Patent Grant
12000633
The present application is based on PCT filing PCT/JP2019/001630, filed Jan. 21, 2019, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a heat exchanger including a plurality of heat transfer tubes and two header distributors, and also to an air-conditioning apparatus.
In the past, regarding a heat exchanger that is applied to, for example, an air-conditioning apparatus, a refrigerant distribution technique has been provided as a technique for causing two-phase gas-liquid refrigerant to flow in a plurality of heat transfer tubes connected to a header distributor, which is a refrigerant distributor. In this technique, distribution characteristics, such as the amounts of liquid refrigerant that flows through the heat transfer tubes, vary depending on flow resistances in the header distributor and the heat transfer tubes and pressure losses caused by the flow resistances. This affects a heat exchange performance. In addition, the heat exchange performance is affected not only by the refrigerant distribution characteristics but also by the pressure losses in the header distributor and the heat transfer tubes.
Therefore, in a technique disclosed in Patent Literature 1, refrigerant that is made to branch from a first header distributor into streams to flow into a plurality of heat transfer tubes, and the streams are then re-collected into single refrigerant to flow in a second header distributor. In this case, an adverse effect on the distribution of the refrigerant at the first header distributor do not affect a downstream side.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2010-190541
However, any of heat exchangers has a problem that when the flow rate of the refrigerant that flows into the header distributor varies, the refrigerant distribution characteristics are worsened and the heat exchange performance is deteriorated. In particular, when the flow rate of refrigerant is low, the heat exchange performance is remarkably deteriorated. Therefore, the specifications of the heat exchanger need to be changed each time a flow rate range of the refrigerant that flows through the heat exchanger is changed.
The present disclosure is applied to solve the above problem, and relates to a heat exchanger the specifications of which do not need to be changed each time the flow rate of refrigerant is changed or the kind of the refrigerant to be used is changed and also to an-air conditioning apparatus provided with such a heat exchanger.
A heat exchanger according to an embodiment of the present disclosure includes: a plurality of heat transfer tubes; a liquid header distributor to which one end of each of the plurality of heat transfer tubes is connected and in which an upward flow of two-phase gas-liquid refrigerant is generated; and a gas header distributor to which an other end of each of the plurality of heat transfer tubes is connected and in which a flow of gas phase refrigerant is generated. The plurality of heat transfer tubes include U-shaped bent portions at each of which a flow passage is bent. The heat exchanger includes a heat exchanger core that includes the plurality of heat transfer tubes and one or more fins. A relationship between the liquid header distributor and the plurality of heat transfer tubes is established such that 9≤ζ is satisfied, where Lh [m] is a length of the liquid header distributor that corresponds to a distance between a central axis of one of the plurality of heat transfer tubes that is the closest to an inlet of the liquid header distributor and a central axis of one of the plurality of heat transfer tubes that is the farthest from the inlet of the liquid header distributor, Lb [m] is a length of a shortest one of the plurality of heat transfer tubes, the length Lb of the shortest one of the plurality of heat transfer tubes corresponding to a distance by which the shortest one of the plurality of heat transfer tubes, which extends from the liquid header distributor to the gas header distributor through the heat exchanger core and the U-shaped bent portions, extends through the heat exchanger core, and ζ is a ratio of the length Lb of the shortest one of the plurality of heat transfer tubes to the length Lh of the liquid header distributor and is expressed by ζ=Lb/Lh.
An air-conditioning apparatus according to another embodiment of the present disclosure includes the heat exchanger.
In the heat exchanger and the air-conditioning apparatus according to the embodiments of the present disclosure, 9≤ζ is satisfied, where the ratio ζ of the length Lb of the shortest one of the heat transfer tubes to the length Lh of the liquid header distributor is expressed by ζ=Lb/Lh. Accordingly, the ratio of the flow resistance in the liquid header distributor to the flow resistance in the heat transfer tubes is sufficiently small. Therefore, the influence of the flow resistance in the liquid header distributor on the distribution of the refrigerant can be reduced, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of the refrigerant changes can be reduced, and the deterioration of the heat exchange performance can be reduced. As a result, it is not necessary to change the specifications of the heat exchanger each time the flow rate of refrigerant or the type of the refrigerant that is used is changed.
Embodiments of the present disclosure will be described with reference to the figures. In each of the figures, components that are the same as or equivalent to those in a previous figure or figures are denoted by the same reference signs. The same is true of the entire text of the specification. In sectional views, hatching is omitted as appropriate for visibility. Configurations of components described in the specification are merely examples, and such descriptions are not limiting.
