End fed liquid heat exchanger for an electronic component

A body having a bottom and first and second ends and a cavity therein. A plurality of substantially parallel spaced fins are positioned in the cavity. A liquid inlet is centrally positioned in the first end of the body and a liquid outlet is centrally positioned in the second end of the body where flowing cooling liquid between the fins from the first end to the second end with higher fluid flow between the fins in the center for preferentially cooling the center of the heat exchanger. A cross-sectional area of the liquid path in the body minimizes pressure drops and avoids abrupt direction changes and cross-sectional changes. The width, height and spacing of the fins may be varied to control the temperature of the areas in the bottom.

BACKGROUND OF THE INVENTION 
It is known to use a liquid cooled heat exchanger for cooling electronic 
components such as electronic chips. The present invention is directed to 
an improved liquid cooled heat exchanger with high performance in a heat 
exchanger having a plurality of substantially parallel spaced cooling 
fins. The present invention provides high efficiency cooling by using a 
liquid inlet and outlet in line with the liquid channels between the fins 
and preferentially cools the center of the heat exchanger while at the 
same time minimizes the pressure drop of the cooling liquid flowing 
through the heat exchanger. 
SUMMARY 
The present invention is directed to an end fed liquid heat exchanger for 
an electron component which includes a body having a bottom, and first and 
second ends, and said body has a cavity therein. A plurality of 
substantially parallel spaced fins are positioned in the cavity and 
connected to the bottom. The fins have first and second ends positioned 
adjacent the first and second body ends, respectively. A liquid inlet is 
centrally positioned in the first end of the body and a liquid outlet is 
centrally positioned in the second end of the body for flowing cooling 
liquid between the fins from their first ends to their second ends thereby 
providing higher liquid flow between the fins in the center of the bottom. 
This increased liquid velocity in the center results in a higher heat 
transfer coefficient to the cooling fins in the center and provides 
preferential cooling to the center of the heat exchanger which typically 
has the hottest temperature. 
Another feature of the present invention is wherein the liquid 
cross-sectional area in the body from the inlet to the outlet except for 
the area between fins is substantially the same for minimizing pressure 
losses. 
Still a further object of the present invention is the provision of a 
curved and tapered transitional section between the inlet and the cavity 
and also between the outlet and the cavity for avoiding abrupt liquid 
direction changes and abrupt liquid cross-sectional area changes. The 
transitional sections also encourage increased liquid flow through the 
center of the heat exchanger. 
Yet a still further object of the present invention is wherein the first 
and second ends of the fins are slanted downwardly and outwardly towards 
the bottom ends for minimizing pressure losses at the ends of the fins and 
also providing the maximum heat exchange area in the center of the bottom. 
Still a further object of the present invention is the adjustment of the 
fin width, height and/or spacing between the fins to control the 
temperature of the areas in the bottom of the heat exchanger. That is, the 
surface area of the fins in the center of the cavity may be greater than 
the surface area of the fins at the edges of the cavity for increasing the 
heat transfer in the center. The additional surface area at the center may 
be provided by providing more fins at the center with smaller spacings 
between the fins at the center or providing smaller width fins thereby 
increasing the number and surface area of the fins or increasing the 
height of the fins in the center. Decreasing the spacing between the fins 
also increases the heat transfer coefficient. 
Still a further object of the present invention is wherein the 
cross-sectional shape of the cavity may be triangular. 
Other and further objects, features and advantages will be apparent from 
the foregoing description of presently preferred embodiments of the 
invention, given for the purpose of disclosure and taken in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, and particularly to FIGS. 1-3, the reference 
numeral 10 generally indicates the end fed liquid heat exchanger of the 
present invention having a body 12 with a bottom 14, a first end 16, and a 
second end 18. The bottom 14 is shown positioned mated against an 
electronic component such as a chip 20 which in turn is connected by 
suitable electrical connections 22 to a substrate 24. The function of the 
heat exchanger 12 is to provide cooling to the chip 20. 
The body 12 includes a cavity 26 and a plurality of substantially parallel 
spaced fins 30a, 30b, 30c, 30d, 30e, 30f, 30g and 30h connected to the 
bottom 14. The number of fins shown is for convenience only and any 
suitable number may be used. 
The thickness and spacing between the fins may vary. By way of example, the 
thickness may be 0.0010 or 0.0020 inches and the spacing between the fins 
may also be any suitable amount such as 0.0010 or 0.0020 inches. 
A liquid inlet 32 is centrally positioned in the first end 16 of the body 
12 and a liquid outlet 34 is centrally positioned in the second end 18 of 
the body 12 for flowing cooling liquid, for example water, between the 
fins. The fins include first ends 31 and second ends 33 with the first 
ends 31 positioned adjacent the first end 16 of the body 12 and the second 
ends 33 being positioned adjacent the second end 18 of the body 12. 
Therefore, fluid from the inlet 32 flows to the outlet 34 from the first 
ends 31 of the fins to the second ends 33 of the fins through the spaces 
or channels therebetween. 
This structure provides preferential cooling to the center of the heat 
exchange 10 which typically has the hottest temperature, even when the 
chip 20 has a nominally uniform distribution of heat sources and nominally 
uniform cooling. The present invention not only provides a high degree of 
cooling, but it provides extra cooling of the areas which would otherwise 
have higher temperatures. That is, normally, the highest fluid velocity in 
the tubular inlet 32 and the tubular outlet 34 is in the axial center of 
the inlet 32 and outlet 34. Therefore, more liquid flows around the center 
fins 30c, 30d, 30e and 30f than the outer fins 30a, 30b, 30g and 30h. The 
increased liquid velocity in the center results in a higher heat transfer 
coefficient to the fins in the center and provides preferential cooling to 
the center of the heat exchanger 10. This results in increased cooling to 
the center of the chips 20 which usually run hotter in uniformly cooled 
designs. This preferential cooling also decreases the temperature 
difference between points on the surface of the chips 20. 
