U.S. patent application number 10/786452 was filed with the patent office on 2005-08-25 for hotspot spray cooling.
This patent application is currently assigned to Isothermal Systems Research. Invention is credited to Cader, Tahir, Knight, Paul A., Tilton, Charles L., Tilton, Donald E., Weir, Thomas D..
Application Number | 20050183844 10/786452 |
Document ID | / |
Family ID | 34861775 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183844 |
Kind Code |
A1 |
Tilton, Charles L. ; et
al. |
August 25, 2005 |
Hotspot spray cooling
Abstract
The present invention is a spray cooling thermal management
device that cools an electronic component creating a varying amount
of heat across its surfaces. Liquid coolant is dispensed upon the
surface of the component. In areas of the chip that generate large
heat fluxes, typically referred to as the core, the liquid coolant
is dispensed as a continuous atomized droplet pattern. The atomized
pattern creates a high heat flux evaporative cooling thin-film over
the one or more core areas. Rather than optimize the atomized
pattern and flow based upon complete thin-film vaporization, the
present invention optimizes the atomized pattern for maximum heat
removal rates. Any excess, non-vaporized, fluid flowing outward
from the hotspot is used to cool the lower heat flux (non-core)
areas of the component through the creation of a thick coolant film
thereon.
Inventors: |
Tilton, Charles L.; (Colton,
WA) ; Tilton, Donald E.; (Colton, WA) ; Weir,
Thomas D.; (Pullman, WA) ; Cader, Tahir;
(Liberty Lake, WA) ; Knight, Paul A.; (Spokane,
WA) |
Correspondence
Address: |
Paul A. Knight
2218 North Molter Road
Liberty Lake
WA
99019
US
|
Assignee: |
Isothermal Systems Research
Liberty Lake
WA
|
Family ID: |
34861775 |
Appl. No.: |
10/786452 |
Filed: |
February 24, 2004 |
Current U.S.
Class: |
165/80.4 ;
257/E23.1 |
Current CPC
Class: |
F28D 15/0266 20130101;
H01L 23/4735 20130101; H01L 2924/0002 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
165/080.4 |
International
Class: |
F28F 007/00 |
Goverment Interests
[0001] This invention was made with Government support under
contract #F33615-03-M-2316 awarded by the Air Force Research
Laboratory. The Government has certain rights in this invention.
Claims
We claim:
1. A spray cooling system comprising: a cooling surface with a
hotspot zone producing a high heat flux; a sprayer in a spaced
apart relationship to said hotspot zone and capable of transforming
a supply of liquid coolant into a continuous pattern of droplets
that impinge and create a thin coolant film generally within said
hotspot zone; and wherein said thin coolant film cools said hotspot
zone primarily through evaporation.
2. The spray cooling system of claim 1, wherein said high heat flux
is greater than 300 watts per square centimeter.
3. The spray cooling system of claim 1, wherein said hotspot zone
includes an array of etched microchannels.
4. The spray cooling system of claim 1, further including a vapor
management protrusion surrounding said sprayer.
5. The spray cooling system of claim 1, wherein said sprayer is an
atomizer.
6. The spray cooling system of claim 1, wherein said sprayer is at
a non-perpendicular angle to said cooling surface.
7. The spray cooling system of claim 1, wherein the mass flow rate
of said impinging droplets is greater than the mass flow rate in
which said thin coolant film is evaporated.
8. A spray cooling system comprising: a cooling surface with a
hotspot zone producing a high heat flux; a sprayer in a spaced
apart relationship to said hotspot zone and capable of transforming
a supply of liquid coolant into a continuous pattern of droplets
that impinge and create a thin coolant film within said hotspot
zone; wherein said thin coolant film cools said hotspot zone
primarily through evaporation; and wherein non-evaporated amounts
of said thin coolant film dispensed within said hotspot zone
creates a thicker coolant film over the remaining areas of said
cooling surface.
9. The spray cooling system of claim 8, further comprising at least
one secondary orifice for adding said coolant to said thick coolant
film.
10. The spray cooling system of claim 9, wherein said secondary
orifice is a incremental drop ejector.
11. The spray cooling system of claim 8, further comprising a vapor
management protrusion surrounding said sprayer.