<Heating Operation of Air-Conditioning Apparatus>
As illustrated in
The high-temperature and high-pressure gas refrigerant that has flowed into the indoor heat exchangers 30 exchanges heat with air supplied by indoor fans, and as a result transfers heat and condenses to change into high-temperature and high-pressure liquid refrigerant. The high-temperature and high-pressure liquid refrigerant then flows out of the indoor heat exchangers 30.
The liquid refrigerant that has flowed out of the indoor heat exchangers 30 is expanded and reduced in pressure at the expansion devices 31 to change into low-temperature and low-pressure two-phase gas-liquid refrigerant. The low-temperature and low-pressure two-phase gas-liquid refrigerant then flows into the outdoor heat exchanger 10.
The two-phase gas-liquid refrigerant that has flowed into the outdoor heat exchanger 10 exchanges heat with outdoor air supplied by an outdoor fan 36, which will be described below, and as a result receives heat and evaporates to change into low-temperature and low-pressure gas refrigerant. The low-temperature and low-pressure gas refrigerant then flows out of the outdoor heat exchanger 10.
The low-temperature and low-pressure gas refrigerant passes through the accumulator 32, and is re-sucked by the compressor 33. Then, the refrigerant is re-compressed and re-discharged. The above circulation of the refrigerant is repeated.
<Cooling Operation of Air-Conditioning Apparatus>
The high-temperature and high-pressure gas refrigerant that has flowed into the outdoor heat exchanger 10 exchanges heat with air supplied by the outdoor fan 36, and as a result transfers heat and condenses to change into high-temperature and high-pressure liquid refrigerant. The high-temperature and high-pressure liquid refrigerant then flows out of the outdoor heat exchanger 10.
The liquid refrigerant that has flowed out of the outdoor heat exchanger 10 is expanded and reduced in pressure at the expansion devices 31 to change into low-temperature and low-pressure two-phase gas-liquid refrigerant. The low-temperature and low-pressure two-phase gas-liquid refrigerant then flows into the indoor heat exchangers 30.
The two-phase gas-liquid refrigerant that has flowed into the indoor heat exchangers 30 exchanges heat with indoor air supplied by the indoor fans, and as a result receives heat and evaporates to change into low-temperature and low-pressure gas refrigerant. The low-temperature and low-pressure gas refrigerant then flows out of the indoor heat exchangers 30.
The low-temperature and low-pressure gas refrigerant passes through the accumulator 32 and is re-sucked by the compressor 33. Then, the refrigerant is re-compressed and re-discharged. The above circulation of the refrigerant is repeated.
The number of indoor heat exchangers 30 and the number of outdoor heat exchangers 10 are not limited to those as illustrated in
<Configuration of Outdoor Heat Exchanger 10>
Instead of the outdoor heat exchanger 10 as described below, the indoor heat exchanger 30 may be used. Each of the outdoor heat exchanger 10 and the indoor heat exchangers 30 will also be referred to simply as a heat exchanger.
The outdoor heat exchanger 10 includes a plurality of heat transfer tubes 11, a liquid header distributor 12, a gas header distributor 13, and a heat exchanger core 14.
The heat transfer tubes 11 extend straight in the heat exchanger core 14. Each of the heat transfer tubes 11 includes one or more U-shaped bent portions 16 at each of which a flow passage is bent in a direction other than a horizontal direction. That is, each of the heat transfer tubes 11 passes through the heat exchanger core 14 two or more times. The U-shaped bent portions 16 are located outside the heat exchanger core 14.
To the liquid header distributor 12, one end of each of the heat transfer tube 11 is connected, and an upward flow of two-phase gas-liquid refrigerant is generated in the liquid header distributor 12. That is, the liquid header distributor 12 causes the two-phase gas-liquid refrigerant to flow upward.
To the gas header distributor 13, the other end of each heat transfer tube 11 is connected, and a downward flow of gas phase refrigerant is generated in the gas header distributor 13. That is, the gas header distributor 13 causes gas phase refrigerant to flow downward.
Since the liquid header distributor 12 causes the two-phase gas-liquid refrigerant to flow upward, and the gas header distributor 13 causes the gas phase refrigerant to flow downward, the liquid header distributor 12 is located at a lower position than the gas header distributor 13.
The heat exchanger core 14 includes the heat transfer tubes 11 and a plurality of heat transfer fins (not illustrated) disposed between the heat transfer tubes 11. The heat transfer tubes 11 are circular tubes in which flow passages having a circular cross section are provided or flat tubes in which flow passages having an elongated cross section are provided. The refrigerant flows through the heat transfer tubes 11. The refrigerant in the heat transfer tubes 11 exchanges heat with air that flows in a region located outside the heat transfer tubes 11. The heat transfer tubes 11 extend straight in the heat exchanger core 14. The heat transfer fins are one or more metal members that are, for example, formed in the shape of plates. The shape of each of the heat transfer fins is not limited, and the heat transfer fins may be elongated or corrugated.
