U.S. patent application number 14/432630 was filed with the patent office on 2015-08-27 for double pipe heat exchanger and refrigeration cycle device.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Yohei Kato, Satoru Yanachi.
Application Number | 20150241132 14/432630 |
Document ID | / |
Family ID | 50434478 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150241132 |
Kind Code |
A1 |
Yanachi; Satoru ; et
al. |
August 27, 2015 |
DOUBLE PIPE HEAT EXCHANGER AND REFRIGERATION CYCLE DEVICE
Abstract
A double pipe heat exchanger includes an inner pipe inside which
a first fluid passes, an outer pipe that has a diameter larger than
the diameter of the inner pipe and that covers the inner pipe, and
second fluid passes through a space between the outer pipe and the
inner pipe, and a heat transfer area enlargement pipe that is
provided in the space and that has a projection-depression shape
made to be larger than a length in the pipe-circumferential
direction of outer contact portions to be contact areas with the
inner wall of the outer pipe, and fin portions between the outer
contact portion and the inner contact portion that traverse the
space in a pipe cross section come into contact with the outer wall
of the inner pipe and the inner wall of the outer pipe in oblique
directions.
Inventors: |
Yanachi; Satoru; (Tokyo,
JP) ; Kato; Yohei; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI ELECTRIC CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
50434478 |
Appl. No.: |
14/432630 |
Filed: |
September 3, 2013 |
PCT Filed: |
September 3, 2013 |
PCT NO: |
PCT/JP2013/073688 |
371 Date: |
March 31, 2015 |
Current U.S.
Class: |
165/154 |
Current CPC
Class: |
F28D 2021/0068 20130101;
F25B 2400/13 20130101; F25B 40/00 20130101; F28F 1/105 20130101;
F28D 7/106 20130101; F28F 1/40 20130101 |
International
Class: |
F28D 7/10 20060101
F28D007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2012 |
JP |
PCT/JP2012/075530 |
Claims
1. A double pipe heat exchanger comprising: an inner pipe inside
which a first fluid passes; an outer pipe that has a diameter
larger than a diameter of the inner pipe and that covers the inner
pipe, the inner pipe and the outer pipe configured to allow a
second fluid to pass through a space defined therebetween; and a
heat transfer area enlargement pipe that is provided in the space
and in which, in a pipe cross section, an angle between the heat
transfer area enlargement pipe and the outer wall of the inner pipe
at each of inner contact portions to he contact areas between an
outer wall of the inner pipe and the heat transfer area enlargement
pipe is smaller than an angle between the heat transfer area
enlargement pipe and the inner wall of the outer-pipe at each of
outer contact portions to be contact areas between an inner wall of
the outer pipe and the heat transfer area enlargement pipe the heat
transfer area enlargement pipe having a projection-depression shape
in the pipe cross section in which fin portions between the inner
contact portions and the outer contact portions that traverse the
space in the pipe cross section come into contact with the outer
wall of the inner-pipe and the inner wall of the outer-pipe in
oblique directions.
2. The double pipe heat exchanger of claim 1, wherein the fin
portions each have an arc shape in the pipe cross section.
3. The double pipe heat exchanger of claim 1, wherein the fin
portions each have a bent shape that projects toward the inner pipe
side in the pipe cross section.
4. The double pipe heat exchanger of claim 1, wherein, in the pipe
cross section of the heat transfer area enlargement pipe, a length
in a pipe-circumferential direction of each of the inner contact
portions is made to be larger than a length in a
pipe-circumferential direction of the outer contact portion.
5. The double pipe heat exchanger of claim 1, wherein the contact
portions are formed such that the outer contact portions are made
to be point contacts in the pipe cross section, and the inner
contact portions are made to be line contacts in the pipe cross
section.