12. The spray cooling system of claim 8, wherein at least a portion
of said cooling surface includes a plurality of microchannels.
13. The spray cooling system of claim 8, wherein said sprayer is at
a non-perpendicular angle with said component.
14. The spray cooling system of claim 8, wherein said sprayer is an
atomizer.
15. A spray cooling system comprising: an electronic component with
a cooling surface having a hotspot zone producing a high heat flux;
a sprayer in a spaced apart relationship to said hotspot zone and
capable of transforming a supply of liquid coolant into a
continuous pattern of droplets that impinge and create a thin
coolant film within said high hotspot zone; wherein said thin
coolant film cools said hotspot zone primarily through evaporation;
and wherein non-evaporated amounts of said thin coolant film
dispensed within said hotspot zone creates a thicker coolant film
over the remaining areas of said cooling surface.
16. The spray cooling system of claim 15, further comprising at
least one secondary orifice for adding said liquid coolant to said
thick coolant film.
17. The spray cooling system of claim 16, wherein said secondary
orifice is an incremental drop ejector.
19. The spray cooling system of claim 15, further comprising a
vapor management protrusion surrounding said sprayer.
20. The spray cooling system of claim 15, wherein at least a
portion of said cooling surface includes a plurality of
microchannels.
21. The spray cooling system of claim 15, wherein said sprayer is
at a non-perpendicular angle with said component.
22. The spray cooling system of claim 15, wherein said sprayer is
an atomizer.
23. A thermal management system comprising: a cooling surface with
a hotspot having a first heat flux; an at least one sprayer in a
spaced apart relationship to said hotspot and capable of
transforming a supply of liquid cooling into a continuous pattern
of droplets that impinge and create a thin coolant film on said
hotspot; wherein said thin coolant film absorbs said first heat
flux; wherein a radial flow of said thin coolant film creates a
thicker coolant film over a second zone of said electronic
component, said second zone producing a second heat flux that is
less than one-third the magnitude of said first heat flux; and
wherein said thicker coolant film absorbs said second heat
flux.
24. The thermal management system of claim 23, further comprising
at least one secondary orifice for adding said coolant to said
thicker coolant film.
25. The thermal management system of claim 24, wherein said at
least one secondary orifice is an incremental drop ejector.
26. The thermal management system of claim 23, further comprising a
vapor management protrusion surrounding said at least one
sprayer.
27. The thermal management system of claim 24, wherein at least a
portion of said cooling surface includes a plurality of etched
microchannels.
28. The thermal management system of claim 24, wherein said sprayer
is at a substantial angle with said component.
29. The thermal management system of claim 24, wherein said second
heat flux is less than 100 watts per square centimeter.
30. The thermal management system of claim 24, wherein said sprayer
is an atomizer.
31. The thermal management system of claim 24, wherein a hydraulic
jump exists between said thin coolant film and said thicker coolant
film.
32. A method of cooling an electronic component with at least one
high heat flux hotspot, said method comprising: dispensing an at
least one stream of liquid droplets with the momentum necessary to
result in high heat flux evaporative cooling of said at least one
hotspot, said dispensing also resulting in a thick film that cools
the non-hotspot areas of said electronic component.
33. The method of claim 32, wherein said at least one stream of
liquid droplets are dispensed at a non-perpendicular angle to said
hotspot.
34. The method of claim 32, wherein said at least one hotspot
includes an array of etched microchannels.
35. A liquid cooling system comprising: an electronic component to
be cooled having a cooling surface with a hotspot producing a first
heat flux, wherein the non-hotspot portion of said cooing surface
produces a second heat flux; wherein said first heat flux is at
least three times greater in magnitude than said second heat flux;
and an at least one sprayer in a spaced apart relationship and at a
non-perpendicular angle to said hotspot, wherein said at least one
sprayer dispenses droplets onto said hotspot in a fashion that
creates a thin coolant film on said hotspot and a thick film on
said non-hotspot portion of said cooling surface, said thin coolant
film capable of cooling said hotspot and said thick film capable of
cooling said non-hotspot portion of said cooling surface.
36. The liquid cooling system of claim 35, wherein said hotspot
includes an array of etched microchannels.
