WO2021176651A1

WO2021176651A1 - Heat exchanger and air conditioner

Info

Publication number: WO2021176651A1
Application number: PCT/JP2020/009421
Authority: WO
Inventors: 幹佐藤; 拓未西山; 健太村田
Original assignee: 三菱電機株式会社
Priority date: 2020-03-05
Filing date: 2020-03-05
Publication date: 2021-09-10
Also published as: JPWO2021176651A1; US20230043875A1; EP4116642A4; EP4116642A1; JP7414951B2

Abstract

Provided is a heat exchanger for an air conditioner that uses a non-azeotropic refrigerant mixture, the heat exchanger enabling the required refrigerant amount to be reduced without causing the heat transfer performance to decline when used as an evaporator. The heat exchanger comprises: a plurality of fins 11 stacked with a prescribed spacing in-between; first heat transfer tubes 31-36 that pass through the plurality of fins 11, that allow a heat transfer medium to flow through, and that have a plurality of grooves formed on the inner peripheral surface of each first heat transfer tube; and second heat transfer tubes 37, 38 that pass through the plurality of fins 11, that have one end connected to one end of the first heat transfer tubes 31-36 to form one heat transfer medium flow passage, that have a pipe diameter smaller than that of the first heat transfer tubes 31-36, and that have an inner surface shape configured such that a pressure loss per unit length is smaller than that of the first heat transfer tubes 31-36.

Description

Heat exchanger and air conditioner

The present invention relates to a heat exchanger of an air conditioner.

It has been pointed out that fluorocarbons, which are used as refrigerants in many refrigeration and air conditioning equipment, have a global warming effect, and various regulations are being implemented worldwide to reduce their emissions. .. For example, in the 2016 revision of the Montreal Protocol Kigari, developed countries, including Japan, will increase the total GWP value, which is determined by the product of GWP (Global Warming Potential) and refrigerant usage, to 15% by 2036 compared to 2011-2013. It was obligatory to reduce.

In order to comply with such regulations, HFCs such as R410A (R32: R125 = 50% by weight: 50% by weight, GWP = 2088) and R32 (GWP = 675), which are widely used in the refrigeration and air conditioning equipment industry, are currently widely used. Conversion from a refrigerant to a refrigerant with a lower GWP is being considered.

More specifically, 2-3-3-3-tetrafluoropropene (R1234yf, GWP = 4), trans-1-3-3-3-tetrafluoropropene (R1234ze (E), GWP = 6), 1 1-2 HFO refrigerants such as trifluoroethylene (R1123, GWP = 4), difluoromethane (R32, GWP = 675), pentafluoromethane (R125, GWP = 3500), 1-11-2-tetrafluoro The application of a mixed refrigerant of an HFC refrigerant such as methane (R134a, GWP = 1430) and the above HFO refrigerant, or an HC refrigerant such as propane (R290, GWP = 3) and isobutane (R600a, GWP = 4) is being studied.

Among these candidate substances, the mixed refrigerant of HFC refrigerant and HFO refrigerant is excellent in terms of refrigerating capacity, theoretical COP, flammability, toxicity, etc., and may be applicable to a wide range of refrigerating and air-conditioning equipment. On the other hand, it is known that when a plurality of refrigerants having different boiling points are mixed, a so-called non-azeotropic mixed refrigerant is obtained, and the characteristics are different from those of a pure refrigerant and an azeotropic mixed refrigerant. For example, in the evaporation process of a non-coboiling mixed refrigerant, the low boiling point component evaporates preferentially, and then the high boiling point component evaporates. Further boiling of the ingredients is suppressed. When a non-azeotropic mixed refrigerant is used, it is necessary to recover from such deterioration of heat transfer of evaporation.

As a method of improving the heat exchange performance of the evaporator, an auxiliary heat exchanger is arranged on the refrigerant inlet side when the heat exchanger is used as an evaporator, the number of refrigerant flow paths of the auxiliary heat exchanger is reduced, and a pipe is used. A method of increasing the diameter is known (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2004-332985

However, in the heat exchanger configured as in the prior art document, when used as a condenser, the auxiliary heat exchanger having an enlarged pipe diameter is located on the refrigerant outlet side. Since the supercooled liquid flows on the refrigerant outlet side of the condenser, there is a problem that the amount of refrigerant required for this refrigeration cycle increases due to the expansion of the pipe diameter, and the amount of refrigerant used increases.

