JP7550573B2 - Air conditioners - Google Patents

Description

The present invention relates to a parallel flow type heat exchanger and an air conditioner.

Air conditioners are equipped with a condenser to condense the refrigerant. The condenser is often a so-called parallel flow type heat exchanger that has a core in which flat multi-hole tubes and corrugated fins are alternately stacked, and headers are placed at both longitudinal ends of the flat multi-hole tubes in the core.

As an example of this type of heat exchanger, Patent Document 1 describes a refrigerant condenser that includes multiple tubes, corrugated fins arranged between adjacent tubes, and a tank connected to the ends of the tubes, in which the multiple tubes are divided into multiple tube groups by a separator provided in the tank, and a refrigerant flows through the multiple tube groups.

Conventionally, this type of heat exchanger is configured so that the tube group located at the most upstream of the refrigerant flow has the greatest number of tubes, and the number of tubes in each tube group decreases toward the downstream. The reason for this is as follows. It is known that the heat transfer coefficient and pressure loss in general in-tube condensation heat transfer are greatly affected by the mass velocity of the refrigerant and the quality of the refrigerant (i.e., the degree of condensation). Specifically, the heat transfer coefficient and pressure loss in in-tube condensation heat transfer tend to be lower as the mass velocity of the refrigerant is lower. In addition, the heat transfer coefficient and pressure loss in in-tube condensation heat transfer tend to be lower as the condensation of the refrigerant progresses and the quality decreases.

Refrigerant in a gaseous state flows into the tube group located at the most upstream of the refrigerant condenser, condenses inside the tubes, and flows out to the tube group downstream. Therefore, in the tube group located at the most upstream of the refrigerant condenser, the heat transfer coefficient is high, but the pressure loss also tends to be high. Therefore, in conventional refrigerant condensers, the tube group located at the most upstream is made the largest in number, thereby achieving a high heat transfer coefficient while suppressing the increase in pressure loss caused by high quality refrigerant.

On the other hand, in the tube groups downstream of the most upstream tube group, condensation of the refrigerant is progressing, so the heat transfer coefficient and pressure loss are lower than in the most upstream tube group. Therefore, in conventional refrigerant condensers, the number of tubes in each tube group is reduced as the quality of the refrigerant decreases, optimizing the heat transfer coefficient and pressure loss.

Japanese Patent Application Publication No. 3-59364

However, there is a strong demand for a heat exchanger that has an even greater heat exchange capacity than the refrigerant condenser in Patent Document 1.

The present invention was made in consideration of this background, and aims to provide a parallel-flow heat exchanger that can increase the amount of heat exchanged while suppressing an increase in pressure loss, and an air conditioner equipped with this heat exchanger.

One embodiment of the present invention is a refrigerant-transmitting ...
a first header disposed at one end of the core in a longitudinal direction of the flat multi-hole pipe and connected to the flat multi-hole pipe;
a second header disposed at the other end of the core in the longitudinal direction and connected to the flat multi-hole tube;
The flat multi-hole tubes are divided into a plurality of flat multi-hole tube groups including a first flat multi-hole tube group located at the top of the core and a second flat multi-hole tube group adjacent to and below the first flat multi-hole tube group,
the first header and the second header are configured to allow the refrigerant to pass through the plurality of flat multi-hole tube bundles sequentially from above to below,
The number of the flat multi-hole tubes belonging to the second flat multi-hole tube group is 14 or more,
In the parallel-flow heat exchanger, the number of the flat multi-hole tubes belonging to the first flat multi-hole tube group is equal to or less than the number of the flat multi-hole tubes belonging to the second flat multi-hole tube group.

Another aspect of the present invention is a parallel flow type heat exchanger having the above-mentioned aspect and a refrigerant present inside the parallel flow type heat exchanger,
The air conditioner has a total number N of the flat multi-hole tubes in the parallel-flow type heat exchanger and a number N 1 of the flat multi-hole tubes belonging to the first flat multi-hole tube group, the total number N _satisfying the relationship of the following formula (1) .
N ₁ > N x 0.0014 x ΔP _TP ^0.48737 -2 ... (1)
( The value of ΔP _TP in the above formula (1) is a value calculated by the following formulas (2) to (4) when the mass flow rate of the refrigerant flowing inside the parallel-flow type heat exchanger is expressed as m ref [kg/s], the flow path cross-sectional area of the flat multi-hole tube is expressed as A ^{tube [m 2} _{] ,} the hydraulic diameter of the flat multi-hole tube is expressed as D _h [m], the length of the flat multi-hole tube is expressed as L _tube [m], the viscosity of the refrigerant in the liquid phase is expressed as μ _L [Pa·s], the viscosity of the refrigerant in the gas phase is expressed as μ _V [Pa·s], the density of the refrigerant in the liquid phase is expressed as ρ _L [kg/m ³ ], and the density of the refrigerant in the gas phase is expressed as ρ _V [kg/m ³ ].
ΔP _TP =0.0661×C ₁ ×Γ ^-1.841 ...(2)
C ₁ = m _ref ^1.75 ×A _tube ^-1.75 ×D _h ^-0.75 ×μ _L ^0.25 ×ρ _L ^-1 ×4 × L _tube ... (3)
Γ=(ρV _/ ρL ₎ 0.5 ^× (μL _/ μV ₎ 0.125 ^... (4))

The core of the parallel flow type heat exchanger (hereinafter referred to as "heat exchanger") has a plurality of flat multi-hole tubes, which are divided into a plurality of flat multi-hole tube groups including a first flat multi-hole tube group arranged at the top and a second flat multi-hole tube group arranged adjacent to and below the first flat multi-hole tube group. The number of flat multi-hole tubes belonging to the second flat multi-hole tube group is 14 or more, and the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is equal to or less than the number of flat multi-hole tubes belonging to the second flat multi-hole tube group.

As described above, conventional heat exchangers are configured so that the number of tubes in the upstream tube group, where a high-quality refrigerant flows, is greater than the downstream tube group, where the quality of the refrigerant has decreased to a certain extent. However, as a result of intensive research by the inventors, it was found that flat multi-hole tubes have a unique heat transfer characteristic in which the heat transfer coefficient is less affected by the mass velocity and quality of the refrigerant once the refrigerant has condensed to a certain extent. By utilizing such heat transfer characteristics, the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is set to be equal to or less than the number of flat multi-hole tubes belonging to the second flat multi-hole tube group, making it possible to increase the effect of increasing the heat exchange area in the second flat multi-hole tube group, rather than the effect of decreasing the heat transfer coefficient, and to increase the amount of heat exchange in the second flat multi-hole tube group.

The heat exchanger is configured so that the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is equal to or less than the number of flat multi-hole tubes belonging to the second flat multi-hole tube group. Therefore, the heat exchanger can increase the heat exchange amount in the second flat multi-hole tube group while suppressing an increase in pressure loss. As a result, the heat exchange amount of the heat exchanger as a whole can be increased.

As described above, the heat exchanger of the above embodiment can increase the amount of heat exchanged while suppressing an increase in pressure loss.

In addition, because the air conditioner has a heat exchanger of the above-mentioned type, it is possible to increase the amount of heat exchange while suppressing an increase in pressure loss in the heat exchanger.

