HEAT EXCHANGER AND REFRIGERATION CYCLE APPARATUS

A heat exchanger includes a plurality of flat heat-transfer tubes and a corrugated fin placed between the plurality of flat heat-transfer tubes. Louvers in fin sections of the corrugated fin are divided into a first louver group formed further upstream in a direction of flow of air than a drain slit in the corrugated fin and a second louver group formed further downstream in the direction of flow of air than the drain slit. Plate portions of the first louver group and plate portions of the second louver group are inclined to a flat-plate portion in the fin sections and inclined in respective directions that are opposite to each other. The drain slit includes a plurality of drain slits formed between the first louver group and the second louver group at an interval in the direction of flow of air.

TECHNICAL FIELD

The present disclosure relates to a heat exchanger including a corrugated fin and to a refrigeration cycle apparatus.

BACKGROUND ART

For example, corrugated-fin-tube-type heat exchangers formed by alternately stacking flat heat-transfer tubes and corrugated fins are widespread. In a case in which such a heat exchanger is used as an evaporator, the surface temperature of a corrugated fin becomes lower than or equal to a freezing point, so that condensed water on a fin surface may freeze. The freezing of the condensed water on the fin surface mounts resistance to air passing through the heat exchanger, causing a deterioration in heat-transfer performance of the corrugated fin. To address this problem, there is a heat exchanger provided with a drain slit formed by a through hole in a corrugated fin so that condensed water on a fin surface is drained through the drain slit (see, for example, Patent Literature 1). It should be noted that the term “condensed water” refers to water having adhered to a surface of the heat exchanger as a result of condensation of moisture in the air.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2015-183908

SUMMARY OF INVENTION

Technical Problem

Although the heat exchanger of Patent Literature 1 has a drain slit through which condensed water on a fin surface is drained, enlarging an opening of the drain slit for improvement in drainage capacity invites a deterioration in heat-transfer performance due to a reduction in heat-transfer area while bringing about improvement in drainage capacity. The heat exchanger of Patent Literature 1 had room for improvement in terms of improving drainage capacity while maintaining heat-transfer performance.

To solve problems such as those noted above, the present disclosure has as an object to provide a heat exchanger that makes it possible to improve drainage capacity while maintaining heat-transfer performance and a refrigeration cycle apparatus.

Solution to Problem

A heat exchanger according to an embodiment of the present disclosure includes a plurality of flat heat-transfer tubes each formed in a flat shape in cross-section, provided with a plurality of flow passages formed by through holes, disposed to stand in an up-down direction, and placed side by side and spaced from one another in a direction orthogonal to a direction of flow of air; and a corrugated fin placed between the plurality of flat heat-transfer tubes. The corrugated fin is formed such that fin sections that are plate-shaped are joined together one after another in a wave shape in a tube axial direction of the plurality of flat heat-transfer tubes, the fin sections each have a drain slit formed such that the drain slit extends in a tube side-by-side placement direction that is a direction in which the plurality of flat heat-transfer tubes are placed side by side and through which water on an upper surface of the fin section falls for drainage, and a plurality of louvers each having a louver slit extending in the tube side-by-side placement direction and a plate portion inclined to a flat-plate portion that is tabular-shaped in the fin section, the plurality of louvers are divided into a first louver group formed further upstream in the direction of flow of air than the drain slit and a second louver group formed further downstream in the direction of flow of air than the drain slit, the plate portions of the first louver group and the plate portions of the second louver group are inclined to the flat-plate portion and inclined in respective directions that are opposite to each other, and the drain slit includes a plurality of drain slits formed between the first louver group and the second louver group at an interval in the direction of flow of air.

Further, a refrigeration cycle apparatus according to an embodiment of the present disclosure includes the aforementioned heat exchanger.

Advantageous Effects of Invention

In the heat exchanger according to an embodiment of the present disclosure, a plurality of drain slits are formed at an interval in the direction of flow of air between the first louver group and the second louver group. Moreover, the first louver group formed upstream of the plurality of drain slits in the direction of flow of air and the second louver group formed downstream of the plurality of drain slits in the direction of flow of air are inclined in opposite directions. For this reason, the heat exchanger according to an embodiment of the present disclosure makes it possible to improve drainage capacity while maintaining heat-transfer performance.

DESCRIPTION OF EMBODIMENTS

In the following, heat exchangers and a refrigeration cycle apparatus according to embodiments are described, for example, with reference to the accompanying drawings. Further, constituent elements given identical reference signs in the following drawings are identical or equivalent to each other, and these reference signs are adhered to throughout the full text of the embodiments described below. Moreover, the forms of constituent elements expressed in the full text of the specification are merely examples and are not limited to forms described herein. In particular, a combination of constituent elements is not limited solely to a combination in one embodiment, but constituent elements described in one embodiment can be applied to another embodiment. Further, in the following description, an upper part of a drawing is described as an “upper side”, and a lower part of a drawing is described as a “lower side”. Furthermore, directive terms (such as “right” and “left”) used to promote understanding are intended for descriptive purposes and are not intended to limit the present disclosure. Further, how high or low temperatures and humidities are is not determined in relation to particularly absolute values but relatively determined according to states, actions, or other conditions in apparatuses or other devices. Moreover, relationships in size between one constituent element and another in the drawings may be different from actual ones.

FIG.1is a diagram illustrating a configuration of a heat exchanger according to Embodiment 1. As shown inFIG.1, the heat exchanger10of Embodiment 1 is a parallel-pipe corrugated-fin-tube-type heat exchanger. The heat exchanger10includes a plurality of flat heat-transfer tubes1, a plurality of corrugated fins2, and a pair of headers3.

The pair of headers3are each a tube that is connected by pipes to other devices included in a refrigeration cycle apparatus, into and out of which refrigerant flows, and that causes the refrigerant to be divided or merged. The refrigerant is a fluid that serves as a heat exchange medium. The pair of headers3include a header3A and a header3B. The header3A and the header3B are placed one above the other and spaced from one another. In a case in which the heat exchanger10is used as an evaporator, liquid refrigerant passes through the upper header3B, and gas refrigerant passes through the lower header3A. In a case in which the heat exchanger10is used as a condenser, gas refrigerant passes through the upper header3B, and liquid refrigerant passes through the lower header3A.

Between the two headers3, the plurality of flat heat-transfer tubes1are placed perpendicular to each header3, and the plurality of flat heat-transfer tubes1are placed parallel to one another. The plurality of flat heat-transfer tubes1are placed side by side and equally spaced from one another in a direction orthogonal to a direction of flow of air In the following, the direction (right-left direction inFIG.1) in which the flat heat-transfer tubes1are placed side by side is referred to as “tube side-by-side placement direction”, and the axial direction (up-down direction inFIG.1) of the flat heat-transfer tubes1is referred to as “tube axial direction”.

Each of the flat heat-transfer tubes1has a flat shape in cross-section. Each of the flat heat-transfer tubes1is a heat-transfer tube of which an outer surface (hereinafter referred to as “flat surface”) of a long side of the flat cross-section has the shape of a planar surface and of which an outer surface of a short side of the flat shape has the shape of a curved surface. Each of the flat heat-transfer tubes1is a multi-hole heat-transfer tube having a plurality of refrigerant flow passages formed by through holes inside the tube. The flat heat-transfer tubes1are each disposed to stand in the up-down direction, have their through holes extending in the up-down direction, and communicate with the two headers3. Each of the flat heat-transfer tubes1is placed so that a long side of the flat cross-section extends along the direction of flow of air. Each flat heat-transfer tube1is joined to the two headers3by having both ends inserted in and brazed to insertion holes (not illustrated) opened separately in each of the two headers3. A usable example of a brazing filler metal is an aluminum-containing brazing filler metal.

Note here that in a case in which the heat exchanger10is used as an evaporator, low-temperature and low-pressure refrigerant flows through the refrigerant flow passages inside the flat heat-transfer tubes1. In a case in which the heat exchanger10is used as a condenser, high-temperature and high-pressure refrigerant flows through the refrigerant flow passages inside the flat heat-transfer tubes1. The arrows inFIG.1indicate the flow of refrigerant in a case in which the heat exchanger10is used as an evaporator.

Embodiment 1 is intended to describe drainage of condensed water that is produced on fin surfaces in a case in which the heat exchanger10is used as an evaporator For this reason, the following describes the flow of refrigerant in the heat exchanger10in a case in which the heat exchanger10is used as an evaporator. As indicated by the arrows inFIG.1, the refrigerant flows into the header3A via a pipe (not illustrated) through which the refrigerant is supplied from an external device (not illustrated) to the heat exchanger10. The refrigerant having flowed into the header3A is distributed and passes through each flat heat-transfer tube1. The flat heat-transfer tube1exchanges heat between the refrigerant passing through the inside of the tube and outside air that is external atmospheric air passing through outside the tube. At this time, the refrigerant removes heat from the atmospheric air while passing through the flat heat-transfer tube1. The refrigerant subjected to heat exchange through each flat heat-transfer tube1flows into the header3B and merges inside the header3B. The refrigerant having merged inside the header3B is refluxed to the external device (not illustrated) through a pipe (not illustrated) connected to the header3B.

Each of the corrugated fins2is placed between one of the flat heat-transfer tubes1and another. The corrugated fins2are disposed to expand the area of heat transfer between the refrigerant and the outside air. Each of the corrugated fins2is formed in a pleated wave shape by a tabular-shaped fin material being subjected to corrugating and bent into a zigzag pattern with repeated mountain folds and valley folds. Note here that bent portions in undulations formed in a wave shape serve as apices of the wave shape. In Embodiment 1, the apices of each of the corrugated fins2are arranged in a height direction. Parts (a) to (e) ofFIG.1will be described later.

FIG.2is a schematic perspective view of part of the heat exchanger according to Embodiment 1. The arrow outlined with a blank inside inFIG.2indicates the direction of flow of air.FIG.3is a schematic cross-sectional view of a flat-plate portion of a corrugated fin according to Embodiment 1 as taken along the direction of flow of air. The diagonal solid arrows inFIG.3indicate the flow of condensed water.

The corrugated fin2is joined to flat surfaces1aof flat heat-transfer tubes1except for an upstream protruding portion2aprotruding further upstream in the direction of flow of air than the flat heat-transfer tubes1. These junctions are brazed and joined by a brazing filler metal. The corrugated fin2is formed by a fin material such as an aluminum alloy. Moreover, the fin material by which the corrugated fin2is formed has a surface cladded with a brazing filler metal layer. The clad brazing filler metal layer is made mainly of, for example, a brazing filler metal containing aluminum-silicon aluminum. Note here that the thickness of the fin material by which the corrugated fin2is formed ranges, for example, from approximately 50 μm to 200 μm.

