HEAT EXCHANGER

Abstract

A heat exchanger to be used as a gas cooler has a refrigerant inlet and a refrigerant outlet provided at upper and lower header sections, respectively, of a first header tank. A value represented by a formula {(L1+L2)/2}+(T×2N) is defined as an average flow path length L0, where L1 represents the total interior length of both the header sections of the first header tank, L2 represents the interior length of the header section(s) of the second header tank, T represents the length of the flat tubes, and N represents the number of the header section(s) of the second header tank. The positions of the refrigerant inlet and outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the upper header section from the refrigerant inlet and flows out of the refrigerant outlet.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a heat exchanger, and more particularly to a heat exchanger that can be favorably used as a gas cooler of a supercritical refrigeration cycle in which a CO₂ (carbon dioxide) refrigerant or a like supercritical refrigerant is used.

Herein and in the appended claims, the term “supercritical refrigeration cycle” means a refrigeration cycle in which refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. The term “supercritical refrigerant” means a refrigerant used in a supercritical refrigeration cycle.

A supercritical refrigeration cycle includes a compressor, a gas cooler, an evaporator, a pressure reducing device, and an intermediate heat exchanger for exchanging heat between refrigerant flowing out of the gas cooler and that flowing out of the evaporator. Japanese Patent Application Laid-Open (kokai) No. 2003-279194 discloses a heat exchanger used as a gas cooler of such a supercritical refrigeration cycle. The disclosed heat exchanger includes first and second header tanks disposed apart from each other and extending vertically; and a plurality of flat tubes disposed at vertical intervals between the two header tanks and having opposite end portions connected to the respective header tanks. The first header tank includes upper and lower header sections, and the second header tank includes a single header section which faces the first and second header sections of the first header tank. A refrigerant inlet is provided at the upper header section of the first header tank, and a refrigerant outlet is provided at the lower header section of the first header tank. The flat tubes form upper and lower paths each composed of a plurality of flat tubes arranged vertically.

Japanese Patent Application Laid-Open (kokai) No. 2004-138306 also discloses a heat exchanger used as a gas cooler of such a supercritical refrigeration cycle. The disclosed heat exchanger includes first and second header tanks disposed apart from each other and extending vertically; and a plurality of flat tubes disposed at vertical intervals between the two header tanks and having opposite end portions connected to the respective header tanks. Each of the first and second header tanks includes upper and lower header sections. A refrigerant inlet is provided at the lower header section of the first header tank, and a refrigerant outlet is provided at the upper header section of the second header tank. The flat tubes form three paths arranged vertically, each composed of a plurality of flat tubes arranged vertically.

However, as a result of various studies, the present invention found that the heat exchanger disclosed in Japanese Patent Application Laid-Open No. 2003-279194 raises the following problem because the refrigerant inlet and the refrigerant outlet are provided at the center portions of the corresponding header sections with respect to the longitudinal direction. That is, refrigerant having flowed into the interior of the upper header section of the first header tank via the refrigerant inlet flows into a plurality of flat tubes communicating with the upper header section; i.e., the flat tubes of the upper path, and flows into the interior of the header section of the second header tank via the flat tubes. The refrigerant then flows into a plurality of flat tubes communicating with the lower header section of the first header tank; i.e., the flat tubes of the lower path, and flows into the interior of the lower header section of the first header tank via the flat tubes. The refrigerant then flows out of the refrigerant outlet. A flow path length of refrigerant which passes through a flat tube of the upper path, which tube is located at a vertical position in the vicinity of the refrigerant inlet, and then passes through a flat tube of the lower path, which tube is located at a vertical position in the vicinity of the refrigerant outlet, differs from that of refrigerant which passes through the uppermost flat tube of the upper path and passes through the lowermost flat tube of the lower path. As a result, the flow rate and flow velocity of the refrigerant become imbalanced or non-uniform among the flat tubes, and the heat radiation is insufficient for use as a gas cooler of a supercritical refrigeration cycle.

