U.S. patent application number 11/977797 was filed with the patent office on 2009-02-19 for method and apparatus for preventing cracking in a liquid cooling system.
Invention is credited to Richard Grant Brewer, Mark McMaster, Girish Upadhya.
Application Number | 20090044928 11/977797 |
Document ID | / |
Family ID | 40490517 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090044928 |
Kind Code |
A1 |
Upadhya; Girish ; et
al. |
February 19, 2009 |
Method and apparatus for preventing cracking in a liquid cooling
system
Abstract
An apparatus for preventing cracking of a liquid system includes
an enclosure and one or more compressible objects immersed in the
enclosure. According to the present invention, the enclosure is
configured to cause a fluid to begin to freeze at a location in the
enclosure, and for freezing to advance towards the one or more
compressible objects.
Inventors: |
Upadhya; Girish; (Austin,
TX) ; Brewer; Richard Grant; (Foster City, CA)
; McMaster; Mark; (Menlo Park, CA) |
Correspondence
Address: |
HAVERSTOCK & OWENS LLP
162 N WOLFE ROAD
SUNNYVALE
CA
94086
US
|
Family ID: |
40490517 |
Appl. No.: |
11/977797 |
Filed: |
October 25, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11049202 |
Feb 1, 2005 |
7293423 |
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11977797 |
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10643641 |
Aug 18, 2003 |
7201012 |
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11049202 |
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60577262 |
Jun 4, 2004 |
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60444269 |
Jan 31, 2003 |
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Current U.S.
Class: |
165/81 |
Current CPC
Class: |
F28F 2265/14 20130101;
H01L 23/473 20130101; H01L 2924/0002 20130101; F28F 3/12 20130101;
F28F 19/006 20130101; H05K 7/20272 20130101; F28D 15/00 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
165/81 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Claims
1. An apparatus for preventing cracking of a liquid system,
comprising: a. an enclosure configured to have multiple zones of
different freeze susceptibilities and to cause freezing to begin in
a high freeze susceptibility zone and for a freeze front to advance
from the high freeze susceptibility zone toward a low freeze
susceptibility zone through one or more zones of progressively
decreasing freeze susceptibility; and b. a compressible object
immersed in a zone of lower freeze susceptibility than the high
freeze susceptibility zone.
2. An apparatus for preventing cracking of a liquid system,
comprising: a. an enclosure configured to have multiple zones of
different surface area to volume ratios and to cause freezing to
begin in a high surface area to volume ratio zone and for a freeze
front to advance from the high surface area to volume ratio zone
toward a low surface area to volume ratio zone; and b. a pressure
relief area in the enclosure located in a zone other than the high
surface area to volume ratio zone.
3. The apparatus of claim 2, wherein the pressure relief area is a
compressible object.
4. A freeze-tolerant heat exchanger, comprising: a. a
micro-structured heat exchange region having a first freeze
susceptibility; b. a manifold region configured to have a second
freeze susceptibility so that fluid within the manifold region
freezes later than fluid within the micro-structured heat exchange
region; and c. a fluid input region including a compressible object
and configured to have a third freeze susceptibility so that fluid
within the fluid input region freezes later than fluid within the
manifold region; wherein the heat exchanger is configured so that a
freeze front advances from the micro-structured heat exchange
region towards the compressible object.
5. The freeze-tolerant heat exchanger of claim 4, wherein the
micro-structured region comprises one or more of the following:
microchannels, microporous foam, and pseudo-foam.
6. A method of preventing cracking of a liquid system, the system
including a pump and a heat exchanger, the method comprising the
steps of: a. configuring the system to have multiple zones of
different surface area to volume ratios and to cause freezing to
begin in a high surface area to volume ratio zone and to advance
towards a low surface area to volume ratio zone; b. providing an
enclosure fluidly coupled to the system at a zone other than the
high surface area to volume ratio zone; and c. placing a
compressible object in the enclosure.
Description
RELATED APPLICATION
[0001] This patent application is a continuation-in-part of the
co-pending U.S. patent application Ser. No. 11/049,202, filed on
Feb. 1, 2005, and titled "METHOD AND APPARATUS FOR CONTROLLING
FREEZING NUCLEATION AND PROPAGATION," which claims priority under
35 U.S.C. .sctn. 119(e) of the U.S. provisional patent application
Ser. No. 60/577,262, filed on Jun. 4, 2004, and titled "MULTIPLE
COOLING TECHNIQUES," both of which are hereby incorporated by
reference. Also, this patent application is a continuation-in-part
of the co-pending U.S. patent application Ser. No. 10/643,641,
filed on Aug. 18, 2003, and titled "REMEDIES TO PREVENT CRACKING IN
A LIQUID SYSTEM," which claims priority under 35 U.S.C. .sctn.