6. The double pipe heat exchanger of claim 1, wherein the heat
transfer area enlargement pipe is formed so as to satisfy
.theta.1<(360/n).times.{doi/(dio+doi)} where .theta.1 is an
angle formed between both end portions of the outer contact portion
and the center of the inner pipe and the outer pipe, dio is an
outer diameter of the inner pipe, doi is an inner diameter of the
outer pipe, n is a number of projecting shapes or depressed shapes
of the heat transfer area enlargement pipe, and the projecting
shapes and the depressed shapes all have an identical shape.
7. The double pipe heat exchanger of claim 1, wherein the outer
contact portions and the inner contact portions are each
brazed.
8. The double pipe heat exchanger of claim 7, wherein the heat
transfer area enlargement e pipe is formed by a cladding material
having a surface covered with a brazing material.
9. A refrigeration cycle device that performs heat exchange between
two kinds of refrigerants using the double pipe heat exchanger of
claim 1.
10. The refrigeration cycle device of claim 9, wherein at least one
of the refrigerants is water or brine.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. national stage application of
PCT/JP2013/073688 filed on Sep. 3, 2013, which is based on and
claims priority from PCT/JP2012/075530 filed on Oct. 2, 2012, the
disclosures of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a double pipe heat
exchanger in which circular pipes having different pipe diameters
are combined to form two channels, and to a refrigeration cycle
device including this double pipe heat exchanger.
BACKGROUND
[0003] Examples of conventional double pipe heat exchangers having
enhanced heat-transfer performances include one in which a circular
pipe having the smaller diameter (hereafter, referred to as an
inner pipe) is inserted into a circular pipe having the larger
diameter (hereafter, referred to as an outer pipe). In addition, a
method is proposed in which the inside of the inner pipe is defined
as a first channel, a channel between the two circular pipes is
defined as a second channel, and a heat transfer area enlargement
pipe that is formed into an undulating shape is inserted into the
second channel and brought into intimate contact with the inner
pipe and the outer pipe, so as to enhance a heat-transfer
performance through an effect of increasing heat-transfer area
(see, e.g., Patent Literature 1).
PATENT LITERATURE
[0004] Patent Literature 1: Japanese Patent Laid-Open No.
2012-63067 (FIG. 1)
[0005] The above-described Patent Literature 1 proposes a double
pipe heat exchanger in which a heat transfer area enlargement pipe
is inserted to expand a heat-transfer area so as to enhance a
heat-transfer performance. However, Patent Literature 1 does not
mention a specific measure and the like taken against the heat
transfer area enlargement pipe that can enhance the heat-transfer
performance efficiently.
SUMMARY
[0006] Thus, the present invention has an object to obtain a double
pipe heat exchanger and a refrigeration cycle device that can
enhance a heat-transfer performance efficiently.
[0007] A double pipe heat exchanger according to the present
invention includes an inner pipe inside which a first fluid passes,
an outer pipe that has a diameter larger than the diameter of the
inner pipe and that covers the inner pipe, the inner pipe and the
outer pipe configured to allow a second fluid to pass through a
space therebetween, and a heat transfer area enlargement pipe that
is provided in the space and in which an angle between the heat
transfer area enlargement pipe and the outer wall of the inner pipe
at each of inner contact portions to be contact areas between an
outer wall of the inner pipe and the heat transfer area enlargement
pipe is smaller than an angle between the heat transfer area
enlargement pipe and the inner wall of the outer-pipe at each of
outer contact portions to be contact areas between an inner wall of
the outer pipe and the heat transfer area enlargement pipe the heat
transfer area enlargement pipe having a projection-depression shape
in a pipe cross section in which fin portions between the inner
contact portions and the outer contact portions that traverse the
space in the pipe cross section come into contact with the outer
wall of the inner-pipe and the inner wall of the outer-pipe in
oblique directions.
[0008] According to the present invention, a heat transfer area
enlargement pipe that is in contact with an outer pipe and an inner
pipe is provided in such a manner that the length in a
pipe-circumferential direction of a contact area with the outer
wall of the inner pipe is made larger than the length of the
contact area with the inner wall of the outer pipe, and it is thus
possible to scatter external force applied to the heat transfer
area enlargement pipe in manufacturing, and to expand a
heat-transfer area while suppressing poor contact in particular
with the inner pipe, so as to enhance a heat-transfer
performance.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a diagram for illustrating the configuration of a
double pipe heat exchanger according to a first embodiment of the
present invention.
