U.S. patent application number 10/120993 was filed with the patent office on 2003-10-16 for modular spray cooling system for electronic components.
This patent application is currently assigned to General Dynamics Land Systems, Inc.. Invention is credited to Knudsen, Gary D., Morrow, Ernest J., Sellers, Sally M..
Application Number | 20030193780 10/120993 |
Document ID | / |
Family ID | 28041123 |
Filed Date | 2003-10-16 |
United States Patent
Application |
20030193780 |
Kind Code |
A1 |
Morrow, Ernest J. ; et
al. |
October 16, 2003 |
MODULAR SPRAY COOLING SYSTEM FOR ELECTRONIC COMPONENTS
Abstract
A modular spray cooling system 10 for cooling electronic
components in enclosures containing electronic components that
dissipate heat and therefore require cooling. The modular system is
mounted in a sealed enclosure 12 with an inside wall 14. A spray
cooling module 26 is detachably mountable within the sealed
enclosure 12. The coolant is distributed to a spray manifold card
48 that is provided with nozzles. Localized cooling is accomplished
with the use of individual nozzles 17. The spray cooling module 26
atomizes the evaporative coolant through nozzles 22 so that liquid
droplets of the coolant are delivered to the electronic components,
and cooling of the components occurs upon evaporation. A method for
cooling electronic components comprises the steps of: providing a
sealed enclosure 12; priming the sealed enclosure 12 with an
evaporative coolant that recirculates therewithin; detachably
placing within the enclosure one or more sealed circuit card
assemblies 24 containing the electronic components to be cooled; a
spray cooling module 26 within the enclosure and delivering power
to a pump within a spray cooling module 26 that is also detachably
mountable within the sealed enclosure 12.
Inventors: |
Morrow, Ernest J.;
(Monticello, FL) ; Sellers, Sally M.;
(Tallahassee, FL) ; Knudsen, Gary D.;
(Tallahassee, FL) |
Correspondence
Address: |
BROOKS & KUSHMAN
1000 TOWN CENTER 22ND FL
SOUTHFIELD
MI
48075
|
Assignee: |
General Dynamics Land Systems,
Inc.
Sterling Heights
MI
|
Family ID: |
28041123 |
Appl. No.: |
10/120993 |
Filed: |
April 11, 2002 |
Current U.S.
Class: |
361/700 ;
165/104.33; 257/714 |
Current CPC
Class: |
H01L 2924/00 20130101;
Y10S 165/908 20130101; H01L 2924/0002 20130101; H05K 7/20345
20130101; H01L 23/4735 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
361/700 ;
257/714; 165/104.33 |
International
Class: |
H05K 007/20 |
Claims
What is claimed is:
1. A modular spray cooling system for cooling electronic
components, the system comprising: a sealed enclosure having an
inside wall, the wall having slots located thereupon; one or more
sealed circuit card assemblies containing the electronic components
to be cooled by an evaporative coolant, each assembly being
detachably accommodated by one or more of the slots; and a spray
cooling module that is also detachably accommodated by one or more
of the slots, the spray cooling module directing the evaporative
coolant toward the one or more sealed circuit card assemblies so
that they are cooled by evaporation of the coolant.
2. The modular spray cooling system of claim 1, wherein the spray
cooling module includes: a housing; a pump within the housing; and
a controller.
3. The modular spray cooling system of claim 1, further including:
a reservoir for collecting cooling fluid condensed from the one or
more sealed circuit card assemblies.
4. The modular spray cooling system of claim 1, further including a
plurality of plates attached to the inside wall of the sealed
enclosure, the plates defining the slots, wherein one or more of
the plurality of plates include one or more nozzles through which
the evaporative spray coolant is distributed.
5. The modular spray cooling system of claim 1, further including a
spray manifold card, at least one of the sealed circuit card
assemblies being interposed between the spray manifold card and the
spray cooling module.
6. The modular spray cooling system of claim 2, wherein the pump
comprises a self-priming gear pump.
7. The modular spray cooling system of claim 2, wherein the spray
cooling module includes a filter.