In the heat exchanger core 14, the plurality of heat transfer tubes 11 are arranged such that at least one heat transfer tube 11 located at an upper portion of the liquid header distributor 12 includes a larger number of U-shaped bent portions 16 than at least one heat transfer tube 11 located at a lower portion of the liquid header distributor 12. Alternatively, in the heat exchanger core 14, the plurality of heat transfer tubes may be arranged such that at least one heat transfer tube 11 located from an intermediate portion of the liquid header distributor 12 to the upper portion of the liquid header distributor 12 includes a larger number of U-shaped bent portions 16 than at least one heat transfer tube 11 located at the lower portion of the liquid header distributor 12.
The liquid header distributor 12 and the gas header distributor 13 include tubes that are thicker than the heat transfer tubes 11. The heat transfer tubes 11 are connected to the liquid header distributor 12 and the gas header distributor 13 such that the heat transfer tubes 11 are arranged and spaced from each other in a longitudinal direction of the liquid header distributor 12 and the gas header distributor 13. The two-phase gas-liquid refrigerant that flows through the liquid header distributor 12 in the longitudinal direction is distributed to the heat transfer tubes 11 in turn. The liquid header distributor 12 distributes refrigerant that is provided mainly as two-phase gas-liquid refrigerant and also contains liquid refrigerant, to the heat transfer tubes 11. The refrigerant evaporates to change into gas phase refrigerant in the heat transfer tubes 11, and is collected in the gas header distributor 13. Then, the refrigerant passes through the accumulator 32 and is sucked by the compressor 33.
In the example illustrated in
The heat transfer tubes 11 in which flow passages extend from the liquid header distributor 12 to the gas header distributor 13 include U-shaped bent portions 16 that are bent upward in such a manner as to be U-shaped. Each of the heat transfer tubes 11 includes one or more U-shaped bent portions 16. The U-shaped bent portions 16 are bent in such a manner as to be U-shaped, in a direction other than the horizontal direction, for example, in a vertical direction or an obliquely upward or downward direction.
Referring to
<Shape of Outdoor Heat Exchanger 10>
The heat exchanger core 14 may be bent two or more times to have a U-shape or a rectangular shape, or have a flat plate shape with no bent portion, depending on the shape of a housing.
In the comparative example, which corresponds to the related art, when two-phase gas-liquid refrigerant that flows upward from the lower portion of the liquid header distributor 12 at a low flow rate is distributed to the heat transfer tubes 11, the refrigerant also flows in the plurality of heat exchanger tubes 11 at a low flow rate. As a result, the pressure loss in the heat transfer tubes 11 is remarkably low, and the ratio of the pressure loss due to gravity in the liquid header distributor 12 is relatively high. Therefore, liquid refrigerant does not easily flow to the upper portion of the liquid header distributor 12, and the liquid refrigerant concentratedly flows to the lower portion of the liquid header distributor 12. As a result, the amount of heat exchange at the at least one heat transfer tube 11 connected to the upper portion of the liquid header distributor 12 is reduced, and the heat exchange performance is reduced.
<Features of Embodiment 1>
In contrast, according to Embodiment 1, as illustrated in
The length Lb of the shortest heat transfer tube 11 corresponds to a distance by which the shortest heat transfer tube 11, which extends from the liquid header distributor 12 to the gas header distributor 13 through the heat exchanger core 14 and the U-shaped bent portions 16, extends through the heat exchanger core 14. In other words, referring to
The length Lh of the liquid header distributor 12 corresponds to the distance between the central axis of one of the heat transfer tubes 11 that is the closest to the inlet of the liquid header distributor 12 and the central axis of one of the heat transfer tube 11 that is the farthest from the inlet of the liquid header distributor 12.
Because of the above features, the influence of the flow resistance due to gravity in the liquid header distributor 12 can be sufficiently reduced, as compared with the influence of the flow resistance due to friction in the heat transfer tubes 11. Therefore, the refrigerant does not concentratedly flow to the lower portion of the liquid header distributor 12, and the refrigerant easily flows to the upper portion of the liquid header distributor 12.
Therefore, when the flow rate of refrigerant is low, the adverse effect on the distribution of the refrigerant can be reduced, and deterioration of the heat exchange performance can also be reduced. Therefore, even when the flow rate range is changed or when the refrigerant is replaced by new one, it is not necessary to change the specifications of the heat exchanger.
