U.S. patent application number 12/731769 was filed with the patent office on 2010-09-30 for fin for heat exchanger and heat exchanger using the fin.
Invention is credited to Lin-jie Huang, Jiang Jianlong.
Application Number | 20100243224 12/731769 |
Document ID | / |
Family ID | 42263624 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100243224 |
Kind Code |
A1 |
Jianlong; Jiang ; et
al. |
September 30, 2010 |
FIN FOR HEAT EXCHANGER AND HEAT EXCHANGER USING THE FIN
Abstract
The present invention discloses a fin for a heat exchanger, the
fin comprises a plurality of fin plates which are adjacent to one
another, each of the fin plates is formed with louvers; and a
connecting portion which connects adjacent fin plates at an end of
the adjacent fin plates. The connecting portion comprises a middle
curved section and side curved sections located on the sides of the
middle curved section, and the curvature radius of the middle
curved section is larger than the curvature radius of the side
curved sections. With the technical solution of the invention,
since the contact area between the flat tubes and the fin
increases, the fin efficiency is increased and thus the heat
exchange performance of the heat exchanger is enhanced
Inventors: |
Jianlong; Jiang; (Zhejiang,
CN) ; Huang; Lin-jie; (East Amherst, NY) |
Correspondence
Address: |
MCCORMICK, PAULDING & HUBER LLP
CITY PLACE II, 185 ASYLUM STREET
HARTFORD
CT
06103
US
|
Family ID: |
42263624 |
Appl. No.: |
12/731769 |
Filed: |
March 25, 2010 |
Current U.S.
Class: |
165/173 ;
165/185 |
Current CPC
Class: |
F28F 2215/08 20130101;
F28F 1/128 20130101 |
Class at
Publication: |
165/173 ;
165/185 |
International
Class: |
F28F 9/02 20060101
F28F009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 2009 |
CN |
200910119663.4 |
Claims
1. A fin for a heat exchanger, said fin comprising: a plurality of
fin plates which are adjacent to one another, each of the fin
plates being formed with louvers, and a connecting portion which
connects adjacent fin plates at an end of the adjacent fin plates;
wherein the connecting portion comprises a middle curved section
and side curved sections located on the sides of said middle curved
section, and the curvature radius of the middle curved section is
larger than the curvature radius of the side curved sections.
2. The fin as claimed in claim 1, wherein the middle curved section
is a circular arc section.
3. The fin as claimed in claim 1, wherein the middle curved section
is an elliptical arc section.
4. The fin as claimed in claim 2, wherein the side curved sections
are circular arc sections.
5. The fin as claimed in claim 1, wherein the connecting portion is
an elliptical arc connecting portion.
6. The fin as claimed in claim 1, wherein said fin is made of
aluminium alloy.
7. The fin as claimed in claim 2, wherein the central angle of the
middle circular arc section is smaller than or equal to
90.degree..
8. The fin as claimed in claim 2, wherein the range of the radius R
of the middle circular arc section is 0.35 mm.ltoreq.R.ltoreq.1
mm.
9. The fin as claimed in claim 8, wherein said side curved sections
are circular arc sections, the range of the radius r of the side
circular arc sections is r.ltoreq.0.2 mm.
10. The fin as claimed in claim 1, wherein said fin has at least
one of the following features: a. the angle b of the fin plates
satisfies the following formula: 1.2f.ltoreq.tan b.ltoreq.3.9f
where b is the angle of the fin plates, f is the friction
coefficient between water and the surface of the fin plates; b. the
range of the pitch P of the fin plates is 2.9 mm.ltoreq.P.ltoreq.9
mm; c. the range of the louver gap S of the louvers is
S.gtoreq.0.57 mm; d. the range of the pitch W_Louver of the louvers
is W_Louver.gtoreq.1 mm; e. the range of the ratio of the height
H_Louver of the louvers and the height H_Fin of the fin is
0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02.
