JPH11337285A - Both-side grooved pipe and heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a both-side grooved pipe which can prevent the spreading of a liquid film on its inner peripheral surface side, well breaks a liquid on its outer peripheral side, and, accordingly, can improve the heat-exchanging efficiency of a heat exchanger and a heat exchanger. SOLUTION: A metallic pipe is provided with many inner peripheral fins 6 on its inner peripheral surface and many outer peripheral fins 2 on its outer peripheral surface. At one spot of the metallic pipe in the peripheral direction, a weld 10 extended in the axial direction of the pipe is formed and the fins 6 and 2 are discontinued correspondingly to the weld 10. On both sides of the weld 10, in addition, outer peripheral projecting stripes 12 and inner peripheral projecting stripers 14 are respectively formed on the outer, and inner peripheral surfaces of the metallic pipe and the areas between the projecting sections 12 and 14 contain no fin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided grooved tube in which fins are formed on both sides of a metal tube for enhancing heat exchange efficiency, and a heat exchanger using the same.

[0002]

2. Description of the Related Art Conventionally, in a heat exchanger such as an air conditioner or a refrigerator, an inner grooved pipe is used as an evaporating pipe or a condensing pipe. A general inner surface grooved tube is formed by forming a number of spiral grooves over the entire inner surface of a metal tube, and spiral fins are formed between the grooves. . A general inner grooved pipe has an outer diameter of about 1 cm, an inner peripheral fin height of about 0.3 mm, and an inner peripheral fin pitch of about 0.4 mm. In these inner grooved tubes, a large number of metal radiating fins are vertically fixed on the outer periphery, and heat is exchanged between a heat medium flowing inside the heat transfer tube and air flowing between the radiating fins. .

[0003] On the other hand, as one type of heat exchanger, there is a heat exchanger used for an absorption cooler (generically referring to an absorption refrigerator and an absorption cooler). The heat exchanger of the absorption type cooler has, for example, several hundred heat transfer tubes arranged in a square tubular heat medium flow path in parallel to each other in a direction perpendicular to the flow. Meanwhile, water is circulated in the heat transfer tube while a heat medium such as a lithium bromide solution that has been forcibly cooled is passed, and the water cooled through the heat transfer tube is used for cooling, refrigeration, and freezing. The heat transfer tube used in this type of heat exchanger has a large diameter and is generally 2c.
It is known that dimples and the like are formed on both surfaces of the tube by deforming the tube wall to increase the surface area of the inner and outer peripheral surfaces. In this case, since the outer diameter of the tube is large, it is easy to form dimples and the like on the inner and outer peripheral surfaces thereof.

[0004]

On the other hand, the present inventors have studied a liquid-liquid type heat exchanger smaller than a conventional absorption chiller, and have conducted a horizontal and spaced-apart comparison. A large number of metal pipes with a small diameter are arranged, and these metal pipes are connected in series or in parallel to flow the heat medium, while another fluid (gas, liquid or droplet) is made to contact the outer peripheral surface of the metal pipe. It has been proposed that heat is exchanged between the fluid and the heat medium. In order to realize such a small heat exchange, a heat transfer tube having a small diameter and having heat exchange fins on both the outer periphery and the inner periphery is required. According to this, it has been found that fins can be formed on both surfaces even with a metal tube having a considerably small diameter.

When a liquid-liquid type heat exchanger as described above is manufactured using a double-sided grooved tube having fine fins formed on both sides, the heat transfer liquid adhering to the outer peripheral surface of the tube causes the outer peripheral surface groove to be formed. Widely wet the outer peripheral surface of the double-sided grooved tube by capillary force,
The problem of poor drainage was found. If the drainage is poor, the liquid film always covers the lower half of the fins, so that direct heat exchange between the heat medium and the metal surface of the fins is hindered, and the heat exchange efficiency is reduced.

In the conventional double-sided grooved pipe, the heat transfer medium liquid is easily blown up along the inner groove of the pipe by the pressure of the heat transfer gas flowing through the pipe, and most of the inner peripheral surface fins of the pipe are liquid. The film is covered, and the metal surface of the fin does not come into direct contact with the heating medium gas. For this reason, there was also a problem that the heat exchange efficiency was suppressed.