The corrugated fin2is formed such that fin sections24, which are plate-shaped, are joined together one after another in a wave shape in the tube axial direction. The corrugated fin2is shaped such that the fin sections24are joined together one after another in the tube axial direction at alternately reversed inclinations when the corrugated fin2is seen from an angle parallel with the direction of flow of air. Each of the fin sections24includes a flat-plate portion21, which is tabular-shaped, and apices20curved at both respective ends of the flat-plate portion21in the tube side-by-side placement direction. The corrugated fin2has its apices20joined to the flat heat-transfer tubes1by making surface contact with the flat surfaces1aof the flat heat-transfer tubes1,

Each of the fin sections24has a plurality of louvers22formed and arranged in the direction of flow of air. Each of the louvers22includes a louver slit22athrough which air passes and a plate portion22bthat guides air to the louver slit22a. The plate portion22bis inclined to the flat-plate portion21. The louver slit22aand the plate portion22bare each formed in the shape of a rectangle extending in the tube side-by-side placement direction. The louver22is formed by the plate portion22bbeing cut and raised from the flat-plate portion21.

The plurality of louvers22are divided into a first louver group22A formed further upstream in the direction of flow of air than the after-mentioned drain slits23formed in the fin section24and a second louver group22B formed further downstream in the direction of flow of air than the drain slits23. The drain slits23are openings through which water having accumulated on an upper surface of the fin section24, particularly the almost horizontal flat-plate portion21, falls onto a lower surface.

Note here that, inFIG.3, I1is an imaginary auxiliary line to the midpoint of the through-thickness direction of a plate portion22bof the first louver group22A and12is an imaginary auxiliary line to the midpoint of the through-thickness direction of a plate portion22bof the second louver group22B. As shown inFIG.3, when the flat-plate portion21has its upper and lower surfaces defined with reference to a direction of gravitational force g, the plate portion22bof the first louver group22A and the plate portion22bof the second louver group22B are inclined in directions set so that the auxiliary line11and the auxiliary line12to the respective midpoints intersect each other below the lower surface. In other words, the plate portion22bof the first louver group22A and the plate portion22bof the second louver group22B are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other. Since the plate portions22bof the louvers22are formed in such directions, condensed water having flowed along the plate portions22bof the louvers22formed in a fin section24is guided toward the drain slits23in a next fin section24below. Therefore, the heat exchanger10, which has this configuration, can bring about great improvement in drainage capacity.

Each of the fin sections24has drain slits23through which condensed water produced on the fin section24is drained. The drain slits23are through holes opened in the corrugated fin2. Each of the drain slits23is formed in the shape of a rectangle that extends in the tube side-by-side placement direction, that is, a direction orthogonal to the direction of flow of air. The drain slits23are formed in a central portion of the fin section24in the direction of flow of air excluding the upstream protruding portion2a. AlthoughFIG.1shows an example of the formation of drain slits23in two rows in the direction of flow of air, the row counts of drain slits23may be one or may be larger than or equal to three. In the case of the formation of drain slits23in a plurality of rows, a region of the fin section24situated between each adjacent two of the rows is a heat-transfer region503. In the case of the formation of drain slits23in a plurality of rows, the drain slits23of the plurality of rows are adjacent to each other in a central portion of the fin section24in the direction of flow of air excluding the upstream protruding portion2a. The term “adjacent to each other” means that there is no louver22between the drain slits23.

The heat-transfer region503between the drain slits23of the plurality of rows is typically as flat as the flat-plate portion21. Further, regions as flat as the flat-plate portion21may be formed between one of the drain slits23of the plurality of rows situated furthest upstream in the direction of flow of air and the first louver group22A and between one of the drain slits23of the plurality of rows situated furthest downstream in the direction of flow of air and the second louver group22b. The row counts of drain slits23is synonymous with the number of drain slits23, and in the following, drain slits23are counted using either of the expressions “row counts” and “number”.

In a case in which the heat exchanger10is used as an evaporator, the temperatures of surfaces of the flat heat-transfer tubes1and the corrugated fins2are lower than the temperature of air passing through the heat exchanger10. This causes moisture in the air to condense into condensed water4on the surfaces of the flat heat-transfer tubes1and the corrugated fins2. Condensed water4produced on a surface of the fin section24of a corrugated fin2flows down onto a next fin section24below through the drain slits23. At this time, in a region of the surface of the fin section24where there is a large amount of condensed water4, the condensed water4easily flows on the surface of the fin section24and easily flows down through the drain slits23. Meanwhile, in a region of the surface of the fin section24where there is a small amount of condensed water4, the condensed water4hardly flows on the surface of the fin section24and easily builds up by being retained on the surface of the fin section24. It is known that such building-up occurs, although the fin section24is inclined when the fin section24is seen from an angle parallel with the direction of flow of air. To address this problem, Embodiment 1 brings about improvement in drainage capacity by locating drain slits23in the following positions.

FIG.4is an explanatory diagram of the positions of drain slits in fin sections of a corrugated fin according to Embodiment 1. Parts (a) to (e) ofFIG.4correspond to fin sections24located in positions indicated by respective parts (a) to (e) ofFIG.1. That is, parts (a) to (e) ofFIG.4show fin sections24adjacent to one another in the tube axial direction. Parts (a) to (c) ofFIG.4each show a configuration in which there are a total of four drain slits formed by drain slits23being formed in two rows in the direction of flow of air with each row formed by two drain slits23in the tube side-by-side placement direction. Parts (d) and (e) ofFIG.4each show a configuration in which there are a total of two drain slits formed by drain slits23being formed in two rows each formed by one drain slit23.

As shown inFIG.4, the drain slits23are placed so that drain slits23in fin sections24adjacent to each other in the tube axial direction are displaced from each other in the tube side-by-side placement direction. Such placement of the drain slits23causes drained condensed water to flow in the following way through the corrugated fin2. The flow of condensed water is described here with reference to two fin sections24adjacent one above the other.

Condensed water produced on the surface of the upper fin section24flows down onto the lower fin section24through the drain slits23in the upper fin section24. Note here that, as mentioned above, drain slits23in fin sections24adjacent to each other in the tube axial direction are displaced from each other in the tube side-by-side placement direction. For this reason, part of a region directly below the drain slits23in the upper fin section24is a portion of the lower fin section24in which no drain slits23are formed and a portion in which condensed water is produced and retained. Therefore, condensed water4having fallen onto the lower fin section24through the drain slits23in the upper fin section24merges with condensed water4having become stagnant by being retained on the surface of the lower fin section24. The condensed water4, which has increased in amount by merging, comes to easily flow down, and is drained through the drain slits23in the lower fin section24. The aforementioned flow of condensed water is repeated in sequence in the up-down direction between two fin sections24adjacent to each other in the tube axial direction, and less condensed water4is thus retained on the surface of each fin section24. This leads to efficient drainage.

Incidentally, in each of parts (a) to (c) ofFIG.4, the drain slits23are formed to, when the drain slits23are seen from an angle parallel with the tube axial direction, overlap the apices20at both respective ends of the flat-plate portion21in the tube side-by-side placement direction. In each of parts (d) and (e) ofFIG.4,24of the drain slits are formed to, when24of the drain slits are seen from an angle parallel with the tube axial direction, overlap the apex20at one end of the flat-plate portion21in the tube side-by-side placement direction. In the following, a portion of a fin section24in which a drain slit23overlaps an apex20is referred to as “drain apex20a”, and a portion of a fin section24in which a drain slit23does not overlap an apex20is referred to as “non-drain apex20b” for explanatory convenience.

In each of parts (a) to (c) ofFIG.4, the drain slits23form two rows each formed by two drain slits23overlapping the apices20at both respective ends of the fin section24in the tube side-by-side placement direction. For this reason, in each of parts (a) to (c) ofFIG.4, the fin section24has four drain apices20a.

In part (d) ofFIG.4, the drain slits23form two rows each formed by one drain slit23overlapping the apex20at one end (right inFIG.4) of the fin section24in the tube side-by-side placement direction. For this reason, the fin section24of part (d) ofFIG.4has two drain apices20a. In part (d) ofFIG.4, each row is not formed by any one drain slit23overlapping the apex20at the other end (left inFIG.4) of the fin section24in the tube side-by-side placement direction. For this reason, the fin section24of part (d) ofFIG.4has two non-drain apices20b.

In part (e) ofFIG.4, the drain slits23form two rows each formed by one drain slit23overlapping the apex20at one end (left inFIG.4) of the fin section24in the tube side-by-side placement direction. For this reason, the fin section24of part (e) ofFIG.4has two drain apices20a. In part (e) ofFIG.4, each row is not formed by any one drain slit23overlapping the apex20at the other end (right inFIG.4) of the fin section24in the tube side-by-side placement direction. For this reason, the fin section24of part (d) ofFIG.4has two non-drain apices20b.

Since each of the apices20is a portion formed by bending a tabular-shaped fin material into the shape of letter V, that apex20has a narrow inner space (seeFIG.6, which will be described later). Therefore, condensed water4produced on an inner surface of an apex20easily builds up by being retained in the inner space of the apex20by the surface tension of the condensed water4. For this reason, the drain apices20aof the apices20make it possible to prevent condensed water from building up in the inner spaces of the apices20and bring about improvement in drainage capacity. It should be noted that although a larger number of drain apices20afurther bring about an effect of improvement in drainage capacity, increasing the number of drain apices20ainvites a deterioration in heat-transfer capacity, as the apices20are portions that are joined to the flat heat-transfer tubes1for heat transfer. Therefore, it is only necessary to determine the proportion of the number of drain apices20ato the number of non-drain apices20bin consideration of drainage capacity and heat-transfer capacity. Further, increasing the number of drain apices20ainvites a deterioration of strength by reducing the junctions between the fin sections24and the flat heat-transfer tubes1. For this reason, a configuration is desirable in which there is a well-balanced allocation of drain apices20aand non-drain apices20bthroughout the corrugated fin2.

Such a configuration makes it possible to expect improvement in drainage capacity while reducing deterioration of heat-transfer performance without decreasing the area of contact between the flat heat-transfer tubes1and the corrugated fin2.