Like the heat exchanger disclosed in Japanese Patent Application Laid-Open No. 2003-279194, the heat exchanger disclosed in Japanese Patent Application Laid-Open No. 2004-138306 also has insufficient heat radiation for use as a gas cooler of a supercritical refrigeration cycle, because the refrigerant inlet and the refrigerant outlet are provided at the center portions of the corresponding header sections with respect to the longitudinal direction.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above problem and to provide a heat exchanger which can radiate heat in a greater quantity when it is used as a gas cooler of a supercritical refrigeration cycle.

To fulfill the above object, the present invention comprises the following modes.

1) A heat exchanger comprising first and second header tanks disposed apart from each other; and a plurality of flat tubes disposed between the first and second header tanks such that the flat tubes are spaced apart from one another in the longitudinal direction of the header tanks, opposite end portions of the flat tubes being connected to the respective header tanks, the first header tank including a plurality of header sections arranged in the longitudinal direction of the first header tank, the second header tank including a single header section or a plurality of header sections which are one fewer in number than the header sections of the first header tank, the single header section or each of the header sections facing two adjacent header sections of the first header tank, a refrigerant inlet being provided at a header section of the first header tank located at one end with respect to the longitudinal direction, a refrigerant outlet being provided at another header section of the first header tank located at the other end with respect to the longitudinal direction, the flat tubes being divided into groups each of which includes a plurality of flat tubes arranged in the longitudinal direction of the header tanks and which form paths which are equal in number to the header sections of the first header tank,

wherein when a value represented by a formula {(L1+L2)/2}+(T×2N) is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header section(s) of the second header tank, T represents the length of the flat tubes, and N represents the number of the header section(s) of the second header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet.

2) A heat exchanger according to par. 1), wherein the first header tank includes two header sections, the second header tank includes a single header section, and the number of paths is two.

3) A heat exchanger according to par. 1), wherein the amount of compressor lubrication oil mixed in a refrigerant to be used is 1 wt. % or less.

4) A heat exchanger comprising first and second header tanks disposed apart from each other; and a plurality of flat tubes disposed between the first and second header tanks such that the flat tubes are spaced apart from one another in the longitudinal direction of the header tanks, opposite end portions of the flat tubes being connected to the respective header tanks, the first header tank including a plurality of header sections arranged in the longitudinal direction of the first header tank, the second header tank including header sections which are equal in number to the header sections of the first header tank and which are arranged in the longitudinal direction of the second header tank, a refrigerant inlet being provided at a header section of the first header tank located at one end with respect to the longitudinal direction, a refrigerant outlet being provided at a header section of the second header tank located at the opposite end with respect to the longitudinal direction, the flat tubes being divided into groups each of which includes a plurality of flat tubes arranged in the longitudinal direction of the header tanks and which form paths which are one greater in number than the header sections of each header tank,

wherein when a value represented by a formula {(L1+L2)/2}+{(T×(N+1)} is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header sections of the second header tank, T represents the length of the flat tubes, and N represents the number of the header sections of each header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet.

5) A heat exchanger according to par. 4), wherein each header tank includes two header sections, and the number of paths is three.

6) A heat exchanger according to par. 4), wherein the amount of compressor lubrication oil mixed in a refrigerant to be used is 1 wt. % or less.

According to the heat exchanger of par. 1), when a value represented by a formula {(L1+L2)/2}+(T×2N) is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header section(s) of the second header tank, T represents the length of the flat tubes, and N represents the number of the header section(s) of the second header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet. Therefore, the flow path length LX of refrigerant does not change greatly with the position of a flat tube of each path through which the refrigerant passes, so that the flow rate and flow speed of refrigerant become uniform among the flat tubes of each path. Accordingly, the heat radiation amount of the heat exchanger used as a gas cooler of a supercritical refrigeration cycle increases as compared with the heat exchangers disclosed in Japanese Patent Application Laid-Open Nos. 2003-279194 and No. 2004-138306, respectively.

