U.S. patent application number 10/949650 was filed with the patent office on 2005-06-09 for use of graphite foam materials in pumped liquid, two phase cooling, cold plates.
This patent application is currently assigned to Thermal Form & Function LLC. Invention is credited to Marsala, Joseph.
Application Number | 20050121180 10/949650 |
Document ID | / |
Family ID | 34393142 |
Filed Date | 2005-06-09 |
United States Patent
Application |
20050121180 |
Kind Code |
A1 |
Marsala, Joseph |
June 9, 2005 |
Use of graphite foam materials in pumped liquid, two phase cooling,
cold plates
Abstract
An improved cooling system provides cooling away from the
surface of electrical and electronic components, by providing an
available heat transfer surface area many times greater than that
of a convoluted fin structure. The component to be cooled is in
thermal contact with a cold plate evaporator device, and a graphite
material is associated with the cold plate device. Refrigerant is
circulated through the graphite material and the cold plate
evaporator device, and the liquid refrigerant is at least partially
evaporated by the heat generated by the component. Due to the open
nature of the graphite material, the permeability of liquids and
vapors is high, allowing for low pressure loss while still
maintaining sufficient two phase flow to carry heat away from the
electronics.
Inventors: |
Marsala, Joseph;
(Manchester, MA) |
Correspondence
Address: |
Law Office of Barbara Joan Haushalter
228 Bent Pines Court
Bellefontaine
OH
43311
US
|
Assignee: |
Thermal Form & Function
LLC
|
Family ID: |
34393142 |
Appl. No.: |
10/949650 |
Filed: |
September 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60506347 |
Sep 26, 2003 |
|
|
|
Current U.S.
Class: |
165/164 ;
257/E23.088; 257/E23.112 |
Current CPC
Class: |
H01L 2924/0002 20130101;
F28F 21/02 20130101; H01L 23/3733 20130101; H01L 23/427 20130101;
H01L 2924/0002 20130101; H01L 2924/00 20130101; F28F 13/003
20130101 |
Class at
Publication: |
165/164 |
International
Class: |
F23L 015/02; F28D
017/00 |
Claims
What is claimed is:
1. An improved cold plate structure comprising: at least one
component generating heat and required to be cooled; at least one
cold plate evaporator device in thermal contact with the at least
one component; a thermally conductive graphite material associated
with the at least one cold plate evaporator device for providing
increased surface area for heat transfer within the cold plate
structure; and a vaporizable liquid refrigerant capable of being
circulated to the at least one cold plate evaporator device and
coming into contact with the graphite material.
2. An improved cold plate structure as claimed in claim 1 further
comprising an outlet means for exporting the vaporizable liquid
refrigerant from the graphite material as a vapor.
3. An improved cold plate structure as claimed in claim 1 further
comprising an outlet means for exporting the vaporizable liquid
refrigerant from the graphite material as a two phase mixture of
liquid and vapor.
4. An improved cold plate structure as claimed in claim 1 further
comprising an inlet means to receive the vaporizable liquid
refrigerant into the cold plate structure.
5. An improved cold plate structure as claimed in claim 1 wherein
the refrigerant comprises R-134a refrigerant.
6. An improved cold plate structure as claimed in claim 1 wherein
the graphite material comprises a graphite foam.
7. An improved cold plate structure as claimed in claim 1 further
comprising a convoluted fin structure used in combination with the
graphite material.
8. An improved cold plate structure as claimed in claim 1 wherein
the graphite material comprises multiple graphite elements.
9. An improved cold plate structure as claimed in claim 1 wherein
the graphite material comprises a graphite material having
corrugations.
10. An improved cold plate structure as claimed in claim 1 wherein
the graphite material comprises a graphite material having one or
more slots cut into the material.
11. An improved cold plate structure as claimed in claim 10 wherein
the one or more slots cut into the material are in a direction of
flow of the vaporizable liquid refrigerant.
12. A method for cooling one or more electrical or electronic
components generating heat and required to be cooled, the method
comprising the steps of: locating at least one cold plate
evaporator device in thermal contact with the one or more
electrical or electronic components; locating a thermally
conductive graphite material proximate to the at least one cold
plate evaporator device for providing increased surface area for
heat transfer within the cold plate structure; and providing a
vaporizable liquid refrigerant capable of being circulated to the
at least one cold plate evaporator device, whereby the refrigerant
is at least partially evaporated by the heat generated by the one
or more electrical or electronic components.