FIG. 1 is a cross-sectional view showing a main part of a parallel-flow type heat exchanger according to a first embodiment. FIG. 2 is a cross-sectional view of the flat multi-hole pipe in the first embodiment. FIG. 3 is an explanatory diagram that illustrates the relationship between the position in the refrigerant flow direction and the amount of heat exchange in each test piece of Example 2. FIG. 4 is an explanatory diagram of an analytical model used in the numerical analysis in the second embodiment. FIG. 5 is an explanatory diagram illustrating a schematic diagram of the calculation performed in each cell in the second embodiment. FIG. 6 is a graph showing the optimum value for the number of flat multi-hole tubes belonging to the first flat multi-hole tube group in Example 3.

The core of the heat exchanger has a plurality of flat multi-hole tubes. The total number of flat multi-hole tubes in the heat exchanger can be set appropriately depending on the dimensions of the heat exchanger, the required rated capacity, pressure loss, etc. The total number of flat multi-hole tubes may be, for example, 28 or more and 168 or less.

The flat multi-hole tubes are divided into a plurality of flat multi-hole tube groups, including a first flat multi-hole tube group and a second flat multi-hole tube group. For example, the flat multi-hole tubes in the heat exchanger may be divided into four flat multi-hole tube groups: a first flat multi-hole tube group located at the top, a second flat multi-hole tube group arranged adjacent to and below the first flat multi-hole tube group, a third flat multi-hole tube group arranged adjacent to and below the second flat multi-hole tube group, and a fourth flat multi-hole tube group arranged adjacent to and below the third flat multi-hole tube group.

The first header and the second header are configured to allow the refrigerant to pass through the multiple flat multi-hole tube groups in a sequential order from top to bottom. For example, if the heat exchanger has four flat multi-hole tube groups, the first header and the second header may be configured to allow the refrigerant to pass through the first flat multi-hole tube group, the second flat multi-hole tube group, the third flat multi-hole tube group, and the fourth flat multi-hole tube group in a sequential order.

To realize such an embodiment, for example, the internal space of the first header is divided into three spaces: an inlet portion connected to the end of the first flat multi-hole tube group, a second turn portion connected to the ends of both the second flat multi-hole tube group and the third flat multi-hole tube group, and an outlet portion connected to the end of the fourth flat multi-hole tube group, and the internal space of the second header is divided into two spaces: a first turn portion connected to the ends of both the first flat multi-hole tube group and the second flat multi-hole tube group, and a third turn portion connected to the ends of both the third flat multi-hole tube group and the fourth flat multi-hole tube group. In this case, by supplying refrigerant to the inlet portion of the first header, the refrigerant passes through the first flat multi-hole tube group, the first turn portion, the second flat multi-hole tube group, the second turn portion, the third flat multi-hole tube group, the third turn portion, and the fourth flat multi-hole tube group in sequence. Then, the refrigerant can be circulated within the heat exchanger by discharging the refrigerant from the outlet portion of the first header to the outside of the heat exchanger.

The number of flat multi-hole tubes belonging to the second flat multi-hole tube group is 14 or more and is equal to or less than the number of flat multi-hole tubes belonging to the first flat multi-hole tube group. This increases the amount of heat exchange when the refrigerant passes through the second flat multi-hole tube group, and thus increases the amount of heat exchange in the entire heat exchanger. From the viewpoint of the balance between the pressure loss and the amount of heat exchange in the heat exchanger, it is preferable that the number of flat multi-hole tubes belonging to the second flat multi-hole tube group is equal to or more than the number of flat multi-hole tubes belonging to each flat multi-hole tube group other than the second flat multi-hole tube group.

Specifically, for example, if a heat exchanger has four flat multi-hole tube groups, the number of flat multi-hole tubes belonging to the second flat multi-hole tube group can be 35% or more and 79% or less, preferably 35% or more and 75% or less, and more preferably 35% or more and 60% or less of the total number of flat multi-hole tubes in the heat exchanger.

The number of flat multi-hole tubes belonging to the first flat multi-hole tube group is equal to or less than the number of flat multi-hole tubes belonging to the second flat multi-hole tube group. The refrigerant flowing into the first flat multi-hole tube group is in a gas phase, i.e., a refrigerant having high quality, so the heat transfer coefficient when the refrigerant passes through the first flat multi-hole tube group tends to be relatively high. In addition, when the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is reduced, the heat exchange area decreases while the mass velocity of the refrigerant increases. Therefore, even if the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is set to be equal to or less than the number of flat multi-hole tubes belonging to the second flat multi-hole tube group, the decrease in the heat exchange amount in the first flat multi-hole tube group can be suppressed. As a result, the heat exchange amount in the entire heat exchanger can be increased.

When the heat exchanger has three or more flat multi-hole tube groups, it is preferable that the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is greater than the number of flat multi-hole tubes belonging to the third flat multi-hole tube group and the flat multi-hole tube group located below the third flat multi-hole tube group. In this case, the pressure loss when the refrigerant passes through the first flat multi-hole tube group can be further reduced and the heat exchange amount can be increased. As a result, the pressure loss in the entire heat exchanger can be further reduced and the heat exchange amount can be increased.

In addition, the heat exchanger may be designed to exhibit excellent heat exchange performance when a specific refrigerant is used. In such a case, it is more preferable that the number N ₁ of the flat multi-hole tubes belonging to the first flat multi-hole tube group satisfies the relationship of the following formula (1).
N ₁ > N x 0.0014 x ΔP _TP ^0.48737 -2 ... (1)

However, N [pieces] in the formula (1) is the total number of flat multi-hole tubes that the heat exchanger has. The value of ΔP _TP is the pressure loss of the heat exchanger. The value of ΔP _TP is calculated by the following formulas ( ² ) to (4) when the mass flow rate of the refrigerant flowing inside the parallel flow type heat exchanger is m _ref [kg/s], the flow path cross-sectional area of the flat multi-hole tube is A _tube [m 2 ], the hydraulic diameter of the flat multi-hole tube is D _h [m], the length of the flat multi-hole tube is L _tube [m], the viscosity of the refrigerant in the liquid phase is μ _L [Pa·s], the viscosity of the refrigerant in the gas phase is μ _V [Pa·s], the density of the refrigerant in the liquid phase is ρ _L [kg/m ³ ], and the density of the refrigerant in the gas phase is ρ _V [kg/m ³ ].
ΔP _TP =0.0661×C ₁ ×Γ ^-1.841 ...(2)
C ₁ = m _ref ^1.75 ×A _tube ^-1.75 ×D _h ^-0.75 ×μ _L ^0.25 ×ρ _L ^-1 ×4 × L _tube ... (3)
Γ=( _ρV / _ρL ) ^0.5 ×( _μL / _μV ) ^0.125 ...(4)

In this way, by setting the number of flat multi-hole tubes belonging to the first flat multi-hole tube group within a range that takes into account the physical properties of the refrigerant, it is possible to optimize the balance between the heat exchange amount and pressure loss in the first flat multi-hole tube group. As a result, it is possible to further reduce pressure loss in the entire heat exchanger and increase the heat exchange amount.

The above formulas (1) to (4) are determined based on the following concept. That is, the inventors conducted a trial-and-error study using numerical analysis and found that the optimal number _N1 of the flat multi-hole tubes belonging to the first flat multi-hole tube group varies greatly depending on the magnitude of the pressure loss ΔP _TP of the heat exchanger. It is considered that the pressure loss ΔP _TP of the heat exchanger occurs mainly when the refrigerant passes through the flat multi-hole tubes.

