HEAT EXCHANGER WITH EXPANDED METAL TURBULIZER
A heat exchanger incorporating a turbulizer or heat transfer surface wherein the turbulizer is a corrugated member having parallel spaced-apart ridges and planar portions extending therebetween. The heat transfer surface has a plurality of micro-openings formed over at least a portion of its surface so as to create a uniform porosity over the portions of the turbulizer in which they are provided.
Latest DANA CANADA CORPORATION Patents:
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 INVENTIONIn 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 INVENTIONAccording 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.
Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring first to
As shown in
Referring next to
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
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.
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
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
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.
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
In the embodiment of
Referring now to
While a particular embodiment of a turbulizer 18 including an imperforate strip 48 has been described in connection with
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.
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.
Claims
1. A heat exchanger, comprising:
- a tubular member having first and second spaced-apart walls defining a fluid flow passage therebetween, the tubular member having a fluid inlet and a fluid outlet, said fluid inlet and fluid outlet being spaced-apart from each other thereby defining a flow direction from the fluid inlet to the fluid outlet for the flow of a first fluid through said fluid flow passage;
- a corrugated heat transfer surface located in said flow passage, the heat transfer surface including parallel spaced-apart ridges with planar portions extending therebetween, alternating ridges being in contact with said first and second spaced apart walls, said corrugated heat transfer surface having a plurality of micro-openings which define porous areas of said corrugated heat transfer surface, said porous areas being located in at least said planar portions, said porous areas having a substantially uniform porosity, and said ridges being oriented perpendicular to the flow direction within said flow passage.
2. A heat exchanger as claimed in claim 1, wherein the planar portions are inclined with respect to the spaced-apart walls.
3. A heat exchanger as claimed in claim 1, wherein the planar portions are perpendicular with respect to said spaced-apart walls.
4. A heat exchanger as claimed in claim 1, wherein the micro-openings are formed in a shape selected from the group consisting of an expanded pie-shape and a diamond shape.
6. A heat exchanger as claimed in claim 1, wherein the ridges are imperforate surfaces, said micro-openings being formed only in said planar portions of said heat transfer surface.
7. A heat exchanger as claimed in claim 1, wherein said micro-openings are formed over the entire surface of said heat transfer surface, including said planar portions and said ridges.
8. A heat exchanger as claimed in claim 1, wherein the porosity of said porous areas of said heat transfer surface is in the range of about 50% to about 80%.
9. A heat exchanger as claimed in claim 1, wherein said micro-openings have an average area within a range from about 0.2 mm2 to about 3 mm2.
10. A heat exchanger as claimed in claim 1, wherein the ridges are curved surfaces.
11. A heat exchanger as claimed in claim 1, wherein the ridges are flat surfaces.
12. A heat exchanger as claimed in claim 1, wherein the corrugated heat transfer surface includes an imperforate strip along the length thereof dividing said heat transfer surface into first and second regions, said imperforate strip being oriented perpendicular to said parallel spaced-apart ridges, with said porous areas being provided on both sides of said imperforate strip.
13. A heat exchanger as claimed in claim 12, wherein the micro-openings in said first region are oriented in a first direction and the micro-openings in the second region are oriented in a second direction.
14. A heat exchanger as claimed in claim 1, comprising a plurality of stacked tubular members.
15. A heat exchanger as claimed in claim 14, wherein said plurality of stacked tubular members are formed by mating plate pairs.
16. A heat exchanger as claimed in claim 15, wherein each plate pair comprises an upper plate and a lower plate, each plate having a raised central portion and a peripheral edge, the peripheral edges of the upper and lower plates being joined together when said upper and lower plates placed in back-to-back relationship, each plate having respective end portions formed with raised end bosses defining inlet and outlet openings, the respective inlet and outlet openings of each plate pair communicating with each other when said plate pairs are stacked together to form manifolds.
Type: Application
Filed: Apr 21, 2008
Publication Date: Oct 22, 2009
Applicant: DANA CANADA CORPORATION (Oakville)
Inventors: Bryan Sperandei (Mississauga), Allan K. So (Mississauga), Thomas Seiler (Milton)
Application Number: 12/106,404