According to the heat exchanger of par. 3), a decrease in the heat radiation quantity of the heat exchanger used as a gas cooler of a supercritical refrigeration cycle can be prevented. That is, when the amount of compressor lubrication oil mixed in a refrigerant to be used is in excess of 1 wt. % or less, a large amount of refrigerant flows through a lower portion of each header section and a lower-side flat tube of each path, so that the heat radiation quantity may decrease even when the above-described flow path length is generally the same.

According to the heat exchanger of par. 4), when a value represented by a formula {(L1+L2)/2}+{(T×(N+1)} is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header sections of the second header tank, T represents the length of the flat tubes, and N represents the number of the header sections of each header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet. Therefore, the flow path length LX of refrigerant does not change greatly with the position of a flat tube of each path through which the refrigerant passes, so that the flow rate and flow speed of refrigerant become uniform among the flat tubes of each path. Accordingly, the heat radiation amount of the heat exchanger used as a gas cooler of a supercritical refrigeration cycle increases as compared with the heat exchangers disclosed in Japanese Patent Application Laid-Open Nos. 2003-279194 and No. 2004-138306, respectively.

According to the heat exchanger of par. 6), a decrease in the heat radiation quantity of the heat exchanger used as a gas cooler of a supercritical refrigeration cycle can be prevented. That is, when the amount of compressor lubrication oil mixed in a refrigerant to be used is in excess of 1 wt. % or less, a large amount of refrigerant flows through a lower portion of each header section and a lower-side flat tube of each path, so that the heat radiation quantity may decrease even when the above-described flow path length is generally the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall front view showing a first embodiment of a heat exchanger according to the present invention;

FIG. 2 is a diagram showing flow of refrigerant within the heater exchanger of FIG. 1;

FIG. 3 is an overall front view showing a second embodiment of the heat exchanger according to the present invention;

FIG. 4 is a diagram showing flow of refrigerant within the heater exchanger of FIG. 3; and

FIG. 5 is a graph showing results of Test Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will next be described with reference to the drawings.

In the following description, the upper, lower, left-hand, and right-hand sides of FIGS. 1 and 3 will be referred to as “upper,” “lower,” “left,” and “right,” respectively. Further, in the following description, the term “aluminum” encompasses aluminum alloys in addition to pure aluminum.

First Embodiment

FIGS. 1 and 2 show a first embodiment.

FIG. 1 shows the overall structure of a heat exchanger according to the present invention. FIG. 2 shows flow of refrigerant within the heater exchanger.

As shown in FIG. 1, a heat exchanger 1 includes two header tanks 2 and 3 formed of aluminum and extending vertically. The header tanks 2 and 3 are disposed in parallel and are spaced apart from each other in the left-right direction. A plurality of flat tubes 4 formed of aluminum are arranged in parallel between the two header tanks 2 and 3 and are spaced apart from one another in the vertical direction. Opposite ends of the flat tubes 4 are connected to the corresponding header tanks 2 and 3. Corrugated fins 6 formed of aluminum are arranged in respective air-passing clearances 5 between adjacent flat tubes 4 and at the outside of the upper-end and lower-end flat tubes 4, and each is brazed to the adjacent flat tube(s) 4. Side plates 7 formed of aluminum are arranged externally of and are brazed to the respective upper-end and lower-end corrugated fins 6.

The right-hand, first header tank 2 includes a plurality of (two in the present embodiment) header sections 8 and 9 arranged vertically and separated by means of a partition 10 located at the center of the tank 2 with respect to the vertical direction. The left-hand, second header tank 3 includes a header section(s), which is one fewer in number than the header sections 8 and 9 of the first header tank 2; i.e., a single header section 11 in the present embodiment, such that the header section 11 extends from an upper end to a lower end of the second header tank 3 and faces or is opposed to the header sections 8 and 9 of the first header tank 2. A refrigerant inlet 12 is provided in the peripheral wall of the upper header section 8 of the first header tank 2, and a refrigerant outlet 13 is provided in the peripheral wall of the lower header section 9 of the first header tank 2.