13. A method as claimed in claim 12 further comprising the step of
providing an outlet means for exporting the vaporizable liquid
refrigerant from the graphite material as a vapor.
14. A method as claimed in claim 12 further comprising the step of
providing an outlet means for exporting the vaporizable liquid
refrigerant from the graphite material as a two phase mixture of
liquid and vapor.
15. A method as claimed in claim 12 further comprising the step of
providing an inlet means to receive the vaporizable liquid
refrigerant into the cold plate structure.
16. A method as claimed in claim 12 wherein the step of providing a
refrigerant comprises the step of providing R-134a refrigerant.
17. A method as claimed in claim 12 wherein the step of providing a
graphite material comprises the step of providing a graphite
foam.
18. A method as claimed in claim 12 further comprising the step of
using a convoluted fin structure in combination with the graphite
material.
19. A method as claimed in claim 12 wherein the graphite material
comprises multiple graphite elements capable of being modified with
corrugations or slots.
20. A method as claimed in claim 19 wherein slot modifications to
the graphite material are in a direction of flow of the vaporizable
liquid refrigerant.
Description
RELATED APPLICATIONS
[0001] This is a regularly filed application, based on provisional
application Ser. No. 60/506,347, filed Sep. 26, 2003.
TECHNICAL FIELD
[0002] The present invention relates to cooling of electrical and
electronic components, and more particularly, to use of graphite
foam materials in a pumped liquid two phase cooling system having
one or more cold plate/evaporators in thermal contact with the
electrical or electronic components to be cooled.
BACKGROUND OF THE INVENTION
[0003] Electrical and electronic components (e.g. microprocessors,
IGBT's, power semiconductors etc.) are most often cooled by
air-cooled heat sinks with extended surfaces, directly attached to
the surface to be cooled. A fan or blower moves air across the heat
sink fins, removing the heat generated by the component. With
increasing power densities, miniaturization of components, and
shrinking of packaging, it is sometimes not possible to adequately
cool electrical and electronic components with heat sinks and
forced air flows. When this occurs, other methods must be employed
to remove heat from the components.
[0004] One method for removing heat from components when direct
air-cooling is not possible uses a single-phase fluid which is
pumped to a cold plate. The cold plate typically has a serpentine
tube attached to a flat metal plate. The component to be cooled is
thermally attached to the flat plate and a pumped single-phase
fluid flowing through the tube removes the heat generated by the
component.
[0005] There are many types of cold plate designs, some of which
involve machined grooves instead of tubing to carry the fluid.
However all cold plate designs operate similarly by using the
sensible heating of the fluid to remove heat. The heated fluid then
flows to a remotely located air-cooled coil where ambient air cools
the fluid before it returns to the pump and begins the cycle again.
This method of using the sensible heating of a fluid to remove heat
from electrical and electronic components is limited by the thermal
capacity of the single phase flowing fluid. For a given fluid to
remove more heat, either its temperature must increase or more
fluid must be pumped. This creates high temperatures and/or large
flow rates to cool high power microelectronic devices. High
temperatures may damage the electrical or electronic devices, while
large flow rates require pumps with large motors which consume
parasitic electrical power and limit the application of the cooling
system. Large flow rates may also cause erosion of the metal in the
cold plate due to high fluid velocities.
[0006] Another method for removing heat from components when
air-cooling is not feasible uses heat pipes to transfer heat from
the source to a location where it can be more easily dissipated.
Heat pipes are sealed devices which use a condensable fluid to move
heat from one location to another. Fluid transfer is accomplished
by capillary pumping of the liquid phase using a wick structure.
One end of the heat pipe (the evaporator) is located where the heat
is generated in the component, and the other end (the condenser) is
located where the heat is to be dissipated; often the condenser end
is in contact with extended surfaces such as fins to help remove
heat to the ambient air. This method of removing heat is limited by
the ability of the wick structure to transport fluid to the
evaporator. At high thermal fluxes, a condition known as "dry out"
occurs where the wick structure cannot transport enough fluid to
the evaporator and the temperature of the device will increase,
perhaps causing damage to the device. Heat pipes are also sensitive
to orientation with respect to gravity. That is, an evaporator
which is oriented in an upward direction has less capacity for
removing heat than one which is oriented downward, where the fluid
transport is aided by gravity in addition to the capillary action
of the wick structure. Finally, heat pipes cannot transport heat
over long distances to remote dissipaters due once again to
capillary pumping limitations.
