U.S. patent application number 11/908754 was filed with the patent office on 2008-08-07 for flat tube single serpentine co2 heat exchanger.
This patent application is currently assigned to CARRIER COMMERCIAL REFRIGERATION, INC.. Invention is credited to Yu Chen, Hans-Joachim Huff, Tobias H. Sienel, Parmesh Verma.
Application Number | 20080184734 11/908754 |
Document ID | / |
Family ID | 37024107 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080184734 |
Kind Code |
A1 |
Verma; Parmesh ; et
al. |
August 7, 2008 |
Flat Tube Single Serpentine Co2 Heat Exchanger
Abstract
A refrigeration system includes 0 compressor for driving 0
refrigerant along flow path in at least a first mode of system; a
first heat exchanger along the flow path downstream of the
compressor in the first mode; a second heat exchanger along the
flow path upstream the compressor in the first mode; and a pressure
regulator or expansion device in the flow path downstream of the
first heat exchanger and upstream of the second heat exchanger in
the first mode, wherein at least one of the first heat exchanger
and the second heat exchanger comprises a flat tube heat
exchanger.
Inventors: |
Verma; Parmesh; (Manchester,
CT) ; Sienel; Tobias H.; (East Hampton, MA) ;
Huff; Hans-Joachim; (West Hartford, CT) ; Chen;
Yu; (East Hartford, CT) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C. (UTC)
900 CHAPEL STREET, SUITE 1201
NEW HAVEN
CT
06510-2802
US
|
Assignee: |
CARRIER COMMERCIAL REFRIGERATION,
INC.
Charlotte
NC
|
Family ID: |
37024107 |
Appl. No.: |
11/908754 |
Filed: |
December 30, 2005 |
PCT Filed: |
December 30, 2005 |
PCT NO: |
PCT/US05/47527 |
371 Date: |
September 14, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60663957 |
Mar 18, 2005 |
|
|
|
Current U.S.
Class: |
62/515 ;
165/177 |
Current CPC
Class: |
F28D 2021/0073 20130101;
F28F 9/262 20130101; F25D 2323/00271 20130101; F25B 2309/061
20130101; F25B 2500/01 20130101; F28D 1/0478 20130101; F25B 9/008
20130101; F25D 2317/0661 20130101; F25D 2317/0651 20130101; F25D
2323/00264 20130101; F25B 39/00 20130101; F25D 19/02 20130101 |
Class at
Publication: |
62/515 ;
165/177 |
International
Class: |
F25B 39/02 20060101
F25B039/02; F28F 1/10 20060101 F28F001/10 |
Claims
1. A refrigeration system comprising: a compressor for driving a
refrigerant along a flow path in at least a first mode of system
operation; a first heat exchanger along the flow path downstream of
the compressor in the first mode; a second heat exchanger along the
flow path upstream of the compressor in the first mode; and a
pressure regulator or expansion device in the flow path downstream
of the first heat exchanger and upstream of the second heat
exchanger in the first mode, wherein at least one of the first heat
exchanger and the second heat exchanger comprises a flat tube heat
exchanger.
2. The system of claim 1 wherein the flat tube heat exchanger
comprises a conduit having a substantially rectangular outside
shape and at least one internal flow port for carrying refrigerant
flow.
3. The system of claim 2 wherein the rectangular outside shape has
a short side and a long side, and wherein the flow paths are
arranged with the short side facing a flow of heat exchange
fluid.
4. The system of claim 3, wherein the short side has a length of
between about 0.5 and about 4.0 mm, and the long side has a length
of between about 12.7 and about 101.6 mm.
5. The system of claim 2, wherein the conduit has a flow hydraulic
diameter of between about 0.1 and about 3.0 mm.
6. The system of claim 1 wherein the flat tube heat exchanger
comprises a flat tube in a serpentine configuration defining a
plurality of substantially parallel flow paths.
7. The system of claim 6 wherein the flat tube heat exchanger is
positioned having the substantially parallel flow paths arranged in
a substantially vertical plane.
8. The system of claim 7, wherein the fins are present in a fin
density of up to about 20 fins per inch.
9. The system of claim 6, wherein the serpentine configuration has
a tube pitch of between about 5 and about 50 mm.
10. The system of claim 1, wherein the first heat exchanger
comprises a plurality of rows of flat tube heat exchanger, and
wherein the rows have a row pitch of between about 12.7 and about
50 mm.
11. The system of claim 1 further comprising fins extending from
the flat tube heat exchanger across a flow path for heat exchange
medium.
