U.S. patent application number 12/629458 was filed with the patent office on 2010-03-25 for parallel flow evaporator with shaped manifolds.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Robert A. Chopko, Allen C. Kirkwood, Michael F. Taras.
Application Number | 20100071392 12/629458 |
Document ID | / |
Family ID | 36337310 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071392 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
March 25, 2010 |
PARALLEL FLOW EVAPORATOR WITH SHAPED MANIFOLDS
Abstract
A method is provided for mitigating two-phase refrigerant
maldistribution in heat exchange channels of a parallel flow
evaporator. An inlet manifold of the evaporator includes a first
stage, at least one intermediate stage, and a final stage. Each
stage includes an expansion chamber, a contraction chamber, and at
least one heat exchange channel interconnecting the stage to an
outlet manifold of the evaporator. The method includes throttling
the two-phase refrigerant in the expansion chamber of each stage,
flowing a portion of the throttled refrigerant through the at least
one heat exchange channel to the outlet manifold, mixing and
jetting the two-phase refrigerant in each contraction chamber to
increase the velocity of the refrigerant, and passing the
refrigerant out an exit of the outlet manifold.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Kirkwood; Allen C.;
(Brownsburg, IN) ; Chopko; Robert A.;
(Baldwinsville, NY) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
36337310 |
Appl. No.: |
12/629458 |
Filed: |
December 2, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10987961 |
Nov 12, 2004 |
|
|
|
12629458 |
|
|
|
|
Current U.S.
Class: |
62/118 ;
62/515 |
Current CPC
Class: |
F25B 39/028 20130101;
F28D 1/05366 20130101; F28F 9/028 20130101; F28F 9/02 20130101 |
Class at
Publication: |
62/118 ;
62/515 |
International
Class: |
F25D 17/02 20060101
F25D017/02; F25B 39/02 20060101 F25B039/02 |
Claims
1. A method for mitigating two-phase refrigerant maldistribution in
heat exchange channels of a parallel flow evaporator, the method
comprising the steps of: providing a two-phase refrigerant to an
inlet manifold of the evaporator, the inlet manifold comprising a
first stage, at least one intermediate stage, and a final stage,
each stage comprising an expansion chamber, a contraction chamber,
and at least one heat exchange channel interconnecting the stage to
an outlet manifold; throttling the two-phase refrigerant in the
expansion chamber of each stage; flowing a portion of the throttled
refrigerant through the at least one heat exchange channel to the
outlet manifold; mixing and jetting the two-phase refrigerant in
each contraction chamber to increase the velocity of the
refrigerant thereby; and passing the refrigerant out an exit of the
outlet manifold.
2. The method as set forth in claim 1, wherein a plurality heat
exchange channels interconnect one stage to the outlet manifold,
and the step of flowing a portion of the throttled refrigerant
includes flowing through the plurality of heat exchange
channels.
3. The method as set forth in claim 1, wherein the at least one
heat exchange channel is fluidly connected to the expansion
chamber.
4. The method as set forth in claim 1, further including the step
of balancing hydraulic resistances between the contraction stage
and the associated heat exchange channel.
5. The method as set forth in claim 4, wherein the hydraulic
resistance of the contraction chamber is at least one and a half
times lower than the hydraulic resistance of the associated
channel.
6. The method as set forth in claim 1, wherein the outlet manifold
further comprises a first stage, at least one intermediate stage,
and a final stage, each stage comprising an expansion chamber and a
contraction chamber, the heat exchange channels interconnecting the
stages in the inlet manifold to the stages in the outlet
manifold.
7. The method as set forth in claim 6, the heat exchange channels
interconnecting the expansion chambers in the inlet manifold to the
expansion chambers in the outlet manifold.
8. The method as set forth in claim 1, wherein the mixing step
comprises placing refrigerant-mixing inserts in the contraction
chambers.
9. The method as set forth in claim 1, wherein the heat exchange
channels are microchannels.
10. In a parallel flow evaporator comprising an inlet manifold, an
outlet manifold, and a plurality of channels fluidly connecting the
inlet manifold to the outlet manifold, a method for mitigating
two-phase refrigerant maldistribution in the channels, the method
comprising the steps of: partially evaporating the two-phase
refrigerant through a repetitive series of stages in the inlet
manifold, wherein each stage comprises an expansion chamber, a
contraction chamber, and at least one of the channels; and
balancing hydraulic resistances between each stage and the
associated channel.
