U.S. patent application number 10/208848 was filed with the patent office on 2003-01-30 for heat exchanger and method of making it.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES LTD.. Invention is credited to Inoue, Masashi, Iokawa, Hiroshi, Kotou, Hiroyuki, Nakado, Koji, Suzuki, Atsushi, Watabe, Shin, Watanabe, Yoshinori, Yasui, Kiyoto, Yoshikoshi, Akira.
Application Number | 20030019618 10/208848 |
Document ID | / |
Family ID | 15553259 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030019618 |
Kind Code |
A1 |
Watanabe, Yoshinori ; et
al. |
January 30, 2003 |
Heat exchanger and method of making it
Abstract
A heat exchanger is constructed by tubes, corrugated fins and
head pipes, which are assembled together. Herein, the tube is
constructed by bending a flat plate whose surfaces are clad with
brazing material to form a first wall and a second wall, which are
arranged opposite to each other with a prescribed interval of
distance therebetween to provide a refrigerant passage. Before
bending, a number of swelling portions are formed to swell from an
interior surface of the flat plate by press. By bending, the
swelling portions are correspondingly paired in elevation between
the first and second walls, so their top portions are brought into
contact with each other to form columns each having a prescribed
sectional shape corresponding to an elliptical shape or an
elongated circular shape each defined by a short length and a long
length. The columns are arranged to align long lengths thereof in a
length direction of the tube corresponding to a refrigerant flow
direction such that obliquely adjacent columns, which are arranged
adjacent to each other obliquely with respect to the length
direction of the tube, are arranged at different locations and are
partly overlapped with each other with long lengths thereof in view
of a width direction perpendicular to the length direction of the
tube. The tubes, corrugated fins and head pipes are assembled
together and are then placed into a heating furnace to heat for a
prescribed time.
Inventors: |
Watanabe, Yoshinori;
(Nagoya-shi, JP) ; Yoshikoshi, Akira; (Nagoya-shi,
JP) ; Suzuki, Atsushi; (Nishi-kasugai-gun, JP)
; Yasui, Kiyoto; (Nishi-kasugai-gun, JP) ; Iokawa,
Hiroshi; (Nishi-kasugai-gun, JP) ; Kotou,
Hiroyuki; (Nagoya-shi, JP) ; Watabe, Shin;
(Nishi-kasugai-gun, JP) ; Inoue, Masashi;
(Nishi-kasugai-gun, JP) ; Nakado, Koji;
(Nishi-Kasugai-gun, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES
LTD.
TOKYO
JP
|
Family ID: |
15553259 |
Appl. No.: |
10/208848 |
Filed: |
August 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10208848 |
Aug 1, 2002 |
|
|
|
09579272 |
May 26, 2000 |
|
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6453989 |
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Current U.S.
Class: |
165/173 |
Current CPC
Class: |
F28F 3/04 20130101; F28F
3/044 20130101; F28D 1/0341 20130101; F28D 1/0391 20130101 |
Class at
Publication: |
165/173 |
International
Class: |
F28F 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 1999 |
JP |
11-153022 |
Claims
What is claimed is:
1. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns formed inside of
the flat tube, wherein each of the plurality of columns is formed
by joining together top portions of swelling portions, which swell
from interior surfaces of the first and second walls by applying
external pressures to exterior surfaces of the first and second
walls to cave in respectively and which are arranged opposite in
connection with each other inside of the flat tube, and wherein
each of the plurality of columns has a prescribed sectional shape
which corresponds to an elliptical shape or an elongated circular
shape each defined by a short length and a long length, wherein the
plurality of columns are arranged to align long lengths thereof
along a length direction of the flat tube in such a manner that
obliquely adjacent columns, which are arranged adjacent to each
other obliquely with respect to the length direction of the tube,
are arranged at different locations but are partly overlapped with
each other with long lengths thereof in view of a width direction
perpendicular to the length direction of the flat tube.
2. A heat exchanger according to claim 1 wherein the flat tube is
constructed using side walls which are arranged at side ends of the
first and second walls and on which a plurality of semi-columns
each having a semi-shape of the column are formed in connection
with the plurality of columns in such a manner that each of the
plurality of semi-columns is arranged obliquely adjacent to a
selected column to partly overlap with its front-end portion or its
back-end portion.
3. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length d1 and a
long length d2, wherein the plurality of columns are arranged
between the first and second walls and are arranged to align long
lengths thereof along a length direction of the flat tube such that
obliquely adjacent columns, which are arranged adjacent to each
other obliquely with respect to the length direction of the flat
tube, are arranged at different locations but are partly overlapped
with each other with long lengths thereof in view of a width
direction perpendicular to the length direction of the flat tube,
wherein each of the plurality of columns has the prescribed
sectional shape which is defined by a relationship of 6 2.0 2 1 3.0
,and wherein using a first center distance p1 being measured
between the obliquely adjacent columns in the width direction of
the flat tube and a second center distance p2 being measured
between the obliquely adjacent columns in the length direction of
the flat tube, the plurality of columns are arranged to meet
relationships of 7 1.5 p1 d1 3.0 and 0.5 p2 d2 1.5 .
4. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length and a
long length, wherein the plurality of columns are arranged between
the first and second walls and are arranged to align long lengths
thereof being slanted with respect to a length direction of the
flat tube such that the long length of the column is slanted with a
prescribed angle of inclination to the length direction of the flat
tube.
5. A heat exchanger according to claim 4 wherein the prescribed
angle of inclination is set within a range of .+-.7.degree..
6. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length d1 and a
long length d2, wherein each of the plurality of columns is formed
by joining together top portions of swelling portions which swell
from interior surfaces of the first and second walls by applying
external pressures to exterior surface of the first and second
walls respectively and which are arranged opposite in connection
with each other inside of the flat tube, and wherein the plurality
of columns are arranged to align long lengths thereof along a
length direction of the flat tube such that obliquely adjacent
columns, which are arranged adjacent to each other obliquely with
respect to the length direction of the flat tube, are arranged at
different locations but are partly overlapped with each other with
long lengths thereof in view of a width direction perpendicular to
the length direction of the flat tube, wherein each of the
plurality of columns has the sectional shape which is defined by a
relationship of 8 2.0 2 1 3.0 ,and wherein using a first center
distance p1 being measured between the obliquely adjacent columns
in the width direction of the flat tube and a second center
distance p2 being measured between the obliquely adjacent columns
in the length direction of the flat tube, the plurality of columns
are arranged to meet relationships of 9 1.5 p1 d1 3.0 and 0.5 p2 d2
1.5 .
7. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length and a
long length, wherein each of the plurality of columns is formed by
joining together top portions of swelling portions which swell from
interior surfaces of the first and second walls by applying
external pressures to exterior surface of the first and second
walls respectively and which are arranged opposite in connection
with each other inside of the flat tube, wherein the plurality of
columns are arranged to align long lengths thereof being slanted
with respect to a length direction of the flat tube such that the
long length of the column is slanted with a prescribed angle of
inclination to the length direction of the flat tube, and wherein
the plurality of columns are arranged to adjoin with each other
such that obliquely adjacent columns, which are arranged adjacent
to each other obliquely with respect to the length direction of the
flat tube, are arranged at different locations but are partly
overlapped with each other with long lengths thereof in view of a
width direction perpendicular to the length direction of the flat
tube.
