EP2612100A2

EP2612100A2 - Compact heat exchanger

Info

Publication number: EP2612100A2
Application number: EP11822714.9A
Authority: EP
Inventors: George Moser; Adam Ostapowicz; Randy Linn
Original assignee: EDC Automotive LLC
Current assignee: EDC Automotive LLC
Priority date: 2010-09-02
Filing date: 2011-09-02
Publication date: 2013-07-10
Also published as: WO2012031200A3; WO2012031200A2; EP2612100A4; US20120055657A1

Abstract

A heat exchanger includes at least two tanks containing a medium to be temperature treated and a plurality of heat exchange tubes extending between the at least two tanks. The heat exchange tubes have exterior surface areas at least partially defining a heat exchange area. A set of cooling fins is located between the heat exchange tubes of the plurality of heat exchange tubes to increase the heat exchange area. The fins are configured to define a plurality of non-straight line paths for the flow of air across the heat exchanger. The non-straight line paths force the flow of air across the heat exchange to change direction and cause impingement of the air onto the fins and tubes as well as turbulence for increasing heat transfer performance.

Description

COMPACT HEAT EXCHANGER

TECHNICAL FIELD

[0001] The present teachings generally relate to heat exchangers. More particularly, the present teachings relate to cooling systems for internal combustion engines.

INTRODUCTION

[0002] This section provides background information related to the present disclosure which is not necessarily prior art.

[0003] Current engine cooling radiators have a number of drawbacks and shortcomings that the present teachings aim to overcome.

[0004] Figure 1 illustrates a prior art heat exchanger in the form of a cooling radiator that is typical of the type used in motor vehicles and for other heat transfer applications. The radiator includes a plurality of tubes that extend between an inlet tank 1 and an outlet tank 2. The tubes 5 are intended to provide an increased surface area exposed to atmosphere. Coolant circulates through the tubes and heat from the coolant is released from the tubes to the atmosphere. The coolant circulates through these multiple parallel tubes from an inlet side to an outlet side. Air flows between the tubes, facilitating the extraction of heat from the tubes. To further increase the heat transfer area of the cooling radiator, fins 6 are disposed between the tubes.

[0005] The heat exchanger is manufactured by inserting the tubes 5 into appropriate openings in the headers 3 and 7. The set of tubes with headers at each end and with fins between the tubes define a heat exchanger core. After the core is assembled, it is brazed in a high temperature brazing oven to achieve a water-tight joint between each tube and the headers. In a subsequent step, plastic tanks 4 and 8 are mounted on the headers, forming a cavity between headers and tanks that fills with coolant in the operation of the heat exchanger. To prevent leakage between the plastic tanks and the headers, a polymer gasket (not shown) may be inserted between headers and plastic tanks. The plastic tanks are held in position and the gaskets are compressed by appropriate metal tabs of the headers. The headers are bent in the final assembly process, wrapping around the plastic tanks and holding them in place.

[0006] The cooling fins 6, function to increase the heat transfer area. Without the cooling fins 6, the heat exchanger would require an increased number of tubes to provide comparable heat transfer. The fins become attached to the tubes in the brazing process, and therefore can drain the heat away from the tubes, serving as an extension of their area. The fins increase the total heat exchange area between the radiator and the atmosphere.

[0007] With reference to Figure 2, another cooling radiator typical of the prior art is illustrated. In this version, the tanks have a round shape. The tanks can be formed of metal, such as aluminum. Tubes and fins are incorporated into the cooling radiator in the manner described with respect to the cooling radiator of Figure 1 .

[0008] Turning to Figure 3, an enlarged portion of a prior art heat exchanger in which the tubes 5 are inserted into the headers 3 is illustrated. The plastic tank 4 is mounted on top of the header. The gasket 9 prevents leakage between tank 4 and header 3. The airflow is perpendicular in a direction to the view of Figure 3, with the air flowing across the heat exchanger core through the triangularly shaped flow channels defined between fins and tubes, such as 10 and 1 1 . Depending on the shape of the fin, the channels may define a different shape than a triangle. A triangle, however, is the most common shape utilized.

