U.S. patent application number 10/723529 was filed with the patent office on 2005-01-13 for pumped liquid cooling system using a phase change refrigerant.
This patent application is currently assigned to Thermal Form & Function LLC. Invention is credited to Marsala, Joseph.
Application Number | 20050005623 10/723529 |
Document ID | / |
Family ID | 34794601 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050005623 |
Kind Code |
A1 |
Marsala, Joseph |
January 13, 2005 |
Pumped liquid cooling system using a phase change refrigerant
Abstract
An improved cooling system provides cooling away from the
surface of electrical and electronic components with very low
parasitic power consumption and very high heat transfer rates. The
component to be cooled is in thermal contact with a cold plate
evaporator device. Refrigerant is circulated by a liquid
refrigerant pump to the cold plate evaporator device, and the
liquid refrigerant is at least partially 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. The system operates
nearly isothermally in both evaporation and condensation.
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: |
34794601 |
Appl. No.: |
10/723529 |
Filed: |
November 26, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10723529 |
Nov 26, 2003 |
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10292071 |
Nov 12, 2002 |
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6679081 |
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Current U.S.
Class: |
62/259.2 ;
257/E23.098; 62/498 |
Current CPC
Class: |
H01L 23/427 20130101;
H01L 2924/0002 20130101; F25B 23/006 20130101; F28D 15/0266
20130101; H01L 23/473 20130101; H01L 2924/00 20130101; H01L
2924/0002 20130101 |
Class at
Publication: |
062/259.2 ;
062/498 |
International
Class: |
F25D 023/12; F25B
001/00 |
Claims
What is claimed is:
1. A cooling system 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 liquid
refrigerant pump having at least an inlet; a vaporizable
refrigerant circulated by the liquid refrigerant pump to the at
least one cold plate evaporator device, whereby the refrigerant is
at least partially evaporated by the heat generated by the at least
one component, creating a vapor; a condenser for condensing the
partially evaporated refrigerant vapor, creating a single liquid
phase; a first liquid conduit for receiving the vaporizable
refrigerant from the liquid refrigerant pump, said first liquid
conduit connected to the at least one cold plate evaporator device;
a second conduit from the at least one cold plate evaporator
device, said second conduit connected to the condenser; and a
liquid return line from the condenser to the inlet of the
refrigerant pump.
2. A cooling system as claimed in claim 1 wherein an additional
volume is contained in the cooling system to provide for storage of
liquid refrigerant when liquid refrigerant is displaced in the cold
plate evaporator device and the condenser by vapor during the
cooling operation.
3. A cooling system as claimed in claim 2 wherein the additional
volume is located between the refrigerant pump and the cold plate
evaporator device.
4. A cooling system as claimed in claim 2 wherein the additional
volume is located between the cold plate evaporator device and the
condenser.
5. A cooling system as claimed in claim 2 wherein the additional
volume is located between the condenser and the refrigerant
pump.
6. A cooling system as claimed in claim 1 wherein the at least one
cold plate evaporator device comprises at least two cold plate
evaporator devices.
7. A cooling system as claimed in claim 6 wherein the at least two
cold plate evaporator devices are in series flow.
8. A cooling system as claimed in claim 6 wherein the at least two
cold plate evaporator devices are in parallel flow.
9. A cooling system as claimed in claim 1 wherein the condenser
comprises an air cooled condenser.
10. A cooling system as claimed in claim 1 wherein the condenser
comprises a water cooled condenser.
11. A cooling system as claimed in claim 1 wherein the condenser
comprises a liquid cooled condenser.
12. A cooling system as claimed in claim 1 wherein the condenser
comprises an evaporative condenser.
13. A cooling system as claimed in claim 1 wherein the liquid
refrigerant pump comprises a hermetic liquid pump.
14. A cooling system as claimed in claim 1 wherein the refrigerant
comprises R-134a refrigerant.
15. A cooling system as claimed in claim 1 wherein the refrigerant
comprises a vaporizable refrigerant.
16. A cooling system as claimed in claim 1 wherein a condensing
temperature of the refrigerant is controlled so as to be above the
ambient dew point where the cold plate evaporator device is
located.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of copending
application Ser. No. 10/292,071, filed Nov. 12, 2002.
TECHNICAL FIELD
[0002] The present invention relates to cooling of electrical and
electronic components, and more particularly, to a liquid
refrigerant pump to circulate refrigerant to multiple cold
plate/evaporators in thermal contact with the electrical or
electronic component 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] It is seen then that there exists a continuing need for an
improved method of removing heat from components when air-cooling
is not feasible.
SUMMARY OF THE INVENTION
[0009] This need is met by the pumped liquid cooling system of the
present invention wherein cooling is provided to electrical and
electronic components with very low parasitic power consumption and
very high heat transfer rates away from the component surface. This
invention also reduces the temperature drop required to move heat
from the component to the ambient sink.
[0010] 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. The system of the present invention
operates nearly isothermally in both evaporation and
condensation.
[0011] 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 to
components with very low parasitic power consumption and very high
heat transfer rates away from the component surface. It is yet
another object of the present invention to reduce the temperature
drop required to move heat from the component to the ambient
sink.
[0012] 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 DRAWINGS
[0013] FIG. 1A is a schematic block diagram illustrating a parallel
configuration of the pumped liquid cooling system in accordance
with the present invention;
[0014] FIG. 1B is a schematic block diagram illustrating a series
configuration of the pumped liquid cooling system in accordance
with the present invention; and
[0015] FIG. 2 illustrates a plurality of cold plate evaporator
devices, each in thermal contact with a component to be cooled.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Referring now to FIGS. 1A and 1B, there is illustrated a
cooling system 10 which circulates a refrigerant as the working
fluid. The refrigerant may be any suitable vaporizable refrigerant,
such as R-134a. The cooling cycle can begin at liquid pump 12,
shown as a Hermetic Liquid Pump. Pump 12 pumps the liquid phase
refrigerant to a liquid manifold 14 where it is distributed to one
or a plurality of branches or lines 16. From the manifold 14, each
branch or line 16 feeds liquid refrigerant to a cold plate 18. The
condensing temperature of the refrigerant is preferably controlled
so as to be above the ambient dew point where the cold plate
evaporator device is located.
