FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
HEAT EXCHANGER AND AIR CONDITIONER;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED
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DESCRIPTION
TECHNICAL FIELD
[0001] The present invention relates to a heat exchanger for an air conditioner.
5 BACKGROUND ART
[0002] It has been pointed out that chlorofluorocarbons used as refrigerants for many
refrigerators and air conditioners have a global warming effect, and various regulations
have been enacted globally in order to reduce emissions of chlorofluorocarbons. For
example, the 2016 Kigali Amendment to the Montreal Protocol requires that
10 industrialized countries including Japan reduce the total GWP value, which is
determined by multiplying the GWP (Global Warming Potential) by the refrigerant
usage, to 15% by 2036, compared to that in 2011 to 2013.
[0003] To comply with such regulations, it has been considered, in the refrigerator and
air conditioner industry, to replace HFC refrigerants that are currently used widely,
15 such as R410A (R32 : R125 = 50 wt% : 50 wt%, GWP = 2088) and R32 (GWP = 675),
with refrigerants of lower GWP.
[0004] More specifically, it has been considered to apply HFO refrigerants such as 2-3-
3-3-tetrafluoropropene (R1234yf, GWP = 4), trans-1-3-3-3-tetrafluoropropene
(R1234ze(E), GWP = 6), and 1-1-2-trifluoroethylene (R1123, GWP = 4); refrigerant
20 mixtures of HFC refrigerants such as difluoromethane (R32, GWP = 675),
pentafluoromethane (R125, GWP = 3500), and 1-1-1-2-tetrafluoromethane (R134a,
GWP = 1430), and the above-identified HFO refrigerants; or HC refrigerants such as
propane (R290, GWP = 3) and isobutane (R600a, GWP = 4).
[0005] Among these substance candidates, the refrigerant mixture of the HFC
25 refrigerant and the HFO refrigerant is superior in terms of refrigeration capacity,
theoretical COP, flammability, and toxicity, for example, and may be applicable to a
wide variety of refrigerators and air conditioners. It is known that a mixture of
multiple refrigerants having different boiling points, which is so-called zeotropic
refrigerant mixture, exhibits properties different from those of pure refrigerants and
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azeotropic refrigerant mixtures. For example, in an evaporation process of zeotropic
refrigerant mixtures, a lower-boiling-point component is evaporated first, and
subsequently a higher-boiling-point component is evaporated, and therefore, the
concentration of the higher-boiling-point component is higher in a liquid phase in the
5 vicinity of the gas-liquid interface, which suppresses further boiling of the lowerboiling-point component. When the zeotropic refrigerant mixture is used, it is
necessary to recover from such degradation in evaporation heat transfer.
[0006] As a method for improving the heat exchange performance of an evaporator, a
method is known that places an auxiliary heat exchanger at a refrigerant entrance side
10 of a heat exchanger used as the evaporator, reduces the number of refrigerant flow
paths of the auxiliary heat exchanger, and increases the pipe diameter thereof (PTL 1,
for example).
CITATION LIST
PATENT LITERATURE
15 [0007] PTL 1: Japanese Patent Laying-Open No. 2004-332958
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0008] For such a heat exchanger configured like the above-cited patent literature, the
auxiliary heat exchanger with the increased pipe diameter is located at a refrigerant exit
20 side of the heat exchanger when used as a condenser. At the refrigerant exit side of
the condenser, subcooled liquid flows, resulting in increase of the amount of refrigerant
necessary for this refrigeration cycle due to the increased pipe diameter, and
accordingly resulting in increase of the refrigerant usage.
[0009] The present invention has been made to solve the problems as described above,
25 and thereby obtain a heat exchanger for an air conditioner for which a zeotropic
refrigerant mixture is used, and this heat exchanger, when used as an evaporator,
enables reduction of the amount of required refrigerant without deteriorating the heat
transfer performance.
SOLUTION TO PROBLEM
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[0010] To achieve the above object, a heat exchanger according to the present
disclosure includes:
a first heat transfer pipe in which a heat medium flows and which has a plurality
of grooves formed in an inner surface of the first heat transfer pipe; and
5 a second heat transfer pipe having one end connected to one end of the first heat
transfer pipe to form one heat medium flow path, the second heat transfer pipe being
smaller in pipe diameter than the first heat transfer pipe, and having an inner surface
shape providing a pressure loss per unit length smaller than that of the first heat transfer
pipe.