The flat tubes 4 are divided into first and second groups which form first and second paths P1 and P2. The interiors of the flat tubes 4 belonging to the first group communicate, at their right ends, with the interior of the upper header section 8 of the first header tank 2, and communicate, at their left ends, with an upper portion of the interior of the header section 11 of the second header tank 3. The interiors of the flat tubes 4 belonging to the second group communicate, at their right ends, with the interior of the lower header section 9 of the first header tank 2, and communicate, at their left ends, with a lower portion of the interior of the header section 11 of the second header tank 3. The refrigerant flows in the same direction among the flat tubes 4 which constitute the path P1, and flows in the same direction among the flat tubes 4 which constitute the path P2. However, the flow direction of the refrigerant flowing through the flat tubes 4 which constitute the path P1 is opposite that of the refrigerant flowing through the flat tubes 4 which constitute the path P2. Although not illustrated in the drawings, each flat tube 4 has a plurality of refrigerant channels formed therein and arranged in its width direction, and is disposed such that its width direction coincides with the direction of flow of air (the direction perpendicular to the sheet of FIG. 1).

When a value obtained by dividing the number of flat tubes 4 which constitute each of the paths P1 and P2 by the number of all the tubes 4 is defined as a “tube ratio,” the tube ratio of each of the paths P1 and P2 preferably falls within a range of 0.45 to 0.55. Notably, the sum of the tube ratio of the path P1 and that of the path P2 becomes 1. When the tube ratio is less than 0.45 or greater than 0.55, an increased pressure loss may be produced in the flat tubes 4 of one of the paths P1 and P2 when the heat exchanger 1 is used as a gas cooler of a supercritical refrigeration cycle in which a CO₂ (carbon dioxide) refrigerant or a like supercritical refrigerant is used and in which refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. More preferably, the tube ratio of each of the paths P1 and P2 falls within a range of 0.48 to 0.52. In this case as well, the sum of the tube ratio of the path P1 and that of the path P2 becomes 1.

Here, the refrigerant is assumed to flow within the heat exchanger 1 as shown in FIG. 2. In this case, an average flow path length L0 can be defined by a formula {(L1+L2)/2}+(T×2N), where L1 represents the sum of the interior length Ia of the upper header section 8 and the interior length Ib of the lower header section 9 of the first header tank 2 (L1=Ia+Ib), L2 represents the interior length Ic of the header section 11 of the second header tank 3 (L2=Ic), T represents the length of the flat tubes 4, and N represents the number of the header section 11 of the second header tank 3. The position of the refrigerant inlet 12 in the vertical direction (the longitudinal direction of the header section 8) and the position of the refrigerant outlet 13 in the vertical direction (the longitudinal direction of the header section 9) are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents an actual flow path length for refrigerant which flows into the upper header section 8 of the first header tank 2 from the refrigerant inlet 12, passes through all the header sections 8, 9, and 11 and the flat tubes 4 of all the paths P1 and P2, and flows out of the refrigerant outlet 13.

For example, in a case where the refrigerant inlet 12 is located at a position indicated by point X1 in FIG. 2, the actual flow path length LX of refrigerant which flows into the upper header section 8 and then flows through the upper-end flat tube 4 of the first path P1 becomes longer than the average flow path length L0 by a length Y1. Meanwhile, the actual flow path length LX of refrigerant which flows into the upper header section 8 and then flows through the lower-end flat tube 4 of the first path P1 becomes shorter than the average flow path length L0 by the length Y1. In view of this, the vertical position of the refrigerant inlet 12 is determined such that the value of (L0+Y1)/L0 and the value of (L0−Y1)/L0 fall within the range of 0.8 to 1.2. Further, in a case where the refrigerant outlet 13 is located at a position indicated by point X2 in FIG. 2, the actual flow path length LX of refrigerant which passes through the lower-end flat tube 4 of the second path P2 and flows into the lower header section 9 becomes longer than the average flow path length L0 by a length Y2. Meanwhile, the actual flow path length LX of refrigerant which passes through the upper-end flat tube 4 of the second path P2 and flows into the lower header section 9 becomes shorter than the average flow path length L0 by the length Y2. In view of this, the vertical position of the refrigerant outlet 13 is determined such that the value of (L0+Y2)/L0 and the value of (L0−Y2)/L0 fall within the range of 0.8 to 1.2.

