JPH03207995A - Butt seam welded heat transfer tube and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance both boiling heat transfer properties and condensing heat transfer properties and to raise a processing efficiency by tuning after a predetermined process by crossing main and sub grooves on the inner wall of a tube, and extruding the part to become a protrusion between the grooves from both sides to the main groove side to form a dovetail cavity. CONSTITUTION:Main grooves 11 and 12 are crossed on the inner surface of a butt seam welded heat transfer tube 100, and a crest 13 is formed therebetween. When the crest 13 is pressed by a wedge-shaped forging roll having a sharp end, the part of the crest 13 is extruded to the trough 11b of the main groove to form a dovetail cavity 14 having a narrower opening than the width of the groove bottom of the groove 11. The desired shapes of the cavity formed by the main and sub groove rolls and a sub groove 12b are such that the ratio of the sectional area S (mm<2>) of the cavity to the opening width d(mm) is S/d <=2, and the cavity of d<=0.1mm is effective to accelerate evaporating heat transfer. When the sectional area of the shaded part is A and the circumferential length is L, an equivalent diameter de is obtained. The de = 0.15 - 0.35mm is effective to accelerate the condensing heat transfer.

Description

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

[Conventional technology]

Figure 12 shows the external appearance of a conventional heat exchanger tube for air conditioning, Figure 13 shows an enlarged view of the internal grooves of the heat exchanger tube for air conditioning, and Table 1 shows typical dimensions of the heat exchanger tube. In these figures, the heat exchanger tubes 1O used in the heat pump air conditioner are mainly internally grooved tubes from the viewpoint of high efficiency and compactness. As shown in FIG. 13, this is a tube in which fine triangular grooves 1 are helically carved on the inner surface of the tube by rolling. By forming the spiral groove 1, the inner surface area is increased, the internal fluid is stirred, the liquid is scraped up to the top of the tube, and the thickness of the liquid film is equalized, thereby increasing the heat transfer rate inside the tube. is improving.

Further, heat transfer tubes used in heat exchangers for heat pump air conditioners are required to have both high boiling heat transfer and high condensing heat transfer due to the characteristics of the product. From this point of view, many high-performance heat transfer surfaces have been proposed using the Menki method, sintering method, machining method, etc., but none have yet been put into practical use at low cost.

An example of a plating method is the one filed in Japanese Patent Laid-Open No. 63-273790. This is a method of forming a porous plating layer on the inner wall of a steel pipe by electrolysis while flowing a copper sulfate solution into the pipe. In this construction method, the boiling heat transfer coefficient is improved to more than twice that of the grooved pipe, but the condensing heat transfer coefficient is rather lower than that of the grooved pipe. This is because the a-condensed liquid is held in microcavities in the porous layer, and most of the heat transfer surface is covered with a fluorocarbon-based refrigerant with high thermal resistance, resulting in a decrease in heat transfer performance. In addition, because the voids in the porous layer are narrow,
There are drawbacks such as impurities contained in the boiling liquid precipitate, clogging the voids and causing performance deterioration.

The sintering method is a method of forming a porous layer by hot-pressing a mixture of metal particles and a binder onto a heat transfer surface. This also has a structure similar to the Menki method, so the above problem occurs. A typical example of the machining method is a heat transfer surface known as "Thermo Excel" as disclosed in Japanese Patent Application Laid-Open No. 51-45353. This is done by cutting grooves to form fins with a rectangular cross section. V-shaped notches are made at the tips of the fins at regular intervals, and then the fin tips are bent with a roller to form a heat transfer surface with tunnel-like cavities with openings made at regular intervals on the upper lid of the cavity. Form. The refrigerant liquid held in the tunnel is heated and blooms, forming bubbles and leaving the opening. At this time, liquid enters from other inert openings, and bubbles are continuously generated. Boiling heat transfer is promoted. Due to its structure, ThermoExcel is effective for boiling heat transfer, but for condensation, the tunnel cavity is clogged with condensate, making condensation heat transfer worse.

was there. In other words, the fin-and-tube heat exchanger used in a heat pump air conditioner is one type of heat exchanger that performs either a heat exchange action or a condensation action, so one that has excellent heat transfer performance in both evaporation and condensation is important. However, there was nothing that could satisfy both requirements.

