U.S. patent application number 11/794970 was filed with the patent office on 2008-05-01 for parallel flow heat exchangers incorporating porous inserts.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Robert A. Chopko, Mikhail B. Gorbounov, Allen C. Kirkwood, Thomas D. Radcliff, Raymond A. Rust Jr., Michael F. Taras, Igor B. Vaisman, Parmesh Verma.
Application Number | 20080099191 11/794970 |
Document ID | / |
Family ID | 36777704 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080099191 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
May 1, 2008 |
Parallel Flow Heat Exchangers Incorporating Porous Inserts
Abstract
A parallel flow (minichannel or microchannel) evaporator
includes a porous member inserted at the entrance of the evaporator
channels which provides refrigerant expansion and pressure drop
controls resulting in the elimination of refrigerant
maldistribution and prevention of potential compressor
flooding.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Kirkwood; Allen C.;
(Brownsburg, IN) ; Chopko; Robert A.;
(Baldwinsville, NY) ; Rust Jr.; Raymond A.;
(Gosport, IN) ; Gorbounov; Mikhail B.; (South
Windsor, CT) ; Vaisman; Igor B.; (West Hartford,
CT) ; Verma; Parmesh; (Manchester, CT) ;
Radcliff; Thomas D.; (Vernon, CT) |
Correspondence
Address: |
MARJAMA MULDOON BLASIAK & SULLIVAN LLP
250 SOUTH CLINTON STREET, SUITE 300
SYRACUSE
NY
13202
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
36777704 |
Appl. No.: |
11/794970 |
Filed: |
December 29, 2005 |
PCT Filed: |
December 29, 2005 |
PCT NO: |
PCT/US05/47310 |
371 Date: |
July 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60649425 |
Feb 2, 2005 |
|
|
|
Current U.S.
Class: |
165/174 |
Current CPC
Class: |
F28F 9/0282 20130101;
F25B 41/30 20210101; F28F 13/003 20130101; F28D 1/05383 20130101;
F25B 39/028 20130101; F28F 9/028 20130101 |
Class at
Publication: |
165/174 |
International
Class: |
F28F 9/02 20060101
F28F009/02 |
Claims
1. A parallel flow (minichannel or microchannel) heat exchanger
comprising: an inlet manifold extending longitudinally and having
an inlet opening for conducting the flow of a fluid into said inlet
manifold and a plurality of outlet openings for conducting the flow
of fluid transversely from said inlet manifold; a plurality of
channels aligned in substantially parallel relationship and fluidly
connected to said plurality of outlet openings for conducting the
flow of fluid from said inlet manifold; and an outlet manifold
fluidly connected to said plurality of said channels for receiving
the flow of fluid therefrom; wherein said heat exchanger contains
at least one porous member positioned within the flow path of said
heat exchanger.
2. A parallel flow heat exchanger as set forth in claim 1 wherein
said heat exchanger is an evaporator.
3. A parallel flow heat exchanger as set forth in claim 1 wherein
said heat exchanger is a condenser.
4. A parallel flow heat exchanger as set forth in claim 1 wherein
said porous member is in the form of an insert positioned in at
least one channel.
5. A parallel flow heat exchanger as set forth in claim 4 wherein
said porous insert is positioned at the channel entrance.
6. A parallel flow heat exchanger of claim 5 wherein the porous
insert is positioned adjacent to the channel entrance.
7. A parallel flow heat exchanger of claim 5 wherein the porous
insert is positioned inside the channel.
8. A parallel flow heat exchanger of claim 1 wherein the porous
insert is positioned in the inlet manifold or in direct fluid
communication with the inlet manifold.
9. A parallel flow heat exchanger of claim 1 wherein the porous
insert is positioned in the outlet manifold or in direct fluid
communication with the outlet manifold.
10. A parallel flow heat exchanger of claim 1 wherein the porous
insert is positioned in the intermediate manifold or in direct
fluid communication with the intermediate manifold.
11. The porous insert of claim 1 wherein said insert is made from a
material selected from the group consisting of a metal and a
ceramic.
12. The porous insert of claim 1 wherein said insert is made from a
material selected from the group consisting of sintered metal,
compressed metal, metal wool or metal wire.