The present invention has been made to solve the above problems without deteriorating the heat transfer performance when used as an evaporator in a heat exchanger of an air conditioner using a non-co-boiling mixed refrigerant. , A heat exchanger capable of reducing the required amount of refrigerant is obtained.

In order to achieve the above objectives, the heat exchangers according to this disclosure are
A first heat transfer tube in which a heat medium circulates inside and a plurality of grooves are formed on the inner peripheral surface,
One end is connected to one end of the first heat transfer tube to form one heat medium flow path, the diameter of the tube is smaller than that of the first heat transfer tube, and the pressure loss per unit length is the first transfer. It is composed of a second heat transfer tube having an inner surface shape smaller than that of the heat tube.

According to the heat exchanger according to the present disclosure, when a non-azeotropic mixed refrigerant is used, the required amount of refrigerant can be reduced without deteriorating the heat exchange heat performance. In addition, the manufacturing cost can be reduced.

It is a refrigerant circuit diagram of the air conditioner including the heat exchanger which concerns on Embodiment 1. FIG. It is a front view of the heat exchanger which concerns on Embodiment 1. FIG. It is sectional drawing of the heat transfer tube used for the heat exchanger which concerns on Embodiment 1. FIG. It is a characteristic figure which shows an example of the heat transfer performance with respect to the dryness of a refrigerant of a general grooved pipe. It is a characteristic figure which shows an example of the pressure loss with respect to the dryness of a refrigerant of a general grooved pipe. It is a Ph diagram which shows the refrigerating cycle operation of the air conditioner equipped with the heat exchanger which concerns on Embodiment 1. FIG. This is an example of a side view in which one refrigerant flow path portion of the heat exchanger according to the first embodiment is extracted. It is a side view of another example in which one refrigerant flow path portion of the heat exchanger according to the second embodiment is extracted. FIG. 5 is an external view of an air conditioner to which the heat exchanger according to the first or second embodiment is applied.

Hereinafter, the heat exchanger and the air conditioner according to the embodiment of the present disclosure will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a refrigerant circuit diagram showing an example of an air conditioner including a heat exchanger according to the first embodiment. The flow direction of the refrigerant is also shown by a solid line and a broken line. In FIG. 1, 100 is an air conditioner, and the outdoor unit 1 and the indoor unit 2 are connected by a gas pipe 3 and a liquid pipe 4 to form one refrigerant circuit. This refrigerant circuit is filled with a mixed refrigerant composed of two or more types of refrigerants having different boiling points.

The outdoor unit 1 is equipped with a compressor 5, an outdoor heat exchanger 6, an expansion valve 7, and a four-way valve 9, and the indoor unit 2 is equipped with an indoor heat exchanger 8. During the cooling operation in which the indoor heat exchanger 8 acts as an evaporator, the refrigerant discharged from the compressor 5 flows into the outdoor heat exchanger 6 through the four-way valve 9, is depressurized by the expansion valve 7, and is decompressed by the expansion valve 7. Outflow. The refrigerant that has flowed into the indoor unit 2 through the liquid pipe 4 evaporates in the indoor heat exchanger 8 and flows out of the indoor unit 2. The refrigerant that has returned to the outdoor unit 1 through the gas pipe 3 is sucked into the compressor 5 again.

During the heating operation in which the indoor heat exchanger 8 acts as a condenser, the refrigerant discharged from the compressor 5 flows into the indoor unit 2 from the gas pipe 3 by setting the flow path of the four-way valve 9. The refrigerant condensed in the indoor heat exchanger 8 returns to the outdoor unit 1 through the liquid pipe 4, and is depressurized by the expansion valve 7. The low-pressure refrigerant exchanges heat with the outdoor air in the outdoor heat exchanger 6 and evaporates, and is sucked into the compressor 5 again via the four-way valve 9.

