U.S. patent application number 09/773119 was filed with the patent office on 2002-08-01 for ductwork improves efficiency of counterflow two pass active heat sink.
Invention is credited to Wagner, Guy R..
Application Number | 20020100577 09/773119 |
Document ID | / |
Family ID | 25097260 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020100577 |
Kind Code |
A1 |
Wagner, Guy R. |
August 1, 2002 |
Ductwork improves efficiency of counterflow two pass active heat
sink
Abstract
The heat removal ability of a spiral finned counterflow two pass
active heat sink ("Wagner" active heat sink) is increased by
eliminating a slight recirculation of heated discharge air back
into the cool intake air by conducting intake air to the Wagner
active heat sink with a ductworks having an orifice proximate the
intake end of the heat sink. The diameter of the orifice is larger
than that of the Wagner active heat sink, and if the heat sink does
not extend into the orifice, then a pusher fan may be located
somewhere near the entrance of the duct to fill it with pressurized
air that then exits from the orifice to form a curtain of cool air
around the outside of the Wagner active heat sink. This curtain of
cool air replaces the certain amount of heated discharge air that
otherwise recirculates back into the input of the heat sink. If the
ductwork can be extended toward the Wagner active heat sink, or the
heat sink moved toward the orifice, such that heat sink penetrates
the orifice and is partly inside the ductwork by an amount related
to the geometry of the fan within the Wagner active heat sink, then
the pusher fan can be eliminated in favor of the suction provided
by the Wagner active heat sink itself.
Inventors: |
Wagner, Guy R.; (Loveland,
CO) |
Correspondence
Address: |
AGILENT TECHNOLOGIES
Legal Department, 51U-PD
Intellectual Property Administration
P.O. Box 58043
Santa Clara
CA
95052-8043
US
|
Family ID: |
25097260 |
Appl. No.: |
09/773119 |
Filed: |
January 31, 2001 |
Current U.S.
Class: |
165/80.3 ;
257/E23.099 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 2924/0002 20130101; H01L 23/467 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
165/80.3 |
International
Class: |
F28F 007/00 |
Claims
I claim:
1. In an active heat sink having fins surrounding a fan that draws
intake air into an end of the fan as well as through intake
portions of the fins surrounding the fan, and which discharges air
through adjacent discharge portions of the fins, a method of
preventing discharged air from recirculating as intake air, the
method comprising the steps of: ducting air to be used as intake
air to a nozzle proximate the end of the fan; pressurizing the
ducted air above the pressure of the discharged air; and directing
a curtain of pressurized air from the nozzle over both the intake
and the discharge portions of the fins.
2. In an active heat sink having fins surrounding a fan that draws
intake air into an end of the fan as well as through intake
portions of the fins surrounding the fan, and which discharges air
through adjacent discharge portions of the fins, a method of
preventing discharged air from recirculating as intake air, the
method comprising the steps of: ducting air to be used as intake
air to a nozzle having an interior surface that surrounds the
intake portions of the fins and that has a periphery proximate a
boundary separating the intake portions of the fins from the
discharge portions of the fins; and inducing, with Bernoulli's
principle and the reduced pressure of the discharged air, a curtain
of air from the nozzle to flow over the discharge portions of the
fins.
Description
REFERENCE TO RELATED APPLICATION
[0001] The subject matter of this Application is related to that
disclosed in U.S. Pat. No. 5,785,116 entitled FAN ASSISTED HEAT
SINK, filed by Wagner on Feb. 1, 1996 and issued on Jul. 28, 1998.
That Patent describes a particular type of internal fan heat sink
for microprocessors, large power VLSI devices and the like, that
dissipate a sufficient amount of power to require a substantial
heat sink. The instant invention pertains to a manner of using that
same type of internal fan heat sink, which heat sink has a number
of unique properties that do not readily lend themselves to summary
description: it is not a garden variety heat sink with a fan
grafted onto it. For this reason U.S. Pat. No. 5,785,116 is hereby
expressly incorporated herein by reference, so that all the unique
properties of that active heat sink, including its manner of
operation and manufacture, will be fully available for the
understanding of this Disclosure.
BACKGROUND OF THE INVENTION
[0002] Integrated circuits are becoming more and more powerful all
the time. Not only is this true in the sense that they do more, and
do it faster (e.g., in the field of microprocessors and
FPGA's--Field Programable Gate Arrays), but these newer parts
dissipate amounts of power that were unimaginable just a few years
ago. For example, there are parts under development that will
dissipate one hundred and thirty watts and will need to get rid of
the attendant heat through a surface area of about one square inch.
There are exotic methods of heat removal that are possible,
including heat pipes, chilled water cooling and even actual
refrigeration. In the main, these techniques are cumbersome or
expensive, and are not suitable for high volume commercial
applications in modestly priced retail equipment, such as personal
computers and workstations.
[0003] The active (meaning fan assisted) heat sink described in
above incorporated Patent to Wagner was developed to deal with this
situation. It is a heat sink having a spiral of fins that surround
a fan around its circumferential periphery and are in its discharge
path. This makes Wagner's active heat sink a two pass device, since
the design draws a portion of its air in through the periphery (one
pass) and then discharges it through more fins (second pass). It is
a counter flow device, since the path of heat flow is generally
opposite to the direction of air flow, so that as air is heated
through contact with the fins it encounters still warmer fins as it
continues along its path. This ensures greater heat transfer by
maintaining temperature differential between the cooling air and
the fins that are to give up their heat to the air. In addition,
Wagner's active heat sink has a number of other desirable
properties, such as low noise and an absence of extra mating
surfaces that interfere with heat flow.
[0004] The preceding several sentences are a brief description of
Wagner's active heat sink, but it is probable that, unless the
reader has actually seen one, he or she will not have a completely
satisfactory mental image of just what such a fine active heat sink
really looks like. We can cure that by including certain of the
figures from the Wagner Patent, which we have done. However, that
still leaves us with the problem of a nice tidy way to refer to it:
"spiral finned counterflow two pass active heat sink" is accurate
as far as it goes, but is also pretty cumbersome. Various heat
sinks of this design are on the market, offered by Agilent
Technologies, Inc. under the trade name "ArctiCooler", but it would
be a risky business to rely on that, since we can't be sure what
that term will eventually come to encompass. So, we will do as we
have already begun to do above: we shall call the kind of
fan-assisted heat sink described in the Specification of the Wagner
Patent a "Wagner active heat sink", or depending upon the
grammatical needs at the time, "Wagner's active heat sink". By
availing ourselves of this coined phrase, we shall avoid much
inconvenience. On the principle that whatever makes for shorter
sentences is good, when it is entirely clear that we are indeed
referring to a Wagner active heat sink, we shall fell free to call
it a "heat sink" as a further simplification.
[0005] It will, of course, be appreciated that as the Wagner active
heat sink gains further acceptance and additional needs and
applications develop, the exact size, relative shape and so forth
will evolve over time. Thus, there are already small ones, medium
and large sizes, and extra heavy duty ones, etc. Thus, it will be
understood that the specific examples shown in U.S. Pat. No.
5,785,116 (Wagner) are merely illustrative of a general class of
active heat sinks (Wagner active heat sinks), and such specific
details as the number of fins, whether they are straight or spiral,
their thickness compared to their height, the number of blades on
the fan, whether the thing is tall or squat, etc., are not
determined by our meaning of the term "Wagner active heat
sink".
[0006] To continue, then, as good as the Wagner active heat sink
is, it is still the case that anything that can be done to enhance
efficiency is desirable, since the wattages to be dissipated are
increasing to such a large degree. One way to get an active heat
sink that handles more heat is to make it bigger, but it would be
better if there were a way to get an existing one to handle more
heat without making it bigger. What to do?
SUMMARY OF THE INVENTION
[0007] A solution to the problem of increasing the heat removal
ability of a Wagner active heat sink is to eliminate a slight
recirculation of heated discharge air back into the cool intake
air. This is accomplished by conducting intake air to the Wagner
active heat sink with a ductworks having an orifice proximate the
intake end of the heat sink. The diameter of the orifice is larger
than that of the Wagner active heat sink, and if the heat sink does
not extend into the orifice, then a pusher fan may be located
somewhere near the entrance of the duct to fill it with pressurized
air that then exits from the orifice to form a curtain of cool air
around the outside of the Wagner active heat sink. This curtain of
cool air replaces the certain amount of heated discharge air that
otherwise recirculates back into the input of the heat sink. If the
ductwork can be extended toward the Wagner active heat sink, or the
heat sink moved toward the orifice, such that heat sink penetrates
the orifice and is partly inside the ductwork by an amount related
to the geometry of the fan within the Wagner active heat sink, then
the pusher fan can be eliminated in favor of the suction provided
by the Wagner active heat sink itself.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a top perspective view of a (prior art) Wagner
active heat sink;
[0009] FIG. 2 is a sectional view of the spiral finned portion of
the heat sink of FIG. 1, with the fan removed for clarity;
[0010] FIG. 3 is a side view of an installed Wagner active heat
sink, showing the directions of airflow, and including the
undesirable recirculation of heated discharge air into the
intake;
[0011] FIG. 4 is a simplified side view of the Wagner active heat
sink of FIG. 1 deployed in conjunction with a first pressurized
ductwork that dispels the recirculation of FIG. 3 with a curtain of
cool air;
[0012] FIG. 5 is a simplified side view of the Wagner active heat
sink of FIG. 1 deployed in conjunction with a second pressurized
ductwork that dispels the recirculation of FIG. 3 with a curtain of
cool air; and
[0013] FIG. 6 is a simplified side view of the Wagner active heat
sink of FIG. 1 deployed in conjunction with a shroud or an
unpressurized ductwork that serves as a baffle to prevent the
recirculation of FIG. 3 while at the same time supplying by suction
from the heat sink itself cool air to the input of the heat
sink.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Refer now to FIG. 1, wherein is shown a top perspective view
of a prior art Wagner active heat sink 1. There is an annular ring
2 of spiral cooling fins, preferable of aluminum, within the center
of which is mounted a fan 3. Not shown is the IC (Integrated
Circuit) or other device that is to be cooled. It would be in
contact with the underside of the heat sink, directly beneath the
hub of the fan.
[0015] Now refer briefly to FIG. 2, which is a sectional view of
the spiral finned portion of the heat sink of FIG. 1, with the fan
3 removed for clarity. Note the shelf 12, which is somewhat below
the bottom of the fan blades are. Somewhat above this shelf (at
about one fourth of the way up the height of the fan blades) is a
boundary (33) that separates where intake air is drawn into the
heat sink and exhaust air is discharged.
[0016] The airflow situation for a Wagner active heat sink is shown
in more detail in FIG. 3. In that figure a heat sink 1 and device 9
to be cooled are mated together, and the combination is mounted
upon or carried by, for example, a printed circuit board 7. Arrows
4 indicate intake air that enters the top of the heat sink 1.
Arrows 5 indicate additional intake air that enters the upper sides
of the heat sink 1. Arrows 8 indicate the paths the intake air from
arrows 4 and 5 follow once inside the heat sink 1. Arrows 6
indicate the path of heated air that is discharged from the heat
sink. Now for the bad news. Some amount of heated discharge air can
flow along paths indicated by arrows 10 and 11 to join the intake
air. This is termed "recirculation", and is undesirable because it
raises the temperature of the intake air entering the heat sink,
and diminishes its efficiency. In general, the amount of
recirculation is determined by the degree of obstruction in the
path of the discharged air. In an ideal case the amount of
recirculation is slight, and the efficiency reduction might be only
5% or 10%. If the discharge path is quite cluttered with large
obstructions (e.g., other heat sinks, etc.) then the efficiency
reduction might be as large as 50%. When the amount of power being
dissipated is large, then even a small fraction of that can be
significant amount of power.
[0017] Refer now to FIG. 4, wherein is shown a simplified side view
23 of a Wagner active heat sink 1 deployed in conjunction with a
pressurized ductwork 13 that dispels the recirculation of FIG. 3
with a curtain of cool air 19. In particular, an air duct 13 has a
nozzle or orifice 17 that is slightly larger in diameter than the
heat sink 1, and which is disposed just above to top of the heat
sink. The ductwork 13, which may be of any suitable material (e.g.,
stamped, rolled or folded sheet metal, extruded plastic, etc.), is
pressurized with air having a positive pressure relative to the
discharge 20 from the heat sink 1. One way to accomplish this is
with a fan 16 located at a distal end of the duct 13, and which
draws in cool air 14 and creates the pressure inside the duct.
Ducted air flows generally along the paths indicated by arrows 15
until it reaches the heat sink. Some of that air enters the top of
the heat sink 1 as indicated by arrows 21, some of it flows out of
the nozzle 17 to travel along the top outer surface of the heat
sink to be drawn in as intake air, as indicated by arrows 18.
Another portion of the ducted airflow 15 continues to travel
downward along the outer surface of the heat sink 1, following a
path indicated by arrows 19. This latter airflow along the path of
arrows 19 is a curtain of cool air that blocks the detrimental
recirculation of arrows 10 and 11 of FIG. 3. There may be some
airflow in the direction of arrows 22, but it does not penetrate
the curtain 19 and is not drawn back into the heat sink.
[0018] The thickness of the air curtain 19 is essentially governed
by the degree by which the nozzle 17 has larger diameter than the
active heat sink 1. A preferred range of thickness for the air
curtain 19 is from about one quarter to one half an inch. In the
figure the periphery of the nozzle 17 is shown as being slightly
above the top of the heat sink 1. It is shown this way for clarity.
The preferred arrangement is that they be about even with each
other.
[0019] FIG. 5 shows a situation whose arrangement 24 is generally
similar to that of FIG. 4, except that the shape of the duct 25 is
different. It may be a plenum chamber, a back side of which may be
an element of the chassis of the apparatus (e.g., a computer) whose
IC 9 needs cooling. In the case shown, pressurized cool air arrives
at the nozzle or orifice from two directions (a typical case would
be that the plenum is as long and as wide as one side of the
instrument chassis, so the air would enter radially from all
directions). We have omitted the depiction of any auxiliary fans
(e.g., 16 in FIG. 4) that would produce this pressurized air. Also,
the figure suggests that airflow within the plenum is in both
directions toward the heat sink. Suppose there were an extended
plenum and more than one heat sink. Then airflow could be in one
direction along the plenum, which air is then supplied to the
different heat sinks in turn.
[0020] Now consider a slightly different case, where it is
undesirable or otherwise impractical to provide a source of air
that is at positive pressure with respect to the discharge of a
Wagner active heat sink, yet it is still desirable to reduce or
eliminate recirculation. An arrangement 27 for dealing with that
situation is depicted in FIG. 6. A nozzle or orifice of a duct
(similar to 25 or 13, but not shown) or perhaps just shroud
extending into a region of cool air suitable for use as intake air,
any of which possibilities are indicated in the figure by reference
character 28, has a diameter larger than that of the heat sink, and
encloses an upper portion of the heat sink 1 that is generally
above location 33. Recall that is at about this height that intake
air is separated from discharge air. What happens is this. Airflow
29 is drawn into the top of the heat sink 1, as one would expect.
Arrows 18 indicate the extent of airflow that is drawn into the
side of the heat sink 1, which ends at location 33. The proximity
of flow along paths 18, in conjunction with a low pressure region
(according to Bernoulli's principle) created by discharge flow
along arrows 20, draws a curtain 30 of cooling air down along the
outside of the heat sink. Arrows 31 and 32 indicate the paths
recirculation would need to take if they were to occur. Arrows 32
indicate paths that air might take to re-enter the heat sink 1
above the level of line 33. Such air is instead swept along by the
curtain 30. Even if some of that air (32) mixes with curtain 30 and
then tries to re-enter above line 33 along path 31, it is blocked
by the shroud or nozzle 28.
[0021] There is yet another way in which airflow for the cases of
FIGS. 4, 5 and 6 can be induced (with or without the fan 16 of FIG.
4). This other way is to locate an exhaust fan 34 within the
chassis. (We show this in conjunction with FIG. 6, but it will be
appreciated that it applies to FIGS. 4 and 5, as well.) If the air
pressure at the top of the heat sink 1 is essentially at the same
pressure as the exterior of the chassis, (especially possible if
the ductwork that is there is for that purpose), then the exhaust
fan creates a pressure differential that produces the air curtain
19.
* * * * *