In addition, conventional copper pipes for air conditioning were manufactured by inserting a bullet-shaped tool called a floating plug with a groove on the outside into the pipe and rolling process, which had a limit on processing speed.
The manufacturing cost was high because the speed was 20 to 30 m/min at most. Therefore, it is desired to realize a low-cost manufacturing method that can achieve processing speeds higher than conventional methods, but this has not been achieved to date.

(Means for Solving the Problems) The present invention provides the following (1) to (3) as means for solving the above problems.
The present invention aims to provide each heat exchanger tube described in item (4) and a method for manufacturing the heat exchanger tube described in item (4).

(1) A main groove regularly formed on the inner wall of the pipe, a minor groove that regularly intersects the main groove and is shallower than the main groove, and a part of the relationship between the main grooves. The protrusion is extruded into the main groove by plastic working of the minor groove to form a cavity whose side cross section is dovetail-shaped, and the cross-sectional area of the same side cross section is Smm''.
A heat exchanger tube having the following relationship: S/d≦2 under the condition of d≦0.1 mm, where cJmm is the opening width between both adjacent protrusions.

(2) a main groove regularly formed on the inner wall of the pipe, and a sub-groove that regularly intersects with the main groove and is shallower than the main groove;
A part of the opposing protrusion between the main grooves is pushed out into the main groove by plastic working of the sub-groove, and the side cross section thereof is dovetail-shaped. AIl
lI12, when the groove circumference is Lwm, its equivalent diameter d
A heat exchanger tube characterized in that it has a relationship of 0.15 to 0.35 m.

(3) A heat exchanger tube comprising the cavity described in (1) above and the sub-groove described in (2) above.

(4) Form regular main grooves and sub-grooves that regularly intersect the main grooves and are shallower than the main grooves by using main groove rolls and sub-groove rolls on the surface of the strip-shaped metal plate, and A part of the protrusion between the grooves is extruded into the main groove during plastic working with a sub-groove roll of the sub-groove to form a dovetail-shaped cavity and the protrusion, and then the band-shaped metal plate is formed with a forming roll. A method for producing a heat exchanger tube, characterized by forming the same metal plate into a tube shape and joining the edges of the same metal plate to form a tube.

[Function] Since the present invention is constructed as described above, it has the following function.

That is, the electric resistance welded heat exchanger tube of the present invention has main grooves and sub-grooves intersecting on the inner wall of the tube, and the protrusion between the main grooves is pushed out between the main grooves to form a dovetail-shaped cavity. The evaporation and condensation heat transfer of the refrigerant is promoted. In the case of evaporation, the opening width at the tip of the dovetail cavity is narrower than the width of the groove bottom, and the width of the entrance is 0.1.
When it is less than m++, bubble nuclei stably exist within the cavity in a fluorocarbon-based refrigerant having a small surface tension. When the bubble nucleus is heated by heat transfer through the heat transfer wall surface, the volume of the vapor bubble increases due to evaporation from the bubble interface, and the pressure inside the Aoi bubble increases. When the internal pressure of the vapor bubble exceeds the critical pressure that exists stably within the cavity, the bubble separates from the cavity opening, and the saturated liquid enters from the other inert opening and passes through the tunnel-shaped cavity. Saturated liquid is supplied. The above foaming cycle is performed continuously, and the promotion of boiling heat transfer is dramatically improved. In addition, a trapezoidal projection is formed by the main groove and the minor groove, but in the case of condensation, the trapezoidal projection has an acute apex angle, and
The longer the flat part of the sub-groove bottom width is, the more the condensate film on the protrusions is attracted to the sub-groove bottom for fluorocarbon-based refrigerants with low surface tension, and the valleys of the sub-groove act as drainage grooves for condensate. , the average liquid film thickness of the protrusions becomes thinner and condensation heat transfer is promoted.