Although not shown, the outdoor heat exchanger 6 and the indoor heat exchanger 8 are provided with fans, respectively, to forcibly force the outdoor and indoor air into the outdoor heat exchanger 6 and the indoor heat exchanger 8. By blowing air, the heat exchange efficiency between the refrigerant and air is improved. As the fan, for example, a cross flow fan, a propeller fan, a turbo fan, or a sirocco fan can be used. Further, a plurality of fans may be provided for one heat exchanger, or one fan may be provided for a plurality of heat exchangers. Further, the air conditioner 100 according to the first embodiment has a minimum configuration capable of cooling operation and heating operation, and devices such as a gas-liquid separator, a receiver, an accumulator, and an internal heat exchanger are appropriately added to the refrigerant circuit. You may.

FIG. 2 is a front view showing an example of the outdoor heat exchanger 6 according to the first embodiment. The outdoor heat exchanger 6 is composed of a plurality of fins 11 laminated at intervals of about 1.5 mm, and heat transfer tubes 31 to 38 penetrating the fins 11. The heat transfer tubes 31 to 38 are formed in a hairpin shape and are heat-transferredly closely fitted to the fins 11. One end or both ends of the heat transfer tubes 31 to 38 are connected by a plurality of U-shaped tubes 14 to form one refrigerant flow path having 12 as a gas side inlet / outlet and 13 as a liquid side inlet / outlet. During the heating operation in which the outdoor heat exchanger 6 acts as an evaporator, the liquid side inlet / outlet 13 corresponds to the inlet of the refrigerant flow path, and the gas side inlet / outlet 12 serves as the outlet of the refrigerant flow path. Further, as shown in FIG. 1, since the refrigerant flow direction is reversed during the cooling operation, the liquid side inlet / outlet 13 is the refrigerant flow path outlet and the gas side inlet / outlet 12 is the refrigerant when the outdoor heat exchanger 6 acts as a condenser. It becomes the flow path entrance.

FIG. 3 is a cross-sectional view of a heat transfer tube used in the heat exchanger according to the embodiment. Of the heat transfer tubes 31 to 38 forming the outdoor heat exchanger 6 shown in FIG. 2, the first heat transfer tubes 31 to 36 have a plurality of peaks and valleys on the inner surface of the tubes as shown in FIG. 3A, for example. It is a formed grooved pipe, and penetrates the fin 11 with the gas side inlet / outlet 12 as one end to form a first heat exchange portion. Further, the

heat transfer tubes

37 and 38, which are the second heat transfer tubes, are smooth tubes as shown in FIG. 3 (b), and penetrate the fins 11 with the liquid side inlet / outlet 13 as one end to form the second heat exchange portion. do. Further, the inner diameter D2 of the

heat transfer tubes

37 and 38 is smaller than the inner diameter D1 of the grooved tubes used for the heat transfer tubes 31 to 36 (D1> D2).

Here, the shape of the groove in the heat transfer tubes 31 to 36 does not matter. Specifically, the inner diameter, the number of fins inside the pipe (hereinafter referred to as the fins inside the pipe), the height of the fins inside the pipe, the helix angle of the fins inside the pipe, the area expansion ratio, and the like are not particularly limited.

Further, the type of the non-azeotropic mixed refrigerant sealed in the air conditioner 100 (hereinafter, described as a refrigerant unless it is necessary to distinguish between a pure refrigerant and an azeotropic mixed refrigerant in the context) does not matter. For example, HFC refrigerants such as difluoromethane (R32, GWP = 675), pentafluoromethane (R125, GWP = 3500), 1-11-2-tetrafluoromethane (R134a, GWP = 1430) and 2-3. -3-3-Tetrafluoropropene (R1234yf, GWP = 4), Trans-1-3-3-3-Tetrafluoropropene (R1234ze (E), GWP = 6), 1-1-2 Trifluoroethylene (R1123) , GWP = 4), difluoroethylene (R1132a, GWP = 1), trans-difluoroethylene (R1132 (E), GWP = 1), 1-1-1--4--4-hexafluoro-2-butene (R1336mzz) It may be a mixed refrigerant with an HFO refrigerant such as (Z), GWP = 2), or trans-1-chloro-3-3-3-trifluoropropene (R1233zd, GWP = 1), cis-1-chloro. HFCO refrigerant such as -2-3-3-3-tetrafluoropropene (R1224yd (Z), GWP = 1), HC refrigerant such as propane (R290, GWP = 3), isobutane (R600a, GWP = 4), etc. A mixed refrigerant may be used.