10 ADVANTAGEOUS EFFECTS OF INVENTION
[0011] With the heat exchanger according to the present disclosure for which a
zeotropic refrigerant mixture is used, the amount of required refrigerant can be reduced,
without deteriorating the heat exchange performance. Moreover, the manufacture cost
can also be reduced.
15 BRIEF DESCRIPTION OF DRAWINGS
[0012] Fig. 1 is a refrigerant circuit diagram of an air conditioner including a heat
exchanger according to Embodiment 1.
Fig. 2 is a front view of the heat exchanger according to Embodiment 1.
Fig. 3 is a cross-sectional view of heat transfer pipes to be used for the heat
20 exchanger according to Embodiment 1.
Fig. 4 is a characteristics plot showing an example of the evaporation heat
transfer performance relative to the dryness fraction of refrigerant in a general grooved
pipe.
Fig. 5 is a characteristic plot showing an example of the pressure loss relative to
25 the dryness fraction of refrigerant in a general grooved pipe.
Fig. 6 is a Ph chart showing a refrigeration cycle operation of an air conditioner
equipped with the heat exchanger according to Embodiment 1.
Fig. 7 is an example of a side view of one refrigerant flow path portion
extracted from the heat exchanger according to Embodiment 1.
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Fig. 8 is another example of a side view of one refrigerant flow path portion
extracted from a heat exchanger according to Embodiment 2.
Fig. 9 is an external view of an air conditioner to which the heat exchanger
according to Embodiment 1 or 2 is applied.
5 DESCRIPTION OF EMBODIMENTS
[0013] A heat exchanger and an air conditioner according to embodiments of the
present disclosure are described hereinafter based on the drawings. It should be noted
that the present invention is not limited by the embodiments.
[0014] Embodiment 1
10 Fig. 1 is a refrigerant circuit diagram showing an example of an air conditioner
including a heat exchanger according to Embodiment 1. The direction of refrigerant
flow is indicated by solid and broken lines. In Fig. 1, an air conditioner 100 includes
an outdoor unit 1 and an indoor unit 2 that are connected to each other by a gas pipe 3
and a liquid pipe 4 to form a single refrigerant circuit. In this refrigerant circuit, a
15 refrigerant mixture made up of two or more types of refrigerants that are different from
each other in boiling point is enclosed.
[0015] 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 indoor unit 2 is equipped with an
indoor heat exchanger 8. During cooling operation in which indoor heat exchanger 8
20 acts as an evaporator, refrigerant discharged from compressor 5 flows through fourway valve 9 into outdoor heat exchanger 6, is reduced in pressure by expansion valve 7,
and then flows out of outdoor unit 1. The refrigerant flowing through liquid pipe 4
into indoor unit 2 is evaporated in indoor heat exchanger 8 and flows out of indoor unit
2. The refrigerant then flows through gas pipe 3, returns to outdoor unit 1, and is
25 sucked again into compressor 5.
[0016] During heating operation in which indoor heat exchanger 8 acts as a condenser,
refrigerant discharged from compressor 5 flows into indoor unit 2 through gas pipe 3
following a flow path setting for four-way valve 9. The refrigerant condensed by
indoor heat exchanger 8 flows through liquid pipe 4, returns to outdoor unit 1, and is
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reduced in pressure in expansion valve 7. The refrigerant with the reduced pressure
exchanges, in outdoor heat exchanger 6, heat with outdoor air, and the refrigerant is
accordingly evaporated and sucked again into compressor 5 through four-way valve 9.
[0017] Outdoor heat exchanger 6 and indoor heat exchanger 8 are each equipped with a
5 fan (not shown), to force outdoor air and indoor air to flow to outdoor heat exchanger 6
and indoor heat exchanger 8 and thereby increase the efficiency in exchanging heat
between refrigerant and air. As the fan, for example, cross flow fan, propeller fan,
turbo fan, or sirocco fan may be used. A single heat exchanger may be equipped with
a plurality of fans, or a plurality of heat exchangers may be equipped with a single fan.
10 Air conditioner 100 according to Embodiment 1 has a minimum configuration required
for enabling cooling operation and heating operation, and a gas-liquid separator, a
receiver, an accumulator, and/or an inner heat exchanger, for example, may
appropriately be added in the refrigerant circuit.