<Performance Evaluation of Embodiment 1>
As indicated in
Therefore, when the ratio ζ is 15.6, the degree to which the performance is deteriorated is small even when the flow rate of refrigerant is low. Therefore, the heating operation can be continuously performed without formation of frost on the heat exchanger core 14. Therefore, the heating operation can be continuously performed in indoor space without stopping the operation, and it is not necessary to perform a defrosting operation. As a result, the operation efficiency can be increased.
The above improvement of the heat exchange performance is achieved because of improvement of the performance of distributing the refrigerant from the liquid header distributor 12 to the heat transfer tubes 11 and improvement of air velocity distribution. This will be described in detail below with reference to
<Outdoor Unit 101 Including Outdoor Heat Exchanger 10>
As illustrated in
As indicated in
<Comparison Between Flow Rates of Refrigerant in Liquid Header Distributor 12 and Heat Transfer Tubes 11 Under Condition in Which Flow Rate of Refrigerant Is Low>
In the comparative example, only a small amount of liquid refrigerant flows through the heat transfer tubes 11 connected to the upper portion of the liquid header distributor 12. Thus, refrigerant evaporates while flowing upward through the flow passage in the liquid header distributor 12, as a result of which the state of refrigerant changes from a two-phase state to a single-phase gas state. The heat exchange efficiency of the refrigerant being in the single-phase gas state is reduced, as compared with that of the refrigerant being in the two-phase state.
Furthermore, in the heat transfer tubes 11 connected to the lower portion of the liquid header distributor 12, a large amount of liquid refrigerant flows. Therefore, the flow passages in the heat transfer tubes 11 connected to the lower portion of the liquid header distributor 12 include regions for evaporation of two-phase gas-liquid refrigerant. However, the flow rate of air that flows outside the heat transfer tubes 11 connected to the lower portion of the liquid header distributor 12 is low. Thus, the heat exchange efficiency is also low at the lower portion of the liquid header distributor 12.
Thus, in the comparative example, the amount of heat exchange is small at both the heat transfer tubes 11 connected to the upper portion of the liquid header distributor 12 and the heat transfer tubes 11 connected to the lower portion of the liquid header distributor 12. Accordingly, the heat exchange efficiency of the entire outdoor heat exchanger 10 is reduced.
In contrast, in Embodiment 1, a large amount of liquid refrigerant also flows through the heat transfer tubes 11 connected to the upper portion of the liquid header distributor 12. As indicated in
<Modification 1>
Regarding the outdoor unit 101 as illustrated in
Also, in Modification 1, the refrigerant distribution characteristics are similar to those illustrated in
In contrast, the outdoor heat exchanger 10 of Modification 1 is similar to that of Embodiment 1. Therefore, the refrigerant distribution characteristics of Modification 1 are similar to those of Embodiment 1 that are indicated on the right side of
<Annular Flow Pattern and Churn Flow Pattern of Refrigerant>
As illustrated in
<Method of Setting Annular Flow Pattern and Churn Flow Pattern of Refrigerant>
The flow pattern of the refrigerant at the inlet of the liquid header distributor 12 is determined from a flow pattern diagram of a vertically upward flow, and is set based on a reference apparent gas velocity UGS [m/s] of the refrigerant at a maximum value in a variation range of the flow velocity of the refrigerant at the inlet of the liquid header distributor 12. Two examples of the setting method will be described.
In a first example, a is a void fraction of the refrigerant, L [m] is an entrance length at an inlet portion of the liquid header distributor, g [m/s2] is the gravitational acceleration, and D [m] is an inside diameter of the liquid header distributor 12. The void fraction α of the refrigerant is expressed by α=x/(x+(ρG/ρL)×(1−x)), where x [−] is the quality of the refrigerant, ρG [kg/m3] is a gas refrigerant density, and ρL [kg/m3] is a liquid refrigerant density. The reference apparent gas velocity UGS [m/s], which is the maximum value in the variation range of the apparent gas velocity of the refrigerant that flows into the liquid header distributor 12, satisfies UGS≥α×L×(g×D)0.5/(40.6×D)−0.22×α×(g×D)0.5. In the first example, the flow pattern is a churn flow.
In a second example, ρG [kg/m3] is the gas refrigerant density, ρL [kg/m3] is the liquid refrigerant density, and σ [N/m] is a surface tension of the refrigerant. The reference apparent gas velocity UGS [m/s], which is the maximum value in the variation range of the apparent gas velocity of the refrigerant that flows into the liquid header distributor 12, satisfies UGS≥3.1/(ρG0.5)×[σ×g×(ρL−ρG)]0.25. In the second example, the flow pattern is an annular flow.
The entrance length L [m] at the inlet portion of the liquid header distributor 12 corresponds to the distance between the inlet portion of the liquid header distributor 12 and the central axis of one of the heat transfer tubes 11 that is the closest to the inlet portion.
