FIELD OF THE INVENTION
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
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.
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.
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.
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
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
Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
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;
FIG. 2 is a perspective view of the heat transfer surface shown in FIG. 1;
FIG. 3 is a side elevation view of the heat transfer surface shown in FIG. 2;
FIG. 4 is a partial perspective view of a single heat exchanger tubular member containing a heat transfer surface according to the present invention;
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;
FIG. 6 is a left side view of the corrugation shown in FIG. 5;
FIG. 7 is a top view of the corrugation shown in FIG. 5;
FIG. 8 is a right side view of the corrugation shown in FIG. 5;
FIG. 9 is a top view of a section of material used to form the corrugation shown in FIGS. 5-8;
FIG. 10 is an enlarged, detail view of the encircled area 100 of FIG. 9;
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;
FIG. 12 is an enlarged, detail view of the encircled area 120 of FIG. 11;
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;
FIG. 14 is a left side view of a single corrugation shown in FIG. 13;
FIG. 15 is a top view of the corrugation of FIG. 13;
FIG. 16 is a right side view of the corrugation of FIGS. 13;
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;
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
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
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.
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.
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.
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.
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.
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%.
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.
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.
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.
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.
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 mm2 to about 3 mm2.
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.
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.
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.
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 mm2to about 3 mm2 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.
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 mm2to about 3 mm2, for example the area may be about 2 mm2.
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.
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.
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.
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.
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;
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.
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.
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.
Patent Application
20090260789
