EP3647711B1

EP3647711B1 - Heat exchanger

Info

Publication number: EP3647711B1
Application number: EP18842154.9A
Authority: EP
Inventors: Hideaki Tatenoi; Yoshihiro Hara; Yasutaka Aoki; Masayuki Sakai
Original assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2017-08-02
Filing date: 2018-06-14
Publication date: 2023-07-26
Anticipated expiration: 2038-06-14
Also published as: CN110998215B; EP3647711A1; JP2019027727A; EP3647711C0; WO2019026436A1; JP6946105B2; CN110998215A; EP3647711A4; ES2955923T3

Description

Technical Field

The present invention relates to a heat exchanger used in, for example, an air conditioner, a freezer, a freezer for transportation, and a water heater.

Background Art

A heat exchanger in which a refrigerant flows through each of a plurality of stacked flat tubes is used in an apparatus such as an air conditioner and a freezer, and constitutes a refrigerant circuit of the apparatus.
The heat exchanger has a configuration in which the plurality of flat tubes are assembled to a plate-like or corrugated fin and a pair of headers. Both end parts of each of the flat tubes are connected to the respective headers, and the refrigerant introduced into the headers from a pipe of the refrigerant circuit is distributed to each of the flat tubes. Heat is exchanged between the refrigerant flowing through the flat tubes and air flowing into gaps among the fins and the flat tubes from a direction orthogonal to flow of the refrigerant.
In a case where the heat exchanger functions as an evaporator, the refrigerant of a gas-liquid two-phase flow flows into the headers. Inside the headers, distribution of a gas-phase refrigerant and a liquid-phase refrigerant having density larger than density of the gas-phase refrigerant is easily deviated in a stacking direction of the flat tubes. Accordingly, a distribution state of the refrigerant to each of the flat tubes is easily deviated.
To uniformize a heat transfer amount over the entire stacked body including the flat tubes and the fins in addition to uniformization of such distribution state of the refrigerant and to accordingly achieve necessary performance sufficiently, setting of paths through which the refrigerant efficiently flows in the headers and the flat tubes, a configuration of each of the headers, a shape of each of the fins, and the like have been variously devised.
To secure a heat transfer area necessary for predetermined heat exchange performance, a plurality of rows of heat exchange elements (assemblies each including flat tubes and fins) are arranged in a direction connecting a windward side and a leeward side in some cases (for example, Patent Literature 1).
In Patent Literature 1, an individual header is not provided on the windward side (front row) and the leeward side (rear row), and the flat tubes in the front row and the flat tubes in the rear row are connected to common headers. A large number of horizontal partition plates are provided inside each of the headers. The flat tube in the front row and the flat tube in the rear row on the same stage in the stacking direction of the flat tubes communicate with the same section partitioned by the horizontal partition plates. The refrigerant having flowed from the refrigerant pipe into each of the sections inside each of the headers flows through the flat tubes in the front row and the rear row on each stage.
Patent Literature 2 discloses a heat exchanger according to the preamble of claim 1.

Citation List

Patent Literature

Patent Literature 1: JP 5840291 B2
Patent Literature 2: WO2016/121123A1

Summary of Invention

Technical Problem

When the large number of partition plates are provided inside each of the headers, heat transfer loss caused by deviation of the refrigerant distribution can be suppressed but the number of parts is increased. Even in the case where the headers are shared by the front row and the rear row as with Patent Literature 1, the partition plates corresponding to the number of stages are still necessary, and the number of parts is increased. Therefore, it is preferable to avoid the inside of each of the headers from being finely partitioned by the partition plates.
Further, in the heat exchanger that functions as an evaporator in winter, frosting progresses from the front row that is largely different in temperature from the air. Therefore, deviation of the frosting state between the front row and the rear row cannot be avoided. Thus, if an air passage is closed by frosting in the front row and an air flow rate in the rear row is reduced, the rear row that can perform heat exchange because a frosting amount is still small cannot function early.
Accordingly, an object of the present invention is to provide a heat exchanger that can secure evaporation performance while suppressing heat transfer loss in a state where deviation of frosting progressing from the front row and deviation of refrigerant distribution from the headers to each of the flat tubes are present.

Solution to Problem

A first heat exchanger according to the present invention is a heat exchanger including a plurality of stacked flat tubes, fins provided on the flat tubes, and headers that are erected in a stacking direction in which the flat tubes are stacked, and connected to the flat tubes. The heat exchanger functions as an evaporator that causes heat exchange between air and a refrigerant flowing into the flat tubes through the headers, to evaporate the refrigerant. Heat exchange elements each including the flat tubes, the fins, and the headers are arranged in a front row located on an upstream side of flow of the air and a rear row located on a downstream side of the flow of the air. A flow path cross-sectional area of each of front-row headers that are the headers in the front row is smaller than a flow path cross-sectional area of each of rear-row headers that are the headers in the rear row such that a flow velocity of the refrigerant flowing through each of the front-row headers is higher than a flow velocity of the refrigerant flowing through each of the rear-row headers.
The first heat exchanger according to the present invention preferably further includes a partition portion configured to partition an inside of at least any of the front-row headers and the rear-row headers by extending in the stacking direction, and the flow path cross-sectional area is preferably set by the partition portion.
In the first heat exchanger according to the present invention, a width of each of the flat tubes in the rear row in a flowing direction of the air is preferably wider than a width of each of the flat tubes in the front row in the flowing direction of the air.
In the first heat exchanger according to the present invention, the heat exchange elements preferably include two or more heat exchange elements connected in series, and a heat exchange element of the heat exchange elements on a most downstream side is preferably located in the front row.
In the first heat exchanger according to the present invention, the heat exchange elements preferably include three or more heat exchange elements connected in series, and a heat exchange element of the heat exchange elements on a most upstream side is preferably located in the front row.

Advantageous Effects of Invention

According to the present invention, as described below, a heat transfer amount in the stacking direction (up-and-down direction) of the flat tubes as a whole of the front row and the rear row can be balanced. Therefore, even when the partition plate for uniformization of refrigerant distribution is not provided, deterioration of heat exchange performance due to deviation of the refrigerant distribution can be avoided. In addition, even in an operation state where frosting occurs, a time before operation is switched to defrosting operation can be prolonged while the heat exchange capability remains at least on a lower stage side in the rear row.

