JP7519626B2 - Heat exchanger and manufacturing method thereof - Google Patents

Description

This disclosure relates to heat exchangers, and in particular to a laminated plate fin heat exchanger constructed by stacking plate-shaped plate fins having flow paths through which a refrigerant flows, and a method for manufacturing the same.

Heat exchangers, which are used to exchange thermal energy between fluids with different thermal energies, are used in many products, and in particular, stacked plate fin heat exchangers are used in, for example, home and vehicle air conditioners, computers, and various electrical appliances.

A stacked plate fin heat exchanger is a type of device that exchanges heat between a fluid (refrigerant) that flows through flow paths formed in the plate fins and a fluid (air) that flows between the stacked plate fins.

In the field of stacked plate fin heat exchangers such as those described above, various configurations have been proposed with the aim of providing products that are compact, lightweight, and highly reliable (see, for example, Patent Documents 1-4).

JP 2012-112562 A Japanese Patent Application Publication No. 09-001385 Patent No. 3283471 Patent No. 5714387

In the field of laminated plate fin heat exchangers, in order to reduce weight, size and improve the efficiency of heat exchange, it has been considered to construct the plate fins thin and using a material with high thermal conductivity, and to pass a fluid (refrigerant) at a higher pressure through the flow passages formed in the plate fins than in conventional heat exchangers.

In a heat exchanger, in order to flow a high-pressure refrigerant through a flow path, it is necessary to configure the flow path to have a desired cross-sectional shape that does not cause variation in the flow rate and flow speed of the refrigerant so that the refrigerant can flow steadily. In particular, in a laminated plate fin heat exchanger configured by stacking multiple plate fins, where multiple plate fins are joined by brazing to form the laminated plate fins, it was an important issue to ensure that the flow path through which the refrigerant flows, formed in the plate fins, had the desired cross-sectional shape and was formed stably and reliably.

The objective of this disclosure is to provide a highly reliable heat exchanger that is lightweight, compact, and efficient, while ensuring that the refrigerant flow paths in the heat exchanger have the desired cross-sectional shape and desired pressure resistance.

The present disclosure aims to solve the above problems and provide a highly reliable device and method for manufacturing the same that achieves miniaturization and efficiency in a laminated plate fin heat exchanger formed by joining multiple plate fins by brazing, and that has a refrigerant flow path with a desired cross-sectional shape and desired pressure resistance.

In order to achieve the above object, a method for manufacturing a heat exchanger according to one aspect of the present disclosure includes:
A method for manufacturing a heat exchanger including a plate fin stack in which plate fins having refrigerant flow paths are stacked with gaps therebetween, comprising the steps of:
The plate fin includes a brazing sheet including a brazing material layer on a surface thereof and a flow passage forming region, the brazing sheet being overlapped and brazed to the brazing sheet, and the refrigerant flow passage is formed by the opposing flow passage forming regions.
The stacked brazing sheets are manufactured so that the flow path cross-sectional ratio, which indicates the ratio of the flow path cross-sectional area in the joined state after brazing to the unjoined flow path cross-sectional area formed by the flow path forming region in the unjoined state before brazing, is within a predetermined range.

Moreover, the heat exchanger according to one aspect of the present disclosure includes:
A heat exchanger including a plate fin stack in which plate fins having refrigerant flow paths are stacked with gaps therebetween,
The plate fin includes a brazing sheet including a brazing material layer on a surface thereof and a refrigerant flow path formed by stacking and brazing a brazing sheet having a flow path forming region,
In the overlapped brazing sheets, a flow passage cross-sectional ratio indicating the ratio of the flow passage cross-sectional area in a joined state after brazing to the unjoined flow passage cross-sectional area formed by the flow passage forming region in an unjoined state before brazing falls within a predetermined range.

As described above, the heat exchanger and manufacturing method thereof disclosed herein can achieve weight reduction, size reduction, and efficiency, while ensuring that the refrigerant flow path in the heat exchanger has the desired cross-sectional shape and desired pressure resistance, thereby providing a highly reliable heat exchanger.

FIG. 1 is a perspective view showing an external appearance of a heat exchanger with stacked plate fins according to a first embodiment of the present disclosure; FIG. 1 is a plan view showing an example of a brazing sheet that constitutes a plate fin in a heat exchanger according to a first embodiment; FIG. 1 is an end view of a plate fin stack according to a first embodiment, cut along a plane perpendicular to the longitudinal direction of the stack. FIG. 1 is an enlarged cross-sectional view showing a schematic diagram of a state before a brazing sheet is joined (soldered) in the first embodiment; FIG. 1 is a cross-sectional view showing a schematic stacked structure of a brazing sheet used in a heat exchanger according to a first embodiment. Cross-sectional photograph showing the brazing sheet being brazed to form the refrigerant flow path Al-Si (aluminum-silicon) binary phase diagram A cross-sectional photograph showing the state in which the molten brazing material penetrates into the core material during brazing. A cross-sectional photograph showing a specific example of a flow path cross-sectional shape of a refrigerant flow path formed by brazing opposing brazing sheets. Graph showing calculation results for coolant flow paths formed in an experiment Graph showing calculation results for coolant flow paths formed in an experiment FIG. 1 is an enlarged cross-sectional view showing a schematic diagram of a brazing sheet according to a first embodiment after being brazed; A graph showing the relationship between "brazing filler layer thickness" and "corrected flow index" in the experimental results. A graph showing the relationship between the "silicon concentration in the brazing material layer" and the "corrected flow index" in the experimental results. Graph showing the regions of "thickness of brazing material layer" and "silicon concentration (Si concentration) in brazing material layer" which are material factors for forming a preferable refrigerant flow path in a heat exchanger in the experimental results.