8. The modular spray cooling system of claim 4, wherein the
evaporative coolant is evaporated at least partially upon contact
with the electronic components, condensed upon contact with an
inside wall of the sealed enclosure or with one of the plurality of
plates, and recirculated by the pump in the spray cooling module
for reuse in the sealed enclosure.
9. The modular spray cooling system of claim 2, also including a
reservoir that collects condensed coolant.
10. The modular spray cooling system of claim 9, also including one
or more fluid passages that enable fluid communication between the
reservoir and the pump.
11. The modular spray cooling system of claim 4, wherein the one or
more nozzles include means for distributing the evaporative spray
coolant substantially perpendicularly from the plate.
12. The modular spray cooling system of claim 4, wherein the one or
more nozzles include means for distributing the evaporative spray
coolant substantially parallel to the plate.
13. A method for cooling electronic components, the method
comprising the steps of: providing an enclosure having an inside
wall; priming the enclosure with an evaporative coolant that may
recirculate therewithin; detachably placing one or more sealed
circuit card assemblies containing the electronic components to be
cooled by the evaporative coolant within the enclosure; providing a
spray cooling module within the enclosure; and delivering power to
a pump within the spray cooling module, the spray cooling module
atomizing the evaporative coolant through nozzles so that droplets
of the coolant are delivered to the electronic components, and
cooling of the electronic components occurs upon evaporation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a modular spray cooling system and
its method of use to cool components that are used in an electronic
circuit which requires control of its operating temperature for
effective functioning.
[0003] 2. Background Art
[0004] Today, the quest continues for delivering higher electronic
power in smaller packages. One aim of the engineer is to design
systems, the temperatures of which can be maintained within
acceptable limits when subjected to higher electrical load factors.
Additionally, the packaging engineer contends with the problems of
efficient use of space.
[0005] To use limited space efficiently, circuit card guides
conventionally are provided to support electronic components or
printed circuit cards within an enclosure. The support arrangement
provides stability and restraint under shock and vibration. Also,
the arrangement often provides a heat path from a component to its
housing. Typically, such arrangements locate electronic cards so
that they lie parallel with each other, often with only a narrow
space between adjacent cards. Each card may be electronically
connected to a plate or backplane that lies perpendicular to the
circuit cards. Because of the proximity of the cards within the
enclosure and the electrical power generated, heating and
consequent temperature rise often occurs if unchecked.
[0006] It is known that one way to remove such heat is to deploy
fans which draw air over the heated component so that circulation
removes heat primarily by convection. But spatial constraints often
inhibit efficiency because air circulation is often insufficient to
remove the heat generated. One adverse consequence is that the
thermal tolerances of the electronic components may be
exceeded.
[0007] U.S. Pat. No. 5,880,931 which issued on Mar. 9, 1999
discloses a spray-cooled circuit card cage which seals the
enclosure and uses spray plates that release a mist of fine
droplets of a coolant fluid. The '931 disclosure observes that
considerable cost is involved in sealing the enclosure and
supporting each circuit card adjacent to an associated spray plate.
The system requires pressure to be applied from an exogenous source
to a fluid entry port. Id., Col. 6, lines 47-48.
[0008] Also, illustrative of prior art approaches is an evaporative
spray coolant for cooling a heat source, as described in U.S. Pat.
No. 5,220,804, which issued on Jun. 22, 1993.
SUMMARY OF THE INVENTION
[0009] In light of problems that are unsolved by previous
approaches, it would be desirable to provide a retrofittable
cooling system for enclosures that contain electronic components or
conductors. As a result, such a retrofittable cooling system may
upgrade the enclosure so that it may contain components that
dissipate heat at a higher rate. If so, redesign of the enclosure
or housing can be avoided. Additionally, savings in space and
weight can be realized and expenditures of time and money can be
reduced.
[0010] The invention is a self-contained modular spray cooling
system for cooling electronic components. The system has a sealed
enclosure with an inside wall. Attached to the inside wall is a
number of plates that include slots which enable sealed circuit
card assemblies containing the electronic component to be
detachably accommodated. A spray cooling module is removably
mountable in a slot near one or more of the sealed circuit card
assemblies within the sealed enclosure.
