Patent Application
20070062679
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The invention will be more clearly understood with reference to the following drawings wherein:
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
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.
Referring to
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
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.
Referring to
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.
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.
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.
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.
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.
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.
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.
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.
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.
As best illustrated in
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