AlthoughFIG.4has shown examples in each of which the drain slits23are formed in positions at which, when the drain slits23are seen from an angle parallel with the tube axial direction, the drain slits23overlap the apices20at both respective ends of the flat-plate portion21in the tube side-by-side placement direction, the drain slits23may be formed in positions indicated byFIG.5.

FIG.5is a diagram showing a modification of the heat exchanger according to Embodiment 1. Part (a) ofFIG.5shows an upper one of fin sections24adjacent to each other in the tube axial direction, and part (b) ofFIG.5shows a lower one of the fin sections24adjacent to each other in the tube axial direction.FIG.6is an explanatory diagram of the flow of condensed water in the configuration ofFIG.5.

InFIG.5, the drain slits23are formed in positions, when the drain slits23are seen from an angle parallel with the tube axial direction, at which the drain slits23do not overlap the apices20at both respective ends of the flat-plate portion21in the tube side-by-side placement direction.

The flow of condensed water in the modification ofFIG.5is described with reference toFIG.6. Of the two fin sections24that forms the apex20surrounded by a dotted circle inFIG.6, the upper fin section24A corresponds to the fin section24of part (a) ofFIG.5, and the lower fin section24B corresponds to the fin section24of part (b) ofFIG.5.

Since the fin section24A and the fin section24B are placed such that the drain slits23do not overlap the apices20when the drain slits23are seen from an angle parallel with the tube axial direction, the apex20between the fin section24A and the fin section24B is a non-drain apex20b. For this reason, the surface tension of the condensed water4causes condensed water to easily build up in the inner space of the non-drain apex20b. In the following, a portion in which condensed water4has built up is referred to as “apex built-up portion30”. The following describes drainage of the condensed water4having built up in the apex built-up portion30.

Condensed water produced and accumulated on the surface of a fin section24C above the fin section24A flows down toward the fin section24A through the drain slit23in the fin section24C. Note here that the drain slit23formed in the fin section24C and the drain slit23formed in the fin section24A are displaced from each other in the tube side-by-side placement direction (right-left direction inFIG.6). For this reason, condensed water4having flowed down through an end (here, a left end inFIG.6) of the drain slit23in the fin section24C in the tube side-by-side placement direction passes through the drain slit23in the fin section24A and merges with the condensed water4having built up in the apex built-up portion30. This merging causes the condensed water4in the apex built-up portion30to flow out from the apex built-up portion30as a result of the breakage of the surface tension and flow on the surface of the fin section24B as indicated by a dotted arrow inFIG.6. This manner can bring about improvement in drainage capacity of fin sections24whose drain slits23are formed in positions at which the drain slits23do not overlap apices20when the drain slits23are seen from an angle parallel with the tube axial direction.

[Relationship Between Row Counts of Drain Slits23and Drainage Capacity]

FIG.7is a diagram showing an example of a result of analysis of drainage characteristics according to the row counts of drain slits. InFIG.7, the vertical axis represents the amount of water remaining in a heat exchanger, and the horizontal axis represents time. A higher speed of reduction in the amount of remaining water indicates higher drainage capacity. Drainage capacity is the amount of water that is drained per unit time. In general, measurements of drainage capacity are made in the following manner. An experimental model of a heat exchanger having fin sections each having a drain slit23forming one row, an experimental model of a heat exchanger having fin sections each including drain slits23each having the same opening area and forming two rows, and an experimental model of a heat exchanger having fin sections each including drain slits23each having the same opening area and forming three rows are fabricated. Then, each of the heat exchangers is put into water in a tank and taken out again, and the amount of water remaining in each heat exchanger is measured with passage of time.FIG.7is a tabulation of examples of computational results yielded by simulating the aforementioned test evaluations using a two-phase gas-liquid three-dimensional analysis developed by the inventors.

It is found fromFIG.7that a larger row counts of drain slits23further brings about higher drainage capacity. A reason for this is that the formation of drain slits23in a plurality of rows makes it possible to increase the total opening area of drain slits23in one fin section24.

Further, in one example of a result of analysis by the inventors, a comparison of drainage capacity between a case in which two drain slits23were provided and a case in which one drain slit23having the total opening area of the two drain slits23was provided showed that higher drainage capacity can be attained in the case in which the two drain slits23were provided. According to an analysis by the inventors, it was found that this improvement in drainage capacity is brought about by the following mechanism. Even with an increase in opening area of a drain slit23, an area in the vicinity of the center of the drain slit23does not contribute to drainage, and in actuality, water flows down along an inner peripheral portion of the drain slit23. Therefore, an increase in opening area of a drain slit23is slightly effective in bringing about improvement in drainage capacity and, on the other hand, causes a great deterioration in performance due to a reduction in heat-transfer area. Configuring drain slits23in a plurality of rows so that the drain slits23have longer inner peripheral lengths is thus effective in bringing about improvement in drainage capacity. This allows the heat exchanger10to improve drainage capacity while reducing deterioration of heat-transfer performance.

Further, the separation of drain slits23to which two louver groups opposite in inclination to each other are situated close is considered to bring about an effect of enhancing drainage with a small drain opening area. According to an experiment and an analysis by the inventors, it was found that compatibility between improvement in drainage capacity and heat-transfer performance cannot be necessarily achieved by simply increasing the opening area. A reason for this is that an increase in opening area causes a reduction in heat-transfer area and results in a deterioration in heat exchanger performance. According to an analysis by the inventors, it was found out that the wetted perimeter length of a drain slit is important for drainage.

According to this result of analysis, an increase in wetted perimeter length can be better achieved by continuously providing small drain slits than by placing a drain slit having a large opening, and improvement in drainage capacity can be brought about. On the basis of this thought, the wetted perimeter length of a drain slit23per louver group can be increased, especially as two louver groups opposite in inclination to each other come close to respective drain slits23. This makes it possible to improve drainage capacity while minimizing as possible the opening area of a drain slit23.

The foregoing allows the heat exchanger10to, by having drain slits23in a plurality of rows between the first louver group22A and the second louver group22B, improve drainage capacity while maintaining heat-transfer performance.

[Relationship Between Ratio of Inter-Louver Air Passage Cross-Sectional Area AL to Drain Slit Opening Area as and Drainage Velocity]

The inventors found out through an experiment and an analysis that there is a relationship between the ratio of an inter-louver air passage cross-sectional area AL to a drain slit opening area As and drainage velocity. This point is explained below.

FIG.8is a diagram showing an example of a graph representing a relationship between the ratio of an inter-louver air passage cross-sectional area AL to a drain slit opening area As and drainage capacity. Drainage capacity is the amount of water that is drained per unit time, and higher drainage capacity means that a larger amount of water is drained per unit time.FIG.8shows as an example a graph of a result of analysis showing a relationship in a case in which drainage capacity is defined as 100% in a case in which the ratio of the inter-louver air passage cross-sectional area AL to the drain slit opening area As is 0.25. As in the case ofFIG.7, this result of analysis is a tabulation of examples of computational results yielded by putting heat exchangers into water in a tank, taking them out again, and calculating, at a given point of time, the amount of water remaining in each heat exchanger.FIG.9is a diagram showing the dimensions of each component for use in a description of the relationship ofFIG.8, and is a schematic plan view of part of a heat exchanger.FIG.10is an explanatory diagram of the dimensions of each component for use in the description of the relationship ofFIG.8, and is a schematic cross-sectional view of a fin section as taken along the direction of flow of air.

Drainage velocity is greatly affected by the ratio of the inter-louver air passage cross-sectional area AL to the drain slit opening area As. The inter-louver air passage cross-sectional area AL is defined as NL×Ls×Lw=NL×((Lp×sin θ)−t)×Lw. The drain slit opening area As is defined as Ns×Sw×Ss.

In these formulas,NL [−] is the number of louvers22,θ [rad] is the angle of a plate portion22binclined to a flat-plate portion21(hereinafter referred to as “louver angle”),Lp [mm] is the pitch between adjacent louvers22,Lw [mm] is the width of a louver22in the tube side-by-side placement direction (hereinafter referred to as “louver width”),t [mm] is the thickness of a corrugated fin,Ns [−] is the row counts of drain slits23,Sw [mm] is the width of a drain slit23in the tube side-by-side placement direction (hereinafter referred to as “drain slit width”), andSs [mm] is the length of a drain slit23in the direction of flow of air (hereinafter referred to as “drain slit length”).

With AL/As being greater than or equal to 4, a decrease in value of AL/As leads to a rise in drainage velocity and an increase in rate of the rise. Therefore, with the inter-louver air passage cross-sectional area AL being constant, an increase in the drain slit opening area As leads to a greater effect of improvement in drainage velocity. For this reason, increasing the drain slit opening area As by providing drain slits23in a plurality of rows makes it possible to increase drainage velocity.

Note, however, that with AL/As lowered to less than 1, the rate of rise in drainage velocity to an increase in the drain slit opening area As decreases, although drainage velocity can be increased. A reason for this is that with AL/As being less than 1, the drain slit opening area As exceeds the inter-louver air passage cross-sectional area AL, so that the amount of water that is drained through the drain slits23is large and limits are put on the characteristics of drainage through the louvers22. Further, with AL/As being less than 1, heat-transfer performance decreases as the drain slit opening area As increases, albeit with high drainage velocity and high drainage capacity. For this reason, in view of a balance between drainage capacity and heat-transfer performance, it is preferable that AL/As≥1.

Meanwhile, with AL/As being greater than 4, drainage velocity does not increase greatly although the drain slit opening area As increases. For this reason, making AL/As greater than 4 is not effective in bringing about improvement in drainage capacity. A possible reason why drainage velocity does not increase greatly although the drain slit opening area As increases is that condensed water guided by the louvers22cannot be sufficiently handled by the drain slits23because the inter-louver air passage cross-sectional area AL is too great for the drain slit opening area As.

The foregoing makes it possible, with AL/As being greater than or equal to 1 and less than or equal to 4, to effectively improve drainage capacity and ensure heat-transfer performance by providing drain slits23. The graph of the relationship ofFIG.8also applies to a corrugated fin2, such as that described in Embodiment 4 below, in which the upstream protruding portion2aof a fin section24is thickened. Further, the graph of the relationship ofFIG.8also applies to a corrugated fin2provided with louvers22and drain slits23regardless of the number or placement of drain slits23. Therefore, a heat exchanger having corrugated fins2provided with louvers22and drain slits23and satisfying 1≤AL/As≤4 can improve drainage capacity while maintaining heat-transfer capacity. InFIGS.9and10, hs denotes the length of the heat-transfer region503(indicated by half-tone dot meshing inFIG.9) in the direction of flow of air. This length hs is described below.