[0010] FIG. 2 is a diagram showing a cross section of the double
pipe heat exchanger according to the first embodiment of the
present invention, in the other direction.
[0011] FIG. 3 is a diagram showing a cross section of a double pipe
heat exchanger according to a third embodiment of the present
invention.
[0012] FIG. 4 is a diagram for illustrating a lift of a heat
transfer area enlargement pipe 3.
[0013] FIG. 5 is a diagram showing parameters that are set to the
double pipe heat exchanger.
[0014] FIG. 6 is a diagram showing brazed portions according to a
fourth embodiment of the present invention.
[0015] FIG. 7 is a diagram showing refrigeration cycle devices each
including the double pipe heat exchanger according to the present
invention.
DETAILED DESCRIPTION
First Embodiment
[0016] FIG. 1 is a diagram for illustrating the configuration of a
double pipe heat exchanger according to a first embodiment of the
present invention. FIG. 1 shows a cross sectional view of the
double pipe heat exchanger taken along the direction of flow of
refrigerant (in an inner pipe 2 in particular). The double pipe
heat exchanger is formed by inserting the inner pipe 2 serving as a
circular pipe having a smaller diameter into the inside of an outer
pipe 1 serving as a circular pipe having a larger diameter. In
addition, end portions of the heat exchanger having a double
cylinder structure is configured such that an inner-wall portion of
the outer pipe 1 (outer-pipe inner wall) comes into contact with an
outer-wall portion of the inner pipe 2 (inner-pipe outer wall)
(such that side-wall portions closing the outer pipe 1 cover the
inner pipe 2).
[0017] The inside of the inner pipe 2 is defined as an inner
channel 4 serving as a first channel, and a space formed between
the inner pipe 2 and the outer pipe 1 is defined as an outer
channel 5 serving as a second channel. An inlet and outlet of the
outer channel 5 for a refrigerant are through holes formed in the
wall surface of the outer pipe 1 and connects contact pipes. In
addition, a first fluid and a second fluid are allowed to flow in
the inner channel 4 and the outer channel 5, respectively. The
first fluid and the second fluid having different temperatures flow
through the respective channels, which enables heat exchange
between the fluids in the double pipe heat exchanger.
[0018] FIG. 2 is a diagram showing a cross section of the double
pipe heat exchanger according to the first embodiment of the
present invention, taken along another direction. FIG. 2 shows an
A-A' cross section in FIG. 1 (a pipe cross section. A cross section
taken along a pipe-circumferential direction when viewed in a
direction in which the fluids flow). The double pipe heat exchanger
of the present embodiment is configured by further inserting a heat
transfer area enlargement pipe 3 having an undulating shape that
includes projections and depressions, into a space portion of the
outer channel 5. In the heat transfer area enlargement pipe 3, an
inner wall (the inner wall of the heat transfer area enlargement
pipe) comes into contact with the inner-pipe outer wall at the
depressed portions, and an outer wall (the outer wall of the heat
transfer area enlargement pipe) comes into contact with the
outer-pipe inner wall at the projecting portions. In addition, a
side wall obliquely traverses the outer channel 5 (the space
between the inner pipe 2 and the outer pipe 1) in the pipe cross
section, and comes into contact with the inner-pipe outer wall and
the outer-pipe inner wall in oblique directions.
[0019] Here, the amount of heat exchange Q, a heat-transfer area A,
a heat transfer coefficient K, and a difference dT in temperature
between the first fluid and the second fluid relating to the heat
exchange generally have a relationship represented by Expression
(1).