12. The system of claim 1 further comprising fins extending from
the flat tube heat exchanger and having slots or louvers to allow
drainage of condensation on the heat exchanger and fins.
13. The system of claim 1 wherein the flat tube heat exchanger has
a single inlet and a single refrigerant outlet.
14. The system of claim 1 wherein the flat tube heat exchanger
comprises flat tubes made of copper or aluminum.
15. The system of claim 1 wherein the flat tube heat exchanger
comprises multiple rows of flat tube heat exchanger components
arranged along a flow path of heat exchange fluid so as to provide
counter flow heat exchange between refrigerant in the flat tube
heat exchanger and heat exchange fluid.
16. The system of claim .about.1 wherein: the refrigerant
comprises, in major mass part, CO.sub.2; and the first and second
heat exchangers are refrigerant-air heat exchangers.
17. The system of claim 1, wherein the system is adapted to operate
under a transcritical vapor compression mode.
18. A beverage cooling device comprising the system of claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This applications claims the benefit of the filing date of
earlier filed provisional application Ser. No. 60/663,957 filed
Mar. 18, 2005. Further, copending application docket 05-258-WO,
entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR
COMPRESSION SYSTEM and filed on even date herewith, and the
aforesaid provisional application Ser. No. 60/663,962, disclose
prior art and inventive cooler systems. The disclosure of said
applications is incorporated by reference herein as if set forth at
length.
BACKGROUND OF THE INVENTION
[0002] The invention relates to the design of the tube of a heat
exchanger and, more particularly, to the design of a heat exchanger
for use in applications where space for the heat exchanger is in
short supply, and/or in connection with transcritical vapor
compression systems.
[0003] Heat exchange efficiency is a concern in connection with
heat exchangers, for example heat exchangers used in various
refrigeration and other air handling applications. Various types of
heat exchangers have been provided, including tubes having fins and
the like. The need remains, however, for a heat exchanger
configuration which provides excellent heat exchange efficiency
while occupying a relatively small space.
[0004] It is the primary object of the present invention to provide
a heat exchanger meeting this need.
[0005] Other objects and advantages of the present invention will
appear herein.
SUMMARY OF THE INVENTION
[0006] According to the invention, the foregoing objects and
advantages have been attained.
[0007] According to the invention, a refrigeration system is
provided which includes a compressor for driving a refrigerant
along a flow path in at least a first mode of system operation; a
first heat exchanger along the flow path downstream of the
compressor in the first mode; a second heat exchanger along the
flow path upstream of the compressor in the first mode; and a
pressure regulator or expansion device in the flow path downstream
of the first heat exchanger and upstream of the second heat
exchanger in the first mode, wherein at least one of the first heat
exchanger and the second heat exchanger comprises a flat tube heat
exchanger.
[0008] The flat tube heat exchanger is preferably a heat exchanger
defined by a serpentine bending of a single flat tube heat
exchanger. Further, the flat tube heat exchanger itself
advantageously comprises a conduit for carrying refrigerant,
wherein the conduit has a height or minor dimension, and a width or
major dimension, and wherein the heat exchanger is arranged with
the short dimension facing into the flow of heat exchange medium
such as air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic illustration of a vapor compression
system;
[0010] FIG. 2 is an illustration of a cassette with a single
serpentine flat tube heat exchanger according to the invention;
[0011] FIG. 3 is a schematic illustration of CO.sub.2 vapor
compression system cassette;
[0012] FIGS. 4 and 5 are schematic illustrations a flat tube single
serpentine single row heat exchanger according to the
invention;
[0013] FIG. 6 illustrates a flat tube two row counterflow
serpentine heat exchanger according to the invention;
[0014] FIGS. 7 and 8 are illustrations of a flat tube single
serpentine evaporator according to the invention; and
[0015] FIGS. 9(a) and 9(b) are schematic cross sections of
embodiments of the flat tube heat exchanger of the present
invention.
DETAILED DESCRIPTION
[0016] The invention relates to vapor compression systems and, more
particularly, to a heat exchanger tube configuration for such
systems, particularly for transcritical vapor compression systems
such as those operated with CO.sub.2.
[0017] For transcritical CO.sub.2 refrigeration systems, to
maintain peak efficiencies it is critical to minimize the
temperature difference between the hot and cold fluid at the exit
of the high-side (gas cooler) heat exchanger. Due to higher
densities of CO.sub.2 in comparison with conventional HFC, for a
given temperature, pressure, and mass flux, the refrigerant-side
heat transfer coefficients and pressure drop for CO.sub.2 are
smaller. Thus for CO.sub.2 heat exchangers it is imperative to have
higher refrigerant mass fluxes which will increase not only
CO.sub.2 heat transfer coefficients but also CO.sub.2 pressure
drop. However, the net effect should be to increase overall heat
exchanger effectiveness while limiting the CO.sub.2 pressure drop
below a certain limit such that higher cycle efficiency can be
attained.