119(e) of the U.S. provisional patent application Ser. No.
60/444,269, filed on Jan. 31, 2003, and titled "REMEDIES FOR
FREEZING IN CLOSED-LOOP LIQUID COOLING FOR ELECTRONIC DEVICES,"
both of which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an apparatus and method of
preventing cracking of a liquid system, such as may be useful for
transferring heat from electronic devices and components thereof.
In particular, the invention protects against expansion of fluid
during freezing by including a variety of means and objects to
protect against expansion of water-based solutions when frozen and
by initiating the expansion of frozen fluid in the direction of
zones having generally decreasing surface area to volume
ratios.
BACKGROUND OF THE INVENTION
[0003] When water or many other liquid mixtures are cooled below
their freezing points, the material changes from a liquid state to
a solid state, and undergoes a significant expansion in volume.
Water that has frozen in pipes or other confined spaces does more
than simply clog the pipes and block flow. When freezing occurs in
a confined space like a steel pipe, the ice will expand and exert
extreme pressure which is often enough to crack the pipe and cause
serious damage. This phenomenon is a common failure mode in
hot-water heating systems and automotive cooling systems.
[0004] Ice forming in a pipe does not always cause cracking where
ice blockage occurs. Rather, following a complete ice blockage in a
pipe, continued freezing and expansion inside the pipe can cause
water pressure to increase downstream. The increase in water
pressure leads to pipe failure and/or cracking. Upstream from the
ice blockage the water can retreat back towards its inlet source,
and there is little pressure buildup to cause cracking.
[0005] Liquid cooling systems for electronic devices are
occasionally subjected to sub-freezing environments during
shipping, storage, or in use. Since these systems are going to be
frozen on occasion, they must be designed to tolerate the expansion
of water when frozen. Additives, such as antifreeze, are
potentially poisonous and flammable and can damage mechanical
components, sensitive sensors, and electronics, which is why pure
or substantially pure water is typically the coolant of choice.
[0006] What is needed is an apparatus for and method of preventing
cracking in a liquid cooling system that can tolerate a
predetermined level of freezing and expansion inside confined
spaces without damaging electronic components or affecting system
performance.
SUMMARY OF THE INVENTION
[0007] The present invention protects components and pipes of a
liquid cooling system from cracking related to an expansion of
volume due to freezing of the fluid within the system. In
particular, one aspect of the present invention provides an
apparatus for and method of controlling freezing nucleation and
propagation in a liquid system having one or more components
coupled and characterized by a plurality of surface area to volume
ratios so that when freezing occurs, the fluid expands from an
initial zone having a highest surface area to volume ratio in the
direction of one or more zones having progressively decreasing
surface area to volume ratios. Thus, one aspect of the present
invention manages and designs surface area to volume ratios of one
or more components as well as regions within the components,
including heat exchangers, inlet and outlet ports and tubular
members, so that when freezing occurs, the volume expands in the
direction that can accept the expanded volume. Additionally,
another aspect of the present invention provides an apparatus and
method for forming a liquid cooling system that utilizes size and
volume reducing means, air pockets, compressible objects, and
flexible objects to protect against expansion of water-based
solutions when frozen. In such a system, pipes, pumps, and heat
exchangers are designed to prevent cracking of their enclosures and
chambers.
[0008] In one aspect, an apparatus for preventing cracking of a
liquid system is disclosed. The apparatus includes an enclosure and
a compressible object. The enclosure is configured to have multiple
zones of different freeze susceptibilities and to cause freezing to
begin in a high freeze susceptibility zone and for a freeze front
to advance from the high freeze susceptibility zone toward a low
freeze susceptibility zone through one or more zones of
progressively decreasing freeze susceptibility. The compressible
object is immersed in a zone of lower freeze susceptibility than
the high freeze susceptibility zone.
[0009] In another aspect, another apparatus for preventing cracking
of a liquid system is disclosed. The apparatus includes an
enclosure and a pressure relief area. The enclosure is configured
to have multiple zones of different surface area to volume ratios
and to cause freezing to begin in a high surface area to volume
ratio zone and for a freeze front to advance from the high surface
area to volume ratio zone toward a low surface area to volume ratio
zone. The pressure relief area is positioned within the enclosure
and in a zone other than the high surface area to volume ratio
zone. The pressure relief area can be a compressible object.