Brief Description of Drawings

[FIG. 1] FIG. 1 is a perspective view schematically illustrating a heat exchanger according to a first embodiment.
[FIG. 2] FIG. 2 is a schematic diagram to explain difference between flow velocity of a refrigerant flowing through a front-row header and flow velocity of a refrigerant flowing through a rear-row header illustrated in FIG. 1.
[FIGS. 3A to 3C] FIGS. 3A to 3C are graphs illustrating a distribution state of a liquid-phase refrigerant to flat tubes in each of a front row and a rear row at respective refrigerant flow rates.
[FIG. 4] FIG. 4 is a schematic diagram to explain action of the heat exchanger illustrated in FIG. 1.
[FIG. 5] FIG. 5 is a schematic diagram illustrating a front-row header and a rear-row header according to a modification of the first embodiment.
[FIG. 6] FIG. 6 is a schematic diagram illustrating a heat exchange element in a front row and a heat exchange element in a rear row according to another modification of the first embodiment.
[FIGS. 7A to 7D] FIG. 7A is a schematic diagram illustrating a heat exchanger according to a second embodiment, FIG. 7B is a schematic diagram illustrating a heat exchanger according to a modification of the second embodiment, and FIGS. 7C and 7D are diagrams illustrating liquid-phase refrigerant distribution in a case where dryness is high.
[FIGS. 8A and 8B] FIG. 8A is a schematic diagram illustrating a heat exchanger according to a third embodiment which is not according to the invention, and FIG. 8B is a schematic diagram illustrating a modification of the third embodiment.
[FIGS. 9A and 9B] FIGS. 9A and 9B are schematic diagrams each illustrating a heat exchanger according to a fourth embodiment, which is not according to the invention, without illustration of fins.

Description of Embodiments

Some embodiments of the present invention are described below with reference to accompanying drawings.

[First Embodiment]

A heat exchanger 1 illustrated in FIG. 1 includes a front-row heat exchange element 10 and a rear-row heat exchange element 20. The heat exchanger 1 constitutes a refrigerant circuit of an air conditioner, a freezer, a water heater, or the like. The refrigerant circuit includes a compressor, a condenser, a decompression unit, and the heat exchanger 1 serving as an evaporator.
As described below, the heat exchanger 1 according to the present embodiment suppresses deterioration of heat exchange performance while accepting deviation of refrigerant distribution from headers 13 and 23 to each of flat tubes 11 and deviation of frosting.

(Heat Exchange Element)

The front-row heat exchange element 10 includes the plurality of stacked flat tubes 11 (tubes), a plurality of fins 12, and a pair of front-row headers 13 (13A and 13B) connected to the flat tubes 11.
The front-row heat exchange element 10 exchanges heat between a refrigerant flowing into each of the flat tubes 11 through one (13A) of the front-row headers 13 and air flowing into gaps among the fins 12 and the flat tubes 11 from a direction orthogonal to the flat tubes 11.
As with the front-row heat exchange element 10, the rear-row heat exchange element 20 includes the plurality of stacked flat tubes 11, the plurality of fins 12, and the pair of rear-row headers 23 (23A and 23B) connected to the flat tubes 11. The rear-row heat exchange element 20 exchanges heat between a refrigerant flowing into each of the flat tubes 11 through one (23A) of the rear-row headers 23 and the air.
The flat tubes 11 and the fin 12 are components common to the front-row heat exchange element 10 and the rear-row heat exchange element 20.
In this example, a direction in which the flat tubes 11 are stacked (stacking direction) is referred to as an up-and-down direction D1.
Further, in flow of the air subjected to heat exchange with the refrigerant flowing through the flat tubes 11, an upstream side is referred to as "front", and a downstream side is referred to as "rear". The air sucked by an unillustrated fan or the like is preferably supplied to an entire region of the heat exchanger 1.
The front-row heat exchange element 10 and the rear-row heat exchange element 20 are arranged in the air flowing direction (illustrated by void arrow). In each of the drawings, the front row is denoted by "F", and the rear row is denoted by "R".
The front-row heat exchange element 10 and the rear-row heat exchange element 20 are connected to pipes of the refrigerant circuit in parallel. The refrigerant of the same flow rate flows through the front-row heat exchange element 10 and the rear-row heat exchange element 20.
The heat exchanger 1 includes the heat exchange elements 10 and 20 in at least a part thereof. The heat exchanger 1 may include unillustrated another heat exchange element in addition to the heat exchange elements 10 and 20.

(Flat Tube)

Each of the flat tubes 11 is a flat tube through which the refrigerant flows, has a predetermined length, and extends linearly. Both end parts of each of the flat tubes 11 are connected to the respective headers 13 (or respective headers 23). Each of the headers 13 and 23 includes insertion holes (not illustrated) each receiving the corresponding end part of the flat tubes 11 to the inside of the headers 13 and 23.
The plurality of flat tubes 11 are stacked in parallel with one another with predetermined intervals in the up-and-down direction D1. The end parts of each of the flat tubes 11 are opened inside the respective headers 13 (or respective headers 23).

(Fin)

The fins 12 according to the present embodiment each have a substantially rectangular plate-like outer shape, and are provided on the flat tubes 11 in order to increase a surface area coming into contact with the air. Each of the fins 12 includes a plurality of notches 121 into which the respective flat tubes 11 are inserted. The fins 12 in the front row F and the fins 12 in the rear row R may have different shapes.
FIG. 1 illustrates only a part of the fins 12 in each of the front row F and the rear row R. The large number of fins 12 are actually provided on the stacked body of the flat tubes 11 with intervals in a length direction of the flat tubes 11 in each of the front row F and the rear row R.
In place of the plate-like fins 12, the other type of fins may be provided on the flat tubes 11. For example, a corrugated fin may be provided between the flat tubes 11 adjacent in the up-and-down direction D1.
The members configuring the heat exchanger 1, such as the flat tubes 11, the fins 12, the front-row headers 13, and the rear-row headers 23 are made of a metal material such as an aluminum alloy and a copper alloy. These members are integrated using a joining material such as brazing filler metal to constitute the heat exchanger 1.