Below, a stacked plate fin heat exchanger will be described as a specific embodiment of the heat exchanger of the present disclosure with reference to the attached drawings. Note that the heat exchanger of the present disclosure is not limited to the specific stacked plate fin heat exchanger configuration described in the following embodiment, but includes those based on technology equivalent to the technical ideas having the technical features described in the following embodiment.

The shapes, configurations, methods (steps, order of steps), etc. shown in the following embodiments are merely examples, and the invention is not limited to the contents of this disclosure. Among the elements in the following embodiments, those that are not described in an independent claim that represents a top-level concept are described as optional elements. In the drawings, each element is depicted diagrammatically as the main subject for ease of understanding.

First, various aspects of the heat exchanger and the manufacturing method thereof according to the present disclosure will be illustrated.
The method for manufacturing a heat exchanger according to the first aspect of the present disclosure includes:
A method for manufacturing a heat exchanger including a plate fin stack in which plate fins having refrigerant flow paths are stacked with gaps therebetween, comprising the steps of:
The plate fin includes a brazing sheet including a brazing material layer on a surface thereof and a flow passage forming region, and the brazing sheet is laminated and brazed to the brazing sheet, and a refrigerant flow passage is formed by the opposing flow passage forming regions.
The stacked brazing sheets are manufactured so that the flow path cross-sectional ratio, which indicates the ratio of the flow path cross-sectional area in the joined state after brazing to the unjoined flow path cross-sectional area formed by the flow path forming region in the unjoined state before brazing, is within a predetermined range.

In the method for manufacturing a heat exchanger of the second aspect of the present disclosure, the flow passage cross-sectional ratio in the first aspect may be within the range of 31.0%≦R≦81.8%.

In the method for manufacturing a heat exchanger of the third aspect of the present disclosure, the flow passage cross-sectional ratio (R) in the first aspect may be within the range of 45.3%≦R≦81.8%.

The method for manufacturing a heat exchanger according to the fourth aspect of the present disclosure may be any of the first to third aspects, in which the relationship between the thickness of the brazing sheet and the silicon concentration of the brazing sheet is within a predetermined range.

The manufacturing method of the heat exchanger of the fifth aspect of the present disclosure may be, in any of the first to third aspects described above, manufactured using a material that exhibits a brazing layer thickness and a brazing layer silicon concentration selected from a range within a selection region (M) shown by an approximate parallelogram in a scatter diagram of materials that shows a correlation between the brazing layer thickness and the brazing layer silicon concentration in the brazing sheet.

A heat exchanger according to a sixth aspect of the present disclosure is a heat exchanger including a plate fin stack in which plate fins having refrigerant flow paths are stacked with gaps therebetween,
The plate fin includes a brazing sheet including a brazing material layer on a surface thereof and a refrigerant flow path formed by stacking and brazing a brazing sheet having a flow path forming region,
In the overlapped brazing sheets, a flow passage cross-sectional ratio indicating the ratio of the flow passage cross-sectional area in a joined state after brazing to the unjoined flow passage cross-sectional area formed by the flow passage forming region in an unjoined state before brazing falls within a predetermined range.

The seventh aspect of the heat exchanger according to the present disclosure may be the sixth aspect, in which the flow passage cross-sectional ratio is within the range of 31.0%≦R≦81.8%.

The heat exchanger of the eighth aspect of the present disclosure may be the sixth aspect, in which the flow passage cross-sectional ratio is within the range of 45.3%≦R≦81.8%.

A ninth aspect of the present disclosure is a method for producing a heat exchanger according to any one of the sixth to eighth aspects, wherein the brazing sheet has a wax layer on at least one surface of a core material,
The material constituting the core material and the brazing material layer may be an aluminum alloy, and the brazing material layer may be made of an aluminum alloy containing silicon.

The heat exchanger of the tenth aspect of the present disclosure may be configured in the ninth aspect, in which the brazing sheet has the wax layer on both sides of the core material.

(Embodiment 1)
Hereinafter, a heat exchanger and a manufacturing method thereof according to a first embodiment of the present disclosure will be described with reference to the accompanying drawings. Fig. 1 is a perspective view showing the appearance of a stacked plate fin heat exchanger (hereinafter simply referred to as a heat exchanger) 1 according to the first embodiment. As shown in Fig. 1, the heat exchanger 1 according to the first embodiment includes an inlet pipe 4 into which a refrigerant, which is a first fluid A, is supplied, a plate fin stack 2 formed by stacking a plurality of rectangular plate-shaped plate fins 2a with gaps therebetween, and an outlet pipe 5 for discharging the refrigerant that has flowed through a refrigerant flow path formed in the plate fins 2a.

In the heat exchanger 1 of the first embodiment, the supply pipe 4 and the exhaust pipe 5 have substantially the same configuration, and the names used are based on the functions that correspond to the operations performed at that time. In this disclosure, the supply pipe 4 and the exhaust pipe 5 are collectively referred to as the sleeve (4, 5).

End plates 3 are arranged at both ends of the plate fin stack 2 in the stacking direction (vertical direction in the heat exchanger 1 shown in FIG. 1), and the end plates 3 have approximately the same shape as the rectangular plate fins 2a in plan view (shape seen from above in the heat exchanger 1 shown in FIG. 1). An inlet pipe 4 or an outlet pipe 5 is joined to both ends of the longitudinal direction of one end plate 3. Note that in the configuration of embodiment 1, an inlet pipe 4 or an outlet pipe 5 is joined to both ends of one end plate 3, respectively. However, depending on the specifications of the device in which the heat exchanger 1 is used, an inlet pipe 4 may be joined to one end plate 3 and an outlet pipe 5 may be joined to the other end plate 3.