[0017] As illustrated in FIG. 2, each cold plate 18 is in thermal
contact with an electrical or electronic component or components 20
to be cooled, causing the liquid refrigerant to evaporate at system
pressure. None, some, or all of the liquid refrigerant may
evaporate at cold plate 18, depending on how much heat is being
generated by component 20. In most cases, some of the refrigerant
will have evaporated and a two-phase mixture of liquid and vapor
refrigerant will leave each cold plate 18, as shown by arrow 22 in
FIGS. 1A and 1B.
[0018] In a preferred embodiment of the present invention, at this
point in the operation of the system, each cold plate 18 discharges
its mixture of two-phase refrigerant to conduit 24, as illustrated
in FIGS. 1A and 1B. For most applications, the conduit 24 is a
tube. The conduit 24 is attached to condenser 28, comprised of a
condensing coil 30 and a fan 32. Condenser coil 30, attached to
conduit 24, condenses the vapor phase back to a liquid and removes
the heat generated by the electronic components 20, shown in FIG.
2. Any unevaporated liquid in conduit 24 merely passes through
condenser 28. In FIGS. 1A and 1B, an ambient air-cooled condenser
28 is shown, using fan 32, although it will occur to those skilled
in the art that any suitable form of heat rejection may be used
without departing from the scope of the invention, such as an air
cooled condenser, a water or liquid cooled condenser, or an
evaporative condenser.
[0019] The condenser 28 operates at a pressure which corresponds to
a temperature somewhat higher than the dew point temperature of the
ambient air. In this way, it is impossible for water condensation
to form, since no system temperature will be below the ambient dew
point temperature. The condenser operating point sets the pressure
of the entire system by means of the entering coolant temperature
and its ability to remove heat from the condenser, thus fixing the
condensing temperature and pressure. Also, since vaporized
refrigerant is being condensed to a liquid phase, the condenser 28
sets up a flow of vaporized refrigerant from the conduit 24 into
the condenser 28, without the need for any compressor to move the
vapor from the cold plate-evaporator 18 to the condenser 28. The
liquid refrigerant exits the condenser 28, travels through conduit
34 as indicated by arrow 35, and moves to an additional volume 36,
which holds a quantity of liquid refrigerant. Pump 12 pumps the
liquid refrigerant from the additional volume 36 into the cold
plate where the refrigerant evaporates, becoming a two-phase
mixture, all without the need of any vapor/liquid separation. The
two-phase mixture leaves the cold plate and goes into the
condenser, which condenses the vapor into liquid, so that only
liquid leaves the condenser.
[0020] The outlet of the additional volume 36 is connected to the
inlet of the liquid refrigerant pump 12. At the pump 12, the
pressure of the refrigerant is raised sufficiently to overcome the
frictional losses in the system and the cooling cycle begins again.
The pump 12 is selected so that its pressure rise is equal to or
exceeds the frictional loss in the system at the design flow
rate.
[0021] Unlike the pumped liquid single-phase system, the present
invention operates isothermally, since it uses change of phase to
remove heat rather than the sensible heat capacity of a liquid
coolant. This allows for cooler temperatures at the evaporator and
cooler components than a single-phase liquid system. Low liquid
flow rates are achieved through the evaporation of the working
fluid to remove heat, keeping the fluid velocities low and the
pumping power very low for the heat removed. Parasitic electric
power is reduced over both the pumped single-phase liquid system
and the vapor compression refrigeration system. The cooling system
of the present invention comprises at least one component
generating heat and required to be cooled, and at least one cold
plate evaporator device in thermal contact with the at least one
component. A vaporizable refrigerant is circulated by the liquid
refrigerant pump to the at least one cold plate evaporator device,
whereby the refrigerant is at least partially evaporated by the
heat generated by the at least component(s), creating a vapor. A
condenser condenses the partially evaporated refrigerant vapor,
creating a single liquid phase. The vaporizable refrigerant from
the pump is received by a first liquid conduit connected to the
cold plate evaporator device(s). A second conduit from the cold
plate evaporator devices), is connected to the condenser. A liquid
return line is provided from the condenser to an inlet of the
refrigerant pump.
[0022] An advantage over the heat pipe system is obtained with the
system 10 of the present invention because the liquid flow rate
does not depend on capillary action, as in a heat pipe, and can be
set independently by setting the flow rate of the liquid pump. Dry
out can thus be avoided. The cold plate/evaporator system of the
present invention is insensitive to orientation with respect to
gravity. Unlike heat pipe systems, the thermal capacity of the
evaporator 18 of the present invention does not diminish in certain
orientations.
[0023] Another advantage of the present invention over heat pipe
and vapor compression based systems is the ability to separate the
evaporator and condenser over greater distances. This allows more
flexibility in packaging systems and design arrangements. The
present invention easily handles variation in thermal load of the
components 20 to be cooled. Since any unevaporated liquid
refrigerant is returned to the pump, multiple cold plates at
varying loads are easily accommodated without fear of damaging a
compressor. Since the current invention does not operate at any
point in the system 10 at temperatures below ambient dew point
temperature, there is no possibility of causing water vapor
condensation and the formation of liquid water.
[0024] 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.
* * * * *