(Front-Row Header)

The pair of front-row headers 13 are both erected in the stacking direction (D1) of the flat tubes 11 in the front row F. The flat tubes 11 in the front row F are connected to these front-row headers 13.
Each of the pair of front-row headers 13 has a cylindrical shape, and has a closed upper end and a closed lower end.
The refrigerant flows into each of the flat tubes 11 through one (13A) of the pair of front-row headers 13, and the refrigerant flows out to the other (13B) of the pair of front-row headers 13 from each of the flat tubes 11.
The front-row header 13A includes an introduction portion 131 that introduces the refrigerant from an unillustrated refrigerant pipe or the like to the inside of the front-row header 13. The inside of the front-row header 13A serves as a flow path through which the refrigerant introduced through the introduction portion 131 flows upward.
The introduction portion 131 is preferably located below the flat tube 11 that is disposed at the lowest part inside the front-row header 13A because a gas-phase refrigerant floating from the introduction portion 131 and a liquid refrigerant lifted together with the gas-phase refrigerant can flow into all of the flat tubes 11 including the flat tube 11 disposed at the lowest part in the front row F.
The refrigerant introduced into the front-row header 13A is distributed and flows into each of the flat tubes 11 in the front row F. Further, heat is exchanged between the air passing through the gaps (air passages) between the fins 12 and the flat tubes 11 and the refrigerant inside the flat tubes 11 while the refrigerant flows through each of the flat tubes 11 (dashed arrows in FIG. 1). At this time, the refrigerant flowing through the flat tubes 11 evaporates by absorbing heat from the air.
The refrigerant having flowed through each of the flat tubes 11 is merged inside the front-row header 13B, and the merged refrigerant flows out from the front-row header 13B to a refrigerant pipe or the like outside the heat exchanger 1. Alternatively, in a case where the heat exchanger 1 includes the other heat exchange element connected to the front-row header 13B, the refrigerant flows out from the front-row header 13B to the other heat exchange element.

(Rear-Row Header)

The rear-row headers 23 are briefly described because the rear-row headers 23 have a configuration similar to the configuration of the front-row headers 13 except that each of the rear-row headers 23 has a flow path cross-sectional area different from a flow path cross-sectional area of each of the front-row headers 13.
The refrigerant flows into each of the flat tubes 11 in the rear row R through one (23A) of the pair of rear-row headers 23, and the refrigerant flows out to the other (23B) of the pair of rear-row headers 23 from each of the flat tubes 11 in the rear row R.
The rear-row header 23A includes an introduction portion 231 that introduces the refrigerant from a refrigerant pipe or the like to the inside of the rear-row header 23.
The refrigerant introduced into the rear-row header 23A through the introduction portion 231 is distributed and flows into each of the flat tubes 11 in the rear row R. The refrigerant flowing through each of the flat tubes 11 in the rear row R is subjected to heat exchange with the air passing through the front row F. Thereafter, the refrigerant is merged inside the rear-row header 23B, and the merged refrigerant flows out from the rear-row header 23B to a refrigerant pipe outside the heat exchanger 1 or to the other heat exchange element.
The heat exchanger 1 is basically used in a state where the front-row headers 13 and the rear-row headers 23 are disposed along the up-and-down direction D1 (vertical direction). At this time, the flat tubes 11 extend in a horizontal direction and are stacked in the up-and-down direction D1.
Note that the front-row headers 13 and the rear-row headers 23 may be slightly inclined with respect to the up-and-down direction D1.

(Main Characteristics of Present Embodiment)

The present embodiment is mainly characterized in that a flow path cross-sectional area Af (FIG. 2) of each of the front-row headers 13 is smaller than a flow path cross-sectional area Ar (FIG. 2) of each of the rear-row headers 23 such that flow velocity of the refrigerant flowing through each of the front-row headers 13 is higher than flow velocity of the refrigerant flowing through each of the rear-row headers 23.
Each of the front-row headers 13 and the rear-row headers 23 according to the present embodiment includes a flow path having a circular cross-section, and an inner diameter of each of the front-row headers 13 is smaller than an inner diameter of each of the rear-row headers 23.
Note that the cross-sectional shape of each of the front-row headers 13 and the rear-row headers 23 may be an optional shape such as a rectangular shape and an elliptical shape.
As illustrated in FIG. 5, the appropriate flow path cross-sectional areas Af and Ar can be set by respectively installing vertical partition plates 14 and 24 inside the front-row header 13 and the rear-row header 23. Only either one of the vertical partition plates 14 and 24 may be installed.
The vertical partition plate 14 is erected along the up-and-down direction D1 orthogonal to a paper surface of FIG. 5, and partitions the inside of the front-row header 13 into a section 141 on the introduction portion 131 side and a section 142 on the flat tubes 11 side.
The refrigerant introduced from the introduction portion 131 into the section 141 flows into the section 142 through an opening 14A that penetrates a lower end part of the vertical partition plate 14 in a thickness direction, and is distributed to each of the flat tubes 11 while flowing upward inside the section 142.
The vertical partition plate 24 has a similar configuration to the above-described vertical partition plate 14, and partitions the inside of the rear-row header 23 into a section 241 on the introduction portion 231 side and a section 242 on the flat tubes 11 side. An opening 24A is provided at a lower end part of the vertical partition plate 24.
When positions of the vertical partition plates 14 and 24 are set such that a dimension G2 of a gap between the vertical partition plate 24 and the end part of each of the flat tubes 11 is larger than a dimension G1 of a gap between the vertical partition plate 14 and each of the flat tubes 11, the flow path cross-sectional area Ar that is larger than the flow path cross-sectional area Af of the section 142 of the front-row header 13 can be provided to the section 242 of the rear-row headers 23.