11. The method as set forth in claim 10, wherein the balancing step
comprises configuring the hydraulic resistance of the contraction
chamber to be at least one and a half times lower than the
hydraulic resistance of the associated channel.
12. The method as set forth in claim 11, wherein configuring the
hydraulic resistance of the contraction chamber comprises sizing a
cross-sectional area of the contraction chamber.
13. The method as set forth in claim 10, wherein a refrigerant flow
rate progressively decreases through the repetitive series of
stages in the inlet manifold.
14. The method as set forth in claim 13, wherein the expansion
chambers of the repetitive series of stages in the inlet manifold
comprise progressively smaller cross-sectional areas defining a
cross-sectional area reduction ratio, the ratio being proportional
to the progressively decreasing refrigerant flow rate.
15. The method as set forth in claim 13, wherein the contraction
chambers of the repetitive series of stages in the inlet manifold
comprise progressively smaller cross-sectional areas defining a
cross-sectional area reduction ratio, the ratio being proportional
to the progressively decreasing refrigerant flow rate.
16. The method as set forth in claim 10, further including the step
of partially evaporating the refrigerant through a repetitive
series of stages in the outlet manifold, wherein the stages
comprise an expansion chamber, a contraction chamber, and at least
one of the channels.
17. The method as set forth in claim 16, wherein a refrigerant flow
rate progressively increases through the repetitive series of
stages in the outlet manifold.
18. The method as set forth in claim 16, wherein the expansion
chambers of the repetitive series of stages in the inlet manifold
comprise progressively smaller cross-sectional areas, and the
expansion chambers of the repetitive series of stages in the outlet
manifold comprise progressively larger cross-sectional areas.
19. The method as set forth in claim 18, wherein the progressively
larger cross-sectional areas of the expansion chambers in the
outlet manifold are proportional to the progressively smaller
cross-sectional areas of the expansion chambers in the inlet
manifold.
20. The method as set forth in claim 10, wherein the heat exchange
channels are microchannels.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuing application of U.S. patent
application Ser. No. 10/987,961, filed Nov. 12, 2004, entitled
"Parallel Flow Evaporator with Shaped Manifolds," which application
is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] This invention generally relates to air conditioning and
refrigeration systems and, more particularly, to parallel flow
evaporators thereof.
[0003] A definition of a so-called parallel flow heat exchanger is
widely used in the air conditioning and refrigeration industry now
and designates a heat exchanger with a plurality of parallel
passages, among which refrigerant is distributed and flown in the
orientation generally substantially perpendicular to the
refrigerant flow direction in the inlet and outlet manifolds. This
definition is well adapted within the technical community and will
be used throughout the text.
[0004] 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 of refrigerant may
occur due to differences in flow impedances within evaporator
channels, non-uniform airflow distribution over external heat
transfer surfaces, improper heat exchanger orientation or poor
manifold and distribution system design. Maldistribution is
particularly pronounced in parallel flow evaporators due to their
specific design with respect to refrigerant routing to each
evaporator circuit. Attempts to eliminate or reduce the effects of
this phenomenon on the performance of parallel flow evaporators
have been made with little or no success. The primary reasons for
such failures have generally been related to complexity and
inefficiency of the proposed technique or prohibitively high cost
of the solution.
[0005] In recent years, parallel flow heat exchangers, and brazed
aluminum heat exchangers in particular, have received much
attention and interest, not just in the automotive field but also
in the heating, ventilation, air conditioning and refrigeration
(HVAC&R) industry. The primary reasons for the employment of
the parallel flow technology are related to its superior
performance, high degree of compactness, structural rigidity and
enhanced resistance to corrosion. Parallel flow heat exchangers are
now utilized in both condenser and evaporator applications for
multiple products and system designs and 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 the evaporator
applications.
