U.S. patent application number 12/106404 was filed with the patent office on 2009-10-22 for heat exchanger with expanded metal turbulizer.
This patent application is currently assigned to DANA CANADA CORPORATION. Invention is credited to Thomas Seiler, Allan K. So, Bryan Sperandei.
Application Number | 20090260789 12/106404 |
Document ID | / |
Family ID | 41200136 |
Filed Date | 2009-10-22 |
United States Patent
Application |
20090260789 |
Kind Code |
A1 |
Sperandei; Bryan ; et
al. |
October 22, 2009 |
HEAT EXCHANGER WITH EXPANDED METAL TURBULIZER
Abstract
A heat exchanger incorporating a turbulizer or heat transfer
surface wherein the turbulizer is a corrugated member having
parallel spaced-apart ridges and planar portions extending
therebetween. The heat transfer surface has a plurality of
micro-openings formed over at least a portion of its surface so as
to create a uniform porosity over the portions of the turbulizer in
which they are provided.
Inventors: |
Sperandei; Bryan;
(Mississauga, CA) ; So; Allan K.; (Mississauga,
CA) ; Seiler; Thomas; (Milton, CA) |
Correspondence
Address: |
RIDOUT & MAYBEE LLP
225 KING STREET WEST, 10TH FLOOR
TORONTO
ON
M5V 3M2
CA
|
Assignee: |
DANA CANADA CORPORATION
Oakville
CA
|
Family ID: |
41200136 |
Appl. No.: |
12/106404 |
Filed: |
April 21, 2008 |
Current U.S.
Class: |
165/177 |
Current CPC
Class: |
F28F 13/12 20130101;
F28D 1/0333 20130101; F28F 3/027 20130101 |
Class at
Publication: |
165/177 |
International
Class: |
F28F 1/00 20060101
F28F001/00 |
Claims
1. A heat exchanger, comprising: a tubular member having first and
second spaced-apart walls defining a fluid flow passage
therebetween, the tubular member having a fluid inlet and a fluid
outlet, said fluid inlet and fluid outlet being spaced-apart from
each other thereby defining a flow direction from the fluid inlet
to the fluid outlet for the flow of a first fluid through said
fluid flow passage; a corrugated heat transfer surface located in
said flow passage, the heat transfer surface including parallel
spaced-apart ridges with planar portions extending therebetween,
alternating ridges being in contact with said first and second
spaced apart walls, said corrugated heat transfer surface having a
plurality of micro-openings which define porous areas of said
corrugated heat transfer surface, said porous areas being located
in at least said planar portions, said porous areas having a
substantially uniform porosity, and said ridges being oriented
perpendicular to the flow direction within said flow passage.
2. A heat exchanger as claimed in claim 1, wherein the planar
portions are inclined with respect to the spaced-apart walls.
3. A heat exchanger as claimed in claim 1, wherein the planar
portions are perpendicular with respect to said spaced-apart
walls.
4. A heat exchanger as claimed in claim 1, wherein the
micro-openings are formed in a shape selected from the group
consisting of an expanded pie-shape and a diamond shape.
6. A heat exchanger as claimed in claim 1, wherein the ridges are
imperforate surfaces, said micro-openings being formed only in said
planar portions of said heat transfer surface.
7. A heat exchanger as claimed in claim 1, wherein said
micro-openings are formed over the entire surface of said heat
transfer surface, including said planar portions and said
ridges.
8. A heat exchanger as claimed in claim 1, wherein the porosity of
said porous areas of said heat transfer surface is in the range of
about 50% to about 80%.
9. A heat exchanger as claimed in claim 1, wherein said
micro-openings have an average area within a range from about 0.2
mm.sup.2 to about 3 mm.sup.2.
10. A heat exchanger as claimed in claim 1, wherein the ridges are
curved surfaces.
11. A heat exchanger as claimed in claim 1, wherein the ridges are
flat surfaces.
12. A heat exchanger as claimed in claim 1, wherein the corrugated
heat transfer surface includes an imperforate strip along the
length thereof dividing said heat transfer surface into first and
second regions, said imperforate strip being oriented perpendicular
to said parallel spaced-apart ridges, with said porous areas being
provided on both sides of said imperforate strip.
13. A heat exchanger as claimed in claim 12, wherein the
micro-openings in said first region are oriented in a first
direction and the micro-openings in the second region are oriented
in a second direction.
14. A heat exchanger as claimed in claim 1, comprising a plurality
of stacked tubular members.
15. A heat exchanger as claimed in claim 14, wherein said plurality
of stacked tubular members are formed by mating plate pairs.
16. A heat exchanger as claimed in claim 15, wherein each plate
pair comprises an upper plate and a lower plate, each plate having
a raised central portion and a peripheral edge, the peripheral
edges of the upper and lower plates being joined together when said
upper and lower plates placed in back-to-back relationship, each
plate having respective end portions formed with raised end bosses
defining inlet and outlet openings, the respective inlet and outlet
openings of each plate pair communicating with each other when said
plate pairs are stacked together to form manifolds.
Description
FIELD OF THE INVENTION
[0001] The invention relates to heat exchangers, and in particular,
to turbulizers used in plate type heat exchangers to increase the
heat transfer performance of the heat exchanger.
BACKGROUND OF THE INVENTION
[0002] In heat exchangers, particularly of the type used to cool or
heat liquids such as oil, it is common to use flow augmentation
devices to increase mixing or flow turbulence or impede the
formation of boundary layers and thus improve the heat transfer
efficiency of the heat exchangers. In the past, various types of
metal fins or turbulizers have been used. One common type of
turbulizer is a corrugated fin where the corrugations are formed
with a pattern of slits and the material of the corrugations is
displaced laterally to produce offset openings. This produces a
tortuous flow path through the turbulizer increasing turbulence and
breaking up boundary layers.
[0003] U.S. Pat. No. 4,945,981 (Joshi) discloses a fin comprising a
plurality of corrugations, the side walls of which are provided
with vertical louvers. Louvered fins are commonly used on the air
side of an air to liquid heat exchanger; however, in this Joshi
patent, the louvered fin is located inside the heat exchanger tubes
or channels that normally contain liquids, such as oils. As well,
the Joshi patent shows the louvered fin as being positioned within
the heat exchanger tubes with the corrugations oriented either
parallel or transverse to the flow of the fluid through the
channel.
[0004] Japanese application JP-62255792 discloses a heat exchanger
having porous thin laminar metallic fins located between adjacent
tubes in the heat exchanger. The fins are formed in a waveform
shape along a first axis, and in a waveform shape along a second
axis where the second axis is perpendicular to the first axis.
However, the fins are located external to and in between the tubes
of the heat exchanger.
[0005] Some difficulties with expanded metal or louvered type
turbulizers is that they produce undesirably high pressure drops or
flow losses in the heat exchanger resulting in an irregular or
non-uniform flow pattern in the fluid passageways of the heat
exchanger. This can produce stagnation in some areas of the heat
exchanger, but even if this does not occur, a non-uniform flow
profile generally indicates less than ideal heat transfer
efficiency through the heat exchanger.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the invention, there is provided
a heat exchanger comprising a tubular member having first and
second spaced-apart walls defining a flow passage therebetween, the
tubular member having respective end portions defining a fluid
inlet and a fluid outlet for the flow of a first fluid through the
flow passage. A corrugated heat transfer surface is located in the
tubular member, the heat transfer surface including parallel spaced
apart ridges with planar portions extending therebetween,
alternating ridges being in contact with the first and second
spaced-apart walls, the corrugated heat transfer surface having a
plurality of micro-openings formed therein defining a uniform
porosity over the surface thereof. The tubular member having a
longitudinal axis, the ridges of the heat transfer surface being
oriented perpendicular to the longitudinal axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Preferred embodiments of the invention will now be
described, by way of example, with reference to the accompanying
drawings, in which:
[0008] FIG. 1 is an exploded perspective view of a preferred
embodiment of a plate type heat exchanger containing a corrugated
heat transfer surface according to the present invention;
[0009] FIG. 2 is a perspective view of the heat transfer surface
shown in FIG. 1;
[0010] FIG. 3 is a side elevation view of the heat transfer surface
shown in FIG. 2;
[0011] FIG. 4 is a partial perspective view of a single heat
exchanger tubular member containing a heat transfer surface
according to the present invention;
[0012] FIG. 5 is a cross-sectional view of a single corrugation of
a heat transfer surface according to one embodiment of the
invention taken along section line 5-5 shown in FIG. 7;
[0013] FIG. 6 is a left side view of the corrugation shown in FIG.
5;
[0014] FIG. 7 is a top view of the corrugation shown in FIG. 5;
[0015] FIG. 8 is a right side view of the corrugation shown in FIG.
5;
[0016] FIG. 9 is a top view of a section of material used to form
the corrugation shown in FIGS. 5-8;
[0017] FIG. 10 is an enlarged, detail view of the encircled area
100 of FIG. 9;
[0018] FIG. 11 is a top view of a section of material used to form
a heat transfer surface according to another embodiment of the
invention;
[0019] FIG. 12 is an enlarged, detail view of the encircled area
120 of FIG. 11;
[0020] FIG. 13 is a cross-sectional view of a single corrugation of
a heat transfer surface according to another embodiment of the
invention taken along section line 13-13 shown in FIG. 15;
[0021] FIG. 14 is a left side view of a single corrugation shown in
FIG. 13;
[0022] FIG. 15 is a top view of the corrugation of FIG. 13;
[0023] FIG. 16 is a right side view of the corrugation of FIGS.
13;
[0024] FIG. 17 is a top view of a section of material used to form
a corrugation of a heat transfer surface according to a further
embodiment of the invention;
[0025] FIG. 18 is an enlarged detail view of a section of material
used to form a heat transfer surface according to another
embodiment of the invention; and
[0026] FIG. 19 is a graph of overall performance comparing the
efficiency of the heat exchanger of the present invention with a
prior art heat exchanger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Referring first to FIG. 1, there is shown a portion of a
heat exchanger 10 according to a preferred embodiment of the
invention. Heat exchanger 10 is formed of a plurality of tubular
members 12. In the embodiment shown, the tubular members 12 are in
the form of plate pairs having an upper plate 14, a lower plate 16
and a turbulizer 18 located therebetween. Plates 14, 16 are
arranged back-to-back and have joined peripheral edges 20. Plates
14, 16 define first and second spaced-apart walls or raised central
portions 22 which define a fluid flow passage therebetween in which
the turbulizer 18 is located. Raised central portions 22 have
respective end portions with raised end bosses 23 which define
respective inlet and outlet openings 24, 26 for the flow of a first
heat exchange fluid, such as oil, through the tubular members 12.
The raised end bosses 23 also serve to space-apart the tubular
members 12 when they are stacked one on top of the other to form
heat exchanger 10. When the tubular members 12 are stacked
together, all of the inlet openings 24 and outlet openings 26 align
in fluid communication with each other, thereby forming respective
inlet and outlet manifolds. If desired, corrugated fins 34 can be
located between the tubular members 12 to act as heat transfer
augmentation devices for a second fluid, such as air, flowing
transversely through the heat exchanger 10. The corrugated fins may
preferably be provided with vertical slits, or louvers, as shown.
While FIG. 1 relates to an oil-to-air heat exchanger 10 having
elongate tubular members 12 and corrugated fins, it will be
appreciated that turbulizers 18 are not necessarily used in this
type of heat exchanger. Rather, it will be appreciated that the
turbulizer 18 may be placed within the fluid flow passageways of a
variety of different heat exchangers, such as oil-to-water heat
exchangers similar to those described by the above-mentioned Joshi
patent. Examples of such oil-to-water heat exchangers include
transmission oil coolers, engine oil coolers and power steering oil
coolers. It will also be appreciated that turbulizers 18 and fins
34 are somewhat schematically shown, and unnecessary details have
been omitted, for convenience.
[0028] As shown in FIG. 1, the tubular members 12 are aligned along
a longitudinal axis 43. Therefore, the direction of fluid flow
within the fluid flow passages is also along the longitudinal axis
43, from the inlet manifold to the outlet manifold.
[0029] Referring next to FIGS. 2 and 3, there is shown a preferred
embodiment of the turbulizer 18 according to the present invention.
It will be appreciated that while a particular turbulizer 18 is
shown, the turbulizer 18 can be made in any width or length
depending on the manufacturing method used and the particular
application.
[0030] Turbulizer 18 is a corrugated member 36 having parallel,
spaced-apart corrugations 37 defining upper and lower ridges 38, 40
and planar portions 41 extending between the ridges 38, 40. It is
preferred, in order to achieve sufficient heat transfer
performance, to provide turbulizer 18 with about 15 to about 35
corrugations per inch. Depending upon the degree of contact
required between the turbulizer 18 and the inner surfaces of the
raised central portions 22 of the plates 14, 16, the corrugations
or upper and lower ridges 38, 40 can be shaped so as to have flat
top portions, as shown in FIGS. 2 and 3, or may have more rounded
top portions as shown in FIG. 5 described below. The corrugations
37 can also be formed in a triangular configuration, if
desired.
[0031] The corrugated member 36 is made from an expanded metal mesh
or screen and has a plurality of micro-openings 42 formed therein
interconnected by webs of fine metal material. It will be
appreciated that the micro-openings 42 are preferably provided over
part or all of the planar portions 41. FIGS. 2 and 3 are intended
to illustrate an embodiment in which the micro-openings 42 are
provided over the entire surfaces of all the planar portions 41,
but most of the micro-openings 42 are omitted from FIG. 2 for the
sake of convenience.
[0032] The micro-openings 42 are preferably arranged in a
substantially regular pattern and are preferably of substantially
the same size, so as to provide an overall uniform porosity across
the portions of the turbulizer surfaces in which they are formed.
For example, in the embodiment shown in FIGS. 2 and 3, the
micro-openings 42 are arranged over part or all of the planar
portions 41 of turbulizer 18, so as to provide the planar portions
41 with an overall uniform porosity. Preferably, the overall
uniform porosity of the turbulizer surfaces in which micro-openings
42 are provided is within the range of about 50% to about 80%. In
other words, in any given surface of the turbulizer 18 in which the
micro-openings 42 are provided, such as the planar portions 41 of
FIGS. 2 and 3, the combined open area formed by the micro-openings
42 in that surface accounts for about 50% to about 80% of the total
area of that surface. In the embodiment of FIGS. 2 and 3,
therefore, the open area defined by the micro-openings 42 accounts
for about 50% to about 80% of the total area of the planar portions
41. It may be preferred in some embodiments of the invention to
limit the overall uniform porosity, defined as above, to the range
of about 50% to 70%.
[0033] It will be appreciated that the number of micro-openings 42
per unit area and the overall uniform porosity of the turbulizer 18
are limited in the sense that the overall strength of the
turbulizer should not be unduly compromised by the size or number
of micro-openings 42 formed in the turbulizer 18.
[0034] Although FIG. 2 illustrates turbulizer 18 having
micro-openings 42 covering the entire surfaces of the planar
portions 41 while leaving the upper and lower ridges 38, 40
imperforate, it will be appreciated that this is not essential.
Rather, it will be appreciated that the micro-openings 42 can be
distributed over all the surfaces of the turbulizer 18, including
the planar portions 41 and the ridges 38, 40, in which all the
surfaces of turbulizer 18 preferably have an overall uniform
porosity within the ranges discussed above. The provision of
imperforate top and bottom surfaces of the ridges 38, 40 may be
preferred as it allows for increased contact between the turbulizer
18 and the raised central portions 22 of the tubular members 12
which can result in a more secure braze or bond between the
components of the heat exchanger 10.
[0035] As mentioned above, the micro-openings 42 are preferably all
of substantially the same size and shape in order to assist in
providing the surfaces of turbulizer 18 with an overall uniform
porosity. It will be appreciated that the micro-openings 42 can be
of any shape and size, but are preferably of a shape and size which
can be formed by slitting and expanding the thin sheet material
without creating cracks in the thin webs of metal material
connecting the micro-openings. The shapes and sizes of
micro-openings defined herein are specific examples of shapes which
the inventors have found to be suitable in order to provide
turbulizers according to the invention having acceptable overall
uniform porosity, heat transfer characteristics, and pressure drop.
It will, however, be appreciated that numerous other shapes and
sizes of micro-openings are possible without departing from the
scope of the invention. Among other possible shapes of
micro-openings, some examples include an expanded "pie shape" with
two angular sides and one arcuate side; regular-or irregular
polygonal shapes including diamond-shape, tetrahedral, rhombic,
hexagonal, triangular etc.; circular or oval shapes; raindrop or
teardrop shapes, etc.
[0036] It will be appreciated that the shapes of micro-openings of
the embodiments illustrated herein are examples of micro-openings
which are conveniently formed by slitting the thin sheet material
from which the tubulizer 18 is formed, followed by stretching the
sheet material, generally in a direction perpendicular to the
direction of the slit, to expand the slit into a micro-opening.
Micro-openings produced in this manner typically have two sides
which meet at acute angles, i.e. angles of less than 90
degrees.
[0037] The dimensions and the area of the individual micro-openings
are dependent on the desired overall uniform porosity of the
turbulizer 18, and are also dependent on the shape. The dimensions
and the area of the individual micro-openings are therefore highly
variable, and the inventors have found that the area of an
individual micro-opening may preferably range from about 0.2
mm.sup.2 to about 3 mm.sup.2.
[0038] FIG. 4 shows a turbulizer 18 positioned inside a tubular
member 12 of heat exchanger 10 with the parallel rows of
corrugations 37 oriented perpendicular to the longitudinal axis 43
of the tubular member 12. Therefore, the parallel rows of
corrugations 37 are perpendicular to the direction of flow of the
first heat exchange fluid within the fluid flow passage defined by
tubular member 12, indicated by arrow A, which is referred to as
the "high pressure drop" direction. As the first heat exchange
fluid flows through the tubular member 12 it flows through the
micro-openings 42 formed in the corrugations 37 thereby causing
turbulence in the fluid and decreasing boundary layer growth. The
turbulence and reduction in boundary layer increases heat transfer
thereby increasing the overall performance of the heat exchanger
10. As well, the relatively high overall uniform porosity provided
by the plurality of micro-openings 42 tends to reduce the pressure
drop or fluid losses normally associated with fluid flow in the
high pressure drop direction as there is less resistance
encountered by the fluid as it flows through the turbulizer 18. The
reduction in pressure drop allows for more uniform flow across the
heat exchanger 10, which also improves the overall performance of
the heat exchanger 10.
[0039] The turbulizer 18 is sized so that the imperforate upper and
lower ridges 38, 40 are in contact with the raised central portions
22 of the upper and lower plates 14, 16 of tubular members 12.
Typically, the heat exchange components are made of a material
suitable for brazing Therefore, the contact between upper and lower
ridges 38, 40 and the inner surfaces of the raised central portions
22 of the plates 14, 16 allows the upper and lower ridges 38, 40 to
be brazed to the inner surfaces of the raised central portions 22
of the plates 14, 16. Applications that require very low pressure
drop may require micro-openings larger than 3 mm in area, with
ensuing heat transfer reduction.
[0040] Referring now to FIGS. 5-8, there is shown one corrugation
37 of a turbulizer 18 according to a preferred embodiment. As in
FIGS. 1-4, the micro-openings 42 in FIGS. 5-8 are formed in an
expanded pie-shape configuration. In the embodiment of FIGS. 5-8,
the turbulizer 18 is provided with micro-openings 42 over its
entire surface, including the entireties of the planar portions 41
and the upper and lower ridges 38, 40. In addition, the ridges 38,
40 of turbulizer 18 of FIGS. 5-8 are rounded, rather than flat.
[0041] In the embodiment of FIGS. 5-8, all of the expanded
pie-shaped openings 42 are of substantially the same size and shape
and are arranged in a substantially regular pattern, oriented in
the same direction on the sheet of material used to form the
turbulizer 18, with substantially regular spacing between adjacent
openings 42. A portion of the material used to form the turbulizer
18 is shown in FIG. 9 in its flattened state prior to the
corrugations 37 being formed therein, with the vertical lines
therein representing the lines along which the material will be
folded to form the planar portions 41 and ridges 38, 40. As all of
the openings 42 in the material are oriented in the same direction
it can be seen, referring now to FIGS. 6-8, that the openings 42 on
a first planar portion 41a of the corrugation 37 are oriented in
the opposite direction as the openings 42 on the other or second
planar portion 41b of the corrugation 37. A detail view of the
openings 42 is shown in FIG. 10 wherein the openings have an
arcuate side 44 and an angular or V-shaped side 46. The area of
each pie-shaped micro-opening 42 is typically near the lower end of
the range of about 0.2 mm.sup.2to about 3 mm.sup.2 mentioned above.
As for the dimensions of the pie shaped openings, the longest
tip-to-tip dimension, measured between the two acute corners, each
of which is formed between angular side 46 and arcuate side 44, is
typically about 1.3 mm. The maximum width dimension of the
pie-shaped micro-openings 42 is measured transverse to the
tip-to-tip dimension, and is typically about 0.5 mm. These same
dimensions are applicable to all the pie-shaped micro-openings 42,
as well as pie-shaped micro-openings 54, 62 described below with
reference to FIG. 17. It will be appreciated that the areas and
dimensions of the pie-shaped micro-openings described herein are
merely examples of areas and dimensions which have been found
acceptable by the inventors, and that the areas and dimensions of
acceptable pie-shaped micro-openings may fall outside these
parameters.
[0042] FIG. 18 shows a close-up of another shape of micro-opening
42 which has been found acceptable by the inventors. This shape is
described herein as diamond-shaped but it could also be generally
described as an irregular hexagonal shape. In this type of
micro-opening the longest tip-to-tip dimension, measured between
the two opposite acute corners, is typically about 2.3 mm and the
maximum width dimension, measured perpendicular to the tip-to-tip
dimension, is typically about 1.2 mm. This type of micro-opening 42
has an area which is closer to the upper end of the range of about
0.2 mm.sup.2to about 3 mm.sup.2, for example the area may be about
2 mm.sup.2.
[0043] Referring now to FIGS. 11 and 12, there is shown a portion
of the material used to form another embodiment of turbulizer 18;
with the vertical lines in FIG. 11 representing the lines along
which the material will be folded to form the planar portions 41
and ridges 38, 40. This embodiment is similar to the one discussed
above in connection with FIGS. 5-10, however, in this embodiment
the expanded pie-shaped micro-openings are rotated 90 degrees with
respect to the ones shown in FIGS. 5-10. Therefore, in this
embodiment, the micro-openings 42 on both planar portions 41a, 41b
of each corrugation 37 are oriented in the same direction as shown
in FIGS. 13-16. The areas and dimensions of the pie-shaped
micro-openings of FIGS. 11 and 12 may preferably be the same as
those of the embodiment shown in FIGS. 5-8.