13. The porous insert of claim 1 wherein said insert is positioned
longitudinally along the manifold.
14. The porous insert of claim 1 wherein there is a gap between
said insert and the manifold inner wall surface.
15. The porous insert of claim 1 wherein said insert is a composite
of at least two different inserts.
16. The porous insert of claim 1 wherein said insert cross-section
is non-rectangular.
17. The porous insert of claim 16 wherein said insert cross-section
is a portion of a circle.
18. The porous insert of claim 1 wherein said inserts are of
variable characteristics between at least two channels.
19. The insert of claim 16 wherein the variable characteristics are
selected from the group of porosity, depth, insertion depth, and
material.
20. A parallel flow (minichannel or microchannel) heat exchanger
comprising: an inlet manifold extending longitudinally and having
an inlet opening for conducting the flow of a fluid into said inlet
manifold and a plurality of outlet openings for conducting the flow
of fluid transversely from said inlet manifold; a plurality of
channels aligned in substantially parallel relationship and fluidly
connected to said plurality of outlet openings for conducting the
flow of fluid from said inlet manifold; and an outlet manifold
fluidly connected to said plurality of said channels for receiving
the flow of fluid therefrom; wherein said heat exchanger contains
at least one porous member positioned within the flow path of said
heat exchanger, wherein said porous member is designed to provide
for at least one of an expansion control and a pressure drop
control in the system.
21. A parallel flow heat exchanger as set forth in claim 20 wherein
said heat exchanger is an evaporator.
22. A parallel flow heat exchanger as set forth in claim 20 wherein
said heat exchanger is a condenser.
23. The heat exchanger of claim 20 wherein the porous member
functions as a primary expansion device.
24. The heat exchanger of claim 20 wherein the porous member
functions as a secondary expansion device.
25. A parallel flow heat exchanger as set forth in claim 20 wherein
said porous member is in the form of an insert positioned in at
least one channel.
26. A parallel flow heat exchanger as set forth in claim 25 wherein
said porous insert is positioned at the channel entrance.
27. A parallel flow heat exchanger of claim 26 wherein the porous
insert is positioned adjacent to the channel entrance.
28. A parallel flow heat exchanger of claim 26 wherein the porous
insert is positioned inside the channel.
29. A parallel flow heat exchanger of claim 20 wherein the porous
insert is positioned in the inlet manifold or in direct fluid
communication with inlet manifold.
30. A parallel flow heat exchanger of claim 20 wherein the porous
insert is positioned in the outlet manifold or in direct fluid
communication with outlet manifold.
31. A parallel flow heat exchanger of claim 20 wherein the porous
insert is positioned in the intermediate manifold or in direct
fluid communication with intermediate manifold.
32. The porous insert of claim 20 wherein said insert is made from
a material selected from the group consisting of a metal and a
ceramic.
33. The porous insert of claim 20 wherein said insert is made from
a material selected from the group consisting of sintered metal,
compressed metal, metal wool or metal wire.
34. The porous insert of claim 20 wherein said insert is positioned
longitudinally along the manifold.
35. The porous insert of claim 20 wherein there is a gap between
said insert and the manifold inner wall surface.
36. The porous insert of claim 20 wherein said insert is a
composite of at least two different inserts.
37. The porous insert of claim 20 wherein said insert cross-section
is non-rectangular.
38. The porous insert of claim 37 wherein said insert cross-section
is a portion of a circle.
39. The porous insert of claim 20 wherein said inserts are of
variable characteristics between at least two channels.
40. The insert of claim 39 wherein the variable characteristics are
selected from the group of porosity, depth, insertion depth, and
material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Reference is made to and this application claims priority
from and the benefit of U.S. Provisional Application Ser. No.
60/649,425, filed Feb. 2, 2005, and entitled PARALLEL FLOW
EVAPORATOR INCORPORATING POROUS CHANNEL INSERTS, which application
is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to air conditioning, heat
pump 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 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
refrigerant 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
furnace-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 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 and
gravity 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 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 (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.
[0009] Moreover, maldistribution phenomenon may cause the two-phase
(zero superheat) conditions at the exit of some channels, promoting
potential flooding at the compressor suction that may quickly
translate into the compressor damage.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the present invention to
provide for a system and method which overcome the problems of the
prior art described above.
