U.S. patent application number 11/064932 was filed with the patent office on 2005-11-03 for interconnected microchannel tube.
Invention is credited to Shabtay, Yoram Leon, Tang, Liangyou.
Application Number | 20050241816 11/064932 |
Document ID | / |
Family ID | 32325064 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241816 |
Kind Code |
A1 |
Shabtay, Yoram Leon ; et
al. |
November 3, 2005 |
Interconnected microchannel tube
Abstract
The invention relates to a microchannel tube for use in a heat
transfer system. The microchannels have openings in the partitions
that separate them from each other, thereby creating many short
interconnected passages through which a heat transfer medium will
flow in a laminar manner. This permits the liquid and vapor phases
of the medium to mix, thereby increasing the efficiency of the
system.
Inventors: |
Shabtay, Yoram Leon;
(Prospect Heights, IL) ; Tang, Liangyou;
(Hendersonville, TN) |
Correspondence
Address: |
WINSTON & STRAWN LLP
1700 K STREET, N.W.
WASHINGTON
DC
20006
US
|
Family ID: |
32325064 |
Appl. No.: |
11/064932 |
Filed: |
February 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11064932 |
Feb 25, 2005 |
|
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10303717 |
Nov 26, 2002 |
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Current U.S.
Class: |
165/180 |
Current CPC
Class: |
F28F 2260/02 20130101;
F28F 1/003 20130101; F28F 3/027 20130101 |
Class at
Publication: |
165/180 |
International
Class: |
F28F 003/00 |
Claims
What is claimed is:
1. A heat transfer tube comprising a sheath formed of copper or a
copper alloy and surrounding a plurality of partitions formed from
a single metal sheet, the partitions forming microchannels therein
through which a heat transfer medium can flow in a laminar manner,
the partitions including sidewalls having a plurality of openings
therein, with the openings comprising between about 1% to 20% of
the area of the partition sidewall such that the heat transfer
medium can flow between the microchannels, such that the flow
passes between the microchannels without encountering obstructions,
thereby avoiding turbulence in the fluid and permitting liquid and
vapor phases of the heat transfer medium to mix evenly across the
microchannels and entire width of the tube in order to optimize
two-phase flow heat transfer through the tube.
2. The heat transfer tube of claim 1, wherein at least 2 to 12
partitions are present so that at least 3 to 13 microchannels are
provided.
3. The heat transfer tube of claim 1, wherein at least 4 to 8
partitions are present so that at least 5 to 9 microchannels are
provided.
4. The heat transfer tube of claim 1, wherein the partition side
walls form a plurality of generally V shaped microchannels.
5. The heat transfer tube of claim 1, wherein each partition has
from about 5 openings per 25 mm of length to about 1 opening every
75 mm of length along the length of the partition.
6. The heat transfer tube of claim 1, wherein the openings are not
larger than about 80% of the height of the sidewall of the
partition.
7. The heat transfer tube of claim 1, wherein the openings are
round, oval, or polygonal where each corner of the polygon is
rounded to avoid acting as stress raisers.
8. The heat transfer tube of claim 7, wherein the sheet forms
serpentine partitions.
9. The heat transfer tube of claim 1, wherein the partition
sidewalls are formed of copper or a copper alloy.
10. The heat transfer tube of claim 1, further comprising fins
attached to an outer surface of the sheath to assist in
transferring heat therefrom.
11. A heat exchanger comprising two opposing headers and a
plurality of the heat transfer tubes according to claim 1 extending
between the headers.
12. A heat exchanger comprising two opposing headers and a
plurality of the heat transfer tubes between the headers, wherein
each heat transfer tube of the plurality comprises a sheath formed
of aluminum or an aluminum alloy and surrounding a plurality of
partitions formed from a single sheet of aluminum or an aluminum
alloy, with the partitions forming microchannels therein through
which a heat transfer medium can flow can flow in a laminar manner,
and the partitions include sidewalls having a plurality of openings
therein, with the openings comprising between about 1% to 20% of
the area of the partition sidewall such that the heat transfer
medium can flow between the microchannels, such that the flow
passes between the microchannels without encountering obstructions,
thereby avoiding turbulence in the fluid and permitting liquid and
vapor phases of the heat transfer medium to mix evenly across the
microchannels and entire width of the tube in order to optimize
two-phase flow heat transfer through the tube.
13. The heat exchanger of claim 12, wherein each heat transfer tube
of the plurality has at least 2 to 12 partitions are present so
that at least 3 to 13 microchannels are provided.
14. The heat exchanger of claim 12, wherein each heat transfer tube
of the plurality has at least 4 to 8 partitions so that at least 5
to 9 microchannels are provided.
