U.S. patent application number 12/920698 was filed with the patent office on 2011-06-09 for heat exchanger tube configuration for improved flow distribution.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Alexander Chen, Yirong Jiang, Silivia Miglioli, Jules R. Munoz, Young K. Park, Parmesh Verma.
Application Number | 20110132585 12/920698 |
Document ID | / |
Family ID | 41056327 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110132585 |
Kind Code |
A1 |
Chen; Alexander ; et
al. |
June 9, 2011 |
HEAT EXCHANGER TUBE CONFIGURATION FOR IMPROVED FLOW
DISTRIBUTION
Abstract
A microchannel heat exchanger includes for each channel, a
serpentine shaped tube for providing a plurality of parallel flow
passes for successively conducting fluid flow therethrough, and
being fluidly interconnected between an inlet and an outlet
manifold. Multiple circuits are obtained by the individual
serpentine shaped tubes. Various methods are provided for forming
the serpentine shaped tubes.
Inventors: |
Chen; Alexander; (Ellington,
CT) ; Munoz; Jules R.; (South Windsor, CT) ;
Park; Young K.; (Simsbury, CT) ; Verma; Parmesh;
(Manchester, CT) ; Miglioli; Silivia; (Genivolta,
IT) ; Jiang; Yirong; (Ellington, CT) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
41056327 |
Appl. No.: |
12/920698 |
Filed: |
February 5, 2009 |
PCT Filed: |
February 5, 2009 |
PCT NO: |
PCT/US09/33141 |
371 Date: |
December 13, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61034503 |
Mar 7, 2008 |
|
|
|
Current U.S.
Class: |
165/152 ;
165/172 |
Current CPC
Class: |
F28F 9/026 20130101;
F28D 1/0478 20130101; F28F 2260/02 20130101; F28D 2021/0071
20130101 |
Class at
Publication: |
165/152 ;
165/172 |
International
Class: |
F28D 1/047 20060101
F28D001/047 |
Claims
1. A heat exchanger of the type having at least one unit having
inlet and outlet manifolds fluidly interconnected by a plurality of
circuits with each circuit having separate parallel mini-channels
for conducting the flow of refrigerant therebetween; wherein said
parallel mini-channels are each formed in a serpentine shape so as
to provide a plurality of parallel flow passes for successively
conducting fluid flow therethrough and with each circuit having an
inlet end fluidly connected to the inlet manifold and an outlet end
fluidly connected to the outlet manifold and with each circuit
having all of its parallel flow passes grouped together, and with
each group being laterally spaced from all of the groups of the
adjacent circuits.
2. A heat exchanger as set forth in claim 1 wherein said parallel
mini-channels are each formed of a unitary member which is bent
into the desired serpentine shape.
3. A heat exchanger as set forth in claim 1 wherein said parallel
mini-channels are formed from a plurality of planar tubes with
U-shaped members interconnected at the ends of adjacent planar
tubes to provide the serpentine shape.
4. A heat exchanger as set forth in claim 1 wherein said parallel
mini-channels are formed, in part, by fluidly interconnected
J-shaped members.
5. A heat exchanger as set forth in claim 1 wherein said plurality
of parallel flow passes have cross sectional areas which increase
or decrease toward the downstream passes.
6. A heat exchanger as set forth in claim 5 wherein said increases
or decreases are in a step wise fashion.
7. A heat exchanger as set forth in claim 1 wherein said inlet
manifold includes a distributor disposed therein to facilitate the
uniform distribution of refrigerant to the individual
mini-channels.
8. A heat exchanger as set forth in claim 1 wherein said parallel
mini-channels have their respective inlet ends oriented
vertically.
9. A heat exchanger as set forth in claim 1 including a pair of
units arranged in spaced relationship in the direction of airflow
therethrough and with the respective directions of refrigerant flow
being in counterflow relationship.
10. A method of promoting uniform refrigerant flow from an inlet
manifold of a heat exchanger to a plurality of parallel
multi-channel, mini-channels fluidly connected thereto, comprising
the steps of: providing a plurality of tubes shaped in a serpentine
manner and arranged to form a plurality of circuits with each
circuit having a plurality of parallel flow passes for successively
conducting fluid flow therethrough and with each circuit having all
of its parallel flow passes grouped together, and with each group
being laterally spaced from all of the groups of the adjacent
circuits; and fluidly connected each circuit at one end thereof to
an inlet manifold and at the other end thereof to an outlet
manifold.