In the following embodiment 1, the stacking direction of the plate fin stack 2 in the heat exchanger 1 shown in FIG. 1 is described as the up-down direction, and one end plate 3 provided on the plate fin stack 2 is located on the upper side, and the other end plate 3 is located on the lower side. However, when the heat exchanger 1 is installed in an apparatus (e.g., an air conditioner), the stacking direction is not specified as the up-down direction (vertical direction).

The end plates 3 arranged at both ends of the plate fin stack 2 in the stacking direction are fixed to each other at a predetermined interval by positioning means (e.g., positioning bolts, etc.), and sandwich the plate fin stack 2. The positioning means that fixes the end plates 3 at both ends while maintaining a predetermined interval has the function of positioning each of the stacked plate fins 2a. The end plates 3 may be composed of a plate material made of a metal material such as aluminum, aluminum alloy, or stainless steel, or may be composed of a laminate formed by stacking brazing sheets described later.

In the heat exchanger 1 of the first embodiment, the first fluid A, refrigerant, flows through a refrigerant flow path 60 (see FIG. 3) that is composed of a flow path forming region 13 formed in each plate fin 2a of the plate fin stack 2. On the other hand, the second fluid B, air, passes through gaps formed between the stacked plate fins 2a in the plate fin stack 2. In the heat exchanger 1 configured in this way, heat exchange takes place between the first fluid A and the second fluid B in the plate fin stack 2.

Each of the multiple plate fins 2a constituting the plate fin stack 2 in the heat exchanger 1 of the first embodiment is configured by bonding (soldering) two brazing sheets (first fin member 10, second fin member 20) facing each other to form a refrigerant flow path 60. The plate fins 2a configured in this manner are pressurized and heated in a stacked state to bond (solder) the plate fin stack 2. When the plate fin stack 2 is heated and bonded, the end plates 3 and sleeves 4 and 5 may also be heated and bonded (soldered) at the same time to produce the heat exchanger.

Figure 2 is a plan view showing an example of the first fin member 10 and the second fin member 20 of the brazing sheet 50 (see Figure 4) constituting the plate fin 2a. In Figure 2, (a) is a plan view of the first fin member 10, and (b) is a plan view of the second fin member 20. The first fin member 10 and the second fin member 20 are thin plates made of aluminum alloy, and their detailed configurations will be described later. The first fin member 10 and the second fin member 20 are processed into a predetermined shape using the thin plate of the brazing sheet 50. The first fin member 10 and the second fin member 20 processed into a predetermined shape are arranged opposite each other at a predetermined position, and are pressed and heated so as to be in close contact with each other, so that the opposing flat predetermined areas are reliably joined (brazed) to each other.

The first fin member 10 shown in FIG. 2(a) has recesses formed on both longitudinal ends for annular header flow passages 11 that are supplied with refrigerant from the supply pipe 4 or that discharge refrigerant to the discharge pipe 5. A header communication flow passage 12 is formed that leads out a predetermined distance from one point on the outer periphery of the header flow passage 11, and the end of a flow passage formation area 13 formed in the heat exchange area of the plate fin 2a is disposed on the extension line of the lead-out direction of the header communication flow passage 12.

The flow passage forming region 13 in the first fin member 10 is formed by a recess, similar to the header communication flow passage 12. The flow passage forming region 13 is formed so as to meander through the entire heat exchange region of the plate fin 2a. Note that the configurations of the header flow passage 11, header communication flow passage 12, and flow passage forming region 13 in the first embodiment are exemplary, and the present disclosure is not limited to this exemplary configuration.

In the configuration of the first embodiment, the second fin member 20 joined (brazed) to the first fin member 10 has flow path forming regions 21 and 22 formed therein, as shown in FIG. 2B. In the first embodiment, the first fin member 10 and the second fin member 20 are joined (brazed) to form a refrigerant flow path 60 in which the header flow path 11 communicates with the flow path forming region 13 via the communication flow path 12. As a result, in the heat exchanger 1 of the first embodiment, the refrigerant supplied from the supply pipe 4 flows through the header flow path 11, the header communication flow path 12, the flow path forming region 21, the flow path forming region 13 (flow path forming region 22), the flow path forming region 21, the header communication flow path 12, and the header flow path 11, and is discharged from the discharge pipe 5.

As shown in FIG. 2B, in the second fin member 20, a flow path forming region 22 is formed in a region facing the linear flow path forming region 13 in the first fin member 10. This flow path forming region 22 is a convex region that protrudes in the same direction as the flow path forming region 13, and is formed to have a lower protruding height than the flow path forming region 13. By arranging this flow path forming region 22 facing the linear flow path forming region 13 of the first fin member 10, the refrigerant flow path 60 in the linear portion of the flow path forming region 13 is secured, and deformation of the cross-sectional shape perpendicular to the flow direction of the refrigerant is suppressed.

The first fin member 10 and the second fin member 20 are formed with heat transfer blocking slits 6, which suppress heat transfer between adjacent flow passage forming regions 13 and increase heat exchange efficiency.