<Other Examples of Embodiment 1>
Preferably, the ratio ζ of the length of the heat transfer tubes 11 to the length of the liquid header distributor 12 should satisfy 9≤ζ≤23. More preferably, the ratio ζ should satisfy 13≤ζ≤20. These ranges are preferable because, as is clear from
As described above, in Embodiment 1, ζ is set to a relatively large value. However, as in the configuration example as illustrated in
The flow resistance in each heat transfer tube 11 including the U-shaped bent portions 16 is increased, as compared with the case where the heat transfer tube 11 is a straight tube. Therefore, in the case where long heat transfer tubes 11 are used, an advantage similar to that obtained by increasing ζ can be obtained by increasing the number of U-shaped bent portions 16 or reducing the curvature of each of the U-shaped bent portions 16. Accordingly, in the case where each heat transfer tube 11 includes two or more U-shaped bent portions 16 as in the configuration example as illustrated in
On the assumption that the size of the heat exchanger core 14 remains unchanged, as the number of U-shaped bent portions 16 is increased, the number of heat transfer tubes 11 connected to the liquid header distributor 12 and the gas header distributor 13 is reduced, and the distribution performance is improved.
The U-shaped bent portions 16 may be bent downward at the lower portion of the liquid header distributor 12 and may be bent upward at the upper portion of the liquid header distributor 12. In such a case, the lengths of the heat transfer tubes 11 connected to the upper portion and the lower portion of the liquid header distributor 12 are less than in the case where all of the U-shaped bent portions 16 are bent upward. Therefore, the balance between pressure losses due to gravity between the passages that extend through the heat transfer tubes 11 connected to the upper portion of the liquid header distributor 12 and the passages that extend through the heat transfer tubes 11 connected to the lower portion of the liquid header distributor 12 can be improved. That is, the differences in pressure loss between the passages can be relatively reduced. As a result, the refrigerant distribution performance can be improved, and the heat exchange performance can be improved.
<Advantages of Embodiment 1>
According to Embodiment 1, the outdoor heat exchanger 10 includes the heat transfer tubes 11. The outdoor heat exchanger 10 also includes the liquid header distributor 12 to which one end of each of the heat transfer tubes 11 is connected and in which an upward flow of two-phase gas-liquid refrigerant is generated. The outdoor heat exchanger 10 also includes the gas header distributor 13 to which the other end of each of the heat transfer tubes 11 is connected and in which a flow of gas phase refrigerant is generated. Each of the heat transfer tubes 11 includes U-shaped bent portions 16 at each of which the flow passage is bent in directions other than a horizontal direction. Where Lh [m] is the length of the liquid header distributor 12, Lb [m] is the length of the shortest one of the heat transfer tubes 11, and ζ is the ratio of the length Lb of the shortest one of the heat transfer tubes 11 to the length Lh of the liquid header distributor 12, and is expressed by ζ=Lb/Lh, the relationship between the liquid header distributor 12 and the heat transfer tubes 11 is established such that 9≤ζ is satisfied. The length Lh of the liquid header distributor 12 corresponds to the distance between the central axis of one of the heat transfer tubes 11 that is the closest to the inlet of the liquid header distributor 12 and the central axis of one of the heat transfer tubes 11 that is the farthest from the inlet of the liquid header distributor 12. The length Lb of the shortest heat transfer tube 11 corresponds to a distance by which the shortest heat transfer tube 11, which extends from the liquid header distributor 12 to the gas header distributor 13 through the heat exchanger core 14 and the U-shaped bent portions 16, extends through the heat exchanger core 14 (Lb=Lb1+Lb2+Lb3).
In the above configuration, the ratio of the flow resistance in the liquid header distributor 12 to the flow resistance in the heat transfer tubes 11 is sufficiently small. Thus, the influence of the flow resistance in the liquid header distributor 12 on the distribution of the refrigerant can be reduced. Therefore, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of refrigerant varies can be reduced, and deterioration of the heat exchange performance can thus be reduced. As a result, it is not necessary to change the specifications of the outdoor heat exchanger 10 each time the flow rate or the kind of the refrigerant that is used is changed.
In Embodiment 1, the relationship between the liquid header distributor 12 and the heat transfer tubes 11 is established such that 9≤ζ≤23 is satisfied.
In the above configuration, the ratio of the flow resistance in the liquid header distributor 12 to the flow resistance in the heat transfer tubes 11 is more suitably reduced. Therefore, the influence of the flow resistance in the liquid header distributor 12 on the distribution of the refrigerant can be further reduced. Accordingly, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of the refrigerant varies can be further reduced, and deterioration of the heat exchange performance can be thus further reduced.