Second Embodiment

FIGS. 3 and 4 show a second embodiment.

FIG. 3 shows the overall structure of a heat exchanger according to the present invention. FIG. 4 shows flow of refrigerant within the heater exchanger.

In the case of a heat exchanger 20 of the present embodiment, a left-hand header tank is a first header tank 21, and a right-hand header tank is a second header tank 22. The first header tank 21 includes a plurality of (two in the present embodiment) header sections 24 and 25 arranged vertically and separated by means of a partition 23 located at a position higher than the center of the tank 21 with respect to the vertical direction. The second header tank 22 includes header sections, which are equal in number to the header sections 24 and 25 of the first header tank 21; i.e., two header sections 27 and 28 arranged vertically and separated by means of a partition 26 located at a position lower than the center of the tank 22 with respect to the vertical direction. The refrigerant inlet 12 is provided in the peripheral wall of the upper header section 24 of the first header tank 21, and the refrigerant outlet 13 is provided in the peripheral wall of the lower header section 28 of the second header tank 22.

The flat tubes 4 are divided into first through third groups which form first through third paths P1 to P3, respectively. The interiors of the flat tubes 4 belonging to the first group communicate, at their left ends, with the interior of the upper header section 24 of the first header tank 21, and communicate, at their right ends, with an upper portion of the interior of the upper header section 27 of the second header tank 22. The interiors of the flat tubes 4 belonging to the second group communicate, at their left ends, with an upper portion of the interior of the lower header section 25 of the first header tank 21, and communicate, at their right ends, with a lower portion of the interior of the upper header section 27 of the second header tank 22. The interiors of the flat tubes 4 belonging to the third group communicate, at their left ends, with a lower portion of the interior of the lower header section 25 of the first header tank 21, and communicate, at their right ends, with the interior of the lower header section 28 of the second header tank 22. The refrigerant flows in the same direction among the flat tubes 4 which constitute the path P1, in the same direction among the flat tubes 4 which constitute the path P2, and in the same direction among the flat tubes 4 which constitute the path P3. However, the flow direction of the refrigerant flowing through the flat tubes 4 which constitute the path P1 is opposite that of the refrigerant flowing through the flat tubes 4 which constitute the path P2; and the flow direction of the refrigerant flowing through the flat tubes 4 which constitute the path P2 is opposite that of the refrigerant flowing through the flat tubes 4 which constitute the path P3.

When a value obtained by dividing the number of flat tubes 4 which constitute each of the paths P1, P2, and P3 by the number of all the tubes 4 is defined as a “tube ratio,” the tube ratio of each of the paths P1, P2, and P3 preferably falls within a range of 0.3 to 0.4. When the tube ratio is less than 0.3 or greater than 0.4, an increased pressure loss may be produced in the flat tubes 4 of one of the paths P1, P2, and P3 when the heat exchanger 20 is used as a gas cooler of a supercritical refrigeration cycle in which a CO₂ (carbon dioxide) refrigerant or a like supercritical refrigerant is used and in which refrigerant on the high-pressure side is in a supercritical state; i.e., assumes a pressure in excess of a critical pressure. More preferably, the tube ratio of each path falls within a range of 0.32 to 0.34.

Other structural features are identical with those of the first embodiment. Like members are denoted by like reference numerals, and their description will not be repeated.