Figure 3 is an end view of the plate fin stack 2 in the first embodiment cut along a plane perpendicular to the longitudinal direction. In Figure 3, the first fin member 10 and the second fin member 20 are joined (brazed) to form a refrigerant flow path 60 by the flow path forming region 13 of the first fin member 10 and the flow path forming region 22 of the second fin member 20. Figure 4 is an enlarged cross-sectional view showing the state before the first fin member 10 and the second fin member 20 are joined (brazed). As shown in Figure 4, a three-layer brazing sheet 50 in which brazing material layers (52, 53) are formed on both sides of a core material 51 is used as the first fin member 10 and the second fin member 20 in the first embodiment. Note that, in the plate fin stack 2, a four-layer brazing sheet 50 in which a sacrificial material layer is formed on one side of the core material 51 may be used, as described later.

<Brazing sheet>
Fig. 5 is a cross-sectional view showing a schematic layered structure of a brazing sheet 50 used as the first fin member 10 and the second fin member 20 in the heat exchanger 1 of the embodiment 1. Fig. 5(a) shows a brazing sheet 50a having a three-layer structure, and Fig. 5(b) shows a brazing sheet 50b having a four-layer structure.

The three-layer brazing sheet 50a shown in Fig. 5(a) has a structure in which aluminum alloy layers are laminated, and has a three-layer structure in which a first brazing layer 52 and a second brazing layer 53 are laminated on both sides of a core material 51. As a specific example of the three-layer brazing sheet 50a, for example, the core material 51 is an aluminum alloy containing manganese (Mn), and the first brazing layer 52 and the second brazing layer 53 are aluminum alloys containing silicon (Si).
Representative examples of the material for the core material 51 include, but are not limited to, 3000 series (aluminum-manganese (Al-Mn) alloys), 5000 series (aluminum-magnesium (Al-Mg) alloys), and 6000 series (aluminum-magnesium-silicon (Al-Mg-Si) alloys). The core material 51 in the brazing sheet 50 (50a, 50b) of the present disclosure may be any aluminum alloy that can achieve the physical properties required depending on various conditions such as the type or structure of the heat exchanger.

The first brazing material layer 52 and the second brazing material layer 53 may be an aluminum alloy containing silicon (Si) used as a brazing material, that is, an aluminum-silicon (Al-Si) alloy. The Al-Si alloy used as a brazing material may contain elements other than Si as long as the elements do not affect the function of the brazing material. The Al-Si alloy used as a brazing material may contain various elements as unavoidable impurities.

The four-layer brazing sheet 50b shown in FIG. 5(b) has a laminated structure of aluminum alloy layers, similar to the three-layer brazing sheet 50a, but has a sacrificial material layer 54 formed between the first solder layer 52 and one side of the core material 51. The sacrificial material layer 54 covers one side of the core material 51, and the second solder layer 53 covers the other side of the core material 51, i.e., the side opposite to the side covered by the sacrificial material layer 54. The material of the sacrificial material layer 54 is an aluminum alloy, similar to the core material 51, the first solder layer 52, and the second solder layer 53, but it is an aluminum alloy containing zinc (Zn).

The aluminum alloy used as the material for the sacrificial material layer 54 contains zinc (Zn) to provide sacrificial anticorrosion properties. The material for the sacrificial material layer 54 may contain elements other than Zn as long as they do not affect the sacrificial anticorrosion properties. The Al-Zn alloy used as the material for the sacrificial material layer 54 may contain various elements as unavoidable impurities.

In manufacturing the heat exchanger of the first embodiment, the first fin member 10 and the second fin member 20 formed from the brazing sheet 50 made of the above-mentioned material are stacked and brazed in a high-temperature (580°C or higher) furnace to join them together and form a refrigerant flow path. The plate fin stack 2 manufactured in this manner is used in the heat exchanger 1 of the first embodiment.

Figure 6 is a cross-sectional photograph showing the state in which the first fin member 10 and the second fin member 20 are brazed to form a refrigerant flow path 60. That is, the cross-sectional photograph of Figure 6 is a specific example showing the state in which the overlapping first fin member 10 and second fin member 20 shown in Figure 4 are brazed at high temperature. The refrigerant flow path 60 in the cross-sectional photograph shown in Figure 6 has a desired flow path cross section, and the second brazing layer 53 of the first fin member 10 and the first brazing layer 52 of the second fin member 20, which are arranged opposite each other, are melted and joined to each other, and the desired refrigerant flow path 60 is formed.

As shown in the cross-sectional photograph of Figure 6, the brazing material layers (53, 52) melt in the region between the core material 51 of the first fin member 10 and the core material 51 of the second fin member 20 to form a fillet (joint) 61. This fillet (joint) 61 is formed when the second brazing material layer 53 of the first fin member 10 and the first brazing material layer 52 of the second fin member 20 are heated to a predetermined high temperature before brazing and melt, and condense in the joint region 61a between the first fin member 10 and the second fin member 20 and in the flow path forming regions 61b on both sides of the refrigerant flow path 60, thereby brazing and joining the first fin member 10 and the second fin member 20. The amount of melting of the brazing material layers (53, 52) during brazing at this time is determined by the amount of melting (actual amount of melting) minus the amount of penetration (amount of thinning) into each core material 51, which determines the amount (shape and size) of the fillet (joint) 61, i.e., the amount of joining (shape and size) of the joining area 61a and the flow path forming area 61b.

The joint strength (pressure resistance) between the brazed first fin member 10 and second fin member 20 is affected by the amount (shape and size) of the fillet (joint) 61, and if a certain amount is not secured, it may lead to damage or refrigerant leakage during use in the plate fin stack 2. In addition, in the flow path forming region 61b that forms the refrigerant flow path 60, if the desired flow path cross-sectional shape is not achieved, there is a problem that the specified heat exchange capacity cannot be guaranteed.