15. The heat exchanger of claim 12, wherein each partition has from
about 5 openings per 25 mm of length to about 1 opening every 75 mm
of length along the length of the partition.
16. The heat exchanger of claim 12, wherein each partition of the
heat transfer tubes of the plurality has openings are not larger
than about 80% of the height of the sidewall of the partition.
17. The heat exchanger of claim 12, wherein the openings of each
heat transfer tube partition of the plurality are round, oval, or
polygonal where each corner of the polygon is rounded to avoid
acting as stress raisers.
18. The heat exchanger of claim 12, wherein the sheets used to form
each partition of the heat transfer tubes of the plurality form
serpentine partitions.
19. The heat exchanger of claim 12, wherein the sheets used to form
the each partition of the heat transfer tubes of the plurality are
folded to a plurality of generally V shaped microchannels.
20. The heat exchanger of claim 12, wherein the each heat transfer
tube of the plurality has fins attached to an outer surface of its
respective sheath to assist in transferring heat therefrom.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 10/303,717, filed Nov. 26, 2002, the entire
content of which is expressly incorporated herein by reference.
FIELD OF INVENTION
[0002] The present invention relates to an interconnected
microchannel tube for use in a heat transfer device such as an
automobile or residential or commercial air conditioning heat
exchangers. The microchannel tubes are interconnected to facilitate
re-mixing of the vapor-liquid phases and improve the efficiency of
the heat exchanger.
BACKGROUND OF THE INVENTION
[0003] Microchannel tubes have been used in recent years in
automotive air conditioning units and in residential or commercial
air-conditioning heat exchangers. In use, a refrigerant flows
through the multiple channels inside a float tube. The refrigerant
evaporates and condenses as it passes through the tubes, absorbing
and releasing heat as it changes phases between liquid and vapor.
U.S. Pat. Nos. 4,998,580 and 5,372,188 ("the '188 patent") each
disclose condensers having small hydraulic diameter flow paths,
i.e., microchannels.
[0004] The microchannel tubes currently in use have channels that
are isolated from each other, such that each channel works
independently from the others when transferring heat. This creates
a heat transfer imbalance between the front edge of the tube to the
leeway side of the tube, in lieu of the flow direction of the
external heat transfer medium. The '188 patent is limited in its
scope as it requires the hydraulic diameter to be in the range of
about 0.015 to 0.07 inches, where the hydraulic diameter is defined
as the cross-sectional area of each of the flow paths multiplied by
4 and divided by the wetted perimeter of the corresponding flow
path.
[0005] U.S. Pat. No. 6,253,840 to Kuroyanagi discloses a
refrigerant evaporator that includes passages defined by
partitions. Within the partitions are refrigerant guide members
within the partition walls to guide the refrigerant downstream to
permit mixing of the vapor and liquid phases. The guide members are
located within openings in the partition walls and guide the
refrigerant in a downstream direction. The height of the partitions
in Kuroyanagi is 2.0 mm, while the openings in the walls have a
width (d in FIG. 7) of 1.5 mm and a length of 5 mm. This is the
size of a group of about 5 openings. Thus, the area of each group
of 5 openings is 7.5 mm.sup.2. FIG. 10 shows a number of different
arrangements for the openings. The arrangement with the fewest
openings (other than the one with zero) is sample (2). Sample 2
indicates that the openings are spaced 5 mm apart or "the interval
between the respective louver groups is increased to be
approximately equal to the length (5 mm) of the respective louver
groups." Column 8, lines 10-13. The patent is clear that this is
the specified spacing of the louver groups. Thus, for a partition
with a length of 20 mm (as shown in FIG. 10), the area of the
partition wall would be 50 mm.sup.2 (25 mm length.times.2 mm
height). There would be two groups of the 5 mm long openings with 5
mm between them and 5 mm between the edge of the partition and each
group of openings. Although the open area of the partitions was not
discussed, it can be calculated as an area of 15 mm.sup.2 or 30% of
the area of the partition sidewall. No matter what length the
sidewall is, the area of the openings will always be greater than
25% of the area of the partition sidewalls, and generally is
greater than 35%. These openings would create undesirably large
pressure drops and create turbulent flow in the heat transfer
medium. This turbulence is exacerbated by the guide members or
louvers present in Kuroyanagi's partitions.
[0006] U.S. Pat. No. 6,247,529 to Shimizu et al discloses a
refrigerant tube for a heat exchanger. The tube has upper and lower
walls with the wall portions containing communication holes.