(Action by Present Embodiment)

As illustrated in FIG. 2, the refrigerant having flowed, at the predetermined flow rate, from the pipe of the refrigerant circuit into the front-row header 13A through the introduction portion 131 is distributed to each of the flat tubes 11 in the front row while flowing upward inside the front-row header 13A at the flow velocity Vf corresponding to the flow path cross-sectional area Af of the front-row header 13A.
In contrast, the refrigerant having flowed, at the flow rate same as the flow rate of the refrigerant flowing into the introduction portion 131 of the front-row header 13A, from the pipe of the refrigerant circuit into the rear-row header 23A through the introduction portion 231 is distributed to each of the flat tubes 11 in the rear row while flowing upward inside the rear-row header 23A at the flow velocity Vr corresponding to the flow path cross-sectional area Ar of the rear-row header 23A.
At this time, since the flow rate of the refrigerant flowing into the front-row header 13 through the introduction portion 131 and the flow rate of the refrigerant flowing into the rear-row header 23 through the introduction portion 231 are equal to each other and Af < Ar is satisfied for the flow path cross-sectional areas, Vf > Vr is established for the flow velocities. In other words, the flow velocity Vf of the refrigerant flowing through the front-row header 13A is higher than the flow velocity Vr of the refrigerant flowing through the rear-row header 23A.
Lengths of arrows illustrated in grey in FIG. 2 schematically represent relative magnitudes of the flow velocities Vf and Vr.
The refrigerant of a gas-liquid two-phase flow expanded by passing through the decompression unit of the refrigerant circuit flows into the front-row header 13A and the rear-row header 23A. A gas-phase component of the refrigerant is referred to as a gas-phase refrigerant, and a liquid-phase component of the refrigerant is referred to as a liquid-phase refrigerant. The liquid-phase refrigerant is carried upward by being caught in the floating gas-phase refrigerant. Density of the liquid-phase refrigerant is larger than density of the gas-phase refrigerant. Therefore, distribution of the gas-phase refrigerant and the liquid-phase refrigerant in the up-and-down direction D1 is easily deviated in each of the front-row header 13A and the rear-row header 23A.
Such a distribution state of the gas-phase refrigerant and the liquid-phase refrigerant is different between the front-row header 13A and the rear-row header 23A based on difference between the flow velocities Vf and Vr.
In the front-row header 13A having the higher flow velocity Vf, the liquid-phase refrigerant is carried to an upper part as compared with the rear-row header 23A having the relatively low flow velocity Vr. Accordingly, a percentage of the liquid-phase refrigerant to the gas-phase refrigerant is relatively high in an upper part of the flow path from an lower end to an upper end of the front-row header 13A, and the percentage of the liquid-phase refrigerant to the gas-phase refrigerant is low in a lower part of the flow path. The liquid-phase refrigerant that makes a phase transition to the gas phase while flowing through the flat tubes 11 absorbs heat from the air based on latent heat. When the flow percentage of the liquid-phase refrigerant is high, a heat transfer amount between the air and the refrigerant is large.
A width of each of the grey arrows illustrated in FIG. 2 represents the percentage of the liquid-phase refrigerant to the gas-phase refrigerant based on the flow rate. In the front-row header 13A, the flow percentage of the liquid-phase refrigerant is gradually increased as it goes upward from a lower side.
In contrast, in the rear-row header 23A having the low flow velocity Vr, the liquid-phase refrigerant is difficult to be carried to an upper part as compared with the front-row header 13A. Therefore, a range where the liquid-phase refrigerant is sufficiently carried from the introduction portion 231 is limited to the lower part of the flow path of the rear-row header 23A.
Accordingly, contrary to the above-described front-row header 13A, the percentage of the liquid-phase refrigerant to the gas-phase refrigerant is high at the lower part of the flow path of the rear-row header 23A, and the percentage of the liquid-phase refrigerant to the gas-phase refrigerant is low at the upper part of the flow path.
Accordingly, in both of the distribution state of the liquid-phase refrigerant distributed from the front-row header 13A to each of the flat tubes 11 in the front row F and the distribution state of the liquid-phase refrigerant distributed from the rear-row header 23A to each of the flat tubes 11 in the rear row R, deviation in the up-and-down direction D1 is found in different forms.
FIGS. 3A to 3C respectively illustrate the flow percentage of the liquid-phase refrigerant (flow ratio to gas-phase refrigerant) in the refrigerant having flowed into the flat tubes 11 in each of the front row F and the rear row R based on experimental results in a case FIG. 3A where the flow rate of the refrigerant introduced into the heat exchanger 1 is small, in a case FIG. 3B where the flow rate is middle, and in a case FIG. 3C where the flow rate is large. The numbers 1, 2, 3, ... are provided to the flat tubes 11 in order from the flat tube 11 located at the uppermost part to the flat tube 11 located at the lower part in each of the front-row header 13A and the rear-row header 23A. Note that, in the experiment to obtain the data in FIGS. 3A to 3C, a front-row heat exchange element and a rear-row heat exchange element each including seven flat tubes 11 were used.
FIGS. 3A to 3C all illustrate a tendency similar to the above description, namely, a tendency that the percentage of the flowing-in liquid-phase refrigerant is high in the flat tube 11 located at the upper part in the front row F whereas the percentage of the flowing-in liquid-phase refrigerant is high in the flat tube 11 located at the lower part in the rear row R.
As illustrated in FIGS. 3A to 3C, the deviation degree of the flow percentage of the liquid-phase refrigerant in the up-and-down direction D1 in the front row F is increased as the flow rate of the refrigerant is increased. In contrast, the deviation degree of the flow percentage of the liquid-phase refrigerant in the up-and-down direction D1 in the rear row R is decreased as the flow rate of the refrigerant is increased. The tendency is qualitatively established because the flow path cross-sectional area of each of the front-row headers 13 is smaller than the flow path cross-sectional area of each of the rear-row headers 23.
As the flow rate relating to FIG. 3C, the flow rate of the heat exchanger 1 under a situation where frosting easily occurs, for example, under a situation where the air conditioner performs heating operation in winter is assumed. When the flow rate is large as described above, uneven distribution of the liquid-phase refrigerant at the upper part in the front row F becomes remarkable as illustrated in FIG. 3C. At this time, in the heat exchange element 10 in the front row F, heat exchange is mainly performed at an upper stage.

