US20160313070A1

US20160313070A1 - Heat-exchanger offset fin and refrigerant heat-exchanger utilizing same

Info

Publication number: US20160313070A1
Application number: US15/102,374
Authority: US
Inventors: Koji Nakado
Original assignee: Mitsubishi Heavy Industries Automotive Thermal Systems Co Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2014-02-10
Filing date: 2015-01-27
Publication date: 2016-10-27
Also published as: WO2015118998A1; JP6333571B2; JP2015152178A; CN105814391A; DE112015000722T5; CN105814391B

Abstract

A heat-exchanger offset fin is a heat-exchanger offset fin which is disposed among a plurality of refrigerant tubes arranged in parallel. A plurality of segments, each of which is an individual fin cut and lifted into strips from the rising surfaces and falling surfaces of the fin which is folded and formed into wave shapes, are disposed it an offset manner with intervals therebetween of at least two rows in the airflow direction. The length of each segment in airflow direction satisfies 0.5 mm ≦L≦1.2 mm. The number of divisions of each segment within a single pitch of the wave-shape fin is three or greater.

Description

TECHNICAL FIELD

The present invention relates to a heat-exchanger offset fin provided among refrigerant tubes and a refrigerant heat-exchanger utilizing the same.
BACKGROUND ART
Conventionally, refrigerant heat-exchangers, in which corrugated fins formed by bending a thin metal plate into wave-shapes are disposed among a plurality of refrigerant tubes arranged in parallel, are known as refrigerant heat-exchangers applied to evaporators, condensers, and the like of air-conditioners. Additionally, in order to further increase the heat exchanging performance of the corrugated fins, refrigerant heat-exchangers having a configuration are also conventionally known in which a plurality of segments, each of which is an individual fin cut and lifted into strips from both the rising surfaces and falling surfaces of the wave shapes of the corrugated fins, are disposed in an offset manner; that is, a configuration in which offset fins are disposed among the refrigerant tubes.
Patent Document 1 describes a heat exchanger for cooling exhaust gas having offset fins disposed within tubes as inner fins, in which groups of four offset fin pieces are disposed with a predetermined interval (slit) in the offset fins. Likewise, Patent Document 2 describes an exhaust heat exchanger having offset fins disposed within an exhaust tube, in which each segment is inclined toward the center of any segment except for segments existing in particular rows and lines so as not to be affected by the thermal boundary layers generated at the leading edges of the upstream side segments.
Furthermore, Patent Document 3 describes an exhaust gas heat exchanger in which a fin pitch fp of offset fins disposed within an exhaust tube of the exhaust gas heat exchanger is of a size that satisfies 2 mm<fp≦12 mm and a fin height fh of the offset fins is of a size that satisfies 3.5 mm<fh≦12 mm; and a length L of the segments that are individual cut and lifted parts satisfies 0.5 mm<L≦7 mm when fh<7 and fp≦5, satisfies 0.5 mm<L≦1 mm when fh<7 and fp>5, satisfies 0.5 mm<L≦4.5 mm when fh≧7 and fp≦5, and satisfies 0.5 mm<L≦1.5 mm when fh≧7 and fp>5.

CITATION LIST

Patent Documents

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-139053A
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2001-41109A
Patent Document 3: Japanese Patent No. 4240136

SUMMARY OF INVENTION

Technical Problem

As described above, attempts have been made to increase the coefficient of heat transfer in the offset fins by determining the length L of each segment on the basis of the relationship with the fin pitch fp and the fin height fh, inclining each of the segments in the airflow direction, and increasing the number of divisions per pitch of the wave fins of each segment. However, individually, these measures for improvement have reached their limits in terms of being able to improve performance by increasing the coefficient of heat transfer on the gas side or preventing pressure loss. Accordingly, there is a need for the provision of a heat-exchanger with increased performance in the field of refrigerant heat-exchangers applied to evaporators, condensers, and the like of vehicle air-conditioning devices.
In light of the foregoing, an object of the present invention is to provide a heat-exchanger offset fin wherein performance is improved by effectively combining individual improvement elements for offset fins, and a refrigerant heat-exchanger using the same.