[Expression 1]
Q=AKdT (1)
[0020] In addition, the heat transfer coefficient K is represented
by Expression (2). Here, .alpha.1 is the heat transfer coefficient
of the first fluid, d1 is the hydraulic diameter of the inner
channel 4, .alpha.2 is the heat transfer coefficient of the second
fluid, and d2 is the hydraulic diameter of the outer channel 5. In
addition, .lamda. is the thermal conductivity of the inner pipe 2,
dio is the outer diameter of the inner pipe 2, and dii is the inner
diameter of the inner pipe 2, and R is a thermal resistance.
[Expression 2]
K=.pi.L/{1/(.alpha.1d1)+1/(.alpha.2d2) +1
n(d.sub.io/d.sub.ii)/2.lamda.+R} (2)
[0021] The heat transfer area enlargement pipe 3 comes into contact
with the inner pipe 2 to serve as a fin, enabling the enlargement
of the heat-transfer area relating to the heat exchange, which
enables the increase of the amount of heat exchanged between the
first fluid and the second fluid.
[0022] Here, contact areas between the inner-pipe outer wall and
the inner wall of the heat transfer area enlargement pipe are
defined as inner contact portions 6 (and the length of the contact
portions in the pipe-circumferential direction is denoted as L1).
In addition, contact areas between the outer-pipe inner wall and
the outer wall of the heat transfer area enlargement pipe are
defined as outer contact portions 7 (and the length of the contact
portion in the pipe-circumferential direction is defined as L2). In
addition, portions serving as fins between the inner contact
portions 6 and the outer contact portions 7 (side wall surfaces in
the projection-depression shape) are defined as fin portions 16.
From the viewpoint of increasing the heat-transfer area by the heat
transfer area enlargement pipe 3, the double pipe heat exchanger is
preferably formed such that the inner contact portions 6 and the
outer contact portions 7 are each brought into contact at one point
(point contact) in the pipe cross section. The reduction of the
contact areas increases, for example, the number of the fin
portions 16 in a pipe circumference, a heat-transfer area per fin
portion 16, and the like, increasing the heat-transfer area of the
whole double pipe heat exchanger. Here, "points" as referred below
do not mean mathematical points, which have no area or the like,
but mean points that have areas to an extent of securing reliable
contacts between the pipes. Note that the contacts will be
described as the point contacts, but the contact areas are linear
in the double pipe heat exchanger as a whole.
[0023] However, when the inner contact portions 6 are formed to be
point contacts, the contact thermal resistance at each inner
contact portions 6 is increased. This reduces the heat transfer
coefficient K in the above-described Expression (2), resulting in
the reduction of the amount of heat exchange Q. In addition,
forming the inner contact portions 6 to be the point contacts may
cause spots of poor contact. If there are spots at which, for
example, the inner-pipe outer wall is not in contact with the inner
wall of the heat transfer area enlargement pipe when the inner
contact portions 6 are formed to be the point contacts, poor heat
transfer occurs, which prevents many heat-transfer areas from being
used efficiently.
[0024] Thus, in the double pipe heat exchanger of the first
embodiment, the outer contact portions 7 are formed to be point
contacts (the length L2 is reduced to zero) so as to expand the
heat-transfer area. In addition, the inner contact portions 6 are
formed to have a contact length in the pipe cross section (contact
areas are to form surfaces in the double pipe heat exchanger as a
whole).
[0025] As seen from the above, according to the double pipe heat
exchanger of the first embodiment, the outer contact portions 7 are
formed to be the point contacts so as to enlarge the heat-transfer
area, and the inner contact portions 6 are formed to have the
contact length, which enables the prevention of the poor contact
between the inner-pipe outer wall and the inner wall of the heat
transfer area enlargement pipe. This does not impair but can
enhance a heat-transfer performance.
Second Embodiment
[0026] The above-described double pipe heat exchanger of the first
embodiment includes, as shown in FIG. 2, the heat transfer area
enlargement pipe 3 having the projection-and-depression
(undulating) shape, in the outer channel 5 formed between the outer
pipe 1 and the inner pipe 2. In the heat transfer area enlargement
pipe 3, as described in the first embodiment, the inner wall of the
heat transfer area enlargement pipe is in contact with the
inner-pipe outer wall, and the outer wall of the heat transfer area
enlargement pipe is in contact with the outer-pipe inner wall. In
addition, the fin portions 16 to be the side walls traverse the
outer channel 5 in the pipe cross section.
[0027] To manufacture the double pipe heat exchanger in which the
heat transfer area enlargement pipe 3 is brought into contact with
the outer pipe 1 and the inner pipe 2 in such a manner, a step of
expanding the inner pipe 2 or a step of shrinking the outer pipe 1
is performed after the heat transfer area enlargement pipe 3 is
inserted into the outer channel 5.
[0028] Here, if portions of the heat transfer area enlargement pipe
3 to be the fin portions 16 are formed to be perpendicular to the
outer pipe 1 and the inner pipe 2, forces applied to portions to be
the inner contact portions 6 or the outer contact portions 7 are
applied directly to the fin portions 16, in expanding or shrinking
the pipe. This incurs the risk of forming the fin portions 16 bent
into an unexpected shape. For this reason, the portions to be the
fin portions 16 are formed not to be perpendicular, reducing loads
posed on the portions to be the fin portions 16 in expanding or
shrinking the pipe. Then, the fin portions 16 are brought into
contact with the inner-pipe outer wall and the outer-pipe inner
wall in oblique directions. For example, when the outer contact
portions 7 are formed to be the point contacts like the
above-described first embodiment, as shown in FIG. 2, an angle a at
which the inner-pipe outer wall comes into contact with the inner
wall of the heat transfer area enlargement pipe and an angle 13 at
which the outer wall of the heat transfer area enlargement pipe
comes into contact with the outer-pipe inner wall are made to be
angles less than 90 degrees, although this is not in particular
intended to limit the angles.
[0029] FIG. 3 is a diagram for illustrating a lift of the heat
transfer area enlargement pipe 3. For example, when the step of
expanding or shrinking the pipe is performed, pressures more than
necessary act on the inner pipe 2 and the heat transfer area
enlargement pipe 3, the inner contact portions 6 of the heat
transfer area enlargement pipe 3 may be deformed, and middle
portions thereof, which should be in contact, may be lifted. The
occurrence of the lift may increase, for example, the contact
thermal resistance, which may impair a heat-transfer
performance.
[0030] Thus, for example, to prevent this lift, the fin portions 16
are brought into contact with the inner-pipe outer wall and the
outer-pipe inner wall in the oblique directions, and in addition,
the heat transfer area enlargement pipe 3 to be inserted into the
outer channel 5 of the double pipe heat exchanger is made to have a
shape in which the portions to be the fin portions 16, between the
portions to be the inner contact portions 6 (depressed portions)
and the portions to be the outer contact portions 7 (projecting
portions), are formed into arc shapes in the pipe cross section.
Forming such a shape allows the heat transfer area enlargement pipe
3 to be deformed to bend, spreading (absorbing) loads on the heat
transfer area enlargement pipe 3 even when the heat transfer area
enlargement pipe 3 is pressed excessively against the inner pipe 2
in expanding the inner pipe 2 or shrinking the outer pipe 1. For
this reason, also in the inner contact portions 6, unreasonable
forces are not applied to the heat transfer area enlargement pipe
3, which can prevent a lift. This does not lose but can enhance a
heat-transfer performance.
[0031] Here, directions in which the portions to be the fin
portions 16 are bent through expanding or shrinking are preferably
directions in which the formed fin portions 16 project toward the
inner pipe 2 side. By forming the projections toward the inner pipe
2 side, the fin portions 16 are deformed toward the inner pipe 2
side, increasing the contact areas between the fin portions 16 and
the inner pipe 2, which enlarges the inner contact portions 6 in
length. Heat can be thereby efficiently transmitted from the inner
pipe 2. In addition, for example, as shown in FIG. 2, the angle
.alpha.<the angle .beta. is satisfied, which reduces gaps
between the heat transfer area enlargement pipe 3 and the inner
pipe 2 in size. Therefore, for example, in brazing the inner
contact portion 6, a brazing material is easy to penetrate. This
allows heat to be further efficiently transmitted from the inner
pipe 2. In addition, the increase of the angle .beta. weakens
pressing force in the contact areas between the fin portions 16 and
the outer pipe 1, which can suppress the enlargement of the outer
contact portions 7 in size.
[0032] Here, it is assumed in the present embodiment that the shape
of the heat transfer area enlargement pipe 3 is the arc shape, but
is not limited to the arc shape, and a shape having a bent portion
at least at one point can bring the advantages of scattering the
loads on the portions to be the fin portions 16 and of preventing a
lift in the inner contact portions 6. In addition, the above
description similarly holds in a double pipe heat exchanger in
which, for example, the outer contact portions 7 are not the point
contact, and similar advantages can be brought.
Third Embodiment
[0033] FIG. 4 is a diagram showing a double pipe heat exchanger
according to a third embodiment of the present invention. FIG. 4
shows a pipe cross section similar to the A-A' section in FIG. 1
described in the first embodiment. The double pipe heat exchanger
of the present embodiment is configured such that the length L1 of
the inner contact portions 6 between the inner-pipe outer wall and
the inner wall of the heat transfer area enlargement pipe and the
length L2 of the outer contact portions 7 between the outer-pipe
inner wall and the outer wall of the heat transfer area enlargement
pipe satisfy L1>L2.
[0034] For example, if the relationship of L1 and L2 is L1<L2,
end points of the inner contact portion 6 may serve as fulcra to
generate deformation when excessive external forces are applied to
the outer pipe 1, the inner pipe 2, and the heat transfer area
enlargement pipe 3. For this reason, as described in the second
embodiment, in the heat transfer area enlargement pipe 3, the
middle portion of the inner contact portion 6 may be lifted from
the inner pipe 2, resulting in the loss of heat-transfer
performance.
[0035] Thus, by satisfying L1>L2, for example, like the first
embodiment, even when external forces are applied so as to bring
the outer pipe 1 into intimate contact with the heat transfer area
enlargement pipe 3 across the outer contact portions 7 each having
a contact length when viewed from the front of the pipe cross
section, forces applied to the outer contact portions 7 are
scattered, which prevents the pipes from being deformed.
[0036] In addition, by satisfying L1>L2, when external forces
are applied so as to bring the inner pipe 2 into intimate contact
with the heat transfer area enlargement pipe 3, and to bring the
outer pipe 1 into intimate contact with the heat transfer area
enlargement pipe 3, external forces applied to the inner contact
portions 6 are substantially identical to external forces applied
to the outer contact portions 7, and thus the outer contact
portions 7 are first deformed when excessive external forces are
applied. This can prevent the inner contact portions 6, which are
most important to reduce the contact thermal resistance, from being
lifted, and does not lose but can enhance a heat-transfer
performance.
[0037] Next, with respect to the double pipe heat exchanger
according to the third embodiment having such characteristics,
conditions of shape parameters to satisfy L1>L2 will be
considered.
[0038] FIG. 5 is a diagram showing parameters that are set for
shape analysis of the double pipe heat exchanger according to the
third embodiment of the present invention. As shown in FIG. 5, the
number of projecting portions (depressed portions) of the heat
transfer area enlargement pipe 3 is denoted by n, and the outer
diameter of the inner-pipe is denoted by dio, and the inner
diameter of the outer pipe is denoted by doi.
[0039] In addition, AO denotes an angle between the top of a
projecting portion of the heat transfer area enlargement pipe 3 and
the top of the next projecting portion, .theta.1 denotes an angle
that serves as a guide for forming the projecting portions, and
.theta.2 denotes an angle that serves as a guide for forming the
depressed portions. In addition, .theta.1' denotes a number b of
angles each of which is .theta.1 divided by a
(.theta.1'=b/a.times..theta.1), and .theta.2' denotes a number b of
angles each of which is .theta.2 divided by a
(.theta.2'=b/a.times..theta.2). Furthermore, a length along which
the inner pipe 2 is in contact with the heat transfer area
enlargement pipe 3 is denoted by L1, and a length along which the
outer pipe 1 is in contact with the heat transfer area enlargement
pipe 3 is denoted by L2. Here, it is assumed that the shape of the
projecting portions and the shape of the depressed portions are all
an identical shape in the heat transfer area enlargement pipe 3.
Then, .theta.0, .theta.1, .theta.2, .theta.1', and .theta.2' are
geometrically represented by Expressions (3) to (6).
[Expression 3]
.theta.o=360/n (3)
[Expression 4]
.theta.2+.theta.1=.theta.o=360/n (4)
[Expression 5]
.theta.1'=b/a.theta.1 (5)
[Expression 6]
.theta.2'=b/a.theta.2 (6)
[0040] In addition, the length L1 of the inner contact portions 6
and the length L2 of the outer contact portions 7 can be
represented by Expressions (7) and (8) respectively.
L1=.pi.2dio(.theta.2'/360) [Expression 7]
L2=.pi.2doi(.theta.1'/360) [Expression 8]
[0041] Based on Expressions (3) to (8), the conditions to satisfy
L1>L2 can be represented by Expression (9).
[Expression 9]
.theta.1>(360/n){doi/(dio+doi)}} (9)
[0042] As described above, according to the double pipe heat
exchanger of the third embodiment, the length L1 of the inner
contact portions 6 between the inner-pipe outer wall and the inner
wall of the heat transfer area enlargement pipe, the length L2 of
the outer contact portions 7 between the outer-pipe inner wall and
the outer wall of the heat transfer area enlargement pipe are made
to have the relationship of L1>L2, and thus the external forces
applied to the outer contact portions 7 can be scattered. In
addition, by making the external forces applied to inner contact
portions 6 substantially identical to the external forces applied
to outer contact portions 7, excessive external forces are not
applied only to the inner contact portions 6 but scattered, which
can prevent a lift in the inner contact portions 6. The above
enables the prevention of excessive deformation of each pipe.
Fourth Embodiment
[0043] Although not in particular described in the above-described
first to third embodiments, it is preferable that each contact area
is brazed with a brazing material 15 so as to further secure the
contact between the inner-pipe outer wall and the inner wall of the
heat transfer area enlargement pipe, and the contact between the
outer-pipe inner wall and the outer wall of the heat transfer area
enlargement pipe.
[0044] FIG. 6 is a diagram showing brazed portions according to a
fourth embodiment of the present invention. For example, after
assembling the inner pipe 2, the outer pipe 1, and the heat
transfer area enlargement pipe 3, a brazing material 15 or the like
is applied, furnace brazing or the like is performed to melt the
brazing material 15, brazing contact portions. For example, if the
pipes are made of an aluminum or the like, an Al--Si-based
(aluminum-silicon-based) alloy in which an aluminum is alloyed with
a silicon is used as the brazing material 15.
[0045] Here, if it is difficult to apply the brazing material 15
after the assembly, a cladding material in which the heat transfer
area enlargement pipe 3 is clad in (covered with) the brazing
material 15 in advance may be used.
Fifth Embodiment
[0046] In a fifth embodiment, there will be described an example of
a refrigeration cycle device to which the double pipe heat
exchanger described in the first to fourth embodiments is applied.
Here, four kinds of configurations of the refrigeration cycle
device will be described.
[0047] FIG. 7 is a diagram showing examples of the configurations
of the refrigeration cycle devices according to the fifth
embodiment. In each refrigeration cycle device of the present
embodiment, a compressor 8, a condensor 9, an expansion valve 10,
an evaporator 11, and a double pipe heat exchanger 12 are connected
with pipes to configure a refrigerant circuit.
[0048] The compressor 8 sucks and compresses a refrigerant, and
discharges the refrigerant at a high temperature and pressure.