[0018] For some applications, such as bottle or beverage coolers
and other refrigeration applications, due to air-side fouling
constraints, additional air-side surface area in the form of fins
is limited thus limiting the total surface area. This necessitates
a heat exchanger to have reduced air-side blockage and
significantly reduced resistance on the refrigerant-side i.e.
CO.sub.2.
[0019] Additionally, in the case of an evaporator, the heat
exchanger should have uniform refrigerant distribution and
satisfactory condensate drainage in order to improve overall heat
exchanger effectiveness and reliable operation of the
compressor.
[0020] The heat exchanger combines the benefits of flat surfaces,
single/multiple ports, single serpentine, multiple rows,
counterflow, cross-counterflow, high heat transfer coefficients,
low cost, suitable materials, corrosion resistant, high burst
strength, ease of manufacturing, and reduced air blockage which
helps to achieve size, efficiency, cost and reliability constraints
of a CO.sub.2 bottle cooler refrigeration system.
[0021] One of the ways to increase overall heat exchanger
effectiveness is to have a flat tube heat exchanger.
[0022] FIG. 1 shows a refrigeration system 10 having a compressor
12, a heat rejection heat exchanger 14 which in a normal mode of
operation, as illustrated by the arrows in FIG. 1, is a downstream
heat exchanger when considered with respect to compressor 12, an
expansion device 16 which is positioned downstream of heat
exchanger 14, and a heat absorption heat exchanger 18 which is
downstream of expansion device 16. Flow in system 10 from heat
exchanger 18 returns back to compressor 12.
[0023] FIG. 1 shows a first flow 20 of heat exchange medium, for
example, air, which is driven across heat exchanger 14 by a fan 22.
This flow serves to take the heat rejected by refrigerant passing
through heat exchanger 14.
[0024] FIG. 1 also shows another flow 24 of air which is driven by
a fan 26 past heat exchanger 18. Flow 24 represents a portion of
air in the treated space, and this air is cooled by refrigerant
passing through heat exchanger 18.
[0025] As set forth above, in accordance with the present
invention, an improved heat exchanger tube configuration is
provided which is particularly useful in vapor compression systems
which use a transcritical refrigerant, for example, CO.sub.2.
[0026] FIG. 2 shows a portion of a transcritical vapor compression
system 28 and shows compressor 12, heat exchanger 14 and heat
exchanger 18 in positions they occupy in this particular
configuration.
[0027] FIG. 3 is a side schematic of a similar structure, and also
shows compressor 12, heat exchanger 14 and heat exchanger 18.
[0028] As will be set forth below, the flat tube heat exchanger in
accordance with the present invention provides enhanced function
per space occupied by the heat exchanger tubes, and can therefore
be utilized to allow the heat exchanger to take up less space,
thereby freeing up such space for use in other capacities. For
example, it should readily apparent from a consideration of FIGS. 2
and 3 that the flat tube heat exchanger of the present invention,
when implemented as heat exchanger 14, allows for a single heat
exchanger to be used as shown in FIG. 2 as compared to several
different components of the heat exchanger as shown in FIG. 3.
[0029] FIGS. 4-8 illustrate various embodiments of the present
invention in connection with a flat tube heat exchanger as
described.
[0030] FIG. 4 shows a schematic illustration of flat tube 30 which
is formed into a substantially serpentine structure as illustrated,
and which is positioned to receive air flow 32 such that air flows
along the long dimension of flat tube 30 and thereby improves heat
exchange efficiency between the medium of air flow 32 and the
refrigerant within flat tube 30.
[0031] FIG. 4 further shows fins 34 which can advantageously be
positioned extending from flat tubes 30 or otherwise connected with
a flat tube heat exchanger according to the invention, so as to
extend further across air flow 32 and enhance heat exchange
capacity between the medium and the refrigerant.