37. The liquid cooling system of claim 35, wherein said first heat
flux is at least three times greater in magnitude than said second
heat flux.
38. The liquid cooling system of claim 35, further including at
least one secondary nozzle for adding a supply of liquid coolant to
said thick film.
39. The liquid cooling system of claim 38, wherein said at least
one secondary nozzle is an incremental drop ejector.
40. A continuously replenished evaporative cooling film created
upon a surface to be cooled, said cooling film comprising: a
thin-film zone generally located over and capable of cooling a high
heat flux portion of said cooling surface; and said thin-film zone
flowing radially into a thicker-film zone located over and capable
of cooling a low heat flux portion of said cooling surface.
41. The continuously replenished evaporative cooling film of claim
40, wherein said thicker-film zone is separated from said thin-film
zone by a hydraulic jump.
42. A cooling film for continuously absorbing heat from a surface
to be cooled, said surface having a first zone with a first heat
flux and second zone having a second heat flux, said cooling film
comprising: means for said cooling film to absorb heat from said
first zone at a greater rate than said second zone.
43. A cooling film for continuously cooing a surface of an
electronic component: said electronic component having a first
component zone generating a first heat flux and a second component
zone generating a second heat flux; said cooling film having a
thin-film evaporative zone located over said first component zone
and having a thickness capable of absorbing said first heat flux in
the general proximity of said first component zone; and said
cooling film having a thick-film cooling zone located over said
second component zone and having a thickness capable of absorbing
said second heat flux.
44. The cooling film of claim 43, wherein said first heat flux is
at least three times greater than said second heat flux.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] None
BACKGROUND
[0003] 1. Field of the Invention
[0004] The present invention relates generally to spray cooling
thermal management systems and more specifically it relates to a
spray cooling system that provides high heat flux evaporative
cooling of electronic component hotspots.
[0005] 2. Description of the Related Art
[0006] Liquid cooling is well known in the art of cooling
electronics. As air cooling heat sinks continue to be pushed to new
performance levels, so has their cost, complexity, and weight. For
some time, liquid cooling solutions have been developed and tested,
but other than specialty applications they have yet to gain
widespread commercial adoption. As computer power consumptions
continue to increase, liquid cooling will provide significant
advantages to computer manufacturers which will force its use. The
present invention provides significant advantages over both air
cooling and prior art liquid cooling solutions.
[0007] Liquid cooling technologies use a cooling fluid for removing
heat from an electronic component. Liquids can hold and transfer
heat at a rate many times that of air. Single-phase liquid cooling
systems place a pure liquid in thermal contact with the component
to be cooled. With these systems, the cooling fluid absorbs heat as
sensible energy. Other liquid cooling systems, such as spray
cooling, are two-phase processes. In these systems, heat is
absorbed by the cooling fluid as latent energy gains. Two-phase
cooling, or commonly referred to as evaporative cooling, provides
the ability to deliver more efficient, more compact and higher
performing liquid cooling systems than single-phase systems.
[0008] An exemplary two-phase cooling method is spray cooling.
Spray cooling uses a pump for supplying fluid to one or more
nozzles that transform the coolant supply into droplets. These
droplets impinge the surface of the component to be cooled and can
create a thin coolant film. Energy is transferred from the surface
of the component to the thin-film. Because the fluid is dispensed
at or near its saturation point, the absorbed heat causes the
thin-film to turn to vapor. This vapor is then condensed, often by
means of a heat exchanger, or condenser, and returned to the
pump.
[0009] Significant efforts have been expended in the development
and optimization of spray cooling. A doctorial dissertation to
Tilton entitled "Spray Cooling" (1989), available through the
University of Kentucky library system, describes how optimization
of spray cooling system parameters, such as droplet size,
distribution, and momentum can create a thin coolant film capable
of absorbing high heat fluxes. As described by the Tilton
dissertation, atomization plays a key role in the development of a
thin coolant film capable of absorbing very high heat fluxes, such
as a coolant film capable of absorbing a heat flux over 800 watts
per square centimeter. Research and development by Isothermal
Systems Research (ISR) has shown spray cooling to be capable of
absorbing heat fluxes in the range of several thousands watts per
square centimeter.
