U.S. patent application number 11/172672 was filed with the patent office on 2007-03-22 for heat exchanger with modified diffuser surface.
Invention is credited to Keith D. Agee, Richard P. Beldam, Roland L. Dilley.
Application Number | 20070062679 11/172672 |
Document ID | / |
Family ID | 37101588 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070062679 |
Kind Code |
A1 |
Agee; Keith D. ; et
al. |
March 22, 2007 |
Heat exchanger with modified diffuser surface
Abstract
A diffuser comprising an inlet passage, an outwardly diverging
sidewall, and an outlet. The inlet, outwardly diverging sidewall
and outlet each have an inside surface that defines an interior
through which a gas or fluid passes in a flow direction from the
inlet to the outlet. Wherein at least a region of the inside
surface includes a plurality of individual surface features that
are configured to reduce or eliminate unwanted boundary layer
separation of gas or fluid that passes thereover.
Inventors: |
Agee; Keith D.; (Torrance,
CA) ; Beldam; Richard P.; (Torrance, CA) ;
Dilley; Roland L.; (Lomita, CA) |
Correspondence
Address: |
HONEYWELL TURBO TECHNOLOGIES
23326 HAWTHORNE BOULEVARD, SUITE #200
TORRANCE
CA
90505
US
|
Family ID: |
37101588 |
Appl. No.: |
11/172672 |
Filed: |
June 30, 2005 |
Current U.S.
Class: |
165/158 ;
165/174 |
Current CPC
Class: |
F28F 9/0263 20130101;
F28F 2009/029 20130101; F28F 9/02 20130101; F28F 13/02
20130101 |
Class at
Publication: |
165/158 ;
165/174 |
International
Class: |
F28F 9/02 20060101
F28F009/02 |
Claims
1. A diffuser that is connected to a heat exchanger for receiving a
gas or fluid and directing the same to the heat exchanger, the
diffuser having a body that comprises: a gas or fluid inlet passage
at one end of the body and extending a distance therein; an
outwardly diverging wall section extending radially away from the
inlet passage with axial distance from the inlet passage; and an
outlet extending axially away from the outwardly diverging wall
section; wherein the inlet passage, the outwardly diverging wall,
and outlet each have an inside surface that defines an interior
through which a gas or fluid passes in a flow direction from the
inlet passage to the outlet, and wherein at least a section of the
inside surface includes a plurality of individual surface features
that are disposed therealong.
2. The diffuser as recited in claim 1 wherein the individual
surface features are projections that each project outwardly a
distance therefrom and that have a radiused cross sectional
profile.
3. The diffuser as recited in claim 1 wherein the plurality of
individual surface features are positioned along at least a region
of the inside surface of the outwardly diverging wall section.
4. The diffuser as recited in claim 3 wherein the plurality of
individual surface features occupy at least about 10 percent of the
surface area of the outwardly diverging wall section.
5. The diffuser as recited in claim 1 wherein the plurality of
individual surface features are arranged within a plurality of
rows, and wherein each row comprises a plurality of the individual
surface features.
6. The diffuser as recited in claim 5 wherein the surface features
in at least one row are arranged so they are not axially aligned
with the surface features in an adjacent row.
7. The diffuser as recited in claim 1 wherein the outwardly
diverging wall section is conical, wherein the plurality of
individual surface features are in the form of dimples positioned
along an inside surface of the outwardly diverging wall section and
projecting outwardly a distance therefrom, and wherein the dimples
are provided in two or more rows that each extend around the
outwardly diverging wall section.
8. The diffuser as recited in claim 1 wherein the outwardly
diverging wall section is curvilinear, wherein the plurality of
individual surface features are in the form of dimples positioned
along an inside wall surface of the outwardly diverging wall
section and projecting outwardly a distance therefrom, and wherein
the dimples are provided in two or more rows that each extend
around the outwardly diverging wall section.
