Note: Descriptions are shown in the official language in which they were submitted.
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D E S C R I P T I O N
Title
CONDENSER FOR AIR COOLED CHILLERS
Background of the Invention
The present invention is directed to air cooled
condensers for heating, ventilating and air conditioning (HVAC)
systems. More specifically, the present invention is directed
to aluminum heat exchangers for use in large air cooled air
conditioning chillers, such chillers cooling a transport fluid
for use in air conditioning elsewhere. In particular the
present invention applies to a condenser using microchannel
tubing, also known as parallel flow tubing or multi-path
tubing.
HVAC condensers presently use fin and tube coils,
primarily with copper tubes and aluminum fins. A significant
weight reduction of the overall unit could be accomplished if
the tubes were also formed of aluminum and then brazed or glued
to the fins. Small sized brazed aluminum heat exchangers as
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microchannel tubing are used in the automotive industry. However,
the application and the sizes are distinct. Automobile radiators
are not as concerned about efficiency as the HVAC industry is.
Also, simply resizing an automotive heat exchanger does not
provide an optimum solution.
In order to accomplish this, the design of an
aluminum heat exchanger with microchannel tubing must be analyzed
and optimized.
U.S. Patent 4,998,580 to Guntly et al. and U.S.
patent 5,372,188 to Dudley et al. are directed to a condenser
with a small diameter hydraulic flow path where hydraulic
diameter is conventionally defined as four times the cross
sectional area of the flow path divided by the wetted perimeter
of the flow path. The Guntly et al. patent requires hydraulic
diameters of about 0.07 inches and less while the Dudley et al.
patent requires a hydraulic diameter in the range of 0.015 to
0.040 inches. This technology is used in the automotive industry
and is not optimum for an air cooled chiller application.
Summary of the Invention
It is desirable to provide an aluminum heat exchanger
with multiple parallel flow paths for use in a large chiller for
air conditioning purposes. It also desirable to significantly
reduce the weight of a large chiller.
It is also desirable to provide a heat exchanger with
multiple parallel flow paths having a hydraulic diameter greater
than about 0.07 inches and less than about 0.30 inches. It is
also desirable to provide a hydraulic diameter in the range
greater than about 0.07 inches and less than or equal to about
0.26 inches. It is also desirable to provide a hydraulic diameter
in the range greater than about 0.07 inches and less than or
equal to about 0.14 inches. It is also desirable to provide a
hydraulic diameter in the range of about 0.14 inches less than or
equal to about 0.26 inches. Finally, in the preferred embodiments
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of the present invention the hydraulic diameter is either about
0.07 inches or about 0.14.
The present invention provides a heat exchanger. The heat
exchanger comprises a first coil assembly including an inlet
manifold, an outlet manifold parallel to and spaced from the
inlet manifold; and a plurality of tubes each operably connected
to and linking the inlet and the outlet manifolds. Each tube has
a multiplicity of flow paths and a hydraulic diameter in the
range of 0.05 < HD < 0.30; and fins arranged in heat transfer
relation between adjacent tubes of the plurality of tubes;
wherein the multiplicity of flow paths are in a parallel
arrangement; and wherein the multiplicity of flow paths has at
least first and second cross sectional shapes.
The present invention also provides an air conditioning
system including a compressor, a first heat exchanger, a fan
motivating air across the first heat exchanger, an expansion
device and a second heat exchanger serially linked into an air
conditioning cycle by tubing. The first heat exchanger includes
an inlet manifold, an outlet manifold, and a multiplicity of
adjacent flow paths surrounded by a common tube wall and
interconnecting the inlet manifold with the outlet manifold. The
flow paths are sized wherein the flow paths are sized and shaped
to form a preferred hydraulic diameter HD within the range of
about 0.08 <- HD < 0.30 inches where hydraulic diameter HD is
defined as four times the cross sectional area of the flow paths
divided by the total wetted perimeter of the flow paths; wherein
the multiplicity of flow paths are in first and second differing
shapes.
The present invention further provides a method of
manufacturing an air cooled chiller. The method comprises the
steps of: forming a first heat exchanger to include a
multiplicity of adjacent flow paths wherein the flow paths are
sized and shaped to first and second differing shapes and each
having a hydraulic diameter within the range of about 0.8 < HD <
0.30 inches where hydraulic diameter = 4 times the cross
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sectional area divided by the total wetted perimeter; providing a
fan to move air across the multiplicity of adjacent flow paths;
providing a compressor, a second heat exchanger, and an expansion
device; and linking the compressor, the first heat exchanger, the
expansion device, and the second heat exchanger serially into an
air conditioning cycle by tubing.
The present invention still further provides a method
of transferring heat in a heat exchanger. The method comprises
the steps of: forming a first heat exchanger to include a
multiplicity of adjacent flow paths wherein the flow paths are
sized and shaped to a preferred hydraulic diameter HD within the
range of 0.7 < HD < 0.30 inches where hydraulic diameter HD as
defined as four times a cross sectional area divided by a total
wetted perimeter; forming the flow paths into first and second
distinct cross-sectional shapes; and transferring heat thru a
wall enclosing said flow paths and to a fluid contained therein.
According to another aspect of the invention, there is
provided a heat exchanger comprising: a first coil assembly
including an inlet manifold; an outlet manifold parallel to and
spaced from the inlet manifold; and a plurality of tubes each
operably connected to and linking the inlet and the outlet
manifolds, each tube having a multiplicity of flow paths in a
parallel arrangement characterized by each of the multiplicity of
flow paths having at least first and second cross-sectional
shapes and a hydraulic diameter HD in the range of 0.07 < HD <
0.30 inches (1.8mm < HD < 7.6mm).
According to another aspect of the invention, there is
provided a method of manufacturing an air cooled chiller
comprising the steps of: forming a first heat exchanger to
include a multiplicity of adjacent flow paths having at least
first and second cross-sectional shapes, wherein the flow paths
are sized and shaped to a preferred hydraulic diameter HD within
the range of 0.07 < HD < 0.30 inches (1.8 < HD < 7.6 mm);
providing a fan to move air across the multiplicity of adjacent
flow paths; providing a compressor, a second heat exchanger, and
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an expansion device; and linking the compressor, the first heat
exchanger, the expansion device, and the second heat exchanger
serially into an air conditioning cycle by tubing.
Brief Description of the Drawings
Figure 1 is a block diagram of an air cooled chiller
system in accordance with the present invention.
Figure 2 shows a first preferred embodiment of the
present invention taken along lines 2-2 of Figure 1.
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Figure 3 is an alternative embodiment of the multi-
path tubes shown in Figure 2.
Figures 4a and 4b are diagrams of fins used in the
heat exchanger shown in Figure 1.
5 Figure 5 is a block diagram of a multiple coil
assembly configuration as a preferred embodiment of Figure 1.
Detailed Description of the Drawing
Figure 1 shows an air conditioning system 10
including a compressor 12, a first heat exchanger 14
functioning as a condenser, an expansion device 16 such as an
expansion valve, and a second heat exchanger 18 functioning as
an evaporator. The compressor 12, the first heat exchanger 14,
the expansion device 16, and the second heat exchanger 18 are
serially linked in an air conditioning cycle by tubing 20. The
first heat exchanger 14 functions as a condenser in releasing
heat from the system, while the second heat exchanger 18
functions as an evaporator in cooling a fluid transported to
and from the heat exchanger 18 by means of conduit 22. Such
systems are generally well known and are sold by The Trane
Company, a Division of American Standard Inc., under the
registered trademarks CenTraVac and Series R.
The present invention is directed to an improved
condenser 14. This improved condenser 14 is preferably formed
of aluminum and has an inlet manifold 30 receiving hot gaseous
refrigerant from the conduit 20 and the compressor 12. This
hot gaseous refrigerant is distributed by the inlet manifold 30
to a plurality of tubes 32. These tubes 32 conduct the hot
gaseous refrigerant from the inlet manifold 30 through the
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tubes 32 to an outlet manifold 34. In the process, the hot
gaseous refrigerant is condensed and returns to the conduit 20
as a liquid where it is modulated through the expansion device
16 to the second heat exchanger 18. The tubes 32 are
preferably microchannel or parallel flow tubing. Microchannel
tubing is shown by applicant's U.S. Patent 5,967,228 to Bergman
et al. which is assigned to the assignee of the present
invention.
Air is moved over the tubes 32 by an air moving
device 36 such as a fan either to or away from the fan 36 as
indicated by arrow 38. To enhance heat transfer from the tubes
32, fins 40 are provided to enhance the heat transfer. These
fins 40 will be subsequently described with reference to Figure
4.
The preferred embodiment of the tubes 32 is shown
in Figure 2 and an alternative embodiment is shown in Figure 3.
The heat transfer tube 32 shown in Figure 2 includes a
multiplicity of adjacent flow paths 40, 42, 44, 46 and 48
throughout the length of the tube 32 and surrounded by a common
tube wall 50. The adjacent flow paths 40 through 48 are
separated by barrier walls 52, 54, 56 and 58 respectively.
In Figure 2, the flow paths 40 and 48 are of
similar shape and cross sectional area and the flow paths 42,
44 and 46 are of similar shape and cross sectional area. The
flow paths 40, 42, 44, 46 and 48 are sized and shaped to form a
preferred hydraulic diameter HD within the range of:
0.7 < HD < 0.30 inches.
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Hydraulic diameter is conventionally calculated
according to the following formula:
Hydraulic Diameter (HD) = cross sectional area X 4
total wetted perimeter
Empirical study shows that a 100 ton air cooled
chiller should have a hydraulic diameter of at least 0.07
whereas a 240 ton air cooled chiller should have a hydraulic
diameter of about 0.14 inches. Linear extrapolation shows that
a 480 ton air cooled chiller should have a hydraulic diameter
of about 0.26 inches. Thus, the preferred range of hydraulic
diameters is 0.07 < HD < 0.30 with an intermediate range of
0.07 < HD <_ 0.26. An optimum range appears to be 0.07 < HD <
0.14, with preferred hydraulic diameter of 0.14.
In determining the hydraulic diameter, the total
cross sectional area of the flow paths 40, 42, 44, 46 and 48 is
either measured or calculated, and the total wetted perimeter
for those same flow paths is determined in a similar manner.
For the sake of expediency, exemplary calculations
are performed for the alternative embodiment shown in Figure 3.
In this Figure 3, like reference numerals are used to denote
like elements.
In the tube 32 shown in Figure 3, each of the
multiplicity of flow paths has an identical size and shape 60.
The cross sectional area for these multiplicity of flow paths
60 can be determined by taking an individual flow path 60a,
determining a height 62 and a width 64, and multiplying the
height 62 and width 64 together to determine an area for a
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single flow path 60a. The total cross sectional area for the
tube 32 is determined by multiplying by the number of flow
paths, in this case 5, by the cross-sectional area per flow
path leading to the calculation that the total cross sectional
area equals 5 times the height 62 time the width 64.
The wetted perimeter for any individual flow path
60 can be calculated as two heights (62) plus two widths (64).
Total wetted perimeter can be determined by multiplying the
wetted perimeter for any particular flow path by the number of
individual flow paths 60, in this case 5, to result in a total
wetted perimeter of 5 times (2H plus 2W). This results in a
hydraulic diameter according to the following formula:
HD = 10(HXW) X 4 /20 (H+W)
which reduces to:
HD = 2H X W/(H + W)
Figure 4a shows a first fin embodiment where a
corrugated fin 40a is used. Similarly, Figure 4b shows the use
of a sinusoidal fin 40b.
Figure 5 is directed to a multiple coil assembly
embodiment of the invention in contrast to Figure 1 which shows
a single coil assembly 70. In practice, multiple coil
assemblies 70, 72, 74 and 76 might be used. The arrangement
shown in Figure 5 is described in applicant's previous U.S.
Patent 5,067,560 to Carey et al. which is assigned to the
assignee of the present invention. The control of such a
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condenser is described in applicant's U.S. Patent 5,138,844
to Clanin et al. which is assigned to the assignee of the
present invention.
In Figure 5, the first coil assembly 70 is
basically perpendicular to ground and a second coil assembly 76
is spaced from the first coil assembly 70 and is generally
arranged in a parallel plane. A third coil assembly 72 is
positioned between the first and second coil assembly 70, 76
and lying in a plane which is not parallel to the planes of
first and second coil assemblies 70, 76. A fourth coil
assembly 74 also lies between the first and second coil
assembly 70, 76 at a line in a plane which is not parallel to
the planes of the first and second coil assembly 70, 76. The
fourth coil assembly 74 preferably is at a complimentary angle
to the third coil assembly 72. The potential airflow paths are
shown by arrows 80.
What has been described is a condenser for use in
the large air cooled chiller. it will be apparent to a person
of ordinary skill in the art that many alterations and
modifications are readily apparent. Such modifications include
varying the material from aluminum to other light weight
materials having a good heat transfer coefficient as well as
modifying the number and shape of the multiple flow paths
within each tube. All such modifications and alterations are
contemplated to fall within the spirit and scope of the
following claims.
