TECHNICAL FIELD
[0001] The present invention relates to a heat exchanger for exchanging heat between a first
fluid and a second fluid, particularly to a heat exchanger suitable for heat pump
type water heaters.
BACKGROUND ART
[0002] In conventional heat pump type water heaters, air conditioners, floor heating devices,
etc., a heat exchanger for exchanging heat between two kinds of fluids (water and
a refrigerant, or air and a refrigerant, for example) is used.
[0003] For example, Patent Literature 1 discloses a heat exchanger 10 as shown in FIGs.
10A and 10B. In the heat exchanger 10, one circular water tube 11 through which water
flows and two circular refrigerant tubes 12 through which a refrigerant flows are
in close contact with each other over their entire lengths, and these tubes 11 and
12 are formed in a track-wound shape. The outer diameter of each of the circular refrigerant
tubes 12 is set to be about half of the outer diameter of the circular water tube
11. The two circular refrigerant tubes 12 are disposed at positions at an angle of
45 degrees from the center of the circular water tube 11 with respect to the horizontal
line therebetween. Patent Literature 1 also shows in FIG. 4 a heat exchanger unit
in which the heat exchangers 10 formed in a track-wound shape are stacked, with a
heat insulation sheet being interposed therebetween.
CITATION LIST
Patent Literature
SUMMARY OF INVENTION
Technical Problem
[0005] With a configuration in which the circular water tube 11 and the circular refrigerant
tubes 12 are wound while being in contact with each other as in the heat exchanger
10 disclosed in Patent Literature 1, it is possible to ensure a large length of contact
among the tubes in a small occupation area. Therefore, the heat exchanger 10 can be
downsized more than other heat exchangers having comparable performances. However,
even this type of heat exchanger is required to be downsized further.
[0006] Under such circumstances, the present invention is intended to provide a heat exchanger
that can be downsized further.
Solution to Problem
[0007] The present invention provides a heat exchanger including a heat transfer tube group
in which a plurality of first heat transfer tubes through which a first fluid flows
and a plurality of second heat transfer tubes through which a second fluid that exchanges
heat with the first fluid flows are arranged alternately while being in contact with
each other. The heat transfer tube group is formed in a spiral shape by being wound
in a perpendicular direction perpendicular to an arrangement direction in which the
first heat transfer tubes and the second heat transfer tubes are arranged. A plurality
of concave portions are provided on both sides, in the perpendicular direction, of
an outer circumferential surface of each of the first heat transfer tubes, along an
extending direction of the first heat transfer tube. The plurality of concave portions
form convex portions on an inner circumferential surface of each first heat transfer
tube.
Advantageous Effects of Invention
[0008] In the above-mentioned configuration, since both of the first heat transfer tube
and the second heat transfer tube constituting the spiral-shaped heat transfer tube
group are provided plurally, small-size tubes can be used as these heat transfer tubes.
This makes it possible to reduce the minimum bend radius of the heat transfer tube
group. Moreover, since the first heat transfer tubes and the second heat transfer
tubes are arranged in a direction perpendicular to the direction in which the heat
transfer tube group is wound, the width of the row of these tubes also can be kept
small. Furthermore, since the first heat transfer tubes and the second heat transfer
tubes are arranged alternately while being in contact with each other, a heat transfer
tube of one type is sandwiched between heat transfer tubes of the other type, except
for the heat transfer tubes located at both side ends. Thus, it is possible to ensure
a large contact area between each first heat transfer tube and second heat transfer
tube, and accordingly it is possible to shorten the entire lengths of the first heat
transfer tube and the second heat transfer tube. With such a configuration, the heat
exchanger of the present invention can be downsized further compared to conventional
heat exchangers having comparable performances.
[0009] Furthermore, in the present invention, concave portions are provided on both sides,
in a direction perpendicular to an arrangement direction in which the first heat transfer
tubes are arranged, of an outer circumferential surface of each of the first heat
transfer tubes, along an extending direction of the first heat transfer tube. The
concave portions form convex portions on an inner circumferential surface of each
first heat transfer tube. Therefore, the first fluid flows through the first heat
transfer tube while colliding with the convex portions, so that the flow of the first
fluid is disturbed. This makes it possible to improve the in-plane temperature uniformity
of the first fluid and enhance the heat exchanging efficiency between the first fluid
and the second fluid. As a result, the heat exchanger can be downsized further.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010]
FIG. 1 is a plan view illustrating a heat exchanger according to one embodiment of
the present invention.
FIG. 2 is an enlarged view of an essential part of FIG. 1.
FIG. 3 is an enlarged cross-sectional view of an essential part of FIG. 1, taken along
the line III-III.