[Relationship Between Length Hs of Heat-Transfer Region503in Direction of Flow of Air and Length Ss of One Drain Slit in Direction of Flow of Air]

In a case in which drain slits23are formed in a plurality of rows, a heat-transfer region503(seeFIGS.9and10) is formed between drain slits. The heat-transfer region503is low in heat-transfer efficiency as a heat transfer surface, as it is a region surrounded by the drain slits23. However, the heat-transfer region503generates a vortex and exerts a heat-transfer enhancement effect downstream of the heat-transfer region503through turbulence enhancement. Because of the characteristics of turbulence enhancement, improvement in heat-transfer performance can be brought about when the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air. Further, according to an analysis by the inventors, improvement in drainage capacity can be brought about as will be described below when the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air.

The distance between drain slits23adjacent to each other in the direction of flow of air becomes shortened when the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air. When the distance between drain slits23adjacent to each other in the direction of flow of air becomes shortened, drops of water falling from the drain slits23merge into a single great drop of water and fall. That is, the two narrow drain slits23serve as one wide slit. Therefore, the effect of improvement in drainage capacity is considered to be greater when the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air.

The effect of improvement in drainage capacity is considered to be brought about when the length hs of the heat-transfer region503in the direction of flow of air is only slightly longer than the length Ss of a drain slit23in the direction of flow of air A reason for this is that the louvers22situated close to the respective drain slits23are inclined in opposite directions and the respective drain slits23are separate from each other. However, when the length hs of the heat-transfer region503in the direction of flow of air becomes far longer than the length Sa of a drain slit23, condensed water tends to remain on the heat-transfer region503and drops of waterfall separately from each of the drain slits23, although there is a benefit from the standpoint of strength increase. For this reason, it is considered that the effect of improvement in drainage capacity decreases when the length hs of the heat-transfer region503in the direction of flow of air becomes longer than the length Ss of a drain slit23in the direction of flow of air. In sum, the formation of a plurality of drain slits23in the direction of flow of air is important to bringing about the effect of improvement in drainage capacity, and it is even more desirable to shorten the distance between drain slits23to minimize as possible a reduction in heat-transfer area.

For reasons similar to those noted above, it is also preferable that the distance between the louver group22A and a drain slit23and the distance between the louver group22B and a drain slit23be short too. If the heat-transfer region503and the drain slits23have flat regions that are long in the direction of flow of air, condensed water tends to remain. It is thus more desirable that the distances in the direction of flow of air between the drain slit23situated furthest upstream in the direction of flow of air and the first louver group22A and between the drain slit23situated furthest downstream in the direction of flow of air and the second louver group22bbe each for example made shorter than or equal to the length of one louver22in the direction of flow of air.

Further, the heat-transfer region503and the drain slits23are alternately present in the direction of flow of air. When this configuration is looked at differently, this configuration is equivalent to a configuration in which a narrow bridge extending in the tube side-by-side placement direction (right-left direction inFIG.9) is built in the middle of one large hole in the direction of flow of air and the large hole is divided into a plurality of holes. Moreover, this bridge is equivalent to the heat-transfer region503. Setting up a configuration in which the heat-transfer region503equivalent to a narrow bridge is provided as a mechanism for improvement in drainage capacity is considered to make it easy for water to be guided along the heat-transfer region503toward the center of the space between the two drain slits23in the direction of flow of air

Water having fallen from the vicinity of the center of the space between drain slits23in one fin section24falls onto the vicinity of the center of the space between drain slits23in a next fin section24below and merges with water guided from another fin section24and falls onto a further next fin section24below. As a result of that, even when the plurality of fin sections24are separated one above the other, smooth drainage through the drain slits23in the up-down direction is achieved. That is, the heat-transfer region503located between the drain slits23or, in other words, a portion of the flat-plate portion21located between the drain slits23also serves as a water conduit. In the following, a portion of the flat-plate portion21located between the drain slits23is sometimes referred to as “water conduit21A”. The water conduit21A has the shape of a long plate whose long side extends in the tube side-by-side placement direction and whose short side extends in the direction of flow of air.

According to the foregoing, a heat exchanger in which the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air can improve drainage capacity while maintaining heat-transfer capacity. In a case in which three or more drain slits23are provided, a plurality of drain slits23need only be provided at intervals that are each shorter than the length Ss of a drain slit23in the direction of flow of air.

Incidentally, the heat-transfer region503acts as a holder to inhibit warpage deformation of a fin material from occurring during punching of drain slits23through the fin material. This point is explained with reference to a corrugated fin of a comparative example including no heat-transfer region503.

FIG.11is an explanatory diagram of warpage deformation during punching in the corrugated fin of the comparative example.FIG.11shows a fin material yet to be subjected to corrugating. Dotted lines extending in a longitudinal direction inFIG.11indicate border lines between fin sections.

The fin material500of the comparative example does not include a heat-transfer region503but has one large opening500athat is to become a drain slit. The opening500ais disposed in a central part of the fin material500in the direction of flow of air excluding the upstream protruding portion2a. For this reason, the opening500adeviates to one side of the fin material500from a center line504in the direction of flow of air. When the opening500adeviates to one side in this manner, moment is produced on the side (upper side inFIG.11) to which the opening500adeviates, and warpage of the fin material500occurs, resulting in deformation.

On the other hand, a corrugated fin2of Embodiment 1 is equivalent to a configuration in which one large opening500ain the comparative example is divided into a plurality of small openings. In this configuration, a heat-transfer region503is formed between small openings. In other words, a fin material portion that is not a hole is formed between small openings. For this reason, this fin material portion acts as a holder to inhibit warpage deformation, and the corrugated fin2of Embodiment 1 can improve warpage deformation.

According to an experiment and an analysis by the inventors, it was found that louver angles greatly affect drainage capacity. This point is explained below.

FIG.12is a diagram showing an example of a result of analysis of drainage characteristics according to louver angles. InFIG.12, the vertical axis represents the amount of water remaining in a heat exchanger, and the horizontal axis represents time. A higher speed of reduction in the amount of remaining water indicates higher drainage capacity. This analysis is conducted in the following manner. A computation model of a heat exchanger having fin sections provided with louvers having a louver angle of 15 degrees, a computation model of a heat exchanger having fin sections provided with louvers having a louver angle of 20 degrees, a computation model of a heat exchanger having fin sections provided with louvers having a louver angle of 30 degrees, and a computation model of a heat exchanger having fin sections provided with louvers having a louver angle of 40 degrees are prepared. Then, the heat exchangers are put into water in a tank and taken out again, and the amount of water remaining in each heat exchanger is measured with passage of time using a two-phase gas-liquid three-dimensional analysis developed by the inventors. The result of analysis ofFIG.12is a tabulation of these results of measurement.

It is found fromFIG.12that an increase in louver angle leads to an increase in speed of reduction in the amount of remaining water and higher drainage capacity. A possible reason for this is that an increase in louver angle leads to a greater gravitational drainage effect to facilitate the breakage of surface tension of condensed water on the surfaces of the louvers22. Moreover, while an increase in louver angle leads to an increase in speed of reduction in the amount of remaining water, the degree of the rise relatively decreases once the louver angle exceeds 30 degrees. Further, an increase in louver angle leads to an increase in air passage resistance on the plate portions22bof the louvers22, making it hard for air to flow. Therefore, in view of compatibility between improvement in drainage capacity and ease of flow of air, it is preferable that the louver angle range from 15 degrees to 30 degrees.

As mentioned above, it is desirable that a corrugated fin2be formed such that there is a well-balanced mixture of drain apices20aand non-drain apices20b. In achieving such a configuration, a fin material yet to be subjected to corrugating needs only be processed so that drain slits23are placed in any of the following patterns. Four patterns of placement of drain slits23in a fin material are described below with reference toFIGS.13to16below.FIGS.13to16below show tabular-shaped fin materials yet to be subjected to corrugating. Further, dotted lines extending in a longitudinal direction inFIGS.13to16indicate border lines I3between fin sections.

A main mechanism for drainage of condensed water in a corrugated fin2is such that the louvers22cause the condensed water to flow down in the direction of flow of air and the water is collected by the drain slits23for drainage. For this reason, even if the drain slits23are identical in opening area and wetted perimeter length to each other, improvement in drainage capacity can be brought about while a reduction in heat-transfer area is minimized as possible, provided the drain slits23have shapes whose long sides extend in the tube side-by-side placement direction and whose short sides extend in the direction of flow of air. In consideration of processability or other properties, it is thus preferable, for example, that the drain slits23have rectangular shapes as illustrated inFIGS.4,5,9, and18or other drawings.

FIG.13is an explanatory diagram of a pattern of placement 1 of openings for drain slits in a corrugated fin according to Embodiment 1. It is a diagram showing a fin material of.

In the pattern of placement 1, the width L2of an opening23athat is to become a drain slit23is longer than the length L1of a fin section24in the tube side-by-side placement direction. The openings23aof adjacent fin sections24are equally spaced from one another. That is, the length L3of each space is the same in every place in a direction parallel with the length of the fin material50. The openings23aare placed across the border lines I3. A fin material50yet to be subjected to corrugating is processed so that openings23athat are to become drain slits23are sized and placed in the foregoing pattern, and a corrugated fin2subjected to corrugating thus can be formed such that there is a well-balanced mixture of drain apices20aand non-drain apices20b.

FIG.14is an explanatory diagram of a pattern of placement 2 of openings for drain slits in a corrugated fin according to Embodiment 1.

In the pattern of placement 2, the width L2of an opening23athat is to become a drain slit23is shorter than the length L1of a fin section24in the tube side-by-side placement direction. The openings23aof adjacent fin sections24are equally spaced from one another. That is, the length L3of each space is the same in every place in a direction parallel with the length of the fin material50. It should be noted that the length L3is a value other than a value obtained by subtracting L2from L1. A reason for this is that if L3is a value obtained by subtracting L2from L1, there is a possibility that all apices20are either drain apices20aor non-drain apices20binstead of being a mixture of drain apices20aand non-drain apices20b. A fin material50yet to be subjected to corrugating is processed so that openings23athat are to become drain slits23are sized and placed in the foregoing pattern, and a corrugated fin2subjected to corrugating thus can be formed such that there is a well-balanced mixture of drain apices20aand non-drain apices20b.