11. A fin for a heat exchanger, said fin comprising: a plurality of
fin plates which are adjacent to one another, each of the fin
plates being formed with louvers, and a curved connecting portion
which connects adjacent fin plates at an end of the adjacent fin
plates; wherein said fin has at least one of the following
features: a. the angle b of the fin plates satisfies the following
formula: 1.2f.ltoreq.tan b.ltoreq.3.9f where b is the angle of the
fin plates, f is the friction coefficient between water and the
surface of the fin plates; b. the range of the pitch P of the fin
plates is 2.9 mm.ltoreq.P.ltoreq.9 mm; c. the range of the louver
gap S of the louvers is S.gtoreq.0.57 mm; d. the range of the pitch
W_Louver of the louvers is W_Louver.gtoreq.1 mm; e. the range of
the ratio of the height H_Louver of the louvers and the height
H_Fin of the fin is 0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02.
12. The fin as claimed in claim 11, wherein said curved connecting
portion is a circular arc connecting portion.
13. The fin as claimed in claim 12, wherein said circular arc
connecting portion has at least one of the following features: the
value of the central angle of the circular arc connecting portion
is smaller than or equal to 90.degree.; the range of the radius R
of the circular arc connecting portion is 0.35 mm.ltoreq.R.ltoreq.1
mM.
14. A heat exchanger comprising: two spaced apart header pipes; a
plurality of tubes extending between the header pipes; and a fin
disposed between adjacent tubes, said fin comprising: a plurality
of fin plates which are adjacent to one another, each of the fin
plates being formed with louvers, and a connecting portion which
connects adjacent fin plates at an end of the adjacent fin plates;
wherein the connecting portion comprises a middle curved section
and side curved sections located on the sides of said middle curved
section, and the curvature radius of the middle curved section is
larger than the curvature radius of the side curved sections.
15. The heat exchanger as claimed in claim 14, wherein said heat
exchanger is a parallel flow heat exchanger with the header pipes
being installed horizontally.
16. A heat exchanger comprising: two spaced apart header pipes; a
plurality of tubes extending between the header pipes; and a fin
disposed between adjacent tubes, said fin comprising: a plurality
of fin plates which are adjacent to one another, each of the fin
plates being formed with louvers, and a curved connecting portion
which connects adjacent fin plates at an end of the adjacent fin
plates; wherein said fin has at least one of the following
features: a. the angle b of the fin plates satisfies the following
formula: 1.2f.ltoreq.tan b.ltoreq.3.9f where b is the angle of the
fin plates, f is the friction coefficient between water and the
surface of the fin plates; b. the range of the pitch P of the fin
plates is 2.9 mm.ltoreq.P.ltoreq.9 mm; c. the range of the louver
gap S of the louvers is S>0.57 mm; d. the range of the pitch
W_Louver of the louvers is W_Louver.gtoreq.1 mm; e. the range of
the ratio of the height H_Louver of the louvers and the height
H_Fin of the fin is 0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02.
17. The heat exchanger as claimed in claim 16, wherein said heat
exchanger is a parallel flow heat exchanger with the header pipes
being installed horizontally.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is entitled to the benefit of and
incorporates by reference essential subject matter disclosed in
Chinese Patent Application No. 200910119663.4 filed on Mar. 25,
2009.
FIELD OF THE INVENTION
[0002] The present invention relates to a heat exchanger, and more
particularly to a fin used with a heat exchanger.
BACKGROUND OF THE INVENTION
[0003] A heat exchanger is a commonly used component in
refrigeration and air conditioning systems, and can be classified
as a condenser, an evaporator and so on based on its functions. To
improve the heat exchanging performance of a heat exchanger, among
others, the heat exchanger is generally provided with a fin.
[0004] FIGS. 1A and 1B show a conventional fin used with a parallel
flow heat exchanger, FIG. 1A is a plan view of the fin, and FIG. 1B
is a sectional view taken along line B-B in FIG. 1A.
[0005] A fin is made of a material with a high thermal conductivity
such as aluminum alloy, and is formed by processing an aluminum
alloy sheet. As shown in FIG. 1A, the fin 1 of the heat exchanger
includes a plurality of fin plates 10 adjacent to one another, and
each of the fin plates is formed with louvers 20 (as shown in FIG.