9. A heat exchanger comprising a plurality of gas or fluid passages
disposed within a shell, the plurality of gas or fluid passages
being defining a first gas or fluid flow passage through the heat
exchanger, and the shell defining a second gas or fluid flow
passage through the heat exchanger that is separate from the first
gas or fluid flow passage, and further comprising a diffuser that
is connected to the heat exchanger and in gas or fluid flow
communication with the first gas or fluid flow passage, the
diffuser comprising: an inlet passage for receiving a gas or fluid
stream and directing the same to the first gas or fluid flow
passage; an outwardly diverging wall section extending away from
the inlet passage; and an outlet that extends away from the
outwardly diverging wall section and that is connected with the
heat exchanger; wherein the outwardly diverging wall section
includes a plurality of projections disposed along an inside
surface and that extend outwardly a distance therefrom, wherein the
projections are provided in two or more rows, and wherein the
projections in each row are separated from one another.
10. The heat exchanger as recited in claim 9 wherein the
projections have a radiused cross sectional profile.
11. The heat exchanger as recited in claim 9 wherein the plurality
of projections occupy at least about 10 percent of the surface area
of the outwardly diverging wall section.
12. The heat exchanger as recited in claim 9 wherein the
projections in at least one row are arranged so they are not
axially aligned with the projections in an adjacent row.
13. The heat exchanger as recited in claim 9 wherein the outwardly
diverging wall section is conical, and wherein the plurality of
projections are dimples having a radiused sued cross sectional
profile.
14. The heat exchanger as recited in claim 9 wherein the outwardly
diverging wall section is curvilinear, and wherein the plurality of
projections are dimples having a radiused cross sectional
profile.
15. A method of reducing boundary layer separation in a gas or
fluid flowing through a heat exchanger comprising an inlet
diffuser, the diffuser having an inlet passage, an outwardly
diverging side wall extending from the inlet passage, and an outlet
extending from the outwardly diverging side wall, the method
comprising the steps of: forming a plurality of individual surface
features on at least a portion of an inside surface of the
outwardly diverging side wall; and flowing a gas or fluid through
the inlet passage, over the surface features and through the
outlet, whereby plurality of individual surface features interrupts
the creation of eddy currents along the outwardly diverging side
wall that reduces boundary layer separation the gas or fluid.
16. The method as recited in claim 15 wherein during the step of
forming, the surface features are provided in the form of
projections that each extend a distance from the inside surface,
wherein the projections are provided in two or more rows, and
wherein the projections within each row are separate from one
another.
17. The method as recited in claim 15 wherein during the step of
forming, the projections are provided in the form of dimples that
each extend a distance from the inside surface and that have a
radiused cross sectional profile.
19. A method of making an inlet gas or fluid diffuser for use with
a heat exchanger, the method comprising the steps of: forming a
diffuser body having a gas or fluid inlet passage at one end of the
body and extending a distance therein, an outwardly diverging wall
section extending radially away from the inlet passage with axial
distance from the inlet passage, and an outlet extending axially
away from the outwardly diverging wall section; modifying a inside
surface of at least a portion of the outwardly diverging wall
section to include a plurality of individual surface features
disposed therealong for reducing boundary layer separation of gas
or fluid that is disposed thereover.
Description
FIELD OF INVENTION
[0001] This invention relates generally to the field of heat
exchangers and, more particularly, to heat exchangers that include
a diffuser that is specially engineering having a modified inside
surface to help control pressure loss and gas or fluid flow
distribution within the heat exchanger.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to heat exchangers that are
generally configured comprising a number of internal fluid or gas
passages disposed within a surrounding body. In an example
embodiment, the internal passages are designed to accommodate
passage of a particular fluid or gas in need of cooling, and the
body is configured to accommodate passage of a particular cooling
fluid or gas, i.e., coolant, used to reduce the temperature of the
fluid or gas in the internal passage by heat transfer through the
structure of the internal passages. A specific example of such a
heat exchanger is one referred to as a shell and tube exchanger,
which can be used in a variety of applications including cooling
the exhaust gas from internal combustion engines.