[0032] FIGS. 5 and 6 further illustrate a flat tube heat exchanger
in accordance with present invention. FIG. 5 shows a single row
flat tube heat exchanger configured into a substantially serpentine
configuration or structure 36 such that the single flat tube
defining the structure is bent in a serpentine manner to define a
plurality of portions 37 or flow paths, which are substantially
parallel to each other. In the embodiment shown in FIG. 5, as in
the embodiment of FIG. 4, there is a single refrigerant inlet 38
and a single refrigerant outlet 40 to handle flow of refrigerant
through structure 36. Structure 36 is advantageously positioned to
interact with a flow 39 of air as shown, preferably with the narrow
edge of flat tube 30 facing into flow 39, and with the longer
dimension or width of flat tube 30 being substantially parallel to
flow 39.
[0033] As shown, the flat tube heat exchanger in accordance with
the present invention is defined by a refrigerant conduit which has
a substantially rectangular outer shape and which has an
internally-defined flow passage for carrying refrigerant.
[0034] The outside shape of flat tube 46, also referring to FIGS.
9a and b, is substantially rectangular. This substantially
rectangular outer shape has a relatively shorter side 47 and a
relatively longer side 49, and the substantially shorter side 47
has a length which is preferably between about 0.45 and about 4 mm.
The relatively longer side 49 or dimension of the rectangular out
shape preferably has a length or dimension which is between about
12.7 and about 101.6 mm.
[0035] With reference also to FIGS. 7 and 8, it should be readily
apparent that the substantially serpentine structure 36 of flat
tube heat exchanger in accordance with the present invention
defines a series of substantially parallel flow paths. In
accordance with the present invention, it has been found that a
tube pitch 50, or distance between the tubes of the substantially
parallel flow paths, as measured from transverse center to center,
is preferably between about 5 and about 50 mm. As shown in FIGS. 4
and 7, it is preferred to position fins, where possible, to further
enhance heat exchange as desired. When possible to include fins, it
is preferred that such fins be positioned in a fin density of up to
about 20 fins/inch.
[0036] From a consideration of FIG. 6, it should also be readily
apparent that serpentine substantially flat tube heat exchanger
structures 36 can be provided in a plurality of rows 42, 44 so as
to treat a flow 39 of air through a first row 42 and then through
second row 44. In this regard, it is preferable in accordance with
the present invention to position such rows with a row pitch 52, or
distance from the center of each row to the center of a next row,
of between about 12.7 and about 50 mm. In accordance with the
present invention, heat exchangers can be provided with up to at
least about 20 rows, and will provide excellent results in
accordance with the present invention.
[0037] As set forth above, the internal flow path for refrigerant
defined within a flat tube heat exchanger can have a variety of
different shapes. FIGS. 9a and 9b illustrate two embodiments. In
the embodiment of FIG. 9a, a cross section through a flat tube 46
in accordance with the present invention is shown wherein the
entire internal space of flat tube 46 is provided for flow of
refrigerant.
[0038] FIG. 9b, on the other hand, shows flat tube 46 having flow
passages defined as a series of substantially circular flow paths
48, in this case five (5) circular flow paths, which extend in
substantially parallel relationship along the length of flat tube
46.
[0039] Such a heat exchanger, as described above, provides higher
overall heat transfer coefficients owing to higher refrigerant mass
fluxes (hence higher CO.sub.2 heat transfer coefficient) and lower
air-side pressure drop due to reduced air-side blockage by a flat
tube compared to a conventional round tube. Based on the flow
cross-sectional area of the flat tube, the overall length of the
flat tube could be designed such that the CO.sub.2 pressure drop is
below an acceptable limit enabling higher cycle efficiencies for
the range of operating conditions.
[0040] Additionally, for operation as an evaporator, the use of a
single circuit (one inlet and one outlet) could eliminate CO.sub.2
maldistribution, which is inherently present in the case of a heat
exchanger (conventional or flat tube) with multiple inlets and
outlets. Moreover the heat exchanger orientation should be such
that the tubes lie in the vertical plane as shown in FIG. 4 and the
fins can be provided with slots/louvers. This would ensure
satisfactory condensate drainage from flat tube and fin surfaces,
which would otherwise be a limiting factor for use of a flat-tube
heat exchanger as an evaporator.
[0041] The flat tube heat exchanger could have one or multiple
ports. Multiple ports help to withstand high operating pressures,
an inherent characteristic of a transcritical CO.sub.2 vapor
compression refrigeration system, and reduces CO.sub.2 pressure
drop which in turn helps to improve thermal performance.
[0042] The flat tube (single or multi ports) could be easily made
out of Copper or Aluminum or other suitable material that can
withstand high burst pressures of transcritical CO.sub.2
refrigeration system and could be bent and/or brazed at one or both
ends to form one continuous serpentine heat exchanger as shown in
the drawings. The fins could be connected mechanically or brazed to
the flat surface of the tubes. Moreover the tube and/or fin
material may be treated (coating, heat etc.) to increase corrosion
resistance of such heat exchangers.
