CROSS REFERENCE TO RELATED APPLICATION(S) Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT Not applicable.

REFERENCE TO A MICROFICHE APPENDIX Not applicable.

TECHNICAL FIELD The present invention is directed toward heat exchangers, and particularly toward compact radiators for use in cooling electronic devices.

BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART Electronic devices such as computer systems are known to generate large amounts of heat, particularly in their processor chips. Excessive heat can degrade the operation of the devices and, moreover, can significantly impact the useful life of the device, including destroying the electronic components if not properly cooled. As a result, such electronic devices typically include some form of cooling system. For example, personal computers will typically include a fan to circulate air through the computer case, and the processing chips are often mounted in a manner so that its heat may be transferred to an element which provides increased surface area and therefore increased heat dissipation as a result of fan blown air passing over that surface area. Liquid cooling systems have also been suggested to provide such cooling for electronic devices, where heat from the processing chips is dissipated into the liquid coolant with the coolant being circulated in a manner so as to reject the heat to air. For example, systems using bar-plate style heat exchangers have been suggested. However, due to sagging of the cover plate of such heat exchangers, such heat exchangers have required tube minor dimensions of at least about 1.2 mm in order to prevent sagging of the cover plate and/or channel blockage due to brazing during manufacture. It is imperative that an adequate amount of cooling be provided with whatever cooling system is used in order to ensure proper operation and useful life of the device. Moreover, such requirements must be met within the strictly confined space of a device in which compactness has long been an important commercial feature. The present invention is addresses the above needs.

SUMMARY OF THE INVENTION In one aspect of the present invention, a compact radiator for a coolant used in cooling an electronic device is provided, including first and second headers, an inlet for receiving the coolant into the first header, an outlet for discharging the coolant from one of the first and second headers, a plurality of parallel flat tubes defining coolant flow paths between the headers, and serpentine fins between adjacent tubes. The tubes have a minor dimension in the range of 0.75 mm to 1.2 mm, and the fins have a height in the range of 3 mm to 7 mm. In one form of this aspect of the invention, the flat tubes are extruded aluminum. In another form of this aspect of the invention, at least the first header includes a baffle, whereby the flat tubes define multiple passes for the coolant. In a further form, the inlet, the outlet, and the baffle are in the first header. In still another form of this aspect of the invention, the minor dimension of the tubes is in the range of 0.75 mm to 0.85 mm. In a further form of this aspect of the invention, the fin height is in the range of 3.0 mm to 3.25 mm. In a further form of this aspect of the invention, the tube major dimension is on the order of 10 to 40 times the tube minor dimension. In further forms, the tube major dimension is on the order of 22 to 32 times the tube minor dimension, or 28 to 32 times, and in a still further form, the minor dimension of the tubes is in the range of 0.75 mm to 0.85 mm and the fin height is in the range of 3.0 mm to 3.25 mm. In yet another form, the tubes have a wall thickness in the range of 0.15 mm to 0.25 mm. In another aspect of the present invention, a compact radiator for a coolant used in cooling an electronic device is provided, including first and second headers, an inlet for receiving the coolant into the first header, an outlet for discharging the coolant from one of the first and second headers, a plurality of parallel flat tubes defining coolant flow paths between the headers, and serpentine fins between adjacent tubes. The tubes have a minor dimension in the range of 0.75 mm to 0.85 mm, and the fins having a height in the range of 3.0 mm to 3.25 mm. In one form of this aspect of the present invention, the flat tubes are extruded aluminum. In another form of this aspect of the invention, at least the first header includes a baffle, whereby the flat tubes define multiple passes for the coolant. In a further form, the inlet, the outlet, and the baffle are in the first header. In a further form of this aspect of the present invention, the tube major dimension is on the order of 10 to 40 times the tube minor dimension and, -A-