[0003] Such heat exchangers are often used in the automotive
industry for the purpose of cooling exhaust gas purpose of cooling
pressurized air for example from a turbocharger or supercharger. In
such applications, packaging constraints are often an issue for
such heat exchangers, since the available space for such a heat
exchanger proximate to the engine is often at a premium. Such heat
exchangers generally include an inlet and outlet diffuser at inlet
and outlet ends of the heat exchanger that operate to direct the
gas or fluid in need of cooling into and out the heat exchanger. A
tube bundle comprising a plurality of internal passages is
interposed between the inlet and outlet diffusers and accommodates
the passage of the to be cooled gas or fluid therein.
[0004] For heat exchangers that are placed into service to cool a
gas, the inlet and outlet diffusers represent wasted space from a
heat transfer perspective, as the gas that is passed through the
diffusers are not in heat transfer contact with the heat exchanger
cooling medium. As a consequence of needing to meet tight spatial
demands, heat exchangers that are constructed for use in such gas
cooling applications incorporate the use of a short diffuser, which
can also provide greater space for the heat exchanger core.
However, the use of such short diffusers are known to a create
boundary layer separation of the gas flow entering the heat
exchanger that operates to increase the pressure drop and disrupt
the flow distribution of gas through the heat exchanger.
[0005] In some applications, such as high temperature exhaust gas
coolers, the uneven flow distribution resulting from the use of
such short diffusers can also cause a reduced resistance to thermal
fatigue and reduced heat transfer efficiency. The higher pressure
drop through the heat exchanger as a result of such short diffusers
can also result in less gas flow through the exchanger or higher
fuel consumption to overcome the pressure drop.
[0006] Much of the pressure loss and flow distribution problems
associated with heat exchangers comprising such short diffusers
arise from boundary layer separation of the gas that is flowing
therein. FIG. 1 is a cross-sectional side view of a conical
diffuser 10 of a heat exchanger placed into a gas cooling service.
As can be seen, after the gas has passed through an opening 11 of
diffuser 10, large zones 12 of eddy losses occur and are present
near the transitional conical smooth inside wall surfaces 13 of the
diffuser downstream of the opening 11. This zone of eddy loses that
occur along the wall surface create both a disruption of the gas
flow and a pressure loss within the heat exchanger prior to
entering the heat exchanger core or tube bundle.
[0007] Attempts have been made to control the character of gas flow
in this region through the use of ribs or fins that are positioned
along the diffuser surface. In such attempts, however, the use of
ribs or fins only affected the boundary separation perpendicular to
the gas flow direction. Additionally, the interior surfaces
comprising the ribs or fins used in such attempts can be difficult
and time consuming to manufacture.
[0008] It is, therefore, desired that a heat exchanger be
constructed comprising a diffuser that is specially engineered in a
manner that reduces or eliminates the above-mentioned boundary
layer separation phenomenon for the purpose of reducing pressure
loss, improving gas flow distribution through the heat exchanger,
and thus improving heat exchanger performance and efficiency. It is
further desired that such heat exchanger diffuser be constructed in
a manner that provides space efficient packaging, and that can be
manufactured in a manner that is cost effective.
SUMMARY OF THE INVENTION
[0009] A diffuser of this invention is connected to a heat
exchanger for receiving a gas or fluid and for directing the
received gas or fluid to the heat exchanger. The diffuser includes
a body that has a gas or fluid inlet passage at one end of the body
and that extends a distance therein. The body includes an outwardly
diverging wall section that extends radially away from the inlet
passage with axial distance from the inlet passage. The body
includes an outlet that extends axially away from the outwardly
diverging wall section. The body inlet passage, outwardly diverging
wall, and outlet each have an inside surface that defines an
interior through which a gas or fluid passes in a flow direction
from the inlet passage to the outlet. At least a section of the
inside surface includes a plurality of individual surface features
that are disposed therealong.
[0010] In an example embodiment, the individual surface features
are projections that each project outwardly a distance from the
inside surface and that are positioned along at least a region of
the inside surface of the outwardly diverging wall section. In a
preferred embodiment, the projections are provided in the form of
rounded dimples, and occupy at least about 10 percent of the
surface area of the outwardly diverging wall section. The
projections can be provided in rows and arranged such that the
projections in one row are staggered from the projections in an
adjacent row so as to avoid straight line passage of gas through
the row of projections.
[0011] Configured in this manner, the surface features in the
diffuser operates to prevent the formation of a large gas
recirculation zone along the inside wall surface, thereby
minimizing the formation of macro-boundary layer has separations
and improving the gas flow and thermal transfer efficiencies of the
heat exchanger.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be more clearly understood with reference
to the following drawings wherein:
[0013] FIG. 1 is a cross-sectional side view of a prior art heat
exchanger conical diffuser showing fluid flow vectors demonstrating
boundary layer separation;
[0014] FIG. 2 is a perspective view of a heat exchanger and
diffuser as constructed in accordance with the invention;
[0015] FIG. 3 is a cross-sectional side view of a section of the
heat exchanger of FIG. 2 illustrating a conical diffuser
embodiment;
[0016] FIGS. 4A and 4B are schematic illustrations of the gas flow
within a conventional diffuser not including the surface features
of this invention, and a diffuser construction in accordance with
this invention comprising the surface features, respectively;
[0017] FIG. 5 is a cross-sectional side view of a section of the
heat exchanger of FIG. 2 illustrating a curvilinear diffuser
embodiment;
[0018] FIG. 6 is a perspective view of the diffuser of FIG. 5
illustrating its inside wall surface; and
[0019] FIG. 7 is a cross-sectional side view of a gas flow handling
device constructed in accordance with the principles of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention relates to heat exchangers used for
reducing the temperature of an entering gas or fluid stream. The
particular application for the heat exchangers of the present
invention is with vehicles and, more particularly, to cool an
exhaust gas stream taken from an internal combustion engine.
However, it will be readily understood by those skilled in the
relevant technical field that heat exchanger constructions of the
present invention as described and illustrated herein are
understood to be used in a variety of different applications, and
thus the invention disclosed herein should not be limited to such
applications
[0021] Generally, heat exchangers constructed in accordance with
principles of this invention include a diffuser that has been
specially engineered to have an inside wall surface configured with
a plurality of surface features that are use to reduce or eliminate
unwanted boundary layer separation of gas within the diffuser
during heat exchanger operation. In an example embodiment, the
plurality of surface features is provided in the form of dimples or
outwardly projecting convex elements.
[0022] FIG. 2 illustrates a shell and tube heat exchanger 20
constructed according to principles of the invention that generally
includes a tube bundle or core 22 (shown in cut away form) disposed
within a surrounding shell 24, wherein the tube bundle or core
comprises a plurality of individual gas or fluid passages 26 that
can be provided in the form of individual tubes. The heat exchanger
20 includes a diffuser 28 that is attached to an inlet end 30 of
the heat exchanger shell 24. In this particular embodiment, the
heat exchanger includes an outlet end 32 that is positioned
opposite from the shell inlet end 30, and that includes a flanged
portion 34 that is configured to facilitate connection with a
suitable gas or fluid handling device (not shown). The shell
includes a coolant inlet and a coolant outlet to facilitate the
passage of a suitable cooling medium through the shell.
[0023] Referring to FIGS. 2 and 3, the diffuser 28 comprises a
radially outwardly projecting flange 36 at an end 38 opposite the
heat exchanger shell 24 that is configured and sized to accommodate
attachment with a suitable gas or fluid handling device used to
transfer the gas or fluid to be cooled to the heat exchanger. The
flange 36 can include means for facilitating attachment to such
fluid handling device, such as openings 40 disposed axially
therethough to facilitate a bolted connection therewith. Moving
axially away from the flange 38, the diffuser 32 includes a neck 42
comprising a cylindrical wall surface that defines an inlet passage
44 extending axially inwardly a distance into the diffuser from the
diffuser end 38. In an example embodiment, the inlet passage 44 has
a constant diameter, but inlet passages configured having a
non-constant diameter are also possible and understood to be within
the scope of the invention. In an example embodiment, the inlet
passage can be configured having a round or circular cross section.
However, it is to be understood that the inlet passage 44 may be
configured having other cross-sectional configurations that are
characterized by a constant or variable dimension moving axially
therethrough.
[0024] Moving axially away from the inlet passage 44, the diffuser
28 includes an outwardly or outwardly diverging wall section 46
that extends outwardly away with distance from the inlet passage.
The outwardly diverging wall section 46 can be conical or
curvilinear in configuration depending on the particular heat
exchanger application. In the embodiment illustrated in FIG. 3, the
diffuser outwardly diverging wall section 46 is conical. The
outwardly diverging wall section 46 extends a distance to an end
section 48 that is configured and sized to facilitate connection
with the shell inlet end 30. The end section 48 can be configured
having a constant or variable diameter extending axially
therethrough, and can have a circular or non-circular cross
section. In the embodiment illustrated in FIG. 3, the end section
48 has a constant diameter that is sized to match with the shell 24
to facilitate connection therewith.
[0025] It is to be understood that the dimensions of the diffuser
inlet passage 44 and the outwardly diverging wall section 46 can
and will vary depending on the particular heat exchanger
application. For applications such as exhaust gas cooling for
internal combustion engines, the length of the diffuser, and thus
the length of the inlet passage and outwardly diverging wall
section will be that which provides a desired balance of reduced
sized to meet noted spatial packaging issues, and heat transfer
efficiency.
[0026] Referring to FIG. 3, the diffuser end section 48 is
configured to not only provide a desired attachment with the shell
24, but is also configured to make a desired attachment with a
header 50 that is connected to the tube bundle 22. In an example
embodiment, the diffuser end section 48 includes a recessed groove
52 extending a depth into the inside wall surface that is sized to
accommodate a complementary end section of the header 50 therein.
Constructed in this manner, the diffuser operates to fix the
position of the header and tube bundle within the shell when it is
attached the shell.
[0027] The diffuser inlet passage 44 and outwardly diverging wall
section 46 together define an interior chamber 54 through which a
gas or fluid entering the diffuser passes therethrough. It will be
understood that the diffuser interior chamber 54 increases in
volume as the outwardly diverging wall section 46 extends away from
the inlet passage 44 and towards the end section 48 and end of the
diffuser. After passing through the diffuser 28, the gas or fluid
then enters and passes into the tube bundle 22 of the heat
exchanger.
[0028] The diffuser outwardly diverging wall section 46 is
configured having a plurality of individual surface features 56
disposed therealong. The surface features are configured and
arranged along at least a region of an inside surface of the
outwardly diverging wall section for the purpose of reducing the
eddy losses and boundary layer separation of gas passed through the
diffuser. The surface features can be positioned along the inside
surface of the diffuser that includes the inlet passage 44 and the
outwardly diverging wall section 46. In an example embodiment, the
surface features 56 are positioned along the outwardly diverging
wall section 46.
[0029] It has been discovered that the placement of the surface
features along at least a region of the of the outwardly diverging
wall section 46 operates to reduce and or eliminate eddy loses and
boundary layer separation of gas passing through the diffuser. In
an example embodiment, the surface features preferably occupy at
least about 10 percent of the surface area of the outwardly
diverging wall section.
[0030] The term "individual" as used herein to refer to the surface
features is understood to mean that each surface feature is
separate from one another and is not provided in the form of a
continuous element, such as an elongate rib or a fin. The
individual surface features can be provided in the form of
individual projections that each extend outwardly a distance from
the wall surface. A feature of using such individual projections
when compared to ribs or fins is that they have are more effective
at reducing the unwanted eddy currents along the diffuser inside
wall surface independent of flow direction.
[0031] The projections can be configured and sized differently
depending upon the particular heat exchanger application. The
projections can be disposed along the inside wall surface in an
ordered or random manner, i.e., having an ordered or random
arrangement of repeating projections. In an example embodiment, the
projections are provided in an ordered pattern that are staggered
relative to one another for the purpose of avoiding a straight-line
gas passage along the diffuser surface. The staggered arrangement
of projections operates to further disrupt and prevent the
formation of eddy currents within the diffuser as the gas passes
therethrough, thereby operating to promote gas flow efficiency
through the diffuser and heat exchanger.
[0032] In an example embodiment, the projections are provided in
the form of convex dimples that have a rounded cross sectional
profile and that project outwardly a predetermined distance from
the diffuser inside wall surface. The size of the dimples and the
amount that each projects from the surface can and will vary
depending on the particular use application. In an example
embodiment, for use with a heat exchanger having a diffuser inlet
passage that is sized approximately 38 mm in diameter, that has a
outwardly diverging wall section that extends from this diameter to
a diameter of approximately 80 mm within a distance of
approximately 30 mm, and that is engineered to handle a volumetric
gas flow of approximately 0.12 cubic meters/sec, the dimples are
sized having a radius of curvature of approximately 1.5 mm and
extend a distance from the inside wall surface of approximately 1
mm. It is to be understood that this is but one representative
example of an embodiment of the diffuser within the scope of this
invention, and diffusers configured having dimples sized
differently than this representative example are understood to be
within the scope of this invention.
[0033] The projections can be integrally formed from the wall
surface by such methods as stamping, embossing or the like.
Alternatively, instead of being formed as integral elements of the
diffuser wall surface, the projections can be formed from separate
elements that are each attached to the diffuser inside surface. In
such example embodiment, and as further discussed below, the
projections operate to minimize any flow separation of gas as it is
passed through the diffuser. The dimples or projections can be
solid or hollow.
[0034] The projections can be shaped having a variety of different
configurations, e.g., they can be round, semispherical, square,
conical, triangular, rectangular, etc., or any combination thereof.
In a preferred embodiment, the projections are provided in the form
of rounded dimples as described above. A feature of the
projections, regardless of the shape, is that they function to
reduce or eliminate the occurrence of eddy flow currents along the
diffuser wall surface to minimize or eliminate unwanted boundary
layer separation of the gas flow passing through the diffuser.
[0035] Alternatively, rather that projections, the surface features
can be provided in the form of a plurality of recessed elements,
e.g., convex dimples that are recessed into the inside wall surface
of the diffuser. Still further, the surface features can be
provided in the form of a combination of convex projections and
concave recessed elements, e.g., that are combined in an ordered or
random arrangement. As noted above, regardless of their particular
configuration, the surface features a preferably provided in a
configuration that will function to reduce or eliminate the
occurrence of eddy flow currents along the diffuser wall surface to
minimize or eliminate unwanted boundary layer separation of the gas
flow passing through the diffuser.
[0036] FIG. 3 schematically illustrates how the surface features
disposed along the inside surface of the diffuser operates to
control the flow of gas therein, and more specifically, how they
operate to reduce formation of eddy currents that are known to
cause unwanted boundary layer separation. More specifically, the
projections operate to prevent what is otherwise a macro-separation
of flow formed along the diffuser walls by a relatively large
recirculation zone, and replace it with a system of
micro-separations of flow formed by many relatively small
recirculation zones causing reduced boundary layer separation and
improved gas flow efficiency.
[0037] As best illustrated in FIGS. 4A and 4B, once the gas passes
through the inlet passage 44, a portion of the gas stream 57 flows
adjacent the outwardly diverging wall section 46. FIG. 4A
illustrates a conventional diffuser that does not include the
surface features of this invention. In this diffuser, the gas
stream 57 is split into a relatively large recirculation zone 58
that is formed and exists along the wall section 46. This large
recirculation zone 58 produces the above-noted macro-separation of
gas within the diffuser that causes the gas stream to flow away
from the diffuser wall and, thereby causes reduced gas flow
distribution efficiency within the diffuser and through the heat
exchanger.