FIG.15is an explanatory diagram of a pattern of placement 3 of openings for drain slits in a corrugated fin according to Embodiment 1.

In the pattern of placement 3, the width L2of an opening23athat is to become a drain slit23is shorter than the length L1of a fin section24in the tube side-by-side placement direction. Moreover, the openings23aof adjacent fin sections24are not equally spaced from one another. That is, the length L3of each space is different in every place in a direction parallel with the length of the fin material50. The pattern3is formed such that with one cycle being a pattern of placement having five openings23ain a direction parallel with the length of the fin material50, this pattern of placement is periodically repeated in a direction parallel with the length of the fin material50.

A fin material50yet to be subjected to corrugating is processed so that openings23athat are to become drain slits23are sized and placed in the foregoing pattern, and a corrugated fin2subjected to corrugating thus can be formed such that there is a well-balanced mixture of drain apices20aand non-drain apices20b. In particular, because the proportion of drain apices20ato non-drain apices20bin one corrugated fin2can be adjusted by adjusting L3, a balance between drainage capacity and heat-transfer performance can be achieved on the basis of design.

FIG.16is an explanatory diagram of a pattern of placement 4 of openings for drain slits in a corrugated fin according to Embodiment 1.

In the pattern of placement 4, the width L2of an opening23athat is to become a drain slit23is different in every place. Moreover, the openings23aof adjacent fin sections24are equally spaced from one another. That is, the length L3of each space is the same in every place in a direction parallel with the length of the fin material50. The pattern4is formed such that with one cycle being a pattern of placement having five openings23ain a direction parallel with the length of the fin material50, this pattern of placement is periodically repeated in a direction parallel with the length of the fin material50.

A fin material50yet to be subjected to corrugating is processed so that openings23athat are to become drain slits23are sized and placed in the foregoing pattern, and a corrugated fin2subjected to corrugating thus can be formed such that there is a well-balanced mixture of drain apices20aand non-drain apices20b. In particular, because the proportion of drain apices20ato non-drain apices20bin one corrugated fin2can be adjusted by adjusting L2, a balance between drainage capacity and heat-transfer performance can be achieved on the basis of design.

In any of the foregoing patterns of placement 1 to 4, the fin material50is formed such that a particular pattern of placement is periodically repeated in a direction parallel with the length of the fin material50. For this reason, a corrugated fin2fabricated by subjecting the fin material50to corrugating is formed such that fin sections24are identical in position of the drain slits23to each other in the tube side-by-side placement direction and are periodically and repeatedly located every several fin sections in the tube axial direction. By having this configuration, the heat exchanger10can be configured as a result such that there is a well-balanced mixture of drain apices20aand non-drain apices20b. This results in making it possible to obtain a heat exchanger10with improved drainage capacity while maintaining heat-transfer performance.

In a case, such as the patterns of placement 1 to 4, in which a particular pattern of placement is periodically repeated in a direction parallel with the length of the fin material50, processing of drain slits23can be performed with corrugated cutters, corrugated punching rollers, or other devices.FIG.17shows how punching is performed with corrugated cutters.

FIG.17is an explanatory diagram of punching of drain slits by corrugated cutters.

Two corrugated cutters501and502are placed opposite each other, and a fin material50is placed between the two corrugated cutters501and502. The fin material50is fed in the direction of an arrow outlined with a blank inside, and the two corrugated cutters501and502thus rotate in the directions of solid arrows. While the two corrugated cutters501and502are rotating, openings23athat are to become drain slits23are punched in the fin material50.

By thus using corrugated cutters or corrugated punching rollers for processing of drain slits23, the processing speed at which a corrugated fin2is manufactured can be increased. The present disclosure is not limited to a configuration in which a pattern of placement is periodically repeated, although manufacturing cannot be performed with corrugated cutters in a case in which a pattern of placement is not configured to be periodically repeated.

As described above, the heat exchanger10of Embodiment 1 is a heat exchanger including the plurality of flat heat-transfer tubes1each formed in a flat shape in cross-section, provided with a plurality of flow passages formed by through holes, disposed to stand in an up-down direction, and placed side by side and spaced from one another in a direction orthogonal to a direction of flow of air; and the corrugated fin2placed between the plurality of flat heat-transfer tubes1, The corrugated fin2is formed such that the fin sections24, which are plate-shaped, are joined together one after another in a wave shape in a tube axial direction of the plurality of flat heat-transfer tubes1. The fin sections24each have a drain slit23formed such that the drain slit extends in a tube side-by-side placement direction that is a direction in which the plurality of flat heat-transfer tubes1are placed side by side and through which water on an upper surface of the fin section24falls for drainage and the plurality of louvers22each having a louver slit22aextending in the tube side-by-side placement direction and a plate portion22binclined to a flat-plate portion21, which is tabular-shaped, in the fin section24. The plurality of louvers22are divided into a first louver group22A formed further upstream in the direction of flow of air than the drain slit23and a second louver group22B formed further downstream in the direction of flow of air than the drain slit23. The plate portions22bof the first louver group22A and the plate portions22bof the second louver group22B are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other. The plurality of drain slits23are formed between the first louver group22A and the second louver group22B at an interval in the direction of flow of air.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can improve drainage capacity while maintaining heat-transfer capacity.

The interval between drain slits23is shorter than the length Ss of a drain slit23in the direction of flow of air. The interval between drain slits23is a length hs in the direction of flow of air of a heat-transfer region503that is a region of the fin section24interposed in the direction of flow of air by a plurality of drain slits23formed. Therefore, the length hs of the heat-transfer region503in the direction of flow of air is shorter than the length Ss of a drain slit23in the direction of flow of air.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can improve drainage capacity while maintaining heat-transfer capacity.

Further, the heat exchanger10of Embodiment 1 is formed such that when the inter-louver air passage cross-sectional area AL is defined as AL=((Lp×sin θ)−t)×NL×Lw and the drain slit opening area As is defined as As=Ns×Sw×Ss, 1≤AL/As≤4 is satisfied.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can improve drainage capacity while maintaining heat-transfer capacity.

The angle of the plate portion22bof each of the plurality of louvers22inclined to the flat-plate portion21ranges from 15 degrees to 30 degrees.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can achieve compatibility between improvement in drainage capacity and ease of flow of air.

The flat-plate portion21has two ends in the tube side-by-side placement direction and the fin section24has, at each of the two ends of the flat-plate portion21, an apex20joined to the plurality of flat heat-transfer tubes1. Some of the plurality of fin sections24have the drain slits23formed in positions at which the drain slits23overlap the apices20at one or both of the two ends when the drain slits23are seen from an angle parallel with the tube axial direction. Further, some of the plurality of fin sections24have the drain slits23formed in positions at which the drain slits23do not overlap both of the apices20at the two ends when the drain slits23are seen from an angle parallel with the tube axial direction.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can achieve a balance between drainage capacity and heat-transfer performance on the basis of design.

The drain slits23in ones of the fin sections adjacent to each other in the tube axial direction are displaced from each other in the tube side-by-side placement direction.

According to the foregoing configuration, the heat exchanger10of Embodiment 1 can improve drainage capacity,

The corrugated fin2is formed such that ones of the fin sections24identical in position of the drain slits23to each other in the direction of flow of air are periodically and repeatedly located in the tube axial direction.

The foregoing configuration makes it possible to obtain a heat exchanger10with improved drainage capacity while maintaining heat-transfer performance.

Embodiment 2 relates to a configuration including a plurality of the heat exchangers10of Embodiment 1 in the direction of flow of air. The following description is focused on points of difference of Embodiment 2 from Embodiment 1, and configurations of Embodiment 2 that are similar to those of Embodiment 1 are not described.

FIG.18is an enlarged schematic plan view of part of a heat exchanger according to Embodiment 2.FIG.19is a diagram showing a pattern of placement of openings for drain slits in a corrugated fin of the heat exchanger ofFIG.18.

The heat exchanger10A according to Embodiment 2 is formed such that a plurality of flat heat-transfer tubes1are placed in two rows that are spaced from one another in the direction of flow of air and a corrugated fin2is provided commonly for the two rows. Here, flat heat-transfer tubes1located windward (also sometimes referred to as “upstream in the direction of flow of air”) are defined as flat heat-transfer tubes1A and flat heat-transfer tubes1located leeward (also sometimes referred to as “downstream in the direction of flow of air”) are defined as flat heat-transfer tubes1B. The dimension L4in a long direction of a flat cross-section of a flat heat-transfer tube1A and the dimension L5in a long direction of a flat cross-section of a flat heat-transfer tube1B may be equal to or different from each other. Although the flat heat-transfer tubes1are formed in two rows here, there may be three or more rows.

The corrugated fin2of the heat exchanger10A according to Embodiment 2 is provided commonly for the flat heat-transfer tubes1A and the flat heat-transfer tubes1B, and are joined to the flat heat-transfer tubes1A and the flat heat-transfer tubes1B by brazing. The corrugated fin2includes louvers22and drain slits23in correspondence with each row.

Drain slits23located windward are first drain slits23A formed in a range corresponding to the length in a long direction of a flat cross-section of a flat heat-transfer tube1A. A plurality of louvers22located windward are divided into a first louver group22A formed further upstream in the direction of flow of air than the first drain slits23A and a second louver group22B formed further downstream in the direction of flow of air than the drain slits23. Although not illustrated, the plate portions22bof the first louver group22A and the plate portions22bof the second louver group22B are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other

Drain slits23located leeward are second drain slits23B formed in a range corresponding to the length in a long direction of a flat cross-section of a flat heat-transfer tube1B, A plurality of louvers22located leeward are divided into a first louver group22A formed further upstream in the direction of flow of air than the second drain slits23B and a second louver group22B formed further downstream in the direction of flow of air than the second drain slits23B. Although not illustrated, the plate portions22bof the first louver group22A and the plate portions22bof the second louver group228are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other.

Although, inFIG.18, two rows of first drain slits23A and two rows of second drain slits238are formed in the direction of flow of air and one row is formed by two first drain slits23A and another row is formed by two second drain slits238in the tube side-by-side placement direction, this configuration is not intended to impose any limitation. Further, although, inFIGS.18and19, the first drain slits23A and the second drain slits238are identical in position in the tube side-by-side placement direction to each other in the fin section24, the first drain slits23A and the second drain slits238may be different in position in the tube side-by-side placement direction from each other in the fin section24as shown inFIGS.20and21.