8. A heat exchanger according to claim 7 wherein the prescribed
angle of inclination is set within a range of .+-.7.degree..
9. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length and a
long length, wherein the plurality of columns are arranged between
the first and second walls and are arranged to align long lengths
thereof in a length direction of the flat tube and wherein the
plurality of columns are arranged in a gradually concentrated
manner along a refrigerant flow direction corresponding to the
length direction of the flat tube.
10. A heat exchanger according to claim 9 wherein the plurality of
columns are arranged to gradually increase in number, size or
density in the refrigerant flow direction.
11. A heat exchanger comprising: a flat tube constructed by a first
wall and a second wall which are arranged opposite and apart in
parallel with each other and are assembled together to form a
refrigerant passage; and a plurality of columns each having a
prescribed sectional shape corresponding to an elliptical shape or
an elongated circular shape each defined by a short length and a
long length, wherein the plurality of columns are arranged between
the first and second walls and are arranged to align long lengths
thereof in a length direction of the flat tube and wherein the
plurality of columns are arranged in a gradually deconcentrated
manner along a refrigerant flow direction corresponding to the
length direction of the flat tube.
12. A heat exchanger according to claim 11 wherein the plurality of
columns are arranged to gradually decrease in number, size or
density in the refrigerant flow direction.
13. A heat exchanger comprising: a plurality of tubes each of which
has a flat shape and contains a plurality of columns therein,
wherein each of the plurality of columns has a prescribed sectional
shape corresponding to an elliptical shape or an elongated circular
shape each defined by a short length and a long length and wherein
the plurality of columns are arranged to align long lengths thereof
along a length direction of the tube such that obliquely adjacent
columns, which are arranged adjacent to each other obliquely with
respect to the length direction of the tube, are arranged at
different locations but are partly overlapped with each other with
long lengths thereof in view of a width direction perpendicular to
the length direction of the tube; a plurality of corrugated fins,
each of which is arranged between the tubes such that crest
portions are brought into contact with an exterior surface of the
tube; and two head pipes which are arranged apart from each other
with a prescribed interval of distance therebetween and between
which the plurality of tubes and the plurality of corrugated fins
are arranged, so that both ends of a refrigerant passage formed
inside of the tube communicate with insides of the two head pipes
respectively.
14. A heat exchanger according to claim 13 wherein each of the
plurality of tubes is constructed by bending a flat plate to form a
first wall and a second wall, which are arranged opposite to each
other with a prescribed interval of distance therebetween to
provide the refrigerant passage, wherein swelling portions are
formed to swell from interior surfaces of the first and second
walls by applying external pressures to the first and second walls
respectively and are arranged at selected positions by which top
portions of the swelling portions are correspondingly brought into
contact with each other to form the columns.
15. A heat exchanger according to claim 14 wherein the first and
second walls are bonded together at selected portions by brazing to
form the tube, while the top portions of the swelling portions are
bonded together by brazing to form the columns.
16. A manufacturing method of a heat exchanger comprising the steps
of: constructing a plurality of tubes each having a flat shape by
bending flat plates whose surfaces are clad with brazing material,
wherein a plurality of swelling portions are formed to swell from
interior surfaces of the tube and their top portions are
correspondingly paired and brought into contact with each other to
form a plurality of columns inside of the tube; providing a
plurality of corrugated fins, which are respectively arranged
between the plurality of tubes; assembling the plurality of tubes
and the plurality of corrugated fins together with two head pipes
such that the plurality of tubes and the plurality of corrugated
fins are alternatively arranged in elevation and are horizontally
held between the two head pipes, wherein each of the plurality of
tubes having refrigerant passages communicates with the two head
pipes respectively; and placing the plurality of tubes, the
plurality of corrugated fins and the two head pipes which are
assembled together into a heating furnace to heat for a prescribed
time.
17. A manufacturing method of the heat exchanger according to claim
16 further comprising the steps of: forming the plurality of
swelling portions to swell from an interior surface of the flat
plate at selected positions by press; and bending the flat plate to
form a first wall and a second wall, which are arranged opposite to
each other with a prescribed interval of distance therebetween to
form a tube, wherein the first and second walls are adjusted in
position such that the plurality of swelling portions are
correspondingly paired with each other in elevation and top
portions thereof are correspondingly brought into contact with each
other to form a plurality of columns inside of the tube.
18. A manufacturing method of the heat exchanger according to claim
16 wherein the plurality of columns each having a prescribed
sectional shape corresponding to an elliptical shape or an
elongated circular shape defined by a short length d1 and a long
length d2 are arranged to align long lengths thereof in a length
direction of the tube such that obliquely adjacent columns, which
are arranged adjacent to each other obliquely with respect to the
length direction of the tube, are arranged at different locations
but are partly overlapped with each other with long lengths thereof
in view of a width direction perpendicular to the length direction
of the tube, wherein each of the plurality of columns is defined in
sectional shape by a relationship of 10 2.0 2 1 3.0 . and wherein
using a first center distance p1 being measured between the
obliquely adjacent columns in the width direction of the tube and a
second center distance p2 being measured between the obliquely
adjacent columns in the length direction of the tube, the plurality
of columns are arranged to meet relationships of 11 1.5 p1 d1 3.0
and 0.5 p2 d2 1.5 .
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to heat exchangers which are
applicable to air conditioners particularly used for vehicles. In
addition, this invention also relates to methods of manufacturing
the heat exchangers.
[0003] This application is based on patent application Ser. No. Hei
11-153022 filed in Japan, the content of which is incorporated
herein by reference.
[0004] 2. Description of the Related Art
[0005] In general, heat-exchanger tubes are used for heat
exchangers which are installed in air conditioners of vehicles, for
example. The heat-exchanger tubes are mainly classified into two
types of tubes (or pipes), which are shown in FIGS. 19 and 20
respectively.
[0006] FIG. 19 shows an example of a so-called "seam welded tube",
which is designated by a reference numeral "1". That is, the seam
welded tube 1 is constructed by a tube 2 having a flat shape and a
corrugated inner fin 4. Herein, the corrugated inner fin 4 is
inserted into the tube 2 by way of its opening 3. The corrugated
inner fin 4 is formed in a corrugated shape having waves whose
crest portions "4a" are bonded to an interior surface of the tube 2
by welding or else.
[0007] FIG. 20 shows an example of an extrusion tube, which is
designated by a reference numeral "5". The extrusion tube 5 has
tube portions "6" and partition walls "7", which are integrally
formed by extrusion molding.
[0008] If a heat exchanger is designed using the seam welded tube 1
shown in FIG. 19, it has an advantage in which since the corrugated
inner fin 4 is inserted into the tube 2, an overall heating area is
enlarged to improve a heat transfer rate. However, there is a
disadvantage in which manufacturing such a heat exchanger needs
much working time in insertion of the corrugated inner fin 4 into
the tube 2 and welding of the corrugated inner fin 4 being bonded
to the interior surface of the tube 2. This causes a problem in
which manufacturing cost is increased by human works.