[0018] Fig. 2 is a front view showing an example of outdoor heat exchanger 6
15 according to Embodiment 1. Outdoor heat exchanger 6 is made up of a plurality of
fins 11 stacked together at intervals of about 1.5 mm therebetween, and heat transfer
pipes 31 to 38 extending through these fins 11. Heat transfer pipes 31 to 38 are
formed in a hairpin shape and closely fit in fins 11 to allow heat transfer. Heat
transfer pipes 31 to 38 have one end or both ends connected by a plurality of U-shaped
20 pipes 14 to form a single refrigerant flow path having a gas-side exit/entrance 12 and a
liquid-side exit/entrance 13. During heating operation in which outdoor heat
exchanger 6 acts as an evaporator, liquid-side exit/entrance 13 is an entrance of the
refrigerant flow path while gas-side exit/entrance 12 is an exit of the refrigerant flow
path. As also shown in Fig. 1, the refrigerant flow direction is the opposite direction
25 during cooling operation, and therefore, when outdoor heat exchanger 6 acts as a
condenser, liquid-side exit/entrance 13 is an exit of the refrigerant flow path while gasside exit/entrance 12 is an entrance of the refrigerant flow path.
[0019] Fig. 3 is a cross-sectional view of the heat transfer pipes used for the heat
exchanger according to the embodiment. Heat transfer pipes 31 to 38 forming
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outdoor heat exchanger 6 shown in Fig. 2 include first heat transfer pipes 31 to 36, and
the first heat transfer pipes are grooved pipes having peaks and valleys on the pipe
inner surface as shown for example in Fig. 3 (a), have one end located at gas-side
exit/entrance 12, and extend through fins 11 to form a first heat exchanger portion.
5 Heat transfer pipes 37, 38 are second heat transfer pipes that are smooth pipes as shown
in Fig. 3 (b), have one end located at liquid-side exit/entrance 13, and extend through
fins 11 to form a second heat exchanger portion. Heat transfer pipes 37, 38 have an
inner diameter D2 smaller than an inner diameter D1 of the grooved pipes used as heat
transfer pipes 31 to 36 (D1 > D2).
10 [0020] The shape of the grooves in heat transfer pipes 31 to 36 is not limited.
Specifically, there is no particular limitation on the inner diameter, the number of fins
in the pipes (hereinafter intra-pipe fins), the height of the intra-pipe fins, the helix angle
of the intra-pipe fins, and the area extension ratio, for example.
[0021] The type of the zeotropic refrigerant mixture (hereinafter referred to as
15 "refrigerant" as long as it is not necessary in terms of context to distinguish between
zeotropic refrigerant mixture, pure refrigerant, and azeotropic refrigerant mixture) to be
enclosed in air conditioner 100 is not particularly limited. For example, the
refrigerant to be used may be a refrigerant mixture of an HFC refrigerant such as
difluoromethane (R32, GWP = 675), pentafluoromethane (R125, GWP = 3500), or 1-1-
20 1-2-tetrafluoromethane (R134a, GWP = 1430), and an HFO refrigerant such as 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), or 1-1-1-4-4-4-hexafluoro-2-
butene (R1336mzz(Z), GWP = 2), or a refrigerant mixture of an HFCO refrigerant such
25 as trans-1-chloro-3-3-3-trifluoropropene (R1233zd, GWP = 1), or cis-1-chloro-2-3-3-3-
tetrafluoropropene (R1224yd(Z), GWP = 1), and an HC refrigerant such as propane
(R290, GWP = 3), or isobutane (R600a, GWP = 4), and the like.
[0022] Fig. 4 is a characteristic plot showing an example of the intra-pipe evaporation
heat transfer performance relative to the dryness fraction of refrigerant in a general
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grooved pipe. The vertical axis indicates the evaporation heat transfer coefficient of
the grooved pipe, represented by a relative value with respect to the evaporation heat
transfer coefficient of a smooth pipe. As for the refrigerant, respective characteristics
of two different refrigerants, i.e., a single refrigerant and a zeotropic refrigerant mixture,
5 are plotted by a broken line and a solid line, respectively.
