U.S. patent application number 12/921414 was filed with the patent office on 2011-01-06 for microchannel heat exchanger with enhanced refrigerant distribution.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20110000255 12/921414 |
Document ID | / |
Family ID | 41319237 |
Filed Date | 2011-01-06 |
United States Patent
Application |
20110000255 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
January 6, 2011 |
MICROCHANNEL HEAT EXCHANGER WITH ENHANCED REFRIGERANT
DISTRIBUTION
Abstract
An evaporator includes a manifold receiving a distributor
insert. The distributor insert receives the flow of refrigerant to
be delivered into the manifold, and has openings to communicate
this refrigerant into a plurality of chambers which are defined
between adjacent dividing elements of the distributor insert within
the manifold. In this manner, these chambers are each associated
with distinct heat transfer tubes and such that these chambers are
isolated from each other.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Lifson; Alexander; (Malius,
NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
41319237 |
Appl. No.: |
12/921414 |
Filed: |
April 13, 2009 |
PCT Filed: |
April 13, 2009 |
PCT NO: |
PCT/US2009/040314 |
371 Date: |
September 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61053677 |
May 16, 2008 |
|
|
|
Current U.S.
Class: |
62/498 ;
165/173 |
Current CPC
Class: |
F25B 39/028 20130101;
F28F 2260/02 20130101; F28D 1/05366 20130101; F28F 9/0273
20130101 |
Class at
Publication: |
62/498 ;
165/173 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F28F 9/02 20060101 F28F009/02 |
Claims
1. A heat exchanger comprising: a plurality of heat transfer tubes;
a manifold for communicating refrigerant into said plurality of
heat transfer tubes, and a distributor insert connected to a source
of refrigerant and having a plurality of orifices in an outer
periphery of said distributor insert and dividing elements on an
outer wall of said distributor insert such that a plurality of
distribution chambers are defined and associated with said
plurality of heat transfer tubes.
2. The heat exchanger as set forth in claim 1, wherein the heat
exchanger is an evaporator, and said manifold is an inlet
manifold.
3. The heat exchanger as set forth in claim 1, wherein said
distributor insert and said dividing elements improve refrigerant
distribution in said heat exchanger.
4. The heat exchanger as set forth in claim 1, wherein said
manifold is an intermediate manifold.
5. The heat exchanger as set forth in claim 1, wherein said
distributor insert extends along only a portion of said manifold,
and is not aligned with heat transfer tubes communicating into said
manifold, but is aligned with heat transfer tubes communicating out
of said manifold.
6. The heat exchanger as set forth in claim 1, wherein said
dividing elements are spaced uniformly along a length of said
distributor insert.
7. The heat exchanger as set forth in claim 1, wherein said
dividing elements are attached to said distributor insert by one of
mechanical attachment and chemical bonding.
8. The heat exchanger as set forth in claim 1, wherein said
dividing elements are flat plates having a cutout portion at an
outer periphery to provide clearance for said heat transfer
tubes.
9. The heat exchanger as set forth in claim 1, wherein the
distributor insert has a round cross-sectional shape.
10. The heat exchanger as set forth in claim 1, wherein said
manifold has an internal bore of a round cross-sectional shape.
11. The heat exchanger as set forth in claim 1, wherein the
refrigerant passing through said distributor insert is a two-phase
refrigerant.
12. The heat exchanger as set forth in claim 1, wherein the heat
exchanger is a microchannel heat exchanger.
13. A refrigerant system comprising: a compressor, said compressor
for compressing a refrigerant and delivering it downstream into a
condenser, refrigerant from said condenser passing through an
expansion device and then into an evaporator; at least one of said
condenser and evaporator including a plurality of heat transfer
tubes for receiving a refrigerant, and passing the refrigerant
along a path from an inlet end to an outlet end, and a manifold for
communicating with an inlet end of said heat transfer tubes, said
manifold receiving a distributor insert, connected to a source of
refrigerant and having a plurality of orifices at an outer
periphery and a plurality of dividing elements between an outer
wall of said distributor insert and an inner wall of said manifold
to define a plurality of separation chambers within said manifold,
with at least some of said heat transfer tubes being associated
with different ones of said separation chambers and isolated from
others of said separation chambers by said dividing elements.
14. The refrigerant system as set forth in claim 13, wherein said
distributor insert extends from an upstream end of said manifold
toward a downstream end of said manifold, and the size of said
separation chambers defined between adjacent ones of said dividing
elements is determined to optimize the flow of refrigerant within
the plurality of heat transfer tubes.
15. The refrigerant system as set forth in claim 13, wherein said
plurality of heat transfer tubes, each including a plurality of
channels, spaced generally perpendicularly to an upstream to
downstream direction of said distributor insert.
16. The refrigerant system as set forth in claim 13, wherein the
heat exchanger is an evaporator, and said manifold is an inlet
manifold.