[0006] As known, refrigerant maldistribution in parallel flow heat
exchangers occurs because of unequal pressure drop inside the
channels and in the inlet and outlet manifolds, as well as poor
manifold and distribution system design. In the manifolds, the
difference in length of refrigerant paths, phase separation,
gravity and turbulence are the primary factors responsible for
maldistribution. Inside the heat exchanger channels, variations in
the heat transfer rate, airflow distribution, manufacturing
tolerances, and gravity are the dominant factors. Furthermore, the
recent trend of the heat exchanger performance enhancement promoted
miniaturization of its channels (so-called minichannels and
microchannels), which in turn negatively impacted refrigerant
distribution. Since it is extremely difficult to control all these
factors, many of the previous attempts to manage refrigerant
distribution, especially in the parallel flow evaporators, have
failed.
[0007] In the refrigerant systems utilizing parallel flow heat
exchangers, the inlet and outlet manifolds or headers (these terms
will be used interchangeably throughout the text) 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 flow independently, refrigerant maldistribution
tends to occur.
[0008] If the two-phase flow enters the inlet manifold at a
relatively high velocity, the liquid phase (i.e. droplets of
liquid) is carried by the momentum of the flow further away from
the manifold entrance to the remote portion of the header. Hence,
the channels closest to the manifold entrance receive predominantly
the vapor phase and the channels remote from the manifold entrance
receive mostly the liquid phase. If, on the other hand, the
velocity of the two-phase flow entering the manifold is low, there
is not enough momentum to carry the liquid phase along the header.
As a result, the liquid phase enters the channels closest to the
inlet and the vapor phase proceeds to the most remote ones. Also,
the liquid and vapor phases in the inlet manifold can be separated
by the gravity forces, causing similar maldistribution
consequences. In either case, maldistribution phenomenon quickly
surfaces and manifests itself in evaporator and overall system
performance degradation.
SUMMARY OF THE INVENTION
[0009] Briefly, in accordance with one aspect of the invention, a
method is provided for mitigating two-phase refrigerant
maldistribution in heat exchange channels of a parallel flow
evaporator. An inlet manifold of the evaporator includes a first
stage, at least one intermediate stage, and a final stage. Each
stage includes an expansion chamber, a contraction chamber, and at
least one heat exchange channel interconnecting the stage to an
outlet manifold of the evaporator. The method includes throttling
the two-phase refrigerant in the expansion chamber of each stage,
flowing a portion of the throttled refrigerant through the at least
one heat exchange channel to the outlet manifold, mixing and
jetting the two-phase refrigerant in each contraction chamber to
increase the velocity of the refrigerant, and passing the
refrigerant out an exit of the outlet manifold.
[0010] By another aspect of the invention, the outlet manifold of
the evaporator includes a first stage, at least one intermediate
stage, and a final stage. Each stage includes an expansion chamber
and a contraction chamber, and the heat exchange channels
interconnect the stages in the inlet manifold to the stages in the
outlet manifold.
[0011] By yet another aspect of the invention, in a parallel flow
evaporator comprising an inlet manifold, an outlet manifold, and a
plurality of channels fluidly connecting the inlet manifold to the
outlet manifold, a method is provided for mitigating two-phase
refrigerant maldistribution in the channels. The method includes
the steps of partially evaporating the two-phase refrigerant
through a repetitive series of stages in the inlet manifold. Each
stage comprises an expansion chamber, a contraction chamber, and at
least one of the channels. The method further includes the step of
balancing hydraulic resistances between each stage and the
associated channel.
[0012] By still another aspect of the invention, balancing
resistances includes configuring the hydraulic resistance of the
contraction chamber to be at least one and a half times lower than
the hydraulic resistance of the associated channel.
[0013] By still another aspect of the invention, the expansion
chambers of the repetitive series of stages in the inlet manifold
include progressively smaller cross-sectional areas defining a
cross-sectional area reduction ratio.
[0014] By still another aspect of the invention, the method for
mitigating two-phase refrigerant maldistribution in heat exchange
channels of a parallel flow evaporator further includes the step of
partially evaporating the refrigerant through a repetitive series
of stages in the outlet manifold. The stages comprise an expansion
chamber, a contraction chamber, and at least one of the
channels.
[0015] By still another aspect of the invention, the expansion
chambers of the repetitive series of stages in the outlet manifold
comprise progressively larger cross-sectional areas.
[0016] By still another aspect of the invention, the progressively
larger cross-sectional areas of the expansion chambers in the
outlet manifold are proportional to the progressively smaller
cross-sectional areas of the expansion chambers in the inlet
manifold.