[0009] If a heat exchanger is designed using the extrusion tube 5
shown in FIG. 20, it has an advantage in which since the partition
walls 7 are formed to partition an inside space of the extrusion
tube 5 into multiple tube portions 6, an overall heating area is
enlarged to improve a heat transfer rate. The extrusion tube 5 is
manufactured using an extrusion molding technique. So, it is
difficult to make the tube portions 6 small so much, and it is
difficult to make thickness of the partition walls 7 sufficiently
thin. In addition, the extrusion molding technique needs an
increasing amount of materials used for formation of the extrusion
tube 5, so that manufacturing cost is being increased. Further, it
is impossible to improve heat-exchange capability so much due to
relatively large thickness of the partition walls 7.
SUMMARY OF THE INVENTION
[0010] It is an object of the invention to provide a heat exchanger
that is improved in pressure strength and heat-exchange capability
without increasing manufacturing cost so much.
[0011] It is another object of the invention to provide a method
for manufacturing the heat exchanger.
[0012] A heat exchanger is constructed by tubes, corrugated fins
and head pipes, which are assembled together. Herein, the tube is
constructed by bending a flat plate whose surfaces are clad with
brazing material to form a first wall and a second wall, which are
arranged opposite to each other with a prescribed interval of
distance therebetween to provide a refrigerant passage. Before
bending, a number of swelling portions are formed to swell from an
interior surface of the flat plate by press. By bending, the
swelling portions are correspondingly paired in elevation between
the first and second walls, so their top portions are brought into
contact with each other to form columns each having a prescribed
sectional shape corresponding to an elliptical shape or an
elongated circular shape each defined by a short length and a long
length. The columns are arranged to align long lengths thereof in a
length direction of the tube corresponding to a refrigerant flow
direction such that obliquely adjacent columns, which are arranged
adjacent to each other obliquely with respect to the length
direction of the tube, are arranged at different locations and are
partly overlapped with each other with long lengths thereof in view
of a width direction perpendicular to the length direction of the
tube. The tubes, corrugated fins and head pipes are assembled
together and are then placed into a heating furnace to heat for a
prescribed time.
[0013] Because of the aforementioned arrangement and formation of
the columns inside of the tube, it is possible to improve an
overall heat transfer rate of the tube on the average, and it is
possible to improve a pressure-proof strength with respect to the
tube.
[0014] Incidentally, each of the columns has the prescribed
sectional shape which is defined by a relationship of 1 2.0 2 1 3.0
.
[0015] In addition, using a first center distance p1 being measured
between the obliquely adjacent columns in the width direction of
the tube and a second center distance p2 being measured between the
obliquely adjacent columns in the length direction of the tube, the
columns are arranged inside of the tube to meet relationships of 2
1.5 p1 d1 3.0 and 0.5 p2 d2 1.5 .
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] These and other objects, aspects and embodiments of the
present invention will be described in more detail with reference
to the following drawing figures, of which:
[0017] FIG. 1 is a front view showing a heat exchanger in
accordance with a first embodiment of the invention;
[0018] FIG. 2 is an enlarged perspective view showing a detailed
construction of a tube which is an essential part of the heat
exchanger of FIG. 1;
[0019] FIG. 3 is a sectional view of the tube taken along a line
III-III in FIG. 2;
[0020] FIG. 4 is a sectional view of the tube take along a line
IV-IV in FIG. 2;
[0021] FIG. 5 is a plan view partly in section showing an end
portion of the tube being inserted into a head pipe;
[0022] FIG. 6A is a perspective view showing a flat plate;
[0023] FIG. 6B is a perspective view showing the flat plate
subjected to press working;
[0024] FIG. 6C is a perspective view showing the flat plate being
bent to construct a tube;
[0025] FIG. 6D is a perspective view showing that the tube and a
corrugated fin are assembled together with a head pipe;
[0026] FIG. 7 is a graph showing comparison between column bodies
having elliptical and circular shapes in section, which are placed
in a flow field, with respect to a relationship between a surface
flow length and a surface local heat transfer rate;
[0027] FIG. 8 is a graph showing comparison between the column
bodies with respect to a relationship between Reynolds number and
drag coefficient;
[0028] FIG. 9 is a graph showing comparison between a tube having
elliptical columns and an extrusion tube with respect to a
relationship between refrigerant circulation and heat transfer
rate;
[0029] FIG. 10 is a graph showing comparison between the tube
having the elliptical columns and extrusion tube with respect to a
relationship between refrigerant circulation and pressure loss;
[0030] FIG. 11A is a sectional view of a tube 11A containing
columns therein;
[0031] FIG. 11B is a sectional view of a tube 11B containing
columns therein;
[0032] FIG. 11C is a sectional view of a tube 11C containing
columns therein;
[0033] FIG. 11D is a sectional view of a tube 11D containing
columns therein;
[0034] FIG. 12 is a graph showing comparison between the tubes 11A,
11B, 11C and 11D with respect to a relationship between refrigerant
circulation and heat transfer rate;
[0035] FIG. 13 is a graph showing comparison between the tubes 11A,
11B, 11C and 11D with respect to a relationship between refrigerant
circulation and pressure loss;
[0036] FIG. 14 is a sectional view of a tube containing columns
used in a heat exchanger in accordance with a second embodiment of
the invention;
[0037] FIG. 15 is a sectional view of a tube containing columns and
semi-columns used in a heat exchanger in accordance with a third
embodiment of the invention;
[0038] FIG. 16 is a plan view showing a modified example of the
tube used for the heat exchanger of the third embodiment;
[0039] FIG. 17 is a sectional view of a tube containing columns
having different shapes and sizes used in a heat exchanger in
accordance with a fourth embodiment of the invention;
[0040] FIG. 18 is a plan view of a refrigerant passage unit, which
is an essential part of a heat exchanger of a fifth embodiment of
the invention;
[0041] FIG. 19 is a perspective view showing an example of a seam
welded tube which is conventionally used for a heat exchanger;
and
[0042] FIG. 20 is a perspective view showing an example of an
extrusion tube which is conventionally used for a heat
exchanger.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] This invention will be described in further detail by way of
examples with reference to the accompanying drawings.
[0044] [A] First Embodiment
[0045] Now, a heat exchanger will be described in accordance with a
first embodiment of the invention with reference to FIGS. 1 to
13.
[0046] FIG. 1 is a front view showing a heat exchanger 10, which is
designed in accordance with the first embodiment of the invention.
Herein, the heat exchanger 10 is constructed by tubes 11 each
having a flat shape, a pair of head pipes 12, 13 and corrugated
fins 14. The head pipes 12, 13 are arranged in contact with both
ends of the tubes 11, wherein they communicate with refrigerant
passages inside of the tubes 11 respectively. Each of the
corrugated fins 14 is arranged between the tubes 11, wherein crest
portions are brought into contact with the tubes 11.