[0011] Additional features include a remotely located plate that
can optionally be mounted in a card slot. The plate can optionally
support individual spray nozzles and/or valves for recovering
condensed fluid. In one embodiment, slotted plates on an inside
wall may also contain coolant passages that provide a flow of an
evaporative coolant.
[0012] The modular spray cooling system includes an evaporative
coolant, distributed as fine droplets which are evaporated at least
partially upon contact with the electronic components. Some of the
coolant evaporates before condensation upon contact with a cooled
inside wall of the sealed enclosure or with one of the plates. The
condensate collects in a reservoir within the sealed enclosure.
Coolant passages lead the condensed evaporative coolant from the
reservoir to a pump for reuse within the sealed enclosure.
[0013] Thus, the system is basically self-contained. It requires no
remotely-located plumbing or propellant. Its design allows for the
ready removal and replacement of the electronic components that are
cooled therewithin.
[0014] The invention also includes a method for cooling electronic
components. It comprises the steps of:
[0015] providing a modular retrofit to an existing sealed enclosure
having an inside wall;
[0016] locating a plurality of plates defining slots, the plurality
of plates being attached to the inside wall, with the option of at
least some of the plurality of plates having coolant passages;
[0017] priming the sealed enclosure with an evaporative coolant
that may recirculate within the sealed enclosure through the
coolant passages; and
[0018] delivering power to a spray cooling module that is also
detachably mountable within the sealed enclosure. The spray cooling
module atomizes the liquid coolant through nozzles so that liquid
droplets of the coolant are delivered to the electronic component,
are vaporized, remove heat associated with the latent heat of
vaporization, and thus cool the components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is an exploded view of a modular spray cooling system
according to the present invention;
[0020] FIG. 2 is an enlargement of a portion thereof;
[0021] FIG. 3 is a top plan view thereof, with a top plate
removed;
[0022] FIG. 4 is a quartering perspective view of one of a number
of nozzles that are provided within a sealed housing of the present
invention;
[0023] FIG. 5 illustrates an array of nozzles that are provided,
for example, along the sides of the plates within the sealed
housing;
[0024] FIG. 6 is a cross-sectional view of a nozzle taken along the
line 6-6 of FIG. 5; and
[0025] FIG. 7 is a logic flow diagram illustrating a series of
processes and decisions made by a controller within the spray
cooling module.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0026] The invention relates to a system and method for cooling
electronic components. Turning first to FIGS. 1-3 taken together,
the system 10 is modular, and thus retrofittable, as suggested by
FIG. 1, in that individual members of the modular spray cooling
system 10 may be readily removed, inserted, or replaced. The system
10 is a state-changing cooling system in which an evaporative fluid
exists in a liquid state, a finely dispersed droplet state, and in
a vapor state.
[0027] With particular reference to FIGS. 1-2, it can be seen that
the system 10 includes a self-contained, sealed enclosure 12 that
has an inside wall 14. Attached to the inside wall 14 are plates 16
that define various slots 18. Optionally, several of the plates 16
define coolant passages that duct the evaporative coolant.
[0028] The electronic components to be cooled are contained within
one or more sealed circuit card assemblies 24. Each assembly is
detachably accommodated by one or more slots.
[0029] Also within the sealed enclosure 12 is a spray cooling
module 26. This module includes a housing 28 within which a pump 30
and a controller 32 are accommodated. Since the pump 30 is located
within the housing 28 of the spray cooling module 26, no external
plumbing or fluid passages are required outside the modular spray
cooling system 10. Preferably, the pump 30 is a self-priming gear
pump. In a preferred embodiment, the spray cooling module 26
includes a filter.
[0030] Continuing with primary reference to FIG. 1, in a vertical
orientation, the condensed cooling fluid collects in a reservoir 34
which preferably is formed at the lowest point of the sealed
enclosure. Coolant passages (e.g. a flexible tube), such as those
depicted by the reference numeral 20, channel the coolant to one or
more ports which serve as fluid inlets to the pump 30 that is
housed within the spray cooling module 26.