[0010] In yet another aspect, a freeze-tolerant heat exchanger is
disclosed. The heat exchanger includes a micro-structured heat
exchange region having a first freeze susceptibility, a manifold
region configured to have a second freeze susceptibility so that
fluid within the manifold region freezes later than fluid within
the micro-structured heat exchange region, and a fluid input region
including a compressible object and configured to have a third
freeze susceptibility so that fluid within the fluid input region
freezes later than fluid within the manifold region, wherein the
heat exchanger is configured so that a freeze front advances from
the micro-structured heat exchange region towards the compressible
object. The micro-structured region can include one or more of
microchannels, microporous foam, and pseudo-foam.
[0011] In another aspect, a method of preventing cracking of a
liquid system is disclosed. The system includes a pump and a heat
exchanger. The method includes configuring the system to have
multiple zones of different surface area to volume ratios and to
cause freezing to begin in a high surface area to volume ratio zone
and to advance towards a low surface area to volume ratio zone. The
method also includes providing an enclosure fluidly coupled to the
system at a zone other than the high surface area to volume ratio
zone, and placing a compressible object in the enclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a schematic diagram of a conventional
closed-loop cooling system, which includes a pump and a heat
exchanger.
[0013] FIG. 2 illustrates one embodiment of a heat exchanger
divided into logical zones characterized by surface area to volume
ratios, in accordance with the present invention.
[0014] FIG. 3 illustrates a schematic diagram of a housing having
an inlet chamber and an outlet chamber.
[0015] FIG. 4 illustrates a schematic diagram of a housing having
inlet and outlet chambers reduced in size and volume in accordance
with the present invention.
[0016] FIG. 5 illustrates a schematic diagram of an air pocket
disposed in an inlet chamber and an outlet chamber of a housing in
accordance with the present invention.
[0017] FIG. 6 illustrates a schematic diagram of a compressible
object disposed in an inlet chamber and an outlet chamber of a
housing in accordance with the present invention.
[0018] FIG. 7A illustrates a schematic diagram of a housing having
inlet and outlet chambers and a plurality of spaced apart flexible
objects coupled to the chambers.
[0019] FIG. 7B illustrates a schematic diagram of a housing having
inlet and outlet chambers and a plurality of spaced flexible
objects coupled to the chambers, the flexible objects being
displaced during fluid expansion to prevent cracking.
[0020] FIG. 8A illustrates a schematic diagram of compressible
objects coupled to inlet and outlet ports within a heat
exchanger.
[0021] FIG. 8B illustrates a schematic diagram of compressible
objects disposed along a bottom surface of a heat exchanger within
adjacent microchannels.
[0022] FIG. 9A illustrates a schematic diagram of compressible
objects coupled to walls of fluid filled tubing within a heat
rejector.
[0023] FIG. 9B illustrates a schematic diagram of compressible
objects disposed along a length of fluid filled tubing within a
heat rejector.
[0024] FIG. 10 illustrates a schematic diagram of compressible
objects disposed within fluid filled channels of a plate within a
heat rejector.
[0025] FIG. 11 illustrates a schematic diagram of compressible
objects disposed in fluid segments of a cooling loop.
[0026] FIG. 12 illustrates a schematic diagram of a housing having
an inlet chamber and an outlet chamber and a plurality of spaced
apart flexible objects coupled to the chambers.
[0027] FIG. 13 illustrates a schematic diagram of a housing having
inlet and outlet chambers and a plurality of spaced apart flexible
objects coupled to the chambers, the flexible objects being
displaced during fluid expansion to prevent cracking.
[0028] FIG. 14 illustrates a flow chart illustrating steps of a
preferred method of one embodiment of the present invention.
[0029] FIG. 15 illustrates a schematic diagram of a housing having
inlet and outlet chambers having a relatively narrowed central
portion and substantially identical expanded end portions.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Reference will now be made in detail to the preferred and
alternative embodiments of the invention, examples of which are
illustrated in the accompanying drawings. While the invention will
be described in conjunction with the preferred embodiments, it will
be understood that they are not intended to limit the invention to
these embodiments. On the contrary, the invention is intended to
cover alternatives, modifications and equivalents, which may be
included within the spirit and scope of the invention as defined by
the appended claims. Furthermore, in the following detailed
description of the present invention, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. However, it should be noted that the present
invention may be practiced without these specific details. In other
instances, well known methods, procedures and components have not
been described in detail as not to unnecessarily obscure aspects of
the present invention.