Shimizu et al. do not include a plurality of partitions formed of a
single sheet in their tube construction. Shimizu et al. do not form
serpentine partitions from their heat transfer tubes and instead
describe a heat transfer tube with partitions comprised of multiple
pieces. Thus, construction of the Shimizu et al. tube is relatively
complex.
[0007] Thus, there is a need for improved, simpler heat transfer
designs for heat exchangers that include microchannel tubes in
order to improve the heat transfer efficiency and to balance heat
transfer more uniformly across the entire width of the tubes. The
present invention now provides such improvements.
SUMMARY OF THE INVENTION
[0008] The invention relates to a heat transfer tube comprising a
sheath surrounding a plurality of partitions forming microchannels
therein through which a heat transfer medium can flow. The
partitions advantageously include sidewalls having a plurality of
openings therein, such that the heat transfer medium can flow in a
laminar manner between the microchannels thereby permitting mixing
of liquid and vapor phases of the heat transfer medium for improved
heat transfer of the tube. The fluid passes between the
microchannels without encountering obstructions to minimize
turbulence in the fluid.
[0009] The hole openings comprise about 1% to 20% of the area of
the partition sidewall, with each partition having from about 5
openings per 25 mm to about 1 opening every 75 mm along the length
of the partition. These openings comprise up to about 80% of the
height of the sidewall of the partition, and can be round, oval,
square, rectangular, or triangular.
[0010] In one embodiment, at least 2 to 12 partitions are present
so that at least 3 to 13 microchannels are provided in the tube.
Preferably, at least 4 to 8 partitions are present so that at least
5 to 9 microchannels are provided in the tube. The partitions are
advantageously formed from a single sheet, preferably one that
forms serpentine partitions.
[0011] The sheath and partitions can be formed of a metal, such as
aluminum or an aluminum alloy, although copper or a copper alloy is
preferred. If desired, fins can be attached to an outer surface of
the sheath to assist in transferring heat therefrom.
[0012] Another embodiment of the invention relates to an
improvement in a heat exchanger that includes a plurality of
microchannels therein and through which a heat transfer medium
flows. The improvement comprises providing a plurality of openings
in the microchannels, such that the heat transfer medium can flow
in a laminar manner between the microchannels thereby permitting
mixing of liquid and vapor phases of the heat transfer medium for
improved heat transfer of the tube. The fluid passes between the
microchannels without encountering obstructions to minimize
turbulence in the fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention will be better understood in relation to the
attached drawings illustrating preferred embodiments, wherein:
[0014] FIG. 1 shows a cross-sectional view of a heat exchanger tube
made according to the present invention;
[0015] FIG. 2 shows a perspective view of a heat exchanger tube
according to the invention; and
[0016] FIG. 3 shows a cross-sectional view of the heat exchanger
taken along 3-3 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Referring to the drawings, the figures shows a heat exchange
tube formed of a sheath 10 and microchannels 12 according to the
present invention. The heat transfer tube is formed by a plurality
of partitions 14 that form a plurality of microchannels 12. A heat
transfer medium runs through the microchannels 12. In one
embodiment, the invention includes at least about 2 to 12
partitions to form at least about 3 to 13 microchannels. In another
preferred embodiment, at least about 4 to 8 partitions are present
forming at least about 5 to 9 microchannels in the sheath.
[0018] The microchannels 12 define a path through which the heat
transfer medium flows. As the heat transfer medium flows through a
microchannel, it evaporates or condenses, thereby changing the
vapor and liquid content of the composition. The microchannel at
the front edge of the tube and the leeway edge of the tube may have
different levels of heat transfer, due to external reasons. It is
therefore possible that the microchannel located near the front
edge of the tube has a much greater amount of the vapor phase (or
liquid phase) than the microchannel located near the leeway edge.
It is therefore necessary to design the microchannels to mix these
phases evenly across the microchannels over the entire width of the
tube in order to optimize two-phase flow heat transfer. It has now
been discovered that apertures or openings between the channels
assists and enables the gaseous phase and liquid phase to be
uniformly mixed and distributed across all the microchannels in a
tube to enhance heat transfer.
[0019] The openings or holes 20 in the partitions 14 may be of any
shape, such as a polygon such as a slot, rectangle, square, or
triangle, but the preferred shape is a circle or oval as these have
no sharp edges that could act as stress raisers in the structure.
When polygons are used, it is preferred for the corners to be
rounded to avoid acting as stress raisers in the apparatus. The
openings 20 permit the liquid and vapor to mix and change phase at
the same time thereby equalizing the liquid and vapor flow. This
mixing will permit the individual heat transfer tube to be about
20% to 50% more efficient than a comparable tube without the
openings 20 in the partitions 14. A heat exchanger constructed with
a plurality of such tubes would be about 10% to 30% more efficient
than conventional heat exchangers.