As a result of the above, when one type of heat transfer tube is used in, for example, a fin-and-tube air heat exchanger, both condensation and evaporation functions can be fully demonstrated. Therefore, the efficiency of heat bomb type air conditioners, which provide heating, cooling, and air conditioning throughout the year, will be further improved. Further, according to the manufacturing method of the present invention, after forming cross-shaped grooves in advance on the surface of the band-shaped metal plate using a main groove roll and a sub-groove roll, and forming a dovetail-shaped cavity provided in the heat exchanger tube, Since it is formed into a tube, processing efficiency is significantly increased and processing costs are reduced.

[Embodiment] An electric resistance welded heat exchanger tube according to an embodiment of the present invention, specifically a heat exchanger tube having intersecting grooves on its inner wall, will be explained with reference to FIGS. 1 to 11.

First, the basic concept of this embodiment will be explained with reference to FIG. 7. After embossing intersecting grooves of the main groove 1l and the sub-groove 12 as shown in FIG. The edges 9] are high-frequency welded together, and the ERW heat exchanger tube 10 is
0 is obtained. At that time, the groove depth of the sub-groove 12 is made shallower than that of the main groove l1, and a part of the trapezoidal protrusion between the main grooves l1, that is, a part of the peak 13, is formed in the main groove by plastic working of the sub-groove l2. It is extruded into Il to form a dovetail-shaped cavity 14 between the peaks 13, and is provided with trapezoidal fins or peaks 13 for promoting condensation and a cavity 14 for promoting evaporation.

Next, details of this example will be explained. FIG. 1 is a partial enlarged view of the inner surface of the electric resistance welded heat exchanger tube 1oo shown in FIG. 7, in which the main groove 1l and the sub-groove l2 are formed in an intersecting manner, and a mountain 13 is naturally formed between them. In addition, in the figure, D is the direction of the main groove, and E is the direction of the minor groove.

FIG. 2 is a diagram conceptually representing the developed plan view of FIG. 1.

Figure 3 is a cross-sectional view taken along arrows 1 and 2 in Figure 2, and the main groove 1l is formed with a rolling roll having a trapezoidal cross section as shown in Figure 4, and then a triangular rolling roll as shown in Figure 6 is used. When embossing is carried out in a cross shape with forming rolls, the ridges 13 are pressed by the wedge-shaped forming rolls with acute angles, and a part of the ridges 13 become the valleys 1 of the main groove.
1b to form a dovetail-shaped cavity 14 in which the width of the upper opening is narrower than the width of the bottom of the main groove 11. Note that 12b is a desert valley.

At this time, the waveform of the rolling roll that processes the main groove 11 is the fourth
In the trapezoidal waveform shown in the figure, it is easy to determine the shape of the cavity 14 when the apex angle of the trapezoid is as small as possible, 10° to 30', and the slope is as vertical as possible and has a cross-sectional profile close to a steep rectangle.

Before machining the sub-grooves 12, the ridges 13 are straight trapezoidal fins with a constant cross section, but by machining the sub-grooves 12, the trapezoidal fins are interrupted at regular intervals, and the crests of trapezoidal projections are formed. 13 is formed. The waveform of the rolling roll for forming the sub-groove 12 has a triangular wavy cross-sectional profile with an acute angle as shown in FIG.
However, in order to ensure the bottom width of the sub-groove 12 to a certain extent, either the trapezoidal shape shown in FIG. 4 or the sinusoidal shape shown in FIG. 5 may be used.

Desirable shapes of the main groove roll, the sub-groove roll, the cavity formed by them, and the sub-groove are as follows.

Main groove roll (see FIG. 8(a)); Groove perpendicular cross-sectional shape 1-111 trapezoid shape l1 Ratio of trapezoid upper side dimension l1 to groove height h1, one ball 1h + trapezoid apex angle θ. −−−−− Groove height t++ less than 30°
----0.3mm or less pI Ratio of groove pitch Il+ to groove height h+ ≧1.5h Sub-groove roll (see Fig. 8); Groove right-angled cross-sectional shape 1-1-triangular pushing tip Ratio of width W and groove height h2 -≦0.3h2 Groove apex angle θz ------706 or less groove height tLz ------0.4 rib or less pz Groove pin p2 and groove height h2 ratio ≧1.5h2 As a result of rolling processing using the above-mentioned main groove roll and sub-groove roll in combination, a hollow portion and a sub-groove having the following structure were obtained.

