COMPACT HEAT EXCHANGER
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.
This application claims the benefit of U.S. Provisional Application No. 61/275,961, filed on Sep. 4, 2009. The entire disclosure of the above application is incorporated herein by reference.
TECHNICAL FIELDThe present teachings generally relate to heat exchangers. More particularly, the present teachings relate to cooling systems for internal combustion engines.
INTRODUCTIONThis section provides background information related to the present disclosure which is not necessarily prior art.
Current engine cooling radiators have a number of drawbacks and shortcomings that the present teachings aim to overcome.
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.
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.
With reference to
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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.
SUMMARYThis section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
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.
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.
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.
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.
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.
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.
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.
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.
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.
A top view of the radiator of
All the types of fins previously shown can also be combined with conventional heat transfer enhancement methods such as louvers.
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.
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.
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
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.
11. 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 11, 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 11, 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.
Type: Application
Filed: Sep 2, 2010
Publication Date: Mar 8, 2012
Inventors: George MOSER (Brighton, MI), Adam OSTAPOWICZ (Westland, MI), Randy LINN (Charlotte, MI)
Application Number: 12/874,334
International Classification: F28D 1/06 (20060101); F28F 1/10 (20060101); B21D 53/02 (20060101);