[0031] FIG. 1 shows a schematic diagram of a closed-loop cooling
system 100, which includes heat exchanger 20 attached to a heat
producing device 55 (shown as an integrated circuit attached to a
circuit board, but which could also be a circuit board or other
heat producing device), a pump 30 for circulating fluid, a heat
rejector 40, which can include a plurality of fins 46 for further
assisting in conducting heat away from the system 100, and a
controller 50 for a pump input voltage based on a temperature
measured at the heat exchanger 20. Fluid flows from an inlet 32, is
pulled through a porous structure (not shown) with the pump 30, and
exits through the outlet 34. While the preferred embodiment uses an
electroosmotic pump, it will be understood that the present
invention can be implemented in a system using other types of
pumps.
[0032] Still referring to FIG. 1, the fluid travels through the
heat exchanger 20 and the heat rejector 40 through tubing lengths
114 and 110 before being recycled back to the inlet 32 of the pump
30 via another tubing 112. The controller 50 is understood to be an
electronic circuit that takes input signals from temperature
sensors in the heat exchanger 20, or from temperature sensors in
the device 55 being cooled, which signals are transmitted along
signal lines 120. The controller 50, based upon the input signals
regulates flow through the pump 30 by applying signals to a power
supply (not shown) associated with the pump 30 along signal lines
122 to achieve the desired thermal performance. While this
embodiment specifies a flow direction, it will be understood that
the present invention can be implemented with the reverse flow
direction.
[0033] As fluid temperature drops below freezing, ice forms into a
blockage. The rate at which ice forms depends on the rate at which
the fluid cools, which depends at least in part on a surface area
to volume ratio. Continued growth of ice in areas of the system 100
can lead to excessive fluid pressure. The resulting pressure can
rupture or damage individual elements, such as the lengths 110,
112, 114 of tubing, channels in the heat exchangers 20 and 40,
and/or chambers inside the pump 30. As will be explained and
understood in further detail below, the individual elements must be
designed in a way that tolerates expansion of the fluid or water
when frozen.
[0034] FIG. 2 illustrates one embodiment of a heat exchanger 200
divided into zones 1, 2, 3A and 3B and characterized by surface
area to volume ratios. The heat exchanger 200 is coupled to tubular
members 210 and 260 disposed in zone 4A and 4B, respectively, and
also characterized by surface area to volume ratios. In this
embodiment, zone 1 is the initial zone and the tubular members
represent a final zone or zones. Zone 1 is preferably one or more
microchannels (not shown) or a porous structure (not shown), such
as microporous foam or pseudo-foam. Alternatively, zone 1 can be
one or more micropins (not shown). Surface areas are calculated for
each zone, preferably based directly on model geometry. A zone can
be constructed of one or more structures, such as copper foam, to
have a desired surface area to volume ratio throughout the heat
exchanger 200. Volumes are calculated for each zone, preferably
based directly on model geometry. The surface area to volume ratio
of each zone is calculated by dividing the surface area of each
zone by the volume of each zone. The resulting surface area to
volume ratio values of adjacent zones are compared. Freeze
progression is deemed favorable when the surface area to volume
ratio of the heat exchanger 200 progressively decreases outward
from zone 1 to the tubular members at the onset of freezing. In
particular, the surface area to volume ratio of zone 1 is
relatively high and the surface area to volume ratios of the
tubular members (zones 4A, 4B) are relatively low.
[0035] During freezing, the fluid expands from a zone having the
highest surface area to volume ratio in the direction of one or
more zones having progressively decreasing surface area to volume
ratios. It will be appreciated that the heat exchanger 200,
including the tubular members 210 and 260, can include many zones
each with a different surface area to volume ratio. The zone
surface area to volume ratio of adjacent zones progressively
decreases from the heat exchanger 200 in the direction of the
tubular members 210 and 260; the zone surface area to volume ratio
decreases in the following order of zones: 1>2>3B>4B and
1>2>3A>4A. In this embodiment, the tubular members 210 and
260 are designed to accommodate the necessary volume expansion.
[0036] The tubular members 210 and 260 preferably include compliant
materials to accommodate an expanded volume equivalent to at least
the cumulative change in volume of the freezing liquid in the
system. Preferably, the tubular members 210 and 260 have elasticity
sufficient to expand outwardly to accommodate the volume expansion
caused by the freezing of the fluid. Alternatively, the one or more
compressible objects (not shown) can be coupled to the tubular
member 210 and 260 wherein pressure exerted on the compressible
object by the freezing fluid increases a volume of the tubular
members 210 and 260. Preferably, the compressible objects (not
shown) are confined within the tubular member and can be made of
closed cell sponge, closed cell foam, air-filled bubbles, sealed
tubes, balloons and/or encapsulated in a hermetically sealed
package. The package can be made of metallic material, metallized
plastic sheet material, or plastic material. The plastic materials
can be selected from teflon, mylar, nylon, a laminate of CTFE and
PE, PET, PVC, PEN or any other suitable package. Other types of
compressible objects can be used. The sponge and foam can be
hydrophobic.