[0047] An inside space of the head pipe 12 is partitioned into two
sections (hereinafter, referred to as an upper section and a lower
section) by a partition plate 15, which is arranged slightly below
a center level of the head pipe 12. A refrigerant inlet pipe 16 is
installed to communicate with the upper section of the head pipe
12, while a refrigerant outlet pipe 17 is installed to communicate
with the lower section of the head pipe 12.
[0048] An overall front area of the heat exchanger 10 is divided
into two areas (i.e., an upper area "a" and a lower area "b") by
the partition plate 15. Refrigerant is introduced to flow in the
tubes 11 in different directions (A) in connection with the two
areas. With respect to the upper area "a", refrigerant flow in a
direction from the head pipe 12 to the head pipe 13. With respect
to the lower area "b", refrigerant flow in another direction from
the head pipe 13 to the head pipe 12.
[0049] Each of the tubes 11 is constructed as shown in FIG. 2. That
is, the tube 11 is made by bending a flat plate 20 to form a first
wall 21 and a second wall 22, which are arranged opposite to each
other and in parallel with each other. So, a refrigerant passage 23
is formed in a space being encompassed by the walls 21, 22.
[0050] A number of dimples 24 are formed on exterior surfaces of
the tube 11 and are made by applying external pressures to the
walls 21, 22 to cave in at selected positions. Because of formation
of the dimples 24, a number of swelling portions 25 are
correspondingly formed to swell from interior surfaces of the tube
11 within the refrigerant passage 23.
[0051] A top portion 25a of the swelling portion 25 has an
elliptical shape in plan view being defined by a short length (or
short diameter) and a long length (or a long diameter), which is
placed along a length direction (i.e., "A" in FIG. 2) of the tube
11. As for two swelling portions 25 which are arranged opposite to
each other, their top portions 25a are brought into contact with
each other as shown in FIG. 3. That is, the two swelling portions
25 whose top portions 25a are brought into contact with each other
are connected together to form a column 26 which is provided
between the first and second walls 21, 22 and whose section has an
elliptical shape. Incidentally, the sectional shape of the column
26 is not necessarily limited to the elliptical shape, so it can be
formed like an elongated circular shape, for example. In addition,
the column 26 is not necessarily made in a hollow shape, so it is
possible to make the column 26 solid.
[0052] The swelling portions 25 are arranged to adjoin with each
other as shown in FIG. 4. Herein, adjacent swelling portions, which
are arranged adjacent to each other obliquely with respect to the
direction A, are arranged in a zigzag manner while being partially
overlapped with each other in view of a direction perpendicular to
the direction A. Therefore, the columns 26 are correspondingly
arranged in a zigzag manner in conformity with the swelling
portions 25.
[0053] In FIG. 2, an air inlet direction by which air is introduced
to perform heat exchange coincides with a width direction B of the
tube 11. The tube 11 has a front-end portion 30 and a back-end
portion 31, which are arranged apart from each other in the air
inlet direction. In addition, splitter plates 32, 33 are formed
together with the front-end portion 30 and the back-end portion 31
respectively. Each of the splitter plates 32, 33 is formed in
prescribed thickness which is relatively thin to act as a flow
straightener for straightening an inlet air flow around the tube
11.
[0054] As shown in FIG. 1, both ends of the tube 11 are inserted
into the head pipes 12, 13 respectively. Specifically, FIG. 5 shows
that one end of the tube 11 is inserted into the head pipe 13. To
actualize insertion, cut sections 34, 35 are formed by partly
cutting out the splitter plates 32, 33 of the tube 11. That is,
each end of the tube 11 has a prescribed end shape, by which it is
inserted into the head pipe (12 or 13).
[0055] A number of tube insertion holes 36 are formed at selected
positions on surfaces of the head pipes 12, 13. Each tube insertion
hole 36 coincides with the end shape of the tube 11 to enable
insertion of the tube 11 therein. To guide insertion of the tube
11, channels 37 (see FIG. 6D) are formed at both ends of the tube
insertion hole 36 to allow cut ends of the splitter plates 32, 33
of the tube 11 being inserted therein.
[0056] The tube insertion hole 36 has an elongated shape whose
width w1 substantially coincides with width w2 of the end portion
of the tube 11 in which the cut sections 34, 35 are formed. In
addition, an overall width w3 of the tube 11 including the splitter
plates 32, 33 is made larger than the width w1 of the tube
insertion hole 36. Thus, when the end portion of the tube 11 is
inserted into the tube insertion hole 36, the cut ends of the
splitter plates 32, 33 of the tube 11 collide with the head pipe
(12 or 13) so that the tube 11 is prevented from being inserted
into the tube insertion hole 36 further more.
[0057] Next, a description will be given with respect to a method
for manufacturing the heat exchanger 10 with reference to FIGS. 6A
to 6D.
[0058] At first, a flat plate (or sheet metal) 20 shown in FIG. 6A
is prepared for manufacture of the tube 11. Brazing material is
clad on the surfaces of the flat plate 20, which are made as an
interior surface and an exterior surface of the tube 11 being
manufactured. In addition, prescribed sections are cut from
selected end portions of the flat plate 20 in advance, wherein they
are designated as the cut sections 34, 35.
[0059] Next, the flat plate 20 is subjected to press working or
roll working to form swelling portions 25 in connection with a
refrigerant passage 23 as shown in FIG. 6B. In addition, a bending
overlap width 40 is formed in connection with a front-end portion
30, while brazing tabs 41 are formed in connection with a back-end
portion 31. Then, the flat plate 20 is bent along with a center
line of the bending overlap width 40, which is shown in FIG. 6C. As
the flat plate 20 is being bent, the bending overlap width 40 is
folded so that two parts thereof come in connection with each
other, while the brazing portions 41 are approaching each other and
are then brought in contact with each other. Further, top portions
25a of the swelling portions 25 are brought in contact with each
other. Thus, it is possible to form the tube 11 having a flat
shape.
[0060] Next, there is prepared a head pipe 12 (or 13) having tube
insertion holes 36 as shown in FIG. 6D. Herein, an end portion of
the tube 11 is inserted into the tube insertion hole 36 of the head
pipe 12 (or 13). In addition, a corrugated fin 14 is arranged
between adjacent tubes 11 in elevation, so that a heat exchanger 20
is being assembled. Thereafter, the assembled heat exchanger 10 is
put into a heating furnace (not shown), wherein it is heated for a
certain time with a prescribed temperature. So, the brazing
material clad on the surfaces of the flat plate 20 (i.e., tube 11)
is melted, so that parts of the heat exchanger 10 are subjected to
brazing. That is, brazing is performed on two parts of the bending
overlap width 40, the brazing portions 41 and the top portions 25a
of the swelling portions 25, all of which are respectively bonded
together. In addition, brazing is performed between the end portion
of the tube 11 and the tube insertion hole 36, which are bonded
together. Further, brazing is performed to actualize bonding
between the tube 11 and crest portions of the corrugated fin 14,
which are brought in contact with each other when the corrugated
fin 14 is arranged in connection with the tube 11.