In Embodiment 1, the outdoor heat exchanger 10 includes the heat exchanger core 14 that includes the heat transfer tubes 11 and one or more fins. The U-shaped bent portions 16 are located outside the heat exchanger core 14. The length Lb of the shortest heat transfer tube 11 corresponds to the distance by which the shortest heat transfer tube 11, which extends from the liquid header distributor 12 to the gas header distributor 13 through the heat exchanger core 14 and the U-shaped bent portions 16, extends through the heat exchanger core 14.
In the above configuration, where the ratio ζ of the length Lb of the shortest heat transfer tube 11 to the length Lh of the liquid header distributor 12 is expressed by ζ=Lb/Lh, 9≤ζ can be easily satisfied.
In Embodiment 1, in the heat exchanger core 14, at least one of the heat transfer tubes 11 that is located from the intermediate portion to the upper portion of the liquid header distributor 12 includes a larger number of U-shaped bent portions 16 than at least one of the heat transfer tubes 11 that is located at the lower portion of the liquid header distributor 12.
In the above configuration, the heat exchange efficiency of a region in which the air velocity is high and which is located from the intermediate portion to the upper portion of the liquid header distributor 12 is improved. In addition, at the lower portion of the liquid header distributor 12, in which the air velocity is low, the flow rate of the liquid refrigerant is reduced, and the heat exchange efficiency is not easily reduced. Therefore, the heat exchange efficiency of the entire outdoor heat exchanger 10 is improved.
In Embodiment 1, the flow pattern of refrigerant that flows in a two-phase gas-liquid state and upward through the liquid header distributor 12 is an annular flow or a churn flow in which gas refrigerant flows through the central region of the liquid header distributor 12 and liquid refrigerant flows along the inner wall surface of the liquid header distributor 12.
In the above configuration, when the flow pattern is the annular flow, gas refrigerant flows along with a large number of droplets through the central region of the liquid header distributor 12 and liquid refrigerant flows along the inner wall of the liquid header distributor 12. When the flow pattern is the churn flow, the liquid refrigerant forms a liquid film having a thickness greater than that in the annular flow and flows while containing a large number of bubbles.
Regarding Embodiment 1, it should be noted that α is the void fraction of the refrigerant, L [m] is the entrance length at the inlet portion of the liquid header distributor 12, g [m/s2] is the gravitational acceleration, and D [m] is the inside diameter of the liquid header distributor 12. Also, where x [−] is the quality of the refrigerant, ρG [kg/m3] is the gas refrigerant density, and ρL [kg/m3] is the liquid refrigerant density, the void fraction α of the refrigerant is expressed by α=x/(x+(ρG/ρL)×(1−x)). The reference apparent gas velocity UGS [m/s], which is the maximum value in the variation range of the apparent gas velocity of the refrigerant that flows into the liquid header distributor 12, satisfies UGS≥α×L×(g×D)0.5/(40.6×D)−0.22×α×(g×D)0.5.
In the above configuration, the flow pattern of the refrigerant that flows in a two-phase gas-liquid state and upward through the liquid header distributor 12 with respect to a direction orthogonal to the flow direction is a churn flow in which gas refrigerant flows through the central region of the liquid header distributor 12 and liquid refrigerant flows along the inner wall surface of the liquid header distributor 12.
According to Embodiment 1, where ρG [kg/m3] is the gas refrigerant density, ρL [kg/m3] is the liquid refrigerant density, and σ [N/m] is the surface tension of the refrigerant, the reference apparent gas velocity UGS [m/s], which is the maximum value in the variation range of the apparent gas velocity of the refrigerant that flows into the liquid header distributor 12, satisfies UGS≥3.1/(ρG0.5)×[σ×g×(ρL−ρG)]0.25.
In the above configuration, the flow pattern of the refrigerant that flows in a two-phase gas-liquid state and upward through the liquid header distributor 12 on a plane orthogonal to the flow direction is an annular flow in which gas refrigerant flows through the central region of the liquid header distributor 12 and liquid refrigerant flows along the inner wall surface of the liquid header distributor 12.
In Embodiment 1, the heat exchanger core 14 is provided to allow air to flow therethrough such that a component of the flow velocity of air in the horizontal direction is larger than a component of the air flow velocity of air in the vertical direction. The outdoor heat exchanger 10 includes the outdoor fan 36 that sends air in a direction along the rotational axis and that is located such that a rotational plane of the outdoor fan 36 is inclined at an angle of 45 degrees or less relative to a horizontal plane.
In the above configuration, the ratio of the flow resistance in the liquid header distributor 12 to the flow resistance in the heat transfer tubes 11 is sufficiently small. Thus, the influence of the flow resistance in the liquid header distributor 12 on the distribution of the refrigerant can be reduced. Therefore, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of refrigerant varies can be reduced, and deterioration of the heat exchange performance can thus be reduced.
