U.S. patent application number 10/132628 was filed with the patent office on 2003-01-16 for method of making an improved heat transfer tube with grooved inner surface.
Invention is credited to Clevinger, Norman R., Narayanamurthy, Ramachandran, Thors, Petur.
Application Number | 20030009883 10/132628 |
Document ID | / |
Family ID | 25272789 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030009883 |
Kind Code |
A1 |
Thors, Petur ; et
al. |
January 16, 2003 |
Method of making an improved heat transfer tube with grooved inner
surface
Abstract
A method of making an improved heat transfer tube. The inner
surface of the tube has a primary set of fins and an intermediate
sets of fins positioned in the areas between the primary fins and
at an angle relative to the primary fins. While intermediate fins
may be used with primary fins arranged in any pattern, in a
preferred embodiment of the inner surface tube design, the
intermediate fins are positioned relative to the primary fins to
result in a grid-like appearance. Tests show that the performance
of tubes having the intermediate fin designs of the present
invention is significantly enhanced. A first set of rollers creates
the primary and intermediate fin designs on at least one side of a
board. A second set of rollers may be used to further enhance the
performance. After the desired pattern has been transferred onto
the board with the rollers, the board is then formed and welded
into a tube, so that, at a minimum, the inner surface design of the
resulting tube includes the intermediate fins as contemplated by
the present invention.
Inventors: |
Thors, Petur; (Decatur,
AL) ; Narayanamurthy, Ramachandran; (Huntsville,
AL) ; Clevinger, Norman R.; (Decatur, AL) |
Correspondence
Address: |
JOHN S. PRATT, ESQ
KILPATRICK STOCKTON, LLP
1100 PEACHTREE STREET
SUITE 2800
ATLANTA
GA
30309
US
|
Family ID: |
25272789 |
Appl. No.: |
10/132628 |
Filed: |
April 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10132628 |
Apr 25, 2002 |
|
|
|
09836808 |
Apr 17, 2001 |
|
|
|
Current U.S.
Class: |
29/890.03 ;
165/133 |
Current CPC
Class: |
Y10T 29/4935 20150115;
F28F 1/40 20130101 |
Class at
Publication: |
29/890.03 ;
165/133 |
International
Class: |
F28F 013/18; B21D
053/02 |
Claims
We claim:
1. A method of manufacturing a tube comprising forming a pattern
along an inner surface of the tube, wherein the pattern comprises a
plurality of primary fins, a plurality of intermediate fins, and a
plurality of grooves defined by adjacent primary fins, wherein the
plurality of intermediate fins are positioned in at least some of
the plurality of grooves.
2. A method of manufacturing a tube comprising: a. a rolling step
of running a board under a fin forming roller so as to roll a
pattern of fins onto a surface of the board, wherein the pattern of
fins t comprises a plurality of primary fins, a plurality of
intermediate fins, and a plurality of grooves defined by adjacent
primary fins, wherein the plurality of intermediate fins are
positioned in at least some of the plurality of grooves; b. a tube
forming step of passing the board onto which the pattern of fins
has been formed through at least one forming roller to form the
board into a desired tube shape with the pattern positioned on the
inside; and c. a board securing step to secure the board in the
desired tube shape.
3. The method of claim 2, wherein the board securing step comprises
a welding step of heating both side edges of the board which has
been formed into a tube shape and adjoining the side edges of the
board.
4. A method of manufacturing a tube comprising: a. running a board
having a length under a channel forming roller to form at least one
channel on a surface of the board and along at least a portion of
the length of the board; b. running the board having the at least
one channel under a fin forming roller to roll a pattern of fins
onto the surface of the board, wherein the pattern of fins
comprises a plurality of primary fins, a plurality of intermediate
fins, and a plurality of grooves defined by adjacent primary fins,
wherein the plurality of intermediate fins are positioned in at
least some of the plurality of grooves; c. passing the board onto
which the at least one channel and pattern of fins has been formed
through at least one tube forming roller to form the board into a
desired tube shape with the at least one channel and the pattern
positioned on the inside; and d. securing the board in the desired
tube shape.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
U.S. patent application Ser. No. 09/836,808, filed Apr. 17,
2001.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of making heat
transfer tubes that may be used in heat exchangers and other
components in air conditioners, refrigerators and other such
devices. The present invention relates more particularly to a
method of making heat transfer tubes having grooved inner surfaces
that form fins along the inner surface of the tubes for improved
heat transfer performance.