11. A method as set forth in claim 10 wherein said at least one
flat tube is formed of a unitary member which is bent into the
desired serpentine shape.
12. A method as set forth in claim 10 wherein said at least one
flat tube is formed from a plurality of planar tubes with U-shaped
members being interconnected at the ends of adjacent planar tubes
to provide the serpentine shape.
13. A method as set forth in claim 10 wherein said parallel
mini-channels are formed, in part, by fluidly interconnecting
J-shaped members.
14. A method as set forth in claim 10 wherein said plurality of
parallel flow passes have cross sectional areas which increase or
decrease toward the downstream passes.
15. A method as set forth in claim 14 wherein said increases or
decreases are in a step wise fashion.
16. A method as set forth in claim 10 wherein said inlet manifold
includes a distributor disposed therein to facilitate the uniform
distribution of refrigerant to the individual mini-channels.
17. A method as set forth in claim 10 and including the step of
orienting the inlet ends of said plurality of flat tubes vertically
with respect to one another.
18. A method as set forth in claim 10 and including the steps of
providing another such heat exchanger in spaced relationship in the
direction of air flow to said one heat exchanger and causing the
respective directions of refrigerant flow through the heat
exchangers to be in counterflow relationship.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a National Stage filing under 35 U.S.C.
.sctn.371 of PCT Application No. PCT/US2009/033141, filed Feb. 5,
2009. This application also claims the benefit of U.S. Provisional
Application Ser. No. 61/034,503 filed Mar. 7, 2008. The entirety of
both applications is incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates generally to air conditioning systems
and, more particularly, to parallel flow heat exchangers.
BACKGROUND OF THE INVENTION
[0003] Refrigerant maldistribution in refrigerant system
evaporators is a well known phenomenon. It causes significant
evaporator and overall system performance degradation over a wide
range of operating conditions. Maldistribution is particularly
pronounced in parallel flow evaporators due to their specific
design with respect to refrigerant routing. Attempts to
eliminate/reduce the effects of this phenomenon on the performance
of brazed aluminum heat exchangers have been made with little or no
success. The primary reasons for such failures have generally been
complexity/inefficiency or prohibitively high cost of the
solution.
[0004] In recent years, parallel flow heat exchangers have received
much attention and interest, not just in the automotive industry
but also in the heating, ventilation, air conditioning and
refrigeration (HVAC&R) industry. The primary reasons for the
employment of the parallel flow technology deals with its superior
performance, high degree of compactness and enhanced resistance to
corrosion. Parallel flow heat exchangers are now utilized in both
condenser and evaporator applications for multiple products and
system designs/configurations. The evaporator applications,
although promising greater benefits and rewards, are more
challenging and problematic. Refrigerant maldistribution is one of
the primary concerns and obstacles for the implementation of this
technology in evaporator applications.
[0005] As known, refrigerant maldistribution in parallel flow heat
exchangers occurs because of unequal pressure drops inside the
mini-channels or microchannels as well as in the inlet and outlet
manifolds. In the manifolds or headers, the difference in length of
refrigerant paths, phase separation, gravity and turbulence are the
primary factors responsible for maldistribution. Inside the heat
exchanger mini-channels, variation in the heat transfer rate,
airflow rate and gravity are the dominant factors. Because it is
extremely difficult to control all these factors many of the
previous attempts to manage refrigerant distribution, especially in
parallel flow evaporators, have failed.
[0006] In the refrigerant systems utilizing parallel flow heat
exchangers, the inlet and outlet headers usually have a
conventional cylindrical shape. When the two-phase flow enters the
header, the vapor phase is usually separated from the liquid phase.
Since both phases move independently, refrigerant maldistribution
tends to occur.
[0007] The problems of unequal flow distribution are particularly
evident in multi-pass mini-channel heat exchangers wherein the
inlet and outlet headers are commonly divided into longitudinally
spaced sections which are interconnected by straight tubes. One
approach to solving these problems is shown and described in U.S.
Pat. No. 7,143,605, wherein an inlet manifold includes an
internally disposed distribution tube with a plurality of orifices
formed therein.
[0008] Serpentine, multiple pass heat exchangers are known in the
art as shown by U.S. Pat. Nos. 7,069,980; 4,962,811; 5,036,909;
6,705,386 and U.S. 2005/0217834 A1. Generally, they do not
incorporate the feature of multiple circuits. U.S. Pat. No.