1B in detail), and two adjacent fin plates are connected by a
curved portion 30.
[0006] FIG. 2 is a partial plan view of the heat exchanger, which
shows an assembled state of the heat exchanger where the flat tube
engages with the fin. As shown in FIG. 2, in an assembled state of
the heat exchanger, the fin 1 contacts the surface 41 of the flat
tube 40 of the heat exchanger via the curved portion 30, thus
achieving thermal conduction between the fin and the flat tube. The
fin exchanges heat with an external medium flowing over the fin,
and thus achieving the heat exchange between the heat exchanger and
the external medium.
[0007] However, since the curved portion of the conventional fin is
formed by a single circular arc section with a small radius, the
conventional fin has the following defects: the curved portion and
the flat tube make contact only on a small area, resulting in a
poor thermal conduction, i.e. resulting in a low fin efficiency;
and furthermore, the fin is liable to collapse due to the binding
force when assembling the heater exchanger.
[0008] Moreover, when the heat exchanger is used as an evaporator,
condensate will build up on the surface of the fin due to the
surface tension of a liquid, resulting in the decrease of the
amount of air flowing through the fin of the heat exchanger, and
thus the performance of the heat exchanger is affected. The
build-up of water on the fin is mainly caused by the surface
tension of the water, and the condensate mainly builds up at the
following three areas: the area 7 where the curved portion is
located, the area 8 between the fin plates, and the area 9 between
the louvers, as shown in FIGS. 3A and 3B, wherein FIG. 3A is a plan
view of a fin, and FIG. 3B is a sectional view taken along line B-B
in FIG. 3A. The problem of condensate building up at the three
areas mentioned above can not be well dealt with by a conventional
fin, resulting in the degradation of the performance of the heat
exchanger.
[0009] In consideration of the problems associated with the
conventional fin, there is a need for further improving the heat
exchange performance of the fin and thus the heat exchanger.
SUMMARY OF THE INVENTION
[0010] The object of invention is to solve the problems associated
with the conventional fin, and to provide a fin for a heat
exchanger which can improve the heat exchange performance of the
heat exchanger and is not liable to collapse when assembling the
heater exchanger.
[0011] Another object of the invention is to provide a fin for a
heat exchanger that can eliminate or improve the build-up of
condensate on the fin and thus enhance the heat exchange
performance of the heat exchanger.
[0012] Still another object of the invention is to provide a heat
exchanger which is provided with a fin in accordance with the
invention.
[0013] To achieve the above objects, according to a first aspect of
the invention, a fin for a heat exchanger comprises: a plurality of
fin plates which are adjacent to one another, each of the fin
plates being formed with louvers, and a connecting portion which
connects adjacent fin plates at an end of the adjacent fin plates.
The connecting portion comprises a middle curved section and side
curved sections located on the sides of the middle curved section,
and the curvature radius of the middle curved section is larger
than the curvature radius of the side curved sections.
[0014] In preferred embodiments of a fin for a heat exchanger in
accordance with the present invention, the connecting portion is an
elliptical arc connecting portion. More preferably, the middle
curved section of the fin may be a circular arc section or an
elliptical arc section. Similarly, the side curved sections are
preferably circular arc sections.
[0015] In preferred embodiments of the present invention, the fin
is made of aluminum alloy.
[0016] Further, the central angle of the middle circular arc
section is preferably smaller than or equal to 90.degree..
Preferably, the range of the radius R of the middle circular arc
section is 0.35 mm.ltoreq.R.ltoreq.1 mm.
[0017] Still further, the side curved sections are preferably
circular arc sections, the range of the radius r of the side
circular arc sections is r.ltoreq.0.2 mm.