[0043] In another design, multiple rows of these flat tube single
serpentine heat exchangers could be interconnected while
maintaining single circuiting and with flow going from one row to
another such that it closely resembles counter-flow arrangement
(between air and CO.sub.2) which is well known for high efficiency.
Counter-flow arrangement is very critical for CO.sub.2 gas coolers
for which the temperature gradient between the hot and cold fluids
must be a minimum to maintain peak cycle efficiency.
[0044] Such a heat exchanger would be very useful for CO.sub.2
bottle cooler applications wherein the design of the heat exchanger
is highly constrained by space and cost limitations and existing
round-tube plate fin heat exchangers cannot provide a feasible
solution.
[0045] This invention is especially beneficial for compact
commercial refrigeration systems such as bottle coolers etc.
[0046] Existing heat exchangers for vapor compression systems are
typically round-tube plate-fin heat exchangers with tube diameters
of 1-7 mm or larger. For transcritical CO.sub.2 vapor compression
systems such tubes provide low efficiency due to higher density of
CO.sub.2 compared with conventional HFC refrigerants like R134a,
R404a etc. Flat tube (multiple ports) heat exchangers with flow
cross-sectional area much smaller than typical round tube heat
exchangers are well known to reduce air-side flow resistance and
improve heat transfer coefficients on the refrigerant side.
However, use of such heat exchangers is limited by major technical
challenges like maldistribution of refrigerant, poor condensate
drainage, reduced burst strength, cross-flow arrangement, and high
cost and complexity of fabrication including, but not limited to,
expensive brazing of multiple tubes connected to manifolds at
either ends, brazing of fins to tube surfaces, and low thermal
conductivity material of the tubes for ease of brazing etc.
[0047] Such a heat exchanger is not found to exist for
transcritical CO.sub.2 bottle cooler systems wherein minimization
of the temperature gradient between hot and cold fluids at the exit
of the gas cooler (high-side heat exchanger) is highly critical to
maintain peak-efficiency.
[0048] For a bottle cooler evaporator, the single serpentine
vertical tube configuration eliminates major technical challenges
like maldistribution and condensate drainage which otherwise would
limit use of such heat exchangers as evaporators, while still
maintaining high CO.sub.2 heat transfer coefficients and reduced
CO.sub.2 pressure drop.
[0049] The heat exchanger combines benefits of flat surfaces,
single or multiple ports, single serpentine, multiple rows, high
heat transfer coefficients, low cost, suitable materials, corrosion
resistance, high burst strength, ease of manufacturing, and reduced
air blockage which helps to achieve size, efficiency, cost and
reliability constraints of a bottle cooler refrigeration
system.
[0050] The compact characteristic of the flat surface heat
exchanger can allow changes to the physical location of the heat
exchanger inside the beverage cooler such that the entire footprint
of the beverage cooler can be reduced while maintaining or
increasing the system efficiency. For example, the high-side heat
exchanger can be moved to other locations, thereby creating
additional space which can be utilized for other purposes such as
air management for the hot or cold surfaces etc.
[0051] The compact characteristics of such a heat exchanger would
also result in reduction in the amount of refrigerant or charge
within the refrigeration system and therefore reduce cost which is
highly constrained for bottle cooler applications.
[0052] As set forth above, range of different specifications of
such flat tube heat exchangers could be, tube width or major
dimension from 12.7 mm to 101.6 mm; tube height or minor dimension
from 0.5 mm to 4 mm; single or multi-port, circular or non-circular
ports, flow hydraulic diameter from 0.1 mm to 3 mm; tube pitch or
transverse center to center distance between tubes from 5 mm to 50
mm; row pitch or longitudinal center to center distance between
tubes from 12.7 mm to 50 mm; fin density from 0 to 20 fins per
inch, single or multiple rows up to 20.
[0053] A preferred embodiment proposed for the high-side heat
exchanger or gas cooler for bottle or beverage cooler applications
would have, 25.4 mm tube width, 2.0 mm tube height, 12 circular
ports, 11.0 mm port hydraulic diameter, 12.7 mm tube pitch, 4 fins
per inch, single row heat exchanger.
[0054] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, when implemented as a
remanufacturing of an existing system or reengineering of an
existing system configuration, details of the existing
configuration may influence details of the implementation.
Accordingly, other embodiments are within the scope of the
following claims.
* * * * *