[0023] As shown in Fig. 4, for the single refrigerant, the grooved pipe exhibits an
evaporation heat transfer coefficient of three or more times higher than that of the
smooth pipe, regardless of the refrigerant dryness fraction, and thus significantly
contributes to improvement of the heat exchange performance. In contrast, when the
10 zeotropic refrigerant mixture is used, improvement of the evaporation heat transfer
coefficient relative to the smooth pipe is not significantly large, unlike the one achieved
for the single refrigerant. In particular, in the region of a low refrigerant dryness
fraction of 0.4 or less, the evaporation heat transfer coefficient of the grooved pipe is
substantially identical to the evaporation heat transfer coefficient of the smooth pipe,
15 and thus fails to contribute to improvement of the heat exchange performance.
[0024] Fig. 5 is a characteristic plot showing an example of the pressure loss relative to
the dryness fraction of refrigerant in a general grooved pipe. The vertical axis
indicates the pressure loss of the grooved pipe, represented by a relative value with
respect to the pressure loss of a smooth pipe. The broken line represents the pressure
20 loss for a single refrigerant, and the solid line represents the pressure loss for a
zeotropic refrigerant mixture.
[0025] As shown in Fig. 5, the pressure loss of the grooved pipe is large relative to the
pressure loss of the smooth pipe, regardless of the refrigerant dryness fraction, and
particularly large in the region of a refrigerant dryness fraction of 0.3 to 0.5. This
25 phenomenon is substantially the same for both the single refrigerant and the zeotropic
refrigerant mixture. For the zeotropic refrigerant mixture, however, the rate of
increase of the pressure loss is larger. It is seen from Figs. 4 and 5 that although use
of the grooved pipe for the heat exchanger improves the heat transfer performance, the
heat transfer performance is not improved and only the pressure loss is increased for a
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refrigerant dryness fraction of 0.4 or less.
[0026] Fig. 6 is a Ph chart showing a refrigeration cycle operation of air conditioner
100 according to Embodiment 1. The vertical axis indicates the pressure, the
horizontal axis indicates the specific enthalpy, and XO is a saturation line connecting
5 points where refrigerant is saturated liquid or saturated gas. State A, State B, State C,
and State D are respective entrance states of a process of compression, condensation,
expansion, and evaporation that form a refrigeration cycle. While the refrigeration
cycle shown in Fig. 6 is not limited to cooling operation or heating operation, the
refrigeration cycle operation is described first for the heating operation in the following.
10 [0027] Low-temperature low-pressure gas refrigerant (State A) at a suction position of
compressor 5 is increased in pressure by compressor 5 into high-temperature highpressure discharged gas (State B). The discharged gas is condensed in indoor heat
exchanger 8 acting as a condenser into high-pressure subcooled liquid (State C). The
refrigerant is subsequently reduced in pressure by expansion valve 7 into low-pressure
15 gas-liquid two-phase refrigerant (State D).
[0028] In the chart, X1 is a line of constant dryness fraction where the refrigerant
dryness fraction is 0.2. It is known that, at the entrance of the evaporator, the
refrigerant (State D) has a dryness fraction of approximately 0.2, for a condensation
temperature in a range of 40C 10C and an evaporation temperature in a range of
20 0C10C that are general operating conditions of air conditioning. In other words, in
an evaporation process from State D to State A in a general air conditioner, the
refrigerant dryness fraction changes from 0.2 to approximately 1.0 under most
operating conditions. In the present embodiment, in outdoor heat exchanger 6 shown
in Fig. 2, the low-pressure gas-liquid two-phase refrigerant in State D absorbs heat
25 from outdoor air until being superheated slightly, and returns to State A to thereby
complete a single refrigeration cycle.
[0029] As set forth above, the heat transfer coefficient improvement effect to be
produced by the grooved pipe is not exhibited for a dryness fraction change from 0.2 to
0.4 in a dryness fraction change of 0.8 (= 1.0  0.2) in this evaporation process. In
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other words, when the heat exchanger is used as an evaporator, it is unnecessary to
employ the grooved pipe, which is means for improving the heat exchange performance,
for a length of 25% (= 0.2/0.8) from liquid-side exit/entrance 13 serving as a refrigerant
entrance. Therefore, in Embodiment 1 as shown in Fig. 2, heat transfer pipes 37, 38
5 leading to liquid-side exit/entrance 13 of outdoor heat exchanger 6 are configured in the
form of smooth pipes. The smooth pipe is lower in cost than the grooved pipe, and
therefore, the manufacture cost of outdoor heat exchanger 6 can be reduced.