(Effects by Present Embodiment)

In the present embodiment, as described above, the flow path cross-sectional area Af of each of the front-row headers 13 and the flow path cross-sectional area Ar of each of the rear-row headers 23 are made different from each other to provide different distribution to the liquid-phase refrigerants in the front row F and the rear row R. This suppresses heat transfer loss and secures heat exchange performance as a whole of the heat exchanger 1.
Action of the preset embodiment is described with reference to FIG. 4 and FIG. 2. According to the present embodiment, even when deviation is present in the liquid-phase flow percentage of the refrigerant distributed to each of the flat tubes 11 in each of the front row F and the rear row R, the heat transfer amount is uniformized and necessary heat exchange performance is secured even under restriction of the capacity of the heat exchanger or the like, as a whole of the heat exchanger 1.
In the front-row header 13 (FIG. 2) having the high flow velocity, the liquid-phase refrigerant is sufficiently carried to the upper part. Therefore, the heat transfer amount between the air and the refrigerant flowing through the flat tube 11 on the upper stage side having the large flow percentage of the liquid-phase refrigerant among the flat tubes 11 in the front row F to which the refrigerant is distributed from the front-row header 13 is large, whereas the heat transfer amount at the lower part is small.
In contrast, in the rear-row header 23 (FIG. 2) having the flow velocity lower than the flow velocity of the front-row header 13, the liquid-phase refrigerant is not sufficiently carried to the upper part. Therefore, the heat transfer amount between the air and the refrigerant flowing through the flat tube 11 on the lower stage side having the large flow percentage of the liquid-phase refrigerant among the flat tubes 11 in the rear row R to which the refrigerant is distributed from the rear-row header 23 is large, whereas the heat transfer amount at the upper part is small.
The air flowing along an arrow 1 illustrated in FIG. 4 passes through the lower stage side having the small heat transfer amount in the front row F and the lower stage side having the large heat transfer amount in the rear row R. At this time, even if heat of the air that has passed through the lower stage side having the low flow percentage of the liquid-phase refrigerant in the front row F is not sufficiently dissipated to the refrigerant, an amount of the liquid-phase refrigerant flowing through the flat tubes 11 on the lower stage side in the rear row R into which the air flows subsequently to the front row F is sufficient to dissipate heat of the air.
Further, the air flowing along an arrow 2 illustrated in FIG. 4 passes through the upper stage side having the large heat transfer amount in the front row F and the upper stage side having the small heat transfer amount in the rear row R. In this case, the air, the heat of which has been already dissipated to the refrigerant that has the high flow percentage of the liquid-phase refrigerant in the upper stage side of the front row F, flows into the rear row R. Accordingly, it is sufficient that the liquid-phase refrigerant of an amount enough to heat exchange with the air after the heat dissipation in the front row F flows through the flat tubes 11 on the upper stage side in the rear row R.
Accordingly, the heat transfer surface is effectively utilized while the heat transfer loss is avoided over the whole of the heat exchanger 1 including the upper stage side and the lower stage side of the front row F and the upper stage side and the lower stage side of the rear row R. Therefore, even when the heat exchanger 1 is small, it is possible to sufficiently secure the heat exchange performance. The flow velocity is made different between the front-row header 13 and the rear-row header 23 as with the present embodiment, which makes it possible to balance the heat transfer amount in the up-and-down direction D1 as the whole of the front row F and the rear row R as described above. This can avoid deterioration of the heat exchange performance due to deviation of the refrigerant distribution. As a result, it is unnecessary to provide the horizontal partition plate in each of the headers 13 and 23 for uniformization of the refrigerant distribution. This makes it possible to avoid increase of the number of parts, and to suppress a manufacturing cost of the heat exchanger 1.
Contrary to the present embodiment, even in a case where the flow path cross-sectional areas are determined so as to establish Af > Ar, and the flow velocity Vf of the front-row header 13 is made lower than the flow velocity Vr of the rear-row header 23, effects similar to the effects by the present embodiment can be achieved in terms of avoidance of performance deterioration due to deviation of the refrigerant distribution.
Further, the present embodiment cope with performance deterioration caused by frosting in addition to performance deterioration caused by deviation of the refrigerant distribution. When temperature of external air as a heat source is low during heating operation, frosting progresses from the front row F that is largely different in temperature with the contact air as compared with the rear row R in the heat exchanger 1 used in an outdoor heat exchanger of the air conditioner. Alternatively, frosting may occur in the heat exchanger 1 used to cool a heat load, for example, a heat exchanger inside a refrigerator/freezer such as a refrigerating/freezing showcase. Also in this case, frosting progresses from the front row F.
To avoid the performance deterioration caused by frosting, it is preferable that relationship between the flow velocity Vf of the front-row header 13 and the flow velocity Vr of the rear-row header 23 be specified such that the flow velocity Vf of the front-row header 13 is larger than the flow velocity Vr of the rear-row header 23, as with the present embodiment. Further, in the present embodiment in which the refrigerant at the same flow rate is introduced to each of the front row F and the rear row R, the flow path cross-sectional areas are specified to Af < Ar.
In the upper stage side having the large flow percentage of the liquid-phase refrigerant in the front row F where frosting easily occurs, frosting easily occurs because the air is sufficiently cooled by the refrigerant having the large flow percentage of the liquid-phase refrigerant. In contrast, frosting hardly occurs on the lower stage side even in the front row F. In other words, deviation of frosting occurs in a manner similar to deviation of the flow percentage of the liquid-phase refrigerant in the up-and-down direction D1 in the front row (for example, FIG. 3C).
It is assumed that frosting on the upper stage side in the front row F having the large flow percentage of the liquid-phase refrigerant progresses as illustrated in FIG. 3C and an air flow rate on the upper stage side in the rear row R is reduced due to closing of the air passage caused by the frost. At this time, however, frosting does not much progress on the lower stage side in the front row F. Therefore, the air flow rate can be maintained at least on the lower stage side in the rear row R on the leeward of the lower stage side of the front row F.
In other words, after the heat exchange capability on the upper stage side including the rear row R is lost due to frosting, the air is fed to the rear row R on the lower stage side. Since the heat exchange capability remains on the heat transfer surface on the lower stage side in the rear row R on which frost is not attached, a time before operation is switched to defrosting operation is prolonged.
According to the present embodiment, suppressing heat transmission loss caused by frosting makes it possible to avoid interruption of the heating operation or the like by defrosting operation, and to continue the heating operation or the like.
FIG. 6 illustrates an example in which each of the flat tubes 11 inserted into the rear-row headers 23 each having a diameter larger than the diameter of each of the front-row headers 13 has a width Dr wider than a width Df of each of the flat tubes 11 in the front row F. To increase the heat transfer area, the large width Dr of each of the flat tubes 11 in the air flowing direction substantially equal to the diameter of each of the rear-row headers 23 is preferably secured. Widening the width Dr of each of the flat tubes 11 in the rear row R makes it possible to improve capability of the heat exchanger 1 without changing a space necessary for installation of the heat exchanger 1.
Note that, instead of widening the width Dr of each of the flat tubes 11 in the rear row R, two flat tubes 11 may be arranged in the width direction.