Assuming that the flow of the refrigerant inside the flat multi-hole tube is turbulent, the pressure loss ΔP _SP when the refrigerant passes through the flat multi-hole tube is expressed by the Darcy-Weisbach equation (see equation (5) below).

In the above formula (5), by using the Blasius pipe friction coefficient for the pipe friction coefficient f, the following formula (6) can be derived.

Since G in the above formula (6) can be expressed as m _ref /A _tube , the relationship of the following formula (3') can be derived by rearranging the above formula (6).
ΔP _SP ∝m _ref ^1.75 ×A _tube ^-1.75 ×D _h ^-0.75 ×μ _L ^0.25 ×ρ _L ^-1 ×4×L _tube ... (3')

From the above, it can be seen that the pressure loss ΔP _TP of the heat exchanger can be expressed by using the parameter C ₁ (the above formula (3)) related to the pressure loss ΔP _SP when the refrigerant passes through the flat multi-hole tube.

In addition, the refrigerant flowing through the heat exchanger is a gas-liquid two-phase flow, so that when calculating the magnitude of the pressure loss ΔP _TP of the heat exchanger, it is necessary to use not only the parameter _C1 described above, but also the parameter Γ (the above formula (4)) for taking into account the influence of the gas-liquid two-phase flow.

Based on the above, the inventors have summarized the results of their numerical analysis, and have found that the optimal number N ₁ ′ of flat multi-hole tubes belonging to the first flat multi-hole tube group can be approximated by the following formula (1 ′), and that the pressure loss ΔP _TP of the heat exchanger can be approximated by the above formula (2).
_N1 '=N×0.0014×ΔP _TP ^0.48737 ...(1')

As will be described in the examples below, the optimum number _N1 ' of the flat multi-hole tubes predicted by the formula (1') is up to 2 more than the optimum number _N1 of the flat multi-hole tubes derived by the numerical analysis. Therefore, the formula (1) can be derived by subtracting 2 from both sides of the formula (1') and setting the left side to _N1 .

When the heat exchanger has three or more flat multi-hole tube groups, the number of flat multi-hole tubes belonging to the third flat multi-hole tube group and the flat multi-hole tube group located below the third flat multi-hole tube group is not particularly limited. However, the quality of the refrigerant flowing through the flat multi-hole tube group located below is usually equal to or lower than the quality of the refrigerant flowing through the flat multi-hole tube group located above. Therefore, by making the number of flat multi-hole tubes belonging to the flat multi-hole tube group located below equal to or lower than the number of flat multi-hole tubes belonging to the flat multi-hole tube group located above, the pressure loss in the entire heat exchanger can be further reduced and the heat exchange amount can be further increased.

For example, if a heat exchanger has four flat multi-hole tube groups, the number of flat multi-hole tubes belonging to the third flat multi-hole tube group can be 5% or more and 21% or less of the total number of flat multi-hole tubes in the heat exchanger. From the viewpoint of the balance between pressure loss and heat exchange capacity, the number of flat multi-hole tubes belonging to the third flat multi-hole tube group is preferably 7% or more and 17% or less, and more preferably 9% or more and 14% or less.

Similarly, the number of flat multi-hole tubes belonging to the fourth flat multi-hole tube group can be, for example, 4% to 14% of the total number of flat multi-hole tubes in the heat exchanger. From the viewpoint of the balance between pressure loss and heat exchange capacity, it is preferable that the number of flat multi-hole tubes belonging to the fourth flat multi-hole tube group be 6% to 12%, and more preferably 6% to 10%.

The flat multi-hole tube in the heat exchanger has a pair of flat wall sections arranged opposite each other with a gap between them, a connecting wall section connecting both ends of the flat wall sections in the width direction, and a partition section dividing the internal space surrounded by the flat wall sections and the connecting wall sections into a plurality of refrigerant flow paths. The shape of each refrigerant flow path in a cross section perpendicular to the longitudinal direction of the flat multi-hole tube can take various forms, such as a circle, an ellipse, an oval, a semicircle, a triangle, or a rectangle, in a cross section perpendicular to the longitudinal direction of the flat multi-hole tube. The number of refrigerant flow paths in the flat multi-hole tube can be set appropriately, for example, within the range of 4 to 20.

It is preferable that the refrigerant flow path of the flat multi-hole tube is non-circular, i.e., has one or more corners, in a cross section perpendicular to the longitudinal direction. By incorporating a flat multi-hole tube having such a refrigerant flow path into the second flat multi-hole tube group, the decrease in the heat transfer coefficient in the second flat multi-hole tube group can be further suppressed. As a result, the effect of increasing the heat exchange amount in the second flat multi-hole tube group can be further improved, and the heat exchange amount of the entire heat exchanger can be further increased. The non-circular cross-sectional shape mentioned above includes, for example, semicircular, triangular, and rectangular shapes. From the viewpoint of further enhancing the above-mentioned effect, it is more preferable that the refrigerant flow path of the flat multi-hole tube has a shape in which the outline in the cross section perpendicular to the longitudinal direction is composed only of straight lines. Such cross-sectional shapes include, for example, triangular and rectangular shapes.

The hydraulic diameter _Dh of the flat multi-hole tube can be set appropriately, for example, within a range of 0.00032 m or more and 0.001 m or less. In this case, the heat transfer efficiency of each flat multi-hole tube can be further improved. The hydraulic diameter _Dh of the flat multi-hole tube described above is expressed by the following formula (7) using the flow passage cross-sectional area A _tube [m ² ] of the flat multi-hole tube and the flow passage wetted perimeter length S _tube [m] of the flat multi-hole tube.
_Dh =4×A _tube /S _tube ...(7)

The length L _tube of the flat multi-hole tube can be appropriately set within the range of 0.4 m to 0.9 m, in which case the heat transfer efficiency in each flat multi-hole tube can be further improved.

When the heat exchanger is configured to use R32 (i.e., difluoromethane) as a refrigerant, it is preferable that the hydraulic diameter _Dh of the flat multi-hole tube is 0.00032 m or more and 0.001 m or less, and the length _Ltube is 0.4 m or more and 0.9 m or less. A flat multi-hole tube having a hydraulic diameter _Dh and a length _Ltube in the specific range can achieve particularly excellent heat exchange efficiency when R32 is used as a refrigerant. Therefore, a flat multi-hole tube having a hydraulic diameter _Dh and a length _Ltube in the specific range is suitable for a heat exchanger configured to use R32 as a refrigerant.

The heat exchanger may have a rated capacity of, for example, 2 kW or more and 12 kW or less. The rated capacity of the heat exchanger described above is the rated cooling capacity value obtained by the cooling capacity test specified in JIS B8615-1:2013.

The use of the heat exchanger is not particularly limited, and it may be configured to be used, for example, in an outdoor unit of a stationary air conditioner for home or commercial use. The heat exchanger may also be configured to be used, for example, in a condenser of a vehicle air conditioner.

The heat exchanger can be connected to components of an air conditioner, such as a compressor, an expansion valve, a pump, or another heat exchanger, via refrigerant piping, and filled with refrigerant to form an air conditioner.