BACKGROUND OF THE INVENTION
[0003] Heat transfer tubes with grooved inner surfaces are used
primarily as evaporator tubes or condenser tubes in heat exchangers
for air conditioning and refrigeration. It is known to provide heat
transfer tubes with grooves and alternating "fins" on their inner
surfaces. The grooves and the fins cooperate to enhance turbulence
of fluid heat transfer mediums, such as refrigerants, delivered
within the tube. This turbulence enhances heat transfer
performance. The grooves and fins also provide extra surface area
and capillary effects for additional heat exchange. This basic
premise is taught in U.S. Pat. No. 3,847,212 to Withers, Jr. et
al.
[0004] It is further known in the art to provide internally
enhanced heat exchange tubes made by differing methods;
namely--seamless tubes and welded tubes. A seamless tube may
include internal fins and grooves produced by passing a circular
grooved member through the interior of the seamless tube to create
fins on the inner surface of the tube. However, the shape and
height of the resulting fins are limited by the contour of the
circular member and method of formation. Accordingly, the heat
transfer potential of such tubes is also limited.
[0005] A welded tube, however, is made by forming a flat workpiece
into a circular shape and then welding the edges to form a tube.
Since the workpiece may be worked before formation when flat, the
potential for varying fin height, shape and various other
parameters is increased. Accordingly, the heat transfer potential
of such tubes is also increased.
[0006] This method of tube formation is disclosed in U.S. Pat. No.
5,704,424 to Kohn, et al. Kohn, et al. discloses a welded heat
transfer tube having a grooved inner surface. In the described and
claimed production method, a flat metallic board material is
rounded in the lateral direction until the side edges are brought
into contact with each other. At that point, the two edges of the
board material are electrically seam welded together to form the
completed tube. As stated therein, an advantage of this method is
that any internal fins or grooves can be embossed onto one side of
the tube while the metallic board is still flat, thereby permitting
increased freedom of design attributes.
[0007] Such design freedom is a key consideration in heat transfer
tube design. It is a common goal to increase heat exchange
performance by changing the pattern, shapes and sizes of grooves
and fins of a tube. To that end, tube manufacturers have gone to
great expense to experiment with alternative designs. For example,
U.S. Pat. No. 5,791,405 to Takima et al. discloses a tube having
grooved inner surfaces that have fins formed consecutively in a
circumferential direction on the inner surface of the tube. A
plurality of configurations are shown in the various drawing
figures. U.S. Pat. Nos. 5,332,034 and 5,458,191 to Chiang et al.
and U.S. Pat. No. 5,975,196 to Gaffaney et al. all disclose a
variation of this design referred to in this application as a
cross-cut design. Fins are formed on the inner tube surface with a
first embossing roller. A second embossing roller then makes cuts
or notches cross-wise over and through the fins. This process is
costly as at least two embossing rollers are required to form the
cross-cut design. Moreover, the fins disclosed in all of the
designs of these patents are separated by empty troughs or grooves.
None of the designs capitalize on this empty area to enhance the
heat transfer characteristics of the tubes.
[0008] While these inner surface tube designs aim to improve the
heat transfer performance of the tube, there remains a need in the
industry to continue to improve upon tube designs by modifying
existing and creating new designs that enhance heat transfer
performance. Additionally, a need also exists to create designs and
patterns that can be transferred onto the tubes more quickly and
cost-effectively. As described hereinbelow, the applicant has
developed new geometries for heat transfer tubes and, as a result,
significantly improved heat transfer performance.