Here, the refrigerant is assumed to flow within the heat exchanger 20 as shown in FIG. 4. In this case, an average flow path length L0 can be defined by a formula {(L1+L2)/2}+{T×(N+1)}, where L1 represents the sum of the interior length Id of the upper header section 24 and the interior length Ie of the lower header section 25 of the first header tank 21 (L1=Id+Ie), L2 represents the sum of the interior length If of the upper header section 27 and the interior length Ig of the lower header section 28 of the second header tank 22 (L2=If+Ig), T represents the length of the flat tubes 4, and N represents the number of the header sections 24 and 25 (27 and 28) of each header tank 21 (22). The position of the refrigerant inlet 12 in the vertical direction (the longitudinal direction of the header section 24) and the position of the refrigerant outlet 13 in the vertical direction (the longitudinal direction of the header section 28) are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents an actual flow path length for refrigerant which flows into the upper header section 24 of the first header tank 21 from the refrigerant inlet 12, passes through all the header sections 24, 25, 27, and 28 and the flat tubes 4 of the paths P1, P2, and P3, and flows out of the refrigerant outlet 13.

For example, in a case where the refrigerant inlet 12 is located at a position indicated by point X3 in FIG. 4, the actual flow path length LX of refrigerant which flows into the upper header section 24 of the first header tank 21 and then flows through the upper-end flat tube 4 of the first path P1 becomes longer than the average flow path length L0 by a length Y3. Meanwhile, the actual flow path length LX of refrigerant which flows into the upper header section 24 of the first header tank 21 and then flows through the lower-end flat tube 4 of the first path P1 becomes shorter than the average flow path length L0 by the length Y3. In view of this, the vertical position of the refrigerant inlet 12 is determined such that the value of (L0+Y3)/L0 and the value of (L0−Y3)/L0 fall within the range of 0.8 to 1.2. Further, in a case where the refrigerant outlet 13 is located at a position indicated by point X4 in FIG. 4, the actual flow path length LX of refrigerant which passes through the lower-end flat tube 4 of the third path P3 and flows into the lower header section 28 of the second header tank 22 becomes longer than the average flow path length L0 by a length Y4. Meanwhile, the actual flow path length LX of refrigerant which passes through the upper-end flat tube 4 of the third path P3 and flows into the lower header section 28 of the second header tank 22 becomes shorter than the average flow path length L0 by the length Y4. In view of this, the vertical position of the refrigerant outlet 13 is determined such that the value of (L0+Y4)/L0 and the value of (L0−Y4)/L0 fall within the range of 0.8 to 1.2.

Each of the heat exchangers 1 and 20 of the first and second embodiments are preferably used as a gas cooler of a supercritical refrigeration cycle which includes a compressor, the gas cooler, an evaporator, an accumulator serving as a gas-liquid separator, an expansion valve serving as a pressure reducing device, and an intermediate heat exchanger for exchanging heat between high temperature, high pressure refrigerant flowing out of the gas cooler and low temperature, low pressure refrigerant flowing out of the evaporator and then passing through the accumulator, and which uses a CO₂ supercritical refrigerant. In such a supercritical refrigeration cycle, preferably, the amount of compressor lubrication oil mixed in the supercritical refrigerant is 1 wt. % or less.

The refrigeration cycle is installed in a vehicle; for example, in an automobile, as a car air conditioner. Although CO₂ is used as a supercritical refrigerant of a supercritical refrigeration cycle, the refrigerant is not limited thereto, and ethylene, ethane, nitrogen oxide, or the like may alternatively be used.

Next, a test example performed by use of the heat exchanger of the first embodiment will be described.

