U.S. patent application number 10/303717 was filed with the patent office on 2004-05-27 for interconnected microchannel tube.
Invention is credited to Shabtay, Yoram Leon, Tang, Liangyou.
Application Number | 20040099408 10/303717 |
Document ID | / |
Family ID | 32325064 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040099408 |
Kind Code |
A1 |
Shabtay, Yoram Leon ; et
al. |
May 27, 2004 |
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. 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;
(Cottontown, TN) |
Correspondence
Address: |
WINSTON & STRAWN
PATENT DEPARTMENT
1400 L STREET, N.W.
WASHINGTON
DC
20005-3502
US
|
Family ID: |
32325064 |
Appl. No.: |
10/303717 |
Filed: |
November 26, 2002 |
Current U.S.
Class: |
165/177 ;
165/183 |
Current CPC
Class: |
F28F 1/003 20130101;
F28F 3/027 20130101; F28F 2260/02 20130101 |
Class at
Publication: |
165/177 ;
165/183 |
International
Class: |
F28F 001/14 |
Claims
What is claimed is:
1. 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 including sidewalls having
a plurality of openings therein, 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.
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 in the tube.
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 in the tube.
4. The heat transfer tube of claim 1, wherein the openings comprise
about 1% to 20% of the area of the partition sidewall.
5. The heat transfer tube of claim 4, wherein each partition has
from about 5 openings per inch to about 1 opening every three
inches along the length of the partition.
6. The heat transfer tube of claim 4, wherein the openings comprise
up to about 80% of the height of the sidewall of the partition.
7. The heat transfer tube of claim 1, wherein the openings are
round, square, rectangular, or triangular.
8. The heat transfer tube of claim 1, wherein the plurality of
partitions are formed from a single sheet.
9. The heat transfer tube of claim 8, wherein the sheet forms
serpentine partitions.
10. The heat transfer tube of claim 1, wherein the sheath is formed
of copper or a copper alloy.
11. The heat transfer tube of claim 10, wherein the partition
sidewalls are formed of copper or a copper alloy.
12. The heat transfer tube of claim 1, wherein the sheath and
partition sidewalls are formed of aluminum or an aluminum
alloy.
13. The heat transfer tube of claim 1, further comprising fins
attached to an outer surface of the sheath to assist in
transferring heat therefrom.
14. A heat exchanger comprising two opposing headers and a
plurality of the heat transfer tubes extending between the headers,
the heat transfer tubes comprising a sheath surrounding a plurality
of partitions forming microchannels through which a heat transfer
medium can flow, the partitions including sidewalls having a
plurality of openings therein, 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.
15. In a heat exchanger that includes a plurality of microchannels
therein through which a heat transfer medium flows, the improvement
which comprises providing a plurality of openings in the
microchannels, 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.
Description
FIELD OF INVENTION
[0001] 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
[0002] 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.
[0003] 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.
[0004] Thus, there is a need for an improved heat transfer design
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
[0005] 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
between the microchannels thereby permitting mixing of liquid and
vapor phases of the heat transfer medium for improved heat transfer
of the tube.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
between the microchannels thereby permitting mixing of liquid and
vapor phases of the heat transfer medium for improved heat transfer
of the tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The invention will be better understood in relation to the
attached drawings illustrating preferred embodiments, wherein:
[0011] FIG. 1 shows a cross-sectional view of a heat exchanger tube
made according to the present invention;
[0012] FIG. 2 shows a perspective view of a heat exchanger tube
according to the invention; and
[0013] FIG. 3 shows a cross-sectional view of the heat exchanger
taken along 3-3 of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0014] 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.
[0015] 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.
[0016] The openings or holes 20 in the partitions 14 may be of any
shape, 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. 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.
[0017] 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.
[0018] The holes may be of various sizes, but are generally not
larger than 80% of the height of the partition. 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 remove about 1% to 20% of
the wall area of each partition. In a preferred embodiment, the
holes remove about 5% to 10% 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.
[0019] The tube and partitions may be 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
* * * * *