[0061] In the heat exchanger 10 described above, each of columns 26
which are arranged inside of the refrigerant passage 23 has a
prescribed sectional shape corresponding to an elliptical shape
whose long length matches with the direction A. Thus, it is
possible to improve a heat transfer rate while reducing flow
resistance. Concretely speaking, a refrigerant flow may firstly
collide with a front-end portion of the column 26 in which
curvature becomes small along side surfaces. Thus, refrigerant flow
is accelerated in flow velocity to progress from the front-end
portion of the column 26 along its side surfaces. So, it is
possible to improve a local heat transfer rate. Then, the
refrigerant flow passes by the front-end portion to reach a
back-end portion of the column 26. In that case, curvature becomes
large along the side surfaces with respect to the back-end portion
of the column 26. This hardly causes flow separation in which an
eddy flow is separated from a main flow in the refrigerant flow.
That is, it is possible to suppress shape resistance of the column
26 being small, so it is possible to reduce flow resistance.
[0062] Next, comparison is made between column bodies whose
sectional shapes correspond to a circular shape and an elliptical
shape respectively and which are arranged in flow fields. Herein,
the column body having the elliptical shape in section is arranged
in the flow field in such a way that a long length matches with a
flow direction. In addition, a surface flow length along a side
surface of the column body is given by a mathematical expression
of
[0063] S/d2 where "s" denotes a length from a stagnation point at a
tip end of the column body along the side surface, while a surface
local heat transfer rate is given by a mathematical expression of 3
Nu Re 1 / 2
[0064] where "Nu" denotes Nusselt number, and "Re" denotes Reynolds
number.
[0065] FIG. 7 shows a result of the comparison between the
aforementioned column bodies with respect to a relationship between
the surface flow length and surface local heat transfer rate. In
addition, FIG. 8 shows a result of comparison between the column
bodies with respect to a relationship between the Reynolds number
Re and a drag coefficient C.sub.D representative of flow
resistance. Incidentally, the column body having the elliptical
section is referred to as an "elliptical" column body, while the
column body having the circular section is referred to as a
"circular" column body.
[0066] According to FIG. 7, the surface local heat transfer rate of
the elliptical column body at its front-end portion (which is close
to the stagnation point) has a remarkably high value as compared
with the circular column body. In addition, the surface local heat
transfer rate of the elliptical column body is reduced as a flow
passes by the front-end portion to reach a back-end portion, but it
is normally higher than the surface local heat transfer rate of the
circular column body.
[0067] FIG. 8 shows that the drag coefficient of the elliptical
column body is normally lower than the drag coefficient of the
circular column body, regardless of variations of the Reynolds
number Re. Roughly speaking, the drag coefficient of the elliptical
column body is approximately a half of the drag coefficient of the
circular column body.
[0068] It is preferable that the elliptical sectional shape of the
column 26 meets a relationship of an inequality (1), as follows: 4
2.0 2 1 3.0 ( 1 )
[0069] where "d1" denotes a short length, and "d2" denotes a long
length shown in FIG. 4.
[0070] In the inequality (1), as a value of d2/d1 becomes lower
than 2.0, the sectional shape of the column 26 is gradually changed
from the elliptical shape to the circular shape, so that the
surface local heat transfer rate is reduced, while the drag
coefficient is increased. In contrast, as the value of d2/d1
becomes higher than 3.0, curvature of the column body in proximity
to its front-end portion becomes too small to cause the foregoing
flow separation, so that the surface local heat transfer rate is
being reduced.
[0071] In addition, the heat exchanger 10 is designed such that the
columns 26 are arranged inside of the refrigerant passage 23 in a
zigzag manner. Herein, refrigerant flow inside of the refrigerant
passage 23 by branches like net patterns, wherein the columns 26
are located at intersections of branches of a refrigerant flow.
That is, the refrigerant flow effectively collides with front-end
portions of the columns 26. Thus, it is possible to improve a heat
transfer rate with respect to the heat exchanger 10.
[0072] Next, comparison is made between the tube 11 (which
corresponds to a tube 11A in shape, see FIG. 11A) in which a number
of columns each having a sectional shape meeting the aforementioned
inequality (1) are formed and the conventional extrusion tube which
is made by extrusion molding with respect to heat exchange
performance. Herein, two kinds of graphs are provided to show
comparison results between them. Specifically, FIG. 9 shows a
relationship between refrigerant circulation and heat transfer
rate, while FIG. 10 shows a relationship between refrigerant
circulation and pressure loss. Those graphs show that both of the
tube 11 having the columns and the extrusion tube are similarly
increased in pressure loss in response to increase of the
refrigerant circulation. However, it is clearly shown that as
compared with the extrusion tube, the tube 11 is capable of
remarkably increasing the heat transfer rate in response to the
increase of the refrigerant circulation.
[0073] In FIG. 4, a reference symbol "p1" designates a center
distance (or pitch) between two columns which are arranged
obliquely adjacent to each other in a direction B (corresponding to
a width direction of the tube). In addition, a reference symbol
"p2" designates a center distance between the two columns which are
arranged obliquely adjacent to each other in a direction A.
According to our experimental results, the center distances p1, p2
should be respectively related to a short length d1 and a long
length d2 of the column by prescribed relationships, which are
expressed by inequalities (2), (3), as follows: 5 1.5 p1 d1 3.0 ( 2
) 0.5 p2 d2 1.5 ( 3 )
[0074] That is, it is preferable that the columns are arranged in a
zigzag manner to meet the aforementioned relationships.
[0075] The inequality (2) is determined by the following
reasons:
[0076] If a value of p1/d1 becomes lower than 1.5, an interval of
distance between obliquely adjacent columns in the direction B is
narrowed to increase flow resistance in the refrigerant passage 23.
If the value of p1/d1 becomes larger than 3.0, the interval of
distance between the obliquely adjacent columns are broadened to
decrease the flow resistance in the refrigerant passage 23, while
flow speed of the refrigerant flowing between the columns is
reduced to decrease the heat transfer rate.
[0077] The inequality (3) is determined by the following
reasons:
[0078] If a value of p2/d2 becomes lower than 0.5, an interval of
distance between obliquely adjacent columns in the direction A is
narrowed so that branch flows of refrigerant around the columns
interfere with each other. This decreases the flow resistance and
correspondingly reduces the heat transfer rate. If the value of
p2/d2 becomes larger than 1.5, the interval of distance between the
obliquely adjacent columns in the direction A is broadened so that
branch flows of refrigerant at back sides of the columns are
reduced. This reduces the heat transfer rate as well.
[0079] Next, comparison is made with respect to four types of tubes
11A, 11B, 11C and 11D, which are different from each other in
arrangement of columns as shown in FIGS. 11A, 11B, 11C and 11D. Two
graphs are provided to show comparison results between them.
Specifically, FIG. 12 shows relationships between refrigerant
circulation and heat transfer rate, and FIG. 13 shows relationships
between refrigerant circulation and pressure loss. Among the four
types of the tubes, all of the columns have a same sectional shape,
in which d1=3.0 and d2=6.1.