[0017] In the drawings as hereinafter described, preferred and
alternate embodiments are depicted; however, various other
modifications and alternate designs and constructions can be made
thereto without departing from the true spirit and scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic illustration of a parallel flow heat
exchanger in accordance with the prior art.
[0019] FIG. 2 is a schematic illustration of one embodiment of the
present invention.
[0020] FIG. 3 is a schematic illustration of an alternative
embodiment of the present invention.
[0021] FIG. 4 is a schematic illustration of yet another embodiment
of the present invention.
[0022] FIG. 5 is a schematic illustration of still another
embodiment of the present invention.
[0023] FIG. 6 is a schematic illustration of still another
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Referring now to FIG. 1, a parallel flow heat exchanger is
shown to include an inlet header or manifold 11, an outlet header
or manifold 12 and a plurality of parallel channels 13 fluidly
connecting the inlet manifold 11 to the outlet manifold 12.
Generally, the inlet and outlet manifolds 11 and 12 are cylindrical
in shape, and the channels 13 are usually tubes (or extrusions) of
flattened or round shape. Channels 13 normally have a plurality of
internal and external heat transfer enhancement elements, such as
fins. For instance, external fins, disposed therebetween for the
enhancement of the heat exchange process and structural rigidity
are typically furnace-brazed. Channels 13 may have internal heat
transfer enhancements and structural elements as well.
[0025] In operation, two-phase refrigerant flows into the inlet
opening 14 and into the internal cavity 16 of the inlet header 11.
From the internal cavity 16, the refrigerant, in the form of a
liquid, a vapor or a mixture of liquid and vapor (the latter is a
typical scenario) enters the tube openings 17 to pass through the
channels 13 to the internal cavity 18 of the outlet header 12. From
there, the refrigerant, which is now usually in the form of a
vapor, passes out the outlet opening 19 and then to the compressor
(not shown).
[0026] As discussed hereinabove, it is desirable that the two-phase
refrigerant passing from the inlet header 11 to the individual
channels 13 do so in a uniform manner (or in other words, with
equal vapor quality) such that the full heat exchange benefit of
the individual channels can be obtained and flooding conditions are
not created and observed at the compressor suction (this may damage
the compressor). However, because of various phenomena as discussed
hereinabove, a non-uniform flow of refrigerant to the individual
channels 13 (so-called maldistribution) occurs. In order to address
this problem, the applicants have introduced design features that
will create a mixing and jetting effects in the two-phase
refrigerant flow in the inlet manifold 11 to thereby bring about a
more uniform homogeneous flow into to the channels 13.
[0027] Referring to FIG. 2, the heat exchanger is formed with a
conventional outlet manifold 12 and channels 13, but with a
differently shaped inlet manifold 21, as shown. Rather than being
cylindrical in the usual manner, the inlet manifold 21 is
hour-glass shaped (i.e. with a plurality of alternating expansion
and contraction chambers). For simplicity, the inlet manifold 21 is
shown to include three expansion chambers 22, 23 and 24 with
interconnecting contraction chambers 26 and 27. Each of the
expansion chambers 22, 23 and 24 is preferably interconnected to an
associated channel 13, as shown. In actual practice, a larger
number of expansion chambers and associated channels 13 would be
provided. Further, each of the expansion chambers may be connected
to more than one channel 13. It is preferred, however, that none of
the channels 13 would be connected directly to a contraction
chamber.
[0028] In operation, the two-phase refrigerant enters the inlet
opening 28 and enters the first expansion chamber 22 where it is
partially expanded with a portion thereof entering the associated
channel(s). The remaining two-phase refrigerant is then forced
through the contraction chamber 26 such that when it enters the
expansion chamber 23 in more homogeneous manner due to increased
velocity, partial evaporation (or throttling) occurs, thereby
presenting a homogeneous condition for the refrigerant mixture
flowing to the associated channel(s) and to the downstream
channels. The remaining refrigerant then passes through the
contraction chamber 27, where more mixing and jetting of the two
(liquid and vapor) refrigerant phases occurs and into the expansion
chamber 24, wherein, once again, a partial evaporation process is
taking place, thereby presenting a homogenous mixture to the
associated channel(s). In this way, the partial evaporation process
is incrementally (i.e. progressively) maintained through the length
of the inlet manifold 21, so as to result in a more uniform
distribution of refrigerant among the channels.