The refrigerant used in the air conditioner is not particularly limited, and may be, for example, hydrofluorocarbon refrigerants such as R410A and R32, or hydrofluoroolefin refrigerants such as R1234yf and R1123. The refrigerant used in the air conditioner is preferably R32. R32 has a relatively large latent heat of condensation and a high thermal conductivity, making it easier to reduce the size and increase the efficiency of the air conditioner.

The air conditioner has a parallel-flow type heat exchanger in which the total number N of flat multi-hole tubes and the number N ₁ of flat multi-hole tubes belonging to the first flat multi-hole tube group satisfy the relationship of formula (1) .
N ₁ > N x 0.0014 x ΔP _TP ^0.48737 -2 ... (1)

As mentioned above, by setting the number of flat multi-hole tubes in the first flat multi-hole tube group within a range that takes into account the physical properties of the refrigerant, it is possible to more effectively suppress the increase in pressure loss throughout the heat exchanger and increase the amount of heat exchange. As a result, the energy consumption of the air conditioner can be further reduced.

The air conditioner may be configured such that the mass flow rate m _ref of the refrigerant inside the heat exchanger can be set, for example, within a range of 0.01 kg/s to 0.03333 kg/s. In this case, the increase in pressure loss in the heat exchanger can be more effectively suppressed and the heat exchange amount can be further increased. As a result, the energy consumption of the air conditioner can be further reduced.

In particular, when the refrigerant of the air conditioner is R32, by setting the mass flow rate m _ref of the refrigerant inside the heat exchanger within the range of 0.01 kg/s or more and 0.03333 kg/s or less, the above-mentioned advantageous effects can be more reliably achieved.

From a similar viewpoint, when the refrigerant of the air conditioner is R32, it is particularly preferable that the hydraulic diameter _Dh of the flat multi-hole tube in the heat exchanger is 0.00032 m or more and 0.001 m or less, the length L _tube is 0.4 m or more and 0.9 m or less, and the mass flow rate m _ref of the refrigerant is in the range of 0.01 kg/s or more and 0.03333 kg/s or less.

An example of the parallel flow type heat exchanger is described below.

Example 1
1, the parallel flow type heat exchanger 1 of this embodiment has a core 11 in which a plurality of flat multi-hole tubes 2 through which a refrigerant flows are arranged in parallel via fins 3, the flat multi-hole tubes 2 and the fins 3 are stacked alternately in the vertical direction, a first header 4 arranged at one end of the core 11 in the longitudinal direction of the flat multi-hole tubes 2, and a second header 5 arranged at the other end of the core 11 in the longitudinal direction. The flat multi-hole tubes 2 are divided into a plurality of flat multi-hole tube groups 21 to 24 including a first flat multi-hole tube group 21 located at the top of the core 11 and a second flat multi-hole tube group 22 adjacent to the lower side of the first flat multi-hole tube group 21.

The number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is 14 or more. The number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 is equal to or less than the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22. The configuration of the heat exchanger 1 of this example will be described in more detail below.

Each component of the heat exchanger 1 may be made of an aluminum material (including aluminum and aluminum alloys). For example, the flat multi-hole tube 2 may be made of 1000 series aluminum or 3000 series alloy. By using a 3000 series alloy as the material for the flat multi-hole tube 2, a refrigerant with a higher pressure can be used. The fins 3 may be made of, for example, 1000 series aluminum or 3000 series alloy. The fins 3 may also be made of a brazing sheet in which a brazing material made of a 4000 series alloy is laminated on both sides of a core material made of 1000 series aluminum or 3000 series alloy.

The first header 4 and the second header 5 may be made of 1000 series aluminum or 3000 series alloy. The first header 4 and the second header 5 may also be made of a brazing sheet in which a brazing material made of a 4000 series alloy is laminated on both sides of a core material made of 1000 series aluminum or 3000 series alloy.

As shown in FIG. 1, the core 11 of the heat exchanger 1 has a plurality of flat multi-hole tubes 2 arranged at intervals in the vertical direction, and fins 3 interposed between the flat multi-hole tubes 2. The flat multi-hole tubes 2 and the fins 3 are joined by brazing. The core 11 in this example further has a side sheet 111 made of aluminum material. The side sheet 111 is joined via the fins 3 to the flat multi-hole tube 2a arranged at the upper end and the flat multi-hole tube 2b arranged at the lower end of the plurality of flat multi-hole tubes 2.

The dimensions of the core 11 can be set appropriately depending on the desired amount of heat exchange and the allowable placement space in the air conditioner. Specifically, the outer dimensions of the core 11 in the vertical direction, i.e., the stacking direction of the core 11, can be set appropriately within the range of 250 mm to 1500 mm. In addition, the outer dimensions of the core 11 in the depth direction, i.e., the width direction of the flat multi-hole tube 2, can be set appropriately within the range of 6 mm to 20 mm.

The outer width dimension of the core may be set according to the desired effective length of the flat multi-hole pipe 2, i.e., the distance from the first header 4 to the second header 5 in the longitudinal direction of the flat multi-hole pipe 2. The effective length of the flat multi-hole pipe 2 may be set appropriately within the range of, for example, 400 mm or more and 1000 mm or less.

The total number of flat multi-hole tubes 2 in the core 11 can be set appropriately within the range of 28 to 168. For example, in this example, the total number of flat multi-hole tubes 2 in the core 11 can be set to 52.

The flat multi-hole tubes 2 in the heat exchanger 1 of this example are divided into four flat multi-hole tube groups, the first flat multi-hole tube group 21 to the fourth flat multi-hole tube group 24. The first flat multi-hole tube group 21 is located at the top of the core 11. The second flat multi-hole tube group 22 is located adjacent to and below the first flat multi-hole tube group 21. The third flat multi-hole tube group 23 is located adjacent to and below the second flat multi-hole tube group 22. The fourth flat multi-hole tube group 24 is located adjacent to and below the third flat multi-hole tube group 23, and is located at the bottom of the core 11.

The internal space of the first header 4 is divided into three spaces: an inlet section 41 connected to the end of the first flat multi-hole tube group 21, a second turn section 42 connected to the ends of both the second flat multi-hole tube group 22 and the third flat multi-hole tube group 23, and an outlet section 43 connected to the end of the fourth flat multi-hole tube group 24. Between the inlet section 41 and the second turn section 42, and between the second turn section 42 and the outlet section 43, first partition plates 44, 45 are provided to divide these spaces.

The internal space of the second header 5 is divided into two spaces: a first turn section 51 connected to both ends of the first flat multi-hole tube group 21 and the second flat multi-hole tube group 22, and a third turn section 52 connected to both ends of the third flat multi-hole tube group 23 and the fourth flat multi-hole tube group 24. A second partition plate 53 is provided between the first turn section 51 and the third turn section 52 to separate them.

The inlet section 41 of the first header 4 is connected to a refrigerant supply pipe 6 configured to supply refrigerant into the heat exchanger 1, and the outlet section 43 is connected to a refrigerant discharge pipe 7 configured to discharge the refrigerant in the heat exchanger 1 to the outside.