[0080] FIG. 12 shows that substantially same values are measured
with respect to the heat transfer rate against the refrigerant
circulation in the tube A (where p1/d1.apprxeq.1.5, p2/d2
.apprxeq.0.6), tube B (where p1/d1.apprxeq.1.5, p2/d2.apprxeq.1.15)
and tube C (where p1/d1.apprxeq.2.0, p2/d2.apprxeq.1.15). As
compared with those tubes A, B and C, the tube D (where
p1/d1.apprxeq.1.27, p2/d2.apprxeq.1.15) shows normally higher
values with respect to the heat transfer rate against the
refrigerant circulation.
[0081] FIG. 13 shows that substantially same values are measured
with respect to the pressure loss against the refrigerant
circulation in the tubes A, B and C. As compared with those tubes
A, B and C, the tube D shows slightly higher values with respect to
the pressure loss against the refrigerant circulation, wherein
small differences of the heat transfer rate emerge between the tube
D and the other tubes (A, B, C).
[0082] In the heat exchanger 10 (see FIG. 4), all the columns 26
are arranged to be separated from each other, wherein obliquely
adjacent columns are arranged being partly overlapped with each
other in the direction A. Such arrangement of the columns provides
improvements in heat transfer rate and pressure-proof strength with
respect to the tube 11 as a whole. Concretely speaking, the surface
local heat transfer rate measured along the side surface of the
column is made highest at the front-end portion and becomes lower
in a direction toward the back-end portion. Consideration is made
with respect to two obliquely adjacent columns which are obliquely
arranged in the direction A, namely, an upstream column and a
downstream column which are arranged at different locations along
the refrigerant flow. Herein, the upstream column and downstream
column are arranged being partly overlapped with each other in the
direction A. That is, a front-end portion of the downstream column
is located in an upstream side rather than a back-end portion of
the upstream column. In that case, the front-end portion of the
downstream column compensates for reduction of the surface local
heat transfer rate at the back-end portion of the upstream column.
Thus, it is possible to improve the overall heat transfer rate of
the tube 11 on the average.
[0083] In the obliquely adjacent columns described above, the
front-end portion of the downstream column is located in the
upstream side rather than the back-end portion of the upstream
column. In other words, the columns partly overlap with each other
in arrangement in the direction A. So, any section of the tube 11
taken along a line perpendicular to the direction A normally
contain the column(s). As shown in FIG. 3, each column is made by
bonding the top portions (25a) of the swelling portions (25)
respectively formed on the first and second walls 21, 22 by
brazing. In other words, each column acts as a joint formed between
the first and second walls 21, 22. Because the columns are arranged
regularly in the direction A, it is possible to secure broad joint
portions between the top portions (25a) of the swelling portions
(25). For this reason, any section of the tube 11 taken in the
direction A contains adhesion between the swelling portions 25 of
the first and second walls 21, 22. Thus, it is possible to increase
joint strength between the first and second walls 21, 22 of the
tube 11, and it is possible to secure a sufficiently high
pressure-proof strength with respect to the tube 11 even if the
thickness of the flat plate 20 is thin.
[0084] [B] Second Embodiment
[0085] Next, a heat exchanger having a tube 11 which is designed in
accordance with a second embodiment of the invention will be
described with reference to FIG. 13, wherein parts equivalent to
those used in the first embodiment will be designated by the same
reference numerals, hence, the description thereof will be
omitted.
[0086] As shown in FIG. 14, swelling portions 42 whose sectional
shapes correspond to ellipses each having a long length and a short
length are formed and arranged in a slanted manner with respect to
a direction A on interior surfaces of the tube 11. That is, each of
the swelling portions 42 is arranged in such a manner that the long
length thereof is arranged with inclination to a horizontal line
corresponding to the direction A by a prescribed angle .theta.. As
similar to the foregoing first embodiment, each pair of the
swelling portions 42 are arranged to conform with each other in
elevation such that their top portions 42 are brought into contact
with each other. Thus, a column 43 is made by jointing together the
pair of the swelling portions 42 inside of the tube 11. In
addition, the swelling portions 42 are arranged in a zigzag manner
with respect to the direction A. That is, obliquely adjacent
swelling portions which are arranged obliquely adjacent to each
other in the direction A are arranged independently from each other
but are partly overlapped with each other along the direction A.
Thus, columns 43 are arranged correspondingly in conformity with
the swelling portions 42.
[0087] Like the foregoing first embodiment, the heat exchanger of
the second embodiment is designed such that obliquely adjacent
columns 43 are arranged being partly overlapped with each other
along the direction A in the tube 11. So, it is possible to provide
improvements in heat transfer rate and pressure-proof strength of
the tube 11. In addition, the second embodiment is characterized by
that each of the swelling portions 42 constructing the columns 43
is arranged in a slanted manner in which its long length is
arranged with inclination to the direction A by the angle .theta..
This technical feature of the second embodiment will be described
in detail in consideration of two columns (43), namely, an upstream
column and a downstream column which are arranged adjacent to each
other but are arranged at different locations within the
refrigerant flow. Herein, a front-end portion of the downstream
column is located slightly different from a back-end portion of the
upstream column by a prescribed offset in a direction B (which is
perpendicular to the direction A, not shown in FIG. 14). For this
reason, the front-end portion of the downstream column does not act
as a "shadow zone" for the refrigerant flow. This increases an
amount of refrigerant that collide with each of front-end portions
of the columns 43. Thus, it is possible to improve the heat
transfer rate with respect to the tube 11 as a whole.
[0088] Incidentally, it is preferable to set the inclination angle
.theta. within a range of .+-.7.degree.. Such a range is determined
by the following reasons:
[0089] If the inclination angle is gradually increased from
0.degree., the heat transfer rate is correspondingly improved so
that the second embodiment is able to demonstrate remarkable
effects in heat-exchange property. However, when the inclination
angle becomes larger or lower than the range of .+-.7.degree., flow
separation is easily caused to occur in the refrigerant flow, so
that the heat transfer rate is reduced.
[0090] [C] Third Embodiment
[0091] Next, a heat exchanger having a tube 11 which is designed in
accordance with a third embodiment of the invention will be
described with reference to FIGS. 15 and 16, wherein parts
equivalent to those used by the first embodiment are designated by
the same reference numerals, hence, the description thereof will be
omitted.
[0092] Like the foregoing first embodiment, the third embodiment is
basically designed such that the tube 11 is constructed by first
and second walls 21, 22 between which columns 26 are formed by
swelling portions 25 and are arranged obliquely adjacent to each
other. In FIG. 15, the third embodiment is characterized by that
side walls 44 are formed and arranged integrally with side-end
portions of the first and second walls 21, 22. Therefore, a
refrigerant passage 23 is formed and encompassed by those walls 21,
22, 44. In addition, semi-columns 46 each having a prescribed shape
corresponding to a semi-shape of the aforementioned column 26 whose
sectional shape corresponds to an ellipse are arranged on the side
walls 44. Each of the semi-columns 46 is formed by a pair of
semi-swelling portions 45 whose top portions are brought into
contact with each other. Herein, the semi-swelling portions 45 are
formed by applying external pressures to exterior surfaces of the
first and second walls 21, 22 to partially cave in at selected
positions.