FIG.20is an enlarged schematic plan view of part of a modification of the heat exchanger according to Embodiment 2.FIG.21is a diagram showing a pattern of placement of openings for drain slits in a corrugated fin of the heat exchanger ofFIG.19.

In the heat exchanger10A of this modification, the first drain slits23A and the second drain slits238are different in position in the tube side-by-side placement direction from each other in the fin section24.

[Adjustment of Drainage Capacity and Heat-Transfer Capacity]

In the heat exchanger10A according to Embodiment 2, drainage capacity and heat-transfer performance can be adjusted separately for the windward side and the leeward side by adjusting the positions of the drain slits23or the widths of the drain slits23. Specifically, drainage capacity can be improved by increasing the number of drain apices20aby adjusting the positions of the drain slits23, and heat-transfer performance can be improved by reducing the number of drain apices20a. Further, drainage capacity can be improved by increasing the widths of the drain slits23, and heat-transfer performance can be improved by reducing the widths of the drain slits23.

Incidentally, in a case in which the heat exchanger10A is used as an evaporator, condensed water is easily produced on the windward side, as the windward side is higher in heat-transfer performance than the leeward side. Therefore, drainage capacity is required on the windward side. Meanwhile, heat-transfer performance is more required on the leeward side than drainage capacity, as the leeward side is lower in heat-transfer performance than the windward side and less condensed water is produced on the leeward side. That is, in a case in which the heat exchanger10A is used as an evaporator, a configuration is required in which drainage is prioritized on the windward side and heat transfer is prioritized on the leeward side.

To achieve this configuration, it is only necessary to adjust the positions of the drain slits23in the following manner That is, the number of drain apices20alocated windward in one corrugated fin2is defined as N, and the number of drain apices20alocated leeward is defined as M. In this case, the positions of the first drain slits23A and the second drain slits23B are adjusted so that N>M is satisfied. This makes it possible to configure a heat exchanger such that drainage is prioritized on the windward side and heat transfer is prioritized on the leeward side. Further, a sum of drain slit widths of the plurality of first drain slits23A located windward in one corrugated fin2is defined as SWF, and a sum of drain slit widths of the plurality of second drain slits23B located windward is defined as SwB. At this time, a configuration is set up in which the relationship SwF>SwBis satisfied. This makes it possible to configure a heat exchanger such that drainage is prioritized on the windward side and heat transfer is prioritized on the leeward side.

Since the heat exchanger10A can be thus formed such that heat transfer is prioritized on the leeward side, the difference in heat-transfer performance between the windward side and the leeward side can be reduced. Since the difference in heat-transfer performance between the windward side and the leeward side can be reduced, the thickness of frost that forms on surfaces of the fin sections under low-temperature air conditions can be made almost uniform. Since the thickness of frost that forms on the surfaces of the fin sections can be made almost uniform, heat exchange performance under low-temperature air conditions is improved as a result.

As noted above, the heat exchanger10A of Embodiment 2 brings about the following effects in addition to effects that are similar to those of Embodiment 1. The heat exchanger10A of Embodiment 2 is formed such that the plurality of flat heat-transfer tubes1arranged in the tube side-by-side placement direction are placed in a plurality of rows and are spaced from one another in the direction of flow of air and the corrugated fin2is provided commonly for the plurality of rows. This configuration makes it possible to adjust drainage capacity and heat-transfer performance on the windward side and the leeward side by adjusting either or both the positions and drain slit widths of the first drain slits23A and the second drain slit238in each row. This allows the heat exchanger10A of Embodiment 2 to improve heat exchange performance under low-temperature air conditions.

Embodiment 3 relates to a configuration in which the heat exchanger10A of Embodiment 2 further includes an interrow drain slit. The following description is focused on points of difference of Embodiment 3 from Embodiment 2, and configurations of Embodiment 3 that are similar to those of Embodiment 2 are not described.

FIG.22is an enlarged schematic plan view of part of a heat exchanger according to Embodiment 3.

The heat exchanger10B according to Embodiment 3 is formed such that an interrow drain slit23C is formed in a non-junction region21athat is not joined to the flat heat-transfer tubes1. The non-junction region21ais a portion of the flat-plate portion21situated between the flat heat-transfer tubes1A and the flat heat-transfer tubes1B. The interrow drain slit23is a through hole opened in the corrugated fin2. Providing the interrow drain slit23C in the non-junction region21amakes it possible to improve drain capacity in a region where there is a decrease in heat-transfer performance. AlthoughFIG.22shows an example in which interrow drain slits23C are formed in two rows in the direction of flow of air, there may be one row formed by an interrow drain slit23C or three or more rows formed by an interrow drain slit23C. Further, although, inFIG.22, the interrow drain slits23C of the two rows are aligned in the tube side-by-side placement direction, the interrow drain slits23C may be displaced as shown inFIG.23.

FIG.23is an enlarged schematic plan view of part of a modification of a heat exchanger according to Embodiment 3.

In the heat exchanger10B of this modification, the interrow drain slits23C of the two rows are displaced from each other in the tube side-by-side placement direction.

FIG.24is a cross-sectional view taken along line A-A inFIGS.22and23. The dot-and-dash line ofFIG.24is a center line indicating the middle positions in the direction of flow of air of interrow drain slits23C formed in two rows. The arrows ofFIG.24indicate the flow of condensed water during drainage.

The heat exchanger10B of Embodiment 3 uses the interrow drain slits23C as main drain slits. For this reason, the interrow drain slits23C are drain slits that divide the plurality of louvers22into the first louver group22A and the second louver group22B. That is, the first louver group22A is a louver group located further upstream in the direction of flow of air than the interrow drain slits23C, and the second louver group22B is a louver group located further downstream in the direction of flow of air than the interrow drain slits23C. Moreover, as described in Embodiment 1, the plate portions22bof the first louver group22A and the plate portions22bof the second louver group22B are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other. Such a configuration causes condensed water having flowed along the plate portions22bof the louvers22to be guided toward the interrow drain slits23C of a lower fin section24, making it possible to improve drainage capacity.

The opening area of each of the interrow drain slits23C is larger than the opening area of each of the first drain slits23A and the second drain slits238. In this configuration, condensed water is guided toward the interrow drain slits23C. For this reason, since the opening area of each of the interrow drain slits23C is larger than the opening area of each of the first drain slits23A and the second drain slits23B, higher drainage capacity can be achieved than in a case in which the opening areas are equal to each other. Although it is preferable that from the point of view of improvement in drainage capacity that the opening area of each of the interrow drain slits23C be larger than the opening area of each of the first drain slits23A and the second drain slits23B, the opening areas may be equal to each other. Further, although an interrow drain slit23C may be formed in one row, it is more preferable for a greater effect of improvement in drainage capacity that interrow drain slits23C be formed in a plurality of rows. The first drain slits23A, the second drain slits23B, and the interrow drain slits23C may be aligned to or displaced from each other in the tube side-by-side placement direction.

Incidentally, a comparison between the configuration ofFIG.22and the configuration ofFIG.23, the configuration ofFIG.23is smaller than the configuration ofFIG.22in terms of the area of a heat-transfer region503that is formed between the interrow drain slits23C of the of the two rows in the direction of flow of air. In each ofFIGS.22and23, the heat-transfer region503is indicated by half-tone dot meshing. The heat-transfer region503can be said to be a low-strength portion, as it is formed between the interrow drain slits23C. The configurationFIG.23makes it possible to make the area of this low-strength portion smaller than the area in the configuration ofFIG.23, thus making it possible to configure a heat exchanger with higher fin strength than the heat exchanger of the configuration ofFIG.22.

As described above, the heat exchanger10B of Embodiment 3 can bring about improvement in drainage capacity in addition to effects that are similar to those of Embodiment 2, as the interrow drain slits23C are formed in a position corresponding to a space between each adjacent two of the rows of flat heat-transfer tubes1in the direction of flow of air. The plate portions22bof the first louver group22A located further upstream in the direction of flow of air than the interrow drain slits23C and the plate portions22bof the second louver group22B located further downstream in the direction of flow of air than the interrow drain slits23C are inclined to the flat-plate portion21and inclined in respective directions that are opposite to each other. This causes condensed water to be guided toward the interrow drain slits23C, making it possible to improve drainage capacity. Further, since the opening area of each of the interrow drain slits23C is larger than the opening area of each of the first drain slits23A and the second drain slits23B, which are drain slits other than the interrow drain slits, higher drainage capacity can be achieved than in a case in which the opening areas are equal to each other.

Embodiment 4 is formed such that the upstream protruding portion2aof a fin section24in the heat exchanger108of Embodiment 3 is thickened. The following description is focused on points of difference of Embodiment 4 from Embodiment 3, and configurations of Embodiment 4 that are similar to those of Embodiment 3 are not described.

FIG.25is an enlarged schematic plan view of part of a heat exchanger according to Embodiment 4.FIG.26is a cross-sectional view taken along line B-B inFIG.25.

In the heat exchanger10C of Embodiment 4, the thickness of the upstream protruding portion2aof the corrugated fin2is greater than the thickness of a portion of the corrugated fin2other than the upstream protruding portion2a. As shown inFIG.26, the upstream protruding portion2ais formed to be thick by folding back a portion of the fin section24protruding further upstream than the flat heat-transfer tubes1.

In a case in which the heat exchanger10C is used as an evaporator, condensed water is easily produced on the upstream protruding portion2aof the corrugated fin2, with which air collides first. For this reason, frost easily forms on the upstream protruding portion2aunder low-temperature air conditions, and the upstream protruding portion2ais required to have the strength to withstand frost formation.

To address this problem, Embodiment 4 is formed such that the upstream protruding portion2aof the corrugated fin2is thicker than a portion of the corrugated fin2that is other than the upstream protruding portion2a. This makes it possible to ensure the strength of the upstream protruding portion2aand inhibit deformation of the upstream protruding portion2ain case of frost formation.

As described above, the heat exchanger10C of Embodiment 4 brings about the following effects in addition to effects that are similar to those of Embodiment 3, as the upstream protruding portion2aof the corrugated fin2is thicker than a portion of the corrugated fin2that is other than the upstream protruding portion2a. That is, the strength of the upstream protruding portion2acan be improved, and deformation of the upstream protruding portion2ain a case in which frost forms on the upstream protruding portion2acan be inhibited. When the upstream protruding portion2adeforms, the flow passage of air is prevented, with the result that a deterioration in heat exchange capacity is invited. However, in Embodiment 4, heat exchange capacity can be maintained since deformation of the upstream protruding portion2acan be inhibited.