[0007] Yet another method which is employed when direct air-cooling
is not practical uses the well-known vapor compression
refrigeration cycle. In this case, the cold plate is the evaporator
of the cycle. A compressor raises the temperature and pressure of
the vapor, leaving the evaporator to a level such that an
air-cooled condenser can be used to condense the vapor to its
liquid state and be fed back to the cold plate for further
evaporation and cooling. This method has the advantage of high
isothermal heat transfer rates and the ability to move heat
considerable distances. However, this method suffers from some
major disadvantages which limit its practical application in
cooling electrical and electronic devices. First, there is the
power consumption of the compressor. In high thermal load
applications the electric power required by the compressor can be
significant and exceed the available power for the application.
Another problem concerns operation of the evaporator (cold plate)
below ambient temperature. In this case, poorly insulated surfaces
may be below the dew point of the ambient air, causing condensation
of liquid water and creating the opportunity for short circuits and
hazards to people. Vapor compression refrigeration cycles are
designed so as not to return any liquid refrigerant to the
compressor which may cause physical damage to the compressor and
shorten its life by diluting its lubricating oil. In cooling
electrical and electronic components, the thermal load can be
highly variable, causing unevaporated refrigerant to exit the cold
plate and enter the compressor. This can cause damage and shorten
the life of the compressor. This is yet another disadvantage of
vapor compression cooling of components.
[0008] U.S. Pat. No. 6,519,955, totally incorporated herein by
reference, addressed the aforementioned problems with a pumped
liquid two phase cooling system. The cold plate uses a convoluted
fin as the heat transfer surface which transfers heat to the
evaporating refrigerant. However, there is a limit to the surface
area which can be made by forming metal into a convoluted fin
shape. This area is even more limited if the convoluted fin needs
to be lanced and offset. With electronics becoming more powerful
and smaller, the heat flux density of the silicon will soon
increase to a point where convoluted fin structures in a two phase
cold plate may not be able to remove the heat fast enough to keep
the junction temperatures within acceptable limits. One way to
improve the heat removal rate is to increase the surface area of
the structure within the two phase cold plate. At the same time,
the fluid velocities must be maintained within the cold plate so
that the heat transfer coefficient remains high. Increasing the
surface area and maintaining high velocities for high heat transfer
coefficients using convoluted fin structures is difficult and is
limited by the ability to form compact fin structures.
[0009] It is seen then that there exists a continuing need for an
improved method of removing heat from components when existing
methods or systems are not feasible.
SUMMARY OF THE INVENTION
[0010] This need is met by the present invention wherein an
increase in the surface area for heat transfer within a cold plate
structure is achieved by employing a high thermal conductivity
foamed graphite material, while still allowing for flow of both
liquid and vapor through the structure to carry away heat generated
by the electronics.
[0011] In accordance with one aspect of the present invention, a
liquid refrigerant pump circulates refrigerant to cold
plate/evaporators which are in thermal contact with the electrical
or electronic component to be cooled. The liquid refrigerant is
then partially or completely evaporated by the heat generated by
the component. The vapor is condensed by a conventional condenser
coil, and the condensed liquid, along with any unevaporated liquid,
is returned to the pump. By replacing or adding to a convoluted fin
structure in a two phase cold plate with a graphite foam material,
the available surface area is increased many times over that of the
fin structure. Since the graphite foam has relatively high thermal
conductivity of the ligament structure in the open cell foam, the
fin efficiency of the heat transfer surface remains high. Also, due
to the open nature of the graphite foam, the permeability of
liquids and vapor through the foam is high, allowing for low
pressure loss while still maintaining sufficient two phase flow to
carry heat away from the electronics.
[0012] Accordingly, it is an object of the present invention to
provide cooling to electrical and electronic components. It is a
further object of the present invention to provide such cooling by
increasing the surface area for heat transfer within the cold plate
structure, while still allowing for flow of both liquid and vapor
through the structure to carry away the heat generated by the
electronics.