17. The refrigerant system as set forth in claim 13, wherein said
manifold is an intermediate manifold.
18. The refrigerant system as set forth in claim 17, wherein said
distributor insert extends along only a portion of said manifold,
and is not aligned with heat transfer tubes communicating into said
manifold, but is aligned with heat transfer tubes communicating out
of said manifold
19. The refrigerant system as set forth in claim 13, wherein the
heat exchanger is a microchannel heat exchanger.
20. The refrigerant system as set forth in claim 13, wherein said
dividing elements are flat plates having a cutout portion at an
outer periphery to provide clearance for said heat transfer tubes.
Description
RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/053,677, which was filed May 16, 2008.
BACKGROUND OF THE INVENTION
[0002] This application relates to heat exchangers of refrigerant
systems that utilize a distributor insert mounted within a
manifold, and incorporating dividing elements separating the
manifold into a plurality of chambers, each associated with at
least one heat exchange tube.
[0003] In recent years, much interest and design effort has been
focused on the efficient operation of heat exchangers (and
condensers and evaporators in particular) of refrigerant systems.
One relatively recent advancement in the heat exchanger technology
is the development and application of parallel flow, or so-called
microchannel or minichannel, heat exchangers (these two terms will
be used interchangeably throughout the text), as the condensers and
evaporators. Also, throughout the text, the reference will be made
to a heat rejection heat exchanger as a condenser, with the
understanding that the heat rejection heat exchanger may operate as
a gas cooler, at least for a portion of the time.
[0004] Such microchannel heat exchangers are provided with a
plurality of parallel heat exchange tubes, among which refrigerant
is distributed and flown in a parallel manner. The heat exchange
tubes are orientated generally substantially perpendicular to a
refrigerant flow direction in the inlet, intermediate and outlet
manifolds that are in flow communication with the heat exchange
tubes. When utilized in condenser and evaporator applications,
these heat exchangers may be designed in multi-pass configuration,
typically with a plurality of parallel heat exchange tubes within
each refrigerant pass, in order to obtain superior performance by
balancing and optimizing heat transfer and pressure drop
characteristics. Single-pass configurations are typically more
desirable in the evaporator applications, since the refrigerant
pressure drop plays a dominant role in the evaporator
performance.
[0005] However, there have been some obstacles to the use of the
microchannel heat exchangers within a refrigerant system. In
particular, a problem, known as refrigerant maldistribution,
typically occurs in the microchannel heat exchanger manifolds when
the two-phase flow enters the manifold. A vapor phase of the
two-phase flow has significantly different properties, moves at
different velocities and is subjected to different effects of
internal and external forces than a liquid phase. This causes the
vapor phase to separate from the liquid phase and to flow
independently. The separation of the vapor phase from the liquid
phase has raised challenges, such as refrigerant maldistribution in
parallel flow heat exchangers.
[0006] It is known in certain refrigerant systems to utilize a
distributor insert for delivering refrigerant into an evaporator
manifold. Such systems have been employed in refrigerated
merchandisers, such as refrigeration display cases. The proposed
inlet distributor insert utilized in refrigerant display cases
would not solve the problem of refrigerant maldistribution
mentioned above.
[0007] Another proposed heat exchanger is constructed of a
plurality of plates. The heat exchange refrigerant channels are
formed of spaced plates, and remote ends of those spaced plates
provide inlet plenums for each refrigerant channel. The plates
separate adjacent plenums, and an insert tube extends through the
plates and into the plenums. This tube includes a plurality of
orifices which direct refrigerant into the individual plenums. This
arrangement would not be practical for microchannel heat
exchangers, and would only be a practical construction for the one
type of heat exchanger formed of the spaced plates.
SUMMARY OF THE INVENTION
[0008] In the disclosed embodiments of this invention, a manifold
for a heat exchanger incorporates a distributor insert positioned
within a manifold cavity. The distributor insert has multiple
refrigerant distribution orifices of a small size protruding
through the distributor walls, and also has dividing elements
located on its periphery. Upon positioning the distributor insert
within the heat exchanger manifold, the dividing elements act as
manifold separation members by defining separate chambers within
the manifold cavity, with each chamber fluidly communicating with
at least one heat exchange tube positioned downstream, with respect
to refrigerant flow.
[0009] In one embodiment, the heat exchanger manifold is an inlet
manifold of an evaporator and, in another embodiment, the heat
exchanger manifold is an intermediate manifold of a condenser or an
evaporator.
[0010] While all separation chambers may be of an identical size
and the distributor dividing elements uniformly spaced, in one
embodiment, they are of a variable size to further fine tune
refrigerant distribution. Although the invention is disclosed in
relation to a two-phase refrigerant, it is also applicable to a
single-phase refrigerant and refrigerant-oil mixtures.