[0031] FIGS. 4-6 illustrate details of the nozzles 22 through which
the evaporative coolant is distributed. Also depicted in FIG. 5 is
a coolant flow passage 20 which is defined within one of the plates
16. In one embodiment, the plates 16 may be hollow, so that their
interstices may define plenum or manifold 46 that contains the
evaporative coolant and thus is in common communication with the
nozzles 22.
[0032] For a constant liquid flow rate, the manner in which the
droplets cover the components to be cooled can have a significant
impact on heat transfer. Such spray parameters include drop
diameter, drop velocity, and the pattern that with which the
droplets impact the electronic device. Increasing the heat transfer
rate per volume of fluid will result in less fluid required for the
system, and decrease the pump and filter sizes. This in turn leads
to less space requirements.
[0033] Varying the nozzle size 42 and shape, and the swirl chamber
44 can alter the spray pattern achieved. Also, the nozzles 22 can
be inserted and removed, and be tailored for the specific
requirements of the position of the nozzle in relation to the
electronic component to be cooled. If the spacing between the
nozzle and the electronic component to be cooled is especially
limited, it may desirable for the nozzle to include means for
distributing the evaporative coolant substantially parallel to the
plates 16. Such means may, for example, include a suitable
selection of nozzle size, the geometry of the swirl chamber 44, and
one or more impediments to perpendicular flow, such as a baffle.
Alternatively, if it is desired that the coolant escape from the
nozzle 22 substantially perpendicularly to the face of the plate
16, this can be accomplished by using a nozzle that lacks
impediments to perpendicular flow, and by suitable selection of
geometry of the swirl chamber 44. Thus, it will be appreciated that
the nozzle plug portion of the system can be varied to provide many
different spray patterns, angles of impact, droplet size, and
droplet velocity. With the ability to easily change nozzle orifice,
the spray manifold can be readily adjusted so that optimal spray
parameters can be obtained.
[0034] If desired, a spray manifold card 48 may be detachably
mountable within one or more of the slots 18. In this
configuration, the circuit card assembly containing components to
be cooled may effectively be sandwiched between the spray cooling
module 26 and the spray manifold card 48. A number of nozzles 22
may also be located on the spray manifold card so that the spray
can effectively cool the adjacent components. Additional cooling
can also be achieved with the use of individual nozzles 17 (FIG. 2)
that are remotely located within the enclosure.
[0035] In operation, the coolant is evaporated at least partially
upon contact with the circuit card assembly 24 that contains the
electronic components to be cooled. Thereafter, the vapor is
condensed upon contact with an inside wall 14 of the sealed
enclosure 12 or with one or more of the plates 16. The condensate
gathers in the reservoir 34 and is communicated by a coolant
passage to the pump before recirculation for reuse within the
sealed enclosure. Thus, least some of the coolant condenses upon an
interior wall of the housing following evaporation. This phase
change is typically accompanied by a rise in temperature at the
wall of the housing. To extract heat from the housing, a finned
surface is provided upon an external surface of the housing. This
finned surface allows heat to be transferred by convection
therefrom. The temperature of the housing is thereby maintained at
a temperature lower than the boiling point of the coolant.
[0036] FIG. 7 illustrates a simplified logic flow associated with
the controller 32 that is contained within the spray cooling module
26. The controller senses a signal which is representative of the
actual temperature within the housing (T.sub.A). The controller
also stores a value representative of the desired temperature
(T.sub.D) and processes a signal that represents the average flow
rate (R) of evaporative coolant in a previous time interval.
Implicit within this disclosure is the presence of means (not
shown) for sensing actual temperature, recording desired
temperature, and for sensing flow rate.
[0037] Next, a decision module within the controller compares
T.sub.A with T.sub.D. If the former exceeds the latter, a signal is
generated which effectively increases the flow rate by augmenting
the output of the pump. If the condition is not met, then the flow
rate is maintained until the external power which energizes the
controller is turned off.