[0037] In another embodiment, at least one air pocket (not shown)
can be disposed in the tubular members 210 and 260 wherein the air
pocket (not shown) accommodates the expansion by the freezing
fluid. Alternatively, at least one flexible object (not shown) is
coupled to the tubular members 210 and 260 wherein pressure exerted
on the flexible object (not shown) by the freezing fluid increases
a volume of the tubular members 210 and 260. The flexible object
(not shown) is preferably secured within the tubular member and
made of one of the following: rubber, plastic, and foam. It will be
appreciated that additional compliant materials may also be
employed to withstand the expansion of freezing fluid.
[0038] In one embodiment, shown in FIG. 3, an apparatus or pump 60
includes a housing 68 having an inlet chamber 62 and an outlet
chamber 64. A pumping mechanism or structure 69 separates the inlet
and outlet chambers 62 and 64 from a bottom surface of the housing
68 to an upper surface of the housing 68. The pumping structure 69
channels liquid from a pump inlet 61 to a pump outlet 66. The
chambers 62 and 64 are filled with fluid. Preferably, the liquid
used in the pump 60 is water. It is contemplated that any other
suitable liquid is contemplated in accordance with the present
invention.
[0039] Still referring to FIG. 3, the pump 60 can be designed so
that there are no large pockets of water in any of the chambers 62
and 64. Since water expands as it freezes, ice takes up more room
than liquid. When freezing occurs in confined spaces, such as
chambers 62 and 64, displacement caused by the expansion of fluids
is proportional to an amount of fluid volume in the chambers 62 and
64. Minimizing the size and volume occupied by the chambers 62 and
64 reduces the displacement, and thereby minimizes the amount of
liquid displaced within the chambers 62 and 64 by freezing.
[0040] As shown in FIG. 4, the volume of inlet and outlet chambers
72 and 74 is substantially reduced compared to the chambers 62 and
64 in FIG. 3. As such, the amount of water present in the pump 70
is greatly reduced. Detailed mechanical analysis of the chambers 72
and 74 is required, but the chambers 72 and 74 can be designed to
withstand force exerted by frozen water. The inlet and outlet
chambers 72 and 74 can be capable of contracting and expanding
between a minimum size and volume condition and a maximum size and
volume condition. It should be understood that the tubing lengths
110, 112, and 114 in FIG. 1 can be reduced in size and volume to
reduce displacement caused by fluid expansion in areas of the
system 100 (FIG. 1).
[0041] In another embodiment, as shown in FIG. 5, an apparatus or
pump 80 includes a housing 88 having an inlet chamber 82 and an
outlet chamber 84. A pumping structure 89 separates the inlet and
outlet chambers 82 and 84 from a bottom surface of the housing 88
to an upper surface of the housing 88. The pumping structure 89
channels liquid from a pump inlet 81 to a pump outlet 86. The
chambers 82 and 84 are filled with fluid to a large extent.
Preferably, the liquid used in the pump 80 is water. It is
contemplated that any other suitable liquid is contemplated in
accordance with the present invention.
[0042] Still referring to FIG. 5, air pockets 85 and 87 are
disposed in the inlet and outlet chambers 82 and 84. The air
pockets 85 and 87 are preferably positioned farthest away from a
location where fluid begins to freeze in the chambers 82 and 84.
Expansion of the ice upon freezing in the chambers 82 and 84 will
take up some space occupied by the air pockets 85 and 87, and cause
a slight increase of pressure in the chambers 82 and 84. However,
air is compressible enough that it can be significantly compressed
with relatively small forces, such that the expansion of the ice is
easily accommodated. Preferably, the air pockets 85 and 87 have a
volume proportional to an amount of fluid in the chambers 82 and
84. The air pockets 85 and 87 can preferably accommodate a
predetermined level of fluid expansion between five to twenty five
percent.
[0043] As mentioned before, ice forming in a confined space does
not typically cause a break where initial ice blockage occurs.
Rather, following a complete ice blockage in a confined space,
continued freezing and expansion inside the confined space cause
fluid pressure to increase downstream. The fluid pressure will
reach a maximum at a last location to freeze in a hermetically
sealed system. The pressure can be very large, unless there is a
trapped air pocket in that region. Thermal design of the chambers
82 and 84 can be altered to select a location where the fluid
begins to freeze, and to arrange for freezing to start from one
location and advance continuously towards an air pocket at another
location. For example, if there is an air pocket at the top surface
of a chamber, the fluid should be nucleated at the bottom surface
of the chamber. As the fluid begins to freeze at the bottom surface
of the chamber, ice expansion displaces water and compresses the
air pocket. Since air is easily compressible, the chamber can
freeze completely without generating large forces at any location
in the chamber.