[0010] In addition to the system parameters described by the Tilton
dissertation, U.S. Pat. No. 5,220,804 provides a method of
increasing a spray cooling system's ability to remove heat. The
'804 patent describes a method of managing system vapor that
further thins the coolant film which increases evaporation,
improves convective heat transfer, and liquid and vapor
reclaim.
[0011] Historically, most electronic cooling solutions have
provided wide area treatment of the cooling surface. Electronic
components are rated to a total wattage that is spread by an
aluminum, copper, or diamond heat spreader to the cooling fluid
(may be air or liquid). In some applications, this wide-area
average heat flux treatment of the cooling surface only marginally
takes advantage of the benefits of liquid cooling over air
cooling.
[0012] Electronic components create varying amounts of heat across
their surfaces and a varying amount of heat as a function of time.
Today's microprocessors, for example, may be constructed on a
silicon die roughly 1 cm by 1 cm. The die may have multiple zones
for different functions. Such zones may be for inputs and outputs
(I/Os), level 1 cache, level 2 cache, and the core. The core may be
roughly 0.5 cm by 0.5 cm and is where the main computer processing
takes place. Although the core may only be 25% of the total area of
the die, it creates almost the entire heat generation by the chip
and may be considered a chip "hotspot". Wherein a chip might be
rated for an average heat load of 110 watts, with an average heat
flux of 110 watts per centimeter squared, the core may generate 100
watts of that heat and have a heat flux of 400 wafts per centimeter
squared. This non-uniform heat flux distribution poses a
significant challenge to the cooling system as it is desirable to
keep the entire chip at nearly the same operating temperature.
Cooling systems that rely on heat spreading may not provide this
ability as they rely on conduction spreading, resulting in
significant temperature gradients across the chip.
[0013] One method of cooling the core of a computer chip is to
divide the chip into thermal zones and to cool each of the chip's
zones at a different rate. U.S. Pat. No. 6,443,323, describes a
method of variably cooling a computer component through the use of
incremental sprayers. The incremental sprayers deposit fluid onto
each zone at a mass flow rate necessary for complete phase change.
Drops are ejected from an orifice in serial. Although this method
improves the efficiency of the system, that is in attaining
complete phase change of all dispensed fluid, the incremental
dispensing method does not provide dispensing characteristics
necessary to create high heat flux thin-film evaporative cooling
and high performance cooling of hotspots. A paper by Don Tilton and
Jay Ambrose (1989), entitled "Closed-System, High-Flux Evaporative
Spray Cooling", describes the early development and analysis of
incremental sprayers and predicts a maximum heat flux capability of
around 300 watts per centimeter squared using water. An ASME paper
published by Bash, Patel, and Sharma entitled "Inkjet Assisted
Spray Cooling of Electronics" (2003), describes an inkjet
dispensing system with a critical heat flux of around 270 watts per
centimeter squared using water.
[0014] Another method of cooling the core is described by U.S. Pat.
No. 6,650,542. Although this method directs and controls the single
phase fluid over a chip hotspot, the disclosed method is not a
phase change process and thus not capable of high heat flux
thin-film evaporative cooling.
[0015] Yet another method of cooling the core is two-phase
microchannels, such as described by U.S. Pat. No. 4,450,472.
Although this method does not use spray cooling, the design does
provide the ability to remove heat in the range of 400-1000 watts
per square centimeter using water. The system discloses a method of
placing a very small microchannel array on an electronic component.
Although microchannel cooling methods may effectively lower the
temperature of the core, due to large pressure drops and resulting
size limitations they do not efficiently address the needs of the
non-hotspot areas of the die.
[0016] For the foregoing reasons, there is a need for a liquid
cooling solution that effectively cools the one or more hotspots of
a computing component. Thus, there is a need for a localized
cooling solution capable of absorbing large heat fluxes. Also, the
high heat flux cooling system must efficiently and reliably cool
the other non-high heat flux areas of the chip. The resulting
cooling solution would allow significant improvements in processor
performance.
BRIEF SUMMARY OF THE INVENTION
[0017] In order to solve the problems of the prior art, and to
provide a spray cooling solution that significantly changes the
thermal constraints of the core, a hotspot spray cooling solution
has been developed.