[0038] FIG. 4B illustrates a diffuser of this invention comprising
a plurality of the surface features provided in the form of
projections 56 along the wall surface 46. As shown, the projections
operate to interrupt formation of a large recirculation zone along
the wall surface, and replaces it with a series of very small
recirculation zones 59 that produce a system of micro-separations.
The replacement of the single large macro-separation by the system
of smaller micro-separations is desired as it operates to reduce
the diversion of gas flow away from the wall, thereby operating to
increase gas flow distribution efficiency within the diffuser and
through the heat exchanger.
[0039] FIGS. 5 and 6 show another embodiment of a diffuser 60 of
this invention comprising the same general elements as that
disclosed above for the diffuser illustrated in FIG. 3, e.g., a
flange 62 at one end 64, a neck 66 defining an inlet flow passage
68, and a outwardly diverging wall section 70 extending radially
outwardly moving axially away from the inlet flow passage 68.
Unlike the diffuser in FIG. 3, however, this embodiment of the
diffuser has a outwardly diverging wall section that is defined by
outwardly diverging sidewalls curvilinear in shape. The diffuser 60
includes a plurality of surface features 72 disposed along an
inside wall surface. As noted above, the plurality of surface
features 72 can be positioned along a portion of or the entire
region of the inlet passage and/or outwardly diverging wall
section.
[0040] It is to be understood that diffusers of this invention can
be constructed comprising a plurality of surface features disposed
along in inside wall surface of any shaped where it is desirable
prevent boundary layer separation. Thus, the representative
examples described and illustrated herein comprising conical and
curvilinear inside wall sections are not intended to be a
limitation on the present invention.
[0041] As noted above, the use of ribs or fins along the diffuser
surface is known. However, the use of such ribs or fins are known
to only affect the boundary separation of gas flow perpendicular to
the gas flow direction. In contrast, the use of the surface
features presented along the inside wall surface of the diffuser
makes it possible to affect the gas flow in all directions within
the diffuser, rather than just one. This result is especially
beneficial in situations where the gas flow may be swirling or at
an angle within the diffuser due to adverse conditions downstream
from the diffuser. Additionally, the formation of the surface
features, e.g., in the form of projections or dimples, during the
process of casting the diffuser is much easier than that required
for forming ribs or fins.
[0042] As noted above, it will be understood by those skilled in
the art that the shape, pattern and depth of the surface features,
can and will vary depending on such factors as the size and shape
of the heat exchanger and diffuser, the volumetric gas flow rate,
and the end use application. In one example embodiment, illustrated
in FIG. 6, the diffuser 60 is shown to include projections 72 that
are shaped in the form of rounded dimples that each project
outwardly a distance away from the outwardly diverging wall section
70. In this particular example, the dimples 72 are arranged in
three rows, moving axially away from the inlet passage 68, that
each extend circumferentially around the wall section.
[0043] A first row of dimples 74 extends circumferentially around
the outwardly diverging wall section 70 and is placed adjacent the
inlet passage 68. The dimples in this first row are spaced apart at
equal intervals from adjacent dimples in the first row. A second
row of dimples 76 also extends circumferentially around the
outwardly diverging wall section 70 and is placed a predetermined
distance axially away from the first row of dimples 74. The dimples
in this second row are spaced apart at equal intervals from
adjacent dimples in the second row. Additionally, the dimples in
the second row are positioned in a manner that is staggered from
the dimples in the first row, such that each dimple in the second
row is positioned axially between two dimples in the first row.
[0044] A third row of dimples 78 also extends circumferentially
around the outwardly diverging wall section 70 and is placed a
predetermined distance axially away from the second row of dimples
76. The dimples in this third row are spaced apart at equal
intervals from adjacent dimples in the third row. Additionally, the
dimples in the third row are positioned in a manner that is
staggered from the dimples in the second row, such that each dimple
in the third row is positioned axially between two dimples in the
second row and is in axial alignment with a dimple in the first
row. In such example embodiment, the first, second and third rows
of dimples are equally spaced axially from one another.