[0007] The present invention has been made based on the above findings, and while preventing the liquid film from spreading on the inner peripheral surface side, it is possible to improve the drainage of the liquid on the outer peripheral surface side, thereby improving the heat exchange efficiency. It is an object to provide a double-sided grooved tube and a heat exchange device.

[0008]

In order to solve the above problems, a double-sided grooved tube according to the present invention has a large number of inner peripheral surface fins formed on an inner peripheral surface of a metal tube and a large number of inner peripheral fins formed on an outer peripheral surface. Outer peripheral surface fins are formed, and a welded portion extending in the pipe axis direction is formed at one location in the circumferential direction of the metal pipe, and the inner peripheral surface fins and the outer periphery are formed at locations corresponding to the welded portions. It is characterized in that each of the face fins is interrupted.

On the other hand, the heat exchange device according to the present invention comprises a number of tubes arranged horizontally and spaced from each other,
One or more flow paths for flowing the first fluid through these pipes are formed, and a second flow path is formed on the outer peripheral surface of the pipe.
The pipe body has a second flow path for contacting a fluid, and the pipe body has a number of inner peripheral surface fins formed on an inner peripheral surface of a metal tube and a number of outer peripheral surface fins on an outer peripheral surface. Is formed at the lower end in the circumferential direction of the metal pipe, a welded portion extending in the pipe axis direction is formed, and at a location corresponding to the welded portion, the inner peripheral surface fin and the outer peripheral surface are formed. The fins are interrupted.

[0010]

FIG. 1 is a sectional view showing an embodiment of a double-sided grooved pipe according to the present invention. This double-sided grooved tube 1
Has a large number of inner peripheral surface fins 6 formed on an inner peripheral surface of a metal tube in parallel with each other, and a number of outer peripheral surface fins 2 formed on an outer peripheral surface of the metal tube in parallel with each other. An inner groove 8 is formed between the inner peripheral fins 6, and the outer peripheral fin 2 is formed.
An outer peripheral surface groove 4 is formed between them.

Although the material of the double-sided grooved tube 1 is not limited, it is generally preferable to be formed of a metal such as copper, copper alloy, aluminum, and aluminum alloy. Double-sided grooved tube 1
The outer diameter, wall thickness, length, and other dimensions are not limited. However, in the case of realizing a small heat exchanger, even if the outer diameter of the double-sided grooved tube 1 is about 0.5 to 1.5 cm, Good.

The double-sided grooved tube 1 is obtained by an electric resistance welding process. A welded portion 10 extending over the entire length in the axial direction of the tube is formed at one location in the circumferential direction, and corresponds to the welded portion 10. At the location, as shown in FIGS. 2 and 3, the inner peripheral fin 6 and the outer peripheral fin 2 are interrupted over a fixed width, and there is no fin having a constant width over the entire length of the double-sided grooved tube 1. A part is formed.

The welded portion 10 has a cross-sectional shape that protrudes gently on the inner and outer peripheral surfaces of the tube. As shown in FIG. Article 14
Are formed. The inner peripheral ridges 14 are equidistant from the weld 10 and extend in parallel with the weld 10, and the ends of the inner peripheral fins 6 are connected to the inner peripheral ridges 14, The fin-free portion is provided between the protruding ridges 14.

As shown in FIG. 3, a pair of outer peripheral ridges 12 are formed on the outer peripheral surface of the double-sided grooved tube 1 on both sides of the welded portion 10. These outer peripheral ridges 12 are equidistant from the welded portion 10, extend parallel to the welded portion 10, the ends of the outer peripheral fins 2 are connected to the outer peripheral ridges 12, and these outer peripheral ridges 12 are provided. The portion between the portions 12 is a finless portion. Accordingly, the outer peripheral side finless portion and the inner peripheral side finless portion are formed at positions facing each other. Forming the finless portion in such an arrangement is preferable from the viewpoint of the manufacturing method.
That is, when fins are not formed near the end faces of the strip material when the strip material is subjected to ERW processing into a tubular shape, the density of the current generated on the end face of the strip material can be made uniform. ,
This is because unevenness in welding can be prevented. Weld 10
Is preferably a ridge having a protrusion amount smaller than the height of the fins 2 and 6.