SUMMARY OF THE INVENTION
[0009] Generally described, the present invention comprises an
improved heat transfer tube and a method of formation thereof. The
inner surface of the tube, after the design of the present
invention has been embossed on a metal board and the board formed
and welded into the tube, will have a primary set of fins and an
intermediate sets of fins positioned in the areas between the
primary fins and at an angle relative to the primary fins. While
intermediate fins may be used with primary fins arranged in any
pattern, in a preferred embodiment of the inner surface tube
design, the intermediate fins are positioned relative to the
primary fins to result in a grid-like appearance. Tests show that
the performance of tubes having the intermediate fin designs of the
present invention is significantly enhanced.
[0010] The method of the present invention comprises rolling a flat
metallic board between a first set of rollers shaped to create the
primary and intermediate fin designs on at least one side of the
board. While previous designs with similar performance use
additional roller sets, the basic designs of the present invention
may be transferred onto the board using a single roller set,
thereby reducing manufacturing costs. Subsequent sets of rollers
may be used, however, to impart additional design features to the
board. After the desired pattern has been transferred onto the
board with the rollers, the board is then formed and welded into a
tube, so that, at a minimum, the inner surface design of the
resulting tube includes the intermediate fins as contemplated by
the present invention.
[0011] Thus, it is an object of the present invention to provide
improved heat transfer tubes.
[0012] It is a further object of the present invention to provide
an innovative method of forming improved heat transfer tubes.
[0013] It is a further object of the present invention to provide
an improved heat transfer tube having intermediate fins.
[0014] It is a further object of the present invention to provide a
method of forming improved heat transfer tubes having intermediate
fins.
[0015] It is a further object of the present invention to provide
an improved heat transfer tube with intermediate fins that may
include primary and intermediate fins of differing heights, shapes,
pitches, and angles.
[0016] It is a further object of the present invention to provide
an improved heat transfer tube with two sets of fins formed in one
rolling operation.
[0017] It is further object of the present invention to provide an
improved heat transfer tube that has at least two sets of fins
having cuts cut cross-wise over and at least partially through the
fins.
[0018] It is further object of the present inventions to provide an
improved heat transfer tube having chambers, formed, in part, by
the walls of the intermediate fins, for enhanced nucleate
boiling.
[0019] These and other features, objects and advantages of the
present invention will become apparent by reading the following
detailed description of preferred embodiments, taken in conjunction
with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of the inner surface of one
embodiment of a tube of the present invention.
[0021] FIG. 2 is an enlarged section view taken at inset circle 2
in FIG. 1.
[0022] FIG. 3 is a fragmentary plan view of one embodiment of a
tube of the present invention spread open to reveal the inner
surface of the tube.
[0023] FIG. 4 is a cross-sectional view taken a long line 4-4 in
FIG. 3, illustrating one embodiment of the primary fins.
[0024] FIG. 5 is a cross-sectional view taken along line 5-5 in
FIG. 3, illustrating one embodiment of the intermediate fins.
[0025] FIG. 6 is a cross-sectional view similar to FIGS. 4 and 5
showing an alternative embodiment of the shape of the primary
and/or intermediate fins.
[0026] FIG. 7 is a cross-sectional view similar to FIGS. 4 and 5
showing another alternative embodiment of the shape of the primary
and/or intermediate fins.
[0027] FIG. 8 is a cross-sectional view similar to FIGS. 4 and 5
showing another alternative embodiment of the shape of the primary
and/or intermediate fins.
[0028] FIG. 9 is a cross-sectional view similar to FIGS. 4 and 5
showing another alternative embodiment of the shape of the primary
and/or intermediate fins.
[0029] FIG. 10 is a cross-sectional view similar to FIGS. 4 and 5
showing another alternative embodiment of the shape of the primary
and/or intermediate fins.
[0030] FIG. 11 is a cross-sectional view similar to FIGS. 4 and 5
showing another alternative embodiment of the shape of the primary
and/or intermediate fins.
[0031] FIG. 12 is a cross-sectional view similar to FIG. 5 showing
another alternative embodiment of the intermediate fins.
[0032] FIG. 13 is a fragmentary plan view of an alternative
embodiment of a tube of the present invention spread open to reveal
the inner surface of the tube.