[0018] In preferred embodiments of the present invention, the fin
has at least one of the following features:
[0019] a. the angle b of the fin plates satisfies the following
formula:
1.2f.ltoreq.tan b.ltoreq.3.9f
[0020] where b is the angle of the fin plates, f is the friction
coefficient between water and the surface of the fin plates;
[0021] b. the range of the pitch P of the fin plates is 2.9
mm.ltoreq.P.ltoreq.9 mm;
[0022] c. the range of the louver gap S of the louvers is
S.gtoreq.0.57 mm;
[0023] d. the range of the pitch W_Louver of the louvers is
W_Louver.gtoreq.1 mm;
[0024] e. the range of the ratio of height H_Louver of the louvers
and the height H_Fin of the fin is
0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02.
[0025] According to a second aspect of the invention, a fin for a
heat exchanger comprises: a plurality of fin plates which are
adjacent to one another, each of the fin plates being formed with
louvers, and a curved connecting portion which connects adjacent
fin plates at an end of the adjacent fin plates. The fin has at
least one of the following features:
[0026] a. the angle b of the fin plates satisfies the following
formula:
1.2f.ltoreq.tan b.ltoreq.3.9f
[0027] where b is the angle of the fin plates, f is the friction
coefficient between water and the surface of the fin plates;
[0028] b. the range of the pitch P of the fin plates is 2.9
mm.ltoreq.P.ltoreq.9 mm;
[0029] c. the range of the louver gap S of the louvers is
S.gtoreq.0.57 mm;
[0030] d. the range of the pitch W_Louver of the louvers is
W_Louver.gtoreq.1 mm;
[0031] e. the range of the ratio of height H_Louver of the louvers
and the height H_Fin of the fin is
0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02.
[0032] Preferably, the curved connecting portion of the fin is a
circular arc connecting portion. Still preferably, the circular arc
connecting portion has at least one of the following features: the
value of the central angle of the circular arc connecting portion
is smaller than or equal to 90.degree.; and the range of the radius
R of the circular arc connecting portion is 0.35
mm.ltoreq.R.ltoreq.1 mm.
[0033] According to a third aspect of the invention, there is
provided a heat exchanger which includes a fin as defined in the
first and second aspects of the invention. Preferably, the heat
exchanger is a parallel flow heat exchanger with the header pipes
being installed horizontally.
[0034] With the technical solution of the invention, since the
contact area between the flat tubes and the fin increases, the fin
efficiency is increased and thus the heat exchange performance of
the heat exchanger is enhanced substantially on one hand; and a
stable contact is achieved between the fin and the flat tubes and
the fin is not liable to collapse after binding on the other hand.
And furthermore, according to the invention, since the optimal
design of the fin is carried out by taking into consideration the
various parameters which affect the build-up of condensate on the
fin surface, the build-up of condensate on the corresponding areas
of the fin is eliminated or improved, and thus the heat exchange
performance of the heat exchanger is improved further.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The invention will be described in detail below with
reference to the accompanying drawings, in which:
[0036] FIG. 1A is a plan view showing a conventional fin used with
a heat exchanger;
[0037] FIG. 1B is a sectional view taken along line B-B in FIG.
1A;
[0038] FIG. 2 is a partial plan view of a heat exchanger, showing
an assembled state of the heat exchanger where the flat tube of the
heat exchanger engages with the fin;
[0039] FIG. 3A and FIG. 3B are views showing the areas where
condensate builds up on the fin, wherein FIG. 3A is a plan view
showing the structure of a fin, and FIG. 3B is a sectional view
taken along line B-B in FIG. 3A;
[0040] FIG. 4 is a partial view, showing a heat exchanger provided
with a fin in accordance with an embodiment of the invention;
[0041] FIG. 5A is a view similar to FIG. 4, showing the structure
of a fin in accordance with the invention;
[0042] FIG. 5B is a sectional view taken along line B-B in FIG.
5A;
[0043] FIG. 6 is a forced diagram of the condensate on the fin
plate of the fin; and
[0044] FIGS. 7A and 7B are schematic views of a parallel flow heat
exchanger, in which FIG. 7A shows a situation where the header
pipes are provided vertically, and FIG. 7B shows a situation where
the header pipes are provided horizontally.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] The invention will be described in detail below by taking a
parallel flow heat exchanger as an example. It should be noted here
that the embodiments of the invention are only illustrative, they
are only used to describe the principle of the invention but not to
limit the invention. It is obvious to one skilled in the art that
the fin according to the invention is not limited to be used with a
parallel flow heat exchanger, it can also be used with other heat
exchangers which use a fin.
[0046] In the following description, components similar to those in
the prior art will be designated with the same reference numerals
and their detailed description will be omitted.
[0047] Reference is now made to FIG. 4 which is a partial view and
shows a heat exchanger using a fin in accordance with the present
invention.
[0048] As shown in FIG. 4A, similar to a conventional fin, the fin
of the present invention includes a plurality of fin plates 10
which are arranged adjacent to one another and are provided with
louvers. The fin plates 10 are connected by a curved portion
30.
[0049] Unlike the conventional fin, the curved portion 30 of the
fin according to the present invention is not formed by a single
circular arc section with a small radius, instead, the curved
portion 30 in accordance with the embodiment shown in the figure is
composed of three circular arc sections: a middle circular arc
section 31 with a large radius (referred as the "large circular arc
section" hereinafter), two circular arc sections 32 with a radius
smaller than the radius of the large circular arc section and
located on the sides of the large circular arc section (referred as
"small circular arc sections" hereinafter). The large circular arc
section 31 and the small circular arc sections are connected
smoothly at their ends.
[0050] Since the section of the curved portion 30, which contacts
the surface 41 of the flat tube 40, is formed by a circular arc
section 31 with a large radius, the contact area between the fin
and the flat tube surface 41 can be increased substantially, and
more stable contact is achieved between the fin and flat tube, so
that the fin is not liable to collapse after binding them together.
As a result, by increasing the contact area between the flat tube
surface and the curved portion 30 of the fin, the fin efficiency is
increased and thus the heat exchange performance of the heat
exchanger can be improved substantially on one hand; and on the
other hand, the fin is not liable to collapse when assembling the
heat exchanger.
[0051] In the above description, both the middle section 31 of the
curved portion 30, which contacts the surface of the flat tube, and
the two side sections 32 of the curved portion 30 are circular arc
sections. However, it is obvious to one skilled in the art that the
middle section 31 and/or the two side sections 32 on the sides of
the middle section 31 are not limited to circular arc sections.
Other curved sections such as elliptic arc sections are also
possible, or the whole curved portion may be formed by an elliptic
arc section, if only the contact area between the curved portion
and the flat tube surface is increased so that the heat exchange
performance of the heat exchanger and the binding stability of the
fin are improved. Furthermore, the two small circular arc sections
32 on the sides of the large circular arc section may have the same
radius or have different radiuses, in other words, the curved
portion 30 does not necessarily have a symmetric configuration,
although it is preferable to have a symmetric configuration in many
cases.
[0052] As described above, when the heat exchanger is used as an
evaporator, condensate will build up due to the surface tension of
liquid, and the amount of air flowing through the fin of the heat
exchanger will decrease and thus the performance of the heat
exchanger is degraded. The condensate builds up mainly on three
areas: the area 7 where the curved portion is located, the area 8
between the fin plates, and the area 9 between the louvers, please
refer to FIGS. 3A and 3B. The way as to how to effectively deal
with the built-up of the condensate on the surface of the fin so as
to improve the heat exchange efficiency of the heat exchanger
according to the invention will be described below in connection
with the various parameters which have effects on the built-up of
the condensate on the fin surface.
[0053] Reference is now made to FIGS. 5A and 5B, in which FIG. 5A
is a view similar to FIG. 4 showing the configuration of the fin
and the various parameters of the fin; FIG. 5B is a sectional view
taken along line B-B in FIG. 5A showing the various parameters of
the louvers.
[0054] The meaning represented by the reference designations in
FIGS. 5A and 5B is as follows:
[0055] b: angle of the fin plates;
[0056] R: the radius of the large circular arc section;
[0057] r: the radius of the small circular arc section;
[0058] P: the pitch of the fin plates;
[0059] c: the central angle of the large circular arc section;
[0060] d: the central angle of the small circular arc section;
[0061] H_Fin: the height of the fin;
[0062] W_Louver: the pitch of the louvers
[0063] H_Louver: the height of the louvers
[0064] S: the louver gap of the louvers;
[0065] a: the tilt angle of the louvers
These parameters are discussed in more detail below.
[0066] 1. angle b of the fin plates
[0067] As is well known, the condensate on the fin plates moves
downwards from the edge of the fin plates; the larger the angle b
is, the more easily the condensate moves. FIG. 6 is a forced
diagram of the water on the fin plates. It can be determined from
the simplified forced diagram that the water can flows downwards
when the following relationship is satisfied:
tan b>f (1)
[0068] where f represents the friction coefficient between the
water and the surface of the fin plates.
[0069] Based on theoretical analysis, when the relationship tan
b>f is satisfied, the water can flow downwards on the fin plates
of the fin, but based on experimental results, the water is more
easily moved downwards on the inclined surface of a material such
as an aluminum alloy when the force acting in the moving direction
of the water is larger than 1.2 times the friction force, i.e. when
the formula mg sin b>1.2 fN is satisfied. As shown in FIG. 6, by
making an analysis of the forces received by the water, we can know
N=mg.times.cos b, and by substituting this for N in the formula mg
sin b>1.2 fN, we can obtain tan b>1.2f. By taking into
consideration such factors as the practical application and the
manufacturing feasibility, the preferable range of tan b is
1.2f.ltoreq.tan b.ltoreq.3.9f (2)
[0070] When the fin is made of an aluminum alloy, the friction
coefficient is about 0.15, accordingly we can obtain the following
formula:
0.18.ltoreq.tan b.ltoreq.0.585
i.e. arctan 0.18.ltoreq.b.ltoreq.arctan 0.585
[0071] 2. the central angle of the large circular arc section c
[0072] As shown in FIG. 5A, the angle b of the fin plates, the
radius R of the large circular arc section, the pitch P of the fin
plates, the central angle c of the large circular arc section and
the height H_Fin of the fin approximately satisfy the following
relationship in geometry (since the radius r and the central angle
d of the small circular arc sections is far smaller than the radius
R and the central angle c of the large circular arc section, the
effect of the radius r and the central angle d of the small
circular arc sections is not considered in the equation):
tan b .apprxeq. P 2 - 2 R sin c 2 H_Fin - 2 R ( 1 - cos c 2 ) ( 3 )
##EQU00001##
[0073] It can be known from equation (3) that, the angle b becomes
larger when the central angle c of the large circular arc section
becomes smaller, and thus the condensate can flow more easily. And
at the same time, when the central angle c of the large circular
arc section becomes smaller, the area of the curved portion becomes
smaller, and as a result, the build-up amount of the condensate
will decrease even if condensate builds up. Therefore, based on
equation (3), if other parameters such as the pitch P of the fin
plates remain unchanged, the condensate drainage performance of the
fin plates of the fin can be improved by decreasing the central
angle c of the large circular arc section. By taking into
consideration such factors as the practical application and the
manufacturing feasibility, the preferable range of the central
angle c of the large circular arc section is
0.degree..ltoreq.c.ltoreq.90.degree..
[0074] 3. the radius R of the large circular arc section and the
radius r of the small circular arc sections
[0075] The area where the curved portion is located is a major area
at which condensate builds up, the build-up of condensate at the
curved portion area is caused by the surface tension of water at
the area. According to the invention, the curved portion is
constituted by the large circular arc section and the small
circular arc sections located on the sides of the large circular
arc section, since the circumferential length of the small circular
arc sections is much smaller that the circumferential length of the
large circular arc section, the formula which describes the surface
tension of the water at the area where the curved portion is
located is approximately as follows:
.DELTA.p=2.sigma./R (4)
[0076] where, .DELTA.p--surface tension of water; .sigma.--surface
tension coefficient of water; R--radius of the large circular arc
section.
[0077] Since the value of the surface tension coefficient .sigma.
of water is basically constant, the surface tension of water is
inversely proportional to the radius R of the large circular arc
section. The larger the radius of the large circular arc section
is, the smaller the surface tension of the water is, and thus
condensate is not liable to build up and the built up condensate
can be more easily drained. Based on theoretical calculation and
actual measurement of the surface tension of the water at the area
where the curved portion is located and the windward force received
by the water, and taking into consideration such factors as the
practical application and the manufacturing feasibility, the
preferable range of the radius R of the large circular arc section
is 0.35 mm.ltoreq.R.ltoreq.1 mm and the preferable range of the
radius r of the small circular arc sections is r.ltoreq.0.2 mm
under the natural state of the fin before the fin is installed in
the heat exchanger.
[0078] As is known in the art, after a fin is installed in a heat
exchanger, the flat tubes are pressed against the fins by a
compression force, and the curved portion of the fin deforms under
the action of the compression force, such that the radius R of the
large circular arc section becomes larger. As a consequence, the
contact area between the tube and the fin is further increased, so
that the fin is less liable to collapse, and at the same time, the
fin efficiency is further improved so as to improve the heat
exchange performance. Furthermore, by increasing the value of R,
the surface tension of the water at the area of the curved portion
is decreased, and thus the condensate can be more easily drained.
Therefore, from the point of improving the heat exchange efficiency
of the heat exchanger and decreasing the build up of the condensate
on the surface of the fin, the preferable range of the radius R of
the large circular arc section is R>0.4 mm after the fins have
been pressured and installed in the heat exchanger.
[0079] 4. the pitch P of the fin plates
[0080] The area between the fin plates is also a major area where
condensate builds up, and the build-up of condensate at this area
is also caused by the surface tension of the water between the fin
plates. The formula which describes the surface tension of water
between the fin plates is as follows:
.DELTA.p=.sigma.(1/R.sub.1+1/R.sub.2) (5)
[0081] where, .DELTA.p--surface tension of water; .sigma.--surface
tension coefficient of water; R.sub.1, R.sub.2--curvature radiuses
of curved surface of water drop at two planes which are
perpendicular to each other.
[0082] If the pitch of the fin plates is increased, R.sub.1,
R.sub.2 will be increased, and the surface tension of the water
between the fin plates will be reduced or eliminated, and thus the
build-up of condensate between the fin plates can be decreased or
eliminated. By taking into consideration such factors as the
practical application and the manufacturing feasibility, the
preferable range of the pitch P of the fin plates is 2.9
mm.ltoreq.P.ltoreq.9 mm.
[0083] 5. louver gap S of louvers and pitch W_Louver of louvers
[0084] The build-up of condensate between the louvers is mainly
caused by the surface tension of the water between the adjacent
louvers. The formula which describes the surface tension of the
water between the louvers is similar to that which describes the
surface tension of the water between the fin plates, and
accordingly, If the louver gap S of the louvers is increased,
R.sub.1, R.sub.2 will be increased, and the surface tension of the
water between the louvers will be reduced or eliminated, and thus
the build-up of condensate between the louvers can be decreased or
eliminated. Based on calculation and experimental verification, it
has been found that the surface tension of water between the
louvers can be effectively weakened when the louver gap of the
louvers satisfies S.ltoreq.0.57 mm. Accordingly, the preferable
range of the louver gap S of the louver is S.ltoreq.0.57 mm.
[0085] It can be known based a geometric analysis that the lover
gap S, the louver pitch W_Louver and the tilt angle of the louvers
satisfy the following equation:
S=W_Louver.times.sin a.gtoreq.0.57 mm (6)
[0086] By making a comprehensive consideration of the tilt angle a
of the louvers, the louver gap S. the actual application and the
manufacturing feasibility and so on, the preferable range of
W_Louver is W_Louver.gtoreq.1 mm.
[0087] 6. the ratio of the louver height H_Louver and the height
H_Fin of the fin
[0088] As described above, the area where the curved portion of the
fins is located is a major area where condensate builds up. The
build-up of condensate at the area of the curved portion is caused
by the surface tension of the water, and if the ratio of the louver
height and the height of the fin is increased so that the louvers
extend to the area where the curved portion is located, the surface
tension of the water at the area of the curved portion will be
destroyed, and thus the condensate built up at the curved portion
will be decreased. Analysis based on experiments shows that, when
the ratio of the height H_Louver of the louvers and the height
H_Fin of the fin is in the range of
0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02, the louvers can extend to
the area where the curved portion is located and destroy the
surface tension of the water at the curved portion area.
Accordingly, the preferable range of the ratio of the height
H_Louver of the louvers and the height H_Fin of the fin is
0.88.ltoreq.H_Louver/H_Fin.ltoreq.1.02, while in the conventional
fins, the ratio of the height H_Louver of the louvers and the
height H_Fin of the fin is below 0.88.
[0089] As described above, the major parameters which have effects
on the build-up of condensate on the surface of the fin include:
the angle b of the fin plates, the central angle c of the large
circular arc section, the radius R of the large circular arc
section and the radius r of the small circular arc sections, the
pitch P of the fin plates, the louver gap S of the louvers and the
pitch W_Louver of the louvers, the ratio of the height H_Louver of
the louvers and the height H_Fin of the fin, and etc. Therefore,
when carrying out an optimal design of the fin so as to meet the
desired design requirements, one can consider only one of the
parameters, or consider some or all of the parameters.
[0090] What needs to be pointed out is that the preferable values
of the various parameters which have effects on the build-up of
condensate on the fin are not only applicable to a fin in which the
section of the curved portion, which contacts the surface of the
flat tubes, is formed by a circular arc section with a large
curvature radius, they are also applicable to a fin in which the
curved portion is formed by a single circular arc section with a
relatively small radius, i.e. the fin described in the background
part of the description.
[0091] Furthermore, a parallel flow heat exchanger can be mounted
in two manners: one is that the header pipes of the heat exchanger
are installed horizontally, the other is that the header pipes of
the heat exchanger are installed vertically, as shown in FIGS. 7A
and 7B. FIG. 7A shows the situation where the header pipes are
installed vertically, and FIG. 7B shows a situation where header
pipes are installed horizontally. In these figures, the header
pipes are designated by the reference numeral 60, the flat tubes
are designated by the reference numeral 40, and the fins are
designated by the reference 1, the fins being disposed between the
adjacent flat tubes. When a parallel flow heat exchanger is used as
an evaporator, the header tubes are usually installed horizontally,
so that the condensate can easily flow downwards from the flat
tubes to facilitate the drainage of the condensate. Therefore, a
fin, the parameters of which have the preferable values mentioned
above, is preferably used in a heat exchanger with the header tubes
installed horizontally, so as to eliminate or improve the build-up
of condensate on the hear exchanger as a whole.
[0092] It can be seen from above description that, according to one
aspect of the invention, since the section of the curved portion of
the fin which contacts the surface of the flat tubes is formed by a
circular arc section with a large curvature radius so that the
contact area between the flat tubes and the fin increases, the fin
efficiency is increased and thus the heat exchange performance of
the heat exchanger is substantially enhanced on one hand; and a
stable contact is achieved between the fin and the flat tubes, and
the fin is not liable to collapse after binding on the other hand.
According to another aspect of the invention, since the fin is
optimally designed by taking into consideration the various
parameters which affect the build-up of condensate on the fin
surface, the build-up of condensate on the corresponding areas of
the fin is eliminated or improved, and thus the heat exchange
performance of the heat exchanger is improved.
[0093] It is obvious to one skilled in the art that the application
the fin of the invention is not limited to a heat exchanger of any
particular type, instead, it can be widely used with various heat
exchangers which need to use fins.
[0094] The embodiments of the invention have been described above
in connection with the drawings. It should be appreciated by one
skilled in the art that the above embodiments are only exemplary
but not limitative, various modifications are possible without
departing from the spirit and scope of the invention.
* * * * *