In this embodiment, as shown in FIG. 2, the inner peripheral fin 6 is formed in a zigzag shape (saw blade shape), while the outer peripheral fin 2 is formed as shown in FIG. It is formed in a simple straight line. As described above, when the inner peripheral surface fin 6 has a zigzag shape having a higher turbulence generation effect than the spiral groove and the outer peripheral surface fin 2 has a simple linear shape (spiral shape), heat exchange by the inner peripheral surface fin 6 is performed. Since the efficiency can be remarkably increased and the strength of a specific portion in the width direction of the strip material can be prevented from being lowered, the cross-sectional shape of the double-sided grooved tube 1 is made completely circular in the process of roll forming. It becomes easier. However, the present invention is not limited to this configuration, and the shapes of the outer peripheral fin 2 and the inner peripheral fin 6 may be arbitrarily changed. For example, the outer peripheral fin 2 is formed in a zigzag shape while the inner peripheral fin 6 is formed.
May be simply spiraled, or both may be in a zigzag or simple spiral shape.

As shown in FIG. 2, the inner peripheral surface fins 6 of this embodiment are formed such that the angle with respect to the tube axis is reversed at approximately 90 ° in the circumferential direction. Although the absolute value of the inclination angle α of the inner peripheral surface fin 6 with respect to the tube axis is not limited, it is generally preferably 8 to 30 °, and more preferably 10 to 25 °. If the absolute value exceeds 30 °, the inner peripheral surface fins 6 become almost perpendicular to the flow, and the pressure loss increases, which is not preferable. If the absolute value is less than 8 °, the fins 2 become nearly parallel to the flow, and the turbulence generation effect of the inner peripheral surface fins 6 decreases.

As shown in FIG. 3, the outer peripheral surface fin 2 is formed at a constant angle (helical angle) β crossing the axis.
It has a spiral shape around the tube axis. The helix angle β is not limited, but is preferably 45 from the viewpoint of enhancing the drainage property due to gravity.
The angle is preferably about 90 °, more preferably about 70 ° to 90 °.

The cross-sectional shape of the fins 2 and 6 may be any shape such as a triangular shape, an isosceles triangular shape, a triangular shape with a rounded apex, a semicircle, an arc, a trapezoidal shape, and a chamfered trapezoidal shape. However, in this embodiment, as shown in FIG. 1, the trapezoid has a vertex that is flattened. When the cross section is trapezoidal in this way, there is an advantage that roll forming is easily performed at the time of manufacturing.

The pitch and height of the fins 2 and 6 in the tube axis direction are not limited, but when used in the heat exchanger of the present invention, the pitch of the fins 2 and 6 is preferably 0.3 to 1.0.
mm, more preferably 0.4 to 0.8 mm.
The fin height is preferably 0.1 to 0.5 mm,
It is more preferably 0.15 to 0.3 mm.

In the above-described embodiment, the inner peripheral surface of the double-sided grooved tube 1 has a fin refraction number of 4 in the circumferential direction. However, the fin refraction number may be 2 or 6, and in these cases, this embodiment is also applicable. The same effect as in the embodiment can be obtained. Also,
When the outer diameter of the double-sided grooved tube 1 is large, the inner peripheral surface of the heat transfer tube can be divided into eight or more regions (having a refraction number of 8).

Although the distance between the inner peripheral surface ridges 14 is not necessarily limited in the present invention, it is preferably 2 to 8%, more preferably 3 to 6% of the entire peripheral length of the inner peripheral surface of the metal tube. If the separation amount is in the range of 2 to 8%, the flow rate of the heat transfer liquid flowing through the finless portion increases, and the spread of the liquid film on the inner peripheral surface of the tube can be suppressed.

The distance between the outer peripheral surface ridges 12 is not necessarily limited in the present invention, but is preferably 3 to 10%, more preferably 4 to 7% of the entire peripheral length of the outer peripheral surface of the metal tube.
It is said. If the distance is in the range of 3 to 10%,
This finless part increases the effect of increasing liquid drainage,
Spreading of the liquid film on the outer peripheral surface of the tube can be suppressed.