[0033] FIG. 14 is a fragmentary plan view of an alternative
embodiment of a tube of the present invention spread open to reveal
the inner surface of the tube.
[0034] FIG. 15 is a fragmentary plan view of an alternative
embodiment of a tube of the present invention spread open to reveal
the inner surface of the tube.
[0035] FIG. 16 is a fragmentary plan view of an alternative
embodiment of a tube of the present invention spread open to reveal
the inner surface of the tube.
[0036] FIG. 17 is a fragmentary perspective view of the inner
surface of an alternative embodiment of a tube of the present
invention.
[0037] FIG. 18 is a fragmentary perspective view of the inner
surface of an alternative embodiment of a tube of the present
invention.
[0038] FIG. 19 is a perspective view of the fin-forming rollers
used to produce one embodiment of the tube of the present
invention.
[0039] FIG. 20 illustrates a cross-sectional shape of a tube of the
present invention.
[0040] FIG. 21 illustrates an alternative cross-sectional shape of
a tube of the present invention.
[0041] FIG. 22 illustrates an alternative cross-sectional shape of
a tube of the present invention.
[0042] FIG. 23 illustrates an alternative cross-sectional shape of
a tube of the present invention.
[0043] FIG. 24 illustrates an alternative cross-sectional shape of
a tube of the present invention.
[0044] FIG. 25 illustrates an alternative cross-sectional shape of
a tube of the present invention.
[0045] FIG. 26 is a graph illustrating condensation heat transfer
using an embodiment of the tube of the present invention with R-22
refrigerant.
[0046] FIG. 27 is a graph illustrating condensation pressure drop
using an embodiment of the tube of the present invention with R-22
refrigerant.
[0047] FIG. 28 is a graph illustrating condensation heat transfer
using an embodiment of the tube of the present invention with
R-407c refrigerant.
[0048] FIG. 29 is a graph illustrating condensation pressure drop
using an embodiment of the tube of the present invention with
R-407c refrigerant.
[0049] FIG. 30 is a graph illustrating the efficiency of one
embodiment of the tube of the present invention with R-407c
refrigerant.
[0050] FIG. 31 is a graph illustrating the efficiency of an
alternative embodiment of the tube of the present invention with
R-22 refrigerant.
[0051] FIG. 32 is a graph illustrating condensation heat transfer
using embodiments of the tube of the present invention with R-22
refrigerant.
[0052] FIG. 33 is a graph illustrating condensation pressure drop
using embodiments of the tube of the present invention with R-22
refrigerant.
DETAILED DESCRIPTION OF THE DRAWINGS
[0053] Like existing designs, the inner surface design of the tube
10 of the present invention, one embodiment of which is illustrated
in FIGS. 1-3, includes a set of primary fins 12 that run parallel
to each other along the inner surface 20 of the tube 10. The
cross-sectional shape of the primary fins 12 may assume any shape,
such as those disclosed in FIGS. 6-11, but preferably is
triangular-shaped, having angled, straight sides 14, a rounded tip
16, and rounded edges 18 at the interface of the sides 14 and inner
surface 20 of the tube 10 (see FIG. 4). The height of the primary
fins H.sub.P may vary depending on the diameter of the tube 10 and
the particular application, but is preferably between 0.004-0.02
inches. As shown in FIG. 3, the primary fins 12 may be positioned
at a primary fin angle .theta. between 0.degree.-90.degree.
relative to the longitudinal axis 22 of the tube 10. Angle .theta.
is preferably between 5.degree.-50.degree. and more preferably
between 5.degree.-30.degree.. Finally, the number of primary fins
12 positioned along the inner surface 20 of a tube 10, and thus the
primary fin pitch P.sub.P (defined as the distance between the tip
or centerpoint of two adjacent primary fins measured along a line
drawn perpendicular to the primary fins), may vary, depending on
the height Hp and shape of the primary fins 12, the primary fin
angle .theta., and the diameter of the tube 10. Moreover, the
primary fin shape, height H.sub.P, angle .theta., and pitch P.sub.P
may vary within a single tube 10, depending on the application.