[0011] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 schematically shows a basic exemplary refrigerant
system.
[0013] FIG. 2 shows a portion of an inlet manifold of an inventive
heat exchanger.
[0014] FIG. 3 shows a portion of an intermediate manifold of an
inventive heat exchanger.
[0015] FIG. 4 shows an exemplary design of a distributor
insert.
[0016] FIG. 5A shows a cross-sectional view of an exemplary heat
transfer tube.
[0017] FIG. 5B shows a cross-sectional view of an exemplary
dividing element.
[0018] FIG. 5C shows a side view of an exemplary dividing element
of FIG. 5B.
[0019] FIG. 5D shows a cross-sectional view of another exemplary
dividing element.
[0020] FIG. 5E shows a side view of an exemplary dividing element
of FIG. 5D.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0021] A basic exemplary refrigerant system 20 is illustrated in
FIG. 1 including a compressor 22 compressing a refrigerant and
delivering it downstream into a condenser 24. From the condenser 24
the refrigerant passes through an expansion device 26 into an inlet
refrigerant pipe 28 leading into an evaporator 30. From the
evaporator 30, the refrigerant is returned to the compressor 22 to
complete the closed-loop refrigerant circuit.
[0022] A portion of the evaporator 30, that includes an inlet
refrigerant manifold 34 incorporating the present invention, is
illustrated in FIG. 2. The evaporator 30 is shown as a microchannel
heat exchanger, as such heat exchangers would particularly benefit
from this inventive design and construction. However, the benefits
of this invention can extend to other types of heat exchangers,
such as, for instance, round tube and plate fin heat exchangers,
and to various applications, such as, for instance, condenser
applications. Furthermore, although the benefits of the invention
will be disclosed in reference to a two-phase refrigerant flow
passing through the heat exchanger, single-phase refrigerant flows
and refrigerant-oil mixtures are also within the scope and can
benefit from the invention.
[0023] As shown in FIG. 2, the inlet refrigerant pipe 28 fluidly
communicates with a distributor insert 32, which provides a
refrigerant flow path along its longitudinal axis. An inlet
manifold 34 of the evaporator 30 receives the distributor insert
32, and in turn fluidly communicates with a plurality of heat
exchange tubes 36 positioned generally perpendicular to and
downstream, with respect to the direction of refrigerant flow, of
the inlet manifold 34. The inlet refrigerant pipe 28 may be
positioned at the end of the inlet manifold 34, in the middle of
the inlet manifold 34 or at any intermediate location in-between.
Further, the inlet refrigerant pipe 28 may comprise two inlet
refrigerant pipes connected at the opposite ends of the inlet
manifold 34 or at any intermediate locations. Obviously, more than
two inlet refrigerant pipes can be utilized, but all of them need
to be fluidly connected and provide refrigerant paths into the
distributor insert 32.
[0024] As known, a plurality of heat transfer fins 38 may be
disposed between and rigidly attached, usually by a furnace braze
process, to the heat exchange tubes 36, in order to enhance
external heat transfer and provide structural rigidity for the heat
exchanger 30. Also, as known, each heat exchange tube 36 of a
microchannel heat exchanger (evaporator) 30 typically has a
plurality of small internal channels 41 providing multiple parallel
refrigerant flow paths along longitudinal axis of each heat
exchange tube 36 (see FIG. 5A). The internal channels 41 enhance
internal heat transfer and also provide structural rigidity for the
heat exchanger 30.
[0025] As also illustrated in FIG. 2, a plurality of refrigerant
distribution orifices 42 of a small size are formed to protrude
through the walls of the distributor insert 32 and to provide the
refrigerant paths from an internal cavity of the distributor insert
32 into the inlet manifold 34. The distribution orifices 42 can be,
for instance, of a round shape, rectangular shape, oval shape or
any other shape. Furthermore, the distributor insert 32 has
dividing elements 44 located on its periphery and rigidly attached
to the outside walls of the distributor insert 32. Upon positioning
the distributor insert 32 within the inlet manifold 34 of the
evaporator 30, the dividing elements 44 form refrigerant separation
chambers 46 within the internal cavity of the inlet manifold 34,
with each chamber communicating refrigerant downstream to at least
one heat exchange tube 36. Typically, each separation chamber would
be fluidly connected to several refrigerant distribution orifices
42 and several heat exchange tubes 46.
[0026] As mentioned above, a plurality of small refrigerant
distribution orifices 42 is provided to direct the refrigerant from
the distributor insert 34 into a plurality of separation chambers
46 defined by adjacent dividing elements 44 of the distributor
insert 32 within the cavity of the inlet manifold 34. The distance
between the dividing elements 44 can be uniform or can be adjusted
to control the ultimate size of the separation chambers 46
associated with any particular cluster of heat transfer tubes 36.