As described above, by brazing the first fin member 10 and the second fin member 20, the first fin member 10 and the second fin member 20 have the desired joint strength (pressure resistance performance) and the refrigerant flow path is formed into the desired flow path cross-sectional shape. At least the following factors influence this.

(1) The thickness of the brazing layer as a material factor;
(2) Silicon concentration (Si concentration) in the brazing material layer as a material factor
(3) brazing temperature as a condition factor, and (4) brazing time as a condition factor.

Of the above influencing factors, (1) to (3) determine the amount of melting of the brazing material layer, and (4) determines the amount of penetration (amount of thinning) into the core material 51.

<Si diffusion during brazing>
Fig. 7 is an Al-Si (aluminum-silicon) binary phase diagram, with the vertical axis representing temperature T [°C] and the horizontal axis representing Si concentration [%]. In the binary phase diagram shown in Fig. 7, the eutectic temperature showing the eutectic isotherm is 577°C, and the two-phase coexistence region shows a Si concentration of 1.6 to 12.1%. The AL liquidus temperature at a Si concentration of 0% is 660°C.

As shown in the phase diagram of FIG. 7, the liquid phase ratio σ at a certain temperature T is basically determined by the Si concentration [Si] of the aluminum alloy. Therefore, the amount of melting of the brazing material layer (53, 52) during brazing can be determined by the "thickness of the brazing material layer," the "Si concentration in the brazing material layer," and the "brazing temperature." However, during brazing, some of the Si atoms in the brazing material layer diffuse into the core material 51, so not all of the brazing material in the brazing material layer is formed in the fillet (joint) 61.

As described above, since the Si atoms in the brazing material layer diffuse into the core material 51 during brazing, the amount of Si required to form the fillet (joint) 61 in the brazing material layer is less than the calculated value calculated from the Si concentration recorded on the mill sheet of the alloy material. In other words, the liquid phase ratio σ that determines the amount of melting in the brazing material layer during brazing is less than the calculated liquid phase ratio value calculated from the SI concentration recorded on the mill sheet.

Therefore, if it were possible to quantify the amount of Si diffusion during brazing, it would be possible to accurately calculate the actual liquid phase ratio σ; however, the amount of Si diffusion varies greatly in actual results, making it difficult to quantify from experimental values, etc.

Therefore, in the present disclosure, by simply modeling the amount of Si diffusion from the theoretical formula of diffusion, it is possible to calculate the amount of melting of the brazing material layer during brazing using the substantial liquid phase ratio (corrected liquid phase ratio) _σ2 that takes into account the effect of Si diffusion during brazing.

<Simple modeling of Si diffusion amount>
Next, a concept for simply modeling the change in the liquid phase ratio σ due to Si diffusion during brazing will be described.

From the binary phase diagram shown in Figure 7, the change in liquid phase ratio σ due to the Si concentration [Si] is expressed by a linear equation for the Si concentration [Si] shown in the following equation [1].

As shown in the above formula [1], the change in the liquid phase ratio σ is expressed by a linear equation of the Si concentration [Si], so it is considered that the change in the liquid phase ratio σ due to Si diffusion during brazing can also be expressed by a linear equation of the Si concentration [Si].

It has been confirmed through experiments by the inventors that the amount of Si diffusion during brazing is proportional to the "square root of the brazing time (√t ₁ )", the "diffusion coefficient (D)", and the "Si concentration gradient between the core material and the brazing material layer (C _b -C _c )". Therefore, the substantial liquid phase ratio (corrected liquid phase ratio) σ ₂ during brazing when taking Si diffusion into consideration can be expressed by the following formula [2].

In the above formula [2], "K ₁ " is a fitting coefficient, "D" is the diffusion coefficient, "C _b " is the Si concentration in the brazing material layer, "C _c " is the Si concentration in the core material, and "t ₁ " is the brazing time.

From the above-mentioned study results, the inventors have found that the substantial melt amount (substantial melt amount) formed during brazing can be calculated by multiplying the "thickness of the brazing material layer" and the "corrected liquid phase ratio σ ₂ " (see formula [3] below).

<Amount of metal loss during brazing>
As described above, during brazing, the brazing material layer melts to form the fillet (joint) 61. The amount of brazing material required to form this fillet (joint) 61 is the amount of the brazing material melted by the amount of the brazing material layer minus the amount of penetration (amount of metal loss) into the core material 51. The amount (shape and size) of the fillet (joint) 61, i.e., the amount (shape and size) of the joint region 61a and the flow path forming region 61b, is determined by this amount of brazing material.

Figure 8 is a cross-sectional photograph showing the state in which the molten solder material has penetrated into the core material 51 during brazing. In the cross-sectional photograph shown in Figure 6 above, the molten solder material has formed a fillet (joint) between the core materials 51, showing that the brazing sheets 50 are securely joined to each other. On the other hand, in the cross-sectional photograph shown in Figure 8, it can be seen that the molten solder material has penetrated into the interior of each core material 51, reducing the joint strength between the brazing sheets 50.

The state shown in the cross-sectional photograph of Figure 8 shows the state when the brazing time has increased beyond a predetermined time, and in this state, the molten brazing material gradually penetrates into the core material 51. When the brazing material penetrates into the core material 51 in this way, the joint strength decreases by the amount of penetration (amount of thinning), i.e., the amount of reduction.

The amount of metal loss caused by the penetration of the brazing material into the core material 51 during brazing is closely related to the "brazing time", and it is known that the "amount of metal loss" is proportional to the square root of the "brazing time". Therefore, the relationship between the "amount of metal loss" and the "brazing time" can be expressed by the following formula [4].