FIG. 4 is an enlarged side view of an essential part of the heat exchanger illustrated
in FIG. 1.
FIG. 5A is a cross-sectional view taken along the line VA-VAin FIG. 4. FIG. 5B is
a cross-sectional view taken along the line VB-VB in FIG. 4.
FIG. 6A is a graph showing a relationship between the maximum depth of concave portions
of a second heat transfer tube and the flow velocity of a refrigerant near an inner
circumferential surface of the second heat transfer tube. FIG. 6B is a graph showing
a relationship between the maximum depth of the concave portions of the second heat
transfer tube and the pressure loss.
FIG. 7 is an enlarged side view of an essential part of a modified heat exchanger.
FIG. 8 is an enlarged side view of an essential part of another modified heat exchanger.
FIG. 9 is a configuration diagram of a heat pump type water heater including the heat
exchanger illustrated in FIG. 1.
FIG. 10A is a plan view illustrating a conventional heat exchanger. FIG. 10B is a
cross-sectional view taken along the line XB-XB in FIG. 10A.
DESCRIPTION OF EMBODIMENTS
[0011] Hereinafter, the embodiments for carrying out the present invention will be described
in detail with reference to the drawings. A description will be made below with respect
to, as an example, a heat exchanger for exchanging heat between water and a refrigerant,
such as carbon dioxide and chlorofluorocarbon alternative, used for an apparatus such
as a heat pump type water heater. However, the present invention is not limited to
this. For example, the present invention is applicable to a heat exchanger for exchanging
heat between water and water (hot water), and an internal heat exchanger for exchanging
heat between a high temperature refrigerant and a low temperature refrigerant in a
heat pump cycle.
[0012] As illustrated in FIG. 1 to FIG. 3, a heat exchanger 1 according to one embodiment
of the present invention includes a heat transfer tube group 2 formed in a spiral
shape so as to have a shape of a flat rectangular plate. The heat transfer tube group
2 has a configuration in which a plurality (4 in the example illustrated) of the first
heat transfer tubes 3 and a plurality (3 in the example illustrated) of the second
heat transfer tubes 4 are joined while being in contact with each other over the approximately
entire lengths and are integrated with each other. Relatively low temperature water
(a first fluid) flows through the first heat transfer tubes 3 and a relatively high
temperature refrigerant (a second fluid) flows through the second heat transfer tubes
4, so that the heat is exchanged between the water and the refrigerant and the water
is heated by the refrigerant.
[0013] The first heat transfer tubes 3 and the second heat transfer tubes 4 may be made
of metal, such as copper, a copper alloy and SUS, having a satisfactory thermal conductivity.
Circular tubes are used suitably as the first heat transfer tubes 3 and the second
heat transfer tubes 4.
[0014] As shown in FIG. 3, the first heat transfer tubes 3 and the second heat transfer
tubes 4 are arranged alternately in a row in a direction (an up and down direction
in FIG. 3) perpendicular to extending directions (central axis directions) of the
first heat transfer tubes 3 and the second heat transfer tubes 4, while being in contact
with each other. In the present embodiment, the first heat transfer tubes 3 and the
second heat transfer tubes 4 are arranged so that their centers lie on the same straight
line. One first heat transfer tube 3 and one second heat transfer tube 4 adjacent
to each other are joined to each other.
[0015] The joining between the first heat transfer tube 3 and the second heat transfer tube
4 may be performed by brazing, soldering, use of a thermally conductive adhesive,
etc. When joined using such a joining agent, the first heat transfer tube 3 and the
second heat transfer tube 4 has a large joining area therebetween and can ensure an
effective heat transfer area sufficiently. It is also possible to join the first heat
transfer tubes 3 and the second heat transfer tubes 4 together by bundling collectively
the first heat transfer tubes and the second heat transfer tubes 4 with a heat-shrinkable
tube.
[0016] Here, the first heat transfer tubes 3 have preferably an outer diameter D
1 equal to or larger than an outer diameter D
2 of the second heat transfer tubes 4 (D
2 ≤ D
1). The first heat transfer tubes 3 in the present embodiment have an outer diameter
and wall thickness larger than those of the second heat transfer tubes 4. For example,
in the case of using carbon dioxide (CO
2) as the refrigerant, the outer diameter D
2 of the second heat transfer tubes 4 is 5.0 mm and the outer diameter D
1 of the first heat transfer tubes 3 is 6.0 mm.
[0017] The heat transfer tube group 2 is wound in a perpendicular direction (hereinafter
referred to as "X direction") perpendicular to an arrangement direction (hereinafter
referred to as "Y direction") in which the first heat transfer tubes 3 and the second
heat transfer tubes 4 are arranged. Specifically, as shown in FIG. 1, the heat transfer
tube group 2 is formed in an approximately-rectangular spiral shape that is wound
while repeating alternately a straight portion 2a and a quarter-arc bent portion 2b
that smoothly is bent approximately 90°.