[0054] Unlike previous designs, the designs of the present
invention capitalize on the empty areas or grooves 24 between the
primary fins 12 to the enhance heat transfer characteristics of the
tubes. Intermediate fins 26 are formed in the grooves 24 defined by
the primary fins 12 to give the inner surface tube design a
grid-like appearance. The intermediate fins increase the turbulence
of the fluid and the inside surface area, and thereby the heat
transfer performance of the tube 10. Additionally, the intermediate
fin designs contemplated by the present invention may be
incorporated onto the same roller as the primary fin design,
thereby reducing the manufacturing costs of the tube 10.
[0055] The intermediate fins 26 preferably extend the width of the
groove 24 to connect adjacent primary fins 12 (as shown in FIG. 3).
Just as with the primary fins 12, the intermediate fins 26 may
assume a variety of shapes, including but not limited to those
shown in FIGS. 5-11. The intermediate fins 26 may be, but do not
have to be, shaped similar to the primary fins 12, as shown in FIG.
5. As with the primary fins 12, the number of intermediate fins 26
positioned between the primary fins 12 (and therefore the
intermediate fin pitch PI, defined as the distance between the tip
or centerpoint of two adjacent intermediate fins measured along a
line drawn perpendicular to the intermediate fins) and the height
of the intermediate fins H.sub.I may be adjusted depending on the
particular application. The height of the intermediate fins H.sub.I
may, but do not have to, extend beyond the height of the primary
fins H.sub.P. As shown in FIG. 3, the intermediate fins 26 are
positioned at an intermediate fin angle .beta. measured from the
counter-clockwise direction relative to the primary fins 12.
Intermediate fin angle .beta. may be any angle more than 0.degree.,
but is preferably between 45.degree.-135.degree..
[0056] As with the primary fins, the intermediate fin shape, height
H.sub.I, pitch P.sub.I, and angle .beta. need not be constant for
all intermediate fins 26 in a tube 10, but rather all or some of
these features may vary in a tube 10 depending on the application.
For example, FIG. 12 illustrates a cross-section of a spread out
tube 10 having an inner surface tube design with a variety of
intermediate fin shapes, heights (H.sub.I-1, H.sub.I-2, and
H.sub.I-3), and pitches (P.sub.I-1 and P.sub.I-2) As shown in FIGS.
13-16, intermediate fins 26 may be used in conjunction with primary
fins 12 arranged in any pattern, including, but not limited to, all
of the patterns disclosed in U.S. Pat. No. 5,791,405 to Takima et
al., the entirety of which being herein incorporated by reference.
For example, FIGS. 13-16 illustrate embodiments where some of the
primary fins 12 are arranged at an angle relative to other of the
primary fins 12. In FIGS. 13 and 14, the primary fins 12 intersect.
Similarly, in FIG. 16, portions of primary and intermediate fins
run along the length of tube 10 while adjacent portions of primary
and intermediate fins are arranged at angles thereto. In FIG. 15,
the primary fins 12 do not intersect, but rather are separated by a
channel 50 that runs along the length of the inner surface 20 of
tube 10. More than one channel 50 may be provided along the inner
surface 20 of tube 10. The depth of channel 50 into tube 10 can be
varied depending on the application. Moreover, the surface of
channel 50 can be, but does not have to be, smooth. Rather,
grooves, ridges, and/or other features to roughen the surface of
channel 50 can be provided.
[0057] Additionally, instead of connecting adjacent primary fins
12, the intermediate fins 26 may be free-standing geometrical
shapes, such as cones, pyramids, cylinders, etc. (as shown in FIG.
18).
[0058] One skilled in the art would understand how to manipulate
inner surface tube design variables of the primary and intermediate
fins, including fin arrangement, shape, height H.sub.P and H.sub.I,
angles .theta. and .beta., and pitches P.sub.P and P.sub.I to
tailor the inner surface tube design to a particular application in
order to obtain the desired heat transfer characteristics.
