Heat sink having a pressure gradient

A heat sink having a pressure gradient includes a heat sink base plate. Individual fins extend from the base plate and have variable spacing. First adjacent fins form a high pressure zone at a first end of the heat sink, wherein the first adjacent fins are separated by a first distance therebetween. Second adjacent fins form a low pressure zone at a second end of the heat sink, opposite the first end, wherein the second adjacent fins are separated by a second distance, greater than the first distance.

BACKGROUND 
The disclosures herein relate generally to heat sinks used in a computer 
chassis and more particularly to a heat sink having variably spaced fins 
providing a pressure gradient to enhance natural convection cooling. 
The many electrical components in a computer chassis create excessive heat 
which must be removed to keep the system functioning. Many heat removal 
schemes are used in this environment including fans, heat sinks and 
combinations thereof. Heat sinks are often mounted in an abutting 
relationship with a thermal plate, such as that provided on a 
microprocessor module, which conducts heat from the module to the heat 
sink. 
In U.S. Pat. No. 5,406,451 a computer system utilizes a heat sink which 
optimizes the benefits of both linear airflow and turbulent airflow within 
the computer housing. The heat sink has rows of metal fingers extending 
from a metal sheet. A fan generates linear airflow within the housing. The 
heat sink is attached to a heat producing element such that the rows of 
fingers are placed parallel to the direction of airflow in the housing. 
The fingers are spaced apart within a single row to generate turbulence in 
the airflow, and the rows are spaced apart to prevent the turbulence of 
one row from interfering with the turbulence of an adjacent row. 
In U.S. Pat. No. 5,452,181 an apparatus for cooling an integrated circuit 
device has a fan detachably mounted to a heat sink, and the heat sink is 
in turn mounted to an exposed surface of the integrated circuit. The heat 
sink includes a pair of mounting posts, and the fan assembly includes 
corresponding mounting recesses for receiving the mounting posts. The 
mounting recesses are dimensioned to form an interference fit with the 
corresponding mounting posts, in order to retain the mounting posts within 
the mounting recesses. Alternatively, the fan assembly has biased tabs, 
which are received within corresponding recesses formed on the integrated 
circuit device to detachably mount the fan to the heat sink and integrated 
circuit. An electrical connector with biased terminals is mounted on the 
fan, and the biased terminals engage corresponding terminals on the 
integrated circuit upon mounting the fan to the heat sink. 
In U.S. Pat. No. 5,504,652, a unitary heat sink is formed of aluminum and 
includes a planar contact portion for contacting the top of an IC. A 
number of leg portions extend from the contact portion such that each leg 
portion has a distal end. The leg portions, being made of the same 
material as the contact portion, are configured to have a sufficient 
resiliency such that deformations of the leg portions provide a spring 
force in the range of 5 to 16 lbs. against the top of the IC. 
In U.S. Pat. No. 5,584,339, a heat sink assembly for the central processor 
of a computer is provided in which the heat sink is selected from metal 
materials for good thermal conductivity. The heat sink comprises an array 
of heat conductive posts which define a free space for a fan. A number of 
grooves disposed between the posts are provided to engage a base plate. 
The fan is coupled to the base plate and can rotate in the free space. Two 
columns or rows of the heat conductive posts take the form of a hook such 
that the base plate when compressed can be engaged with these hooks. The 
base plate is provided with protrusions to secure to the grooves. 
A present trend in the electronics industry is to provide systems not only 
to be thermally compatible, but more importantly to comply with acoustic 
requirements, i.e. noise. In addition, cost, component space and 
reliability requirements prohibit the use of auxiliary fans to be 
implemented in low-end, cost effective systems. Recent thermal 
arrangements pose a challenge to provide innovative solutions to thermal 
management of high power processors in the system. 
Without an auxiliary fan in the system, and with the microprocessor 
residing adjacent a rear end of the chassis, there is a very low air 
velocity measured at the heat sink/processor interface. A great deal of 
simulation and experimentation has been performed to attempt to enhance 
the venting patterns on the power supply and the system chassis. The 
installation of an auxiliary fan is not always an acceptable solution 
because it increases the unit cost, noise, and introduces an added 
reliability concern. 
Therefore, what is needed is a heat sink cooling device which does not rely 
on a fan supplement to enhance air flow across the heat sink and is 
capable of a self-generated increase in the flow of cooling air across the 
heat sink to enhance natural convection. 
SUMMARY 
One embodiment accordingly, provides a heat sink having a high pressure 
zone and an adjacent low pressure zone provided by a variable fin array 
which creates a natural "chimney" effect, high-to-low pressure gradient 
for enhanced air flow across the sink. To this end, a heat sink includes a 
heat sink base plate and a plurality of fins extending from the plate. 
First adjacent fins form a high pressure zone at a first end of the heat 
sink, wherein the first adjacent fins are separated by a first distance 
therebetween. Second adjacent fins form a low pressure zone at a second 
end of the heat sink, opposite the first end, wherein the second adjacent 
fins are separated by a second distance therebetween, greater than the 
first distance. 