in still further forms, the tube major dimension is on the order of 22 to 32 times the tube minor dimension, or 28 to 32 times. in yet another form of this aspect of the present invention, the tubes have a wall thickness in the range of 0.15 mm to 0.25 mm. In a further aspect of the present invention, a compact radiator for an electronic device that rejects heatto a coolant is provided, including first and second headers, an inlet for receiving the coolant into the first header, an outlet for discharging the coolant from one of the first and second headers, a plurality of extruded aluminum parallel flat tubes each defining a plurality of coolant flow paths between the headers, and serpentine fins between adjacent tubes. The tubes have a minor dimension in the range of 0.75 mm to 0.85 mm and a tube major dimension on the order of 22 to 32 times the tube minor dimension, and the fins have a height in the range of 3.0 mm 3.25 mm. In one form of this aspect of the present invention, the tube wall thickness is in the range of 0.15 mm to 0.25 mm. In yet another aspect of the present invention, an electronic device is provided, including at least one heat generating processor chip, a compact radiator, a liquid coolant path, and a pump adapted to circulate liquid coolant through the radiator and liquid coolant path. The radiator includes first and second headers, an inlet for receiving the coolant into the first header, an outlet for discharging the coolant from one of the first and second headers, a plurality of parallel flat tubes defining flow paths between the headers, the tubes having a minor dimension in the range of 0.75 mm to 1.2 mm, and serpentine fins between adjacent tubes, the fins having a height in the range of 3 mm to 7 mm. The liquid coolant path is defined from the radiator outlet to the at least one processor chip and then to the radiator inlet. In one form of this aspect of the invention, the flat tubes are extruded aluminum. In another form of this aspect of the invention, at least the first header includes a baffle, whereby the flat tubes define multiple passes for the coolant. In a further form, the inlet, the outlet, and the baffle are in the first header. In another form of this aspect of the invention, the minor dimension of the tubes is in the range of 0.75 mm to 0.85 mm. In still anotherform of this aspect of the invention, the fin height is in the range of 3.0 mm to 3.25 mm. In a further form of this aspect of the invention, the tube major dimension is on the order of 10 to 40 times the tube minor dimension. In further forms, the tube major dimension is on the order of 22 to 32 times, or 28 to 32 times, the tube minor dimension, and in a still further form, the minor dimension of the tubes is in the range of 0.75 mm to 0.85 mm and the fin height is in the range of 3.0 mm to 3.25 mm. In yet another form, the tubes have a wall thickness in the range of 0.15 mm to 0.25 mm.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a radiator incorporating the present invention; Figure 2 is a front face view of the radiator of Fig. 1 ; Figure 3 is a top view of the radiator of Fig. 1 ; Figure 4 is a cross-sectional view taken along line 4-4 of Fig. 2; Figure 5 is a cross-sectional view taken along line 5-5 of Fig. 2; Figure 6 is a diagram of an electronic device incorporating a radiator embodying the present invention; and Figure 7 is a partially broken away, front face view of a multi-pass radiator incorporating the present invention. DETAILED DESCRIPTION OF THE INVENTION A compact radiator 10 according to the present invention is illustrated in Figs. 1-5. The radiator 10 includes a pair of headers 14, 16, each having inlet/outlet connectors 20, 22 for liquid coolant. Extending between the headers 14, 16 is the radiator core 26 including a plurality of spaced parallel flat tubes 30 with serpentine fins 40 therebetween. End plates 44 may be provided for strength on the top and bottom of the core 26, or additional tubes may alternately be positioned above and below the last rows of fins 40. The radiator core 26 may be made of aluminum, copper, or brass components. Further, the tubes 30 may be extruded, welded or folded/brazed . Extruded aluminum tubes 30 have been found to be particularly suitable. Moreover, though the present invention is not limited to the following dimensions, the following radiator dimensions may be advantageously used in accordance with the present invention:

RADIATOR DIMENSION DIMENSION RANGE Minor tube dimension 0.75 mm to 1.2 mm Major tube dimension 12 to 30 mm Fin height 3 to 7 mm Tube wall thickness 0.15 mm to 0.25 mm Tube aspect ratio (major tube 10:1 to 40:1 dimension to minor tube dimension) Tube pitch to tube minor dimension 3:1 to 10:1 A particularly advantageous configuration tube 30 is formed by extruding aluminum into a size having a major dimension of about 24 mm and a minor dimension of 0.75 to 0.85 mm, and tube wall thicknesses of about 0.2O mm. Upwards of ten separate flow paths or channels 50 (see Fig. 4) are defined from front to back of each tube 30, having an opening height (minor dimension) of around 0.40 mm and a depth (major dimension) of around 2.0 mm. Serpentine fins 40 having a height in the range of 3.0 mm to 3.25 mm may be used with these tubes 30 to particular advantage. Radiator cores 26 according to the above provide advantageous heat exchange by minimizing the air flow bio ckage resulting from the front face of the tubes and may be manufactured cost-effectively, especially for low volume applications. Fig. 6 illustrates an electronic d evice 60 with in which a radiator 10 in accordance with the present invention may be advantageously incorporated. As illustrated diagrammatically, the electronic device 60 includes a housing including at least one heat generating component, such as a processor chip 64, and a path or circuit 66 for coolant (e.g. liquid coolant) which passes near the chip 64 so that the coolant absorbs heat rejected by the chip 64. The radiator 10 is a part of the path 66. A suitable pump 70 circulates the coolant in the path 66 so that the coolant absorbs heat as it passes by the processor chip 64, then passes to an inlet connector 22 of one header 14, then is cooled by passing through the tubes 30 to the other header 16, and then passes out the outlet connector 24 back to the processor chip 64. A suitable fan 74 may also be provided to circulate a ir through the radiator core 26 to facilitate cooling of the coolant in the tubes 30. Fig.7 illustrates another embod iment ofa radiator80 incorporating the present invention, wherein the radiator 80 is a multi-pass heat exchanger. Specifically, a two-pass radiator 80 is illustrated in Fig. 7, wherein both the inlet connector 22' and outlet connector 24' are in the same header 82, separated by a baffle 84. As will be appreciated by those skilled in the art, the core 26' of the radiator 80 may be substantially the same as the previously described core 26, though in this embodiment the coolant will flow from the inlet connector 22" to the top four (of eight as illustrated) tubes 30", then through the second header 86 to the bottom four tubes 30". Coolant exiting the bottom four tubes 30" then is discharged through the outlet connector 24'. It should be recognized, moreover, that still further multi-pass configurations could be used within the scope of the present invention, including more than two passes (with baffles in both headers), and different numbers of tubes (including different numbers of tubes in different passes). It should also be recognized that different flow directions (e.g., with vertical tubes) within the scope of the present invention. It should be appreciated that advantageous cooling for an electronic device may be provided through the use of the present invention, with such cooling provided in a very compact space as is particularly desired for such devices. Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.