Therefore, the flow of the refrigerant in the heat exchanger 1 of this example is as follows. That is, the refrigerant flowing into the inlet portion 41 from the refrigerant supply pipe 6 is distributed to each flat multi-hole tube 2 belonging to the first flat multi-hole tube group 21 at the inlet portion 41. The refrigerant that has passed through the first flat multi-hole tube group 21 flows into the first turn portion 51 in the second header 5. The refrigerant that has joined at the first turn portion 51 is distributed to each flat multi-hole tube 2 belonging to the second flat multi-hole tube group 22. The refrigerant that has passed through the second flat multi-hole tube group 22 then passes through the second turn portion 42 in the first header 4, the third flat multi-hole tube group 23, the third turn portion 52 in the second header 5, and the fourth flat multi-hole tube group 24 in sequence, and flows into the outlet portion 43 of the first header 4. Then, the refrigerant that has joined at the outlet portion 43 is discharged to the outside of the heat exchanger 1 from the refrigerant discharge pipe 7.

In the heat exchanger 1 of this example, the number of flat multi-hole tubes 2 belonging to each of the flat multi-hole tube groups 21 to 24 may be set so that the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is 14 or more, and the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 is equal to or less than the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22.

For example, in this example, as shown in FIG. 1, the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 can be 19, the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 can be 25, the number of flat multi-hole tubes 2 belonging to the third flat multi-hole tube group 23 can be 4, and the number of flat multi-hole tubes 2 belonging to the fourth flat multi-hole tube group 24 can be 4.

As shown in FIG. 2, the flat multi-hole tube 2 in this example has a rectangular shape in a cross section perpendicular to the longitudinal direction. The outer dimensions of the flat multi-hole tube 2 can be set appropriately within the range of, for example, a thickness of 1.1 mm to 3.0 mm and a width of 6 mm to 20 mm. For example, in this example, the thickness of the flat multi-hole tube 2 can be 1.15 mm and the width can be 13.85 mm.

The flat multi-hole tube 2 has a pair of flat wall portions 211 arranged opposite each other with a gap between them, a connecting wall portion 212 connecting both ends of the flat wall portions 211 in the width direction, and a partition portion 214 dividing the internal space surrounded by the flat wall portions 211 and the connecting wall portion 212 into a plurality of refrigerant flow paths 213. In a cross section perpendicular to the longitudinal direction, the flat multi-hole tube 2 may have a rectangular shape as shown in FIG. 2, or may have an elliptical shape (not shown). As shown in FIG. 1, a fin 3 is joined to the flat wall portion 211 of the flat multi-hole tube 2.

The number of refrigerant flow paths 213 in the flat multi-hole tube 2 can be set appropriately, for example, within the range of 4 to 20. For example, in this example, as shown in FIG. 2, the number of refrigerant flow paths 213 in the flat multi-hole tube 2 can be 15. In addition, the refrigerant flow paths 213 in the flat multi-hole tube 2 in this example have a rectangular shape in a cross section perpendicular to the longitudinal direction.

As shown in FIG. 1, corrugated fins can be used as the fins 3. The plate thickness of the fins 3 can be, for example, 0.06 to 0.12 mm. The height of the fins 3 in the vertical direction can be 6 to 8 mm.

The flat portions 31 (see FIG. 1) of the fins 3, i.e., the portions between the bent portions 32 joined to the flat multi-hole tubes 2, may be provided with louvers that protrude in the thickness direction of the fins 3. The number of louvers may be 6 to 16 per flat portion 31. The louvers may extend in a direction inclined 20 to 60 degrees with respect to the width direction of the fins 3. Note that the illustration of the louvers has been omitted in FIG. 1 for the sake of convenience.

The first header 4 has a cylindrical header body 46 that extends in the vertical direction, i.e., in the stacking direction of the core 11, and caps 47, 48 that close the upper and lower ends of the header body 46.

The header body 46 can be, for example, a cylindrical tube with an outer diameter of 15 to 25 mm and a wall thickness of 1.0 to 2.5 mm, but is not limited to this shape. In addition, the caps 47, 48 and the first partition plates 44, 45 are joined to the header body 46 by brazing.

The internal space of the first header 4, surrounded by the header body 46 and the caps 47, 48, is divided into three spaces by the two first partition plates 44, 45. The portion from the upper end 411 of the first header 4 to the first partition plate 44 arranged above constitutes the inlet section 41 of the first header 4. The end of the flat multi-hole tube 2 belonging to the first flat multi-hole tube group 21 is inserted into the inlet section 41.

The inlet portion 41 is connected to a refrigerant supply pipe 6 for supplying refrigerant into the heat exchanger 1. The end of the refrigerant supply pipe 6 is inserted into the inlet portion 41, and the refrigerant supply pipe 6 communicates with each of the flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 via the inlet portion 41. As a result, the inlet portion 41 is configured to distribute the refrigerant supplied from the refrigerant supply pipe 6 to each of the flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21.

The portion of the first header 4 from the first partition plate 44 arranged above to the first partition plate 45 arranged below constitutes the second turn section 42. The ends of the flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 and the third flat multi-hole tube group 23 are inserted into the second turn section 42. As a result, the second turn section 42 is configured to merge the refrigerant that has passed through each flat multi-hole tube 2 belonging to the second flat multi-hole tube group 22 and to distribute the refrigerant to each flat multi-hole tube 2 belonging to the third flat multi-hole tube group 23.

The portion from the lower end 412 of the first header 4 to the first partition plate 45 arranged below constitutes the outlet section 43. The end of the flat multi-hole tube 2 belonging to the fourth flat multi-hole tube group 24 is inserted into the outlet section 43.

The outlet section 43 is also connected to a refrigerant discharge pipe 7 for discharging the refrigerant in the heat exchanger 1 to the outside. The end of the refrigerant discharge pipe 7 is inserted into the outlet section 43, and the refrigerant discharge pipe 7 and each of the flat multi-hole tubes 2 belonging to the fourth flat multi-hole tube group 24 are connected via the outlet section 43. As a result, the outlet section 43 is configured to merge the refrigerant discharged from each of the flat multi-hole tubes 2 belonging to the fourth flat multi-hole tube group 24 and to discharge it to the outside of the heat exchanger 1 via the refrigerant discharge pipe 7.

The flat multi-hole pipe 2, the refrigerant supply pipe 6, and the refrigerant discharge pipe 7 inserted into the first header 4 are joined to the header body 46 of the first header 4 by brazing.

The second header 5 has a cylindrical header body 56 that extends vertically, i.e., in the stacking direction of the core 11, and caps 57, 58 that close the upper and lower ends of the header body 56. The internal space of the second header 5 surrounded by the header body 56 and the caps 57, 58 is divided into two spaces by a single second partition plate 53.

The header body 56 can be a cylindrical tube with an outer diameter of 15 to 25 mm and a wall thickness of 1.0 to 2.5 mm, similar to the header body 46 of the first header 4, but is not limited to this shape. In addition, the caps 57, 58 and the second partition plate 53 are joined to the header body 56 by brazing.

The portion from the upper end 511 of the second header 5 to the second partition plate 53 constitutes the first turn section 51. The ends of the flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 and the second flat multi-hole tube group 22 are inserted into the first turn section 51. As a result, the second turn section 42 is configured to merge the refrigerant that has passed through each flat multi-hole tube 2 belonging to the first flat multi-hole tube group 21 and to distribute the refrigerant to each flat multi-hole tube 2 belonging to the second flat multi-hole tube group 22.