[0059] The tubes having patterns in accordance with the present
invention may be manufactured using production methods and
apparatuses well known in the art, such as those disclosed in U.S.
Pat. No. 5,704,424 to Kohn, et al., the entirety of which is herein
incorporated by reference. As explained in Kohn, et al., a flat
board, generally of metal, is passed between sets of rollers which
emboss the upper and lower surface of the board. The board is then
gradually shaped in subsequent processing steps until its edges
meet and are welded to form a tube 10. The tube may be formed into
any shape, including those illustrated in FIGS. 20-25. While round
tubes have traditionally been used and are well-suited for purposes
of the present invention, enhanced heat transfer properties have
been realized using tubes 10 having a cross-sectional shape flatter
than traditional round tubes, such as those illustrated in FIGS.
22, 23, and 25. Consequently, it may be preferable during the
shaping stage of production, but before the welding stage, to form
tubes 10 having a flatter shape. Alternatively, the tubes 10 may be
formed into the traditional round shape and subsequently compressed
to flatten the cross-sectional shape of the tube 10. One of
ordinary skill in the art would understand that the tube 10 may be
formed into any shape, including but not limited to those
illustrated in FIGS. 20-25, depending on the application.
[0060] The tube 10 (and therefore the board) may be made from a
variety of materials possessing suitable physical properties
including structural integrity, malleability, and plasticity, such
as copper and copper alloys and aluminum and aluminum alloys. A
preferred material is deoxidized copper. While the width of the
flat board will vary according to the desired tube diameter, a flat
board having a width of approximately 1.25 inches to form a
standard 3/8" tube outside diameter is a common size for the
present application.
[0061] To form the desired pattern on the board, the board is
passed through a first set of deforming or embossing rollers 28,
which consists of an upper roller 30 and a lower roller 32 (see
FIG. 19). The pattern on the upper roller 30 is an interlocking
image of the desired primary and intermediate fin pattern for the
inner surface of the tube 10 (i.e. the pattern on the upper roller
interlocks with the embossed pattern on the tube). Similarly, the
pattern of the lower roller 32 is an interlocking image of the
desired pattern (if any) of the outer surface of the tube 10. FIG.
19 illustrates one set of rollers 28, the upper roller 30 having a
pattern that includes an intermediate fin design as contemplated by
the present invention.
[0062] Note, however, that to manufacture a tube in accordance with
the embodiment shown in FIG. 15, one or more longitudinal channels
50 are preferably first embossed along at least a portion of the
length of the board with an embossing roller having ridges around
the circumference of the roller. These ridges form the channels in
the smooth board. The number of ridges provided on the roller
coincides with the number of channels embossed on the board. After
channel formation, the board is then subjected to the rollers 28 as
described above. In this way, the pattern on the upper roller 30 is
not embossed onto the depressed channels 50 in the board.
[0063] The patterns on the rollers may be made by machining grooves
on the roller surface. As will be apparent to one of ordinary skill
in the art, because of the interlocking-image relationship between
the rollers and the board, when the board is passed through the
rollers, the grooves on the rollers form fins on the board and the
portions of the roller surface not machined form grooves on the
board. When the board is subsequently rolled and welded, the
desired inner and outer patterns are thereby located on the
tube.
[0064] An advantage of the tubes formed in accordance with the
present invention is that the primary and intermediate fin designs
of the tubes may be machined on the roller and formed on the board
with a single roller set, as opposed to the two sets of rollers
(and consequently two embossing steps) that have traditionally been
necessary to create existing inner surface tube designs, such as
the cross-cut design, that enhance tube performance. Elimination of
a roller set and embossing stage from the manufacturing process can
reduce the manufacturing time and cost of the tube.
[0065] However, while only one roller set is necessary to create
the primary and intermediate fin designs of the present invention,
subsequent and additional rollers may be used impart additional
design features to the board. For example, a second set of rollers
may be used to make cuts 38 cross-wise over and at least partially
through the fins to result in a cross-cut design, as shown in FIG.
17.