[0018] Preferably, a gap S (see FIG. 2 and FIG. 3) is formed between an outer-located winding
portion and an inner-located winding portion adjacent to each other, that is, between
an n-th portion (n is a natural number) and an n+1-th portion when counting from the
outside, in the heat transfer tube group 2. The thus formed gap S can prevent direct
heat transfer between winding portions adjacent to each other in the heat transfer
tube group 2. As a spacer, a copper tube or a resin sheet, for example, may be disposed
at an appropriate location between the outer-located winding portion and the inner-located
winding portion adjacent to each other in the heat transfer tube group 2 in order
to ensure the gap S. Alternatively, a heat insulating material may be interposed between
the winding portions adjacent to each other. In this case, the same advantageous effects
also can be obtained as in the case of forming the gap S.
[0019] As shown in FIG. 2, all bend radii R of the bent portions 2b in the heat transfer
tube group 2 preferably are uniform. Such a configuration can reduce the number of
the types of jigs used in the bending process, improving the workability.
[0020] In the present embodiment, the water flows through the first heat transfer tubes
3 from a peripheral side toward a central side of the spiral shape of the heat transfer
tube group 2, and the refrigerant flows through the second heat transfer tubes 4 from
the central side toward the peripheral side of the spiral shape of the heat transfer
tube group 2. Such a configuration allows the water and the refrigerant to form mutually
opposed flows, and thereby the heat is exchanged effectively therebetween.
[0021] Specifically, a first outlet member 6 and a second inlet member 7 are disposed on
the central side of the spiral shape of the heat transfer tube group 2, and a first
inlet member 5 and a second outlet member 8 are disposed on the peripheral side of
the spiral shape of the heat transfer tube group 2. The members 5 to 8 have a rectangular
parallelepiped shape extending in the Y direction, and have internal spaces 51, 61,
71 and 81, respectively, at one end surface in the longer direction (the end surface
illustrated in FIG. 1). One end of each first heat transfer tube 3 is connected to
one side surface of the first outlet member 6, and the other end of each first heat
transfer tube 3 is connected to one side surface of the first inlet member 5. One
end of each second heat transfer tube 4 is connected to one side surface of the second
inlet member 7, and the other end of each second heat transfer tube 4 is connected
to one side surface of the second outlet member 8. That is, the first inlet member
5 forms water inlets for guiding water into the respective first heat transfer tubes
3, whereas the first outlet member 6 forms water outlets for discharging collectively
the water that has flowed through the first heat transfer tubes 3. The second inlet
member 7 forms refrigerant inlets for guiding refrigerant into the respective second
heat transfer tubes 4, whereas the second outlet member 8 forms refrigerant outlets
for discharging collectively the refrigerant that has flowed through the second heat
transfer tubes 4.
[0022] Furthermore, in the present embodiment, a plurality of concave portions 3a and 4a
as shown in FIG. 4, FIGs. 5A and 5B are provided in a specified region E
1 of each longer-side straight portion 2a and a specified region E
2 of each shorter-side straight portion 2a in the heat transfer tube group 2 illustrated
in FIG. 1. In this way, the concave portions 3a and 4a preferably are provided avoiding
the bent portions 2b when the bend radii R of the bent portions 2b are small. Thereby,
damages during the bending process can be prevented. Here, the specified regions E
1 and E
2 each may be across the entire length of the corresponding straight portion 2a or
may be narrower than this. Alternatively, the lengths of the specified regions E
1 and E
2 may decrease toward the inner side of the spiral shape. Moreover, the concave portions
3a and 4a do not need to be provided on both of the longer-side straight portions
2a and the shorter-side straight portions 2a, and may be provided to either the longer-side
straight portions 2a or the shorter-side straight portions 2a.
[0023] Specifically, in the specified regions E
1 and E
2, the plurality of concave portions 3a are provided on both sides, in the X direction,
of an outer circumferential surface 31 of each of the first heat transfer tubes 3
at a specified pitch along the extending direction of the first heat transfer tube
3. Also, the plurality of concave portions 4a are provided on both sides, in the X
direction, of an outer circumferential surface 41 of each of the second heat transfer
tubes 4 at a specified pitch along the extending direction of the second heat transfer
tube 4. As shown in FIG. 5A, the concave portions 3a provided on the first heat transfer
tube 3 form convex portions 3b on an inner circumferential surface 32 of each first
heat transfer tube 3. As shown in FIG. 5B, the concave portions 4a provided on the
second heat transfer tube 3 form convex portions 4b on an inner circumferential surface
42 of each second heat transfer tube 4. The concave portions 3a need only be provided
on both sides, in the X direction, of the outer circumferential surface 31 of each
of the heat transfer tubes 3, and the concave portions 4a need only be provided on
both sides, in the X direction, of the outer circumferential surface 41 of each of
the heat transfer tubes 4, and thus the concave portions 3a and 4a do not necessarily
have to be located just lateral to the centers of the heat transfer tubes 3 and 4,
respectively. For example, in FIG. 4, the concave portions 3a may be provided at positions
upward or downward off the positions just lateral to the center of the heat transfer
tube 3, and the concave portions 4a may be provided at positions upwardly or downwardly
off the positions just lateral to the center of the heat transfer tube 4.
[0024] In the present embodiment, the concave portions 3a provided on one side, in the X
direction, of the outer circumferential surface 31 of each of the first heat transfer
tubes 3 and the concave portions 3a provided on the other side, in the X direction,
of the outer circumferential surface 31 of each of the first heat transfer tubes 3
are disposed alternately along the extending direction of the first heat transfer
tube 3. Likewise, the concave portions 4a provided on one side, in the X direction,
of the outer circumferential surface 41 of each of the second heat transfer tubes
4 and the concave portions 4a provided on the other side, in the X direction, of the
outer circumferential surface 41 of each of the second heat transfer tubes 4 are disposed
alternately along the extending direction of the second heat transfer tube 4. Furthermore,
in the present embodiment, the concave portions 3a provided on each first heat transfer
tube 3 and the concave portions 4a provided on each second heat transfer tube 4 are
linear recesses extending in a direction parallel to the extending direction of the
first heat transfer tube 3 or the second heat transfer tube 4.
[0025] For example, when carbon dioxide is used as the refrigerant, the concave portions
4a with a length of 5.0 mm are provided on both sides, in the X direction, of each
of the second heat transfer tube 4 at a pitch of 10 mm, and the concave portions 3a
with a length of 5.0 mm are provided on both sides, in the X direction, of each of
the first heat transfer tube 3 at a pitch of 10 mm. The pitch refers to a center-to-center
distance between adjacent concave portions on one side in the X direction. The maximum
depths (depths at the lowest points located at the deepest positions) of the concave
portions 3a and 4a are 5% or more but 20% or less of the outer diameters of the heat
transfer tubes 3 and 4, respectively.
[0026] In order to form the heat transfer tube group 2 with such a configuration, the first
heat transfer tubes 3 and the second heat transfer tubes 4 both of which are straight
are stacked alternately, these tubes stacked are joined by the above-mentioned method,
and then the concave portions 3a and 4a are formed on both sides, right and left,
of the heat transfer tube group 2 by pressing, for example. Thereafter, the heat transfer
tube group 2 is bent, on the same plane, into an approximately-rectangular spiral
shape. Alternatively, it is also possible to bend individually, on the same plane,
the first heat transfer tubes 3 and the second heat transfer tubes on which the concave
portions 3a and 4a respectively are formed in advance by pressing, etc. into an approximately-rectangular
spiral shape and stack them.
[0027] As described above, in the heat exchanger 1 in the present embodiment, since both
of the first heat transfer tube 3 and the second heat transfer tube 4 constituting
the spiral heat transfer tube group 2 are provided plurally, small-size tubes can
be used as these heat transfer tubes. This makes it possible to reduce the minimum
bend radius of the heat transfer tube group 2. Moreover, since the first heat transfer
tubes 3 and the second heat transfer tubes 4 are arranged in a direction perpendicular
to the direction in which the heat transfer tube group 2 is wound, the width of the
row of these tubes also can be kept small. Furthermore, since the first heat transfer
tubes 3 and the second heat transfer tubes 4 are arranged alternately while being
in contact with each other, a heat transfer tube of one type is sandwiched between
heat transfer tubes of the other type, except for the heat transfer tubes located
at both side ends. Thus, it is possible to ensure a large contact area between each
first heat transfer tube 3 and second heat transfer tube 4, and accordingly it is
possible to shorten the entire lengths of the first heat transfer tube and the second
heat transfer tube. With such a configuration, the heat exchanger 1 of the present
invention can be downsized further compared to conventional heat exchangers having
comparable performances.
[0028] Furthermore, in the heat exchanger 1 in the present embodiment, the concave portions
3a are provided on both sides, in the X direction, of the outer circumferential surface
31 of each of the first heat transfer tubes 3, along the extending direction of the
first heat transfer tube 3. The concave portions 3a form the convex portions 3b on
the inner circumferential surface 32 of each first heat transfer tube 3. Therefore,
the water flows through the first heat transfer tubes 3 while colliding with the convex
portions, so that the flow of the water is disturbed. This makes it possible to improve
the in-plane temperature uniformity of the water and enhance the heat exchanging efficiency
between the water and the refrigerant. As a result, the heat exchanger can be downsized
further. In addition, since the concave portions 3a are not provided in the Y direction
in which the first heat transfer tubes 3 and second heat transfer tubes 4 are in contact
with each other but are provided in the X direction, the above-mentioned effects can
be obtained without increasing thermal contact resistance of these tubes.
[0029] Moreover, in the present embodiment, the concave portions 4a also are provided on
both sides, in the X direction, of the outer circumferential surface 41 of each of
the second heat transfer tubes 4, along the extending direction of the second heat
transfer tube 4. The concave portions 4a form the convex portions 4b on the inner
circumferential surface 42 of each second heat transfer tube 4. Also, the refrigerant
flows through the second heat transfer tubes 4 while colliding with the convex portions
4b. Accordingly, the flow of the refrigerant is disturbed as well, so that the heat
exchanging efficiency between the water and the refrigerant is enhanced further. As
the second heat transfer tubes 4 for the refrigerant, grooved tubes in each of which
a plurality of grooves are provided on the inner circumferential surface can be used
instead of the circular tubes in each of which the concave portions 4a are provided
on the outer circumferential surface 41. However, since such grooved tubes are expensive,
the cost may be reduced by using, as in the present embodiment, the circular tubes
in each of which the concave portions 4a are provided on the outer circumferential
surface 41.
[0030] As shown in FIGs. 10A and 10B, in the heat exchanger 10 having a track-wound shape,
in other words, including a pair of straight portions disposed in parallel so as to
face each other and a pair of semicircular arc portions bent 180° so as to connect
end portions of these straight portions to each other, a large dead space with a shape
of an approximately right-angled triangle is formed outside each semicircular arc
portion, making a factor of increasing the occupancy area. In contrast, in the heat
exchanger 1 in the present embodiment, since the heat transfer tube group 2 is formed
in an approximately-rectangular spiral shape and the bent portions 2b located at corners
of the spiral shape have the uniform bend radii R, the bend radius of each bent portion
2b located in the outermost winding portion is significantly smaller than that of
the track-wound shape. This makes it possible to reduce the dead spaces formed outside
the heat exchanger 1. From another viewpoint, the configuration in the present embodiment
is different from the track-wound configuration in that the bend radii of the bent
portions 2b do not decrease from the peripheral side toward the central side of the
spiral shape. Therefore, the heat transfer tube group 2 can reach near the center
of the spiral shape, and thus the dead spaces near the center can be reduced. Moreover,
the uniform bend radii R of the bent portions 2b lead to satisfactory workability.
[0031] Furthermore, since small-size tubes can be used as the first heat transfer tubes
3 and the second heat transfer tubes 4 as described above, it is possible to make
the bend radii of the bent portions 2b of the spiral-shape heat transfer tube group
2 smaller and reduce further the dead spaces having the shape of an approximately
right-angled triangle that are formed outside the heat exchanger 1 by the bent portions
2b.
[0032] Furthermore, in the present embodiment, the first inlet member 5 and the second outlet
member 8 are disposed on the peripheral side of the spiral shape of the heat transfer
tube group 2, and the first outlet member 6 and the second inlet member 7 are disposed
on the central side of the spiral shape of the heat transfer tube group 2. In other
words, the relatively low temperature water flows through the first heat transfer
tubes 3 from one end located on the peripheral side of the spiral shape toward the
other end located on the central side of the spiral shape, and the relatively high
temperature refrigerant flows through the second heat transfer tubes 4 from one end
located on the central side of the spiral shape toward the other end located on the
peripheral side of the spiral shape. That is, when the heat exchanger 1 is observed
as a whole, both of the water and the refrigerant flow so that the temperatures thereof
increase from the periphery toward the center of the heat exchanger 1, and thereby
the high temperature portion from which a large amount of heat is radiated to the
outside can be disposed in a small area and the radiation loss can be suppressed more
effectively. Moreover, since the viscosity of water lowers as its temperature increases,
the configuration in which water flows so that its temperature increases toward the
center of the spiral shape is preferable also from the viewpoint of pressure loss.
[0033] The inwardly-protruding convex portions 4b of the second heat transfer tubes 4 through
which the refrigerant flows have the following effects. Usually, the refrigerant contains
an oil, such as PAG (polyalkylene glycol), for lubricating compressors, etc. This
causes the flow in each second heat transfer tube 4 to be a two-layer flow, forming
an oil film on the inner circumferential surface 42 of the second heat transfer tube
4. In order to maintain a high heat exchanging efficiency, the thickness of the oil
film preferably is as small as possible. The convex portions 4b are effective also
in reducing the thickness of the oil film. More specifically, the presence of the
convex portions 4b increases the flow velocity of the refrigerant near the inner circumferential
surface 42, thereby increasing the difference between the velocity of the oil film
flowing on the inner circumferential surface 42 and the velocity of the refrigerant.
In such a situation, the refrigerant takes away a large amount of the oil from the
surface of the oil film, reducing the thickness of the oil film. On the other hand,
when the convex portions 4b have an excessively large height, the pressure loss is
increased and the performance of the heat exchanger 1 is deteriorated. Therefore,
it is preferable to set appropriately the maximum depth of the concave portions 4a
and hold the height of the convex portions 4b within a proper range.
[0034] For example, FIGs. 6A and 6B show the results of analyses on the flowability of the
refrigerant, which was carbon dioxide, when the maximum depth of the concave portions
4a of the second heat transfer tube 4 was changed. The analyses were made using a
software "FULENT 6.3", under the conditions that the refrigerant had a mass flow rate
of 650 kg/m
2s, a temperature of 60°C and a pressure of 10 MPa, and the oil concentration in the
refrigerant was 1.0 mass%. The concave portions 4a with a length of 5.0 mm were provided
on both sides, in the X direction, of each of the second heat transfer tubes 4 at
a pitch of 10 mm, as shown in FIG. 4. The second heat transfer tubes 4 had an outer
diameter of 5.0 mm and an inner diameter of 4.1 mm. Then, a calculation was made in
each of the cases where the maximum depth of the concave portions 4a was 0 mm, 0.4
mm, 0.5 mm, and 0.6 mm. 0 mm of the maximum depth of the concave portions 4a indicates
that circular tubes having no concave portions 4a were used.
[0035] As shown in FIG. 6A, the flow velocity of the refrigerant near the inner circumferential
surface 42 is converged when the maximum depth of the concave portions 4a is in the
range of 0.4 to 0.5 mm. This means that the thickness of the oil film is not reduced
even if the maximum depth of the concave portions 4a is increased to be more than
that. On the other hand, as shown in FIG. 6B, the pressure loss is increased rapidly
when the maximum depth of the concave portions 4a is in the range of 0.4 to 0.5 mm.
Therefore, it is preferable that the maximum depth of the concave portions 4a is in
the range of 0.3 to 0.6 mm, which is slightly wider than the above-mentioned range
in two directions.
[0036] The above-mentioned heat exchanger 1 is used suitably for a heat pump type water
heater 200. FIG. 9 shows the heat pump type water heater 200 including the heat exchanger
1 of the present embodiment. The heat pump type water heater 200 has a heat pump unit
201 and a tank unit 203. The tank unit 203 has a hot water reservoir tank 202 for
holding the hot water produced in the heat pump unit 201. The hot water held in the
hot water reservoir tank 202 is supplied to a hot water tap 204. The heat pump unit
201 includes a compressor 205 for compressing the refrigerant, a radiator 207 that
allows the refrigerant to radiate heat, an expansion valve 209 for expanding the refrigerant,
an evaporator 211 for evaporating the refrigerant, and a refrigerant tube 213 connecting
these devices in this order. The heat exchanger 1 in the present embodiment is used
as the radiator 207. In the heat pump unit 201, a positive displacement expander capable
of recovering the expansion energy of the refrigerant may be used instead of the expansion
valve 209.
[0037] The present invention is not limited to the above-mentioned embodiment and can be
modified variously. For example, the number and the outer diameter of the first heat
transfer tubes 3 and the second heat transfer tubes 4 can be selected appropriately
according to the performance required for the heat exchanger 1 and the types of the
first fluid and the second fluid. In addition, the number of windings that the heat
transfer tube group 2 makes and the size of its spiral shape also can be determined
appropriately.
[0038] Furthermore, the heat transfer tube group 2 does not need to be formed in an approximately-rectangular
spiral shape. For example, it may be formed in a circular spiral shape, or in a track-wound
shape as shown in FIG. 10A. However, from the viewpoint of the dead space as mentioned
above, it is preferable that the heat transfer tube group 2 is formed in an approximately-rectangular
spiral shape.