[0030] Moreover, if it is used under an extremely low evaporation temperature
condition, refrigerator oil dissolved in the liquid refrigerant may separate from the
10 refrigerant and stay in the vicinity of the wall of the heat transfer pipe. Stay of the
refrigerator oil may deteriorate the reliability of compressor 5, and should therefore be
avoided as much as possible. Thus, for the second heat exchanger portion located
near liquid-side exit/entrance 13 where a large amount of liquid refrigerant is present,
smooth pipes in which less friction occurs can be employed to reduce the amount of
15 staying refrigerator oil, and thereby improve the reliability of the air conditioner.
[0031] Next, cooling operation is described. During cooling operation, indoor heat
exchanger 8 acts as an evaporator and outdoor heat exchanger 6 acts as a condenser.
High-temperature high-pressure gas refrigerant in State B is discharged from
compressor 5, flows into outdoor heat exchanger 6 to exchange heat with outdoor air,
20 and is then condensed into subcooled liquid refrigerant in State C. In an SC portion
which is the last stage of this condensation process, i.e., SC portion that is a region after
refrigerant becomes saturated liquid, most of the amount of refrigerant necessary for
this refrigeration cycle is concentrated.
[0032] In outdoor heat exchanger 6 in Embodiment 1, heat transfer pipes 37, 38
25 forming the second heat exchanger portion located at the refrigerant exit side when the
outdoor heat exchanger is used as a condenser, have a smaller diameter than that of the
other heat transfer pipes, and therefore, the amount of refrigerant present in the SC
portion is reduced. Accordingly, the amount of refrigerant enclosed in air conditioner
100 is also reduced, which can contribute to reduction of the total GWP value and can
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lessen the environmental load.
[0033] Moreover, the smaller diameter of heat transfer pipes 37, 38 increases the
refrigerant flow rate in the second heat exchanger portion to promote convection heat
transfer, and therefore, it is possible to recover from the deterioration of the heat
5 transfer performance due to the smooth pipe, and to suppress deterioration of the heat
exchange performance.
[0034] Fig. 7 is an example of a side view of one refrigerant flow path portion
extracted from the heat exchanger according to Embodiment 1. While Fig. 2 shows
the heat exchanger arranged in a single line, Fig. 7 shows that heat transfer pipes 31 to
10 38 forming one refrigerant flow path are arranged in two lines in the direction of air
flow. Of eight heat transfer pipes 31 to 38, six heat transfer pipes 31 to 36 are
grooved pipes and two heat transfer pipes 37, 38 are smooth pipes thinner than the
grooved pipes. Namely, 25% of the total length of the refrigerant flow path that is
located relatively closer to liquid-side exit/entrance 13 is formed by the smooth pipes.
15 In Fig. 7, a first heat exchanger portion formed by heat transfer pipes 31 to 36 and a
second heat exchanger portion formed by heat transfer pipes 37, 38 are constituted in
the form of a single unit, which reduces the number of process steps required for
manufacture to thereby enable reduction of the manufacture cost.
[0035] As seen from the above, in the heat exchanger according to Embodiment 1, heat
20 transfer pipes leading to gas-side exit/entrance 12 of a single refrigerant flow path are
grooved pipes, while heat transfer pipes leading to liquid-side exit/entrance 13 are
smooth pipes thinner than the grooved pipes, and the ratio of the length of the smooth
pipes is less than or equal to 25% of the total length. Therefore, when a zeotropic
refrigerant mixture is used, the amount of required refrigerant can be reduced without
25 deteriorating the heat transfer performance. The manufacture cost can also be reduced.
[0036] Embodiment 2
Fig. 8 is another example of a side view of one refrigerant flow path portion
extracted from outdoor heat exchanger 6 according to Embodiment 2. Heat transfer
pipes 31 to 36 are arranged in an upper portion of outdoor heat exchanger 6 to form a
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first heat exchanger portion, and heat transfer pipes 37, 38 are arranged in a lower
portion of outdoor heat exchanger 6 to form a second heat exchanger portion. As
shown in Fig. 8, respective fins 11 for the first heat exchanger portion and the second
heat exchanger portions are separate from each other, and therefore, the first heat
5 exchanger portion and the second heat exchanger portion can be adjusted independently
of each other, in terms of the intervals between the heat transfer pipes and the gap
between fins 11.