Solution to Problem

The heat-exchanger offset fin and refrigerant heat-exchanger using the same of the present invention adopt the following means in order to solve the problems described above.
Specifically, a heat-exchanger offset fin according to a first aspect of the present invention is a heat-exchanger offset fin which is disposed among a plurality of refrigerant tubes arranged in parallel. A plurality of segments, each of which is an individual fin cut and lifted into strips from the rising surfaces and falling surfaces of the fin which is folded and formed into wave shapes, are disposed in an offset manner with intervals therebetween of at least two rows in the airflow direction. A length L of each segment in the airflow direction satisfies 0.5 mm≦L≦1.2 mm. The number of divisions of each segment within a single pitch of the wave-shape fin is three or greater.
According to the first aspect of the present invention, the plurality of segments, each of which is an individual fin cut and lifted into strips from the rising surfaces and falling surfaces of the fin which is folded and formed into a wave-shape, are disposed in an offset manner with intervals therebetween of at least two rows in the airflow direction. Additionally, the length L of each segment in the airflow direction satisfies 0.5 mm≦L≦1.2 mm. Therefore, for each of the segments, the thermal boundary layer generated at the leading edge of the segments positioned upstream in the airflow direction will not be prevented from affecting the segments arranged on the downstream side and, as a result of not inhibiting the leading edge effects, the leading edge effect of each of the segments, that is, the effects of the airflow colliding with the leading edge of each segment and the coefficient of heat transfer increasing in a localized manner at the leading edge portion, can be maximized. As a result, along with improving the coefficient of heat transfer on the air side and, by extension, improving heat exchanging performance, air side pressure loss can be prevented and this pressure loss can be held to a level of practical use due to the length L in the airflow direction of each segment being optimized. Additionally, due to the fact that the number of divisions of each segment within a single pitch of the wave-shape fin is configured to be three or greater, the intervals between the fins can be narrowed and the speed of the air flow increased, and further improvements in the coefficient of heat transfer on the air side can be achieved. As such, the performance of the offset fin can be improved from both perspectives of the coefficient of heat transfer and the pressure loss on the air side, and performance thereof can be further enhanced.
Furthermore, with a heat-exchanger offset fin according to a second aspect of the present invention, in the heat-exchanger offset fin described above, each of the segments having three or greater divisions within a single pitch is repeatedly arranged in a stepped shape with three or more steps.
According to the second aspect of the present invention, due to the fact that each of the segments having three or greater divisions within a single pitch is repeatedly arranged as a stepped shape with three or more steps, all of the segments can be arranged in an offset manner with intervals therebetween of at least two rows in the airflow direction, effects caused in all the segments by the thermal boundary layer of the upstream side segments can be eliminated, and the leading edge effects can be maximized, leading to a steady improvement in the coefficient of heat transfer on the air side. Thus, further improvement of the heat exchanging performance of the offset fin can be achieved.
Furthermore, with a heat-exchanger offset fin according to a third aspect of the present invention, in any of the heat-exchanger offset fin described above, each of the segments is inclined at a predetermined angle with respect to the airflow direction.
According to the third aspect of the present invention, due to the fact that each of the segments are inclined at the predetermined angle with respect to the airflow direction, the interval between each of the segments can be widened exactly by the amount of inclination, and the airflow will be rectified. Therefore, further improvement of the coefficient of heat transfer resulting from the leading edge effects of each of the segments can be achieved and the effects of preventing pressure loss on the air side can be maintained. Thus, performance of the offset fins can be further enhanced. Note that, considering the relationship with pressure loss, the inclination angle of the segments is preferably about 7°.
Furthermore, with a refrigerant heat-exchanger according to a fourth aspect of the present invention, any of the heat-exchanger offset fins described above is disposed among a plurality of refrigerant tubes arranged in parallel at a predetermined interval.
According to the fourth aspect of the present invention, due to the fact that any of the heat-exchanger offset fins described above is disposed among the plurality of refrigerant tubes arranged in parallel at the predetermined interval, heat exchange between a refrigerant flowing in the refrigerant tubes and the air stream flowing on the offset fin side can be further promoted due to the offset fin performance improvements, and the heat exchanging performance thereof can be improved. Thus, performance of the refrigerant heat-exchanger applied to evaporators and condensers can be further improved, performance of the air conditioner can be improved, and also the space-saving of the unit can be achieved as a result of reducing the size of the evaporators and condensers.