[0093] Each of the semi-columns 46 whose sectional shapes
correspond to semi-ellipses is arranged in connection with the
columns 26 whose sectional shapes correspond to ellipses and which
are arranged in a zigzag manner. That is, one semi-column 46 is
arranged on the side wall 44 at a prescribed location, which
approximately corresponds to a center position between two columns
(each designated by a reference numeral "26a") being arranged
adjacent to each other along a direction A within the columns 26.
In addition, the semi-column 46 is also arranged adjacent to a
column 26b, which is arranged obliquely adjacent to the column 26a,
along a direction B.
[0094] According to the heat exchanger of the third embodiment
having the tube 11 in which the semi-columns 46 each having the
semi-shape of the column 26 are arranged on the side walls 44, it
is possible to provide improvements in heat transfer rate and
pressure-proof strength of the tube 11. Concretely speaking, the
columns 26 whose sectional shapes correspond to ellipses are
arranged in a zigzag manner along the direction A in the tube 11,
wherein one or two columns 26 are arranged in each section taken
along the direction B. In other words, there are two kinds of
sections each taken along the direction B, namely, a first section
in which two columns 26a are arranged and a second section in which
one column 26b is arranged. Those sections are arranged alternately
along the direction A in the tube 11. As compared with the first
section having the two columns 26a, the second section having the
column 26b is reduced in joint strength because of a small total
joint area formed between the first and second walls 21, 22 which
are jointed together by the column 26b. In other words, the second
section having the column 26b is reduced in pressure-proof strength
as compared with the first section having the two columns 26a. To
compensate reduction of the pressure-proof strength, the
semi-columns 46 each having a semi-shape of the column 26 are
arranged in connection with the second section having the column
26b so as to increase a total joint area between the first and
second walls 21, 21 which are jointed together by the column 26b
and two semi-columns 46 with respect to the second section.
Therefore, it is possible to increase the joint strength with
respect to the second section. In other words, it is possible to
increase the pressure-proof strength of the second section being
substantially equivalent to the pressure-proof strength of the
first section having the two columns 26a.
[0095] By provision of the semi-columns 46, turbulence is caused to
occur in refrigerant flows along the side walls 44, so it is
possible to improve an overall heat transfer rate of the tube 11
because of increasing turbulence effects.
[0096] FIG. 16 shows a modified example of the heat exchanger of
the third embodiment, which is designed as a laminated heat
exchanger used for an evaporator. Herein, the heat exchange of FIG.
16 has a refrigerant passage unit 47 equipped with a U-shaped
refrigerant passage 50 having a refrigerant inlet 48 and a
refrigerant outlet 49 at upper ends. That is, refrigerant is
introduced into the refrigerant inlet 48 to flow inside of the
U-shaped refrigerant passage 50, wherein it firstly flows down to a
lower end and then flows upwardly toward the refrigerant outlet 49.
The U-shaped refrigerant passage 50 is not formed in a straight
shape like the foregoing refrigerant passage 23 but is basically
designed to have columns as similar to the refrigerant passage 23
inside of the tube 11 shown in FIG. 15. That is, semi-columns are
arranged along side walls of the refrigerant passage 50. Thus, it
is possible to improve pressure-proof strength and heat transfer
rate with respect to the refrigerant passage unit 47.
[0097] [D] Fourth Embodiment
[0098] Next, a heat exchanger having a tube 11 which is designed in
accordance with a fourth embodiment of the invention will be
described with reference to FIG. 17, wherein parts equivalent to
those used by the first embodiment are designated by the same
reference numerals, hence, the description thereof will be
omitted.
[0099] The heat exchanger of the fourth embodiment is designed as a
condenser that condenses refrigerant by radiating heat to the
external air. The present heat exchanger uses the tube 11 shown in
FIG. 17, which is characterized by that each of swelling portions
25 is gradually enlarged in size along a direction A while
maintaining figure similarity in sectional shape. Along with the
direction A, relatively small swelling portions are formed and
arranged in an upstream side, while relatively large swelling
portions are formed and arranged in a downstream side. Hence,
densities (or occupied areas) of the swelling portions in the
upsteam side are relatively small, while the swelling portions are
closely and tightly arranged with each other in the downstream
side. Therefore, columns 26 are correspondingly formed and arranged
in coformity with the swelling portions 25. As a result, sectional
areas of a refrigerant passage 23 taken along lines perpendicular
to the direction A become small in the direction A from the
upstream side to the downstream side of the tube 11.
[0100] In the case of the heat exchanger that is designed as the
condenser, dryness is reduced in response to progress of
refrigerant that flow from the upstream side to the downstream
side, in other words, a liquid phase is increased as compared with
a gas phase in response to the progress of the refrigerant. For
this reason, pressures which are imparted to interior wall surfaces
of the tube 11 by refrigerant are gradually reduced along the
direction A. To compensate reduction of the pressures, the tube 11
used by the heat exchanger of the fourth embodiment is designed
such that sectional areas of the refrigerant passage 23 are
gradually reduced in response to the reduction of the pressures.
So, it is possible to provide substantially constant pressures
being imparted to the interior wall surfaces of the tube 11. Thus,
it is possible to secure substantially a constant heat transfer
rate having a relatively high value within an overall area of the
tube 11 in its length direction. In addition, it is possible to
reduce pressure loss being constantly low within the overall area
of the tube 11 in its length direction.
[0101] As described above, the tube 11 of the fourth embodiment is
characterized by that the columns 26 are made being gradually
enlarged in sizes while maintaining a certain figure similarity in
the direction A directing from the upstream side to the downstream
side. So, the sectional areas of the refrigerant passage 23 taken
along lines perpendicular to the direction A are made being
gradually reduced in the direction A from the upstream side to the
downstream side. The fourth embodiment can be modified such that
the columns 26 are changed in size as well as shape without
maintaining figure similarity. Or, it can be modified such that the
columns 26 are not changed in sizes but are changed in arrangement
(or density) in the direction A.
[0102] [E] Fifth Embodiment
[0103] Next, a heat exchanger 10 which is designed in accordance
with a fifth embodiment of the invention will be described with
reference to FIG. 18.
[0104] The heat exchanger of the fifth embodiment is designed as an
evaporator that absorbs heat from the external air to gasify
refrigerant. The present heat exchanger is constructed by
laminating refrigerant passage units 53, each of which is formed by
overlapping together flat plates 51, 52 each roughly having a
rectangular shape as shown in FIG. 18. Herein, the flat plates 51,
52 are assembled together by jointing their peripheral portions and
center portions together. Thus, a U-shaped refrigerant passage 56
which is shaped like a flat tube is formed in the refrigerant
passage unit 53 having a refrigerant inlet 54 and a refrigerant
outlet 55 at upper ends. Thus, refrigerant is introduced into the
refrigerant inlet 54 to flow inside of the U-shaped refrigerant
passage 56, wherein it flows down to a lower end and then flows
upwardly toward to the refrigerant outlet 55.
