WO2021106347A1

WO2021106347A1 - Heat-exchanger tube

Info

Publication number: WO2021106347A1
Application number: PCT/JP2020/036509
Authority: WO
Inventors: 伸洋本間; 詔悟山田; 勇樹寺本; 外山　猛敏; 陽介内多
Original assignee: 株式会社デンソー
Priority date: 2019-11-27
Filing date: 2020-09-28
Publication date: 2021-06-03

Abstract

This heat-exchanger tube comprises: an outer tube (21) inside of which cooling water flows; and an inner fin (22) that is provided inside of the outer tube. The potential of the lowest section of the inner fin is lower than the potential of the highest section of a core material (210) of the outer tube. The surface layer of the inner surface of the outer tube and/or the surface layer of the inner fin has a brazing material layer.

Description

Heat exchanger tube

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2019-214461 filed on November 27, 2019 and Japanese Patent Application No. 2020-148188 filed on September 3, 2020. , Claiming the benefit of that priority, the entire contents of that patent application are incorporated herein by reference.

This disclosure relates to heat exchanger tubes.

Conventionally, there is a sheet material described in Patent Document 1 below. The sheet material described in Patent Document 1 is used as a tube through which cooling water flows in a radiator, a heater core, or the like. The tube has a core material made of an aluminum alloy. The outer surface of the core material is covered with a brazing material, and a sacrificial layer is formed on the inner surface of the core material. The sacrificial layer is made of a material that is potentially lower than the core material, specifically, an aluminum alloy containing Zn (zinc) in a predetermined ratio. The potential here indicates "pitting potential". According to such a configuration, in an environment where the tube is easily corroded by the cooling water, the sacrificial layer is preferentially corroded over the core material, so that the corrosion of the core material is less likely to proceed. As a result, the corrosion resistance of the tube can be improved.

Japanese Patent No. 5339560

In a tube as described in Patent Document 1, when heated at the time of brazing, Zn contained in the sacrificial layer diffuses into the core material. When Zn diffuses into the core material, the potential of the core material decreases, so that the potential difference between the core material and the sacrificial layer becomes small. This means that the sacrificial layer becomes difficult to function, which raises the concern that the core material will corrode. In particular, when the plate thickness of the tube is thin, Zn easily diffuses into the core material of the tube, so that the potential difference between the core material and the sacrificial layer becomes very small, and the core material may be significantly corroded. is there. On the other hand, if the thickness of the core material is increased, even if Zn contained in the sacrificial layer diffuses into the core material, it becomes easier to maintain the potential difference between the core material and the sacrificial layer, thus ensuring corrosion resistance. It is possible. However, if the thickness of the core material is increased, there is a concern that it becomes difficult to reduce the weight of the heat exchanger.

The purpose of the present disclosure is to provide a tube of a heat exchanger that can be thinned and can ensure corrosion resistance.

The tube of the heat exchanger according to one aspect of the present disclosure includes an outer tube through which cooling water flows, and an inner fin provided inside the outer tube. The potential of the lowest part of the inner fin is lower than the potential of the most precious part of the core material of the outer tube. A brazing material layer is provided on at least one of the surface layer of the inner surface of the outer tube and the surface layer of the inner fin.

According to this configuration, since the inner fin is potentially based with respect to the outer tube, the inner fin is more likely to corrode than the outer tube. Therefore, since the inner fin substantially functions as a sacrificial anode material, the corrosion resistance of the outer tube can be ensured. Further, if the inner fin substantially functions as a sacrificial anode material, it is not necessary to form a sacrificial layer at least on the inner surface of the core material of the outer tube. As a result, it is not necessary to increase the thickness of the core material of the outer tube in order to secure the potential difference between the sacrificial layer and the core material, so that the outer tube can be thinned.

FIG. 1 is a block diagram showing a schematic configuration of a heat exchanger. FIG. 2 is a cross-sectional view showing a cross-sectional structure taken along the line II-II of FIG. FIG. 3 is a graph showing the relationship between each portion of the outer tube and the inner fin of the first embodiment and the electric potential. FIG. 4 is a chart showing the results of experiments conducted by the inventors. FIG. 5 is a chart showing a configuration example of the outer tube and the inner fin of the second embodiment. FIG. 6 is a chart showing the results of other experiments conducted by the inventors. FIG. 7 is a cross-sectional view showing the cross-sectional structures of the outer tube and the inner fin of the reference example. FIG. 8 is a cross-sectional view showing the cross-sectional structures of the outer tube and the inner fin of the third embodiment. FIG. 9 is a chart showing the results of other experiments conducted by the inventors. FIG. 10 is a chart showing the results of other experiments conducted by the inventors. FIG. 11 is a chart showing the results of other experiments conducted by the inventors.