5,036,909 does include multiple circuits but they are constructed
to be in a nested, one inside the other, relationship. Such a
design presents problems of inflexibility in design, manufacture
and use. The present invention overcomes these problems.
DISCLOSURE OF THE INVENTION
[0009] Briefly, in accordance with one aspect of the invention, the
plurality of parallel mini-channels are serpentine in shape so as
to thereby provide a plurality of parallel flow passes but which
are connected to the inlet and outlet manifolds only at the
respective inlet and outlet ends. In this way, the inlet manifold
can be relatively short and be directly connected to fewer inlet
ends of the microchannels for uniform flow distribution. Further,
each circuit has all of its flow passes laterally spaced from all
of the flow passes of the adjacent circuits.
[0010] In accordance with another aspect of the invention, a method
of promoting uniform refrigerant flow from an inlet manifold to a
plurality of parallel mini-channels, including the steps of
providing a flat tube shaped in a serpentine manner to form a
plurality of flow passes for successively conducting fluid flow
therethrough and fluidly connecting an end thereof to an inlet
manifold and the other end thereof to an outlet manifold, with each
circuit having all of its flow passes spaced laterally from all of
the flow passes of the adjacent circuits.
[0011] In the drawings as hereinafter described, preferred and
modified embodiments are depicted; however, various other
modifications and alternate constructions can be made thereto
without departing from the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic illustration of a multi-pass
microchannel heat exchanger in accordance with the prior art.
[0013] FIG. 2 is a perspective view of single three pass parallel
mini-channel member in accordance with the present invention.
[0014] FIG. 2A is a perspective view of a single four-pass parallel
mini-channel member in accordance with the present invention.
[0015] FIG. 3 is a perspective view of a single component
thereof.
[0016] FIG. 3A is an alternative embodiment thereof.
[0017] FIG. 4 is an exploded view of components of another
embodiment thereof.
[0018] FIG. 4A is an alterative embodiment thereof.
[0019] FIG. 5A is a schematic illustration of a heat exchanger in
accordance with the prior art.
[0020] FIG. 5B is a schematic illustration of a heat exchanger in
accordance with the present invention.
[0021] FIG. 6 is an alternative embodiment thereof.
[0022] FIG. 7 is yet another alternative embodiment thereof.
[0023] FIGS. 8A, 8B and & 8C are schematic illustrations of
various possible embodiments of the inlet manifold.
DETAILED DESCRIPTION OF THE INVENTION
[0024] A multi-pass mini-channel heat exchanger in accordance with
the prior art is shown in FIG. 1 and includes a primary manifold
11, a secondary manifold 12 and a plurality of mini-channel tubes
13 fluidly interconnected therebetween. The primary manifold 11 has
dividers 14 and 16 provided therein to thereby form independent
sections 17, 18 and 19 that are fluidly isolated from each other.
The section 17 functions as an inlet manifold and the section 19
functions as an outlet manifold. Similarly, the secondary manifold
12 has a divider 21 which forms the sections 22 and 23 which are so
mutually isolated.
[0025] The heat exchanger as shown comprises a four pass, seven
circuit configuration. That is, there are seven tubes in each of
the four pass groupings 24, 26, 27 and 28. The tubes in the pass
grouping 24 thus fluidly interconnects the section 17 of the
primary manifold 11 to the section 22 of the secondary manifold 12,
with the pass grouping 26 then fluidly interconnecting the section
22 to the section 18 of the primary manifold. Similarly, the pass
grouping 27 fluidly interconnects the section 18 in the primary
header 11 to the section 23 of the secondary manifold 12, and the
pass grouping 28 fluidly interconnects the section 23 of the
secondary manifold 12, to section 19 of the primary manifold 11.
The refrigerant then flows through the assembly as indicated by the
arrows.
[0026] It should be understood that, with such a configuration,
uniform distribution of refrigerant flow to the individual channels
is very difficult to obtain. The primary reason is that the
distribution to the seven tubes has to be made at the entrance of
each of the pass groupings 24, 26, 27 and 28. During each pass
transition, such as in section 22, two-phase mixture exiting pass
grouping 24 will be allowed to mix, and will have the tendency to
phase separate, leading to maldistribution to pass grouping 26. It
should be pointed out that, as in the conventional configuration,
the mini-channel tubes are spaced with fins in between.