[0011] The objective of the present invention is to introduce a
pressure drop control for the parallel flow (microchannel or
minichannel) evaporator that will essentially equalize pressure
drop through the heat exchanger circuits and therefore eliminate
refrigerant maldistribution and the problems associated with it.
Further, it is the objective of the present invention to provide
refrigerant expansion at the entrance of each channel, thus
eliminating a predominantly two-phase flow in the inlet manifold,
which is one of the main causes for refrigerant maldistribution. It
has been found that the introduction of a porous media inserted in
each parallel flow evaporator channel, or at the entrance of each
parallel flow evaporator channel, accomplishes these objectives.
For instance, these porous media inserts can be brazed in each
channel during furnace brazing of the entire heat exchanger,
chemically bonded or mechanically fixed in place. Furthermore,
these inserts can be used as primary (and the only) expansion
devices for low-cost applications or as secondary expansion
devices, in case precise superheat control is required and a
thermostatic expansion valve (TXV) or an electronic expansion valve
(EXV) is employed as a primary expansion device.
[0012] Any suitable porous insert which accomplishes the above
objectives may be used. Suitable and inexpensive porous inserts may
be made of sintered metal, compressed metal, such as steel wool,
specialty designed porous ceramics, etc. When inexpensive porous
media insert is placed in each channel of the parallel flow
evaporator, or at the entrance of each parallel flow evaporator
channel, it represents a major resistance to the refrigerant flow
within the evaporator. In such circumstances, the main pressure
drop region will be across these inserts and the variations in the
pressure drop in the channels or in the manifolds of the parallel
flow evaporators will play a minor (insignificant) role. Further,
since refrigerant expansion is taking place at the entrance to each
channel, a predominantly single-phase liquid refrigerant is flown
through the inlet manifold, especially in the case when the porous
inserts are utilized as the primary and the only expansion devices.
Hence, uniform refrigerant distribution is achieved, evaporator and
system performance is enhanced and, at the same time, precise
superheat control is not lost (whenever required). Furthermore, low
extra cost for the proposed method makes this invention very
attractive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a farther understanding of the objects of the invention,
reference will be made to the following detailed description of the
invention which is to be read in connection with the accompanying
drawing, where:
[0014] FIG. 1 is a schematic illustration of a parallel flow heat
exchanger in accordance with the prior art.
[0015] FIG. 2 is a partial side sectional view of one embodiment of
the present invention.
[0016] FIG. 3 is an end view of a porous insert positioned at the
entrance to a channel of the present invention.
[0017] FIG. 4 is a perspective view of the porous insert
illustrated in FIG. 3.
[0018] FIG. 5a is a side sectional view illustrating a further
embodiment of the present invention.
[0019] FIG. 5b is a side sectional view illustrating yet a further
embodiment of the present invention.
[0020] FIG. 6 is an end view of a plurality of channels in one
embodiment of the invention.
[0021] FIG. 7a is a perspective view which illustrates a porous cap
embodiment of the invention.
[0022] FIG. 7b is a perspective view which illustrates a second
porous cap embodiment.
[0023] FIG. 7c is a perspective view which illustrates a third
porous cap embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Referring now to FIG. 1, a parallel flow (minichannel or
microchannel) heat exchanger 10 is shown which includes an inlet
header or manifold 12, an outlet header or manifold 14 and a
plurality of parallel disposed channels 16 fluidly interconnecting
the inlet manifold 12 to the outlet manifold 14. Typically, the
inlet and outlet headers 12 and 14 are cylindrical in shape, and
the channels 16 are tubes (or extrusions) of flattened or round
cross-section. Channels 16 normally have a plurality of internal
and external heat transfer enhancement elements, such as fins. For
instance, external fins 18, uniformly disposed therebetween for the
enhancement of the heat exchange process and structural rigidity,
are typically furnace-brazed. Channels 16 may have internal heat
transfer enhancements and structural elements as well.
[0025] In operation, refrigerant flows into the inlet opening 20
and into the internal cavity 22 of the inlet header 12. From the
internal cavity 22, the refrigerant, in the form of a liquid, a
vapor or a mixture of liquid and vapor (the most typical scenario
in the case of an evaporator with an expansion device located
upstream) enters the channel openings 24 to pass through the
channels 16 to the internal cavity 26 of the outlet header 14. From
there, the refrigerant, which is now usually in the form of a
vapor, in the case of evaporator applications, flows out of the
outlet opening 28 and then to the compressor (not shown).