The portion from the lower end 512 of the second header 5 to the second partition plate 53 constitutes the third turn section 52. The ends of the flat multi-hole tubes 2 belonging to the third flat multi-hole tube group 23 and the fourth flat multi-hole tube group 24 are inserted into the third turn section 52. As a result, the third turn section 52 is configured to merge the refrigerant that has passed through each flat multi-hole tube 2 belonging to the third flat multi-hole tube group 23, and to distribute the refrigerant to each flat multi-hole tube 2 belonging to the fourth flat multi-hole tube group 24.

The flat multi-hole tube 2 inserted into the second header 5 is joined to the header body 56 of the second header 5 by brazing.

The core 11 of the heat exchanger 1 of this example has multiple flat multi-hole tube groups 21 to 24, and is configured so that the refrigerant flows in the order of the first flat multi-hole tube group 21, the second flat multi-hole tube group 22, the third flat multi-hole tube group 23, and the fourth flat multi-hole tube group 24. In addition, the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is 14 or more, and the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 is equal to or less than the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22. Therefore, the heat exchanger 1 can increase the heat exchange amount in the second flat multi-hole tube group 22 while suppressing an increase in pressure loss. As a result, the heat exchange amount of the heat exchanger 1 as a whole can be increased.

As a result of the above, the heat exchanger 1 of this example can increase the amount of heat exchanged while suppressing an increase in pressure loss.

Example 2
In this example, two types of heat exchangers 1 (specimen A and specimen B) were fabricated in which the number of flat multi-hole tubes 2 belonging to each of the flat multi-hole tube groups 21 to 24 was changed, and the heat exchange capacity of these heat exchangers 1 was evaluated. The specific configuration of each specimen is described below. Note that, among the symbols used in this and subsequent examples, those that are the same as those used in the previous examples represent the same components, etc. as those in the previous examples, unless otherwise specified.

<Test specimen A>
The basic shape of the test specimen A is similar to that of the heat exchanger 1 of Example 1. Specific dimensions of each part of the test specimen A are as follows.
・Effective width: 664mm
External dimensions in the depth direction: 13.85 mm
Dimensions of flat multi-hole tube 2: width 13.85 mm, thickness 1.15 mm
Number of refrigerant flow paths in the flat multi-hole tube 2: 15 Hydraulic diameter D _h of the flat multi-hole tube 2: 0.530 mm
・ Flow path cross-sectional area of flat multi-hole tube 2 A _tube : 5.433 mm ²

Total number of flat multi-hole tubes 2: 52 Number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21: 19 Number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22: 25 Number of flat multi-hole tubes 2 belonging to the third flat multi-hole tube group 23: 4 Number of flat multi-hole tubes 2 belonging to the fourth flat multi-hole tube group 24: 4

Fin 3 height: 7.61 mm
Fin 3 pitch: 1.1 mm

The above-mentioned effective width refers to the distance from the first header 4 to the second header 5 in the longitudinal direction of the flat multi-hole pipe 2, that is, the length of the portion where heat exchange between the flat multi-hole pipe 2 and the outside air actually takes place. Also, the pitch of the fins 3 refers to the periodic length of the bends 32 in the fins 3.

<Test specimen B>
Test specimen B has the same configuration as test specimen A, except that the number of flat multi-hole tubes 2 belonging to each of the flat multi-hole tube groups 21 to 24 was changed as follows.

Number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21: 22 Number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22: 15 Number of flat multi-hole tubes 2 belonging to the third flat multi-hole tube group 23: 10 Number of flat multi-hole tubes 2 belonging to the fourth flat multi-hole tube group 24: 5

Next, the method for measuring the heat exchange rate of test specimen A and test specimen B will be explained. First, test specimen A or test specimen B is placed in a wind tunnel device installed in a constant temperature and humidity test room. Next, the air temperature in the test room is set to a dry bulb temperature of 35°C and a wet bulb temperature of 24°C, and air is blown from the wind tunnel device to the heat exchanger at one of the wind velocities shown in Table 1. After that, R32 is supplied as a refrigerant from the refrigerant supply pipe 6 of each test specimen. The condensation temperature of R32 is 45°C.

Then, the heat balance between the air and the refrigerant is measured while circulating the refrigerant so that the temperature of the refrigerant in the refrigerant supply pipe 6 is 65°C (i.e., degree of superheat: 20K) and the temperature of the refrigerant in the refrigerant discharge pipe 7 is 40°C (i.e., degree of subcooling: 5K). The "Amount of heat exchange" column in Table 1 shows the amount of heat exchange when the heat balance between the air and the refrigerant reaches a steady state. The "Ratio" column in Table 1 also shows the ratio of the amount of heat exchange of test piece A to the amount of heat exchange of test piece B at each wind speed, expressed as a percentage (%).

As shown in Table 1, test specimen A, in which the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is greater than or equal to the number of flat multi-hole tubes 2 belonging to the other flat multi-hole tube groups 21, 23, and 24, can increase the heat exchange amount at any wind speed compared to test specimen B, in which the number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is less than the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21.

Fig. 3 is a diagram showing a schematic diagram of the relationship between the position in the refrigerant flow direction and the amount of heat exchange in each test specimen. The vertical axis of Fig. 3 is the product of the heat transfer coefficient α _ref between the flat multi-hole tube 2 and the refrigerant and the heat exchange area A _i,cell between the flat multi-hole tube 2 and the refrigerant in each of the flat multi-hole tube groups 21 to 24. The horizontal axis of Fig. 3 is the position in the refrigerant flow direction when the refrigerant supply tube 6 is used as a reference. The product of α _ref and A _i,cell is a value that is an index of the amount of heat exchange, and the larger the product of α _ref and A _i,cell, the larger the amount of heat exchange can be.

As shown in Fig. 3, when the refrigerant flows into the test specimen A, first, heat is exchanged between the high-quality refrigerant and the air. Therefore, at the inlet of the first flat multi-hole tube group 21, the product of α _ref and A _i,cell rises steeply due to the high heat transfer coefficient α _ref resulting from the high-quality refrigerant. Then, the quality of the refrigerant gradually decreases as it advances through the first flat multi-hole tube group 21. Accordingly, the product of α _ref and A _i,cell gradually decreases as it advances through the first flat multi-hole tube group 21.

On the other hand, in the second flat multi-hole tube group 22, the heat exchange area A _i,cell with the refrigerant increases as the number of the flat multi-hole tubes 2 increases. This makes it possible to increase the product of α _ref and A _i,cell . In addition, the flat multi-hole tubes 2 can suppress the decrease in the heat transfer coefficient α _ref when a refrigerant that has been condensed to a certain degree passes through them due to the above-mentioned unique heat transfer characteristics. Therefore, by increasing the number of the flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22, the heat exchange amount in the second flat multi-hole tube group 22 can be increased as shown in FIG. 3, and thus the heat exchange amount in the entire heat exchanger can be increased.

Example 3
In this example, the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 is considered. In this example, in order to consider the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21, a numerical analysis is performed using the following analytical model.