Advantageous Effects of Invention

According to the heat-exchanger offset fin of the present invention, for each of the segments, the thermal boundary layer generated at the leading edge of the segments positioned on the upstream side in the airflow direction will be prevented from affecting the segments arranged on the downstream side and, as a result of not inhibiting the leading edge effects of the segments, the leading edge effects of each of the segments, that is, the effects of the airflow colliding with the leading edge of each segment and the coefficient of heat transfer increasing in a localized manner at the leading edge portion, can be maximized and, along with improving the coefficient of heat transfer on the air side and, by extension, improving heat exchanging performance, air side pressure loss can be prevented and this pressure loss can be held to a level of practical use due to the length L in the airflow direction of each segment being optimized. Additionally, due to the fact that the number of divisions of each segment within a single pitch of the wave-shape fin is configured to be three or greater, the intervals between the fins can be narrowed and the speed of the air flow increased, and further improvements in the coefficient of heat transfer on the air side can be achieved. Therefore, the performance of the offset fin can be improved from both perspectives of the coefficient of heat transfer and the pressure loss on the air side, and performance thereof can be further enhanced.
Additionally, according to the present invention, heat exchange between a refrigerant flowing in the refrigerant tubes and the air stream flowing on the offset fin side can be further promoted due to the offset fin performance improvements, and the heat exchanging performance thereof can be improved. Thus, performance of the refrigerant heat-exchanger applied to evaporators and condensers can be further improved, performance of the air conditioner can be improved, and also the space-saving of the unit can be achieved as a result of reducing the size of the evaporators and condensers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a refrigerant heat-exchanger according to an embodiment of the present invention.

FIG. 2 is a perspective view of an offset fin used in the heat-exchanger described above.

FIG. 3 is a view equivalent to a cross-section taken along line A-A of FIG. 2.

FIG. 4 is a view in the arrow B direction of FIG. 2.

FIG. 5 is a graph comparing performance of the offset fin described above, variations thereof, and a single offset fin.

FIG. 6 is a graph showing changes in air pressure loss based on the length L of each segment of the offset fin described above.

FIG. 7 is a graph showing changes in the coefficient of heat transfer based on the length L of each segment of the offset fin described above.

FIGS. 8A to 8H are views equivalent to cross-sections illustrating the arrangement specifications of the segments of the offset fin used in the performance comparisons and analyses shown in FIGS. 5 to 7.