[0009] Figure 4 illustrates a top view of the prior art heat exchanger of Figure 3. The tube 5 is inserted into the header 3. The plastic tank 4 is attached to the header 3. The lines identified at reference character 13 represent the lines of contact between the fin and the tube. The distance between these lines of contact is the width of the triangularly shaped channels through which the air flows. As most conventional engine cooling fans are puller fans, the fan blade 12 located between the radiator sucks air into the motor compartment, thereby causing the airflow through the radiator. The airflow is aided by the wind caused by the movement of the vehicle, known as ram air. The arrows in Figure 4 represent the direction of the airflow as it flows across the radiator through the triangular flow channels. It is important to note that these arrows are all parallel straight lines.

[0010] While known radiators have proven to be generally acceptable for their intended purpose, they are all associated with drawbacks. One drawback associated with prior art radiators is a relatively low heat transfer performance. The low heat transfer performance is generally due to the fact that the airflow takes place in the above described devices in a straight-line, undisturbed pattern. Most of the air particles flowing across the radiator do not come in contact with the fins or tubes that define the flow channels and simply cross undisturbed to the other side of the radiator. That is a condition that favors laminar flow, characterized by the heat exchange taking place primarily in the immediate proximity of the walls, while the majority of the flow of the cooling medium (air in this case) contributes little to the heat transfer.

SUMMARY

[0011] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0012] It is an object of the present invention to increase the rate of heat transfer by causing significant turbulence in the airflow across a heat exchanger. The coefficient of heat exchange dramatically increases with turbulence, a fact that can be used to cost effectively increase the performance of a radiator. Generally, the amount of heat Q transferred by a heat exchanger can be described by the formula:

Q = U ^* A ^* Delta T

wherein A is the heat exchange area, Delta T is the difference in temperature between the coolant (water) and the air, and U is the coefficient of heat transfer.

[0013] To increase heat transfer, theoretically these three parameters can be manipulated. In practice however, in modern heat exchanger design it has become difficult to increase the heat exchange area A, because of the cost (aluminum prices) and the additional weight (impact on fuel efficiency). On the contrary, there are considerable efforts underway to reduce weight, size and cost of heat exchangers. The other parameter, Delta T, is determined by other factors that the heat exchanger design normally does not control. That leaves the coefficient of heat exchange U as the most desirable way to achieve a modern high performance heat exchanger at a cost-effective level. Changing the coefficient of heat transfer U is particularly advantageous since U changes in a disproportionate and most favorable way when turbulence is introduced and the boundary layers that limit heat exchange are physically removed.

[0014] The present teachings causes turbulence and the destruction of the boundary layers by forcing impingement of the airflow onto the walls of the flow channels as well as creating collisions between the air particles and the walls, as well as collisions between air particles against each other. The result is a turbulent flow with significantly higher heat transfer. The penalty for this increase in heat transfer is an increase in pressure drop across the heat exchanger. With proper design, this effect can be eliminated or rendered negligible, because the disproportionately higher heat exchange coefficient U makes it possible to reduce radiator width and/or the fin density (i.e. increase the fin pitch), therefore restoring the pressure drop to an acceptable level.

[0015] According to one particular aspect, the present teachings provide a heat exchanger with fins shaped in a way that force a change of direction of the airflow as it crosses the core.

[0016] According to another particular aspect, the present teachings provide a heat exchanger including at least two tanks containing a medium to be temperature treated and a plurality of heat exchange tubes extending between the at least two tanks. The heat exchange tubes have exterior surface areas at least partially defining a heat exchange area. A set of cooling fins is located between the heat exchange tubes of the plurality of heat exchange tubes to increase the heat exchange area. The fins are configured to define a plurality of non-straight line paths for the flow of air across the heat exchanger. The non-straight line paths force the flow of air across the heat exchange to change direction and cause impingement of the air onto the fins and tubes as well as turbulence for increasing heat transfer performance. [0017] According to yet another particular aspect, the present teachings provide a machine for making a fin of a heat exchanger. The machine includes a set of meshing gears in order for imprinting a wavy pattern onto a metal strip and thus generate a wavy fin. The gears have teeth shaped in one of an angular or curved fashion, such as helical, double helical, multiple helical, hypoid or any other type of gears necessary to provide a non- straight line path for the airflow moving across the fin.

[0018] According to still yet another particular aspect, the present teachings provide an adjustable compression fin for a fin and tube heat exchanger. The compressible fine includes elastic flanks that allow the fin to change its height under compression, therefore ensuring a good contact between the fin and the tube without having to specify very tight tolerances for the distance between tubes in the heat exchanger.