An outline of the analytical model is shown in Figures 4 and 5. As shown in Figure 4, the analytical model has four refrigerant paths P1 to P4 corresponding to the first flat multi-hole tube group 21 to the fourth flat multi-hole tube group 24. These refrigerant paths P1 to P4 are divided into a plurality of calculation cells C in the longitudinal direction of the flat multi-hole tubes 2. As shown in FIG. 5, the amount of heat exchange and pressure loss of the entire heat exchanger can be calculated by sequentially calculating the amount of state of the refrigerant at the outlet (temperature T _{ref, in} [K], pressure P _ref,in [Pa], and specific enthalpy h _{ref ,in} [kJ/kg]) and the amount of state of the air (temperature T air,in [K]) based on the amount of state of the refrigerant at the inlet of the cell (temperature T _ref,in [K], pressure P _ref,out [Pa], and specific enthalpy h ref,out [kJ/kg]) and the amount of state of the air (temperature T _air,in [K]) along the flow direction of the refrigerant.

The state quantity of the refrigerant at the outlet of each cell can be calculated by repeatedly solving the energy conservation equation and momentum conservation equation in the cell. Specifically, the temperature T _ref,out and specific enthalpy h _ref,out of the refrigerant at the outlet of the cell can be calculated by using the energy conservation equation between the air and the flat multi-hole tube 2 (see the following equation (8)) and the energy conservation equation between the flat multi-hole tube 2 and the refrigerant (see the following equation (10)).

The energy conservation equation on the air side of each cell can be expressed by the following equation (8).
α _air・LMTD・A _{o, cell} = V _air・A _{front, cell}・ρ _air・C _p (T _{air, out} - T _{air, in} ) ... (8)

The symbols in the formula (8) have the following meanings:
α _air : Heat transfer coefficient between air and the flat multi-hole tube 2 and the fin 3 [W/(m ² ·K)]
A _o,cell : Heat exchange area between the flat multi-hole tube 2 and the fin 3 per cell and the air [m ² ]
V _air : wind speed of air flowing into the air inlet of each cell [m/s]
A _{front, cell} : Area of the air inlet of each cell [m ² ]
ρ _air : air density [kg/m ³ ]
C _p : specific heat of air at constant pressure [J/(kg·K)]
T _air,out : Air temperature at the air outlet of each cell [K]
T _air,in : Air temperature at the air inlet of each cell [K]

The wind speed V _air of the air flowing into the air inlet of each cell is the volumetric flow rate [m ³ /s] of the air flowing into the cell divided by the area A _front,cell [m ² ] of the air inlet of the cell.

The symbol LMTD in the formula (8) is the logarithmic mean temperature difference between the refrigerant inlet/outlet temperature and the air inlet/outlet temperature in each cell. The value of LMTD can be calculated by the following formula (9) using the wall temperature T _wall [K] of the flat multi-hole tube 2.
LMTD=(T _{air, out} - T _{air, in} )/log {(T _{air, out} - T _wall )/(T _{air, in} - T _wall )} ... (9)

The energy conservation equation on the refrigerant side in each cell can be expressed by the following equation (10).
α _ref・(T _ref −T _wall )・A _i,cell = M _ref・(h _ref,in −h _ref,out )...(10)

The symbols in the formula (10) have the following meanings.
α _ref : Heat transfer coefficient between the refrigerant and the flat multi-hole tube 2 [W/(m ² ·K)]
T _ref : refrigerant temperature [K]
A _i,cell : Heat exchange area between the refrigerant and the flat multi-hole tube 2 per cell [m ² ]
M _ref : Mass flow rate of refrigerant [kg/s]
h _ref,in : Specific enthalpy of the refrigerant at the inlet of each cell h _ref,out : Specific enthalpy of the refrigerant at the outlet of each cell

Since the amount of heat exchange between the air and the flat multi-hole tubes 2 is equal to the amount of heat exchange between the flat multi-hole tubes 2 and the refrigerant, the right side of the formula (8) and the right side of the formula (10) can be connected with an equal sign, thereby obtaining the following formula (11).
V _air・A _{front, cell}・ρ _air・C _p (T _{air, out} −T _{air, in} )=M _ref・(h _ref,in −h _{ref, out} ) (11)

The heat transfer coefficient α _air between the air and the flat multi-hole tube 2 in the above formula (8) and the heat transfer coefficient α _ref between the refrigerant and the flat multi-hole tube 2 in the above formula (10) can be determined by separate calculation. In addition, for the state quantity of the refrigerant at the inlet of each cell, an appropriately set initial value may be used when there is no cell upstream of the cell to be calculated, and when there is a cell upstream of the cell to be calculated, the state quantity at the outlet of the upstream cell may be used. In addition, for the state quantity of the air at the inlet of each cell, an appropriately set initial value may be used.

Therefore, in the above formulas (8), (10), and (11), there are three unknown state quantities: the air temperature T _air,out at the air outlet of the cell, the wall temperature T _wall of the flat multi-hole tube 2, and the specific enthalpy h _ref,out of the refrigerant at the refrigerant outlet. On the other hand, since the above formulas (8), (10), and (11) are conservative equations, these unknown state quantities can be determined by using an iterative method. Specifically, these unknown state quantities can be determined by using a bisection method.

Moreover, the pressure P _ref,out of the refrigerant at the refrigerant outlet of the cell can be calculated using the following formula (12).
P _ref,out =P _ref,in -ΔP _f -ΔP _m ...(12)

In the above formula (12), the symbol ΔP _f is the value of the friction loss in the pipe based on the underground-Oyama formula, and ΔP _m is the pressure change associated with the phase change of the refrigerant. The value of the pressure change ΔP _m associated with the phase change of the refrigerant can be expressed by the following formula (13).
ΔP _m =G ²・(1/ρ _V −1/ρ _L )・(x _ref,in −x _ref,out ) (13)

The symbols in the formula (13) have the following meanings:
G: mass velocity of refrigerant [kg/(m ² s)]
x _{ref, in} : Quality of refrigerant at the inlet of the cell [-]
x _ref,out : refrigerant quality at the cell refrigerant outlet [-]

The validity of the above-mentioned analytical model can be confirmed, for example, by comparing the calculation results of the model simulating test specimens A and B in Example 1 with the experimental results. Table 2 shows the calculation results of the model simulating test specimens A and B.

As shown in Table 2, the heat exchange amount of test piece A calculated by numerical analysis was greater than that of test piece B at all wind speeds. Furthermore, the heat exchange amount of test piece A increased as the wind speed increased. In this way, the heat exchange amount calculated by the above-mentioned analytical model shows the same tendency as the experimental results. From these results, it can be seen that the above-mentioned analytical model is valid.

Next, using the above analysis model, we search for a distribution method for the flat multi-hole tube 2 that maximizes the heat exchange amount under each of the analysis conditions A to J shown in Table 3. The configuration of the analysis model other than the values shown in Table 3 is as follows.

・Effective width: 700mm
External dimensions in the depth direction: 13.85 mm
Total number of flat multi-hole tubes 2: 52 Height of fins 3: 7.61 mm
Fin 3 pitch: 1.1 mm

Refrigerant: R32
Dry bulb temperature of air: 35°C
・Wet bulb temperature of air: 24℃

・Flat multi-hole pipe A
Dimensions: Width 13.85 mm, thickness 1.15 mm
Number of refrigerant channels: 15 Hydraulic diameter D _h : 0.530 mm
Flow path cross-sectional area A _tube : 5.433 ^mm2

・Flat multi-hole pipe B
Dimensions: Width 13.85 mm, thickness 1.93 mm
Number of refrigerant channels: 13 Hydraulic diameter D _h : 0.740 mm
Flow path cross-sectional area A _tube : 12.23 ^mm2

Table 3 shows the optimal number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 under each of the analysis conditions A to J. Although not shown in the table, under each of the analysis conditions A to J, the optimal number of flat multi-hole tubes 2 belonging to the second flat multi-hole tube group 22 is equal to or greater than the optimal number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21.