In Embodiment 1, the liquid header distributor 12 is provided at a lower position than the gas header distributor 13.
In the above configuration, refrigerant that flows in the liquid header distributor 12 is in a single-phase liquid state or a two-phase gas-liquid state and has a higher density than refrigerant that flows through the gas header distributor 13. Therefore, in the case where the gas header distributor 13 is provided at a higher position than the liquid header distributor 12, a pressure loss due to gravity in the liquid header distributor 12 and the gas header distributor 13 can be reduced.
In Embodiment 1, the air-conditioning apparatus 100 includes the above outdoor heat exchanger 10.
In the above configuration, in the air-conditioning apparatus 100 that includes the outdoor heat exchanger 10, it is not necessary to change the specifications of the heat exchanger each time the flow rate or the type of the refrigerant that is used is changed.
As illustrated in
Referring to
Since the outdoor heat exchanger 10 is divided into two sections and thus includes two heat exchanger cores 14, the outdoor heat exchanger 10 can thus obtain a higher heat exchange performance. In addition, in the case where the rotational axis of the outdoor fan 36 extends in the vertical direction, the flow rate of the refrigerant that flows through the heat transfer tubes 11 at the upper portion of the outdoor heat exchanger 10, at which the air velocity is high, is improved. Therefore, the heat exchange performance can be further improved.
<Modification 2>
As illustrated in
In the case where the outdoor heat exchanger 10 is divided into three or more sections, the outdoor heat exchanger 10 can obtain a higher heat exchange performance. In addition, in the case where the rotational axis of each outdoor fan 36 extends in the vertical direction, the flow rate of the refrigerant that flows through the heat transfer tubes 11 at the upper portion of the outdoor heat exchanger 10, at which the air velocity is high, is increased. Therefore, the heat exchange performance can be further improved.
<Advantages of Embodiment 2>
In Embodiment 2, the outdoor heat exchanger 10 is divided into two or more sections. Each of the sections includes heat transfer tubes 11, a liquid header distributor 12, and a gas header distributor 13.
In the above configuration, since the outdoor heat exchanger 10 is divided into two or more sections, a higher heat exchange performance can be obtained.
As illustrated in
When the flow rate of refrigerant is low, the tube-shaped conversion joints 40 serve to adjust the balance of flow resistance between the liquid header distributor 12 and the heat transfer tubes 11. Thus, the adverse effect on the distribution of the refrigerant can be reduced, and the deterioration of the heat exchange performance can thus be reduced.
It is illustrated by way of example that the tube-shaped conversion joints 40 are connected to all of the branch tubes 41 and the heat transfer tubes 11 connected to the liquid header distributor 12. However, the tube-shaped conversion joints may be connected to heat transfer tubes 11 connected to the gas header distributor 13. Also, the tube-shaped conversion joints may be connected to some of the heat transfer tubes 11. In this case, in the case where the tube-shaped conversion joints are connected to some of the heat transfer tubes 11 at which the flow rate of refrigerant is relatively high, the pressure loss can be more greatly reduced.
<Advantages of Embodiment 3>
In Embodiment 3, in the outdoor heat exchanger 10, at least one or more of the heat transfer tubes 11 are connected to the liquid header distributor 12 or the gas header distributor 13 through the tube-shaped conversion joints 40.
In the above configuration, when the flow rate of refrigerant is low, the tube-shaped conversion joints 40 serve to adjust the balance of flow resistance between the liquid header distributor 12 and the heat transfer tubes 11. Thus, the adverse effect on the distribution of the refrigerant can be reduced, and the deterioration of the heat exchange performance can thus be reduced.
As illustrated in
In the above configuration, when the outdoor heat exchanger 10 operates as an evaporator, refrigerant flows in a two-phase gas-liquid state into each of the two sections into which the liquid header distributor 12 is divided. The refrigerant that has flowed into each of the two sections of the liquid header distributor 12 passes through the heat transfer tubes 11 connected to the two sections of the liquid header distributor 12 and then through the gas header distributor 13, and flows out of the outdoor heat exchanger 10.
When the flow rate of refrigerant is low, the influence of the pressure loss in the liquid header distributor 12 may be greater than the influence of the pressure loss in the heat transfer tubes 11, and the distribution of the refrigerant may be adversely affected. However, in Embodiment 4 as described with reference to
In the case where two outdoor fans 36 are provided as illustrated in
<Advantages of Embodiment 4>
According to Embodiment 4, both or either one of the liquid header distributor 12 and the gas header distributor 13 is divided into two or more sections.