Hereinafter, an embodiment of the tube of the heat exchanger will be described with reference to the drawings. In order to facilitate understanding of the description, the same components are designated by the same reference numerals as possible in each drawing, and duplicate description is omitted.
<First Embodiment>
First, an outline of the heat exchanger in which the tube of the first embodiment is used will be described. As shown in FIG. 1, the heat exchanger 10 of the present embodiment includes a plurality of tubes 20, a plurality of outer fins 30, and

tanks

40 and 41.

As shown in FIG. 2, the tube 20 has an outer tube 21 and an inner fin 22.
The outer tube 21 is made of a member having a flat tubular shape having a cross-sectional shape orthogonal to the direction indicated by the arrow X. As shown in FIG. 1, the outer tubes 21 of the plurality of tubes 20 are stacked and arranged at predetermined intervals in the direction indicated by the arrow Z in the drawing. The outer tube 21 is formed so as to extend in the direction indicated by the arrow X in the drawing. Cooling water is flowing inside the outer tube 21. Air flows in the direction indicated by the arrow Y in the gap between the adjacent

outer tubes

21 and 21.

As shown in FIG. 2, the inner fin 22 is arranged inside the outer tube 21. The inner fin 22 is a so-called corrugated fin formed by bending a thin metal plate in a wavy shape. The tip of the bent portion of the inner fin 22 is joined to the inner surface 21a of the outer tube 21 by brazing. The inner fin 22 is provided to increase the heat transfer area for the cooling water flowing inside the outer tube 21.

As shown in FIG. 1, the outer fins 30 are arranged in the gap between the adjacent

outer tubes

21 and 21. The outer fin 30 is also a corrugated fin like the inner fin 22. The tip of the bent portion of the outer fin 30 is joined to the outer surface of the outer tube 21 by brazing. The outer fins 30 are provided to increase the heat transfer area for the air flowing between the adjacent

outer tubes

21 and 21.

The tank 40 is connected to one end of each of the plurality of outer tubes 21. The tank 41 is connected to the other end of each of the plurality of outer tubes 21. The

tanks

40 and 41 are formed in a tubular shape. The

tanks

40 and 41 function as a portion for distributing the cooling water to the outer tubes 21 or as a portion for collecting the cooling water flowing through the outer tubes 21.

In the heat exchanger 10, heat exchange is performed between the cooling water flowing inside the outer tube 21 and the air flowing outside the outer tube 21. This makes it possible for the air to absorb the heat of the cooling water to cool the cooling water, and for the cooling water to absorb the heat of the air to heat the cooling water.

Next, the materials of the outer tube 21 and the inner fin 22 will be described in detail.
As shown in FIG. 3, the outer tube 21 of the present embodiment has a structure having a sacrificial layer 211 on the outer surface of the core material 210. The core material 210 is made of an aluminum alloy. The sacrificial layer 211 is made of a sacrificial anode material and is formed of an aluminum alloy containing a material that is potentially lower than the core material 210, for example, Zn in a predetermined ratio. The sacrificial layer 211 makes it difficult for the core material 210 to corrode by preferentially corroding the core material 210. The outer surface 21b of the outer tube 21 is susceptible to, for example, salt corrosion. By providing the sacrificial layer 211 on the outer surface of the core material 210, the corrosion resistance of the outer tube 21 on the outer surface side against salt damage corrosion and the like is enhanced. The core material 210 is exposed on the inner surface 21a of the outer tube 21.

The inner fin 22 is made of a material that is potentially lower than the core material 210 of the outer tube 21, for example, an aluminum alloy containing Zn in a predetermined ratio. As a result, in an environment where the outer tube 21 is easily corroded by the cooling water, the inner fin 22 is preferentially corroded over the outer tube 21, so that the corrosion resistance on the inner surface 21a side of the outer tube 21 can be improved. it can.

The outer tube 21 has a brazing material layer on the inner surface 21a before the brazing step is performed in order to join the inner surface 21a of the outer tube 21 and the inner fin 22 to each other. The brazing filler metal layer is made of, for example, an aluminum alloy containing Si (silicon) in a predetermined ratio.

The inventors experimentally determined the corroded state of the outer tube 21 when the potential difference between the core material 210 of the outer tube 21 and the inner fin 22 was changed. The experimental results are as shown in FIG. This experiment was conducted under the following conditions.
First, an inner fin having a fin pitch of 3 [mm] was sandwiched between two outer tubes having a plate thickness of 300 [μm], and subjected to brazing heat treatment at 600 [° C.] for 3 minutes. The surface of the outer tube opposite to the joint surface was masked with an insulating resin and used as a test sample. A sacrificial layer is formed on the outer surface of the core material of each outer tube, and no sacrificial layer is formed on the inner surface on the opposite side. This test sample was subjected to a cycle corrosion test for 3 months. Cycle immersion test, Cl ^- and 500 [ppm], _SO ^{4 2-} to 100 [ppm], the ^{Cu 2+} was immersed for 8 hours in hot water at 88 [° C.] containing 10 [ppm], then 16 at room temperature This is a test in which the step of immersing for hours is one cycle. After performing a cycle corrosion test, corrosion products are removed by immersion in concentrated nitric acid, those with no corrosion penetration on the flat part of the tube are passed as corrosion resistance, and those with corrosion penetration are resistant. It was judged to be unacceptable due to corrosiveness. Further, among those having no corrosion penetration, those having a corrosion depth of 100 [μm] or less were judged to have good corrosion resistance. In FIG. 4, those having a good corrosion resistance are marked with a circle, those having a poor corrosion resistance are marked with a cross, and those having a good corrosion resistance are marked with a double circle. Has been done. As the core material of the outer tube, an aluminum alloy in the 1000s (pure Al type), an aluminum alloy in the 3000s (Al—Mn type), and an aluminum alloy in the 6000s (Al—Mg—Si type) were used. The pitting potential was measured at a test temperature of 25 [° C.] using a 5% NaCl aqueous solution (pH = 3, acetic acid acidity) as a test solution.

As is clear from the experimental results of FIG. 4, when the 1000 series aluminum alloy and the 3000 series aluminum alloy are used as the core material of the outer tube, the potential of the most precious part of the core material of the outer tube is set to "Vt". _When the potential of the lowest part of the inner fin is "Vf _min " and the potentials Vt _max and Vf _min satisfy the following equation f1, the corrosion resistance of the outer tube can be ensured. ..

Vt _max −Vf _min ≧ 80 [mV] (f1)
In particular, when the potentials Vt _max and Vf _min satisfy the following equation f2, the corrosion resistance of the outer tube can be further improved.
Vt _max −Vf _min ≧ 100 [mV] (f2)
Further, when an aluminum alloy in the 6000 series is used as the core material of the outer tube, if the potentials Vt _max and Vf _min satisfy the above formula f2, the corrosion resistance of the outer tube can be similarly ensured. It becomes.

According to the tube 20 of the heat exchanger 10 of the present embodiment described above, the actions and effects shown in the following (1) to (3) can be obtained.
(1) The potential of the lowest portion of the inner fin 22 is lower than the potential of the most noble portion of the core material 210 of the outer tube 21. According to this configuration, since the inner fin 22 substantially functions as a sacrificial anode material, the corrosion resistance of the outer tube 21 can be ensured. Further, if the inner fin 22 substantially functions as a sacrificial anode material, it is not necessary to provide a sacrificial layer at least on the inner surface 21a of the outer tube 21. As a result, it is not necessary to increase the thickness of the core material 210 of the outer tube 21 in order to secure the potential difference between the sacrificial layer and the core material, so that the outer tube 21 can be thinned.