[0044] FIG. 17 shows a portion of the material used to form another
embodiment of the turbulizer 18, according to the present
invention, with the vertical lines in FIG. 17 representing the
lines along which the material will be folded to form the planar
portions 41 and ridges 38, 40. This embodiment is similar to those
discussed above in connection with FIGS. 5-16, having expanded
pie-shaped micro-openings with an arcuate side 44 and an angular or
V-shaped side 46. As shown, the material is formed with an
imperforate strip 48 down the centre thereof. When the material is
corrugated to form a turbulizer, the imperforate strip 48 runs
perpendicular to the rows of corrugations 37 and serves to add
strength to the overall structure of the turbulizer 18. While only
one imperforate strip 48 is shown, it will be understood that
multiple, spaced-apart imperforate strips may be provided, as
desired. As well, in the subject embodiment, the imperforate strip
48 divides the turbulizer into a first and second region 50, 52,
one on either side of the imperforate strip 48. In the first region
50, it will be noted that the plurality of micro-openings 54 are
oriented in a first direction the same as that shown in FIGS. 11-16
with the V-shaped portions 46 directed toward the corresponding end
58 of the corrugation 37 and the arcuate portion 44 directed toward
the imperforate strip 48. In the second region 52, the plurality of
micro-openings 62 are the mirror image of those in the first region
50 with the arcuate portion 44 being directed toward the
imperforate strip 48 and the angled portion 46 directed toward the
corresponding end 68 of the corrugation 37.
[0045] While a particular embodiment of a turbulizer 18 including
an imperforate strip 48 has been described in connection with FIG.
17, it will be understood that imperforate strips can be
incorporated into any of the turbulizer embodiments described
herein.
[0046] To form the turbulizer 18 of any of the embodiments
disclosed herein, generally, a thin sheet of aluminum or any other
suitable material is formed with a plurality of slits in an
appropriate pattern corresponding to the desired porosity for the
turbulizer. The material is then stretched thereby expanding the
plurality of slits to form the plurality of micro-openings 42
formed in the surface of the turbulizer. The expanded mesh material
is then bent or folded transversely along bend lines to form the
corrugations 37. The bend lines are spaced-apart from each other
along the length of the material so that when the material is bent
ridges 38, 40 are formed along the bend lines with planar portions
41 of the material extending between the ridges. The steps of
stretching/expanding and bending of the material may be performed
simultaneously.
[0047] In another embodiment, rather than forming the turbulizer of
heat transfer surface 18 from a sheet of material with a plurality
of slits that must be expanded, the turbulizer is formed from a
sheet of material with a plurality of piercings or punctures spaced
over the surface thereof to form the micro-openings 42. Therefore,
the sheet of material only requires bending to form the
corrugations 37 that make up the turbulizer 18;
[0048] As discussed above, turbulizers according to the invention
provide improved heat exchange by creating turbulence and reducing
boundary layer formation in the fluid, while also reducing the
pressure drop typically associated with fluid flowing across a heat
exchanger with a turbulizer positioned in the "high pressure drop"
direction. FIG. 19 illustrates test results comparing the
"goodness" of an oil-to-water heat exchanger having a louvered fin
as disclosed by the Joshi patent, positioned in the high pressure
drop direction, with an oil-to-water heat exchanger having a
turbulizer 18 according to the present invention.
[0049] Goodness is a measure of the ratio of heat exchange to
pressure drop and is indicative of overall performance of a heat
exchanger. The performance of the Joshi heat exchanger and the heat
exchanger according to the invention were measured at three
different flow rates: 37 l/min, 75 l/min and 132 l/min. Runs A, B
and C relate to tests conducted with a heat exchanger according to
the present invention, and Runs D, E and F relate to tests
conducted with the Joshi heat exchanger. As shown by the test
results, a heat exchanger employing a turbulizer according to the
present invention demonstrated consistently better results for all
flow rates.
[0050] While the present invention has been described with
reference to certain preferred embodiments, it will be understood
by persons skilled in the art that the invention is not limited to
these precise embodiments and that variations or modifications can
be made without departing from the scope of the invention as
described herein. For example, while the exemplary embodiment has
been described mainly in terms of a plurality of stacked tubular
members 12 in the form of plate pairs having raised central
portions 22 and joined peripheral edges, it will be understood that
the tubular members may instead be formed as a unitary tubular
structure. As well, rather than having identical upper and lower
plates 14, 16, the tubular members may be formed with a female
plate having upwardly turned margins and a mating male plate.
Furthermore, while the heat exchanger 10 has been described as
including a plurality of stacked tubular members, it will be
understood that the heat exchanger 10 may comprise as many or as
few tubular members as is required for a particular application.
For instance, the heat exchanger 10 may comprise only a single
tubular member.
* * * * *