FIG. 4 is a longitudinal sectional view showing one embodiment of the heat exchange device according to the present invention. In this heat exchanger, the double-sided grooved tubes 1 according to the present invention are arranged horizontally and parallel to each other with an interval therebetween, and these double-sided grooved tubes 1 are connected in a meandering shape. The heat medium flows through the double-sided grooved tube 1. Further, the outer frame body 20 is provided with a second flow path for bringing the second fluid into contact with the double-sided grooved pipe 1. The second flow path may be, for example, a spray mechanism for dropping a liquid as a second fluid into the double-sided grooved pipe 1, or may fill the outer frame 20 with a gas or liquid circulated from the outside. May be adopted.

FIG. 5 is a longitudinal sectional view showing another embodiment of the heat exchange device according to the present invention. This heat exchanger has a cylindrical main body 60, and both ends of the main body 60 are closed by partition walls 62. A large number of double-sided grooved tubes 1 are fixed horizontally across the partition walls 62, and both ends of each double-sided grooved tube 1 penetrate the partition 62. At both ends of the main body 60, the lid 6 is formed so as to form an airtight space between the main body 60 and the partition wall 62.
4 and 66 are attached. Further, a horizontal partition 66A is formed on one of the lids 66, whereby the spaces 68 and 70 are partitioned. An outlet 72 is formed on the space 68 side, and an inlet 74 is formed on the space 70 side.
, The fluid A passes through the space 70 and passes through the lower half double-sided grooved tube 1, is inverted in the space defined by the lid 64, and is again turned into the upper half double-sided grooved tube 1. It passes through, passes through the space 68, and is discharged from the discharge port 72. Inside the main body 60, baffle plates 80 are fixed at regular intervals in the axial direction. As shown in FIG. 6, the baffle plate 80 is in the shape of a disk partially cut out, and the cutout portions are alternately turned upward or downward. In addition, an inlet 76 is formed at one end of the main body 60, and an outlet 78 is formed at the other end. The fluid B introduced from the inlet 76 is discharged from the outlet 78 while meandering by the baffle plate 80. It has become.

In each of the apparatuses shown in FIGS. 4 to 6, as shown in FIG.
The outer peripheral fin 2 and the inner peripheral fin 6 are both interrupted at the lower end of the double-sided grooved tube 1. Therefore, when the liquid dropped or condensed on the outer peripheral surface of the double-sided grooved tube 1 flows to the lower end along the outer peripheral fin 2, it is collected on the lower surface of the outer peripheral ridge portion 12 and dripped from here. To go. Therefore, the outer peripheral surface of the double-sided grooved pipe 1 has good liquid drainage and the outer peripheral surface fin 2 is not excessively covered with the liquid film, so that the metal surface of the outer peripheral surface fin 2 is easily exposed and the outer peripheral surface fin 2 is exposed. It is possible to promote heat exchange between the second fluid and the second fluid. Further, when the outside of the double-sided grooved tube 1 is filled with liquid, turbulence of the liquid is promoted by the outer peripheral fins 2 of the double-sided grooved tube 1 and forced convection heat transfer can be improved. .

At the same time, a finless portion extending in the tube axis direction is also formed at the lower end of the inner peripheral surface of the double-sided grooved tube 1, so that the heat transfer liquid flowing through the double-sided grooved tube 1 is free of the fins. Blows quickly along the area. Therefore, the liquid does not spread over the entire inner peripheral surface of the double-sided grooved tube 1 along the inner peripheral fins 6, and the degree of exposure of the metal surface of the inner peripheral fins 6 is increased, thereby exchanging heat with the heat transfer gas. It is possible to promote. By simultaneously obtaining the above two functions, the heat exchange device can increase the heat exchange efficiency between the second fluid and the heat medium in the pipe.

Next, FIG. 8 is a side view showing an example of an apparatus for manufacturing the double-sided grooved pipe 1 having the above configuration. Reference numeral 30 in the figure
Is an uncoiler for continuously feeding out a metal plate strip T having a constant width. The fed plate strip T passes through a pair of holding rolls 32 and passes between a pair of grooved rolls 34 and 36. The inner circumferential fins 6, the inner circumferential grooves 8, and the inner circumferential ridges 14 as shown in FIG. 2 are formed by the grooved rolls 34, while the grooved rolls 36 form as shown in FIG. The outer peripheral surface fin 2, the outer peripheral surface groove 4, and the outer peripheral surface ridge 12 are formed.