[0027] In FIG. 2 there is an illustration of a single parallel
mini-channel tube that is applied to obtain a three pass heat
exchanger. It comprises three planar portions 29, 31 and 32 and the
two arcuate portions 33 and 34. The planar portions 29, 31 and 32
are arranged in parallel relationship, with the planar portions 29
and 31 being fluidly interconnected by the arcuate portion 33, and
with the respective ends of the planar portions 31 and 32 being
fluidly interconnected by the arcuate portion 34. An inlet end 36
is fluidly connected to an inlet manifold, and the outlet end 37 is
fluidly connected to an outlet manifold. Thus, the refrigerant
passes from the inlet manifold and through the entire three passes
to the outlet manifold without requiring any redistribution of the
refrigerant when entering the next pass.
[0028] It should be understood that the flat tube structure as
shown represents a single circuit in a three pass configuration,
and a multi-circuit heat exchanger can be obtained by simply
juxtaposing other identically shaped tubes in parallel relationship
with the tube as shown. These features will be more fully described
hereinafter.
[0029] It should be recognized that although the tube is shown as
being flat in its configuration, it may be formed in other shapes
such as round, oval, or racetrack shaped in cross-section, for
example. An advantage to the flat shape as shown is that this is
conventional geometry for microchannel or mini-channel heat
exchangers. Further, the flat tubes enable the design of a small
inactive heat exchanger area at the top and bottom due to their
flat profile.
[0030] The tube as shown in FIG. 2 represents a finished three-pass
tube which may be fabricated by any of various manufacturing
processes. One method that can be applied is to simply form the
three pass tube from a single unitary member which is bent around
to form the 180.degree. turns at the arcuate portions 33 and 34.
With such an approach, care must be taken not to crimp the tube so
as to restrict the flow of refrigerant through the arcuate portions
33 or 34. The distance between the planar portions 29, 31 and 32
can be selected to fit the design of the overall heat
exchanger.
[0031] FIG. 2A shows another tube which is formed in a four-pass
configuration with combination of two long bends and one short
bend. Here, it will be seen that the bends are substantially
90.degree. bends rather than curvilinear bends as shown in FIG. 2.
Accordingly, the considerations for preventing crimping are
different and probably more critical than with the arcuate sections
of the FIG. 2 embodiment. Critical in this regard is the type of
material that is used (e.g. preferably a more ductile material),
the bend radius, the wall thickness, and the internal parallel
arrangements inside the tubes, which are all factors that can
influence the bend shape and form.
[0032] Another approach to fabrication is that shown in FIG. 3
wherein a shorter section of tube is bent around a 180.degree. turn
near its one end to form a J-shaped member 38 comprising a planar
element 39 and an arcuate element 41. This provides only a single
pass from the inlet manifold 42 but can easily be combined with
other similar J-shaped members to obtain a multi-pass arrangement.
That is, to add a second pass to that shown, one can easily connect
an end of the planar element 39 of a second J-shaped member to the
end of the arcuate element 41 of the member as shown to obtain a
second pass. A third pass then can be obtained by connecting a
planar element to connect its one end to the end of the arcuate
element 41 of the second J-shaped member, with the other end
thereof being fluidly connected to the outlet manifold. Connections
between individual members can be made by brazing or the like.
[0033] Another possible fabricating process that may be used that
shown in FIG. 4 wherein the arcuate sections 45 and 43 may be
formed from shorter portions of a tube and then connected to the
planar elements to obtain a three pass tube. That is, arcuate
section 45 fluidly interconnects the ends of planar elements 44 and
46, and arcuate section 43 fluidly interconnects the ends of planar
elements 46 and 47.
[0034] The applicants have recognized that, as the refrigerant is
expanded as it successively flows through the various passes, it is
desirable to progressively increase the cross sectional areas of
the tubes in the downstream direction. Ideally, this would be
accomplished on a continuous basis but, as a practical matter, such
a design would be difficult to implement. Accordingly, this may
also be accomplished in a step wise manner. Such a step wise
approach can easily be implemented in the methods of fabrication as
shown in FIGS. 3 and 4 by gradually increasing the cross sectional
area of the successive planar elements within any particular
circuit as shown in FIGS. 3A and 4A.
[0035] Considering now the manner in which the tubes may be
combined to form a multiple circuit heat exchanger, a prior art,
nested, approach is shown in FIG. 5A wherein circuits 48 and 49 are
fluidly interconnected between inlet header 51 and 52. Each of the
circuits 48 and 49 is formed in a serpentine shape so as to provide
five passes between the inlet header 51 and the outlet header 52.