A principal advantage of this embodiment is that the pressure gradient heat 
sink performs a natural cooling draft by accelerating the movement of air 
from the high pressure zone, to the low pressure zone and to the ambient 
environment. Thus, the accelerated low velocity air flow enhances the 
natural convection of heat from the heat sink.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In one embodiment, computer system 10, FIG. 1, includes a microprocessor 
12, which is connected to a buss 14. Bus 14 serves as a connection between 
microprocessor 12 and other components of computer system 10. An input 
device 16 is coupled to microprocessor 12 to provide input to 
microprocessor 12. Examples of input devices include keyboards, 
touchscreens, and pointing devices such as mouses, trackballs and 
trackpads. Programs and data are stored on a mass storage device 18, which 
is coupled to microprocessor 12. Mass storage devices include such devices 
as hard disks, optical disks, magneto-optical drives, floppy drives and 
the like. Computer system 10 further includes a display 20, which is 
coupled to microprocessor 12 by a video controller 22. A system memory 24 
is coupled to microprocessor 12 to provide the microprocessor with fast 
storage to facilitate execution of computer programs by microprocessor 12. 
It should be understood that other busses and intermediate circuits can be 
deployed between the components described above and microprocessor 12 to 
facilitate interconnection between the components and the microprocessor. 
A chassis 26, FIG. 2, includes many components of computer system 10, such 
as for example, microprocessor 12, storage device 18 such as a hard drive, 
and system memory 24. Also included in chassis 26 is a power supply 28, a 
heat sink 30 mounted adjacent power supply 28 and also adjacent 
microprocessor 12. Input device 16 such as a keyboard, is positioned 
adjacent chassis 26 and is connected to a motherboard 32 which 
interconnects the components of system 10. Chassis 26 includes at least 
one vent 36 and power supply 28 also includes a vent 42 and a fan 40. 
In FIG. 3, a partial view of chassis 26 includes a rear wall 34 of chassis 
26 which has the rear chassis vent 36 formed therein. Other vents (not 
shown) are also provided in other wall portions of chassis 26. Air flows 
into chassis 26 through rear vent 36 in the rear wall 34 and circulates 
within chassis 26. Various components within chassis 26 generate a 
substantial amount of heat during operation of the system 10. A large 
portion of the heat generated is provided by processor 12 mounted adjacent 
heat sink 30. Heat sink 30 includes a high pressure zone 30a and a low 
pressure zone 30b. The low pressure zone 30b is adjacent power supply 28 
which includes an intake vent 38 and fan 40 which draws air through power 
supply 28 from intake vent 38 and exhausts the air through outlet vent 42 
in rear wall 34 of chassis 26. 
Heat sink 30, FIG. 4, includes a heat sink base plate 44 and a plurality of 
fins 46 extending from the base plate 44. Fins 46 include a plurality of 
first adjacent fins 46a, and additional adjacent fins 46a forming high 
pressure zone 36a at a first end 48 of heat sink 30. First and additional 
adjacent fins 46a, are separated by first distance dl, therebetween. Fins 
46 also include a plurality of second adjacent fins 46b, and additional 
adjacent fins 46b, forming low pressure zone 36b at a second end 50 of 
heat sink 30. Second and additional adjacent fins 46b, are separated by a 
second distance d.sub.n, therebetween, which is greater than first 
distance d.sub.1. 
Heat sink 130, FIG. 5, includes a heat sink base plate 144 and a plurality 
of fins 146 extending from the base plate 144. Fins 146 include a 
plurality of first adjacent fins 146a, forming a high pressure zone 136a 
at a first end 148 of heat sink 130. First adjacent fins 146a, are 
separated by first distance d.sub.1, therebetween. Fins 146 also include a 
plurality of second adjacent fins 146b, forming low pressure zone 36b at a 
second end 150 of heat sink 130. Second adjacent fins 146b, are separated 
by second distance d.sub.n, therebetween, which is greater than first 
distance d.sub.1. Heat sink 130 further includes additional adjacent fins 
146c, between first adjacent fins 146a, and second adjacent fins 146b. The 
additional adjacent fins 146c are separated by an intermediate distance 
d.sub.2 therebetween. The intermediate distance d.sub.2 is greater than 
the first distance d.sub.1 and less than the second distance d.sub.n. 
Heat sink 230, FIG. 6, includes a heat sink base plate 244 and a plurality 
of fins 246 extending from the base plate 244. Fins 246 include a 
plurality of first adjacent fins 246a, forming a high pressure zone 236a 
at a first end 248 of heat sink 230. First adjacent fins 246a, are 
separated by first distance d.sub.1, therebetween. Fins 246 also include a 
plurality of second adjacent fins 246b forming low pressure zone 236b at a 
second end 250 of heat sink 230. Second adjacent fins 246b, are separated 
by second distance d.sub.n, therebetween, which is greater than first 
distance d.sub.1. Heat sink 230 further includes additional adjacent fins 
246c, 246d, 246e, between first adjacent fins 246a and second adjacent 
fins 246b. The additional adjacent fins 246c, 246d, 246e, are separated by 
a plurality of varying intermediate distances d.sub.2, d.sub.3 which are 
greater than the first distance d.sub.1, and less than the second distance 
d.sub.n. 