_{(2) The potential Vf min} of the lowest portion of the inner fin 22 _{and the potential Vt max} of the most noble portion of the core material 210 of the outer tube 21 satisfy the above formula f1 or formula f2. According to this configuration, the corrosion resistance of the outer tube 21 can be ensured more appropriately.
(3) According to the experimental results of the inventors shown in FIG. 4, the potential Vf _min _{of the most base part of the inner fin and the potential Vt max} of the most precious part of the core material of the outer tube have the above formula f2. When satisfied, in the case of an outer tube provided with a sacrificial layer on the outer surface, corrosion penetration does not occur in the outer tube having a plate thickness of 300 [μm]. Further, the corrosion depth of the outer tube is 100 [μm] or less. Therefore, the plate thickness Ht of the outer tube 21 can be set within the range of the following equation f3, considering that the plate thickness that can tolerate a corrosion depth of 100 [μm] is 120 [μm].

120 [μm] ≤ Ht ≤ 300 [μm] (f3)
<Second Embodiment>
Next, a second embodiment of the tube 20 of the heat exchanger 10 will be described.

The tube 20 of the first embodiment has a brazing material layer on the inner surface 21a of the outer tube 21, and Zn is added to the core material of the inner fin 22. On the other hand, the tube 20 of the present embodiment has a structure in which the inner fin 22 has a brazing material layer.
Specifically, the outer tube 21 and the inner fin 22 of the present embodiment are configured by any of the patterns P1 to P6 shown in FIG. 5, for example. The patterns P1 to P6 shown in FIG. 5 show the configurations of the outer tube 21 and the inner fin 22 before being joined by brazing. In FIG. 5, an aluminum alloy is used for the portion described as "core material", and an aluminum alloy to which Zn is added is used for the portion described as "core material (Zn)". .. Further, an aluminum alloy to which Si is added is used in the portion described as "brazing material layer", and Si and Zn are contained in the portion described as "brazing material layer (Zn)". The added aluminum alloy is used.

Patterns P1 and P2 show a case where a brazing material layer is formed on the surface layers 22a and 22b of the inner fin 22 shown in FIG. 3 and the core material 210 is exposed on the inner surface 21a of the outer tube 21. In such a case, if Zn is added to both the core material of the inner fin 22 and the brazing material layer constituting the surface layers 22a and 22b as shown in the pattern P1, the core material 210 of the outer tube 21 is the most precious. The potential of the lowest part of the inner fin 22 is lower than the potential of the part. Alternatively, as shown in pattern P2, even when Zn is added only to the brazing material layers constituting the surface layers 22a and 22b of the inner fin 22, the Zn of the brazing material layer is added to the inner fin during brazing. Since it diffuses into the core material of 22, the potential of the lowest part of the inner fin 22 is lower than the potential of the most precious part of the core material 210 of the outer tube 21.

Patterns P3 and P4 show a case where a brazing material layer is formed on the surface layers 22a and 22b of the inner fin 22, and a brazing material layer is also formed as a surface layer on the inner surface 21a of the outer tube 21. In such a case, if Zn is added to both the core material of the inner fin 22 and the brazing material layer constituting the surface layers 22a and 22b as shown in the pattern P3, the core material 210 of the outer tube 21 is the most precious. The potential of the lowest part of the inner fin 22 is lower than the potential of the part. Alternatively, even when Zn is added only to the brazing material layers constituting the surface layers 22a and 22b of the inner fin 22 as shown in the pattern P4, the Zn of the brazing material layer is added to the inner fin 22 during brazing. Since it diffuses into the core material of the outer tube 21, the potential of the lowest part of the inner fin 22 is lower than the potential of the most precious part of the core material 210 of the outer tube 21.

The pattern P5 shows a case where a brazing material layer is formed on the surface layers 22a and 22b of the inner fin 22 and the core material 210 is exposed on the inner surface 21a of the outer tube 21. Further, the pattern P6 shows a case where the brazing material layer is formed on the surface layers 22a and 22b of the inner fin 22 and the brazing material layer is also formed as the surface layer on the inner surface 21a of the outer tube 21. In such a case, as shown in patterns P5 and P6, if Zn is added to the core material of the inner fin 22, the potential of the inner fin 22 is higher than the potential of the most precious part of the core material 210 of the outer tube 21. The potential of the lowest part is lower.

By using patterns P1 to P6 to lower the potential of the lowest part of the inner fin 22 than the potential of the most precious part of the core material 210 of the outer tube 21, the inner fin 22 is closer to the inner fin 22 than the outer tube 21. Will preferentially corrode. Therefore, it is possible to obtain the same or similar action and effect as the tube 20 of the first embodiment.

