U.S. patent application number 14/394060 was filed with the patent office on 2015-03-19 for aluminum alloy tube-fin heat exchanger.
The applicant listed for this patent is Carrier Corporation. Invention is credited to Ruoshuang Huang, Mary Teresa Lombardo.
Application Number | 20150075760 14/394060 |
Document ID | / |
Family ID | 48183023 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075760 |
Kind Code |
A1 |
Huang; Ruoshuang ; et
al. |
March 19, 2015 |
ALUMINUM ALLOY TUBE-FIN HEAT EXCHANGER
Abstract
A heat exchanger includes a tube including a first aluminum
alloy; and a plurality of fins in thermally conductive contact with
the exterior of said tube, the fins including a second aluminum
alloy comprising a base alloy selected from the group consisting of
AA1100, AA8006, and AA8011 and zinc or magnesium in an amount
sufficient to provide the second aluminum alloy with an
electrochemical solution potential of at least 10 mV more negative
than the electrochemical solution potential of the first aluminum
alloy, as determined according to ASTM G69-97.
Inventors: |
Huang; Ruoshuang;
(Farmington, CT) ; Lombardo; Mary Teresa;
(Windsor, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Carrier Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
48183023 |
Appl. No.: |
14/394060 |
Filed: |
April 12, 2013 |
PCT Filed: |
April 12, 2013 |
PCT NO: |
PCT/US2013/036324 |
371 Date: |
October 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61623386 |
Apr 12, 2012 |
|
|
|
Current U.S.
Class: |
165/181 |
Current CPC
Class: |
C22C 1/06 20130101; F28D
1/04 20130101; F28F 1/24 20130101; F28F 21/084 20130101; B32B
15/016 20130101; F28F 1/12 20130101; C22C 1/00 20130101; F28F
19/004 20130101 |
Class at
Publication: |
165/181 |
International
Class: |
F28F 1/12 20060101
F28F001/12; F28F 21/08 20060101 F28F021/08 |
Claims
1. A heat exchanger, comprising: a tube comprising a first aluminum
alloy; and a plurality of fins in thermally conductive contact with
the exterior of said tube, said fins comprising a second aluminum
alloy comprising a base alloy selected from the group consisting of
AA1100, AA8006, and AA8011 and zinc or magnesium in an amount
sufficient to provide said second aluminum alloy with an
electrochemical solution potential of at least 10 mV more negative
than the electrochemical solution potential of said first aluminum
alloy, as determined according to ASTM G69.
2. The heat exchanger of claim 1, wherein the first aluminum alloy
has an electrochemical solution potential of -695 mV to -770 mV as
determined according to ASTM G69.
3. The heat exchanger of claim 2, wherein the first aluminum alloy
has an electrochemical solution potential of -710 mV to -750
mV.
4. The heat exchanger of claim 1, wherein the second aluminum alloy
comprises from 0.1 to 10 wt. % zinc or magnesium.
5. The heat exchanger of claim 4, wherein the second aluminum alloy
comprises from 0.25 to 8 wt. % zinc or magnesium.
6. The heat exchanger of claim 4, wherein the second aluminum alloy
comprises from 0.7 to 8 zinc or magnesium.
7. The heat exchanger of claim 4, wherein the second aluminum alloy
comprises from 0.15 to 4 wt. % zinc.
8. The heat exchanger of claim 4, wherein the second aluminum alloy
comprises from 0.25 to3 wt. % zinc.
9. The heat exchanger of claim 4, wherein the second aluminum alloy
comprises from 0.7 to 1.5 wt. % zinc.
10. The heat exchanger of claim 1, wherein the second aluminum
alloy has an electrochemical solution potential of at least 40 mV
more negative than the electrochemical solution potential of the
first aluminum alloy.
11. The heat exchanger of claim 1, wherein said base alloy is
AA1100.
12. The heat exchanger of claim 1, wherein said base alloy is
AA8006.
13. The heat exchanger of claim 1, wherein said base alloy is
AA8011.
14. The heat exchanger of claim 1, wherein said first aluminum
alloy is AA3003.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein generally relates to
heat exchangers and, more particularly, to heat exchangers having
alloy tubes and aluminum collar-style fins tubes.
[0002] Heat exchangers are widely used in various applications,
including but not limited to heating and cooling systems including
hydronic fan coil units, heating and cooling in various industrial
and chemical processes, heat recovery systems, and the like, to
name but a few. Many heat exchangers for transferring heat from one
fluid to another fluid utilize one or more tubes through which one
fluid flows while a second fluid flows around the tubes. Heat from
one of the fluids is transferred to the other fluid by conduction
through the tube wall. Many configurations also utilize fins in
thermally conductive contact with the outside of the tube(s) to
provide increased surface area across which heat can be transferred
between the fluids and/or to impact flow of the second fluid
through the heat exchanger. One such heat exchanger is known as a
round tube plate fin (RTPF) heat exchanger.