The upstream protruding portion2athickened by folding back a portion of the fin protruding further upstream than the flat heat-transfer tubes1. This makes it possible to easily form a thick upstream protruding portion2a. From the point of view of ensuring the strength of the upstream protruding portion2a, it is conceivable that the thickness of the whole corrugated fin may be increased. However, in this case, the thicknesses of the plate portions22bof the louvers22increase too. This causes a decrease in the inter-louver air passage cross-sectional area and causes a deterioration in the capacity of drainage of condensed water through the space between the louvers. On the other hand, in the heat exchanger10C of Embodiment 4, only the upstream protruding portion2ais thickened. This allows the heat exchanger10C of Embodiment 4 to improve the strength of the upstream protruding portion2awithout inviting a deterioration in drainage capacity.

Although Embodiment 4 is formed such that the upstream protruding portion2aof the flat-plate portion21is thickened in the heat exchanger of Embodiment 3, Embodiment 4 may be formed such that the upstream protruding portion2aof the flat-plate portion21is thickened in the heat exchanger of Embodiment 1 or 2.

Embodiment 5 relates to an air-conditioning apparatus as an example of a refrigeration cycle apparatus including a heat exchanger of any of Embodiments 1 to 4.

FIG.27is a diagram showing a configuration of an air-conditioning apparatus according to Embodiment 5.

The air-conditioning apparatus uses a heat exchanger of any of Embodiments 1 to 4 as an outdoor heat exchanger230. Note, however, that this is not intended to impose any limitation. A heat exchanger of any of Embodiments 1 to 4 may be used as an indoor heat exchanger110, or heat exchangers of any of Embodiments 1 to 4 may be used as both the outdoor heat exchanger230and the indoor heat exchanger110.

As shown inFIG.27, the air-conditioning apparatus forms a refrigerant circuit in which an outdoor unit200and an indoor unit100are connected with a gas refrigerant pipe300and a liquid refrigerant pipe400. The outdoor unit200includes a compressor210, a four-way valve220, the outdoor heat exchanger230, and an outdoor fan240. Although a case is described in which one outdoor unit200and one indoor unit100are connected by pipes in the air-conditioning apparatus of Embodiment 5, the numbers are arbitrary.

The compressor210compresses and discharges sucked refrigerant. Although not limited in particular, the compressor210can change the capacity of the compressor210by arbitrarily varying the operating frequency, for example, through an inverter circuit or other circuits. The four-way valve220is a valve configured to switch the flows of refrigerant between cooling operation and heating operation.

The outdoor heat exchanger230exchanges heat between refrigerant and outdoor air. During heating operation, the outdoor heat exchanger230serves as an evaporator to evaporate and gasify the refrigerant. Further, during cooling operation, the outdoor heat exchanger230serves as a condenser to condense and liquefy the refrigerant. The outdoor fan240sends the outdoor air to the outdoor heat exchanger230and facilitates heat exchange at the outdoor heat exchanger230.

Meanwhile, the indoor unit100includes the indoor heat exchanger110, a decompression device120, and an indoor fan130. The indoor heat exchanger110exchanges heat between air in a room to be air-conditioned and refrigerant. During heating operation, the indoor heat exchanger110serves as a condenser to condense and liquefy the refrigerant. Further, during cooling operation, the indoor heat exchanger110serves as an evaporator to evaporate and gasify the refrigerant.

The decompression device120decompresses and expands the refrigerant. The decompression device120is formed, for example, by an electronic expansion valve or other devices. In a case in which the decompression device120is formed by an electronic expansion valve, the decompression device120adjusts its opening degree in accordance with an instruction from a controller (not illustrated) or other devices. The indoor fan130passes the air in the room through the indoor heat exchanger110and supplies, into the room, the air passed through the indoor heat exchanger110.

Next, the actions of the pieces of equipment of the air-conditioning apparatus are described with reference to the flow of refrigerant, First, heating operation is described. During heating operation, the four-way valve220is switched to a state illustrated by dotted lines ofFIG.27. High-temperature and high-pressure gas refrigerant compressed and discharged by the compressor210passes through the four-way valve220and flows into the indoor heat exchanger110. The gas refrigerant having flowed into the indoor heat exchanger110condenses and liquefies by exchanging heat with air in a space to be air-conditioned. The refrigerant having liquefied is decompressed by the decompression device120into two-phase gas-liquid refrigerant and then flows into the outdoor heat exchanger230. The refrigerant having flowed into the outdoor heat exchanger230evaporates and gasifies by exchanging heat with outdoor air sent from the outdoor fan240. The refrigerant having gasified passes through the four-way valve220and is sucked again into the compressor210. Such circulation of the refrigerant causes the air-conditioning apparatus to perform air conditioning related to heating.

Next, cooling operation is described. During cooling operation, the four-way valve220is switched to a state illustrated by solid lines ofFIG.27. High-temperature and high-pressure gas refrigerant compressed and discharged by the compressor210passes through the four-way valve220and flows into the outdoor heat exchanger230. The gas refrigerant having flowed into the outdoor heat exchanger230condenses and liquefies by exchanging heat with outdoor air supplied by the outdoor fan240. The refrigerant having liquefied is decompressed by the decompression device120into two-phase gas-liquid refrigerant and then flows into the indoor heat exchanger110. The refrigerant having flowed into the indoor heat exchanger110evaporates and gasifies by exchanging heat with air in the space to be air-conditioned. The refrigerant having gasified passes through the four-way valve220and is sucked again into the compressor210. Such circulation of the refrigerant causes the air-conditioning apparatus to perform air conditioning related to cooling.

Since the air-conditioning apparatus of Embodiment 5 includes a heat exchanger of any of Embodiments 1 to 4, it is possible to improve drainage capacity while maintaining heat-transfer performance in the heat exchanger.

Although, in Embodiment 5, the refrigeration cycle apparatus has been described as being an air-conditioning apparatus, this is not intended to impose any limitation. The refrigeration cycle apparatus may be a cooling apparatus configured to cool, for example, a refrigerating-freezing warehouse, a hot water supply apparatus, or other apparatuses.

Embodiment 6 is equivalent to a modification of the aforementioned Embodiment 3. The following description is focused on points of difference of Embodiment 6 from Embodiment 3, and configurations of Embodiment 6 that are similar to those of Embodiment 3 are not described.

FIG.28is an enlarged schematic plan view of part of a heat exchanger according to Embodiment 6.FIG.29is a cross-sectional view taken along line B-B inFIG.28. Embodiment 3 made no particular mention of the numbers of drain slits23A and drain slits23B, andFIG.22showed an example in which there are two drain slits23A and two drain slits23B. The drain slits23A are drain slits formed in the middle of the first louver group22A in the direction of flow of air, and the drain slits23B are drain slits formed in the middle of the second louver group22B in the direction of flow of air. On the other hand, the heat exchanger10D of Embodiment 6 is formed such that the numbers of drain slits23A and drain slits23B are each limited to one as shown inFIG.28. That is, the numbers of drain slits23A and drain slits23B are each not limited to plural numbers but may be one. It should be noted that there are a plurality of interrow drain slits23C.

The drainage behavior of condensed water on a fin surface of Embodiment 6 is described. The condensed water on the fin surface is collected in the vicinity of an intermediate portion (hereinafter referred to as “near the center of the space between the rows”) of the fin section24in the direction of flow of air (i.e. the direction of an arrow outlined with a blank inside inFIG.28) by the first louver group22A and the second louver group22B and drained through the interrow drain slits230. For this reason, the amount of condensed water near the center of the space between the rows is large. Therefore, the amounts of condensed water in the vicinity of the center of a region of formation of the first louver group22A and in the vicinity of the center of a region of formation of the second louver group22B are each relatively smaller than the amount of condensed water near the center of the space between the rows. In other words, this puts limits on drainage near the center of the space between the rows. The term “center” here means the center in the direction of flow of air.

Thus, the amounts of condensed water in the vicinity of the center of the region of formation of the first louver group22A and in the vicinity of the center of the region of formation of the second louver group22B are each relatively smaller than the amount of condensed water near the center of the space between the rows. For this reason, the heat exchanger10D includes a plurality of interrow drain slits23C, which are each relatively large in the amount of condensed water, and one drain slit23A and one drain slit B, which are each relatively small in the amount of condensed water. This allows the heat exchanger10D to excel in heat-transfer performance with improvement in capacity of drainage of condensed water.

Further, according to the distribution of condensed water based on an analysis by the inventors, it is more preferable for compatibility between improvement in drainage capacity and improvement in heat-transfer performance suited for the distribution of condensed water that the heat exchanger10D satisfy the following relationship:

AC>AAorAC>AB, preferablyAC>AA+AB,where AA[mm2] is the opening area of a drain slit23A formed in the middle of the first louver group22A in the direction of flow of air, AB[mm2] is the opening area of a drain slit23B formed in the middle of the second louver group22B in the direction of flow of air, and AC[mm2] is the opening area of an interrow drain slit230.

Further, althoughFIG.28shows a case in which the drain slit23A, the drain slit23B, and the interrow drain slits23C are not periodically displaced in the tube side-by-side placement direction, the drain slit23A, the drain slit23B, and the interrow drain slits23C may of course be formed to be periodically displaced as described in Embodiment 1.

Further, as described in Embodiment 1 too, a portion of the flat-plate portion21located between drain slits23also serves as a water conduit21A, and in the configuration of Embodiment 6, a portion of the flat-plate portion21located between the interrow drain slits23C is equivalent to a water conduit21A. If this water conduit21A is long in the direction of flow of air, the interval between the interrow drain slits23C widens, the region of placement of the drain slits23and the louvers22narrows accordingly. For this reason, it is preferable that the water conduit21A be formed to be as short as possible in the direction of flow of air. When the water conduit21A is formed to be as short as possible in the direction of flow of air, the heat exchanger10D can be mounted with drain slits23and louvers22at high densities in the fin section24for improved performance. Specifically, it is preferable that the water conduit21A be formed so that the length δ1[mm] of the water conduit21A in the direction of flow of air satisfies δ1<δ2, where δ2[mm] is the distance in the direction of flow of air between one of the plurality of louvers22and one of the plurality of (here, two) drain slits23that are adjacent to each other in the direction of flow of air or, in other words, the distance in the direction of flow air between one of the plurality of louvers22that is at an end close to the center of the space between the row and the interrow drain slit23C closest to this louver22.