[0018] The present invention is a spray cooling thermal management
device that cools an electronic component creating a varying amount
of heat across its surfaces. Liquid coolant is dispensed upon the
surface of the component. In areas of the chip that generate large
heat fluxes, typically referred to as the core, the liquid coolant
is dispensed as a continuous atomized droplet pattern. The atomized
pattern creates a high heat flux evaporative cooling thin-film over
the one or more core areas. Rather than optimize the atomized
pattern and flow based upon complete thin-film vaporization, the
present invention optimizes the atomized pattern for maximum heat
removal rates. Any excess, non-vaporized, fluid flowing outward
from the hotspot is used to cool the lower heat flux (non-core)
areas of the component through the creation of a thick coolant film
thereon.
[0019] Other embodiments of the invention include supplemental
nozzles that deposit cooling fluid into the thick-film. This
embodiment provides an efficient and simple method of controlling
the cooling rates over the less critical system zones and provides
further flexibility in optimizing the atomization for the high heat
flux areas.
[0020] Another embodiment of the present invention utilizes an
atomizer that dispenses the coolant at a non-perpendicular angle to
one or more component hotspots. This embodiment provides
directional control of the excess fluid of the hot spot. The
thick-film is encouraged to flow in a predetermined direction.
[0021] Another embodiment of the present invention uses a
liquid-vapor separator for separating liquid and vapor from the
exit stream of a spray module prior to condensing the vapor. The
result is a near pure vapor at the inlet of the condenser which is
potentially more efficient and has a more repeatable performance
than a condenser with substantial two-phase flow at its inlet.
[0022] Yet another embodiment of the present invention enhances the
surface of the chip to be spray cooled through the use of etched
open microchannels. These microchannels are formed either directly
into the top surface of the chip or through the use of a secondary
etched microchannel plate bonded to the top surface of the
chip.
[0023] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In the course of the detailed description to follow,
reference will be made to the attached drawings. These drawings
show different aspects of the present invention and, where
appropriate, reference numerals illustrating like structures,
components, and/or elements in different figures are labeled
similarly. It is understood that various combinations of the
structures, components, and/or elements other than those
specifically shown are contemplated and within the scope of the
present invention:
[0025] FIG. 1 is a perspective view of a computer chip mounted onto
a substrate;
[0026] FIG. 2 is a top view of computer chip with multiple
zones;
[0027] FIG. 3 is a perspective view of a spray module mounted onto
the substrate and encompassing the chip from FIG. 1;
[0028] FIG. 4 is a section view, along line A-A of FIG. 3, showing
the inside the a spray module according to the present
invention;
[0029] FIG. 5 is a partial view of FIG. 4 showing a spray plate
located over the chip to be cooled according to the present
invention;
[0030] FIG. 6 is a side view of a spray plate with hotspot vapor
management protrusions;
[0031] FIG. 7 is an alternative embodiment of the present invention
showing a secondary nozzle spraying onto the thick-film;
[0032] FIG. 8 is another alternative embodiment of the present
invention showing an angled atomizer;
[0033] FIG. 9 is a bottom perspective view of a spray plate with a
hotspot vapor management protrusion;
[0034] FIG. 10 is a block diagram of a simple spray cool
system;
[0035] FIG. 11 is a block diagram of a spray cool system using a
liquid and vapor separator;
[0036] FIG. 12 is a side section view of a separator of FIG. 11;
and
[0037] FIG. 13 is a side partial view of a spray cooled secondary
etched microchannel plate, with the microchannels enlarged for
clarity.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Many of the fastening, connection, manufacturing and other
means and components utilized in this invention are widely known
and used in the field of the invention are described, and their
exact nature or type is not necessary for a person of ordinary
skill in the art or science to understand the invention; therefore
they will not be discussed in detail.
[0039] Applicant hereby incorporates by reference the following
U.S. patents: U.S. Pat. No. 5,220,804 for a high heat flux
evaporative cooling system; and U.S. Pat. No. 5,860,602 and U.S.
Pat. No. 6,016,969, each for a laminated array of pressure swirl
atomizers, and U.S. Pat. No. 6,108,201 for a fluid control
apparatus and method for spray cooling and U.S. patent application
Ser. No. 10/281,391 for an actuated atomizer. Although a laminated
pressure swirl atomizer array is hereby incorporated by reference
and shown in the accompanying drawings, the present invention is
not limited to such an apparatus, in fact, many dispensing means
are applicable to the present invention, including but not limited
to, inserted atomizers, jet orifices, and actuated atomizers.