Here, the compressor 8 may be configured by, for example, a
compressor that controls a rotation speed with an inverter circuit
or the like to adjust the amount of discharged refrigerant. The
condensor 9 to be a heat exchanger is for performing heat exchange
between, for example, air supplied from a blower (not shown) and
the refrigerant to condense the refrigerant into a liquid
refrigerant (to condense and liquefy the refrigerant).
[0049] In addition, the expansion valve (pressure-reducing valve or
throttle) 10 is for decompressing and expanding the refrigerant.
The expansion valve is configured by, for example, flow control
means such as an electronic expansion valve, and may be configured
by, for example, refrigerant amount adjusting means or the like
such as an expansion valve and a capillary including a temperature
sensitive cylinder. The evaporator 11 is for performing heat
exchange between air or the like to evaporate the refrigerant into
a gas refrigerant (to evaporate and gasify).
[0050] In addition, the double pipe heat exchanger 12 of the
refrigeration cycle device in FIG. 7(a) performs heat exchange
between a refrigerant at a high temperature and pressure flowing
from the condensor 9 and a refrigerant at a low temperature and
pressure flowing from the evaporator 11. Using the double pipe heat
exchanger 12 in such a manner enables increasing the temperature of
the refrigerant in the condensor 9. It is thereby possible to
enhance a capability in heating, and to increase a COP (Coefficient
Of Performance: a value obtained by dividing a capability by an
input). In addition, the refrigerant flowing from the evaporator 11
can be gasified, which can prevent the liquid refrigerant from
returning to the compressor 8.
[0051] The double pipe heat exchanger 12 of a refrigeration cycle
device in FIG. 7(b) performs heat exchange between a high-pressure
liquid refrigerant at a refrigerant outlet of the condensor 9 and a
middle-pressure two-phase refrigerant that has passed through the
flow control valve 13. Then, the refrigerant that has been
subjected to the heat exchange and has changed into a
middle-pressure gas refrigerant is caused to perform bypassing to a
suction-side pipe to the compressor 8.
[0052] In such a manner, the refrigeration cycle device in FIG.
7(b) causes the refrigerant that has passed through the condensor 9
to diverge before passing through the expansion valve 10 and to
perform bypassing using the double pipe heat exchanger 12, which
can reduce the amount of refrigerant flowing downstream side from
the expansion valve 10. It is thereby possible to reduce pressure
drop, increasing the COP.
[0053] The double pipe heat exchanger 12 of the refrigeration cycle
device in FIG. 7(c) performs heat exchange between a high-pressure
liquid refrigerant at the refrigerant outlet of the condensor 9 and
a middle-pressure two-phase refrigerant that has passed through the
flow control valve 13. Then, the refrigerant that has been
subjected to the heat exchange and has changed into a
middle-pressure gas refrigerant is injected into a middle portion
of a compression part of the compressor 8. Here, the compressor 8
of the refrigeration cycle device in FIG. 7(c) is a compressor
having a multistage configuration that can perform the
injection.
[0054] In such a manner, the refrigeration cycle device in FIG.
7(c) causes the refrigerant that has passed through the condensor 9
to diverge before passing through the expansion valve 10 and to
perform bypassing using the double pipe heat exchanger 12, which
can reduce the amount of refrigerant flowing downstream side from
the expansion valve 10. In addition, the injection into the middle
portion of the compressing part of the compressor 8 having the
multistage configuration can be performed, and thus an input such
as the discharge temperature of the compressor can be reduced,
increasing the COP.
[0055] The refrigeration cycle device in FIG. 7(d), the double pipe
heat exchanger 12 is used as a condensor. Then, a fluid to be
subjected to heat exchange with a refrigerant flowing through a
refrigerant circuit is assumed to be water, brine, or the like
(hereafter, the description will be made assuming that the fluid is
water).
[0056] In FIG. 7(d), a pump 14 forms the flow of water and supplies
the water into the double pipe heat exchanger 12. In the double
pipe heat exchanger 12, the water is heated through the heat
exchange with the refrigerant. Here, the double pipe heat exchanger
12 is used as the condensor, and can be used as an evaporator.
* * * * *