Fig. 6 shows _{a graph in which the ratio N1 /} N of the number N1 of flat multi-hole tubes belonging to the first flat multi-hole tube group to the total number N of flat multi-hole tubes in the heat exchanger is plotted using the value of _ΔPTP in the following formula (2). The vertical axis of Fig. 6 is the value of _N1 /N, and the horizontal axis is the value of _ΔPTP in the following formula (2). The dashed line in Fig. 6 is a curve expressed by the following formula (1'). The scale of the horizontal axis in Fig. 6 is a logarithmic scale.

ΔP _TP =0.0661×C ₁ ×Γ ^-1.841 ...(2)
N ₁ ^' = N x 0.0014 x ΔP _TP ^0.48737 ... (1')

However, the value of ΔP _TP in formula (2) is a value calculated by the following formulas (3) and (4) when the mass flow rate of the refrigerant flowing inside the parallel-flow type heat exchanger is expressed as m _ref [kg/s], the flow path cross-sectional area of the flat multi-hole tube is expressed as A _tube [m ² ], the hydraulic diameter of the flat multi-hole tube is expressed as D _h [m], the length of the flat multi-hole tube is expressed as L _tube [m], the viscosity of the refrigerant in the liquid phase is expressed as μ _L [Pa·s], the viscosity of the refrigerant in the gas phase is expressed as μ _V [Pa·s], the density of the refrigerant in the liquid phase is expressed as ρ _L [kg/m ³ ], and the density of the refrigerant in the gas phase is expressed as ρ _V [kg/m ³ ].
C ₁ = m _ref ^1.75 ×A _tube ^-1.75 ×D _h ^-0.75 ×μ _L ^0.25 ×ρ _L ^-1 ×4 × L _tube ... (3)
Γ=( _ρV / _ρL ) ^0.5 ×( _μL / _μV ) ^0.125 ...(4)

From the graph shown in FIG. 6, it can be seen that the curve represented by the above formula (1') closely approximates the optimal value of the flat multi-hole tube 2 belonging to the first flat multi-hole tube group 21 under the analysis conditions A to J. Therefore, by using the above formula (1'), the optimal value of the flat multi-hole tube 2 belonging to the first flat multi-hole tube group 21 can be easily predicted.

The "Predicted value by formula (1')" column in Table 3 shows the optimal value of the flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 calculated by the formula (1'). From these results, it can be seen that the value predicted by the formula (1') is up to two more than the optimal number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 derived by numerical analysis.

Therefore, by setting the lower limit of the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 to a number two less than the optimal number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 predicted by the above formula (1'), the number of flat multi-hole tubes 2 belonging to the first flat multi-hole tube group 21 can be easily optimized, and the heat exchange amount of the entire heat exchanger can be increased.

As described above, configuration examples of the parallel-flow heat exchanger according to the present invention have been described based on Examples 1 to 3, but the specific aspects of the parallel-flow heat exchanger according to the present invention are not limited to those described in the above examples, and the configuration can be changed as appropriate within the scope of the spirit of the present invention.

Reference Signs List 1 Parallel flow type heat exchanger 11 Core 2 Flat multi-hole tube 21 First flat multi-hole tube group 22 Second flat multi-hole tube group 3 Fin 4 First header 5 Second header

Claims (5)

An air conditioner having a parallel flow type heat exchanger and a refrigerant present inside the parallel flow type heat exchanger,
The parallel flow type heat exchanger includes a core in which a plurality of flat multi-hole tubes configured to allow a refrigerant to flow therethrough are arranged in parallel with fins interposed therebetween, and the flat multi-hole tubes and the fins are stacked alternately in the vertical direction;
a first header disposed at one end of the core in a longitudinal direction of the flat multi-hole pipe and connected to the flat multi-hole pipe;
a second header disposed at the other end of the core in the longitudinal direction and connected to the flat multi-hole tube;
The flat multi-hole tubes are divided into a plurality of flat multi-hole tube groups including a first flat multi-hole tube group located at the top of the core and a second flat multi-hole tube group adjacent to and below the first flat multi-hole tube group,
the first header and the second header are configured to allow the refrigerant to pass through the plurality of flat multi-hole tube bundles sequentially from above to below,
The number of the flat multi-hole tubes belonging to the second flat multi-hole tube group is 14 or more,
the number of flat multi-hole tubes belonging to the first flat multi-hole tube group is equal to or less than the number of the flat multi-hole tubes belonging to the second flat multi-hole tube group,
an air conditioner, wherein a total number N of the flat multi-hole tubes in the parallel-flow type heat exchanger and a number N ₁ of the flat multi-hole tubes belonging to the first flat multi-hole tube group satisfy the relationship of the following formula (1):
N ₁ > N x 0.0014 x ΔP _TP ^0.48737 -2 ... (1)
( The value of ΔP _TP in the above formula (1) is a value calculated by the following formulas (2) to (4) when the mass flow rate of the refrigerant flowing inside the parallel-flow type heat exchanger is expressed as m ref [kg/s], the flow path cross-sectional area of the flat multi-hole tube is expressed as A ^{tube [m 2} _{] ,} the hydraulic diameter of the flat multi-hole tube is expressed as D _h [m], the length of the flat multi-hole tube is expressed as L _tube [m], the viscosity of the refrigerant in the liquid phase is expressed as μ _L [Pa·s], the viscosity of the refrigerant in the gas phase is expressed as μ _V [Pa·s], the density of the refrigerant in the liquid phase is expressed as ρ _L [kg/m ³ ], and the density of the refrigerant in the gas phase is expressed as ρ _V [kg/m ³ ].
ΔP _TP =0.0661×C ₁ ×Γ ^-1.841 ...(2)
C ₁ = m _ref ^1.75 ×A _tube ^-1.75 ×D _h ^-0.75 ×μ _L ^0.25 ×ρ _L ^-1 ×4 × L _tube ... (3)
Γ=(ρV _/ ρL ₎ 0.5 ^× (μL _/ μV ₎ 0.125 ^... (4)) 2. The air conditioner according to claim 1, wherein the parallel-flow type heat exchanger is configured to use R32 as a refrigerant, the flat multi-hole tube has a hydraulic diameter _Dh of 0.00032 m or more and 0.001 m or less, and the flat multi -hole tube has a length L _tube of 0.4 m or more and 0.9 m or less. 3. The air conditioner according to claim 1, wherein the rated capacity of the parallel-flow type heat exchanger is 2 kW or more and 12 kW or less. The air conditioner according to any one of claims 1 to 3 , wherein the refrigerant is R32. The air conditioner is configured to set the mass flow rate m _ref of the refrigerant inside the parallel-flow type heat exchanger to 0.01 kg/s or more and 0.03333 kg/s or less. The air conditioner according to any one of claims 1 to 4 .

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