Heat sink 330, FIG. 7, includes a heat sink base plate 344 and a plurality 
of fins 346 extending from the base plate 344. Fins 346 include a 
plurality of first adjacent fins 346a, forming a high pressure zone 336a 
at a first end 348 of heat sink 330. First adjacent fins 346a are 
separated by first distance d.sub.1, therebetween. Fins 346 also include a 
plurality of second adjacent fins 346b forming low pressure zone 336b at a 
second end 350 of heat sink 330. Second fins 346b, are separated by second 
distance d.sub.n, therebetween, which is greater than first distance 
d.sub.1. The first adjacent fins 346a have a first fin width w.sub.1, and 
the second adjacent fins have a second fin width w.sub.2, which is greater 
than the first fin width w.sub.1. 
Heat sink 330, FIG. 8, includes heat sink base plate 344 and fins 346 
extending from base plate 344. The fins 346 have a first end f.sub.1 
attached to base plate 344 and a second terminal end f.sub.2. In addition, 
the fins 346 are formed in a plurality of outside rows r.sub.1 and a 
plurality of inside rows r.sub.2 adjacent the outside rows r.sub.1. 
Further inside rows r.sub.3 may also be provided. The second terminal end 
f.sub.2 of the fins 346 of the outside r.sub.1 are bifurcated to provide 
additional surface area. 
In operation, heat is generated by several components within the computer 
chassis. Air enters the chassis through vents in the chassis walls. The 
heat sink is adjacent the power supply and includes the high pressure zone 
and the low pressure zone, and is positioned so that the low pressure zone 
is adjacent the power supply. Heated air in the chassis moves across the 
heat sink in a natural draft from the high pressure zone to the low 
pressure zone resulting in a high-to-low pressure exhaustion of air from 
the low pressure end of the heat sink. The low velocity draft of air tends 
to travel freely in the high-to-low pressure gradient of the heat sink. 
As it can be seen, the principal advantages of these embodiments are that 
the re-aligned fin array creates a natural chimney, high-to-low pressure 
gradient for air flow. The heat sink performs a natural draft cooling by 
pulling air from the high pressure end to the low pressure end and 
exhausting the air from the low pressure end to the environment. The 
resulting low velocity air tends to flow naturally in the high-to-low 
pressure gradient heat sink. Thus, the accelerated low velocity air flow 
enhances the natural convection of heat from the heat sink. The heat sink 
is easy to manufacture and at a low cost. 
As a result, one embodiment provides a heat sink having a base plate and a 
plurality of fins extending from the base plate including first adjacent 
fins forming a high pressure zone at a first end of the heat sink. The 
first adjacent fins are separated from each other by a first distance. 
Second adjacent fins form a low pressure zone at a second end of the heat 
sink, opposite the first end. The second adjacent fins are separated from 
each other by a second distance, which is greater than the first distance. 
Another embodiment provides a computer system including a chassis and a 
microprocessor mounted in the chassis. An input and a mass storage are 
coupled to the microprocessor. A display is coupled to the microprocessor 
by a video controller. A memory is coupled to provide storage to 
facilitate execution of computer programs by the microprocessor in the 
chassis. A heat sink has a base plate mounted adjacent the microprocessor. 
A plurality of fins extend from the base plate and include first adjacent 
fins forming a high pressure zone at a first end of the heat sink. The 
first adjacent fins are separated from each other by a first distance. 
Second adjacent fins form a low pressure zone at a second end of the heat 
sink, opposite the first end. The second adjacent fins are separated from 
each other by a second distance, greater than the first distance. 
A further embodiment provides a method of accelerating natural air flow 
across a heat sink. A plurality of fins are extended from a heat sink base 
plate. A high pressure zone is formed at a first end of the heat sink by 
separating first adjacent fins by a first distance therebetween. A low 
pressure zone is formed at a second end of the heat sink, opposite the 
first end by separating second adjacent fins by a second distance 
therebetween, which is greater than the first distance. 
A still further embodiment provides a pressure gradient heat sink having a 
heat sink base plate. Means extend from the base plate for providing a 
cooling draft by accelerating air movement from a high pressure zone of 
the heat sink to a low pressure zone of the heat sink. The high pressure 
zone includes a first finned array at a first end of the heat sink. The 
low pressure zone includes a second finned array, different from the first 
finned array, and positioned at a second end of the heat sink, opposite 
the first end. 
Although illustrative embodiments have been shown and described, a wide 
range of modification, change and substitution is contemplated in the 
foregoing disclosure and in some instances, some features of the 
embodiments may be employed without a corresponding use of other features. 
Accordingly, it is appropriate that the appended claims be construed 
broadly and in a manner consistent with the scope of the embodiments 
disclosed herein.