[0038] In practicing a method for cooling electronic components
using the disclosed system, the first step is to provide a spray
cooling module within a sealed enclosure having an inside wall. A
plurality of plates is located, each plate defining a slot. The
plates are attached to the inside wall. At least some of the plates
have a coolant passage. The sealed enclosure is then primed with an
evaporative coolant that may recirculate within the sealed
enclosure through the coolant passages.
[0039] Next, circuit card assemblies are detachably placed within
the slots. Each sealed circuit card assembly contains electronic
components to be cooled by the evaporative coolant. Finally, power
is delivered to a pump in the spray cooling module. The spray
cooling module atomizes the liquid coolant through nozzles so that
liquid droplets of the coolant are delivered to the electronic
component. Cooling of the component occurs through the extraction
of heat associated with the latent heat of vaporization of the
coolant.
[0040] Preferably, the evaporative coolant is a dielectric fluid
with a relatively high breakdown voltage, i.e. up to about twice
the voltage across the bus bars. As is known, a dielectric is a
substance with very low electrical conductivity, i.e., is an
insulator. Liquid dielectrics include hydrocarbon oils, askarel,
and silicone oils. As used herein, the term "breakdown voltage"
refers to the maximum voltage that the dielectric can withstand
without breakdown. Beyond that voltage, considerable current passes
as an arc, usually with more or less decomposition of the fluid
along the path of the current.
[0041] Preferably, the evaporative fluid of the subject invention
is a thermally stable liquid, such as a perfluorocarbon. One
example is the Fluorinert.TM. electronic liquid FC-77 that is
available from the 3M Company of Minneapolis, Minn. An alternative
dielectric is sold under the name Flutec.TM. which is manufactured
by F2 Chemicals Limited of Lancashire, England. The inertness of
such fluids permits their use as a direct contact, single and
multiple phase coolant in the electronic environment. Their high
dielectric strength and low electrical conductivity render them
suitable for applications in high voltage transformers and power
electronics. Ideally, such fluids have a low global warming
potential and zero ozone-depletion potential.
[0042] Although several dielectric fluids are suitable for use as
the evaporative coolant, satisfactory results have been obtained
with the product sold by 3M company of Minneapolis, Minn. under the
trademark Fluorinert.TM.. Using Fluorinert.TM., heat fluxes of 20
W/cm.sup.2 are possible with traditional pool boiling. Other
published research has suggested that heat fluxes from 25 to 160
W/cm.sup.2 can be obtained. This large range of observed heat flux
is in part attributable to the drop patterns at impact. To obtain
high heat fluxes for a given flow rate of coolant, the spray should
sustain a thin film of liquid on the surface of the device to be
cooled. If the liquid film becomes too thick, vapor bubbles can be
supported within the liquid film, with a consequent diminution in
the advantages of spray cooling. If the film becomes too thin,
localize dry out can occur. This in turn, leads to overheating.
Droplet diameters in the range of 200 to 500 microns are more
effective than smaller diameters. Drops with high velocities have
been shown to breakup upon impact. In contrast, drops with a
velocity that is too slow do not have enough momentum to penetrate
the vapor generated from the heat of the components and effectively
whet the surface.
[0043] If additional spray is needed to cool specific components or
an especially hot card, such as a power supply, individual nozzles
and spray plates can be located as needed and space permits.
[0044] The modular spray cooling system described herein can be
used to retrofit existing sealed circuit card enclosures with a
self-contained system that provides a wider margin in thermal
design. With increased thermal capacity, faster processors can be
used.
[0045] In the environment under consideration, the evaporative
fluid is dispensed in liquid droplets that impact upon the
electronic components. Ideally, the temperature of the liquid
droplets prior to impact is just below the fluid's boiling point.
In this manner, at least a portion of the incident evaporative
fluid becomes vaporized, with a desired efficiency of at least
15-20%. As defined in this disclosure, "efficiency" is defined as
the ratio of the actual heat transferred to the theoretical maximum
heat transferred. The theoretical maximum heat transfer is the
sensible and latent heat associated with 100% vaporization of the
liquid impacting the surface.
[0046] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *