Patent ID: 12215933

DETAILED DESCRIPTION

The example embodiments described herein relate to compact automotive heat exchangers having a fluid flow passage provided with a wavy fin turbulizer. The heat exchangers described herein may be configured as cooling plates for cooling heat-generating components such as power electronics components for battery or hybrid electric vehicles. Examples of power electronics components include transistors, diodes, resistors, capacitors, inductors, field effect transistors (FETS), isolated gate bipolar transistors (IGBTs), wide-bandgap semiconductors, power inverters, DC to DC converters, DC to AC converters, and combinations thereof. The heat exchangers may be configured for cooling other heat-generating components in conventional or electric vehicles, such as battery cells. Alternatively, the heat exchangers described herein may be configured as gas to liquid heat exchangers, such as charge air coolers, for cooling a hot gas stream flowing over the exterior surfaces of the heat exchanger.

An embodiment of a compact automotive heat exchanger10for cooling one or more heat-generating components12is described below with reference toFIGS.1to6.

Compact automotive heat exchanger10is generally flat and planar, in the form of a flat elongate tube, having an area in a first plane (xz plane) and a thickness in a second plane (yz plane), the thickness of heat exchanger10being relatively small in comparison to its width and length. The heat exchanger10comprises a first plate wall14having an inner surface16and an opposite outer surface18, and a second plate wall20having an inner surface22and an outer surface24. The outer surface18of the first plate wall14is adapted for thermal contact with the heat-generating component12, typically through an electrically insulating substrate (such as a layer of thermal interface material or “TIM”) and is also referred to herein as the outer heat transfer surface.

The first and second plate walls14,20are generally flat and parallel to each other, and spaced apart in the thickness dimension of the cooling plate10. A fluid flow passage26for circulation of a heat transfer fluid is defined between the inner surfaces16,22of the first and second plate walls14,20, and is enclosed at its outer peripheral edges by a peripheral sidewall28which connects the first and second plate walls14,20.

Heat exchanger10further comprises an inlet port30and an outlet port32spaced apart in the first plane and in fluid communication with the fluid flow passage26. In the present embodiment, the inlet and outlet ports30,32each comprise apertures in the first plate wall14, however, it will be appreciated that the inlet and outlet ports30,32may have different configurations. For example, one or both of the inlet and outlet ports30,32may instead be formed in the second plate wall20or in the peripheral sidewall28. Alternatively, the inlet and outlet ports30,32may comprise through-openings formed through both the first and second plate walls14,20. Although not shown in the drawings, the inlet and outlet ports30,32may be provided with fittings for connection to fluid conduits.

The fluid flow passage26contains a wavy fin turbulizer34, which may be formed by stamping, folding and/or rolling of a thin sheet of metal which is inserted between the plate walls14,20during assembly of heat exchanger10. Instead of being separately formed from a sheet of metal, the wavy fin turbulizer34may be integrally formed with one of the plate walls14or20, for example by machining or impression casting wavy fins onto a flat plate, or by integrally forming the flat plate with wavy fins by casting. In other embodiments, the wavy fins may be metallurgically bonded to one of the plate walls14or20, for example by brazing. For example, the plate wall14or20(with the integrally formed or metallurgically bonded wavy fins) may comprise a cover of a flow passage formed in a cast housing of a compact automotive heat exchanger.

In the embodiments shown in the drawings, the wavy fin turbulizer34is separately formed from a sheet of metal and inserted between plate walls14or20during assembly of heat exchanger10. However, unless otherwise indicated, the following discussion also applies to embodiments where the wavy fin turbulizer34is either formed with or bonded to one of the plate walls14or20before it is inserted into the fluid flow passage26.

As shown inFIGS.3and4, the turbulizer34has a length L (x-axis) and a width W (z-axis), and has a rectangular shape. As shown inFIGS.4and5, turbulizer34has height H (y-axis). The length L is such that the turbulizer34fits lengthwise between the inlet and outlet ports30,32, the turbulizer34having first and second ends36,38which are spaced apart longitudinally (along x-axis). The first end36of turbulizer34is located proximate to inlet port30, with an inlet manifold space40optionally provided between inlet port30and the first end36of turbulizer34. The second end38of turbulizer34is located proximate to the outlet port32, with an outlet manifold space42optionally provided between outlet port32and the second end38of turbulizer34.

The turbulizer34has first and second longitudinal side edges44,46, which extend along the x-axis and are transversely spaced apart (along z-axis) from each other. The width W of turbulizer34is such that it fits between the longitudinal portions of peripheral sidewall28. As shown inFIG.3, the first side edge44of turbulizer34is located proximate to a first longitudinal portion of peripheral sidewall28(labelled28A), and the second side edge46of turbulizer34is located proximate to a second longitudinal portion of peripheral sidewall28(labelled28B). It can be seen fromFIG.3that there are side channels48,50between the side edges44,46of turbulizer34and the respective longitudinal portions28A,28B of peripheral sidewall28, these side channels48,50extending throughout the length of the turbulizer34. In conventional heat exchanger design, the width of side channels48,50is minimized, since they permit bypass flow around the side edges44,46of turbulizer34, and therefore have a negative effect on heat transfer performance. However, in the present embodiment, the width of side channels48,50is not necessarily minimized, for reasons discussed below.

As shown inFIG.5, the height H of turbulizer34is such that the turbulizer34is in contact with the inner surfaces16,22of the first and second plate walls14,20. In some embodiments, the turbulizer34may be metallurgically bonded to one or both of the inner surfaces16,22, for example by brazing, to enhance heat conduction.

The turbulizer34comprises a plurality of longitudinally-extending corrugations52arranged in a regular repeating pattern across its width W. The corrugations52comprise longitudinally-extending sidewalls54extending from the first end36to the second end38of turbulizer34. Where the wavy fin turbulizer34is formed from a separate sheet of metal, each sidewall54is joined to an adjacent sidewall54along its top or bottom edge by a top wall56or a bottom wall58, shown inFIG.5. The terms “top” and “bottom” as used herein are used for the purpose of illustration only, and do not imply that the turbulizer34must have a specific orientation when in use.

In cases where the wavy fin turbulizer34is formed with or bonded to one of the plate walls14or20before it is inserted into the fluid flow passage26, it does not necessarily include top walls56and/or bottom walls58. In such embodiments, the wavy fin turbulizer34may simply comprise fin-like sidewalls54projecting directly from the plate wall14or20on which the turbulizer34is mounted, typically at an angle of 90 degrees to the plate wall14or20.

The sidewalls54may be substantially regularly spaced apart across the width W of turbulizer34, with flow channels60being defined between the sidewalls54. As shown inFIG.5, the sides of flow channels60are enclosed by sidewalls54, while the top and bottom of each flow channel60is enclosed by a top or bottom wall56,58, and an inner surface16,22of one of the plate walls14,20. In embodiments where the wavy fin turbulizer34is formed with or bonded to one of the plate walls14or20before it is inserted into the fluid flow passage26, the top and bottom of each flow channel60may be enclosed by an inner surface16,22of one of the plate walls14,20.

The flow channels60have first and second open ends62,64at the first and second ends36,38of turbulizer34. In the present embodiment, the sidewalls54of turbulizer34are free of perforations such as would be provided in an offset strip fin or a louvered fin. Therefore, all or substantially all the fluid entering any flow channel60at its first open end62will be discharged from its second open end64.

In operation, heat transfer fluid enters the fluid flow passage26through inlet port30and is distributed transversely in inlet manifold space40. The fluid enters the first open ends62of flow channels60. As it flows through the length of turbulizer34, the fluid absorbs heat from an external source, such as a heat-generating component12or a hot gas stream, the heat being conducted through one or both plate walls14,20. The fluid is discharged from the turbulizer34through the second open ends64of flow channels60, entering the outlet manifold space42and then exiting the fluid flow passage26through the outlet port32.

The flow channels60, sidewalls54, top walls56and bottom walls58of wavy fin turbulizer34each have an undulating, serpentine profile (shape), which can be seen when the turbulizer34is viewed in plan view, either from the top or the bottom. As shown inFIG.6, each sidewall54and flow channel60of the turbulizer34comprises a periodic curve made up of a plurality of wave forms66defined along the length of turbulizer34, and comprising alternating crests68and troughs70. The crests and troughs68,70of adjacent sidewalls54and flow channels60are transversely aligned across the width W of turbulizer34, as shown inFIG.6.

Each wave form66has a wavelength λ defined in the longitudinal direction (x-axis) between two adjacent crests68or troughs70, and an amplitude A defined in the transverse direction (z-axis), wherein the crests68and troughs70are spaced apart along the z-axis by twice the amplitude A.

The amplitude A is at a maximum at the crests68and troughs70, and the amplitude A is zero along an imaginary centerline72of a sidewall54or flow channel60. The imaginary centerline72is a straight longitudinal line (shown as a dotted line inFIG.6) which is midway between the crests68and troughs70, and also marks the inflection points74between adjacent crests68and troughs70. If each crest68is considered a convex curve and each trough70is considered a concave curve, the inflection points74mark the points along the curve where the curvature changes from convex to concave. The transitions between convex and concave curves at inflection points74in turbulizer34are smooth transitions.

As mentioned above, the flow channels60are defined between the sidewalls54of turbulizer34. Therefore, the widths of flow channels60are defined by the spacing (pitch) of sidewalls54, and by the thickness of the sheet material comprising turbulizer34. In the present embodiment, all the flow channels60have the same nominal channel width Wc throughout the length L of turbulizer34, and the actual channel width Wc any point is determined by measuring across the flow channel60at an angle of about 90 degrees to the sidewalls54defining the flow channel60. For example,FIG.6shows the channel width Wc at a crest68, and between a crest68and a trough70, at or proximate to an inflection point74. In the present example, the channel width Wc at the inflection point is about 88% of the channel width Wc at the crest68, which is substantially the same as the nominal channel width Wc.

The sidewalls54and flow channels60are smoothly curved throughout the length L of turbulizer34, free of any angular crests68and/or troughs70. The sidewalls54and flow channels60have constant curvature throughout their length, and are free of any completely flat and straight sections connecting the crests68and troughs70.

In addition to having constant curvature, the crests68and troughs70of turbulizer34have a non-circular shape or profile, with the radius of curvature constantly changing throughout the period of each wave form66making up the turbulizer34. Therefore, each wave form66making up the profile of the turbulizer34has an infinite number of radii, with a minimum radius at the crests68and troughs70, and a maximum radius at the inflection points74. This results in a smoothly curved, yet relatively flat and straight transition through the inflection points74between the crests68and troughs70. The use of the word “flat” with regard of the transition through the inflection point does not mean that the sidewall54or flow channels60lacks curvature, but rather refers to the included angle between the sidewall54and the imaginary line72, at the point of inflection74.

Examples of non-circular curves on which the profile of wavy fin turbulizer34may be based include non-circular conic section. Exemplary shapes include elliptical, sinusoidal, parabolic and hyperbolic.

Conventional wavy fin turbulizers generally have a circular profile, with each crest and trough describing a circular arc of constant radius. In a wavy fin turbulizer having a circular profile there is a more pronounced transition at the inflection points between the (convex) crests and the (concave) troughs, with a higher angle relative to line72, than in a comparable wavy fin turbulizer34based on a non-circular curve as discussed herein, having the same amplitude and wavelength.

The inventors have found that wavy fin turbulizers34as described herein have a lower pressure drop than comparable wavy fin turbulizers with a circular profile, and with the same wavelength and amplitude. In addition, the inventors have found that the non-circular profiles of the wavy fin turbulizers34described herein have a beneficial effect on particle pass-through. The inventors believe that these benefits are at least partly due to the degree of flatness of the curve profile between the crests68and troughs70, particularly in the region of the inflection points74, which results in reduced flow channel narrowing. This is now explained with reference toFIG.7, which compares the curvature of a hyperbolic wavy fin turbulizer and a circular wavy fin turbulizer through one half of a wavelength, i.e. between a crest68and a trough70.

FIG.7shows a pair of sidewalls54(solid lines) having a hyperbolic profile, as may be provided in a wavy fin turbulizer34described herein.FIG.7also shows a pair of sidewalls540(dotted lines) having a continuously curved circular profile, as may be provided in a conventional wavy fin turbulizer. Because the sidewalls54and540are superimposed, a single number60is used to identify a flow channel between sidewalls54and a flow channel between sidewalls540. The inflection points74, crests68and troughs70of sidewalls54and540are similarly identified inFIG.7. The sidewalls54and540have the same wavelength and amplitude.

Due to their circular profile, the sidewalls540have a constant radius between the crest68or trough70and the inflection point74. The constant circular radius provides the sidewalls540with a relatively pronounced curvature in the area of the inflection point74. In contrast, the hyperbolic profile of sidewalls54has greater curvature at the crest68and trough70, and lesser curvature in the area of the inflection point74. As a result, the hyperbolic profile of sidewalls54produces a flatter, straighter transition through the inflection point74as compared to the circular profile of sidewalls540. This can be seen by comparing the angles between the sidewalls54and540and an imaginary horizontal line72passing through the inflection points. The included angle between horizontal line72and sidewall540is greater than the angle between horizontal line72and sidewall54.

The flatter, straighter transition of the hyperbolic profile of sidewalls54also results in a smaller degree of flow channel narrowing than the circular profile of sidewalls540. It this regard, the hyperbolic and circular curves of sidewalls54and540converge at the crests68and troughs70, which are the points of maximum channel width. Therefore, the maximum channel widths are the same for the hyperbolic profile of sidewalls54and the circular profile of sidewalls540, and are indicated by Wcmax inFIG.7. The minimum channel widths between sidewalls54and540are indicated by Wcmin1and Wcmin2inFIG.7, respectively, and are at or proximate to the inflection point74.

It can be seen fromFIG.7that the minimum channel width Wcmin1between hyperbolic sidewalls54(about 85% of Wcmax) is greater than the minimum channel width Wcmin2between circular sidewalls540(about 74% of Wcmax). In general, the maximum degree of flow channel narrowing in wavy fin turbulizers34according to embodiments described varies from about 5-15%, whereas the maximum degree of flow channel narrowing in comparable conventional wavy fin turbulizers, with the same wavelength and amplitude, is about 20-30%. In other words, in the wavy fin turbulizers34described herein, the flow channels60of the turbulizer34have a nominal flow channel width and a minimum flow channel width, wherein the minimum flow channel width is about 85-95% of the nominal flow channel width. In general, the degree of flow channel narrowing in wavy fin turbulizers increases with increasing amplitude and/or decreasing wavelength.

The smaller degree of flow channel narrowing in the wavy fin turbulizers34according to embodiments described herein provide turbulizers34with lower pressure drop. In addition, because the minimum channel width in turbulizers34is closer to the nominal channel width, the turbulizers34described herein have better particle pass-through than conventional wavy fin turbulizers. This reduces the need to increase the nominal channel width of a turbulizer34as described herein, to meet particle pass-through requirements. This difference in flow channel narrowing is significant and allows greater flexibility in specifying the nominal channel width to accommodate strict particle pass-through requirements without unduly sacrificing heat transfer performance.

As mentioned above,FIG.7shows the profile of a conventional wavy fin turbulizer having a continuously curved circular profile. In some conventional wavy fin turbulizers, the circular radius at the crests and troughs is smaller than that shown inFIG.7, resulting in a chevron or herringbone pattern in which the circular crests and troughs are connected by straight sections extending through the inflection points. The inventors have found that wavy fin turbulizers with chevron or herringbone profiles have suboptimal heat transfer performance vs. pressure drop, due to the presence of relatively sharp bends at the crests and troughs. Furthermore, as the circular radius of the crests and troughs is decreased, it approaches the shape of an angular corner, and such turbulizers become difficult or impossible to produce, due to manufacturing constraints.

AlthoughFIG.7illustrates the benefits of providing the sidewalls54of a wavy fin turbulizer34with a hyperbolic profile, other non-circular sidewall profiles provide similar benefits. This is illustrated inFIG.8, which shows the subtle distinctions between sidewalls having circular (A), parabolic (B), sinusoidal (C) and hyperbolic (D) profiles.

In some applications all internal surfaces of heat exchanger10, including the wavy fin turbulizer34, may require plating with a thin layer of metal. For example, where the turbulizer34, plate walls14,20and peripheral sidewall28are comprised of copper, it may be required to plate all surfaces within the fluid flow passage26with a thin, uniform layer of nickel. The plated surfaces are the surfaces which will be in contact with heat transfer fluid. This plating must be performed after the heat exchanger is assembled, by contacting all surfaces inside the fluid flow passage26with an aqueous plating solution. The plating process may comprise an electrolytic or electro-less plating process.

As shown inFIG.3, the side channels48,50along the side edges44,46of turbulizer34are irregularly shaped due to the wavy construction of turbulizer34, in that they include alternating wide and narrow areas along the length of turbulizer34, the wide and narrow areas differing by about twice the amplitude A. Normally it is desired to minimize the width of side channels48,50to minimize the volume of bypass flow through side channels48,50, which has a negative effect on heat exchanger performance. However, where plating of surfaces inside fluid flow passage26is required, sufficiently wide side channels48,50must be maintained in order to permit the plating solution to uniformly plate all surfaces defining the side channels48,50, comprising the turbulizer34, plate walls14,20and peripheral sidewalls28.