[0045] For the purpose of helping to optimize gas flow within the
diffuser 60, the first row of dimples is positioned along on the
inside surface of the outwardly diverging wall section 70 at a
point where the wall section 70 starts to diverge sharply, e.g.,
when the tangent to the wall is at an angle greater than about 20
degrees from the gas flow direction. The third row of dimples 78 is
positioned along the inside surface of the outwardly diverging wall
section 70 at a point where the wall section 70 begins to converge
again as it extends towards the end of the diffuser that connects
with the shell. The second row of dimples 76 is interposed along
the surface of the outwardly diverging wall section 70 between the
first row of dimples 74 and the third row of dimples 78.
[0046] While diffusers have been described and illustrated as
including surface features positioned circumferentially around an
entire portion of a diffuser inside wall surface, it is to be
understood that diffusers of this invention can be constructed
having surface features that are positioned at only selected
regions of an inside wall surface, e.g., not provided in rows that
extend completely around the inside wall surface. For example, for
those applications known to have an asymmetric gas flow patters
entering the diffuser, diffusers of this invention may comprise the
surface features positioned along only that part or region of the
diffuser inside surface that is likely to encounter the gas
flow.
[0047] A feature of heat exchangers comprising a diffuser having
the surface features described above is that such surface features
operate to reduce or eliminate the formation of a large
recirculation zone along the inside wall surface, thereby reducing
or eliminating the occurrence of macro boundary layer separation
within the gas flow stream passing therethough. The use of such
surface features, thus enables the heat exchanger designer to
construct a compact heat exchanger in a manner that avoids unwanted
pressure losses, that improves gas flow distribution, and that
improved and thermal heat transfer inefficiencies within the heat
exchanger. Further, the use of such surface features, e.g., when
provided in the form of dimples, enables the control of gas flow to
reduce or prevent large recirculation zones in multiple directions,
thereby operating to further optimize gas flow through the heat
exchanger. A still other feature of diffusers of this invention,
when such surface features are provided in the form of projections
such as dimples, is that they can be formed in a cost effective
manner even when the diffuser surface has a complex shape, e.g., by
molding process.
[0048] Although the concept of using a plurality of surface
features, to reduce or prevent boundary layer separation of gas
flow, has been disclosed and illustrated within the context of a
heat exchanger, e.g., within a diffuser positioned at the inlet of
such heat exchanger, it is to be understood that the invention
concept of using such surface features can additionally be applied
to avoid unwanted boundary layer separation and optimize gas or
fluid flow in other applications that may not involve or exist
within a heat exchanger.
[0049] FIG. 7 illustrates a tube bend 80 that is used for the
transport of gas or fluid therethrough. In such tube bend, the
issue of boundary layer separation may exist due to the creation of
eddy currents and related large recirculation zones that exist
along a region of the inside wall surface 82 adjacent an inside
radius 84 of the tube. In such application, the placement of the
surface features described above along such region 82 can operate
to reduce or eliminate eddy current formation in this region, thus
operating to reduce or eliminate boundary layer separation at this
region and optimize gas or fluid passage therethrough. The same is
true for diffusers that incorporate a bend or other type of
geometric feature, in addition to that described above, that would
cause boundary layer separation.
[0050] Although the invention as described and illustrated above
has been presented in the context of a shell and tube-type heat
exchanger, it is to be understood that the dimpled diffuser of this
invention can be used with other types of heat exchangers and any
gas or fluid conducting volume whose shape might create eddy
losses, and where it is desirable to improve flow distribution and
reduce those eddy losses. For example, the dimpled diffusers of the
present invention may be used with intake manifolds, charge air
ducting and the like. Such embodiments are intended to be within
the scope of this invention. Additionally, while a particular
embodiment of the diffuser of this invention has been described and
illustrated, it is to be understood that modifications and
variations of this configuration may be apparent to those skilled
in the art, and that such modifications and variations are intended
to be within the scope of this invention.
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