<Corrected flow index F ₂ >
Next, a description will be given of the "corrected flow index F ₂ " which is defined taking into consideration the "substantial melting amount" which is substantially melted from the brazing material layer during brazing and the above-mentioned "amount of metal loss". The "corrected flow index F ₂ " is an index for forming a refrigerant flow path 60 having a desired flow path cross section and for ensuring a predetermined bonding strength (pressure resistance performance) between opposing brazing sheets 50 to be bonded. The "corrected flow index F ₂ " is defined as shown in the following formula [5].

As described above, the "corrected flow index _F2 " is an index that takes into account the following influencing factors during brazing: (1) the "thickness of the brazing material layer" as a material factor, (2) the "silicon concentration (Si concentration) in the brazing material layer" as a material factor, (3) the "brazing temperature" as a condition factor, and (4) the "brazing time" as a condition factor.

Therefore, by determining the "corrected flow index F2" when a predetermined bonding strength (pressure resistance performance) is reliably secured between the opposing brazing sheets ₅₀ to be joined and a refrigerant flow path 60 having a desired flow path cross section is formed, it is possible to determine the ranges of the "thickness of the brazing material layer" and the "silicon concentration (Si concentration) in the brazing material layer" which are the desired material factors during brazing.

Figure 9 is a cross-sectional photograph showing the specific shape of the cross section of the refrigerant flow channel 60 formed by brazing opposing brazing sheets 50. Note that the cross section of the flow channel is a cross section taken in a direction perpendicular to the direction in which the refrigerant flows in the refrigerant flow channel 60.

Figure 9 (a) shows a case where the cross section of the refrigerant flow path 60 has a desired shape, and is a cross-sectional photograph showing a similar shape to the approximately mountain-shaped shape that is the ideal shape in the design. Figure 9 (b) shows a cross section of the flow path that is approximately elliptical, with a large amount of actual melting and a large area occupied by the fillet (joint), and the joint strength (pressure resistance performance) is high, but the cross section of the refrigerant flow path 60 is small. Figure 9 (c) shows a further increase in the amount of actual melting, an even larger area occupied by the fillet (joint), and a small circular cross section of the refrigerant flow path 60. Figure 9 (d) shows a state in which the refrigerant flow path 60 between the brazed brazing sheets 50 is blocked, resulting in a blocked flow path.

The inventors conducted various brazing experiments under different conditions in the manufacture of the plate fin stack 2 of the heat exchanger 1, and obtained the following experimental results.

<Relationship between the cross-sectional shape and cross-sectional area of the refrigerant flow path>
In various brazing experiments, the flow channel cross-sectional area S was measured as a specific experimental result of the formed coolant flow channel 60. As shown in Fig. 4 above, the designed unjoined cross-sectional area Sa when the brazing sheets 50 arranged opposite each other were in an unjoined state was ^203,000 µm2.

In the case of the approximately mountain-shaped design shown in FIG. 9A, the flow path cross-sectional area S was in the range of 92,000 μm ² ≦S≦166,000 μm ² .

In the case of the substantially elliptical shape shown in FIG. 9B, the flow path cross-sectional area S was in the range of 63,000 μm ² ≦S<92,000 μm ² .

In the case of the small circular shape shown in FIG. 9(c), the flow channel cross-sectional area S was S<63,000 μm ² .

From the above experimental results, in order to ensure a predetermined refrigerant flow rate and refrigerant flow speed in the refrigerant flow channel 60 formed by brazing, the desirable flow channel cross-sectional shape is the shape shown in Fig. 9(a). Furthermore, the allowable range of the flow channel cross-sectional area S for the flow channel cross-sectional shape is 63,000 ^µm2 ≦ S < 166,000 ^µm2 .

In this disclosure, in order to standardize the formation of the refrigerant flow path, a flow path cross-sectional ratio R is used, which is the ratio of the flow path cross-sectional area S to the unjoined cross-sectional area Sa (see FIG. 4) formed by the flow path formation region (13, 21, 22) in the unjoined state before brazing. That is, the refrigerant flow path 60 is brazed so that the flow path cross-sectional ratio (R), which indicates the ratio of the flow path cross-sectional area (S) in the joined state after brazing to the unjoined flow path cross-sectional area (Sa), is within a predetermined range. The flow path cross-sectional ratio R in a desirable flow path cross-sectional shape can be expressed in the range of 45.3%≦R≦81.8%. Also, the flow path cross-sectional ratio R in an acceptable flow path cross-sectional shape can be expressed in the range of 31.0%≦R≦81.8%.

10 and 11 are graphs showing the results of calculations for the refrigerant flow channel 60 formed in the experiment of the above-mentioned "corrected flow index F ₂ ". In FIG. 10, the horizontal axis shows the "corrected flow index F ₂ ", and the vertical axis shows the "flow channel cross-sectional area S [μm ² ]". In FIG. 11, the horizontal axis shows the "corrected flow index F ₂ ", and the vertical axis shows the "joining cross-sectional area J [μm ² ]". FIG. 12 is an enlarged cross-sectional view showing a state after the first fin member 10 and the second fin member 20 are joined (brazed). In the cross-sectional view shown in FIG. 12, the flow channel cross-sectional area, which is the cross-sectional area of the refrigerant flow channel 60, is indicated by "S". In addition, the joining cross-sectional area J is defined as 1/2 of the value obtained by subtracting the flow channel cross-sectional area S shown in FIG. 12 from the unjoined cross-sectional area Sa of the refrigerant flow channel in the cross-sectional view shown in FIG. 4 that shows the state before joining (brazing). That is, it can be expressed as [joint cross-sectional area J = (unjoined cross-sectional area Sa - flow path cross-sectional area S) / 2]. This is because after brazing (joining), a joint area (fillet) having a substantially triangular cross section is formed on both sides of the refrigerant flow path 60. In the cross-sectional view of Figure 12, the joint cross-sectional area J is indicated by cross-hatching.