<Third Embodiment>
Next, a third embodiment of the tube 20 of the heat exchanger 10 will be described. Hereinafter, the differences from the tube 20 of the first embodiment will be mainly described.
If the inner fin 22 is formed of a material that is potentially lower than the core material 210 of the outer tube 21, as in the tube 20 of the first embodiment shown in FIG. 3, the inner fin 22 is better than the outer tube 21. Is preferentially corroded, so that the corrosion resistance of the outer tube 21 can be improved. However, when the inner fin 22 of the first embodiment is used as it is, the strength of the inner fin 22 is remarkably increased because the inside of the inner fin 22 is preferentially corroded over the surface layers 22a and 22b of the inner fin 22. It may decrease.

Specifically, in the manufacturing process of the tube 20, in order to join the outer tube 21 and the inner fin 22 by brazing, they are put into a furnace and heated. At that time, since the Zn existing in the surface layers 22a and 22b of the inner fin 22 evaporates, the content of Zn in the inner fin 22 is higher than the content of Zn in the surface layers 22a and 22b. easy. This means that the potential at the center of the inner fin 22 in the plate thickness direction is lower than the potential of the surface layers 22a and 22b of the inner fin 22. Therefore, when the corrosion of the surface layers 22a and 22b of the inner fin 22 progresses in a hole shape, for example, and the corrosion reaches the inside of the inner fin 22, the inside of the inner fin 22 is more than the surface layers 22a and 22b of the inner fin 22. Will corrode preferentially. When the inside of the outer tube 21 is filled with cooling water, the distance that the inner fin 22 functions as the sacrificial anode material with respect to the outer tube 21 becomes longer. Therefore, when the inside of the inner fin 22 is preferentially corroded, as shown in FIG. 7, the inner fin 22 has a hollow structure in which the surface layers 22a and 22b remain while a space is formed inside the inner fin 22. That is, since the inner fin 22 is substantially divided into two, the strength thereof may be significantly reduced. Further, when the inner fin 22 divided into two pieces is damaged due to the decrease in strength, the damaged debris is included in the cooling water and flows. If the debris flows to the water pump that pumps the cooling water, the water pump may malfunction.

Therefore, in the tube 20 of the present embodiment, in order to suppress such hollowing out of the inner fin 22, the potential of the center of the inner fin 22 in the plate thickness direction and the potential of the surface layer are set to the potential of the core material 210 of the outer tube 21. The potential at the center of the inner fin 22 in the plate thickness direction is set to be equal to or higher than the potential of the surface layer of the inner fin 22.

Next, a specific structure of the tube 20 of the present embodiment will be described.
The inventors have experimentally determined the corroded form of the inner fin 22. In this experiment, a tube 20 having a structure as shown in FIG. 8 was used. As shown in FIG. 8, in this tube 20, the outer tube 21 has a structure having a sacrificial layer 211 on the outer surface of the core material 210 and a brazing material layer 212 on the inner surface of the core material 210. Further, the inner fin 22 has a structure having a sacrificial layer on the surface layers 22a and 22b. The structures of the outer tube 21 and the inner fin 22 shown in FIG. 8 show the respective structures before brazing.

In the tube 20 shown in FIG. 8, the inventors have found that the potential Vt _max _{of the most precious part of the core material 210 of the outer tube 21, the potential Vf cent} of the center C of the inner fin 22 in the plate thickness direction, and the inner fin 22. The corrosion form of the inner fin 22 when _{the potential Vf surf} of the surface layers 22a and 22b was changed was determined by an experiment. In this experiment, an outer tube 21 having a plate thickness Ha of "200 [μm]" and an inner fin 22 having a plate thickness Hb of "100 [μm]" were used. Each plate thickness Ha and Hb is the plate thickness before brazing. When the outer tube 21 and the inner fin 22 are brazed, they are brazed via the brazing material layer 212 of the outer tube 21, so that the thickness of the brazing material layer 212 is slightly reduced. Specifically, the thickness of the brazing material layer 212 is about "20 [μm]" before brazing, but decreases to about "10 [μm]" after brazing.