[0039] In the present embodiment, the first heat transfer tubes 3 and the second heat transfer
tubes 4 are arranged so that their centers lie on the same straight line. However,
when the outer diameter D
1 of the first heat transfer tubes 3 is different from the outer diameter D
2 of the second heat transfer tubes 4, the first heat transfer tubes 3 and the second
heat transfer tubes 4 may be arranged so that their outermost points on one side in
the perpendicular direction perpendicular to the arrangement direction lie on the
same straight line, for example. In this case, the centers of the first heat transfer
tubes 3 and the centers of the second heat transfer tube 4 lie in a staggered manner.
[0040] Although the concave portions 3a provided on one side, in the X direction, of the
outer circumferential surface 31 of each of the first heat transfer tubes 3 and the
concave portions 3a provided on the other side, in the X direction, of the outer circumferential
surface 31 of each of the first heat transfer tubes 3 are disposed alternately along
the extending direction of the first heat transfer tube 3 in the above-mentioned embodiment,
they may be disposed at positions facing each other in the X direction. However, when
the concave portions 3a are parallel to the extending direction of the first heat
transfer tube 3, since the concave portions 3a thus disposed elongate narrow portions
in the first heat transfer tube 3, the concave portions 3a preferably are disposed
as in the above-mentioned embodiment. This is also the case with the concave portions
4a provided on the second heat transfer tubes 4.
[0041] Furthermore, as shown in FIG. 7, the concave portions 3a provided on both sides,
in the X direction, of the outer circumferential surface 31 of each of the first heat
transfer tubes 3 may be linear recesses extending in a direction inclined with respect
to the extending direction of the first heat transfer tube 3. The concave portions
4a provided on both sides, in the X direction, of the outer circumferential surface
41 of each of the second heat transfer tubes 4 may be linear recesses extending in
a direction inclined with respect to the extending direction of the second heat transfer
tube 4. Such concave portions 3a and 4a allow the water or the refrigerant to flow
while stirring them effectively. Particularly, in the case where the heat exchanger
1 is used for the heat pump type water heater 200 as shown in FIG. 9, it is preferable
that the concave portions 4a provided on the second heat transfer tube 4 through which
the refrigerant flows are inclined with respect to the extending direction of the
second heat transfer tube 4. In some cases, the refrigerant contains an oil for lubricating
the compressor 205, and a relatively large amount of this oil accumulates on the bottom
of the second heat transfer tube 4, lowering the heat exchanging efficiency. In such
a case, the inclined concave portions 4a could stir the refrigerant and suppress the
accumulation of the oil. In the case where the inclined concave portions 3a and 4a
are provided on the heat transfer tubes 3 and 4, respectively, the concave portions
3a provided on one side, in the X direction, of the heat transfer tube 3 and the concave
portions 3a provided on the other side, in the X direction, of the heat transfer tube
3 may be disposed at positions facing each other in the X direction, and the concave
portions 4a provided on one side, in the X direction, of the heat transfer tube 4
and the concave portions 4a provided on the other side, in the X direction, of the
heat transfer tube 4 may be disposed at positions facing each other in the X direction,
as shown in FIG. 7. Alternatively, the concave portions 3a provided on one side, in
the X direction, of the heat transfer tube 3 and the concave portions 3a provided
on the other side, in the X direction, of the heat transfer tube 3 may be disposed
alternately along the extending direction of the heat transfer tube 3, and the concave
portions 4a provided on one side, in the X direction, of the heat transfer tube 4
and the concave portions 4a provided on the other side, in the X direction, of the
heat transfer tube 4 may be disposed alternately along the extending direction of
the heat transfer tube 4, as shown in FIG. 8.
[0042] Furthermore, the shapes and positions of the concave portions 3a and 4a also can
be selected appropriately in combination such that the first heat transfer tube 3
is provided with the concave portions 3a parallel to the extending direction whereas
the second heat transfer tube 4 is provided with the concave portions 4a inclined
with respect to the extending direction, and that the concave portions 3a provided
on both sides of the first heat transfer tube 3 are disposed alternately whereas the
concave portions 4a provided on both sides of the second heat transfer tube 4 are
disposed at the positions facing each other.
[0043] The concave portions of the present invention do not need to be linear recesses as
long as they form convex portions on the inner circumferential surface of each first
heat transfer tube or second heat transfer tube. For example, the first heat transfer
tube 3 and the second heat transfer tube 4 may be formed in a wave shape meandering
in the X direction so that valley portions of the wave shape may serve as the concave
portions. That is, the convex portions of the present invention do not need to reduce
the cross-sectional area of a space enclosed by the inner circumferential surface
of the first heat transfer tube or the second heat transfer tube. The convex portions
may be portions protruding inwardly while maintaining the cross-sectional area. However,
from the viewpoint of workability, it is preferable that the concave portions of the
present invention are recesses, particularly linear recesses extending in a specified
direction, forming the convex portions 3b that reduce the cross-sectional area of
a space enclosed by the inner circumferential surface of the first heat transfer tube
3 or the second heat transfer tube 4, as in the above-mentioned embodiments.