In the graph of FIG. 10, when the flow path cross-sectional area S is within the allowable range and the formed refrigerant flow path 60 exhibits desirable bonding strength (pressure resistance), it is indicated by an "O". Also, in FIG. 10, when the flow path cross-sectional area S of the formed refrigerant flow path 60 exceeds the allowable range, it is indicated by a thin "X", and when the bond strength (pressure resistance) of the formed refrigerant flow path 60 is below a predetermined value, it is indicated by a thick "X". The dashed curve in FIG. 10 is an approximation curve.

In order to ensure the necessary heat exchange capacity in the refrigerant flow passage 60 of the heat exchanger, as described above, the flow passage cross-sectional ratio R in the allowable flow passage cross-sectional shape must be in the range of 31.0%≦R≦81.8%. Therefore, based on the inventor's experimental results, the preferable corrected flow index _F2 is calculated to be in the range of 366 or less, which is the area indicated by the arrow below the dashed dotted line in the graph shown in FIG. 10 ( _F2 ≦366).

In the graph of FIG. 11, when the formed refrigerant flow path 60 exhibits desirable bonding strength (pressure resistance) and has a flow path cross-sectional area S within an acceptable range, it is indicated by a "○". In FIG. 11, when the bond strength (pressure resistance) of the formed refrigerant flow path 60 is below a predetermined value, it is indicated by a thick x, and when the flow path cross-sectional area S of the formed refrigerant flow path 60 exceeds the acceptable range, it is indicated by a thin x. The dashed curve in FIG. 11 is an approximation curve.

As shown in the graph of FIG. 11, when calculated from the experimental results of the inventors, the preferable corrected flow index _F2 is in the range of "130" or more, which is the area indicated by the arrow above the dashed dotted line in the graph shown in FIG. 11 (130≦ _F2 ).

Therefore, when the corrected flow index _F2 is used as an index for the flow passage cross-sectional area S and the joint area J of the coolant flow passage 60, the range falls within the inequality shown below.

By deriving the above inequality [6], the inventors discovered that it is possible to specify the ranges of the material factors "solder layer thickness" and "silicon concentration (Si concentration) in the solder layer" that satisfy inequality [6].

In FIG. 13, the vertical axis indicates "thickness of brazing material layer [mm]" and the horizontal axis indicates "corrected flow index F ₂ ." In FIG. 14, the vertical axis indicates "Si concentration [%]" and the horizontal axis indicates "corrected flow index F ₂ ." In the graphs of FIG. 13 and FIG. 14, as in the above-mentioned FIG. 10 and FIG. 11, when the flow passage cross-sectional area S is within the allowable range and the formed refrigerant flow passage 60 shows desirable bonding strength (pressure resistance performance), it is indicated by "○", when the flow passage cross-sectional area S exceeds the allowable range, it is indicated by a thin x mark, and when the bonding strength (pressure resistance performance) shows a predetermined value or less, it is indicated by a thick x mark. In the graphs of FIG. 13 and FIG. 14, the region between the two dashed lines is a preferable region in the corrected flow index F ₂ .

Figure 15 is a graph showing the regions of the "solder layer thickness" and "silicon concentration (Si concentration) in the solder layer" which are material factors for forming a preferred refrigerant flow path 60 in the manufacture of the heat exchanger 1. In Figure 15, the vertical axis shows the "solder layer thickness [mm]" and the horizontal axis shows the "silicon concentration (Si concentration) in the solder layer". In the graph of Figure 15, the region surrounded by an approximate parallelogram shows the selection region M of the material factors ("solder layer thickness" and "silicon concentration (Si concentration) in the solder layer") for forming a preferred refrigerant flow path 60. Within this selection region M, the refrigerant flow path 60 will have the desired flow path cross-sectional shape, as shown in the cross-sectional photograph shown in Figure 15 (a). On the other hand, if it is outside the selection region M surrounded by the approximate parallelogram shown in the graph of FIG. 15, the refrigerant flow path 60 is blocked, or the shape does not meet the specified flow path cross-sectional area, as shown in the cross-sectional photograph of FIG. 15(b), or the bonding surface is small and the bonding strength (pressure resistance performance) does not meet the specified strength, as shown in the cross-sectional photograph of FIG. 15(c).

Next, we will explain why the selected area M in the graph in Figure 15 has an approximately parallelogram shape that descends to the lower right.

First, the reason why the two lower sides (first boundary line L1 and second boundary line L2) of the approximate parallelogram representing the selected area M slope downward and to the right is as follows.

The first boundary line L1 and the second boundary line L2 in the selection region M are lower limit lines for the joint strength (pressure resistance performance). In order to ensure a certain joint strength, it is necessary to ensure a certain amount of melted brazing material. As mentioned above, if the thickness of the brazing material layer is thick and the Si concentration in the brazing material layer is high, the amount of melted brazing material increases. In other words, in order to ensure a certain amount of melted brazing material or more, if the brazing material layer is thin, the Si concentration in the brazing material layer needs to be high, and conversely, if the brazing material layer is thick, the Si concentration in the brazing material layer needs to be low. As a result, in the graph shown in FIG. 15, the first boundary line L1 and the second boundary line L2, which are the two lower sides of the selection region M, are lines that descend to the lower right.