Externally to the channels 16, air is circulated preferably
uniformly over the channels 16 and associated fins 18 by an
air-moving device, such as fan (not shown), so that heat transfer
interaction occurs between the air flowing outside the channels and
refrigerant within the channels.
[0026] According to one embodiment of the present invention, a
porous insert 30 is inserted at the entrance of each channel 16.
When the channels 16 have internal structural elements such as
support members 16a (FIG. 3), usually included for structural
rigidity and/or heat transfer enhancement purposes, the porous
inserts 30 incorporate slots 32 to accommodate the support members
16a when in position at the channel entrance (See FIG. 4). Further,
in case a various degree of expansion and/or hydraulic impedance
are desired to be provided by the inserts 30 or 32, for instance,
to counter-balance other abovementioned factors effecting
refrigerant distribution amongst the channels 16, characteristics
such as porosity values or geometric dimensions (insert depth,
insertion depth, etc.) of the inserts can be altered to achieved
the desired result for each channel 16.
[0027] FIG. 5a illustrates another embodiment in which all the
entrances to the channels 16 are covered by a single porous member
34 positioned within a manifold 40. Further, a support member 36
may be used to assist in setting up a relative position of the
porous member 34 and the channels 16 within the manifold 40. It
should be noted that an assembly of the porous member 34 and
support member 36 can be manufactured from and combined in a single
member made from porous material.
[0028] FIG. 5b is a further embodiment of the structure of FIG. 5a
in which the porous member is a composite of two different porous
materials 34 and 34a. Obviously, a number of composite materials
within the porous member can be more than two.
[0029] FIG. 6 illustrates a side view of FIG. 5a.
[0030] FIG. 7a illustrates a unitized elongated porous member 34b
which seals multiple channels 16 at a predetermined distance from
the channel entrance.
[0031] FIG. 7b illustrates an elongated porous member 34c which
caps the ends of multiple channels 16.
[0032] FIG. 7c a modification of the structure of FIG. 7b in which
the porous member 34d is accurate in shape and caps the ends of the
channels 16. The shape of the porous member 34d can be of any
suitable configuration, rather than a rectangular in cross-section.
Further, the porous member 34d is preferably positioned within the
manifold 40 in such way that there is a gap between the inner wall
of the manifold 40 and the porous member 34a allowing for more
uniform refrigerant distribution prior to entering the porous
member 34d and channels 16.
[0033] It should be understood that any type of porous member
and/or material which accomplishes the objectives of the present
invention may be used. Similarly, as illustrated by FIGS. 2-7, any
design or configuration which accomplishes the objectives of the
invention may be employed in the use of the present invention.
[0034] Also, it has to be noted that the porous inserts can be used
in the condenser and evaporator applications within intermediate
manifolds as well. For instance, if a heat exchanger has more than
one refrigerant pass, an intermediate manifold (between inlet and
outlet manifolds) is incorporated in the heat exchanger design. In
the intermediate manifold, refrigerant is typically in a two-phase
state, and such heat exchanger configurations can similarly benefit
from the present invention by incorporating the porous inserts into
such intermediate manifolds. Further, the porous inserts can be
placed into an inlet manifold of the condenser and an outlet
manifold of the evaporator for providing only hydraulic resistance
uniformity and pressure drop control and with less effect on
overall heat exchanger performance.
[0035] Since, for particular applications, the various factors that
cause the maldistribution of refrigerant to the channels are
generally known at the design stage, the inventors have found it
feasible to introduce the design features that will counter-balance
them in order to eliminate the detrimental effects on the
evaporator and overall system performance as well as potential
compressor flooding and damage. For instance, in many cases, it is
generally known whether the refrigerant flows into the inlet
manifold at a high or low velocity and how the maldistribution
phenomenon is affected by the velocity values. A person of
ordinarily skill in the art will recognize how to apply the
teachings of this invention to other system characteristics.
[0036] While the present invention has been particularly shown and
described with reference to the preferred embodiments 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.
* * * * *