[0044] To arrange a location of initial freezing in the chamber, it
may be necessary to provide a thermal path from the location of
initial freezing to its surroundings. As the fluid or chamber is
cooled from above a freezing point, the thermal path serves to
efficiently reject thermal energy stored in the location. For
example, an optional metallic insert 288 is mounted from the
location of initial freezing in the chamber to the top surface of
the chamber would serve. Preferably, the metallic insert 288 is
formed of a material that will not contaminate the fluid, such as
copper. Alternatively, locally increasing the surface to volume
ratio of the chamber or reducing package insulation in the chamber
could also work as a replacement for the metallic insert 288. A
critical factor is use of any material or structure that assists a
particular location become cold fastest, and so that progression of
freezing is continuous from that location to the air pockets 85 and
87 of FIG. 5.
[0045] In some cases, it may be difficult to control the
positioning and location of the air pockets 85 and 87 in the
chambers 82 and 84. Further, it may be difficult to dispose an air
pocket in each chamber of the system 100 (FIG. 1). In a further
embodiment, as shown in FIG. 6, one or more compressible objects 95
and 97 are immersed in pump 90. The pump 90 includes a housing 98
having an inlet chamber 92 and an outlet chamber 94. A pumping
structure 99 separates the inlet and outlet chambers 92 and 94 from
a bottom surface of the housing 98 to an upper surface of the
housing 98. The pumping structure 99 channels liquid from a pump
inlet 91 to a pump outlet 96. The chambers 92 and 94 are filled
with fluid to a large extent. Preferably, the liquid used in the
pump 90 is water. It is contemplated that any other suitable liquid
is contemplated in accordance with the present invention.
[0046] Still referring to FIG. 6, the one or more compressible
objects 95 and 97 are immersed and coupled to inlet and outlet
chambers 92 and 94. The objects 95 and 97 can be a closed cell
hydrophobic foam or sponge. Preferably, the objects 95 and 97
accommodate a predetermined level of fluid expansion between five
to twenty-five percent. To accommodate the fluid expansion, the
objects 95 and 97 can preferably have a size and volume
proportional to an amount of fluid in the chambers 92 and 94.
[0047] The objects 95 and 97 can be comprised of a compressible
material, such as an open-cell or closed-cell foam, rubber, sponge,
air-filled bubbles, elastomer, or any related material, and a
protective layer covering all surfaces of the compressible
material. A purpose of having the protective layer is to prevent
contact between the compressible material and a surrounding fluid.
The protective layer can be formed by many means, including
wrapping and sealing, dip-coating, spray-coating, or other similar
means. The protective layer can be a vacuum laminated cover, such
as a spray-on layer, a deposited layer, or a layer formed by
reacting or heating surfaces of the compressible material. In
addition, it is possible to form a protective layer on the surface
of the compressible material by thermally fusing, melting, or
chemically modifying the surface. The protective layer can be
flexible enough so that a volume of the compressible material can
be reduced by pressure. In order to achieve this degree of
flexibility, the protective layer can be much thinner than the
compressible material. Further, the protective layer can be formed
from a material that is not chemically attacked by the fluid used
in the cooling system, or degraded by temperature cycles above and
below freezing. The protective layer can be hermetically sealed so
that gas cannot enter or leave the volume within the protective
layer. The protective layer can be formed from a variety of
materials, including teflon, mylar, polyethylene, nylon, PET, PVC,
PEN or any other suitable plastic, and can additionally include
metal films on interior or exterior surfaces to improve
hermeticity. In addition, the protective layer can be a metallized
plastic sheet material, as used in potato chip packaging, and can
serve as an impervious layer, blocking all gas and liquid
diffusion. Furthermore, in cases where occasional bubbles are
moving through the cooling system, as when an electroosmotic pump
is generating hydrogen and oxygen gas bubbles, the protective layer
can be hydrophilic to help reduce the possibility that the bubbles
will attach to the surfaces.
[0048] In a further embodiment, as shown in FIG. 7A, an apparatus
or pump 103 includes a housing 108 having an inlet chamber 102 and
an outlet chamber 104. A pumping structure 109 separates the inlet
and outlet chambers 102 and 104 from a bottom surface of the
housing 108 to an upper surface of the housing 108. The pumping
structure 109 channels liquid from a pump inlet 101 to a pump
outlet 106. The chambers 102 and 104 are filled with fluid to a
large extent. Preferably, the liquid used in the pump 103 is water.