Next, the reason why the upper two sides (third boundary line L3 and fourth boundary line L4) of the approximate parallelogram representing the selected area M descend in a downward and rightward direction is as follows.

The third boundary line L3 and the fourth boundary line L4 in the selection region M are lower limit lines for the flow cross section of the refrigerant flow path 60. In order to ensure a specified flow cross section, it is necessary to melt the brazing material to a certain amount or less. As mentioned above, if the brazing material layer is thick and the Si concentration in the brazing material layer is high, the amount of melted brazing material increases. In other words, in order to ensure a certain amount of melted brazing material or more, if the brazing material layer is thin, the Si concentration in the brazing material layer needs to be high, and conversely, if the brazing material layer is thick, the Si concentration in the brazing material layer needs to be low. As a result, in the graph shown in FIG. 15, the third boundary line L3 and the fourth boundary line L4, which are the upper two sides in the selection region M, are lines that descend to the lower right.

As described above, in the manufacture of the heat exchanger of embodiment 1, it can be understood that in order to form the desired refrigerant flow path 60 by stacking and brazing specific brazing sheets 50 together, it is possible to select the material factors "thickness of the brazing material layer" and/or "silicon concentration (Si concentration) in the brazing material layer" so that the thickness falls within the selection region M in the graph of FIG. 15.

In the configuration described in the first embodiment, the range surrounded by the first boundary line L1, the second boundary line L2, the third boundary line L3, and the fourth boundary line L4 that specify the selected region M can be expressed by the following inequalities [7], [8], [9], and [10]. Note that in inequalities [7], [8], [9], and [10], the brazing material layer thickness is "y" and the brazing material layer Si concentration is "x".

In the first embodiment, the interior of the parallelogram that specifies the selected region M is a range that satisfies all of the above inequalities [7], [8], [9], and [10]. If it is within the range of the selected region M, the refrigerant flow path 60 formed in the plate fins 2a has a desired cross-sectional shape, and it is possible to configure a highly reliable heat exchanger in which the plate fins 2a are brazed with the desired joint strength (pressure resistance).

In the first embodiment, the brazing sheet 50 is described as having a brazing layer (52, 53) on both sides of the core material 51. However, the brazing layer may function as a sacrificial corrosion protection layer, or an aluminum alloy layer containing silicon (Si) and zinc (Zn) may be formed on one side of the core material 51. The sacrificial corrosion protection layer may contain elements other than Zn as long as they do not affect the sacrificial corrosion protection function. Various elements may also be contained as unavoidable impurities.

As described above and in detail in the first embodiment, the heat exchanger of the present disclosure uses a plate fin laminate formed by laminating brazing sheets. In a heat exchanger configured in this manner, a heat exchanger can be provided in which the refrigerant flow paths formed in the plate fin laminate have a desired cross-sectional shape, and each plate fin is brazed with a desired joint strength (pressure resistance), preventing refrigerant leakage at the joints. As a result, the heat exchanger and its manufacturing method of the present disclosure achieves weight reduction, size reduction, and efficiency, and can provide a highly reliable heat exchanger in which the refrigerant flow paths in the heat exchanger reliably have the desired cross-sectional shape and the desired pressure resistance.

Although the present disclosure has been described in the embodiments with a certain degree of detail, these configurations are exemplary and the disclosed contents of the embodiments may vary in the details of the configuration. In the present disclosure, substitutions, combinations, and changes in the order of elements in the embodiments may be realized without departing from the scope and spirit of the claimed invention.

The heat exchanger disclosed herein is small and lightweight, and has a configuration that reliably provides the desired cross-sectional shape and pressure resistance, making it possible to use it in a variety of products and providing products with high market value.

REFERENCE SIGNS LIST 1 Heat exchanger 2 Plate fin laminate 2a Plate fin 3 End plate 4 Supply pipe 5 Discharge pipe 6 Heat transfer blocking slit 12 Header communication flow passage 13 Flow passage forming region 21, 22 Flow passage forming region 50 Brazing sheet 51 Core material 52 First solder layer 53 Second solder layer 54 Sacrificial material layer 60 Coolant flow passage 61 Fillet (joint)
61a: Joint region 61b: Flow passage forming region

Claims (1)

A method for manufacturing a heat exchanger including a plate fin stack in which plate fins having refrigerant flow paths are stacked with gaps therebetween, comprising the steps of:
A plurality of brazing sheets each including a brazing material layer on a surface thereof and each having a flow passage forming region are selected;
The plate fin is formed by stacking and brazing the selected brazing sheets, and a refrigerant flow path is formed by opposing flow path forming regions.
In the brazing sheets that are stacked, a flow path cross-sectional ratio, which indicates a ratio of a flow path cross-sectional area in a joined state after brazing to an unjoined flow path cross-sectional area formed by a flow path forming region in an unjoined state before brazing , is manufactured so as to be within a range of 45.3%≦R≦81.8%,
The brazing sheet is selected by selecting the brazing sheet that satisfies a relationship between the thickness of the brazing layer and the silicon concentration of the brazing layer within a selected region shown by a substantially parallelogram in a material scatter diagram showing a correlation between the thickness of the brazing layer in the brazing sheet and the silicon concentration of the brazing layer,
A method for manufacturing a heat exchanger, wherein the selected region is a region surrounded by the inequalities of equations 1, 2, 3, and 4, where x is the silicon concentration (wt %) of the brazing material layer and y is the thickness (mm) of the brazing material layer .

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