The fins 2, 6 are formed by the grooved rolls 34, 36.
The plate material T on which is formed is gradually rounded into a tube through a pair of rolls 38 and a plurality of forming rolls 40 arranged in a pair, and a gap amount between both end edges to be abutted by a rolling separator 42 is kept constant. After being knocked,
Both edges are heated by passing through the induction heating coil 44.
The plate material T which has been formed into a tube and heated is passed through a pair of squeeze rolls 46, and is pressed from both sides so that the heated side edges are abutted and welded. A bead is formed on the outer peripheral surface of the double-sided grooved pipe 1 thus welded by a protruding molten material, and a bead cutter 48 for cutting the bead is provided.

The double-sided grooved tube 1 from which the bead has been cut is forcibly cooled by passing through a cooling tank 50, and then by passing through a plurality of pairs of sizing rolls 52, and reduced to a predetermined outer diameter as required. Diameter. Furthermore, a double-sided grooved tube 1 having a reduced diameter
Is wound by the rough coiler 54.

According to the above-described apparatus and manufacturing method, the double-sided grooved tube 1 can be easily manufactured.
Further, when the outer peripheral fin 2 is formed in a simple spiral shape and the inner peripheral fin 6 is formed in a zigzag shape, the strength does not decrease at a specific portion in the width direction of the plate material T. In addition, there is no problem that the double-sided grooved tube 1 is manufactured by being distorted into a polygonal shape.

[0031]

EXAMPLES Next, the effects of the double-sided grooved pipe according to the present invention will be demonstrated with reference to examples. A double-sided grooved tube of the embodiment in which a W-shaped fin is formed on the inner surface and a spiral fin is formed on the outer surface, an inner grooved tube of Comparative Example 1 in which only the spiral fin is formed on the inner surface, and An inner grooved tube of Comparative Example 2 in which only W-shaped fins were formed was manufactured, and the heat transmittance of these tubes was measured.

The dimensions of the heat transfer tubes are as follows. [Example] Outer diameter (including outer peripheral fins): 7.58 mm Tube thickness (including outer peripheral fins and inner peripheral fins): 0.61 mm Height of inner peripheral fins: 0.177 mm inner peripheral surface Fin pitch: 0.36 mm Angle of inclination of inner peripheral fin with respect to axis (w shape (zigzag shape)): 16 ° Height of outer peripheral fin: 0.160 mm Pitch of outer peripheral fin: 0.50 mm Angle of inclination with respect to axis (spiral shape): 18 ° [Comparative Example 1] Outer diameter: 7.35 mm Pipe wall thickness (including inner peripheral fin): 0.43 mm Height of inner peripheral fin: 0.16 mm Inner circumference Pitch of face fin: 0.36 mm Angle of inclination of inner circumferential fin with respect to axis (spiral shape): 18 mm [Comparative Example 2] Outer diameter: 7.35 mm Pipe wall thickness (including inner circumferential fin): 0.43 mm Height of inner fin: 0 .18 mm Pitch of inner peripheral fin: 0.36 mm Angle of inclination of inner fin relative to axis (w shape (zigzag shape)): 16 °

Next, each of the heat transfer tubes P was set in a test apparatus 90 shown in FIG. 9, and an evaporation test and a condensation test were performed. The overall length of the test device 90 is 3.5 m and the inner diameter is 1.35 cm. As shown in the figure, tap water was flowed from one end of the test apparatus 90, and chlorofluorocarbon was flowed from one end of the heat transfer tube P, and the heat transmittance through the heat transfer tube P was measured. The refrigerant flow rates were 20, 30, and 40 kg / h, and the measurement conditions were as follows. [Evaporation test conditions] Evaporation temperature of chlorofluorocarbon: 5 ° C. Rise temperature during passage of chlorofluorocarbon: 3 ° C. Flow rate of tap water: 1.5 m / s [Condensation test condition] Condensation temperature of chlorofluorocarbon: 45 ° C. Temperature: 5 ° C Tap water flow rate: 1.5 m / s

FIG. 10 shows the result. As shown in this graph, according to the double-sided grooved tube of the embodiment according to the present invention,
Comparative Examples 1 and 2 show the heat transmission rates during evaporation and condensation.
, And the improvement in the condensation rate was particularly remarkable.