DESCRIPTION OF EMBODIMENT

An embodiment of the present invention will be described below, referring to FIG. 1 to FIG. 8.
FIG. 1 illustrates a perspective view of a refrigerant heat-exchanger according to an embodiment of the present invention; FIG. 2 illustrates a perspective view of an offset fin used in this heat-exchanger; FIG. 3 illustrates a view equivalent to a cross-section taken along line A-A of FIG. 2; and FIG. 4 is a view in the arrow B direction of FIG. 2.
A refrigerant heat-exchanger 1 is a device for application to an evaporator, condenser, or the like of an air conditioner, and effects heat exchange between refrigerant flowing within the refrigerant tubes and air flowing along the outer side of the refrigerant tubes.
The refrigerant heat-exchanger 1 is constituted by a pair of top-bottom or left- right headers 2 and 3, pairs thereof having a set vertical or horizontal interval therebetween and provided both on the upstream side and downstream side of an airflow direction F; a plurality of refrigerant tubes 4, forming a flat shape, arranged in parallel at a predetermined interval by both ends thereof being connected with the headers 2 and 3; and offset fins 5 disposed among the parallel refrigerant tubes 4. Refrigerant fed from a refrigerant inlet pipe 6 connected to one of the headers, i.e. 2, is made to flow through the refrigerant tubes 4 in one pass or two or more passes, evaporation or condensation taking place due to the heat transfer between the refrigerant and the air during the passing of the refrigerant and, thereafter, the refrigerant is discharged through a refrigerant outlet pipe 7 connected to the other header, i.e. 3.
The refrigerant heat-exchanger 1 described above and all of the components constituting it including the pair of headers 2 and 3, the offset fins 5, and the like are made from aluminum alloy. That is, the refrigerant heat-exchanger 1 is an all-aluminum alloy heat-exchanger. As illustrated in FIGS. 2 to 4, the offset fins 5 are fins with a fin width w of 34 mm, formed by bending a thin plate made from aluminum alloy having a plate thickness tf of 0.06 mm into a wave-shape having a fin pitch pf of 1.3 mm. Each of the rising surfaces 8 and the falling surfaces 9 illustrated in FIGS. 2 to 4 constitute each of fin segments (strip) 10. By bending the thin plate into a wave-shape, a configuration is attained in which the plurality of segments (strips) 10, each of which is an individual fin cut and lifted into strips, are disposed in an offset manner.
Additionally, in the present embodiment, in order to improve the performance of the offset fins 5, the length L in the airflow direction F of the strip segments 10, each of which is an individual fin cut and lifted from the rising surfaces 8 and falling surfaces 9 of the wave-shape fin, is configured so that 0.5 mm≦L≦1.2 mm; and also that, as illustrated in FIG. 3, the plurality of segments 10 is configured to be arranged with intervals therebetween of at least two rows with respect to a row direction along the airflow direction F. Each of the rows of the previously recited “two rows” are rows formed by four of the segments 10 aligned in a direction orthogonal to the direction F in FIG. 3. That is, there are 34 rows in the offset fin of FIG. 3. Additionally, the previously recited “row direction along the airflow direction F” is a direction along the airflow direction F. The offset fin of FIG. 3 can be said to have four rows (each having 34 of the segment 10) laid out along the direction F. Additionally, for each of the segments 10, a number of divisions n in a direction orthogonal to the airflow direction F within a single pitch of the wave-shape fin is three or greater. This, as illustrated in FIG. 3, means that in each of the four rows laid out along the direction F, the segment 10 is disposed at three or more positions in the direction orthogonal to the direction F.
Furthermore, when dividing each of the segments 10 into three or more sections and arranging them in the direction orthogonal to the airflow direction F, all of the segments 10 are configured to be arranged with intervals therebetween of at least two rows with respect to the row direction along the airflow direction F and, thus, as illustrated in FIGS. 2 and 3, are configured in a sequentially repeating arrangement in the airflow direction F in a stepped shape with three or more steps.
Next, the results of analyses and calculations of samples conducted in order to confirm the performance of the offset fin 5 described above will be explained while referring to FIGS. 5 to 8.
First, the details of samples No. 1 to No. 9 of offset fins used in the analyses and calculations are explained while referencing FIGS. 8A to 8H.
In each sample, the plate thickness tf of the fin material was 0.06 mm, the fin pitch pf was 1.3 mm, and the fin width w was 34 mm; also, the length L in the airflow direction F of each of the segments 10 was 1 mm, and the disposal, arrangement, or the like of the segments 10, each of which is an individual fin, was varied.
(1) As illustrated in FIG. 8A, in the fin of Sample No. 1, the interval in the row direction of each of the segments 10 was set to one row and the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to two.
(2) As illustrated in FIG. 8B, in the fin of Sample No. 2, the interval in the row direction of each of the segments 10 was set to two rows, the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to three, and the segments 10 were configured to have a repeating arrangement in the airflow direction F as a stepped shape with three steps.
(3) As illustrated in FIG. 8C, the fin of Sample No. 3 was the same as the fin of Sample No. 2 described above except that the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to four, and the segments 10 were configured to have a sequentially repeating arrangement in the airflow direction F as a stepped shape with four steps.
(4) As illustrated in FIG. 8D, the fin of Sample No. 4 was the same as the fin of Sample No. 2, with the variation that each of the segments 10 were disposed inclined 7° with respect to the airflow direction F.
(5) As illustrated in FIG. 8E, the fin of Sample No. 5 was the same as the fin of Sample No. 2, with the variation that the stepped shape had sequentially repeating arrangements such as to fold back at a center portion along the airflow direction F.
(6) As illustrated in FIG. 8F, in the fin of Sample No. 6, the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to three, but was configured in a repeating arrangement so that the stepped shape folded back at the third step. As a result, there were some segments 10 present where the interval in the row direction between each of the segments 10 was one row.
(7) As illustrated in FIG. 8G, the fin of Sample No. 7 was the same as the fin of Sample No. 6, with the variation that each of the segments 10 were disposed inclined 7° with respect to the airflow direction F.
(8) As illustrated in FIG. 8H, the fin of Sample No. 8 was a conventionally known louvered corrugated fin configured to have a shape that folds back at the center portion of the airflow direction F.
(9) The fin of Sample No. 9 is not illustrated in the drawings, but was the same as the fin of Sample No. 6 described above except that the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to four, and, as a result, there were some segments 10 present where the interval in the row direction between each of the segments 10 was one row.
For Sample Nos. 1 to 7, changes in the air pressure loss ΔPa (Pa) and the coefficient of heat transfer hm (W/m2K) based on the length L (mm) of each of the segments 10 were calculated and the analyzed results are shown on FIGS. 6 and 7. Here, the equations of the coefficient of heat transfer hm.pp and the air pressure loss ΔPa.pp are in the calculation regions shown in FIG. 8, and are as follows:

Definition of “Loss Coefficient”

fL=¼[{1+3.445/(Re·2de/L·¼)̂0.5}̂2−1]×(2de/L)
Wherein, Re: Reynold's number, de: equivalent diameter, and L: segment length.

Pressure Loss; ΔPa.pp

ΔPa.pp=2fL·(L/(2de))·pa uθ̂2×c×NL
Wherein, c: Coefficient of pressure loss correction, pa: air density, uθ: flow rate between segments, NL: total number of segments in depth direction in one pitch

Coefficient of heat transfer; hm.pp

Nu=3.77+[0.066·(Re·Pra·de/(2L))̂1.2]/[1+0.1·(Pra)̂0.87·(Re·de/(2L))̂0.7]
Nu=hm.pp·de/λa
Wherein, Pra: Air Prandtl number, λa: Coefficient of thermal conductivity of air
FIG. 6 shows the results of analyzing the changes in air pressure loss ΔPa based on the length L (mm) of each of the segments 10. Here, when the pressure loss base line (estimate) of the air pressure loss ΔPa (Pa) was set to 100.0 Pa, from the perspective of the relationship with the length L of each of the segments (strips) 10, the air pressure loss ΔPa (Pa) is preferably restricted to within the dotted lines illustrated in FIG. 6, and Sample Nos. 2 to 5 and No. 7 fall within that range. Due to the number of divisions within a single pitch of the segments 10 and the intervals in the row direction or, rather, the incline with respect to the airflow direction F, and the like, while these samples have air pressure loss that is relatively higher than that of Sample Nos. 1 and 6, it is possible to set each of them within the range of practical use.
On the other hand, FIG. 7 shows the results of analyzing the changes in the coefficient of heat transfer hm based on the length L (mm) of each of the segments (strips) 8. Here, when the coefficient of heat transfer base line (estimate) of the coefficient of heat transfer hm (W/m2K) was set to 400.0 Pa, from the perspective of the relationship with the length L of each of the segments (strips) 8, the preferable range of the coefficient of heat transfer hm is within the dotted lines illustrated in FIG. 6, and Sample Nos. 2 to 5 and No. 7 fall within that range. Due to the number of divisions within a single pitch of the segments 10 and the intervals in the row direction or, rather, the incline with respect to the airflow direction F, and the like, while these samples have a coefficient of heat transfer that is relatively higher than that of Sample Nos. 1 and 6, it is still possible to improve performance.
Furthermore, in FIG. 5, a performance comparison chart with a single offset fin is shown, evaluating the offset fins described above from the perspectives of both the coefficient of heat transfer and air pressure loss.
Here, the advantage (performance) of the arrangement of the segments 10 in each of the offset fins was evaluated on the basis of whether the pressure loss ratio (ΔPa.ratio) and the coefficient of heat transfer ratio (hm.ratio) satisfied the relationships below:
ΔPa/ΔPa.PP<1.0
hm/hm.PP>1.0
As a result, the offset fins of Sample Nos. 3 and 4 can be evaluated as being the most superior in terms of performance. The offset fins of Sample Nos. 3 and 4, compared to the offset fin of Sample No. 2, had a greater number of divisions of the segments 10 within a single pitch, or had a configuration in which the segments 10 were inclined at a predetermined angle (7°) with respect to the airflow direction F. From this, it is clear that, even though the pressure loss ratio (ΔPa.ratio) increases slightly, increasing the number of divisions of the segments 10 and/or inclining the segments 10 at a predetermined angle is effective in increasing the coefficient of heat transfer ratio (hm.ratio).
Particularly, it is clear from a comparison of Sample Nos. 6 and 7 that inclining the segments 10 is effective for improving the coefficient of heat transfer ratio.
Additionally, just as with the offset fins of Sample Nos. 3 and 4, it was discovered that the offset fins of Sample Nos. 2 and 5 fall within the evaluation region described above and that both the pressure loss ratio and the coefficient of heat transfer ratio are well within the region of practical use. In the offset fins of both Sample Nos. 2 and 5, the interval in the row direction of each of the segments 10 was set to two rows and the number of divisions n, in the direction orthogonal to the airflow direction F within a single pitch, of each of the segments 10 was set to three.
The interval in the row direction of each of the segments 10 was set to two rows or more and, for each of the segments 10, the thermal boundary layer generated at the leading edge of the segments 10 disposed on the upstream side in the airflow direction was prevented from affecting the segments arranged on the downstream side. From this, it was discovered that not inhibiting the leading edge effects of each of the segments 10 was effective in improving the coefficient of heat transfer hm on the air side, that is, the effects of locally increasing the coefficient of heat transfer at the leading edge portion can be maximized by the leading edge effects of each segment or, rather, the effects of the airflow colliding with the leading edge of each segment 10.
Additionally, as described above, in cases where each of the plurality of segments 10 are disposed in an offset manner with intervals therebetween of at least two rows along the airflow direction, it was discovered that, compared to offset fins such as those of Sample Nos. 6 and 7 where the stepped shape was configured to be a repeating arrangement with a three-step or four-step fold back resulting in segments 10 being present where the interval in the row direction was one row, it is preferable to configure each of the segments 10 with a stepped shape with three or more steps and a repeating arrangement so that all of the segments 10 are separated by an interval of two rows or greater such as those of Sample Nos. 2 to 5. This is clear as well from the fact that with the fin of Sample No. 9 (as with the fin of Sample No. 6, the stepped shape is configured to be a repeating arrangement with a four-step fold back) where the number of divisions within a single pitch is set to four, performance is lower than that of the fins of Sample Nos. 2 and 5.