[0019] According to still yet another particular aspect, the present teachings provide a heat exchanger shaped so that the fin and tube area substantially match the area swept by a cooling fan. The tanks may be shaped in a substantially semi-circular way, and the tube and fin area is substantially circular in shape. A singular, substantially circular tank may be divided by a partition or baffle into two separate compartments, with one compartment serving as the inlet tank and the second compartment serving as the outlet tank, and with a tube and fin area substantially circular in shape circumscribed by the tank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0021] Figures 1 through 5 are various views of cooling devices in accordance with the prior art.

[0022] Figure 6 is a top view of a cooling device in accordance with the present teachings, the cooling devices shown partially cut-away.

[0023] Figure 7 is a schematic view of airflow through a prior art, straight-fin heat exchanger. [0024] Figure 8 is a schematic view similar to Figure 7, illustrating airflow through an angled fin arrangement in accordance with the present teachings.

[0025] Figures 9 A and 9B are views of a prior art fin for a heat exchanger.

[0026] Figure 10A and 10B are views of a heat exchanger fin constructed in accordance with the present teachings.

[0027] Figure 1 1 is a schematic view of airflow through a heat exchanger constructed in accordance with the present teachings.

[0028] Figure 12 is another schematic view of airflow through a heat exchanger constructed in accordance with the present teachings.

[0029] Figure 13 is another schematic view of airflow through a heat exchanger constructed in accordance with the present teachings.

[0030] Figure 14 is another schematic view of airflow through a heat exchanger constructed in accordance with the present teachings.

[0031] Figure 15 is a simplified view of a portion of a prior art heat exchanger.

[0032] Figure 16 is a view similar to Figure 15, highlighting manufacturing errors often associated with prior art heat exchangers.

[0033] Figure 17 is an enlarged view of a portion of Figure 16, illustrated with proper brazing to eliminate manufacturing errors associated with prior art heat exchangers.

[0034] Figures 18A and 18B are views of another heat exchanger fin constructed in accordance with the present teachings.

[0035] Figure 19A and 19B are views of another heat exchanger fin constructed in accordance with the present teachings.

[0036] Figures 20A and 20B are views of another heat exchanger fin constructed in accordance with the present teachings.

[0037] Figure 21 is a prior art view of an arrangement including a cooling fan located behind a radiator.

[0038] Figure 22 is a heat exchanger constructed in accordance with the present teachings.

DETAILED DESCRIPTION OF VARIOUS ASPECTS [0039] A top view of the radiator of Figure 2 is shown in Figure 5 partially cut-away. As discussed above, airflow through the radiator is in a straight line compared to the incoming airflow. Thus, the airflow is substantially undisturbed. A top view of a radiator in accordance with the present teachings is shown in Figure 6. In contrast to the prior art view of Figure 5, Figure 6 shows the same radiator equipped with an angled fin, which forces the air to change direction. The orientation of the outgoing airflow is different from the orientation of the incoming of the incoming airflow. That change in direction causes a substantial disruption and turbulence.

[0040] Figure 7 shows the airflow through an airflow channel in a prior art, straight-fin heat exchanger. The circles represent air particles, and the line connecting the circles represents the path that the particles follow. The path in this case is a simple straight line. The air particles cross through the heat exchanger core without impinging on or coming close to the walls, and without significantly interacting with other air particles which follow straight-line parallel paths.

[0041] Figure 8 shows the effect of the angled fin of present teachings. The air particles collide against a wall shortly after entering the flow channel. As the result of that collision, the air particles are deflected at an angle equal to the angle of incidence. Shortly after that, the air particles collide against the opposite wall, and are deflected again, this time in the opposite direction. After that, they finally exit the core. The described path is the theoretical path that a particle would follow if it didn't interact with the other particles. In actuality, whenever a particle collides with a wall and gets deflected, it also clashes with other particles which are also being deflected. The result is the local chaos called turbulence, which is highly beneficial effect to the rate of heat exchange. The direction of the airflow exiting the core is basically parallel to the fin orientation.

[0042] Figures 9A and 9B show a typical prior art, triangular straight fin in top view and in cross section, respectively). Figures 10A and 10B show corresponding views of a similar triangular fin constructed in accordance with the present teachings to include an angular orientation.