It is contemplated that any other suitable liquid is contemplated
in accordance with the present invention.
[0049] Still referring to FIG. 7A, a plurality of spaced apart
flexible objects 105 and 107 are coupled to the inlet and outlet
chambers 102 and 104. In this embodiment, the flexible objects 105
and 107 are preferably constructed from a flexible material, such
as rubber or plastic. The flexible material is preferably designed
and arranged such that it can be partially displaced, such as shown
in FIG. 7B, to accommodate expansion of ice without cracking itself
or other rigid elements of the inlet and outlet chambers 102 and
104. Preferably, the flexible objects 105 and 107 accommodate a
predetermined level of fluid expansion between five to twenty five
percent. The flexible objects can be spaced apart from one another
a predetermined distance. Preferably, the flexible objects 105 and
107 are capable of contracting and expanding between a minimum
volume condition and a maximum volume condition.
[0050] FIG. 8A illustrates a schematic diagram of compressible
objects 132 and 134 coupled to inlet and outlet ports 131 and 135
within a heat exchanger 130. Fluid generally flows from one or more
inlet ports 131 and flows along a bottom surface 137 in
microchannels 138 of any configuration and exits through one or
more outlet ports 135, as shown by arrows. The compressible objects
132 and 134 are preferably designed and arranged such that they can
be partially displaced to accommodate expansion of ice without
cracking themselves or other rigid elements of the inlet and outlet
ports 131 and 135 in FIG. 8A.
[0051] FIG. 8B illustrates a schematic diagram of compressible
objects 145 disposed along a bottom surface 147 of a heat exchanger
140 within microchannels 148. As shown in FIG. 8B, the compressible
objects 145 can be arranged within the microchannels 148 such that
the compressible objects 145 form part of a seal from a top surface
149 to the bottom surface 147. In both FIGS. 8A and 8B,
compressible objects act as freeze protection within a heat
exchanger. The positioning of the compressible objects 145 is
intended to minimize flow resistance, and to avoid degrading heat
transfer from the bottom surface 147 to the fluid. Placement of the
compressible objects 145 on sides of the microchannels is also
possible, although less advantageous than the positioning as shown
in FIG. 8B. Positioning on the bottom surface 148 would severely
degrade performance of the heat exchanger 140 because of a high
thermal resistance of the compressible objects 145.
[0052] FIG. 9A illustrates a schematic diagram of compressible
objects 152 and 154 coupled to walls 151 and 155 of fluid filled
tubing 150 within a heat rejector. The tubing 150 can be
substantially longer than other portions of the system, for example
centimeters in length in certain parts of the system 100 (FIG. 1),
and as much as a meters in length in other parts. Placement of a
length of the compressible objects 152 and 154 to the walls 151 and
155 of the tubing 150 will act as freeze protection within a heat
rejector. Alternatively, as shown in FIG. 9B, compressible element
165, such as compressible foam structures, can be threaded along a
length of the tubing 160. The compressible element 165 can float
freely within the tubing 160. Because the compressible element 165
is thinner than the tubing 160, it can simply be threaded without
concern for forming a blockage in the tubing 160. A length of the
compressible elements 165 will vary according to the lengths of the
tubing 160.
[0053] FIG. 10 illustrates a schematic diagram of various possible
configurations for compressible objects 171, 173, 175 and 177
disposed within fluid filled channels 170 of a plate 180 within a
heat rejector. As shown in FIG. 10, fluid can be routed through the
channels 170 disposed within the plate 180 that allows fluid flow
between a fluid inlet 172 and a fluid outlet 174. A heat rejector
can include fins 190 mounted to and in thermal contact with the
plate 180. The compressible objects 171, 173, 175 and 177 disposed
within the channels 170 provide freeze protection, thereby
improving performance of the entire system.
[0054] In addition to the use of size and volume reducing means,
air pockets, compressible objects, and flexible objects discussed
above, other techniques can be used to prevent cracking in a liquid
cooling system, as would be recognized by one of ordinary skill in
the art. For example, as shown in FIG. 11, compressible elements
182 can partly fill all fluid segments of a cooling loop. In all
these cases, it will be appreciated by one of ordinary skill that
routine mechanical design analysis is useful to compute stress
throughout the cooling system including but not limited to the
chambers, lengths of tubing, and other enclosures that contain
either the air pockets or compressible objects to design a system
for which stresses do not accumulate in any location in sizes large
enough to cause the enclosures to fail. In a closed-loop cooling
system for an electronic device, relatively large reservoirs of
fluid are likely to be in the chambers of the pump or the tubing in
a heat exchanger. System design should strive to minimize these
volumes of fluid, thereby reducing the volume of the compressible
material used. Failing that, or if large volumes of fluid are
needed to guarantee sufficient fluid over extended use, the
embodiments described above can reduce forces generated during
freezing to manageable levels.