[0037] As seen from the above, for the heat exchanger according to Embodiment 2, the
first heat exchanger portion of the grooved pipes and the second heat exchanger portion
10 of the smooth pipes can be manufactured separately from each other, and therefore, the
fin pitch and the interval between heat transfer pipes can be set appropriately depending
on respective heat exchanging characteristics.
[0038] Embodiment 3
Fig. 9 is an external view showing an example of an air conditioner equipped
15 with the heat exchanger according to Embodiment 1 or 2. Air conditioner 100 is
formed by connecting outdoor unit 1 and indoor unit 2 by gas pipe 3 and liquid pipe 4.
For both outdoor heat exchanger 6 housed in outdoor unit 1 and indoor heat exchanger
9 housed in indoor unit 2, the heat exchanger shown in connection with Embodiment 1
or 2 is used (not shown).
20 [0039] As seen from the above, for air conditioner 100 illustrated in connection with
Embodiment 3, the heat exchanger according to Embodiment 1 or 2 can be used as
outdoor heat exchanger 6 and indoor heat exchanger 8, and therefore, the amount of
refrigerant enclosed in air conditioner 100 can be reduced without deteriorating the heat
exchange performance, which can contribute to reduction of the total GWP value and
25 lessen the environmental load.
[0040] According to Embodiments 1 and 2, eight heat transfer pipes form a single
refrigerant flow path, of which two pipes located near liquid-side exit/entrance 13 are
smooth pipes. However, if four heat transfer pipes form a single refrigerant flow path,
for example, it is one heat transfer pipe located near liquid-side exit/entrance 13 that is
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a smooth pipe and, if six heat transfer pipes form a single refrigerant flow path, it is
also one heat transfer pipe located near liquid-side exit/entrance 13 that is a smooth
pipe. As long as the length of the refrigerant flow path formed by the smooth pipe(s)
is at least less than or equal to 25% of the total length, the effect of enhancing the heat
5 transfer performance by the grooved pipes is not deteriorated. Moreover, these
advantageous effects are achieved not only for outdoor heat exchanger 6 but also for
indoor heat exchanger 8.
[0041] The features illustrated in connection with the above embodiments are an
example of the details of the present disclosure, and may be combined with other
10 known techniques, or may partially be omitted or changed without going beyond the
scope of the present disclosure.
REFERENCE SIGNS LIST
[0042] 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;
15 12 gas-side exit/entrance; 13 liquid-side exit/entrance; 14 U-shaped pipe; 31-36
grooved pipe; 37, 38 smooth pipe; 100 air conditioner

We Claim:
1. A heat exchanger comprising:
a first heat transfer pipe in which a heat medium flows and which has a plurality
5 of grooves formed in an inner surface of the first heat transfer pipe; and
a second heat transfer pipe having one end connected to one end of the first heat
transfer pipe to form one heat medium flow path, the second heat transfer pipe being
smaller in pipe diameter than the first heat transfer pipe, and having an inner surface
shape providing a pressure loss per unit length smaller than that of the first heat transfer
10 pipe.
2. The heat exchanger according to claim 1, wherein
when the heat exchanger acts as an evaporator, another end of the second heat
transfer pipe is an entrance for the heat medium, and
15 when the heat exchanger acts as a condenser, another end of the first heat
transfer pipe is an entrance for the heat medium.
3. The heat exchanger according to claim 2, wherein the heat medium is a
zeotropic refrigerant mixture.
20
4. The heat exchanger according to claim 3, wherein the second heat transfer
pipe has a length of less than or equal to 25% of a length of the heat medium flow path.
5. The heat exchanger according to any one of claims 1 to 4, comprising a
25 first heat exchanger portion formed by the first heat transfer pipe, and a second heat
exchanger portion formed by the second heat transfer pipe and separate from the first
heat exchanger portion.
6. An air conditioner comprising the heat exchanger according to any one of
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claims 1 to 5, the heat exchanger being used either as an outdoor heat exchanger or an
indoor heat exchanger.