TEST EXAMPLE 1

A heat exchanger used in the test was configured such that a heat exchanger core section composed of the flat tubes 4 and the corrugate fins 6 has a height Hc of 380 mm and a width Wc of 660 mm; the width of the flat tubes 4 is 16 mm; the total number of the flat tubes 4 is 51; the number of the flat tubes 4 of the first path P1 is 26 (tube ratio: 0.51); and the number of the flat tubes 4 of the second path P2 is 25 (tube ratio: 0.49). The heat radiation quantity of the heat exchanger was obtained, while the ratio LX/L0; the ratio of the above-described flow path length Lx to the above-described average flow path length L0, was varied, under the conditions that inlet air temperature (temperature of air flowing into the heat exchange core section) was 35 to 40° C.; and front-face air speed (flow speed of air flowing into the heat exchange core section) was 1.5 to 2.5 m/s.

FIG. 5 shows the relation between the ratio LX/L0 and the heat radiation quantity. The results shown in FIG. 5 demonstrate that the heat exchanger has an excellent heat radiation performance when the ratio LX/L0 falls within the range of 0.8 to 1.2.

Claims

1. A heat exchanger comprising first and second header tanks disposed apart from each other; and a plurality of flat tubes disposed between the first and second header tanks such that the flat tubes are spaced apart from one another in the longitudinal direction of the header tanks, opposite end portions of the flat tubes being connected to the respective header tanks, the first header tank including a plurality of header sections arranged in the longitudinal direction of the first header tank, the second header tank including a single header section or a plurality of header sections which are one fewer in number than the header sections of the first header tank, the single header section or each of the header sections facing two adjacent header sections of the first header tank, a refrigerant inlet being provided at a header section of the first header tank located at one end with respect to the longitudinal direction, a refrigerant outlet being provided at another header section of the first header tank located at the other end with respect to the longitudinal direction, the flat tubes being divided into groups each of which includes a plurality of flat tubes arranged in the longitudinal direction of the header tanks and which form paths which are equal in number to the header sections of the first header tank, wherein when a value represented by a formula {(L1+L2)/2}+(T×2N) is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header section(s) of the second header tank, T represents the length of the flat tubes, and N represents the number of the header section(s) of the second header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet.

2. A heat exchanger according to claim 1, wherein the first header tank includes two header sections, the second header tank includes a single header section, and the number of paths is two.

3. A heat exchanger according to claim 1, wherein the amount of compressor lubrication oil mixed in a refrigerant to be used is 1 wt. % or less.

4. A heat exchanger comprising first and second header tanks disposed apart from each other; and a plurality of flat tubes disposed between the first and second header tanks such that the flat tubes are spaced apart from one another in the longitudinal direction of the header tanks, opposite end portions of the flat tubes being connected to the respective header tanks, the first header tank including a plurality of header sections arranged in the longitudinal direction of the first header tank, the second header tank including header sections which are equal in number to the header sections of the first header tank and which are arranged in the longitudinal direction of the second header tank, a refrigerant inlet being provided at a header section of the first header tank located at one end with respect to the longitudinal direction, a refrigerant outlet being provided at a header section of the second header tank located at the opposite end with respect to the longitudinal direction, the flat tubes being divided into groups each of which includes a plurality of flat tubes arranged in the longitudinal direction of the header tanks and which form paths which are one greater in number than the header sections of each header tank, wherein when a value represented by a formula {(L1+L2)/2}+{(T×(N+1)) is defined as an average flow path length L0, where L1 represents the total interior length of all the header sections of the first header tank, L2 represents the total interior length of all the header sections of the second header tank, T represents the length of the flat tubes, and N represents the number of the header sections of each header tank, the position of the refrigerant inlet and the position of the refrigerant outlet are determined to satisfy the relation 0.8≦LX/L0≦1.2, where Lx represents a flow path length for refrigerant which flows into the first header tank from the refrigerant inlet, passes through all the header sections and the flat tubes of all the paths, and flows out of the refrigerant outlet.

5. A heat exchanger according to claim 4, wherein each header tank includes two header sections, and the number of paths is three.

6. A heat exchanger according to claim 4, wherein the amount of compressor lubrication oil mixed in a refrigerant to be used is 1 wt. % or less.