[0020] As noted above, the openings in the partition sidewalls
preferably comprise between about 1% to 20% of the area of the
partition sidewall. This smaller area of the openings is necessary
to keep the mixing of the vapor and liquid phases of the heat
transfer medium from becoming too vigorous. This permits the flow
to remain in the laminar range, as turbulent flow causes a pressure
drop that is too large and may affect the efficiency of the system.
It is believed that the area of holes that are greater than about
30 to 40% would create turbulent flow that would create an
undesirably large pressure drop. The use of internal baffles,
louvers or other internal protuberances to direct the flow of the
fluid downstream causes additional turbulence.
[0021] The present invention also relates to a heat transfer tube
that includes a sheath surrounding a plurality of partitions formed
from a single metal sheet, the partitions forming microchannels
therein through which a heat transfer medium can flow in a laminar
manner, the partitions including sidewalls having a plurality of
openings therein, with the openings comprising about 1% to 20% of
the area of the partition sidewall such that the heat transfer
medium can flow between the microchannels thereby permitting mixing
of liquid and vapor phases of the heat transfer medium for improved
heat transfer of the tube.
[0022] The smaller area of the present openings is necessary to
keep the mixing of the vapor and liquid phases of the heat transfer
medium from becoming too vigorous. This permits the flow to remain
in the laminar range, as turbulent flow causes a pressure drop that
is too large and may affect the efficiency of the system. In the
present invention, the goal is to avoid turbulent flow and instead
keep the flow in the laminar regime, and this is achieved by the
smaller area of the openings and the omission of guide members or
louvers.
[0023] The mixing of the gaseous and liquid phases of the heat
transfer medium is important to this efficiency, but the mixing
cannot be too vigorous. It is generally desirable to keep the flow
within the laminar regime, as turbulent flow also causes a pressure
drop that is too large that may affect the efficiency of the
system.
[0024] To further avoid such turbulent flow, the holes should not
contain louvers or any other type of protrusion or obstruction
extending from the openings or otherwise provided in the
microchannels. In this way, the fluid flow is not directed or
disturbed, but can simply mix smoothly with the gas in the tubes.
The fluid passes between the microchannels without encountering
obstructions, such as louvers or other protrusions.
[0025] The holes may be of various sizes, but are generally not
larger than 80% of the height of the partition, and may even be up
to about 50% of the height. The width of the hole is generally no
larger than its height. As a typical height of a partition is about
2 mm, the maximum size hole would be a square that is about 1.6 mm
by about 1.6 mm. A circular hole having a diameter of about 1.5 mm
is usable as would be an oval having a larger diameter of 1.5 mm
and a smaller diameter of 1 mm or even of 0.5 mm, with the larger
diameter arranged to span the height of the partition. Along the
length of the tube, there are typically from about 5 holes per each
25 mm in length up to about one hole every 75 mm in length, and
preferably 2 holes per 25 mm in length to 1 hole for each 50 mm in
length. There is no criticality in the placement of the holes and
they can be arranged in a uniform fashion or in a staggered or
offset arrangement. The holes are simply cut out of the partition
wall and preferably remove about 1% to 20% of the wall area of each
partition. In a more preferred embodiment, the holes remove about
5% to 10% of the wall area. In yet another embodiment, the holes
remove about 1% to 15% of the wall area. The area between the holes
must be large enough to not detract from the mechanical strength of
the tube and its ability to support the pressure of the flowing
heat transfer medium therein.
[0026] The area is calculated by simply multiplying the length of
the tube by its height to determine the wall area, and by
multiplying the length of the opening by its height (for a square
or rectangular opening) to determine the area for an individual
opening. That number is then multiplied by the number of openings
along the length of the wall. Finally, the total area of the
openings is divided by the wall area.
[0027] For example, for a tube with a length of 250 mm and a height
of 2 mm with 20 circular openings each having a diameter of 1.5 mm,
the percentage of the area of the walls taken up by the holes is
calculated as follows:
[0028] area of wall=250 mm.times.2 mm=500 mm.sup.2
[0029] area of openings=.pi.(0.75 mm).sup.2=1.767
mm.sup.2.times.20=35.343 mm.sup.2
[0030] 35.343 mm.sup.2/500 mm.sup.2=7.07%
[0031] Thus, in this example, the openings remove about 7% of the
area of the sidewalls.