[0043] Figure 1 1 is a schematic view of a heat exchanger fin in accordance with the present teachings. The fin is illustrated to include a plurality of portions with different angles. In the embodiment illustrated, the fin has first and second portions. The first portion of the fin in Fig. 1 1 is straight, while the second portion is slanted. Many different combinations are anticipated within the scope of the present teachings.

[0044] Figure 12 is a schematic view of another fin in accordance with the present teachings. In this embodiment, the fin includes three different angles, which creates a very high degree of turbulation. This fin may also create a substantial pressure drop, thereby possibly necessitating a more powerful cooling fan.

[0045] Figure 13 is a schematic view of another heat exchanger fin in accordance with the present teachings. In this embodiment, the fin includes two angles.

[0046] Figure 14 shows another configuration wherein the heat exchanger fin is formed in a curved shape rather than straight segments. This configuration creates less turbulation but also less pressure drop.

[0047] Figure 15 illustrates a common problem in heat exchanger manufacturing that may be addressed with the present teachings. At first glance Figure 15 appears to be a correctly made heat exchanger. Upon closer inspection, Figure 16 reveals that some of the fins are in contact with the tubes, which substantially deteriorates the heat exchange. Such errors are often introduced due to manufacturing tolerances, insufficient pressure between parts while brazing and other reasons. A second problem that can be seen in Figure 16 is that when contact occurs, it will likely be in form of a line contact rather than surface contact. Line contact may not provide sufficient area for proper heat exchange. Proper brazing can reduce the issue of line contact as shown in Figure 17. Perfect brazing as shown in Figure 17, however, often does not happen. The braze material 25 can fill gaps and create surface contact (as opposed to line contact) only when the gaps are sufficiently small and uniform since the process relies on capillarity. When the gaps are too wide, capillarity does not happen, and therefore the issue of insufficient contact between fin and tube may be commonly allowed to persist.

[0048] Figures 18A and 18B illustrate another fin in accordance with the present teachings that can significantly contribute to a better heat transfer and thereby address the shortcomings of the prior art discussed above with respect to Figures 15-17. In this fin, the top and bottom of the fin are not pointed, but instead shaped like a short flat segment at the top and bottom of the fin. The purpose of this shape is to increase contact between the fin and the tube by providing a surface contact rather than a line contact. A better and more reliable brazing joint between the fin and tube is also achieved with this type of fin. The joint between the fin and tube is critical, because if it is incomplete then the heat transfer is substantially reduced. It is a common problem in practice that it is difficult with conventional fins to achieve perfect, simultaneous contact of all fins with the corresponding tubes. Typically, a significant number of joints actually have a small air gap, which is very detrimental to the heat transfer. The fin of Figures 18A and 18B can alleviate this problem.

[0049] Figures 19A and 19B show that the fin of Figures 18A and 18B can be further enhanced for certain applications by forming it with curved flanks instead of straight flanks. This fin can be made with a height slightly larger than the distance between the tubes in the core, so that initially the fin appears to be "too high". However, when the core is compressed in the core assembly machinery, the curved flanks of the fin can easily bend and buckle with a spring-like behavior and adjust to the actual distance between tubes, regardless of the manufacturing tolerances, thereby providing excellent contact between fin and tube.

[0050] Figures 20A and 20B show that the fin of Figure 16 can be further enhanced for certain applications by forming it with an angle instead of straight, thereby creating change of direction and turbulence that further increase heat transfer.

[0051] All the types of fins previously shown can also be combined with conventional heat transfer enhancement methods such as louvers.

[0052] It is also possible make the fin with perforations and cutouts on its flanks, thereby allowing the airflow to cross from one airflow channel to a neighboring airflow channel. This further enhances turbulence and heat exchange.

[0053] Figure 21 shows a typical situation with a cooling fan located behind the radiator. The fan 30 sweeps an area 31 , creating maximum airflow across that swept area and limited flow across the area beyond the diameter of the fan. Therefore the part of the radiator located beyond the swept area has suboptimal cooling performance because of lower airflow speed.