[0105] When the center portions of the flat plates 51, 52 are
jointed together, a partition portion 57 is formed to partition the
refrigerant passage 56 into two sections (i.e., a right section and
a left section in FIG. 18). Herein, the partition portion 57 is
formed in a slanted manner. That is, a lower end 57b of the
partition portion 57 is arranged substantially at a center with an
equal distance being measured from both ends of the flat plates 51,
52, while an upper end 57a of the partition portion 57 is arranged
close to the refrigerant inlet 54 rather than the refrigerant
outlet 55. As a result, sectional areas of the refrigerant passage
56 taken along lines perpendicular to a flow direction of
refrigerant are made small in upstream areas but are made large in
downstream areas. That is, the sectional shapes of the refrigerant
passage 56 are gradually increased along refrigerant flow from an
upstream side to a downstream side.
[0106] In addition, external wall surfaces of the flat plates 51,
52 which are arranged opposite to each other are pressed to cave in
at selected positions to form a number of swelling portions 58.
Therefore, plural columns 59 are formed by jointing together top
portions of the corresponding swelling portions 58, which are
formed on interior wall surfaces of the flat plates 51, 52 and are
arranged in connection with each other.
[0107] In the refrigerant passage 56, the columns 59 are uniformly
arranged to maintain constant distances in a refrigerant flow
direction and its perpendicular direction. That is, a constant
distance is maintained between adjacent columns 59 in the
refrigerant flow direction. In addition, a constant distance is
also maintained between adjacent columns 59 in a direction
perpendicular to the refrigerant flow direction. Due to such
uniform arrangement of the columns 59 and a slanted arrangement of
the partition portion 57, it is possible to make sectional areas of
the refrigerant passage 56, taken along lines perpendicular to the
refrigerant flow direction, being larger in a direction from the
upstream side to the downstream side.
[0108] In the case of the heat exchanger which is designed as the
evaporator, dryness is increased in response to progress of
refrigerant that flow from the upstream side to the downstream
side, in other words, gas phase is increased as compared with
liquid phase in response to the progress of the refrigerant. For
this reason, pressures imparted to interior wall surfaces of the
refrigerant passage 56 are gradually increased in the refrigerant
passage unit 53. To cope with increases of the pressures, the heat
exchanger of the fifth embodiment using the refrigerant passage
unit 53 is designed such that the sectional areas of the
refrigerant passage 56 are made gradually larger in response to the
increases of the pressures. Thus, it is possible to secure
substantially a constant heat transfer rate having a relatively
high value within an overall area of the refrigerant passage 56 in
its refrigerant flow direction. In addition, it is possible to
reduce pressure loss being constantly low within the overall area
of the refrigerant passage 56 in its refrigerant flow
direction.
[0109] In the aforementioned refrigerant passage unit 53, the
columns 59 are uniformly arranged in the refrigerant passage 56
such that a constant distance is maintained between the adjacent
columns, so that the sectional areas of the refrigerant passage 56
are gradually increased in the refrigerant flow direction from the
upstream side to the downstream side. The fifth embodiment can be
modified such that the columns 59 are subjected to uniform
arrangement but are gradually enlarged in size along the
refrigerant flow direction toward the downstream side. Or, it can
be modified such that the columns 59 are not changed in size but
are gradually increased in number along the refrigerant flow
direction toward the downstream side, in other words, densities of
the columns 59 are gradually increased along the refrigerant flow
direction toward the downstream side.
[0110] As described heretofore, this invention has a variety of
technical features and effects, which are summarized as
follows:
[0111] (1) A heat exchanger of this invention basically uses tubes,
each of which is designed such that a number of columns are
arranged inside of a refrigerant passage and are made by jointing
together top portions of swelling portions of first and second
walls, which are arranged opposite to each other. According to one
aspect of the invention, adjacent columns are arranged at different
locations in a refrigerant flow in such a way that a front-end
portion of a downstream column is arranged in an upstream side as
compared with a back-end portion of an upstream column. Herein, the
front-end portion of the downstream column compensates for
reduction of a surface local heat transfer rate at the back-end
portion of the upstream column. Thus, it is possible to improve an
overall heat transfer rate of the tube on the average.
[0112] (2) Because the adjacent columns are arranged such that the
front-end portion of the downstream column is arranged in the
upstream side as compared with the back-end portion of the upstream
column, the columns normally exist being partly overlapped with
each other in any sections of the tube being taken along lines
perpendicular to its length direction, in other words, the swelling
portions of the first and second walls are bonded together at any
sections of the tube. Thus, it is possible to improve a joint
strength for jointing the first and second walls together as well
as a pressure-proof strength of the tube as a whole.
[0113] (3) According to a second aspect of the invention,
semi-columns are arranged on side walls of the tube constructed by
the first and second walls and are made by jointing together top
portions of semi-swelling portions. This increases joint areas
between the first and second walls, so it is possible to increase
an overall joint strength between the first and second walls. By
provision of the semi-columns on the side walls of the tube,
turbulence is caused to occur in refrigerant flows along the side
walls. This increases turbulent effects, so it is possible to
improve an overall heat transfer rate with respect to the tube.
[0114] (4) According to a third aspect of the invention, the
columns each having an elliptical sectional shape having a long
length and a short length are formed and arranged in a slanted
manner such that the long length is slanted with a certain angle of
inclination to the length direction of the tube. This provides an
offset in a width direction of the tube between the front-end
portion of the downstream column and the back-end portion of the
upstream column. In other words, the front-end portion of the
downstream column does not act as a shadow zone in the refrigerant
flow. That is, it is possible to increase amounts of refrigerant
colliding with front-end portions of the columns, so it is possible
to improve an overall heat transfer rate with respect to the
tube.
[0115] (5) In order to use the heat exchanger as the condenser, the
columns arranged inside of the tube are gradually increased in
number or density along the refrigerant flow direction, so that
sectional areas of the refrigerant passage taken along lines
perpendicular to a length direction of the tube are gradually
reduced in response to pressures, which are imparted to interior
wall surfaces of the tube and which are gradually reduced in a
refrigerant flow direction from an upstream side to a downstream
side. Therefore, it is possible to stabilize the pressures being
substantially constant. Thus, it is possible to secure
substantially a constant heat transfer rate having a relatively
high value within an overall area of the tube in its length
direction. In addition, it is possible to reduce pressure loss
being constantly low within the overall area of the tube in its
length direction.
[0116] (6) In order to use the heat exchanger as the evaporator,
the columns arranged inside of the tube are gradually decreased in
number or density in the refrigerant flow direction, so that the
sectional areas of the refrigerant passage are gradually enlarged
in response to pressures, which are imparted to the interior wall
surfaces of the tube and which are gradually increased in the
refrigerant flow direction from the upstream side to the downstream
side. Therefore, it is possible to stabilize the pressures being
substantially constant. Thus, it is possible to secure
substantially a constant heat transfer rate having a relatively
high value within an overall area of the tube in its length
direction. In addition, it is possible to reduce pressure loss
being constantly low within the overall area of the tube in its
length direction.
[0117] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiments are therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalence of such
metes and bounds are therefore intended to be embraced by the
claims.
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