FIG. 4 is a characteristic diagram showing an example of the heat transfer performance in the pipe with respect to the dryness of the refrigerant in a general grooved pipe. The vertical axis is the heat transfer coefficient of heat of vaporization of the grooved pipe, and is represented by a value relative to the heat transfer coefficient of heat of vaporization of the smooth pipe. As the refrigerant, the two characteristics of the single refrigerant and the non-azeotropic mixed refrigerant are plotted with broken lines and solid lines, respectively.

As shown in FIG. 4, in the case of a single refrigerant, the grooved pipe has a heat transfer coefficient of vaporization that is three times or more the smooth pipe ratio regardless of the dryness of the refrigerant, which greatly contributes to the improvement of heat exchange performance. .. On the other hand, when a non-azeotropic mixed refrigerant is used, the improvement in the heat transfer coefficient of vaporization in the smooth tube ratio is not as great as in the case of a single refrigerant. In particular, in the low dryness region where the dryness of the refrigerant is 0.4 or less, the heat transfer coefficient of heat of vaporization of the grooved tube is almost the same as the heat transfer coefficient of heat of vaporization of the smooth tube, and does not contribute to the improvement of heat exchange performance.

FIG. 5 is a characteristic diagram showing an example of pressure loss with respect to the dryness of the refrigerant in a general grooved pipe. The vertical axis is a relative value representing the pressure loss of the grooved pipe as a smooth pipe ratio. The broken line is the pressure loss in the case of a single refrigerant, and the solid line is the pressure loss in the case of a non-azeotropic mixed refrigerant.

As shown in FIG. 5, the pressure loss of the grooved pipe is large with respect to the pressure loss of the smooth pipe regardless of the dryness of the refrigerant, and is particularly large in the region of the dryness of the refrigerant of 0.3 to 0.5. This phenomenon is the same for both a single refrigerant and a non-azeotropic mixed refrigerant, but the non-azeotropic mixed refrigerant has a larger rate of increase in pressure loss. From FIGS. 4 and 5, it can be said that the heat transfer performance is improved by adopting the grooved pipe for the heat exchanger, but the heat transfer performance is not improved when the dryness of the refrigerant is 0.4 or less, and only the pressure loss is increased. ..

FIG. 6 is a Ph diagram showing the refrigeration cycle operation of the air conditioner 100 according to the first embodiment. The vertical axis is pressure, the horizontal axis is specific enthalpy, and X0 is a saturation line connecting points where the refrigerant is in a saturated liquid or saturated gas state. The state A, the state B, the state C, and the state D are the inlet states of each of the compression-condensation-expansion-evaporation processes forming the refrigeration cycle. The refrigeration cycle shown in FIG. 6 is not limited to whether it is a cooling operation or a heating operation, but first, the refrigeration cycle operation will be described below assuming the case of a heating operation.

The low-temperature low-pressure gas refrigerant (state A) at the suction position of the compressor 5 is boosted by the compressor 5 to become a high-temperature high-pressure discharge gas (state B). This discharged gas is condensed by the indoor heat exchanger 8 that acts as a condenser, and becomes a high-pressure supercooled liquid (state C). Subsequently, the pressure is reduced by the expansion valve 7 to become a low-pressure gas-liquid two-phase refrigerant (state D).

Here, X1 in the figure is an isobaric line with a refrigerant dryness of 0.2. It is known that the refrigerant (state D) at the inlet of the evaporator is about 0.2 in the range of the condensation temperature of 40 ° C. ± 10 ° C. and the evaporation temperature of 0 ° C. ± 10 ° C., which are general air conditioning operation conditions. .. That is, in the evaporation process from the state D to the state A in a general air conditioner, the dryness of the refrigerant changes from 0.2 to 1.0 under most operating conditions. In this embodiment, in the outdoor heat exchanger 6 shown in FIG. 2, the refrigerant in the low-pressure gas-liquid two-phase state D absorbs heat from the outdoor air until it slightly overheats, and then returns to the state A to perform one refrigeration cycle. Form.