[0054] Figure 22 addresses the problem described in Figure 21 . The heat exchanger is shaped in a form that substantially matches the area swept by the cooling fan. That can be achieved with different geometries and designs. In Figure 22, the tanks have a semicircular shape, with the fin and tube area located directly in front of the swept area of the fan. The advantage of this configuration is that the tubes and fins are exposed to maximum airflow and can provide maximum cooling performance. An additional advantage is that the tubes and fins located outside the swept area have been eliminated, reducing weight and cost. When the circular radiator uses the high performance, high turbulence non-straight line fin provided by this invention, then there is the additional advantage of using the fan power in a targeted way on the area that really counts, overcoming the additional pressure loss created by the high performance fin. It should be noticed that in the circular heat exchanger the tubes are of varying length. This could lead to different flow rate between the different tubes because the longer tubes would have a higher pressure loss. That can be compensated by using slightly different tube cross-sections: the longer tubes can be made with a slightly larger cross- section to balance coolant flows.

[0055] It will be appreciated that the present teachings provide a heat exchanger with features that can individually or in combination provide a significant increase in heat transfer performance. Such an increase in thermal performance can be used to design a compact heat exchanger with reduced frontal area, radiator thickness, weight and cost.

[0056] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims

CLAIMS What is claimed is:

1 . A heat exchanger comprising:

at least two tanks containing a medium to be temperature treated;

a plurality of heat exchange tubes extending between the at least two tanks, the heat exchange tubes having exterior surface areas at least partially defining a heat exchange area; and

a set of cooling fins located between the heat exchange tubes of the plurality of heat exchange tubes to increase the heat exchange area, the fins configured to define a plurality of non-straight line paths for the flow of air across the heat exchanger;

wherein the non-straight line paths force the flow of air across the heat exchange to change direction and cause impingement of the air onto the fins and tubes as well as turbulence for increasing heat transfer performance.

2. The heat exchanger of claim 1 , wherein the heat exchanger is an automotive engine cooling radiator.

3. The heat exchanger of claim 1 , wherein the heat exchanger is an HVAC heat exchanger.

4. The heat exchanger of claim 1 , wherein the heat exchanger is a heater core.

5. The heat exchanger of claim 1 , wherein the heat exchanger is an industrial or residential heat exchanger including but not limited to heating, cooling and refrigeration.

6. The heat exchanger of claim 1 , wherein the fin has a wavy shape disposed at an angle with respect to the longitudinal axis of the fin.

7. The heat exchanger of claim 1 , wherein the fin has a wavy shape bent into different sections at different angles with respect to the longitudinal axis of the fin.

8. The heat exchanger of claim 1 , wherein the fin is formed with a wavy shape similar to typical heat exchanger fin but bent into a curved shape with respect to the longitudinal axis of the fin.

9. The heat exchanger of claim 5 wherein heat transfer is further enhanced by providing louvers and/or perforations on the flanks of the fin to further increase turbulence and heat transfer.

10. A machine for making a fin of a heat exchanger, the machine comprising:

a set of meshing gears in order for imprinting a wavy pattern onto a metal strip and thus generating a wavy fin, the gears having teeth shaped in one of an angular or curved fashion, such as helical, double helical, multiple helical, hypoid or any other type of gears necessary to provide a non-straight line path for the airflow moving across the fin.

1 1 . The machine of claim 9, wherein the fin machine uses a combination of gear and rack instead of two gears to generate the fin.

12. An adjustable compression fin for a fin and tube heat exchanger characterized by having elastic flanks that allow the fin to change its height under compression, therefore ensuring a good contact between the fin and the tube without having to specify very tight tolerances for the distance between tubes in the heat exchanger.

13. The fin of claim 1 1 , wherein the flanks are curved in order to facilitate predictable buckling and bending under compression, thus enhancing the adjustability of the fin.

14. The fin of claim 1 1 , wherein the fin has substantially flat segments at the top and bottom of the fin to provide surface area contact as opposed to line contact with the tubes, thus enhancing heat transfer.

15. The heat exchanger of claim 1 , wherein the heat exchanger is an automotive engine cooling radiator with plastic tanks.

16. The heat exchanger of claim 1 , wherein the heat exchanger is an automotive engine cooling radiator with metal tanks.

17. The heat exchanger of claim 14, wherein the heat exchanger is an automotive engine cooling radiator that contains a transmission oil cooler or other embedded or integrated heat exchangers such as condenser, steering fluid cooler, brake fluid cooler and others.

18. The heat exchanger of claim 16, wherein the embedded transmission oil cooler is an all-metal heat exchanger that is integral to the radiator and is formed by simultaneous brazing of the radiator and the transmission oil cooler, without the transmission oil cooler requiring a separate brazing process.

19. The heat exchanger of claim 1 , which is made completely of metal, such as a brazeable aluminum alloy.