[0029] Although the refrigerant flow in the inlet manifold 21 is
progressively diminishing, it is essential not to introduce
excessive flow impedance in the inlet manifold 21 relative to other
flow resistances in the heat exchanger. Thus, the cross-section
areas of the contraction chambers 26 and 27 must be properly sized
for a particular application and for a particular configuration of
the heat exchanger to maintain the balance between the desired
partial evaporation process and undesired additional hydraulic
resistance for the refrigerant flowing to the downstream channels.
Generally, flow impedance of the contraction chamber should be at
least one and a half times lower than the hydraulic resistance of
the associated channels 13. It is also desirable to balance the
impedance of the contraction chambers in the inlet manifold 21 with
corresponding pressure drops in the outlet manifold as will be
further described hereinafter.
[0030] An alternative embodiment of the present invention is shown
in FIG. 3, wherein the inlet manifold 31 is again hour-glass shaped
but with expansions chambers 32, 33 and 34 being progressively
smaller in a cross section to accommodate the reduced refrigerant
flow, as it moves from the inlet 38 toward the downstream end
thereof. Further, the contraction chambers 36 and 37 are also
preferably formed of a progressive smaller size for the same
reasons. Generally, the cross-section area reduction ratio of the
expansion chambers is proportional to the refrigerant flow rate
ratio reduction entering and leaving the chamber. If this ratio is
not uniform, the average value should be used instead for the
estimates. The contraction chambers can be sized by employing an
identical procedure and values.
[0031] In FIG. 4, a further embodiment is shown wherein the inlet
manifold 21 is identical to that as described in respect to FIG. 2
or that shown in FIG. 3, but the outlet manifold 41 also being
hour-glass shaped with expansion chambers 42, 43 and 44 and
contraction chambers 46 and 47 alternately disposed as shown. These
expansion and contraction chambers are not necessarily and most
likely will not be of the same sizes as those of the inlet manifold
21, since the refrigerant flowing within the outlet manifold 41 in
a completely different thermodynamic state. Although if the chamber
of the inlet manifold 21 are progressively smaller in size toward
the downstream end thereof, the chambers of the outlet manifold 41
should preferably be progressively larger toward the downstream end
thereof, as shown in FIG. 5, and identical aspect ratio can be
utilized in sizing the outlet manifold chambers. In this way, the
impedances that are presented in the inlet manifold 21 are matched
by those in the outlet manifold 41 such that, the most favorable
conditions for the uniform refrigerant flow distribution among the
parallel channels 13 are created throughout the heat exchanger,
enhancing the system performance and improving compressor
reliability, by preventing flooded conditions at the compressor
suction.
[0032] An alternative embodiment of the present invention is shown
in FIG. 6, wherein the inlet manifold 51 is again hour-glass shaped
with the expansions chambers 52, 53 and 54 and the contraction
chambers 55 and 56 disposed in between the expansion chambers.
Additionally, refrigerant-mixing inserts 57 are placed within the
contraction chambers 55 and 56 to promote mixing and even more
homogeneous conditions at the entrance of the adjacent downstream
expansion chambers. Although inserts 57 can be spiral in shape or
have internal fins or indentations, any other configurations
promoting mixing are also acceptable. In all other aspects this
embodiment is similar to the embodiments discussed above.
[0033] In has to be understood that the expansion and contraction
chambers may be of any shape, cross-section area and configuration
as long as a repetitive process of partial evaporation is created
and a proper balance of hydraulic resistances is maintained.
[0034] Furthermore, it should be noted that both vertical and
horizontal channel orientations will benefit from the teaching of
the present invention, although higher benefits will be obtained
for the latter configuration. Also, although the teachings of this
invention are particularly advantageous for the evaporator
applications, refrigerant system condensers may benefit from them
as well.
[0035] While the present invention has been particularly shown and
described with reference to preferred and alternate embodiments as
illustrated in the drawings, it will be understood by one skilled
in the art that various changes in detail may be effected therein
without departing from the true spirit and scope of the invention
as defined by the claims.
* * * * *