The inventors have found that defining the width of side channels48,50in relation to the nominal width of flow channels60allows for complete and uniform plating of all internal surfaces within the fluid flow passage26of heat exchanger10. In particular, the inventors have found that the ratio of minimum side channel (48,50) width to flow channel (60) width should be at least ⅓ to provide complete and uniform plating within fluid flow passage26.

The inventors have found that the negative effects of increased bypass flow through side channels48,50is offset by the improved performance provided by the profile of the wavy fin turbulizer34, which is discussed above.

In the present embodiment, where plating of internal surfaces is required, it is important that the wavy fin turbulizer34is properly positioned along the z-axis, to avoid one side channel48or50being too wide, and the other side channel48or50being too narrow. Ideally the wavy fin turbulizer34is centered between the first and second longitudinal portions of peripheral sidewall28A,28B, such that the side channels48,50are of substantially equal width. In order to maintain proper position of turbulizer34, it may be desirable to provide positioning elements protruding from the inner surfaces16,22of the first and second plate walls14,20.

Examples of positioning elements76are illustrated inFIGS.3and5. As shown inFIG.3, a plurality of positioning elements76may be provided along each side edge46,48of turbulizer34. As shown inFIG.5, the positioning elements76may be low, button-like projections or dimples protruding inwardly into the fluid flow passage26from the inner surface22of second plate wall20. Alternatively, or in addition, similar positioning elements76may be provided on the inner surface16of first plate wall14. Although not shown, additional positioning elements may be provided to maintain the longitudinal positioning (along x-axis) of turbulizer34.

Although the wavy fin turbulizers34described herein have constant profiles throughout their length L and width W, this may not be essential in all embodiments. For example, the heat flux across the entire heat transfer surface18may not be constant, particularly where the heat exchanger10is configured as a cooling plate for cooling heat-generating components12such as power electronics components for battery or hybrid electric vehicles, wherein the heat is transferred to the heat transfer surface18only through the component substrate. The profile of the turbulizer34may be varied along its length and/or width to provide greater heat transfer performance in areas of higher heat flux (the substrates of components12), and lower heat transfer performance in areas of lower heat flux (between the substrates of components12). For example, in areas of lower heat flux, the flow channel width may be increased, amplitude decreased, and wavelength increased. Conversely, in areas of higher heat flux, the flow channel width may be decreased, amplitude increased, and wavelength decreased.

As mentioned above, the heat exchanger10described herein may include a wavy fin turbulizer34which is integrated with one of the plate walls14,20, rather than being formed from a separate sheet of metal.FIGS.9and10show an example of such an integrated fin/plate wall structure78, wherein the wavy fin turbulizer34is integrally formed with the first plate wall14, for example by casting, impression casting and/or machining. The wavy fin turbulizer34comprises upstanding, fin-like sidewalls54projecting vertically (along y-axis) from the inner surface16of the first plate wall14. Where the sidewalls54of wavy fin turbulizer34are integrally formed with one of the plate walls14,20, it is unnecessary to provide the wavy fin turbulizer34with top and bottom walls56,58since the plate wall14,20supports and maintains the position of the sidewalls54. Accordingly, in the embodiment ofFIGS.9-10, the wavy fin turbulizer34does not include top or bottom walls56,58, and the sidewalls54are directly connected to the inner surface16of first plate wall14. However, the wavy fin turbulizer34ofFIGS.9and10includes the features described above, including constant, non-circular curvature of the sidewalls54. In addition, the position of turbulizer34on plate wall14,20is such that sufficiently wide side channels will be provided along the side edges44,46, once the integrated fin/plate78is incorporated into a heat exchanger as described above.

The integrated fin/plate78ofFIGS.9and10may comprise a cover plate of heat exchanger10, and be sealingly secured to the peripheral sidewall28by brazing or the like. In some cases part or all of the peripheral sidewall28may be integrated with the integrated fin/plate78, and the inlet and outlet ports30,32may be formed in the first plate wall14of integrated fin/plate78.

Although the invention has been described in connection with certain embodiments, it is not restricted thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.