From the preceding analysis results, it can be said that in order to increase the performance of the offset fin, the plurality of segments 10 disposed are preferably provided so as to satisfy the following three conditions, which the fins of Sample Nos. 2 to 5 fully satisfy.
A. Each of the plurality of segments 10 is disposed in an offset manner with intervals therebetween of at least two rows along the airflow direction.
B. The length L in the airflow direction of each of the segments 10 satisfies 0.5 mm≦L≦1.2 mm and more preferably satisfies 0.6 mm≦L≦1.0 mm.
C. The number of divisions of each of the segments 10 within a single pitch of the wave-shape fin is three or greater.
However, in cases where the number of divisions within a single pitch of each of the segments 10 is configured to be three or greater, the stepped shaped is preferably configured to be a repeating arrangement of a stepped shape with three or more steps. Note that, with respect to the number of divisions within a single pitch, the greater the number of divisions, the more difficult production will become. Therefore, three to four divisions is an optimal range. Additionally, while providing each of the segments 10 with an incline at a predetermined angle results in an increase in the coefficient of heat transfer, it also leads to a decrease in ease of production. Therefore, implementation of these features should be decided based on potential merits and demerits.
As described above, in the present embodiment, the plurality of the segments 10, each of which is an individual fin cut and lifted into strips from the rising surfaces 8 and falling surfaces 9 of the wave-shape fins constituting the offset fin 5, are disposed in an offset manner with intervals therebetween of at least two rows in the airflow direction F, and the length L in the airflow direction F of each of the segments 10 satisfies 0.5 mm≦L≦1.2 mm. Therefore, for each of the segments, the thermal boundary layer generated at the leading edge of the segments 10 arranged on the upstream side in the airflow direction F will be prevented from affecting the segments 10 arranged on the downstream side and, as a result of not inhibiting the leading edge effects of each of the segments 10, the leading edge effects of each segment 10, that is, the effects of the airflow colliding with the leading edge of each segment 10 and the coefficient of heat transfer hm increasing in a localized manner at that portion, can be maximized and, along with improving the coefficient of heat transfer hm on the air side and, by extension, improving heat exchanging performance, air side pressure loss ΔPa can be prevented and can be held to a level of practical use due to the length L of each segment 10 being optimized.
Additionally, due to the fact that the number of divisions, of each of the plurality of offset segments 10 within a single pitch of the wave-shape fin, is configured to be three or greater, the intervals between the fins can be narrowed and the speed of the air flow increased, and further improvements in the coefficient of heat transfer hm on the air side can be achieved.
As such, the performance of the offset fin 5 can be improved from both perspectives of the coefficient of heat transfer hm and the pressure loss ΔPa on the air side, and performance thereof can be further enhanced.
Particularly, due to the fact that each of the segments 10 having three or greater divisions within a single pitch is repeatedly arranged as a stepped shape with three or more steps, all of the segments 10 can be arranged in an offset manner with intervals therebetween of at least two rows in the airflow direction, effects caused in all the segments 10 by the thermal boundary layer of the upstream side segments 10 can be eliminated, and the leading edge effects can be maximized, leading to a steady improvement in the coefficient of heat transfer on the air side. Thus, further improvement of the heat exchanging performance of the offset fin can be achieved.
Furthermore, in the present embodiment, each of the segments 10 is inclined at a predetermined angle (7°) with respect to the airflow direction F. Therefore, the interval between each of the segments 10 is widened exactly by the amount of inclination, and the airflow is rectified. As a result, further improvement of the coefficient of heat transfer hm resulting from the leading edge effects of each of the segments 10 can be achieved and the effects of preventing air side pressure loss ΔPa can be maintained. As such, the performance of the offset fin 6 can be improved even more.
Additionally, the refrigerant heat-exchanger 1 of the present embodiment is configured so that the heat-exchanger offset fin 5 described above is disposed among the plurality of refrigerant tubes 4 that are arranged in parallel at a predetermined interval. Therefore, the heat exchange between the refrigerant flowing within the refrigerant tubes 4 and the air stream flowing on the offset fin 5 side can be further promoted due to the offset fin performance improvements, and the heat exchanging performance thereof can be improved. Thus, performance of the refrigerant heat-exchanger 1 applied to evaporators and condensers can be further improved, air conditioning performance can be improved, and also the space-saving of the unit can be achieved as a result of reducing the size of the evaporators and condensers.
Note that the present invention is not limited to the invention according to the embodiments as described above, and changes can be made as appropriate without departing from the gist thereof. For example, in the embodiment described above, a heat exchanger in which a plurality of refrigerant tubes are arranged between a pair of headers and an offset fin is disposed among these refrigerant tubes is given as an example of the refrigerant heat-exchanger, however it is obvious that a heat exchanger having a configuration in which flat tubes are formed into a tortuous shape by bending and offset fins are arranged among these parallel tubes, and the like, can be applied. Additionally, the refrigerant tubes may be refrigerant tubes of any configuration such as, extrusion molded tubes, laminate tubes, and the like.