[Second Embodiment]

Next, a second embodiment of the present invention is described with reference to FIGS. 7A to 7D.
In the second embodiment, an example of application to a heat exchanger including a plurality of paths connected in serial is described.
A heat exchanger 2 illustrated in FIG. 7A includes the heat exchange elements 10 and 20 corresponding to the paths connected in series. This is different from the heat exchange elements 10 and 20 that are connected to the pipe of the refrigerant circuit in parallel, of the heat exchanger 1 according to the first embodiment.
FIG. 7A schematically illustrates the heat exchange elements 10 and 20. The heat exchange elements 10 and 20 each have a similar configuration to the respective heat exchange elements 10 and 20 in the first embodiment (FIG. 1) .
In other words, as illustrated in FIG. 1, the front-row heat exchange element 10 includes the flat tubes 11, the fins 12, and the front-row headers 13. The rear-row heat exchange element 20 also includes the flat tubes 11, the fins 12, and the rear-row headers 23. Since the flow path cross-sectional area Af of each of the front-row headers 13 is smaller than the flow path cross-sectional area Ar of each of the rear-row headers 23, the refrigerant flow velocity Vf of each of the front-row headers 13 is higher than the refrigerant flow velocity Vr of each of the rear-row headers 23.
As with the first embodiment, the heat transfer amount in the up-and-down direction D1 as the whole of the front row F and the rear row R can be balanced based on the flow velocity difference, and the time before operation is switched to the defrosting operation when frosting occurs can be prolonged.
The rear-row heat exchange element 20 corresponds to a first path P1 on the most upstream side. The front-row heat exchange element 10 corresponds to a second path P2 subsequent to the first path P1. In this example, the second path P2 is a path on the most downstream side.
Dryness of the refrigerant is increased while the refrigerant flows from the most upstream path P1 to the most downstream path P2.
When the refrigerant is introduced from an unillustrated refrigerant pipe to the rear-row header 23A (FIG. 1) of the first path P1, the refrigerant is distributed from the rear-row header 23A to each of the flat tubes 11 in the rear row R. The refrigerant having flowed through each of the flat tubes 11 is merged inside the rear-row header 23B (FIG. 1), and the merged refrigerant flows into the second path P2 in the front row F through a U-shaped pipe 17. Thereafter, the refrigerant is distributed from the front-row header 13B (FIG. 1) in the second path P2 to each of the flat tubes 11 in the flat row F, and the refrigerant having flowed through each of the flat tubes 11 flows out from the front-row header 13A (FIG. 1) to the refrigerant pipe.
When the refrigerant absorbs heat from the air and dryness of the refrigerant is increased, an absolute amount of the flow percentage of the liquid-phase refrigerant is reduced. Therefore, it is particularly difficult to cause the liquid-phase refrigerant to flow into the flat tube 11 on the upper stage side inside the header in the most downstream path P2.
FIG. 7C and FIG. 7D both illustrate the liquid-phase refrigerant distribution in a case where dryness of the refrigerant is high, based on the experiment; however, the flow path cross-sectional area of a header is different in FIG. 7C and FIG. 7D. FIG. 7C illustrates a case where the header has a typical flow path cross-sectional area (for example, flow path cross-sectional area Am in FIG. 8), and FIG. 7D illustrates a case where the flow path cross-sectional area of the header is smaller than the typical area. Since the refrigerant flow rate is the same in FIGS. 7C and 7D, the flow velocity inside the header is higher in the header having the small flow path cross-sectional area (FIG. 7D). Accordingly, as compared with the header in which the flow velocity is relatively low in FIG. 7C, the liquid-phase refrigerant reaches up to the flat tube 11 located at the upper part in the header illustrated in FIG. 7D.
Based on the above description, the most downstream path P2 where dryness is the highest is disposed in the front row F as illustrated in FIG. 7A. In the front-row headers 13 where the flow velocity is high because of the small flow path cross-sectional area, the liquid-phase refrigerant can be sufficiently lifted to the upper part so as to flow into the flat tube 11 located at the upper part. As a result, the heat transfer surface of the most downstream path P2 can be sufficiently used and can contribute to performance.

[Modification of Second Embodiment]