[0035]

As described above, according to the double-sided grooved tube according to the present invention, a large number of inner peripheral fins and outer peripheral fins are formed on the inner peripheral surface and the outer peripheral surface, respectively. A welded portion extending in the pipe axis direction is formed at the location, and the inner peripheral surface fin is interrupted at a position corresponding to the welded portion, so by using the welded portion downward, the inner peripheral surface is used. Of the liquid film can be suppressed. Further, when the outside of the double-sided grooved tube is filled with the liquid, turbulence of the liquid is promoted by the outer peripheral fins of the double-sided grooved tube, and forced convection heat transfer can be improved.

According to the heat exchanger of the present invention,
All the double-sided grooved pipes having the above-described configuration are attached with the welded portion facing downward, and both the outer peripheral fin and the inner peripheral fin are interrupted at the lower end of the double-sided grooved pipe, so that the double-sided grooved pipe is cut off. The liquid adhering to the outer peripheral surface of the attached pipe flows to the lower end along the outer peripheral surface fin, is collected at the end, and is dropped. Therefore, the drainage property on the outer peripheral surface of the double-sided grooved pipe is good, and the outer peripheral fin is not excessively covered with the liquid film, so that heat exchange between the outer peripheral fin and the second fluid can be promoted. It is. At the same time, since a finless portion extending in the tube axis direction is also formed at the lower end of the inner peripheral surface of the double-sided grooved tube, the first fluid liquid flowing in the double-sided grooved tube flows along the finless portion. It is quickly blown away. Therefore, the liquid film does not spread on the entire inner peripheral surface of the double-sided grooved tube through the inner peripheral fins, increasing the degree of exposure of the metal surface of the inner peripheral fins and promoting heat exchange with the heat transfer gas. It is possible to By simultaneously obtaining the above two functions, the heat exchange device can enhance the heat exchange efficiency between the second fluid and the first fluid.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a double-sided grooved pipe according to the present invention.

FIG. 2 is a development view of an inner peripheral surface of the double-sided grooved tube.

FIG. 3 is a development view of an outer peripheral surface of the double-sided grooved tube.

FIG. 4 is a schematic diagram showing one embodiment of a heat exchange device according to the present invention.

FIG. 5 is a longitudinal sectional view showing another embodiment of the heat exchange device according to the present invention.

FIG. 6 is a sectional view taken along line VI-VI in FIG. 5;

FIG. 7 is a cross-sectional view showing an arrangement state of double-sided grooved tubes in the heat exchanger.

FIG. 8 is a schematic view of an apparatus for manufacturing a double-sided grooved pipe.

FIG. 9 is a schematic diagram of an apparatus used for an experiment.

FIG. 10 is a graph showing experimental results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Double-sided grooved pipe 2 Outer surface fin 4 Outer surface groove 6 Inner surface fin 8 Inner surface groove 10 Welded part 12 Outer surface ridge 14 Inner surface ridge 20 Outer frame

Claims (4)

[Claims] 1. A double-sided grooved tube in which a number of inner peripheral fins are formed on an inner peripheral surface of a metal tube and a number of outer peripheral fins are formed on an outer peripheral surface thereof. A welded portion extending in the pipe axis direction is formed at one location in the circumferential direction, and the inner peripheral surface fin and the outer peripheral surface fin are each interrupted at a location corresponding to the welded portion. tube. 2. A pair of ridges are formed on both sides of the weld on each of an outer peripheral surface and an inner peripheral surface of the metal pipe, and each pair of ridges is formed apart from the weld. The double-sided grooved tube according to claim 1, wherein the inner peripheral surface fin and the outer peripheral surface fin are not formed in the sandwiched region. 3. The double-sided grooved tube according to claim 1, wherein the inner peripheral fin has a zigzag shape, and the outer peripheral fin has a simple spiral shape. 4. It has a number of tubes arranged horizontally and spaced apart from each other, one or more flow paths for flowing a first fluid through these tubes are formed, and A heat exchange device comprising a second flow path for bringing a second fluid into contact with an outer peripheral surface, wherein the tubular body has a plurality of inner peripheral surface fins formed on an inner peripheral surface of a metal tube, The surface is a double-sided grooved tube on which a number of outer peripheral fins are formed, and a welded portion extending in the tube axis direction is formed at the lower end in the circumferential direction of the metal tube. A heat exchanger wherein the inner peripheral fin and the outer peripheral fin are each interrupted.