[0032] The present invention preferably includes partitions formed
of a single sheet. This single piece partition is advantageous in
that it aids in the ease of construction and assembly of the tube.
The tube and partitions are generally formed of sheet metal. While
it is possible to form the tube and partitions from an aluminum
sheet, it is preferable to form the tube and partitions from a
copper or copper alloy sheet. The latter is advantageous as it does
not require a cladding layer for brazing as does aluminum. The heat
exchange tube may be formed of two pieces, the outer sheath and the
inner partitions, which may be corrugated fins. The tube can also
be formed by a single pieces of metal sheet using a folding
process. The holes are simply cut into the inner partition to form
the flow paths between the microchannels.
[0033] The sheath 10 and partitions may be constructed of any
suitable brazable material known to those of ordinary skill in the
art, such as metals, alloys, or even composites. As noted above,
preferred materials include copper and copper alloys or aluminum
and aluminum alloys. Typical alloying elements for copper alloys
include zinc, tin or nickel. In one embodiment, the tube is a
welded thin wall tube made of brass. For convenience, the
partitions may be constructed of the same materials as the
sheath.
[0034] The partition insert 14 is attached to the sheath 10,
generally by brazing with a suitable brazing filler material. For
sheaths made of copper and copper alloys, the brazing process may
include coating the partitions 14 with braze paste before it is
inserted into the sheath 10, or inserting the partitions 14 into
the sheath 10 together with a braze foil on each side of the
partitions 14 in order to attach the partitions 14 to the sheath
10. The partition insert may be coated with the braze paste by
means of a roller. A preferred brazing alloy is a
copper-nickel-tin-phosphorus alloy, such as OKC600, which is
commercially available. OKC600 comprises about 1% to 5% nickel,
about 15% to 20% tin, about 4% to 7% phosphorus, and the balance
copper. It is not necessary to add flux to this braze material,
since phosphorus acts as a flux, making the
copper-nickel-tin-phosphorus a self-fluxing alloy. The resulting
joint and construction also has better corrosion properties since
no flux is present. Also, clean-up is facilitated as there is no
flux residue to remove.
[0035] For constructions of aluminum or aluminum alloys, the inside
of the sheath 10 has a clad layer, while the partition 14 is
uncladded. Alternatively, a cladding layer may be used on the
partition 14, rather than on the inside of the sheath 10. This
cladding enhances the brazing operation.
[0036] If desired, fins 16 may be attached to the outer surface of
the sheaths 10 and run between the sheaths 10 to facilitate the
conduction of heat away from the sheath 10, and to provide
additional surface area for convective heat transfer by air flowing
over the heat exchanger. The sheaths may be coated by rolling or
spraying with a brazing material to facilitate adhesion of the fins
16. OKC600 is a preferred brazing material for copper or copper
alloy sheaths. For sheaths 10 made of aluminum or aluminum alloy,
either the outside of the sheath 10 or the fins 16 should be clad
to permit adhesion to the sheath. The clad layer melts during
brazing and with the help of flux, creates a brazed joint.
[0037] A plurality of tubes may be joined to form a heat exchanger.
The heat exchanger includes a header at each end of the plurality
of tubes. The headers may be formed of the same material as the
tubes and insert. In one embodiment, the headers are formed of
copper or copper alloy and are slotted to collect the tubes. The
fins are inserted between the tubes during the assembly process.
The headers are pasted with a brazing paste, capped with pasted
caps, and pipes are inserted if necessary and pasted with brazing
paste at the joint.
[0038] The configuration of the microchannels with holes
therebetween permits the refrigerant to pass between the channels
to improve the heat distribution and performance. It basically
increases the flow path of the heat transfer medium causing it to
become more circuitous. The microchannels actually form many short
interconnected passages through which the medium will flow. In this
way, the liquid and vapor phases of the medium are more evenly
mixed across the tube width thereby enhance the heat transfer of
the heat exchanger and increase the energy efficiency of the
system.
[0039] The brazing application generally takes place in a furnace.
One concern during the process is to prevent oxidation of the tube
or the brazing material. The furnace should have a dew point of
less than about -40.degree. C. and an oxygen content of less than
about 100 ppm. Often, an inert gas atmosphere is used, such as
nitrogen having a dew point of about -65.degree. C. and an oxygen
content of about 10 ppm.
[0040] It is to be understood that the invention is not to be
limited to the exact configuration as illustrated and described
herein. Accordingly, all expedient modifications readily attainable
by one of ordinary skill in the art from the disclosure set forth
herein, or by routine experimentation therefrom, are deemed to be
within the spirit and scope of the invention as defined by the
appended claims.
* * * * *