INDUSTRIAL APPLICABILITY
[0044] The heat exchanger of the present invention is useful as a heat exchanger for a heat
pump, particularly as a heat exchanger for a heat pump type water heater. In addition,
the present invention is applicable to a heat exchanger for exchanging heat between
liquids or between gases.
1. A heat exchanger comprising a heat transfer tube group in which a plurality of first
heat transfer tubes through which a first fluid flows and a plurality of second heat
transfer tubes through which a second fluid that exchanges heat with the first fluid
flows are arranged alternately while being in contact with each other, the heat transfer
tube group being formed in a spiral shape by being wound in a perpendicular direction
perpendicular to an arrangement direction in which the first heat transfer tubes and
the second heat transfer tubes are arranged,
wherein a plurality of concave portions are provided on both sides, in the perpendicular
direction, of an outer circumferential surface of each of the first heat transfer
tubes, along an extending direction of the first heat transfer tube, and the plurality
of concave portions form convex portions on an inner circumferential surface of the
first heat transfer tube.
2. The heat exchanger according to claim 1, wherein the concave portions provided on
one side, in the perpendicular direction, of the outer circumferential surface of
the first heat transfer tube and the concave portions provided on the other side,
in the perpendicular direction, of the outer circumferential surface of the first
heat transfer tube are disposed alternately along the extending direction of the first
heat transfer tube.
3. The heat exchanger according to claim 1, wherein the concave portions provided on
one side, in the perpendicular direction, of the outer circumferential surface of
the first heat transfer tube and the concave portions provided on the other side,
in the perpendicular direction, of the outer circumferential surface of the first
heat transfer tube are disposed at positions facing each other in the perpendicular
direction.
4. The heat exchanger according to any one of claims 1 to 3, wherein a plurality of concave
portions also are provided on both sides, in the perpendicular direction, of an outer
circumferential surface of each of the second heat transfer tubes, along an extending
direction of the second heat transfer tube, and the plurality of concave portions
form convex portions on an inner circumferential surface of the second heat transfer
tube.
5. The heat exchanger according to claim 4, wherein the concave portions provided on
one side, in the perpendicular direction, of the outer circumferential surface of
the second heat transfer tube and the concave portions provided on the other side,
in the perpendicular direction, of the outer circumferential surface of the second
heat transfer tube are disposed alternately along the extending direction of the second
heat transfer tube.
6. The heat exchanger according to claim 4, wherein the concave portions provided on
one side, in the perpendicular direction, of the outer circumferential surface of
the second heat transfer tube and the concave portions provided on the other side,
in the perpendicular direction, of the outer circumferential surface of the second
heat transfer tube are disposed at positions facing each other in the perpendicular
direction.
7. The heat exchanger according to any one of claims 1 to 6, wherein the concave portions
are linear recesses extending in a specified direction.
8. The heat exchanger according to claim 7, wherein the specified direction is a direction
parallel to the extending direction of the first heat transfer tube or the second
heat transfer tube.
9. The heat exchanger according to claim 7, wherein the specified direction is a direction
inclined with respect to the extending direction of the first heat transfer tube or
the second heat transfer tube.
10. The heat exchanger according to any one of claims 1 to 9, wherein the heat transfer
tube group is formed in an approximately-rectangular spiral shape that is wound while
repeating alternately a straight portion and a bent portion that is bent approximately
90°C with a uniform bend radius.
11. The heat exchanger according to any one of claims 1 to 10, wherein a gap is formed
between an outer-located winding portion and an inner-located winding portion adjacent
to each other in the heat transfer tube group.
12. The heat exchanger according to any one of claims 1 to 10, wherein a heat insulating
material is interposed between an outer-located winding portion and an inner-located
winding portion adjacent to each other in the heat transfer tube group.
13. The heat exchanger according to any one of claims 1 to 12, wherein the first fluid
is heated by the second fluid.
14. The heat exchanger according to claim 13, wherein the first fluid is water and the
second fluid is a refrigerant.
15. The heat exchanger according to any one of claims 1 to 14, wherein both of the first
heat transfer tubes and the second heat transfer tubes are circular tubes, and the
first heat transfer tubes have an outer diameter equal to or larger than that of the
second heat transfer tubes.
16. The heat exchanger according to any one of claims 1 to 15, wherein the first fluid
flows through the first heat transfer tubes from a peripheral side toward a central
side of the spiral shape, and the second fluid flows through the second heat transfer
tubes from the central side toward the peripheral side of the spiral shape.