In a case where a heat exchanger 2A includes three or more paths connected in series as illustrated in FIG. 7B, a fourth path P4 on the most downstream side is preferably disposed in the front row F and the first path P1 on the most upstream side is also preferably disposed in the front row F as with illustration in FIG. 7A.
The second path P2 and a third path P3 are disposed in the rear row R.
The heat exchanger 2A includes the four paths P1 to P4. The first path P1 and the second path P2 on the upstream side are located at the lower part in the heat exchanger 2A, and the third path P3 and the fourth path P4 on the downstream side are located at the upper part in the heat exchanger 2A.
On the upstream side of a serial circuit in the heat exchanger 2A, pressure loss at the same flow path cross-sectional area is lower than pressure loss on the downstream side because the liquid-phase refrigerant is larger on the upstream side than on the downstream side where dryness is increased. Accordingly, the flow path cross-sectional area of each of the paths P1 and P2 on the upstream side is suppressed (number of stages (number of flat tubes 11) is reduced) to a degree not causing excess pressure loss as compared with the paths P3 and P4 on the downstream side, thereby suppressing a height of the heat exchanger 2A.
FIG. 7B also schematically illustrates the heat exchange elements 10 and 20. The heat exchange elements 10 and 20 each have a similar configuration to the respective heat exchange elements 10 and 20 in the first embodiment (FIG. 1).
As with the first embodiment, the heat transfer amount as the whole of the front row F and the rear row R can be balanced based on the flow velocity difference between the front-row headers 13 and the rear-row headers 23, and the time before operation is switched to the defrosting operation when frosting occurs can be prolonged.
When the refrigerant is introduced to the header 13A (FIG. 1) of the first path P1 in the configuration illustrated in FIG. 7B, the refrigerant is distributed from the front-row header 13A to each of the flat tubes 11 in the front row F. The refrigerant having flowed through each of the flat tubes 11 is merged inside the front-row header 13B (FIG. 1), and the merged refrigerant flows into the second path P2 in the rear row R through a U-shaped pipe 181. Thereafter, the refrigerant is distributed from the rear-row header 23B of the second path P2 to each of the flat tubes 11, and the refrigerant having flowed through each of the flat tubes 11 flows from the rear-row header 23A into the rear-row header 23A of the third path P3 on the upper stage side through a U-shaped pipe 182. Furthermore, the refrigerant flows through the flat tubes 11 of the third path P3, and flows into the front-row header 13B of the fourth path P4 through a U-shaped pipe 183. Thereafter, the refrigerant flows through the flat tubes 11 of the fourth path P4 and then flows out to the refrigerant pipe.
According to the configuration illustrated in FIG. 7B, the most downstream path P4 where the dryness is the highest is disposed in the front row F as with the second embodiment illustrated in FIG. 7A. This makes it possible to sufficiently use the heat transfer surface of the most downstream path P4 and to contribute to performance.
In addition, the flow path cross-sectional area is small in the header 13 in the most upstream path P1 where the refrigerant pressure loss is relatively small due to the lowest dryness of the refrigerant flowing into the header 13, in particular, in the header 13A as an inlet of the path P1. This makes it possible to suppress rise of evaporation temperature caused by the refrigerant pressure loss. Suppressing rise of the evaporation temperature makes it possible to avoid deterioration of evaporation performance.

[Third Embodiment]

Next, a third embodiment is described with reference to FIGS. 8A and 8B.
A heat exchanger 3 according to the third embodiment illustrated in FIG. 8A includes the front-row heat exchange element 10 and the rear-row heat exchange element 20 as with the heat exchanger 1 (FIG. 2) according to the first embodiment.
In the first embodiment (FIG. 2), the flow path cross-sectional area Af smaller than the flow path cross-sectional area Ar of the rear-row header 23 is provided to the front-row header 13 such that the flow velocity Vf of the front-row header 13 is larger than the flow velocity Vr of the rear-row header 23. In contrast, in the third embodiment, a distributer 15 (flow rate adjusting unit) that can adjust the flow rate of the refrigerant to be introduced to each of the front-row header 13 and the rear-row header 23 is used.
The distributer 15 including a capillary tube and the like divides the refrigerant flowing in from the unillustrated refrigerant pipe, at a predetermined flow ratio such that a flow rate Rf of the refrigerant flowing into the front-row header 13 is larger than a flow rate Rr of the refrigerant flowing into the rear-row header 23.
As a result, the flow velocity Vf corresponding to the flow rate Rf and the flow path cross-sectional area Am is given to the front-row header 13, and the flow velocity Vr corresponding to the flow rate Rr and the flow path cross-sectional area Am is given to the rear-row header 23.
In the present embodiment, since the flow path cross-sectional area Am of the front-row header 13 and the flow path cross-sectional area Am of the rear-row header 23 are equivalent to each other, Rf/Rr = Vf/Vr is established.
According to the present embodiment, the distributer 15 is provided. Therefore, even when the flow path cross-sectional area of the front-row header 13 and the flow path cross-sectional area of the rear-row header 23 are equivalent to each other, the flow velocity difference of the refrigerant is given to the front-row header 13 and the rear-row header 23, and action and effects similar to the action and the effects according to the first embodiment can be achieved based on the distribution of the flow percentage of the liquid-phase refrigerant in the up-and-down direction D1 caused by the flow velocity difference.
Further, using the same headers with the same diameter makes it possible to prevent misassembly of the front-row heat exchange element 10 and the rear-row heat exchange element 20 in manufacturing of the heat exchanger 3.
In place of the distributer 15, a throttle 16 (flow rate adjusting unit) may be used as illustrated in FIG. 8B. The throttle 16 is provided on one conduit introduced to the rear-row header 23 out of conduits divided at the equivalent flow rate from the unillustrated refrigerant pipe. Pressure loss is given by the throttle 16 to the refrigerant flowing to the rear-row header 23. As a result, the flow rate Rr of the refrigerant introduced to the rear-row header 23 is smaller than the flow rate Rf of the refrigerant introduced to the front-row header 13.

[Fourth Embodiment]