As described above, of the change in dryness 0.8 (= 1.0-0.2) during this evaporation process, the effect of improving the heat transfer coefficient of the grooved pipe is exhibited between 0.2 and 0.4. Not done. That is, when used as an evaporator, it is not necessary to adopt a grooved pipe which is a means for improving heat exchange performance at a length of 25% (= 0.2 / 0.8) from the liquid side inlet / outlet 13 which is the refrigerant inlet. .. Therefore, in the first embodiment, as shown in FIG. 2, the

heat transfer tubes

37 and 38 connected to the liquid side inlet / outlet 13 of the outdoor heat exchanger 6 are composed of smooth tubes. Since the smoothing pipe is cheaper than the grooved pipe, the manufacturing cost of the outdoor heat exchanger 6 can be reduced.

In addition, when used under conditions where the evaporation temperature is extremely low, it is conceivable that the refrigerating machine oil dissolved in the liquid refrigerant may separate and stay near the heat transfer tube wall. Retention of refrigerating machine oil may impair the reliability of the compressor 5, and should be avoided as much as possible. By adopting a smooth pipe having a small amount of friction in the pipe in the second heat exchange portion near the liquid side inlet / outlet 13 in which the amount of the liquid refrigerant is large, the amount of the refrigerating machine oil retained is reduced and the reliability of the air conditioner is improved.

Next, the case of cooling operation will be described. In the cooling operation, the indoor heat exchanger 8 acts as an evaporator, and the outdoor heat exchanger 6 acts as a condenser. The high-temperature high-pressure gas refrigerant in the state B discharged from the compressor 5 flows into the outdoor heat exchanger 6 to exchange heat with the outdoor air, and is condensed to become the supercooling liquid refrigerant in the state C. Most of the amount of refrigerant required for this refrigeration cycle is concentrated in the SC portion, which is the final stage of the condensation process, that is, the SC portion, which is the region after the refrigerant has become saturated.

In the outdoor heat exchanger 6 according to the first embodiment, the diameters of the

heat transfer tubes

37 and 38 constituting the second heat exchange section on the refrigerant outlet side when used as a condenser are smaller than those of the other heat transfer tubes. Therefore, the amount of refrigerant present in the SC portion becomes small. As a result, the amount of refrigerant sealed in the air conditioner 100 is also reduced, which can contribute to lowering the total amount of GWP and reduce the environmental load.

In addition, by reducing the diameters of the

heat transfer tubes

37 and 38, the refrigerant flow velocity in the second heat exchange section increases and convection heat transfer is promoted, so the deterioration in heat transfer performance due to the smooth tube is recovered. However, the deterioration of heat exchange performance can be suppressed.

FIG. 7 is an example of a side view in which one refrigerant flow path portion of the heat exchanger according to the first embodiment is extracted. Although described as one row of heat exchangers in FIG. 2, in FIG. 7, heat transfer tubes 31 to 38 forming one refrigerant flow path are arranged in two rows in the air flow direction. Of the eight heat transfer tubes 31 to 38, six of the heat transfer tubes 31 to 36 are grooved tubes, and two of the

heat transfer tubes

37 and 38 are smooth tubes thinner than the grooved tubes. That is, 25% of the total refrigerant flow path length on the side close to the liquid side inlet / outlet 13 is a smooth pipe. In FIG. 7, since the first heat exchange section composed of the heat transfer tubes 31 to 36 and the second heat exchange section composed of the

heat transfer tubes

37 and 38 are integrally formed, the number of steps required for manufacturing is small and the manufacturing cost is low. Can be reduced.

As described above, according to the heat exchanger according to the first embodiment, the heat transfer tube connected to the gas side inlet / outlet 12 of one refrigerant flow path is a grooved tube, and the heat transfer tube connected to the liquid side inlet / outlet 13 is a grooved tube. Since the smoothing tube is made thinner and the length of the smoothing tube is 25% or less of the total length, the required amount of refrigerant can be reduced without deteriorating the heat transfer performance when a non-co-boiling mixed refrigerant is used. .. In addition, the manufacturing cost can be reduced.