[0066] In an alternative design, the primary and intermediate fins
form the sidewalls of a chamber. The tops of the primary fins may
be formed, such as, for example, by pressing them with a second
roller, to extend or flare laterally to partially, but not
entirely, close the chamber. Rather, a small opening through which
fluid is able to flow into the chamber remains at the top of the
chamber. Such chambers enhance nucleate boiling of the fluid and
thereby improve evaporation heat transfer.
[0067] In addition to potentially reducing manufacturing costs,
tubes having designs in accordance with the present invention also
outperform existing tubes. FIGS. 26-29 graphically illustrate the
enhanced performance of such tubes in condensation obtainable by
incorporating intermediate fins into the inner surface tube design.
Performance tests were conducted on four condenser tubes for two
separate refrigerants (R-407c and R-22). The following copper
tubes, each of which had a different inner surface design, were
tested:
[0068] (1) "Turbo-A.RTM.," a seamless or welded tube made by
Wolverine Tube for evaporator and condenser coils in air
conditioning and refrigeration with internal fins that run parallel
to each other at an angle to the longitudinal axis of the tube
along the inner surface thereof (designated "Turbo-A.RTM.");
[0069] (2) a cross-cut tube made by Wolverine Tube for evaporator
and condenser coils (designated "Cross-Cut");
[0070] (3) a tube with an intermediate fin design in accordance
with the present invention (designated "New Design"); and
[0071] (4) a tube with an intermediate fin design in accordance
with the present invention whereby the primary and intermediate
fins have been cross-cut with a second roller (designated "New
Design X").
[0072] FIGS. 26 and 27 reflect data obtained using R-22
refrigerant. FIGS. 28 and 29 reflect data obtained using R-407
refrigerant. The general testing conditions represented by these
graphs are as follows:
1 Evaporation Condensation Saturation Temperature 35.degree.
(1.67.degree. C.) 105.degree. F. (40.6.degree. C.) Tube Length 12
ft (3.66 m) 12 ft (3.66 m) Inlet Vapor Quality 10% 80% Outlet Vapor
Quality 80% 10%
[0073] The data was obtained for flowing refrigerant at different
flow rates. Accordingly, the "x" plane of all the graphs is
expressed in terms of mass flux (lb./hr. ft.sup.2). FIGS. 26 and 28
show heat transfer performance. Accordingly, the "y" plane of these
two graphs is expressed in terms of heat transfer co-efficient
(Btu/hr. ft.sup.2). FIGS. 27 and 29 show pressure drop information.
Accordingly, the "y" plane of these two graphs is expressed in
terms of pressure per square inch (PSI).
[0074] The data for the R-407c refrigerant (FIGS. 28 and 29), which
is a zeotropic mixture, indicates that the condensation heat
transfer performance of the New Design is approximately 35%
improved over the Turbo-A.RTM. design. Further, the New Design
provides increased performance (by approximately 15%) over the
standard Cross-Cut design, which is currently regarded as the
leading performer in condensation performance among widely
commercialized tubes. In terms of pressure drop performance, the
New Design performs as well as the Turbo-A.RTM. design and
approximately 10% lower than the standard Cross-Cut design. The
pressure drop is a very important design parameter in heat
exchanger design. With the current technology in heat exchangers, a
5% decrease in pressure drop can sometimes provide as much benefit
as a 10% increase in heat transfer performance.
[0075] The new design makes use of an interesting phenomenon in
two-phase heat transfer. In a tube embodiment of the present
invention, where a fluid is condensing on the inside of the tube,
the pressure drop is mainly regulated by the liquid-vapor
interface. The heat transfer is controlled by the liquid-solid
interface. The intermediate fins affect the liquid layer, thereby
increasing the heat transfer, but do not impact the pressure drop.
The relationship between the heat transfer and pressure drop is
captured by the efficiency factor.
[0076] With use of the R-22 refrigerant (FIGS. 26 and 27), the New
Design X outperformed the Turbo-A.RTM. and Cross-Cut designs with
respect to heat transfer by nearly the same percentages as the New
Design did in the R-407c tests. The inventor has no reason to
believe that similar performance improvement will not be obtained
using other refrigerants such as R-410(a) or R-134(a), and other
similar fluids.
