The present invention generally relates to oil coolers and, more particularly, apparatus and methods for increasing heat transfer when the oil cooler is hot.
Oil cooler fins can be of a turbulating type to provide maximum heat transfer when hot. However, when cold, the oil does not require cooling and the high viscosity creates high pressure drop when flowing through a highly turbulated fin surface.
To mitigate this problem, oil coolers often have a bypass line at low oil temperatures. This adds cost and complexity to the system, since an actuator and a control are needed.
As can be seen, there is a need for improved apparatus and methods for increased heat transfer in oil coolers having turbulated fins.
In one aspect of the present invention, an oil cooler comprises a cooler core having an oil fin; wherein the oil fin includes a moveable window; wherein the moveable window includes a base and a first flap on one side of the base; wherein the first flap moves between a closed position and an open position; wherein the first flap is in the open position when the cooler core is in a hot condition.
In another aspect of the present invention, an oil cooler comprises a cooler core having a first oil fin element and a second oil fin element; wherein the first and second oil fin elements provide: a first oil path within the first oil fin element; a second oil path within the second oil fin element; a third oil path between the first and second oil fin elements; wherein the first oil fin element includes a first window flap that moves between a first closed position and a first open position; wherein the second oil fin element includes a second window flap that can move between a second closed position and a second open position; wherein, when the first window flap is in the first open position, the first window flap extends into the third oil path; wherein, when the second window flap is in the second open position, the second window flap extends into the third oil path.
In a further aspect of the present invention, an oil cooler comprises a cooler core having a cooling passageway and an oil passageway; wherein the oil passageway includes a serpentine-shaped fin; wherein the fin creates an oil flow path; wherein the fin has one side with a first coefficient of thermal expansion (COE) and a second side with a second coefficient of thermal expansion; wherein the first COE is greater than the second COE; wherein the fin has a first moveable window on one side of the oil flow path; and wherein the first moveable window moves into the oil flow path when the cooler core is in a hot condition.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features.
Broadly, this invention provides an oil cooler with fins made of a bimetallic material. One side of the fin material has a high thermal expansion and the other side has a substantially lower thermal expansion. When heated and allowed to expand, the material will bend into a curve since the high expansion material will increase in length. The remaining part of the fin can be a typical brazed design such as a bar plate or a stamped plate. Window flaps are cut out on three sides of a leg of the fin.
In a cold state, the fins are straight, allowing free flow of cold oil with a minimum pressure drop. As the oil temperature increases, the window flap starts to curve into the flow stream, increasing the turbulence and the heat transfer. The hotter the oil, the greater the increased bending and resulting turbulence.
In an embodiment, the difference between the first and second coefficients of thermal expansion can be from about 2×10−6 K−1 to about 20×10−6 K−1 Thus, as an example, the first material may be 1.5×10−6 K−1, and the second material may be 17.3×10−6K−1
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The moveable window 16, and in particular one or both of the flaps 16a, 16b, can move between a closed position and an open position. Typically, when the core 10a is in a cold condition, the flap(s) are in the closed position. And when the core 10a is in a hot condition, the flap(s) are in the open position. A cold condition is generally defined as less than 60° C. A hot condition is generally defined as greater than 80° C.
The window(s) 16 move as the core 10a changes between cold and hot conditions due to the differential in coefficients of thermal expansion of the windows). For example, in a cold condition, the window material having a higher coefficient of thermal expansion may not tend to change shape. The same can apply to the material having the lower coefficient of thermal expansion. In a hot condition, the window material having a higher coefficient of thermal expansion can tend to change shape, while the material having a lower coefficient of thermal expansion does not tend to change shape or has a lesser tendency to change shape.
In embodiments, the flaps 16, 26 may be pre-formed when the fin is formed, in a direction such that when the fin is exposed to temperature the window opens rather than closes providing less turbulation and pressure drop. This could be beneficial in improving heat transfer at the exit of the heat exchanger where the power temperature potential does not normally permit as much heat transfer.
In embodiments, distances between the flaps 16, 26 can be the same or different. Similarly, the lengths and/or widths of the flaps 16, 26 can be the same or different.
In embodiments, the fin 18 can be implemented in heat exchangers where a pressure drop is lower when less cooling is required. For example, in charge air coolers, a lower boost, there is less heating from a compressor so less cooling is needed. In a standard charge air cooler, the turbulation need to provide adequate cooling at high boost would just create excess pressure drop at low boost.
The figures illustrating the fin spacing, window flap length, and type are not intended to be limited to the ratios indicated. The fin spacing in the figures show a wide space next to a narrow space. This combination is considered effective, but equal spacing may also be used. The fin spacing may be relatively dense at 20 or more fins/inch or relatively open at 10 or less fins per inch. The amount to which the window flap extends into the flow path is a function of flap length and choice of the two materials for the bimetallic structure. A combination of materials with a greater difference between the low expansion material and the high expansion material will bend more. A longer flap length will extend farther into the passage for the same degree of bending. Judicious use of these features in combination with selection of fin spacing permits good control over the fin turbulation characteristics, providing effective turbulation regardless of spacing.
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.