This arrangement allows the headers 51 and 52 to be relatively
small with the inlet header 51 providing for a single distribution
between the two circuits, and with the distribution in each circuit
remaining throughout the flow of refrigerant through the heat
exchanger. However, in order for the tubes of the circuit 49 to be
nested within the tubes of the circuit 48 as shown, their
size/shape needs to be selected accordingly. Further, if one wants
to add a third circuit, it would be necessary to provide a third
differently shaped tube that could be nested outside of the circuit
48 or inside the circuit 49. Such a change, in turn, may require
the redesigning of the entire heat exchanger when considering the
features of the fin density, fin height, tube details, etc.
[0036] Referring to FIG. 5B, the heat exchanger of the present
invention is shown to include circuits 53 and 54, with each having
five passes between the inlet header 56 and outlet header 57.
However, rather than having the tubes of the circuit 54 nested
within the tubes of the circuit 53 as in the prior art, the entire
five passes of the circuit 54 are grouped together with the group
being laterally spaced from the entire group of five passes of the
circuit 53. This arrangement allows the tubes of the circuit 54 to
be substantially identical to the tubes of the circuit 53, with
only the lengths of the inlet lines 58 and 59 and the lengths of
outlet lines 61 and 62 being different. That is, the five passes of
the circuit 53 are substantially identical to the five passes of
the circuit 54. This allows them to be mass produced to reduce
cost. It also allows them to be stacked vertically, horizontally or
in the airflow directions for optimal performance. Further,
additional circuits can be easily added by simply placing one or
more circuits in spaced relationship to the circuit 54.
[0037] In FIG. 6 there is shown an alternative embodiment of a heat
exchanger having a five pass, four circuit arrangement to again
obtain a total of twenty tubes. Here, the four circuits 63, 64, 66
and 67 are fluidly connected between an inlet header 68 and an
outlet header 69, with each of the circuits containing five groups
of passes between its inlet and outlet ends.
[0038] Referring now to FIG. 7, there are shown two heat exchanger
units 70 and 71 in spaced relationship with respect to the
direction of airflow therethrough. Unit 70 has circuits 72 and 73
fluidly interposed between inlet header 74 and outlet header 76.
Unit 71 has circuits 77 and 78 fluidly connected between inlet
header 79 and outlet header 81. As will be seen, the inlet and
outlet headers of the respective units 70 and 71 are substantially
reversed. The purpose is to obtain better efficiency when
considering the operation of the two units in combination. That is,
in the heat exchanger unit 70, the refrigerant entering from the
left side of each of the circuits 72 and 73 will tend to be cooler
than the refrigerant near to the downstream ends of those circuits
(i.e. toward the right side). Similarly, with the inlet header 79
on the right side of the unit 71, the refrigerant flowing in the
passes nearer to the right side of circuits 77 and 78 will be
cooler than the refrigerant in those passes on the left side of
those circuits. Because of this counterflow relationship between
the flow in the units 70 and 71, a more balanced heat transfer and
better efficiency will result. The arrangement of circuits as set
forth in the present invention facilities such a design.
[0039] The applicants have recognized that if a heat exchanger is
arranged in such a manner that the tubes emanating therefrom are in
a parallel horizontal arrangement, but with the tubes being
vertically spaced, then gravity will tend to cause more of the
heavier liquid refrigerant to flow to the lower tubes and more of
the lighter vapor to the upper tubes, thereby causing
maldistribution. Accordingly, one of the arrangements of 8A, 8B or
8C is preferable, wherein the inlet manifold is shown at 82 and the
mini-channels are shown at 83. As will be seen in FIGS. 8A and 8B,
the incoming fluid is flowing upwardly or downwardly, respectively,
and therefore each of the tubes is effected the same as the other
tubes with respect to the force of gravity. Thus, even distribution
is more likely to occur.
[0040] In FIG. 8C, in order to further enhance the uniform
distribution of refrigerant to the tubes 83, a distributor 84 is
installed within the inlet header 82 as shown.
[0041] While the present invention has been particularly shown and
described with reference to the preferred mode as illustrated in
the drawing, it will be understood by one skilled in the art that
various changes in detail may be effected therein without departing
from the spirit and scope of the invention as defined by the
claims.
* * * * *