FIG.30is a diagram showing another example of a heat exchanger according to Embodiment 6. In this example, the interrow drain slits23C are formed in a portion of the fin section24situated between respective distal ends of the flat heat-transfer tube1A and the flat heat-transfer tube1B adjacent to each other in the direction of flow of air and the respective distal ends are opposite to each other. The opposite distal ends here include, on one hand, furthest leeward distal ends1Ab (hereinafter referred to as “leeward distal ends1Ab”) of the flat heat-transfer tubes1A and, on the other hand, furthest windward distal ends1Ba (hereinafter referred to as “windward distal ends1Ba”) of the flat heat-transfer tubes1B. It is even more preferable to provide the interrow drain slits23C only in such a region or, in other words, a region in which no flat heat-transfer tubes are placed side by side, drainage capacity is thus improved for the following reason. In a configuration in which the interrow drain slits23C are provided only in a region in which no flat heat-transfer tubes are placed side by side, condensed water4near the center of the space between the rows is intensively drained with effective use of three places, namely the interrow drain slits23C, leeward end surfaces of the flat heat-transfer tubes1A, and windward end surfaces of the flat heat-transfer tubes1B.

As described above, the heat exchanger10D of Embodiment 6 brings about effects that are similar to those of Embodiment 3. Further, since the length δ1of the water conduit21A in the direction of flow of air satisfies the relationship δ1<δ2, the heat exchanger10D can be mounted with drain slits23and louvers22at high densities in the fin section24for improved performance.

Further, the heat exchanger10D of Embodiment 6 is formed such that the interrow drain slits23C are formed in a portion of the fin section24situated between the leeward distal ends1Ab of the flat heat-transfer tubes1A and the windward distal ends1Ba of the flat heat-transfer tubes1B in the direction of flow of air. This causes the heat exchanger10D to have improved drainage capacity.

Embodiment 7 differs from the heat exchanger10D of Embodiment 6 in positional relationship between upstream ends of flat heat-transfer tubes1A located windward and an upstream end of a corrugated fin2. The following description is focused on points of difference of Embodiment 7 from Embodiment 6, and configurations of Embodiment 7 that are similar to those of Embodiment 6 are not described.

FIG.31is an enlarged schematic plan view of part of a heat exchanger according to Embodiment 7. The heat exchanger10E of Embodiment 7 is formed such that a furthest windward distal end2aa(hereinafter referred to as “windward distal end2aa”) of the corrugated fin2in the direction of flow of air (i.e. the direction of an arrow outlined with a blank inside inFIG.31) is depressed further leeward than the furthest windward distal ends1Aa (hereinafter referred to as “windward distal ends1Aa”) of the flat heat-transfer tubes1A in the direction of flow of air. Looked at differently, the heat exchanger10E of Embodiment 7 is formed such that the windward distal ends1Aa of the flat heat-transfer tubes1A in the direction of flow of air protrude further windward than the windward distal end2aaof the corrugated fin2. It should be noted that the flat heat-transfer tubes1A are flat heat-transfer tubes of the furthest windward row of the plurality of (here, two) rows in which the flat heat-transfer tubes1are placed. L1is the length of the heat exchanger10E in the direction of flow of air, and is the distance in the direction of flow of air between the windward distal end1Aa of a flat heat-transfer tube1A and a furthest leeward distal end1Bb (hereinafter referred to as “leeward distal end1Bb”) of a flat heat-transfer tube1B.

The following describes the workings of the foregoing configuration.

In a case in which the heat exchanger10E is used as an evaporator, refrigerant below freezing flows through inside the heat-transfer tubes, and air passes through the heat exchanger10E; meanwhile, the air is cooled by sequentially exchanging heat with the refrigerant inside the heat-transfer tubes while passing through the heat exchanger10E from the windward side to the leeward side. Then, the air thus cooled causes condensed water to be produced on the fin surfaces. In the heat exchanger10E, the temperature difference between the refrigerant and the air increases toward the windward side, and the amount of heat exchange increases toward the windward side. For this reason, the amount of condensed water that is produced on the fin surfaces increases toward the windward side of the heat exchanger10E, and the amount of frost formation too increases toward the windward side of the heat exchanger10E.

In the heat exchanger10E, projecting portions11aprojecting further windward than the corrugated fin2and including the distal ends1Aa of the flat heat-transfer tubes1A are portions in which frost formation tends to occur. Note here that since the heat exchanger10E is formed such that the distal end2aaof the corrugated fin2is depressed further leeward than the windward distal ends1Aa of the flat heat-transfer tubes1A in the direction of flow of air, the heat exchanger10E can provide wide space for frost formation. Since the heat exchanger10E can provide wide space for frost formation, the heat exchanger10E can reduce the temperature difference between the fin section24per se and the air on the windward side.

Note here that the space for frost formation is a space around portions of windward parts of the plurality of flat heat-transfer tubes1A located windward ofFIG.31in which the corrugated fin2is not provided, and to the extent that no fin exists, a large space in which frost can form can be secured. Further, in the windward parts of the plurality of flat heat-transfer tubes1A, in which no fin exits, the heat transfer coefficient is small, so that the amount of heat exchange can be reduced. That is, the heat exchanger10E can reduce the amount of frost formation. This allows the heat exchanger10E to ensure an almost uniform amount of frost formation on the fin section24in the direction of flow of air, making it possible to improve heating capacity under low-temperature air conditions.

Further, during defrosting operation through which frost formed on the corrugated fin2is melted, the heat exchanger10E can drain a large portion of the amount of frost formation through the projecting portions11aof the flat heat-transfer tubes1A, so that improvement in defrosting performance can be expected. Further, since no corrugated fin2exits in the projecting portions11aof the flat heat-transfer tubes1A, frost having adhered to the projecting portions11amay fall along surfaces of the projecting portions11ain a half-melted state in which the frost is yet to completely become condensed water, so that the heat exchanger10E can improve drainage capacity.

The inventors found through an example of an experiment a relationship between the amount of depression of a corrugated fin2and an effect of improvement in low-temperature heating capacity by uniformizing of the amount of frost formation. This point is explained below.

FIG.32is a diagram showing a relationship between (Lf/L1)×100 and low-temperature heating capacity in the heat exchanger according to Embodiment 7. InFIG.32, the horizontal axis represents (Lf/L1)×100 [%], and the vertical axis represents low-temperature heating capacity [%]. Lfis the amount of depression of a corrugated fin2, and is the distance in the direction of flow of air between the windward distal end2aaof the corrugated fin2and the windward distal end1Aa of a flat heat-transfer tube1A. L1is the length of the heat exchanger10E in the direction of flow of air, and is the distance in the direction of flow of air between the windward distal end1Aa of a flat heat-transfer tube1A and the leeward distal end1Bb of a flat heat-transfer tube1B. The vertical axis shows a result of improvement in low-temperature heating capacity in comparison with a configuration in which there are no projecting portions11awhere the low-temperature heating capacity in a case in which there are no projecting portions11ais 50%.

As shown inFIG.32, it was confirmed that when (Lf/L1)×100 is higher than or equal to 4.5%, great improvement in low-temperature heating capacity can be brought about with a 46% increase in low-temperature heating capacity in comparison with the configuration in which there are no projecting portions11a. It should be noted that excessively increasing the amount of projection Lfor, in other words, excessively increasing the amount of depression of the corrugated fin2requires a structure for ensuring a desired heat-transfer area, as the area of the fin section24decreases. Specific examples of the structure for ensuring a desired heat-transfer area include increasing the dimensions of the heat-transfer tubes and the corrugated fin2. This structure leads to a great decrease in cost performance. For this reason, in consideration of the balance between the effect of improvement in low-temperature heating capacity and the ensuring of a heat-transfer area, it is preferable that Lfbe as small as possible.

According toFIG.32, there is improvement in low-temperature heating capacity when (Lf/L1)×100 is higher than 0% and lower than or equal to 11%. When Lf/L1exceeds 11%, a decrease in heat-transfer area becomes remarkable for the effect of improvement in low-temperature heating capacity. For this reason, a configuration in which Lf/L1is higher than 0% and lower than or equal to 11% is preferable.

FIG.33is a diagram showing a relationship between an amount of depression of a corrugated fin and a refrigerant flow passage inside a flat heat-transfer tube in Embodiment 7. InFIG.33, Lt is the distance in the direction of flow of air between the windward distal end1Aa of a flat heat-transfer tube1A and a windward distal end11baof a refrigerant flow passage11binside the flat heat-transfer tube1A. The heat exchanger1E satisfies the relationship Lt≥Lf. In the configuration in which this relationship is satisfied, the flat heat-transfer tube1A is formed to have no refrigerant flow passages11bformed in the range in which the corrugated fin2is depressed in the direction of flow of air. In other words, in the configuration in which this relationship is satisfied, there are no refrigerant flow passages11bformed in the projecting portions11a. For this reason, the temperature of the projecting portions11acan be made relatively higher than the refrigerant temperature. This allows the heat exchanger10E to reduce the temperature difference between the projecting portions11aper se and air and prevent frost from being intensively formed on the projecting portions11a, making it possible to achieve uniform frost formation in a windward part of the heat exchanger10E. As a result of that, the heat exchanger10E can improve low-temperature heating capacity. Further, through uniform formation of frost, the heat exchanger10E can improve defrosting performance and drainage performance.

As described above, the heat exchanger10E of Embodiment 7 can bring about the following effects in addition to effects that are similar to those of Embodiment 6. The heat exchanger10E is formed such that the windward distal end2aaof the corrugated fin2is depressed further leeward than the windward distal ends1Aa of the flat heat-transfer tubes1A located windward. For this reason, the heat exchanger10E can reduce the temperature difference between the fin section24per se and the air on the windward side, making it possible to ensure an almost uniform amount of frost formation on the fin section24in the direction of flow of air As a result of that, the heat exchanger10E can improve heating capacity under low-temperature air conditions.

Further, by satisfying the relationship Lt≥Lf, the heat exchanger10E can achieve uniform frost formation in the windward part of the heat exchanger10E by preventing frost from being unevenly formed on the projecting portion11a. As a result of that, the heat exchanger10E can improve low-temperature heating capacity. Further, through uniform formation of frost, the heat exchanger10E can improve defrosting performance and drainage performance.

REFERENCE SIGNS LIST