[0077] FIGS. 30 and 31 compare the efficiency factors of the
Cross-Cut design with the efficiency factors of the New Design
(FIG. 30) and the New Design X (FIG. 31). The efficiency factor is
a good indicator of the actual performance benefits associated with
a tube inner surface because it reflects both the benefit of
additional heat transfer and the drawback of additional pressure
drop. In general, the efficiency factor of a tube is defined as the
increase in heat transfer of that tube over a standard tube (in
this case, the Turbo-A.RTM.) divided by the increase in pressure
drop of that tube over the standard tube. The efficiency factors
plotted in FIGS. 30 and 31 for the Cross-Cut were calculated as
follows: 1 ( Heat Transfer of Cross - Cut / Heat Transfer of Turbo
- A .RTM. ) ( Pressure Drop of Cross - Cut / Pressure Drop of Turbo
- A.RTM. )
[0078] The efficiency factors of the New Design and the New Design
X, plotted in FIGS. 30 and 31, respectively, were similarly
calculated.
[0079] As can be seen in FIGS. 30 and 31, the efficiency factors
for the New Design and the New Design X are all (with the exception
of one) above "1", which indicates that the efficiency of both of
these new designs is better than that of the standard Turbo-A.RTM.
by as much as 40% in R-22 condensation (FIG. 31) and by up to 35%
in R-407c condensation (FIG. 30). Moreover, by comparing the
efficiency factors of the Cross-Cut (FIGS. 30 and 31) plotted
against the New Design (FIG. 30) and New Design X (FIG. 31), it is
apparent that the efficiencies of the new designs are consistently
better than the Cross-Cut tube by 20% in R-22 condensation (FIG.
31) and 10% in R-407c condensation (FIG. 30).
[0080] Additionally, tests also demonstrate that tubes having inner
surfaces similar to those shown in FIGS. 13 and 15 also outperform
Turbo-A.RTM. tubes. The results of such tests are shown in FIGS. 32
and 33, wherein a tube having an inner surface in accordance with
FIG. 13 is designated "New Design 2" and a tube having an inner
surface in accordance with FIG. 15 is designated "New Design 3."
FIGS. 32 and 33 reflect data obtained using R-22 refrigerant under
the same condensation testing conditions described above.
[0081] FIGS. 32 and 33 show heat transfer performance and pressure
drop, respectively. The data, as reflected in FIGS. 32 and 33,
indicates that the condensation heat transfer performance of the
New Design 2 and New Design 3 is approximately 80% and 40%
improved, respectively, over the Turbo-A.RTM. design. Further,
while the pressure drop for the New Design 2 increased over
Turbo-A.RTM., the New Design 3 exhibited pressure drop comparable
to Turbo-A.RTM.. This data suggests that significant heat transfer
benefits can be realized by incorporating the New Design 3 into
existing systems to replace Turbo-A.RTM. tubes. In addition, by
preventing the pattern from forming on a portion of the tube (i.e.,
in the channels 50), the amount of material in a unit length of
tube is reduced. This results in significant cost savings to
customers.
[0082] Moreover, the New Design 2 may be particularly beneficial
incorporated into redesigned systems. This is particularly
significant in light of recent measures to increase efficiencies of
air-conditioning equipment. By using the New Design 2 surface, one
can attain increased performance in the same size of equipment or
reduce the size of equipment. Thus, it would be possible to reduce
or eliminate expensive redesign efforts. In addition, by reducing
the size of the system, one also reduces the amount of other
components, like metal for the base, aluminum for the fins and
tubing lines, that can result in considerable savings to the
customer.
[0083] Thus it is seen that a tube providing intermediate fins
represents a significant improvement over cross-cut and single
helical ridge designs. This new design thus advances the state of
the art. It will be understood by those of ordinary skill in the
art that various modifications may be made to the preferred
embodiments within the spirit and scope of the invention as defined
by the appended claims.
* * * * *