9 to 10 show the results of experiments conducted by the inventors.
FIG. 9 shows the experimental results when a 1000-series aluminum alloy (pure Al-based) was used as the core material 210 of the outer tube 21. In this experiment, the corrosion resistance of the outer tube 21 and the corrosion morphology of the inner fin 22 were investigated while changing the potential difference “Vt _max −Vf _min ” and the potential difference “Vf _cent −Vf _surf”.

The potential difference "Vf _cent- _{Vf surf} " is the difference between _{the potential Vf cent at} the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22. The potential difference "Vf _cent- _{Vf surf} " was varied in the range of "-20 [mV]", "0 [mV]", and "20 [mV]".

The potential difference “Vt _max −Vf _min ” is the difference between _{the potential Vt max} of the most noble portion of the core material 210 of the outer tube 21 _{and the potential Vf min} of the lowest portion of the inner fin 22. _{For example, if the potential Vf cent} of the center C in the plate thickness direction of the _{inner fin 22 is lower than the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22, the potential Vf _min is the potential Vf _cent . _{Further, if the potential Vf surf} of the surface layers 22a and 22b of the _{inner fin 22 is lower than the potential Vf cent} of the center C in the plate thickness direction of the inner fin 22, the potential Vf _min is the potential Vf _surf . The potential difference "Vt _max- Vf _min " is "50 [mV]", "80 [mV]", "100 [mV]", "150 [mV]", "200 [mV]", "250 [mV]". , "270 [mV]", and "300 [mV]".

Regarding the column of "tube corrosion resistance" in FIG. 9, as in FIG. 4, those having passed the corrosion resistance of the outer tube 21 are marked with a circle, and those failing are marked with a cross. , Good ones are marked with double circles.
Further, in the column of "inner fin corrosion form", a double circle mark is described for those whose corrosion form is layered corrosion, and a circle mark is described for those whose corrosion form is random corrosion. Those that are corroded are marked with a triangle, and those that are corroded are marked with a cross. Layered corrosion is a form of corrosion in which the surface is peeled off in layers. Random corrosion is a form of corrosion in which holes are formed at random locations on the surface. The hollow corrosion is a corrosion mode in which the inside is lost. Corrosion and disappearance is a corrosion mode in which the entire inner fin is corroded and disappears.

As is clear from the experimental results of FIG. 9, when the potential difference “Vt _max −Vf _min ” satisfies “Vt _max −Vf _min ≧ 80 [mV]”, “tube corrosion resistance” is acceptable or good. It becomes. Regarding the corrosion resistance of the outer tube 21, the same experimental results as in the "1000 series aluminum alloy (pure Al type)" column of FIG. 4 have been obtained.

On the other hand, when the potential difference "Vt _max- Vf _min " is "270 [mV]" or more, when the potential difference "Vf _cent- _{Vf surf} " is "0 [mV]" and "20 [mV]", that is, the inner _{When the potential Vf cent} of the center C in the plate thickness direction of the _{fin 22 is equal to} or higher than the potential Vf surf of the surface layers 22a and 22b of the inner fin 22, the corrosion form of the inner fin is layered corrosion or random corrosion, so that it is more than hollow corrosion. Can also obtain good results. However, when the potential difference “Vt _max −Vf _min ” becomes “300 [mV]” or more, the inner fin 22 is corroded and disappears. _{That is, when the most potentially noble potential Vf max of the} inner fin 22 that remains last when the inner fin 22 is corroded is lower than the potential Vt max of the most noble portion of the core material 210 of the outer tube 21 by "280 mV" or more. , The inner fin 22 is corroded and disappears, which is not preferable.

On the other hand, FIG. 10 shows the experimental results when a 3000 series aluminum alloy (Al—Mn type) is used instead of the 1000 series aluminum alloy (pure Al type) as the core material 210 of the outer tube 21. In this case, the same experimental results as those shown in FIG. 9 were obtained with respect to "tube corrosion resistance" and "inner fin corrosion form".

Further, FIG. 11 shows the experimental results when a 6000 series aluminum alloy (Al—Mg—Si system) is used instead of the 1000 series aluminum alloy (pure Al system) as the core material 210 of the outer tube 21. .. In this case, regarding "tube corrosion resistance", the potential difference "Vt _max- Vf _min " must satisfy "Vt _max- Vf _min ≥ 100 [mV]", but regarding "inner fin corrosion form", , The same experimental results as those shown in FIG. 9 were obtained.