Embodiment 2.
FIG. 8 is a side view of another example in which one refrigerant flow path portion of the outdoor heat exchanger 6 according to the second embodiment is extracted. The first heat exchange section is formed by arranging the heat transfer tubes 31 to 36 on the upper part of the outdoor heat exchanger 6, and the

heat transfer tubes

37 and 38 are arranged on the lower part of the outdoor heat exchanger 6 to form the second heat exchange section. Is forming. As shown in FIG. 8, since the fins 11 of the first heat exchange section and the second heat exchange section are separated from each other, the first heat exchange section and the second heat exchange section are separated from each other by the heat transfer tubes and the fins 11. Can be adjusted independently.

As described above, according to the heat exchanger according to the second embodiment, the first heat exchange part of the grooved tube and the second heat exchange part of the smoothing tube can be manufactured separately, and thus the heat exchange of each can be performed separately. The fin pitch and the distance between the heat transfer tubes can be set appropriately according to the characteristics.

Embodiment 3.
FIG. 9 is an external view showing an example of an air conditioner equipped with the heat exchanger according to the first or second embodiment. The air conditioner 100 includes an outdoor unit 1 and an indoor unit 2 connected by a gas pipe 3 and a liquid pipe 4. Although not shown, the outdoor heat exchanger 6 housed in the outdoor unit 1 and the indoor heat exchanger 9 housed in the indoor unit 2 both use the heat exchangers shown in the first or second embodiment.

As described above, according to the air conditioner 100 shown in the third embodiment, the heat exchange performance is achieved by using the heat exchanger according to the first or second embodiment for the outdoor heat exchanger 6 and the indoor heat exchanger 8. Since the amount of the refrigerant sealed in the air conditioner 100 can be reduced without impairing the above, it is possible to contribute to lowering the total amount of GWP and reduce the environmental load.

Further, in the first and second embodiments, of the eight heat transfer tubes forming one refrigerant flow path, two near the liquid side inlet / outlet 13 are smooth tubes. For example, four heat transfer tubes form one refrigerant. When forming a flow path, one near the liquid side inlet / outlet 13 is used as a smoothing tube, and when forming one refrigerant flow path with six heat transfer tubes, one near the liquid side inlet / outlet 13 is used as a smoothing tube. If the length of the refrigerant flow path formed of the smooth pipe is at least 25% or less of the total length, the effect of increasing the heat transfer performance by the grooved pipe is not impaired. Further, these effects can be obtained not only when applied to the outdoor heat exchanger 6 but also when applied to the indoor heat exchanger 8.

Further, the configuration shown in the above-described embodiment shows an example of the contents of the present disclosure, can be combined with another known technique, and is configured without departing from the gist of the present disclosure. It is also possible to omit or change a part of.

1: Outdoor unit 2: Indoor unit 3: Gas pipe 4: Liquid pipe 5: Compressor, 6: Outdoor heat exchanger, 7: Expansion valve, 8: Indoor heat exchanger, 9: Four-way valve, 11 : Fin, 12: Gas side inlet / outlet, 13: Liquid side inlet / outlet, 14: U-shaped pipe, 31-36: Grooved pipe, 37, 38: Smooth pipe, 100: Air exchanger

Claims

A first heat transfer tube in which a heat medium circulates inside and a plurality of grooves are formed on the inner peripheral surface,
One end is connected to one end of the first heat transfer tube to form one heat medium flow path, the diameter of the tube is smaller than that of the first heat transfer tube, and the pressure loss per unit length is the first transfer. A second heat transfer tube with an inner surface shape that is smaller than the heat tube,
A heat exchanger consisting of.
When the heat exchanger is operated as an evaporator, the other end of the second heat transfer tube is used as the heat medium inlet.
The heat exchanger according to claim 1, wherein the other end of the first heat transfer tube is the inlet of the heat medium when the heat exchanger is operated as a condenser.
The heat exchanger according to claim 2, wherein the heat medium is a non-azeotropic mixed refrigerant.
The heat exchanger according to claim 3, wherein the length of the second heat transfer tube is 25% or less of the length of the heat medium flow path.
The first heat exchange part formed by the first heat transfer tube and the second heat exchange part formed by the second heat transfer tube are divided into any one of claims 1 to 4. The heat exchanger described.
An air conditioner in which the heat exchanger according to any one of claims 1 to 5 is used on the outdoor side or the indoor side.