This distance between the dividing elements 44 may vary from one
cluster of heat transfer tubes 36 to another, or in an extreme
case, from one heat transfer tube 36 to another. As an example, for
a single inlet refrigerant pipe 28 located at the end of the inlet
manifold 34, the size of the chambers 46 may be uniform along the
longitudinal axis of the manifold 34 or, for instance, may decrease
from the manifold inlet end to its remote end, where refrigerant
velocity is expected to be lower. Any particular configuration of
the dividing elements 44 could depend on operational parameters and
particular application.
[0027] The distributor insert 32 receives the two-phase refrigerant
from the inlet refrigerant pipe 28 and delivers this refrigerant,
through a plurality of small distribution orifices 42, into the
heat exchanger manifold 34 that has been divided into the
separation chambers 46 by the dividing elements 44 of the
distributor insert 32. A relatively small size of the distributor
insert 32 provides significant momentum for the refrigerant flow
preventing the phase separation of the two-phase refrigerant. The
plurality of the distribution orifices 42 uniformly directs the
two-phase refrigerant into the plurality of separation chambers 46
of the manifold 34 defined by the spaced dividing elements 44 of
the distributor insert 34. Since the size of the separation
chambers 46 is relatively small, the refrigerant liquid and vapor
phases do not have conditions and time to separate, as in the prior
art, when the two-phase refrigerant was expanded into the entire
inlet manifold cavity. Even in cases where some separation of the
refrigerant phases occurs, it would be within a relatively small
manifold chamber 46, and on average, the refrigerant distribution
would be still predominantly uniform across the entire heat
exchanger 30. Therefore, the inventive distributor concept having a
plurality of small distribution orifices 42 and dividing elements
44 prevents refrigerant maldistribution and assures uniform
refrigerant distribution into the heat exchange tubes 36. In this
manner, the refrigerant being delivered into the heat exchange
tubes 36 through the distributor insert orifices 42 and separation
chambers 46 of the inlet manifold 34 will not have different
quantities of vapor and liquid phases flowing through different
heat exchange tubes and heat exchanger tube clusters.
[0028] An outer periphery of the dividing elements 44 is tightly
received within an inner wall of the inlet manifold 34. Similarly,
an inner periphery of the dividing elements 44 is closely received
on an outer wall of the insert 32. In this manner, adjacent
separation chambers 46 are maintained predominantly isolated from
each other preventing refrigerant migration from one separation
chamber 46 to another. Therefore, the overall characteristics of
the refrigerant flow into the heat exchange tubes 36 can be
controlled such that the effects of phase separation and/or
refrigerant migration can be eliminated or minimized.
[0029] FIG. 3 shows another embodiment 300, wherein the manifold
301 is an intermediate manifold, downstream of heat exchange tubes
302, and feeding the refrigerant into heat exchange tubes 312. As
shown, the distributor insert 306 has orifices 308, a top separator
plate 304, and intermediate separator plates 310. This embodiment
functions as in the prior embodiment to reduce refrigerant phase
separation and maldistribution. In this embodiment, the heat
exchanger could be a condenser, or an evaporator.
[0030] The dividing elements 44 can be of any shape and form, such
as, for instance, flat plates (see FIG. 5B), as long as they do not
drastically block refrigerant flow into the heat exchange tubes 36
and isolate one separation chamber 46 from another (e.g. by a small
clearance or mechanical/chemical bonding). Furthermore, dividing
elements 44 may have cutouts 200, in case the heat exchange tubes
36 penetrate inside the inlet manifold 34 (see FIGS. 5B and 5C).
The dividing elements 44 may be attached to the distributor insert
32 mechanically (e.g. snapped into place into small groves
manufactured on the outer wall of the distributor insert 32), or by
brazing, welding or soldering. The dividing elements 44 may be also
attached to the inner wall of the inlet manifold 34 (e.g. by
furnace brazing). Both attachment processes can be performed, for
instance, during furnace brazing of the entire heat exchanger
30.
[0031] FIGS. 5D and 5E show another embodiment, wherein the
dividing elements 44 do not include the cutout 200, but do include
a groove or indentation 202. The purpose of this indentation is to
provide a holding cavity for brazing flux such that the distributor
insert can be inserted into a manifold and brazed upon construction
of the overall heat exchanger
[0032] In general, each of the disclosed embodiments teaches a
distributor insert which will receive refrigerant, and distribute
refrigerant through a plurality of orifices into separation
chambers defined between dividing elements. Since the insert and
the dividing elements are attached to each other as a rigid
sub-assembly, the entire assembly can be inserted into a manifold.
This will allow the use of this feature without requiring any
specific heat exchanger design, as has been the case in the prior
art.
[0033] Although an embodiment of this invention has been disclosed,
a worker of ordinary skill in the art would recognize that certain
modifications would come within the scope of this invention. For
that reason, the following claims should be studied to determine
the true scope and content.
* * * * *