Cavity (see Figure 8 (Cl)): A cavity structure that satisfies the following relationship between the cross-sectional area S of the cavity and the opening width d in a cross section perpendicular to the main groove at the intersection of the main groove and the minor groove. S/d≦2 (d≦0.1) Minor groove: In the minor groove shape shown in Fig. 9 (C), if the cross-sectional area of the groove passage surrounded by diagonal lines is A, and the circumference is L, then The equivalent diameter de of the minor groove 4A is de = 1. The processing conditions and roll shape are adjusted so that the shape of the minor groove L after rolling becomes de = 0.15 to 0.35 mm.

Regarding the example obtained as described above, the outer diameter was 9.5
We prepared several types of test tubes with intersecting grooves as shown in Figure 1 on the inner surface of 2 mmφ electric resistance welded heat transfer tubes, and with different shapes of cavity l4, and investigated the evaporation and condensation heat transfer characteristics.The results are as follows. It was on the street. (However, the numbers are omitted.) In other words, Fig. 9(a) shows the grass heat transfer ratio (the heat transfer ratio compared to the bare tube) with the ratio of the cross-sectional area S (m'') of the cavity and the opening radius d (lIII+) as the horizontal axis. This is the result of organizing the test data along the vertical axis (transmission ratio), and there is a peak value near S/d = 0.5,
It was found that the larger the S/d, the lower the heat transfer coefficient. Therefore, a cavity that satisfies the conditions of S/d≦2 and d≦0.1 is effective in promoting evaporative heat transfer.

In addition, in Fig. 9(b), the equivalent diameter of the minor groove is de, and the 9th
Determine the equivalent diameter de with the cross-sectional area of the shaded area in Figure (C) as A and the circumference as L, and use this as the horizontal axis and the condensing heat transfer ratio (heat transfer coefficient ratio compared to the bare tube) as the vertical axis, and test data. As a result of arranging the above, there is a peak value around de of 0.25■, and if we define the range in which the heat transfer coefficient tends to decrease before and after that, it is 4! It is effective in promoting heat transfer. Note that if the groove bottom width is made too wide, the groove pinch will become too wide, and the peaks of the trapezoidal protrusions will be easily crushed by mechanical tube expansion, so there is a limit to how wide the groove bottom can be made.

12th. The results of comparing the heat transfer performance of this example with the conventional spiral grooved tube shown in FIG. 13 are shown in FIGS. 10 and 1l. In both figures, the vertical axis represents the heat transfer coefficient ratio with the spiral grooved tube, and the horizontal axis represents the refrigerant flow rate.

In the case of evaporation, the heat transfer coefficient is approximately twice as high as that of a spirally grooved tube, and in the case of condensation, it is approximately 1.5 times as high as that of a spirally grooved tube.

Furthermore, as a result of investigating the effects on processing, it was found that the processing speed of conventional drawing processing (forming processing using a floating plug) of a grooved tube is approximately 20 to 30 m/min, but the processing speed used in the processing of this example The machining speed is about 60 to 80 m.
/Ilin is about 2 to 3 times faster than conventional drawing, and therefore reduces the cost of copper tubes.

As described above, according to this embodiment, the main groove and the sub-groove are embossed in advance so as to intersect with each other on the metal plate, and the resulting peaks (trapezoidal protrusions) form a dovetail-shaped cavity. Since the tube is extruded so as to be concentrated, it has the advantage that a heat transfer tube with high boiling heat transfer properties and high condensation heat transfer properties can be obtained. Furthermore, since the processing efficiency is high, there is also the advantage that heat exchanger tubes can be obtained at low cost.

[Effects of the Invention] Since the present invention is structured as described above, it has the following effects.