Applicant herein incorporates by reference co-pending U.S. patent
application entitled "Hotspot Coldplate Spray Cooling System", also
filed on Feb. 24, 2004. This application is related to co-pending
U.S. patent application entitled "Etched Open Microchannel Spray
Cooling", also filed on Feb. 24, 2004.
[0040] Now referring to FIG. 1, a computer chip 2 is shown mounted
to a substrate 4, as typical in computing applications. Computer
chip 2 may be a microprocessor, Field Programmable Gate Array
(FPGA), Application Specific Integrated Circuit (ASIC), or any
other commonly used electronic component. Chip 2 is attached to
substrate 4 using any one of a wide range of commonly known
packaging technologies (not shown), including: ball grid array, pin
grid array, land grid array, and wirebond. The present invention is
not limited to any one particular interconnect or packaging
method.
[0041] FIG. 2 shows a typical microprocessor version of chip 2. The
top surface of chip 2 has several zones, each with a unique
function, unique power consumption, and thus, a unique heat
generation rate. Although multiple zones are identified by FIG. 2,
they can be lumped into high and low heat flux zones. Low heat
generation zones may be, but are not limited to, memory (L1 and L2
cache), I/Os and controllers. A core 3, where significant
computations take place, generates heat at a much greater rate than
the low heat generation zones. A chip may have multiple hotspots as
areas of execution and floating point calculations may be done in
separate locations on the die, each hotspot located over a
core.
[0042] FIG. 3, and according to the present invention, shows a
spray module 10 attached to substrate 4 and encompassing chip 2.
Spray module 10 may be attached to substrate 4 through the use of
adhesives, soldering, or mechanical fastening such as but not
limited to the methods described by U.S. Pat. No. 6,108,201
incorporated herein by this reference. Spray module 10 is used for
dispensing a supply of liquid coolant onto the surface of chip 2.
Fluid enters module 10 through an inlet 14 and exits through an
outlet 16. Although only one outlet 16 is shown, multiple are
possible. In fact, wherein computer desktops are most often
orientated in one of two orientations, desktop or tower, it may be
preferable to have a plurality of outlet 16 at ninety degree angles
to each other.
[0043] Spray module 10 is part of a well known and understood
two-phase cooling cycle (shown in FIG. 10). A pump 5 is used for
supplying a cooling fluid at an optimal spray cooling flow rate and
pressure level. The cooling fluid can be any one of the well known
spray cooling fluids, including but not limited to FC-72,
Fluorinert (a Trademark of 3M), water and water mixtures. From pump
5, the high pressure cooling fluid enters spray module 10 where it
absorbs heat from chip 2. A condenser 8 cools the fluid and returns
liquid to pump 5. The system and components of the spray cool
system are well known and understood in the field, and thus, they
will not be discussed in further detail.
[0044] Spray module 10, according to the present invention, has an
outer housing 12 that provides the structural rigidity to the
overall module. Housing 12 can be constructed from many materials,
including aluminum and plastic. Ideally, housing 12 is designed to
provide the ability to be molded or die-casted (as shown in FIG.
4), thus providing low manufacturing costs.
[0045] Also shown in FIG. 4, a fluid supply enters inlet 14 located
at the top of housing 12, by means of a supply tube (not shown).
The connection between inlet 14 and the supply tube is preferably
removable through the use of a common quick disconnect fitting. The
coolant flowing through inlet 14 then enters a manifold area
created between housing 12 and a spray plate 30.
[0046] Spray plate 30 provides the means for dispensing the cooling
fluid onto chip 2. Plate 30 is shown inserted into a pocket within
housing 12, where it can be glued, fastened or swaged into place.