Additionally, the heat exchanger is provided with a curved and tapered 
transitional section 40 between the inlet 32 and the cavity 26 and a 
curved and tapered transitional section 42 between the outlet 34 and the 
cavity 26 for keeping velocity changes to a minimum to minimize pressure 
losses. In addition, the transitional sections 40 and 42 encourage liquid 
flow to be moved to the center of the cavity 26 rather an at the edges 38, 
thereby aiding the desired preferential cooling of the center. 
The transitional sections 40 and 42 avoid abrupt liquid direction changes 
and abrupt liquid cross-sectional changes. That is, a curved section 44 
provides a curved entry between the inlet 32 and the cavity 26 and the 
curved section 46 provides a curved exit between the cavity 26 and the 
outlet 34 and each of the sections 40 and 42 include tapered sides 48 
which mate with the fin section, as best seen in FIG. 2, to encourage 
liquid flow to be more in the center of the heat exchanger than at the 
edges 38. Also the liquid cross-sectional area in the body from the inlet 
32 to the outlet 34, except for the cavity 26, is substantially the same 
for minimizing velocity changes to minimize pressure losses. That is, the 
cross-sectional area of the inlet 32, the transitional area 40, the 
transitional area 42, and the outlet area 34 are substantially the same. 
However, the cross-sectional area of the space between the fins in the 
cavity 26 is preferably about one-half the area of the other sections for 
increasing the heat transfer coefficient. 
It is to be noted that the ends 31 and 33 of the fins preferably have 
slanted or chamfered ends which slant downwardly and outwardly towards the 
bottom ends. This feature provides a lower pressure drop operation by 
minimizing pressure losses at the entrance and exit of the fins. In 
addition, the slant edges 31 and 33 provide for a relatively lower 
temperature difference on the chip surface 20 by providing more fin area 
in the central region where it is needed than at the first ends 31 and 
second ends 33 where less fin area is required. The slant ends 31 and 33 
may also be selected to control the cross-sectional area of the 
transitional sections 40 and 42. 
While all of the fins may be of equal thickness and spaced apart with equal 
spacing, the cooling in the center can be enhanced further by increasing 
the surface area of the fins in the center, relative to the fins at the 
edges, by varying the width of the fins and/or the channel spacing between 
the fins. Cooling can be increased by providing one or more additional 
fins in the center with smaller spacing, for example, five fins with 0.010 
inches spacing versus four fins with 0.020 inch spacing. This will 
increase the surface area by 25% and will increase the local heat transfer 
coefficient by approximately 80%. This will result in an increased overall 
heat transfer rate of 2.25. 
Referring to FIG. 3, it is noted that all of the fins, 30a-30h, are of 
equal thick fins 30c, 30d, 30e and 30f have been spaced closer together 
and therefore increase the total surface area of fins in the center of the 
body 12 as compared with the fins 30a, 30b, 30g and 30h at the edges of 
the body 12 as well as increasing the heat transfer coefficient in the 
center thereby increasing the local heat transfer at the center, 
particularly in view of the greater liquid velocity flow in the center. 
In FIG. 4, another embodiment of fins is shown in which center fins 50c, 
50d, 50e and 50f are not only thinner than the fins 50a, 50b, 50g and 50h 
at the edges but are also spaced closer together thereby further 
increasing the surface area of the fins in the center and further 
increasing the local heat transfer coefficient. 
Other and further embodiments may be provided such as shown in FIGS. 5 and 
6 wherein like parts to those shown in FIGS. 1-3 are similarly numbered 
with the addition of the suffix "a". It is to be noted that the cavity 26a 
containing the fins 60a, 60b, 60c, 60d, 60e, 60f is triangularly shaped in 
cross section whereby the liquid flow through the center of the cavity 26a 
is not only at an increased velocity, but its volume is considerably 
greater than the volume of the liquid flowing near the edges 38a. This 
feature further increases the cooling efficiency in the center of the heat 
exchanger 10a by providing fins nearer the center with greater heights and 
therefore with greater surface area. As shown in FIG. 6, the fins 60a-60f 
are equal in thickness and spacing, but again this can be varied to 
control the temperature of the areas of the bottom 14a as desired. 
Using the design of the present invention, it has been calculated that the 
present invention will provide cooling to 100 watt chips of one square 
centimeter in size, and yet maintain the temperature within 85.degree. C. 
Further, the present invention is calculated to maintain the temperature 
difference on the chip to within 15.degree. to 20.degree. C. The present 
invention provides lower thermal resistance by providing higher heat 
transfer by higher liquid velocities at preferential center locations and 
by providing more fin area at the center such as by providing a greater 
number of fins and/or smaller spacing of the fins with various widths and 
heights, by providing a liquid flow profile to encourage preferential flow 
to the center, all of which provides a lower temperature difference on the 
chip. The present invention also provides lower pressure drops through the 
heat exchanger by keeping the velocity changes to a minimum along the path 
of the liquid flow, by curving the fluid flow walls which cause any 
direction changes for liquid flow, and by using a regenerative technique 
to reduce the overall pressure drop. 
The present invention, therefore, is well adapted to carry out the objects 
and attain the ends and advantages mentioned as well as others inherent 
therein. While presently preferred embodiments of the invention have been 
given for the purpose of disclosure, numerous changes in the details of 
construction and arrangement of parts will readily suggest themselves to 
those skilled in the art and which are encompassed within the spirit of 
the invention and the scope of the appended claims.