[0013] Other objects and advantages of the invention will be
apparent from the following description, the accompanying drawings
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
[0014] FIG. 1 is an exploded view illustrating the cold plate
assembly in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The present invention relates to cooling electronic
components, including at least microprocessor semiconductors and
power semiconductors, using a pumped liquid two phase cooling
system, such as is described and claimed in U.S. Pat. No.
6,519,955, totally incorporated herein by reference. Specifically,
the present invention is an improvement to the cold plate portion
of the system which absorbs heat directly from the electronics to
be cooled. The purpose of the present invention is to increase the
surface area for heat transfer within the cold plate structure with
a high thermal conductivity foamed graphite material, while still
allowing for flow of both liquid and vapor through the structure to
carry away the heat generated by the electronics.
[0016] Referring now to FIG. 1, there is illustrated a two phase
cold plate assembly 10 such as is used in a pumped refrigerant
forced convection cooling system for removing heat from electronic
systems. The present invention incorporates graphite foam into the
two phase cold plate, replacing or assisting the heat transfer
capabilities of a more conventional convoluted fin structure.
Graphite foam is and can be made by a number of processes known in
the art, and by a variety of manufacturers. For the purpose of
teaching this invention, the graphite foam made by Oak Ridge
National Laboratory (ORNL) can be used, but it is understood that
the invention is not limited to the graphite foam made by the ORNL
process. The graphite foam made by ORNL is taught in the following
U.S. Pat. Nos. 6,033,506; 6,037,032; 6,387,343; 6,261,485;
6,399,149; 6,287,375; 6,398,994; 6,344,159; 6,430,935, and is known
and understood by persons skilled in the relevant art.
[0017] In the drawing, a cold plate evaporator device 10, such as
the two phase cold plate assembly illustrated, comprises a cold
plate top lid 12 with a flat surface 14 on which may be mounted an
electronic device or devices (not shown) which require cooling. The
cold plate top lid 12 attaches to a cold plate body 16. A graphite
foam material 18 is thermally attached to the underside of the top
lid 12, typically proximate to the electronic heat source. The
graphite foam 18 may be attached to the cold plate top lid by any
suitable means, such as, but not limited to, thermally conductive
epoxy or adhesives, solder, brazing and so on. The graphite foam 18
may be plated so the various solders and braze materials will wet
both the foam and the cold plate surface. The plating may be any
suitable material, such as electroless nickel plating. The cold
plate body 16 may include a cut out area 20 for receiving the
graphite foam as the top lid 12 is attached to the cold plate body
16.
[0018] The cold plate structure 10 has an inlet 22 so that a
vaporizable liquid refrigerant may be pumped into the cold plate
and come into thermal contact with the graphite foam. The cold
plate assembly 10 also has an outlet 24 so the vaporizable
refrigerant may leave the graphite foam as a vapor or as a two
phase mixture of liquid and vapor. Any vaporizable refrigerant may
be used as long as it is compatible with the graphite foam and
other materials of construction. The cold plate is typically
constructed such that the outlet extends through an o-ring 26 and a
pipe attachment 28, as shown in the drawing.
[0019] The present invention requires that the vaporizable
refrigerant, for example, R-134a refrigerant, be pumped to the cold
plate assembly 10 and pass through the graphite foam 18 in forced
convection heat transfer. The heat from the electronic device(s) to
be cooled causes some or all of the refrigerant within the graphite
foam 18 to evaporate. The liquid refrigerant may pass through the
graphite foam 18 from any direction, parallel, perpendicular or
multi-pass, in any fluid distribution 30 flow, shown in the drawing
for exemplary purposes only, and not to be considered as limiting
the flow pattern to any particular pattern. Consequently, there is
no limiting flow geometry requirement for the present
invention.
[0020] With respect to the graphite foam 18, the graphite foam may
be corrugated or have slots cut into it in the flow direction to
reduce the pressure drop of the refrigerant through the foam. Any
number of graphite foam elements may be used in a single cold plate
or multiple cold plates in parallel or series flow, without
departing from the spirit and scope of the present invention.
Additionally, the graphite foam elements may be combined with more
conventional heat transfer surfaces such as convoluted fin.
[0021] Having described the invention in detail and by reference to
the preferred embodiment thereof, it will be apparent that other
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims.
* * * * *