Due to the one piece design of housing 12, it is not necessary to
provide a fluid tight seal between spray plate 30 and housing 12,
but it is desirable to provide a tight fit and thus minimize
pressure losses. Spray plate 30 contains one or more nozzles that
provide the means of transforming the supply of coolant into one or
more continuous droplet streams. In FIG. 4, an atomizer 32 is shown
located over core 3. Although one atomizer 32 is shown, depending
upon the type of fluid used, the size of core 3, and the spray cone
angle of atomizer 32, there may be one or more atomizers placed
above core 3. To minimize mixing between adjacent atomizers, it is
preferable to use a single atomizer per hotspot. A method of
creating spray plate 30 is described by U.S. Pat. No. 5,860,602 and
U.S. Pat. No. 6,016,969 for a laminated pressure swirl atomizer.
Another method is to insert button-style atomizers into plate 30.
In the event that chip 2 produces highly variable heat fluxes as a
function of time, that is it cycles from peak performance to
"sleep" mode, it may be advantageous to make atomizer 32 variable
and controllable as described by U.S. patent application Ser. No.
10/281,391. The variable atomizer in conjunction with an electronic
control system makes it possible to achieve direct component
temperature feedback and overall thermal performance control.
[0047] As previously mentioned, it is highly desirable to remove
heat directly from core 3 prior to it spreading to the rest of chip
2. Atomizer 32 provides the means for removing significant amounts
of heat directly from core 3. Through the use of atomizer 32,
droplet size, distribution and momentum can all be controlled and
optimized in a fashion that provides a thin-film 40 over core 3, as
shown in FIG. 5. As described by the dissertation by Tilton, the
thickness of thin-film 40 can significantly affect the ability of
the coolant to remove heat. Generally, the thinner thin-film 40
becomes the more heat it can remove.
[0048] Creation and optimization of thin-film 40 is application
specific. If impinging droplets impact film 40 with too little
momentum, the droplets will be entrained into the escaping vapor
and they will not reach the cooling surface. If the impinging
droplets have too much momentum, the droplets will splash from the
surface and not contribute to cooling. Both conditions can not be
completely avoided but should be minimized. In addition to the
above optimization, ideally, impinging droplets will collide with
thin-film 40 in a fashion that destroys nucleating bubbles.
Nucleating bubbles aid in the desired vaporization of liquid
coolant, but reduce the contact area between the higher conductive
liquid and the lower conductive vapor. Ideally, nucleating bubbles
are destroyed before they can achieve significant size.
[0049] Optimization of coolant dispensing characteristics may also
yield a unique event that occurs when droplets impinge a flat
surface, called hydraulic jump. This jump process occurs when a
thin-film fluid flows radially and then jumps in height based upon
its Froude number going from supercritical (thin-film) to
subcritical (thick-film). As documented by the Tilton dissertation,
a supercritical thin-film may be, but is not limited to, the range
of 100 micrometer to 400 micrometers thick, and the jumped
thick-film may be in the range, but is not limited to, 3000
micrometers to 4000 micrometers using water. A hydraulic jump
provides the means of creating thin-film 40 and thick-film 42 and
the ability to cool core 3 of chip 2 at a rate greater than the
non-core areas of chip 2. A hydraulic jump may also provide a
thermal buffer in the event that spray becomes momentarily
interrupted.
[0050] As shown in FIG. 5, and in the fashion described above,
atomizer 32 is located generally over core 3 so that thin-film 40
is also created directly over core 3. Rather than attempt to extend
thin-film 40 over the entire surface of chip 2, as is attempted by
the prior art, the present invention optimizes its spray
characteristics over just core 3. This is likely to result in a
jumped thick-film 42 over the non-core areas of chip 2. Wherein
thin-film 40 may be capable of absorbing heat fluxes up to a
thousand or more watts per square centimeter over the small area of
core 3, thick-film 42 may be capable of efficiently and reliably
providing heat removal rates generally less than 100 watts per
square centimeter over the large area low-heat-flux zones of chip
2.
[0051] Heat removal rates of both zones, 40 and 42, may be improved
the use of surface enhancements. One such enhancement is etched
microchannels on the top surface of chip 2. The process of etching
microchannels is described by U.S. Pat. No. 4,450,472 and U.S.
patent application Ser. No. 10/052,859, both are herein
incorporated by reference. Although these methods are disclosed as
part of closed channel microchannel cooling systems, open etched
microchannels may significantly increase the effectiveness of the
present spray cooling invention. Open channel spray cooled
microchannels are not limited by pressure drops created by the need
for small hydraulic diameters, as is the case with closed
microchannel systems. Open microchannel spray cooling is also
limited by the need to use fluid manifolding. Therefore, open
microchannel spray cooling may provide the ability to have smaller
hydraulic diameters, and higher resulting heat transfer
coefficients, than closed microchannel cooling systems. As an
alternative surface enhancement embodiment and as shown in FIG. 13,
a secondary etched microchannel plate 44 may be thermally attached
to chip 2 providing the benefits of surface enhancements and the
potential use of a non-dielectric fluid. Both open channel spray
cooling microchannel methods provide increased nucleation sites,
improved vaporization conditions and increased surface areas; all
of which are known to benefit spray cooling.
[0052] As an alternative embodiment of the present invention and
shown in FIGS. 4 and 6, a hotspot vapor management protrusion 34
extends from spray plate 30 in the direction of and in a spaced
apart relationship to chip 2. As described by U.S. Pat. No.
5,220,804 and U.S. Pat. No. 6,108,201, vapor management protrusion
34 forces the vapor within the system, and more particularly vapor
in close proximity to the atomization zone, to flow downward and
outward along thin-film 40. The result is a further thinning of
thin-film 40 and increased heat removal rates. The gap between chip
2 and vapor management protrusion 34 is a variable of design, often
optimized through experimentation, but ISR typically uses gaps
between 1/2 mm and 3/4 mm. In the event that multiple hotspots are
present on a given chip, it may be desirable to have multiples of
atomizer 32 and multiples of vapor management protrusion 34. Also
located in protrusion 34, and shown in FIG. 9, is a plurality of
vapor return orifices 37 which allow for the recirculation of vapor
within spray module 10.
[0053] In addition to cooling chip 2 by the above described fluid
dispensing process, FIG. 7 shows a secondary nozzle 36 used to
assist in the creation and performance of thick-film 42. In areas
of moderate heat fluxes, such as critical memory areas, it may be
desirable to increase the cooling in those areas by creating
localized thinner zones within thick-film 42. In addition, nozzle
36 may simply add fluid to thick-film 42 in the event that atomizer
32 does not produce enough excess fluid to maintain thick-film 42
over the low heat flux areas of chip 2. Unlike the requirements
placed on atomizer 32, nozzle 36 is not required to produce a thin
evaporative film capable of very large heat fluxes. In this case,
nozzle 36 may be, but is not limited to, an incremental sprayer, a
drop on demand orifice, a jet orifice, a piezoelectric actuated jet
impingement orifice, or an actuated atomizer. All methods provide
the means of supplementing the cooling fluid to thick-film 42.
[0054] FIG. 8 shows another alternative embodiment of the present
invention. In this embodiment, atomizer 32 dispenses fluid at a
generally non-perpendicular angle to core 3. By spraying at a
non-perpendicular angle to core 3, thick-film 42 is further
encouraged to flow over and cover the non-hotspot areas of chip 2.
This embodiment may also achieve benefits through they the addition
of secondary nozzle 36 or vapor management protrusion 34. Angled
spray cooling may also benefit from the addition of etched
microchannels parallel to the direction of spray.
[0055] Cooling fluid that exits spray module 10 is not likely to be
a pure vapor, as ideal in terms of cycle efficiency. Although prior
art systems try to optimize the spray system for complete fluid
vaporization within module 10, the present invention is optimized
for cooling the performance enhancing core of a chip. Although the
higher performance of the present invention is at the cost of
complicated two phase flow within condenser 8, FIG. 12 shows an
addition to the system that simplifies its design and use. A
separator 7 may be placed between condenser 8 and spray module 10.
Separator 7 separates liquid from vapor and transfers the higher
energy vapor to condenser 8 and the lower energy liquid to pump 5
(FIG. 13). In addition, vapor and liquid may be separated through
the use of a spiral separator as described by U.S. Pat. No.
5,314,529. Liquid--vapor separation allows the size of condenser 8
to be minimized.
[0056] While the hot spot cooling system herein described
constitute preferred embodiments of the invention, it is to be
understood that the invention is not limited to these precise form
of assemblies, and that changes may be made therein with out
departing from the scope and spirit of the invention.
* * * * *