling 5℃ 5m Heat transfer tube effective length 5m 40kg/h Refrigerant Flow rate: 40kg/h From Figures 4 and 5, the heat transfer coefficient in the pipe is H2/H+ = 1
/4, which is higher than the conventional inner grooved 1f (H2=0), and when H2/H1>3/4, the performance decreases. The reason for this is thought to be that the liquid film accumulates in the groove surrounded by the first protrusion and the second protrusion, and does not spread in the axial direction.

From Figures 6 and 7, the pressure loss is H2/H+≦37
4, it is almost the same as the conventional internally grooved tube (H2=o), but it increases significantly when H2/H+ > 3/4. The tendency for pressure drop to increase significantly is H2/H14
When the protrusion height is increased at 3/4 (H+ ≧0.
26mm, H220, 20mm).

In order to improve performance without increasing pressure loss, H2/H+≧3/4. It can be seen that it is desirable to set H2<0.20.

Even if the height of the second protrusion is made equal to the height of the first protrusion, as shown in Figure 8, by making the second protrusion discontinuous, pressure loss can be reduced without deteriorating heat transfer performance. can be made equivalent to the value of conventional heat exchanger tubes. Furthermore, in the embodiments of the present invention, a heat exchanger tube having two types of helical protrusions with different twist angles has been described, but the present invention is not limited to this.As shown in FIG. It does not matter if it is in a zigzag shape.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to significantly improve heat transfer performance without increasing pressure loss compared to conventional heat transfer tubes, and moreover, it is possible to significantly improve heat transfer performance by eliminating complicated protrusions that improve heat transfer performance.
It can be applied in just one process, so conventional equipment is sufficient.
This method has remarkable industrial effects, such as being able to stably process long pieces without slowing down the processing speed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the method for manufacturing a heat exchanger tube of the present invention, FIG. 2 is a front view showing an example of a grooved roll of the manufacturing method of the present invention, and FIG. A perspective view showing an example of the protrusions provided, and FIGS. 4 and 5 show the ratio of heat transfer coefficients between the heat exchanger tube of the present invention and a conventional heat exchanger tube. FIG. 4 shows the evaporative heat transfer coefficient ratio, and FIG. is an explanatory diagram of the condensation heat transfer coefficient ratio, and Figures 6 and 7 show the ratio of pressure loss between the heat exchanger tube of the present invention and the conventional heat exchanger tube. Figure 6 shows the ratio during evaporation, and Figure 7 shows the ratio during condensation. Explanatory drawings, FIG. 8 is a plan view showing an example of another protrusion of the metal strip after rolling in the present invention, FIG. 9 is a plan view showing an example of still another protrusion of the metal strip after rolling in the present invention, 10th
Figures (a) and (b) show examples of conventional heat exchanger tubes.
A) is a longitudinal sectional view, (B) is a side sectional view, FIG. 11 is an explanatory diagram showing the effect of a conventional heat exchanger tube, and FIG. 12 is an explanatory diagram showing the manufacturing process of a conventional internally grooved tube by the rolling method. , Figure 13 (a)
, (b) are explanatory diagrams showing the conventional manufacturing process of an internally grooved tube by rolling and welding methods, (a) is a plan view, and (b) is a side view. l) Metal strip, (2) Grooved roll, (3) Smooth roll, 4
), (5) Spiral groove, (61, (7) projection, 8-
11 (If-nl, (8i1-=・(8h) forming roll, 9) high-frequency induction welder, flO), (II) finishing roll, 12) heat exchanger tube, (13) protrusion, (14) groove,
(15) Liquid film, 16) Smooth tube, (17) Floating plug, 1g) Dice, (19) Grooved plug, (20)
Rolling roller, 21) Finishing die. Fig. 2 Fig. 3 Fig. 8 Fig. 11 Fig. 9 Fig. 12 (a) Fig. 10 (b)

Claims (4)

[Claims] (1) A heat exchanger tube characterized by having two or more types of continuous or discontinuous protrusions that intersect on the inner surface of the tube. (2) The heat exchanger tube according to claim (1), wherein the height of the secondary protrusion that intersects the main protrusion is 3/4 or less of the height of the main protrusion. (3) The heat exchanger tube according to claim (1) or (2), wherein the height of the secondary protrusion is less than 0.2 mm. (4) The continuously supplied metal strip is pressurized by a grooved roll and a smooth roll to form protrusions on one side of the metal strip, and then formed into a tube shape with the protrusions inside, and both edges of the metal strip are pressed. In manufacturing heat exchanger tubes that are joined to form protrusions on the inner surface of the tube,
A method for manufacturing a heat exchanger tube, comprising forming two or more types of continuous or discontinuous grooves that intersect with the circumferential surface of the grooved roll to pressurize the metal strip.