Next, a fourth embodiment is described with reference to FIGS. 9A and 9B.
FIGS. 9A and 9B each illustrate a heat exchanger 4 having the same configuration. Illustration in FIGS. 9A and 9B is different only in an image of distribution of the liquid-phase refrigerant.
The heat exchanger 4 according to the fourth embodiment includes two heat exchange elements 10 stacked in the up-and-down direction D1 in the front row F, and two heat exchange elements 20 stacked in the up-and-down direction D1 in the rear row R.
In the heat exchanger 4, the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 are disposed while being shifted in the up-and-down direction D1. The front-row heat exchange elements 10 and the rear-row heat exchange elements 20 each have an equal height from a lower end to an upper end.
Further, the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 are connected to the pipe of the refrigerant circuit in parallel or in series, and the refrigerant of the same flow rate flows through the front-row heat exchange elements 10 and the rear-row heat exchange elements 20.
The heat exchanger 4 includes the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 that each have a similar configuration to the front-row heat exchange element 10 and the rear-row heat exchange element 20, respectively, according to the first embodiment. Unlike the first embodiment, however, the flow path cross-sectional area of each of the front-row headers 13 and the flow path cross-sectional area of each of the rear-row headers 23 are equivalent to each other.
Since the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 are shifted in the up-and-down direction D1, the positions of the introduction portions 131 connected to the front-row headers 13 and the positions of the introduction portions 231 connected to the rear-row headers 23 are different in the up-and-down direction D1.
In a case where the flow rate of the refrigerant is small or in a case where dryness is high, the flow velocity of the liquid-phase refrigerant having flowed into each of the headers 13 and 23 is low as illustrated by grey arrows representing distribution images of the liquid-phase refrigerant along the up-and-down direction D1 in FIG. 9A. Therefore, the liquid-phase refrigerant easily flows into the flat tubes 11 at the lower part, namely, on the lower stage side of each of the headers 13 and 23.
In contrast, in a case where the flow rate of the refrigerant is large or in a case where dryness is low, the flow velocity of the liquid refrigerant is high as illustrated by grey arrows representing distribution images of the liquid-phase refrigerant along the up-and-down direction in FIG. 9B. Therefore, the liquid-phase refrigerant easily flows into the flat tubes 11 at the upper part, namely, on the upper stage side of each of the headers 13 and 23.
As a result, as described with reference to FIG. 4, the heat transfer amount in the up-and-down direction D1 as the whole of the front row F and the rear row R can be balanced, and the time before operation is switched to the defrosting operation when frosting occurs can be prolonged.
Further, using the same headers with the same diameter makes it possible to prevent misassembly of the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 in manufacturing of the heat exchanger 4.
In the fourth embodiment, the inside of the front-row header 13 and the rear-row header 23 may be partitioned into a plurality of sections, and introduction portions that introduce the refrigerant to the respective sections may be prepared. Also in this case, the introduction portions in the front row F and the introduction portions in the rear row R can be made different in height position from each other by shifting the front-row heat exchange elements 10 and the rear-row heat exchange elements 20 in the up-and-down direction D1. Therefore, similar action and effects can be achieved.
Other than the above description, the configurations described in the above-described embodiments can be selected or appropriately modified without departing from the scope of the present invention as defined in the appended claims.
For example, any of the heat exchangers according to the present invention may include one or more middle rows located between the front row F and the rear row R in addition to the front row F and the rear row R.
In each of the above-described embodiments, each of the heat exchange elements 10 and 20 includes one line of flat tube element including the plurality of flat tubes 11 stacked in the up-and-down direction D1. The configuration is not limited thereto, and each of the heat exchange elements according to the present invention may include two lines, namely, two flat tube elements arranged side by side in the air flowing direction, and these flat tube elements may be connected to the same headers.

Reference Signs List

1 to 4: Heat exchanger
10: Front-row heat exchange element
11: Flat tube
12: Fin
13, 13A, 13B: Front-row header
14: Vertical partition plate (partition portion)
14A: Opening
15: Distributer (flow rate adjusting unit)
16: Throttle (flow rate adjusting unit)
17: U-shaped pipe
20: Rear-row heat exchange element
23, 23A, 23B: Rear-row header
24: Vertical partition plate (partition portion)
24A: Opening
121: Notch
131: Introduction portion
141: Section
142: Section
181, 182, 183: U-shaped pipe
231: Introduction portion
241: Section
242: Section
Af, Ar, Am: Flow path cross-sectional area
D1: Up-and-down direction
Df,: Dr Width
F: Front row
G1: Dimension
G2: Dimension
P1 to P4: Path
R: Rear row
Rf, Rr: Flow rate
Vf, Vr: Flow velocity

Claims

A heat exchanger (1), comprising:
a front-row heat exchange element (10) and a rear-row heat exchange element (20);

the front-row heat exchange element (10) includes a plurality of stacked flat tubes (11);

fins (12) provided on the flat tubes (11); and

front row headers (13) erected in a stacking direction in which the flat tubes (11) are stacked, and connected to the flat tubes (11), wherein

the front-row heat exchange element (10) is configured to function as an evaporator that causes heat exchange between air and a refrigerant flowing into the flat tubes (11) through the headers (13), to evaporate the refrigerant,

the rear-row heat exchange element (20) includes a plurality of stacked flat tubes (11);

fins (12) provided on the flat tubes (11); and

rear row headers (23) erected in a stacking direction in which the flat tubes (11) are stacked, and connected to the flat tubes (11), the rear-row heat exchange element (20) is configured to function as an evaporator that causes heat exchange between air and a refrigerant flowing into the flat tubes (11) through the headers (23), to evaporate the refrigerant,

the front-row heat exchange element (10) and the rear-row heat exchange element (20) are in use arranged in the air flowing direction with the front-row heat exchange element (10)arranged in a front row (F) located on an upstream side of the flow of the air and the rear-row heat exchange element (20) arranged in a rear row (R) located on a downstream side of the flow of the air,

characterised in that

a flow path cross-sectional area (A_f) of each of front-row headers (13) is smaller than a flow path cross-sectional area (A_r) of each of rear-row headers (23), the heat exchanger being configured such that a flow velocity of the refrigerant flowing through each of the front-row headers (13) is higher than a flow velocity of the refrigerant flowing through each of the rear-row headers (23).
The heat exchanger according to claim 1, further comprising a partition portion (14) configured to partition an inside of at least any of the front-row headers (13) and the rear-row headers (13) by extending in the stacking direction, wherein
the flow path cross-sectional area is set by the partition portion (14).
The heat exchanger according to claim 1 or 2, wherein a width of each of the flat tubes (11) in the rear row (R) in a flowing direction of the air is wider than a width of each of the flat tubes (11) in the front row (F) in the flowing direction of the air.
The heat exchanger according to any one of claims 1 to 3, wherein
the heat exchange elements include two or more heat exchange elements connected in series, and

a heat exchange element of the heat exchange elements on a most downstream side is located in the front row (F).
The heat exchanger according to claim 4, wherein
the heat exchange elements include three or more heat exchange elements connected in series, and

a heat exchange element of the heat exchange elements on a most upstream side is located in the front row (F).