In other words, a main groove and a sub-groove are formed on the inner wall of the pipe so as to cross each other, and a part of the protrusion between the two grooves is pushed out from both sides toward the main groove to form a dovetail-shaped cavity, which improves boiling heat transfer. An electric resistance welded heat exchanger tube having high condensation heat transfer properties can be obtained.

In addition, the main grooves and sub-grooves are formed regularly on the surface of the band-shaped metal plate in advance.
After processing it into a cross shape and performing other necessary processing,
Since the band-shaped metal plate is shaped into a tubular shape, processing efficiency is high, and an electric resistance welded heat exchanger tube can be obtained at low cost.

[Brief explanation of drawings]

Fig. 1 is a developed perspective view of an ERW heat exchanger tube according to an embodiment of the present invention, Fig. 2 is a developed plan view of Fig. 1, and Fig. 3 is a
1-2 arrow sectional view, Figures 4, 5, and 6 are perspective views of the rolling dies for main grooves, minor grooves, etc. in the above embodiment, and Figure 7 is a perspective view of 11 heat exchanger tubes in the above embodiment. Fig. 8 is a diagram for quantitatively showing the shape of the rolls used in the processing of the above embodiment and the desirable shape of the cavity formed by them, and (a) is a partial cross-section of the main groove roll. Fig. 9(b) is a partial cross-sectional view of the sub-groove roll, (C) is a partial cross-sectional view of the hollow part of the inner wall of the ERW heat exchanger tube formed by them, and Fig. 9 is a characteristic diagram of the above embodiment. (a) is a diagram showing the boiling heat transfer ratio of the cavity in relation to the cross-sectional area S/opening radius d of the cavity, (b)
is a diagram showing the condensation heat transfer ratio of the sub-groove with respect to the equivalent diameter de of the sub-groove, and (C) shows the relationship between the equivalent diameter de used in (c) above, the cross-sectional area A and the circumference L of the sub-groove. FIG. 11 is a comparison diagram of the condensing heat transfer performance, and FIG.
The figure is a perspective view of a conventional grooved heat exchanger tube, and FIG. 13 is a partially enlarged view of the inner surface of the conventional grooved heat exchanger tube of FIG. 12. 11... Main groove 12... Minor groove 13... Mountain 9l... Edge 1lb... Valley of main groove! 2b...Trough of sub-groove 14...Cavity portion 100...Electrence welded heat exchanger tube. agent

Claims (4)

[Claims] (1) A main groove regularly formed on the inner wall of the pipe, a sub-groove that regularly intersects with the main groove and is shallower than the main groove, and a part of the main groove that faces the main groove. The protrusion is pushed out into the main groove by plastic working of the minor groove, forming a cavity whose side cross section is dovetail-shaped, and the cross-sectional area of the same side cross section is Smm^.
2. A heat exchanger tube characterized by having the following relationship: S/d≦2 under the condition of d≦0.1 mm, where dmm is the opening width between both adjacent protrusions. (2) a main groove regularly formed on the inner wall of the pipe, and a sub-groove that regularly intersects with the main groove and is shallower than the main groove;
A part of the opposing protrusion between the main grooves is pushed out into the main groove by plastic working of the sub-groove, and the side cross section thereof is dovetail-shaped. Amm
^2, When the groove circumference is Lmm, its equivalent diameter de(
de=4A/L) is 0.15 to 0.35 mm. (3) A heat exchanger tube comprising the cavity according to claim (1) and the sub-groove according to claim (2). (4) Form regular main grooves and sub-grooves that regularly intersect the main grooves and are shallower than the main grooves by using main groove rolls and sub-groove rolls on the surface of the strip-shaped metal plate, and A part of the protrusion between the grooves is extruded into the main groove during plastic working with a sub-groove roll of the sub-groove to form a dovetail-shaped cavity and the protrusion, and then the band-shaped metal plate is formed with a forming roll. A method for manufacturing a heat exchanger tube, characterized by forming the same metal plate into a tube shape and joining the edges of the same metal plate to form a tube.