Based on the experimental results of FIGS. 9 and 10, in order to secure the corrosion resistance of the outer tube 21, if the potential difference “Vt _max −Vf _min ” satisfies “Vt _max −Vf _min ≧ 80 [mV]”. good. Here, since "Vf _min " is the potential of the lowest portion of the inner fin 22, the potential Vf _cent _{of the center C in the plate thickness direction of the inner fin 22 and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22. Whichever is the lower potential. Focusing on this, in order to secure the corrosion resistance of the outer tube 21, the potentials Vf _cent and Vf _surf need to satisfy either one of the following equations f4 and f5.

Vt _max −Vf _cent ≧ 80 [MV] (f4)
Vt _max- Vf _surf ≧ 80 [mV] (f5)
Further, based on not only the experimental results of FIGS. 9 and 10 but also the experimental results of FIG. 11, the potentials Vf _cent and Vf _surf may more preferably satisfy either one of the following formulas f6 and f7. ..

Vt _max −Vf _cent ≧ 100 [mV] (f6)
Vt _max- Vf _surf ≧ 100 [mV] (f7)
On the other hand, based on the experimental results of FIGS. 9 to 11, in order to suppress the hollow corrosion of the inner fin 22, the potential Vf _cent of the center C in the plate thickness direction of the inner fin 22 and the surface layer 22a of the inner fin 22 The potential Vf _{surf of} 22b may satisfy the following equation f8.

Vf _cent- _{Vf surf} ≧ 0 [mV] (f8)
When the above formula f8 is satisfied, the above formula f5 has a relationship including the above formula f4, and the above formula f7 has a relationship including the above f6.
Further, based on the experimental results of FIGS. 9 to 11, in order to prevent the inner fin 22 from corroding and disappearing, the potential Vf _max of the most precious part of the inner fin 22 and the core material 210 of the outer tube 21 _{The potential Vt max} of the most noble part may satisfy the following equation f9.

Vt _max −Vf _max ≦ 250 [mV] (f9)
_{In particular, if the potential Vf cent at} the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22 satisfy the following equation f10, the corrosion form of the inner fin 22 is further improved. It is possible.

Vf _cent- _{Vf surf} ≧ 20 [mV] (f10)
According to the tube 20 of the heat exchanger 10 of the present embodiment described above, the actions and effects shown in the following (4) to (7) can be obtained.
_{(4) Make} the potential Vf cent of the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22 lower than _{the potential Vt max} of the most precious part of the core material 210 of the outer tube 21. .. _{Further, the potential Vf cent at} the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22 satisfy the above equation f8. That is, the potential Vf _{cent is set} to the potential Vf _surf or higher. As a result, the corrosion resistance of the outer tube 21 can be ensured, and the hollow corrosion of the inner fin 22 can be suppressed.

_{(5) It is preferable that the potential Vf cent at} the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22 satisfy the above formula f4 or f5. According to this configuration, the corrosion resistance of the outer tube 21 can be further improved.

_{(6) It is preferable that the potential Vf cent at} the center C of the inner fin 22 in the plate thickness direction _{and the potential Vf surf} of the surface layers 22a and 22b of the inner fin 22 satisfy the above formula f10. According to this configuration, it is possible to more preferably suppress the corrosion of the inner fin 22.

_{(7) It is preferable that the potential Vf max} of the most noble portion of the inner fin 22 and the potential Vt of the core material 210 of the outer tube 21 satisfy the above formula f9. According to this configuration, it is possible to more preferably suppress the corrosion of the inner fin 22.

<Other Embodiments>
The above embodiment can also be implemented in the following embodiments.
-The sacrificial layer 211 may not be provided on the outer surface of the outer tube 21. According to the experimental results of the inventors, when the potential Vf _min _{of the lowest part of the inner fin and the potential Vt max} of the most precious part of the core material of the outer tube satisfy the above equation f2, the outer surface is sacrificed. In the case of the outer tube without the layer, as shown in FIG. 6, the outer tube having a plate thickness of 200 [μm] does not undergo corrosion penetration. The corrosion depth of the outer tube is 100 [μm] or less. Therefore, the plate thickness Ht of the outer tube 21 can be set within the range of the following equation f4, considering that the plate thickness that can tolerate a corrosion depth of 100 [μm] is 120 [μm]. ..