In the above configuration, the liquid header distributor 12 and/or the gas header distributor 13 is divided, whereby the influence of the pressure loss in the liquid header distributor 12 or the gas header distributor 13 is reduced. Thus, the adverse effect on the distribution of the refrigerant can be reduced, and the deterioration of the heat exchange performance can thus be reduced.
As illustrated in
In the above configuration, in the case where the outdoor heat exchanger 10 operates as an evaporator, first, refrigerant flows in a two-phase gas-liquid state into the subcooling heat exchanger 15. Then, the refrigerant exchanges heat with air such that the quality thereof is increased, and then flows out of the subcooling heat exchanger 15. The refrigerant that has flowed out of the subcooling heat exchanger 15 flows into the liquid header distributor 12. Then, the refrigerant exchanges heat with air to change into a single-phase gas refrigerant, and flows out of the gas header distributor 13.
In the above case, the quality of the two-phase gas-liquid refrigerant that flows into the liquid header distributor 12 is raised higher than in the case where the subcooling heat exchanger 15 is not provided. Therefore, the flow velocity of the gas phase refrigerant is increased, and as a result the flow velocity of the liquid phase refrigerant is also increased. Accordingly, the flow resistance in the liquid header distributor 12 is reduced, as compared with the flow resistance in the heat transfer tubes 11. As a result, the ratio of the flow resistance in the liquid header distributor 12 to the flow resistance in the heat transfer tubes 11 is small. Thus, the influence of the flow resistance in the liquid header distributor 12 on the distribution of the refrigerant can be reduced. Therefore, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of refrigerant varies can be reduced, and deterioration of the heat exchange performance can thus be reduced.
When the outdoor heat exchanger 10 operates as a condenser, first, the refrigerant flows into the gas header distributor 13. Then, the refrigerant exchanges heat with air to condense and liquefy, and flows out of the liquid header distributor 12. The refrigerant that has flowed out of the liquid header distributor 12 flows into the subcooling heat exchanger 15. Then, the refrigerant exchanges heat with air to change into single-phase liquid refrigerant, and flows out of the subcooling heat exchanger 15. In this case, the flow velocity of the refrigerant in the subcooling heat exchanger 15 is increased. As a result, the heat exchange performance can be improved.
<Advantages of Embodiment 5>
According to Embodiment 5, the outdoor heat exchanger 10 is provided with the subcooling heat exchanger 15 that is connected to the outdoor heat exchanger 10. The subcooling heat exchanger 15 is located upstream of the outdoor heat exchanger 10 in the direction in which the refrigerant flows when the outdoor heat exchanger 10 operates as an evaporator.
In the above configuration, the quality of the two-phase gas-liquid refrigerant that flows into the liquid header distributor 12 is higher than in the case where the subcooling heat exchanger 15 is not provided. Therefore, the flow velocity of the gas phase refrigerant is increased, thereby also increasing the flow velocity of the liquid phase refrigerant. Accordingly, the flow resistance in the liquid header distributor 12 is reduced, as compared with the flow resistance in the heat transfer tubes 11. As a result, the ratio of the flow resistance in the liquid header distributor 12 to the flow resistance in the heat transfer tubes 11 is small. Thus, the influence of the flow resistance in the liquid header distributor 12 on the distribution of the refrigerant can be reduced. Therefore, an adverse effect on the refrigerant distribution characteristics that is caused when the flow rate of refrigerant varies can be reduced, and deterioration of the heat exchange performance can thus be reduced. When the outdoor heat exchanger 10 operates as a condenser, first, the refrigerant flows into the gas header distributor 13. Then, the refrigerant exchanges heat with air in the heat transfer tubes 11 to condense and liquefy, and flows out of the liquid header distributor 12. The refrigerant that has flowed out of the liquid header distributor 12 flows into the subcooling heat exchanger 15. Then, the refrigerant exchanges heat with air to change into single-phase liquid refrigerant, and flows out of the subcooling heat exchanger 15. In this case, the flow velocity of the refrigerant in the subcooling heat exchanger 15 is increased, and the heat exchange performance can thus be improved.
Embodiments 1 to 5 of the present disclosure may be combined when being applied, or may be applied to other configures.
10: outdoor heat exchanger, 11: heat transfer tube, 12: liquid header distributor, 13: gas header distributor, 14: heat exchanger core, 15: subcooling heat exchanger, 16: U-shaped bent portion, 30: indoor heat exchanger, 31: expansion device, 32: accumulator, 33: compressor, 34: four-way valve, 35: refrigerant pipe, 36: outdoor fan, 40: tube-shaped conversion joint, 41: branch tube, 100: air-conditioning apparatus, 101: outdoor unit
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/001630 | 1/21/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/152738 | 7/30/2020 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20220128279 A1 | Apr 2022 | US |