[0055] In another embodiment, shown in FIG. 12, an apparatus or
pump 200 includes a housing 208 having an inlet chamber 202 and an
outlet chamber 204. A pumping structure 209 separates the inlet and
outlet chambers 202 and 204 from a bottom surface of the housing
208 to an upper surface of the housing 208. The pumping structure
209 channels liquid from a pump inlet 201 to a pump outlet 206. The
chambers 202 and 204 are filled with fluid. Preferably, the liquid
used in the pump 200 is water. It is contemplated that any other
suitable liquid is contemplated in accordance with the present
invention.
[0056] Still referring to FIG. 12, the housing 208 can be designed
to withstand expansion of the fluid when freezing occurs. A
plurality of flexible objects 207 are coupled to at least one wall
of the housing 208. The housing 208 consists of rigid plates and
support the chambers 202 and 204. The plates make up a plurality of
sides of the chambers 202 and 204 and are joined by the flexible
objects 207. The flexible objects 207 can be fastened to the
plates. The flexible objects 207 can be formed on any or each of
the plurality of sides of the chambers 202 and 204, which includes
corner edges, and allow the plates to be displaced outward when
acted upon by force, as shown in FIG. 13. The flexible objects can
be elastomer hinges or any suitable polymer hinge, so long as it
can alter its shape when met by force.
[0057] In an alternative embodiment, as shown in FIG. 14, a method
of preventing cracking in a pump is disclosed beginning in the Step
300. In the Step 310, a housing is provided having an inlet chamber
and an outlet chamber separated by a pumping structure. In the Step
320, a plurality of spaced apart flexible objects are disposed to
form at least one wall of the housing such that pressure exerted on
the plurality of spaced apart flexible objects increases a volume
of the housing. The flexible objects can accommodate a
predetermined level of fluid expansion.
[0058] The predetermined level of fluid expansion can be between
five to twenty-five percent. The flexible objects are preferably
spaced apart a predetermined distance. Additionally, the flexible
objects are preferably capable of contracting and expanding between
a minimum volume condition and a maximum volume condition. The pump
can be electro-osmotic. The housing can include rigid plates.
Furthermore, the flexible objects can be fastened to the rigid
plates. The flexible objects can be made of rubber, plastic or
foam.
[0059] In another embodiment, shown in FIG. 15, an apparatus or
pump 400 includes a housing 410 having hourglass-shaped inlet and
outlet chambers. The hourglass-shaped chambers can have a
relatively narrowed middle or central portion 405 and substantially
identical expanded end portions 407. A pumping structure 420
separates the inlet and outlet chambers from a bottom surface of
the housing 410 to an upper surface of the housing 410. The
apparatus can include a thermal path from a location of initial
freezing to its surroundings.
[0060] As the fluid or chamber is cooled from above a freezing
point, the thermal path serves to efficiently reject heat stored in
the location. For example, an optional metallic insert 430 is
mounted from the location of initial freezing in the chamber to the
top surface of the chamber would serve. Preferably, the metallic
insert 430 is formed of a material that will not contaminate the
fluid such as copper. A critical factor is use of any material or
structure that assists a particular location become cold fastest,
and so that progression of freezing is continuous from that
location to the expanded end portions 407 of the chambers. The
combination of having hourglass-shaped chambers and the metallic
insert 430 allows for freezing to initiate at the narrowed middle
or central portion 405 of the hourglass-shaped chambers and expand
outward to the expanded end portions 407, where liquid can be
further displaced at the inlet, outlet, or both, or a volume
accommodating structure can be implemented at the expanded end
portions 407 as described above.
[0061] In the above-described embodiments, the present invention is
applied to a pump or a housing having an inlet chamber and an
outlet chamber. Alternatively, the present invention may be applied
to any enclosure in a liquid cooling system. The liquid cooling
system preferably includes an electro-osmotic pump and a heat
exchanger. As such, the size and volume reducing means, the air
pockets, the compressible objects, and the compressible objects can
be applied to any or each enclosure in the system, including
tubing, of the liquid cooling system.
[0062] The present invention has been described in terms of
specific embodiments incorporating details to facilitate the
understanding of the principles of construction and operation of
the invention. Such reference herein to specific embodiments and
details thereof is not intended to limit the scope of the claims
appended hereto. It will be apparent to those skilled in the art
that modification s may be made in the embodiment chosen for
illustration without departing from the spirit and scope of the
invention.
* * * * *