[0003] Heat exchanger tubes may be made from a variety of
materials, including metals such as aluminum or copper and alloys
thereof. Aluminum alloys are lightweight, have a high specific
strength and high-heat conductivity. Due to these excellent
mechanical properties, aluminum alloys are used as heat exchangers
for heating or cooling systems in commercial, industrial,
residential, transport, refrigeration, and marine applications.
However, aluminum alloy heat exchangers have a relatively high
susceptibility to corrosion. Corrosion eventually leads to a loss
of refrigerant from the tubes and failure of the heating or cooling
system. Sudden tube failure results in a rapid loss of cooling and
loss of functionality of the heating or cooling system.
Accordingly, improvements in corrosion performance of aluminum
alloy heat exchangers would be well received in the art.
BRIEF DESCRIPTION OF THE INVENTION
[0004] According to one aspect of the invention, a heat exchanger
includes [0005] a tube comprising a first aluminum alloy; and
[0006] a plurality of fins in thermally conductive contact with the
exterior of the tube, the fins comprising a second aluminum alloy
such as AA1100, AA8006, and AA8011 and zinc or magnesium in an
amount sufficient to provide the second aluminum alloy with an
electrochemical solution potential of at least 10 mV more negative
than the electrochemical solution potential of the first aluminum
alloy, as determined according to ASTM G69-97.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The subject matter which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0008] FIG. 1 depicts a perspective view of a heat exchanger
incorporating heat exchanger fins treated according to an
embodiment of the invention;
[0009] FIG. 2 depicts a sectional view of the tube and fins
incorporating the treated heat exchanger fins according to an
embodiment of the invention; and
[0010] FIG. 3 is a plot of galvanic corrosion current density for
exemplary tube and fin alloys according to an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring now to the drawings, FIG. 1 depicts an exemplary
RTPF heat exchanger 10 having heat exchanger fins 60 that are
treated for galvanic corrosion protection according to an
embodiment of the invention. Particularly, the heat exchanger 10
includes one or more flow circuits for carrying refrigerant through
the heat exchanger 10. For the purposes of explanation, the heat
exchanger 10 is shown with a single flow circuit refrigerant tube
20 consisting of an inlet line 30 and an outlet line 40. The inlet
line 30 is connected to the outlet line 40 at one end of the heat
exchanger 10 through a 90 degree tube bend 50. It should be
evident, however, that more circuits may be added to the unit
depending upon the demands of the system. The refrigerant tube 20
is generally made of an aluminum alloy based core material. The
heat exchanger 10 further includes a series of fins 60 comprising
radially disposed plate like elements spaced along the length of
the flow circuit. The fins 60 are provided between a pair of end
plates 70 and 80 and are supported by the lines 30, 40 in order to
define a gas flow passage through which conditioned air passes over
the refrigerant tube 20 and between the spaced fins 60. Also, in
some embodiments, the fins 60 are generally made of an aluminum
alloy substrate material such as, for example, materials selected
from the 1000 series, 7000 series, or 8000 series aluminum
alloys.
[0012] FIG. 2 depicts a sectional view of the heat exchanger 10
including the refrigerant tube 20 and fins 60 according to an
embodiment of the invention. In a typical arrangement, as shown in
FIG. 2, an aluminum alloy refrigerant tube 20 with the circuit flow
lines 30, 40 are fabricated with the generally coplanar aluminum
alloy plates for the heat exchanger fins 60. The attachment point
of the fins 60 and lines 30, 40 are brazed to form a permanent
connection.
[0013] The first aluminum alloy as described herein is used to form
tubes for the tube fin heat exchanger. The first aluminum alloy can
be selected from any of a number of known and commercially
available aluminum alloys having an electrochemical solution
potential of -695 mV to -770 mV as determined according to ASTM
G69-97, more specifically -710 mV to -750 mV. Representative alloys
that can be used as the first aluminum alloy include, but are not
limited to alloys of the 3000 series as well as other alloy series
such as the 1000 series, 5000 series. Exemplary alloys include 3003
and 3102.
[0014] The second aluminum alloy described herein is used to
prepare finstock for the fabrication of fins. The second aluminum
alloy comprises a base alloy selected from the group consisting of
can be selected from AA1100, AA8006, and AA8011, and mixtures
thereof The compositions of these alloys and techniques for
preparing them are well-known in the art. Exemplary embodiments of
such compositions are described, for example, in Aluminum and
Aluminum Alloys, ASM Specialty Handbook, J. R. Davis, ASM
International, the disclosure of which is incorporated herein by
reference in its entirety. The fin alloy comprises zinc or
magnesium in an amount sufficient to provide the second aluminum
alloy with an electrochemical solution potential of at least 10 mV
more negative than the electrochemical solution potential of the
tube alloy, as determined according to ASTM G69. In a more specific
exemplary embodiment, zinc or magnesium is present in an amount
sufficient to provide the second aluminum alloy with an
electrochemical solution potential of at least 40 mV more negative
than the electrochemical solution potential of the tube alloy. In
exemplary embodiments, zinc or magnesium can be included at a level
of 0.1 to 10 wt. % zinc or magnesium, more specifically 0.25 to 8
wt. % zinc or magnesium, and even more specifically 0.7 to 8 wt. %
zinc or magnesium. In other exemplary embodiments, the second
aluminum alloy comprises 0.15 to 4 wt. % zinc, more specifically
from 0.25 to 3 wt. % zinc, and even more specifically 0.7 to 1.5
wt. % zinc.
[0015] In another embodiment, the second aluminum alloy that
includes a Zn or magnesium can be formed by melting the base alloy
in a crucible and adding Zn or Mg as compact pieces of high purity
Zn or Mg when the melt temperature is high enough to melt and mix
with the Zn or Mg (e.g., 1300 degrees Fahrenheit for Zn). The melt
is cured using rapid solidification and thin sheets of fins 60 are
formed by rolling. In one exemplary embodiment, cured fins 60
comprise mostly aluminum and preferably, Zn material in an amount
up to about 1 percent Zn by weight. In other embodiments, the Zn
material has a coating thickness of about 1 micron to about 10
micron.
[0016] The embodiments described herein utilize an aluminum alloy
for the fins of a tube fin heat exchanger having an aluminum alloy
tube, i.e., a so-called "all aluminum" heat exchanger. For such
heat exchangers, the alloy out of which the fins are made should be
more anodic than the alloy out of which the tube(s) are made. This
ensures that any galvanic corrosion will occur in the fin rather
than in the tube, as tube corrosion can cause a potentially
catastrophic failure involving loss of refrigerant. Conventional
anodic aluminum alloys such as alloy 7072 suffer from limitations
on formability, which is particularly problematic for heat
exchangers having low fpi (fins per inch) counts, with
correspondingly high collar dimensions. For some heat exchanger
designs with lower fpi counts, 7072 fins are subject to cracking
and other defects at lower fpi counts due to 7072's limited
formability. For such designs, 7072 is limited in the minimum fpi
count that can be achieved.
[0017] The invention is further described by the following
non-limiting examples.
Example 1
[0018] Aluminum alloy for use as a fin material was prepared by
modifying alloy 1100 with the addition of 1.0 wt. % zinc. The
resulting alloy was evaluated for galvanic compatibility with tube
alloy 3003 according to ASTM G71-81. The evaluation was performed
in a galvanic corrosion test solution such as the solution
described in G69-97 or other galvanic corrosion test solutions used
to evaluate susceptibility to galvanic corrosion. For comparison
purposes, comparison alloy 7072 was also evaluated for galvanic
compatibility with tube alloy 3003. The results are shown in FIG.
3, which indicates that both fin alloys are sufficiently anodic
with respect to tube alloy 3003 so that any galvanic corrosion in a
tube fin heat exchanger would occur in the fin rather than the
tube, with 3003 having a solution potential of -742 mV, modified
1100 having a solution potential of -792 mV, and 7072 having a
solution potential of -835 mV. Also for comparison purposes,
comparison alloy 1100 was also evaluated for galvanic compatibility
with tube alloy 3003. The results are shown in FIG. 3, which
indicates that the 1100 fin alloy is not sufficiently anodic with
respect to the tube alloy 3003. Thus any galvanic corrosion in a
tube fin heat exchanger would occur in the tube rather than the
fin, with 3003 having a solution potential of -742 mV, and 1100
having a solution potential of -752 mV.
Example 2
[0019] Tube fin heat exchangers were prepared having various tube
sizes and fpi/fin collar values using aluminum alloy tubes and
collar-type fins prepared from zinc-modified AA1100 according to
the invention. The heat exchangers with 7072 exhibited significant
splitting of the fins, particularly at lower fpi counts. Exemplary
lowest achievable FPI counts at different fin thicknesses are shown
in the Table below:
TABLE-US-00001 TABLE Minimum FPI Fin Thickness AA1100 + 1% Zn
AA7072 0.0035''-0.004'' 13-10 20-13 0.005''-0.006'' 10-6 14-10
0.008''-0.009'' 7-5 11-7
[0020] The heat exchangers of the invention with zinc-modified 1100
fin alloy exhibited no splitting and were capable of achieving
lower minimum fpi counts than the comparison of fins made from the
7072 alloy.
[0021] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
* * * * *