REFERENCE SIGNS LIST

1 Refrigerant heat exchanger
4 Refrigerant tubes
5 Offset fin
8 Rising surface
9 Falling surface
10 Segment (strip)

Claims

1. A heat-exchanger offset fin which-is disposed among a plurality of refrigerant tubes arranged in parallel, wherein:

a plurality of segments, each of which is an individual fin cut and lifted into strips from rising surfaces and falling surfaces of a fin which is folded and formed into a wave-shape, are disposed in an offset manner with intervals therebetween of at least two rows in an airflow direction;

a length of each of the segments in the airflow direction satisfies 0.5 mm≦L≦1.2 mm, and a number of divisions of each segment within a single pitch of the wave-shape fin is three or greater.

2. The heat-exchange offset fin according to claim 1, wherein each of the segments having the number of divisions within a single pitch of the wave-shape fin of three or greater is repeatedly arrange d as a stepped shape with three or more steps.

3. The heat exchanger offset fin according to claim 1, wherein each of the segments are inclined at a predetermined angle with respect to the airflow direction.

4. A refrigerant heat-exchanger comprising the heat-exchanger offset fin described in claim 1 among a plurality of refrigerant tubes arranged in parallel at a predetermined interval.

5. The heat-exchanger offset fin according to claim 2, wherein each of the segments are inclined at a predetermined angle with respect to the airflow direction.

6. A refrigerant heat-exchanger comprising the heat-exchanger offset fin described in claim 2 among a plurality of refrigerant tubes arranged in parallel at a predetermined interval.

7. A refrigerant heat-exchanger comprising the heat-exchanger offset fin describe in claim 3 among a plurality of refrigerant tubes arranged in parallel at a predetermined interval.