120 [μm] ≤ Ht ≤ 200 [μm] (f4)
-In the tube 20 of the third embodiment, the thickness of each of the outer tube 21 and the inner fin 22 may be changed. For example, the plate thickness of the inner fin 22 is not limited to "100 [μm]" and can be set in the range of "80 [μm]" to "200 [μm]".
-The present disclosure is not limited to the above specific examples. Specific examples described above with appropriate design changes by those skilled in the art are also included in the scope of the present disclosure as long as they have the features of the present disclosure. Each element included in each of the above-mentioned specific examples, and their arrangement, conditions, shape, and the like are not limited to those illustrated, and can be changed as appropriate. The combinations of the elements included in each of the above-mentioned specific examples can be appropriately changed as long as there is no technical contradiction.

Claims

The outer tube (21) through which cooling water flows inside,
An inner fin (22) provided inside the outer tube is provided.
The potential of the lowest part of the inner fin is lower than the potential of the most noble part of the core material (210) of the outer tube.
A tube of a heat exchanger having a brazing material layer on at least one of the surface layer of the inner surface of the outer tube and the surface layer of the inner fin.
When the potential of the most noble part of the core material of the outer tube is "Vt max " and the potential of the most base part of the inner fin is "Vf min ", the potentials Vt max and Vf min are expressed by the following equations Vt max. -Vf min ≥ 80 [mV]
The tube of the heat exchanger according to claim 1.
When the potential of the most noble part of the core material of the outer tube is "Vt max " and the potential of the most base part of the inner fin is "Vf min ", the potentials Vt max and Vf min are expressed by the following equations Vt max. -Vf min ≥ 100 [mV]
The tube of the heat exchanger according to claim 1.
A sacrificial layer (211) is provided on the surface layer of the outer surface of the outer tube.
When the plate thickness of the outer tube including the sacrificial layer is Ht, the plate thickness Ht is the following formula 120 [μm] ≤ Ht ≤ 300 [μm].
The tube of the heat exchanger according to any one of claims 1 to 3.
No sacrificial layer is provided on the surface layer of the outer surface of the outer tube.
When the plate thickness of the outer tube is Ht, the plate thickness Ht is the following formula 120 [μm] ≤ Ht ≤ 200 [μm].
The tube of the heat exchanger according to any one of claims 1 to 3.
The potential of the center of the inner fin in the plate thickness direction and the potential of the surface layer are lower than the potential of the most precious part of the core material of the outer tube.
The potential at the center of the inner fin in the plate thickness direction is equal to or higher than the potential on the surface layer of the inner fin.
The tube of the heat exchanger according to claim 1, wherein a brazing material layer is formed on at least one of the surface layer of the inner surface of the outer tube and the surface layer of the inner fin.
The potential at the center of the inner fin in the plate thickness direction is defined as "Vf cent", the potential at the surface layer of the inner fin is defined as "Vf surf ", and the potential at the most precious part of the core material of the outer tube is defined as "Vt max ". to time, the potential Vf cent, Vf surf, Vt max, the following equation Vt max -Vf surf ≧ 80 [mV ]
The tube of the heat exchanger according to claim 6.
The potential at the center of the inner fin in the plate thickness direction is defined as "Vf cent", the potential at the surface layer of the inner fin is defined as "Vf surf ", and the potential at the most precious part of the core material of the outer tube is defined as "Vt max ". to time, the potential Vf cent, Vf surf, Vt max, the following equation Vt max -Vf surf ≧ 100 [mV ]
The tube of the heat exchanger according to claim 6.
When the potential at the center of the inner fin in the plate thickness direction is "Vf cent " and the potential on the surface layer of the inner fin is "Vf surf ", the potentials Vf cent and Vf surf are as follows: Vf cent − Vf surf ≧ 20 [mV]
The tube of the heat exchanger according to any one of claims 6 to 8.
When the potential of the most noble part of the inner fin is "Vf max " and the potential of the most noble part of the core material of the outer tube is "Vt max ", the potentials Vf max and Vt max are expressed by the following equations Vt max. -Vf max ≤ 250 [mV]
The tube of the heat exchanger according to any one of claims 6 to 9.