# Patent

## Title
Remedies to prevent cracking in a liquid system

## Abstract

A liquid cooling system utilizing minimal size and volume enclosures, air pockets, compressible objects, and flexible objects is provided 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. Also described are methods of preventing cracking in a liquid cooling system. In all these cases, the system must be designed to tolerate expansion when water is frozen.

## Background
This patent application is a divisional of U.S. patent application No. 10/643,641 filed Aug. 18, 2003 and entitled “REMEDIES TO PREVENT CRACKING IN A LIQUID SYSTEM.”
Related Application
This application claims priority under 35 U.S.C. § 119(e) of the co-pending 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.” The 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” is hereby incorporated by reference.


FIELD OF THE INVENTION
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 utilizes a variety of means and objects to protect against expansion of water-based solutions when frozen.
BACKGROUND OF THE INVENTION
When water or many other fluid mixtures are cooled below freezing, the material changes from a liquid state to a solid state, and undergoes a significant expansion in volume, which is as much as 10% or more for water or water-based mixtures. When water freezes in a pipe, it undergoes a similar expansion. 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.
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.
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.
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
A liquid system utilizing size and volume reducing means, air pockets, compressible objects, and flexible objects is provided 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.
In a first aspect of the invention, an apparatus for preventing cracking of a liquid system is disclosed. The apparatus comprises at least one heat exchanger; one or more inlet ports extending through a first opening for conveying a fluid to a plurality of channels and passages; one or more outlet ports extending through a second opening for discharging the fluid from the plurality of channels and passages; and one or more compressible objects positioned substantially adjacent the inlet ports and the outlet ports in an unpressured condition such that the compressible objects reduce a volume of the inlet ports and the outlet ports and further wherein pressure exerted on the compressible objects increases a volume of the inlet ports and the outlet ports.
The compressible objects can preferably accommodate a predetermined level of fluid expansion. The predetermined level of fluid expansion can be between 5 to 25 percent. The compressible objects are preferably capable of contracting and expanding between a minimum volume and a maximum volume. The compressible objects can be secured within the inlet port and the outlet port. Alternatively, the compressible objects can be positioned at any location throughout the system. The compressible objects can be made of sponge, foam, air-filled bubbles, balloons and 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, PET, PVC, PEN or any other suitable package.
In a second aspect of the invention, an apparatus for preventing cracking of a liquid system is disclosed. The apparatus comprises at least one heat exchanger having a top element and a bottom element; a plurality of channels and passages formed within the bottom element to provide flow of a fluid therethrough; and one or more compressible objects positioned within one or more of the plurality of channels and passages such that in an uncompressed state the compressible objects reduce a volume of each of the plurality of channels and passages having one or more of the compressible objects and further wherein under pressure exerted within the channels and passages the compressible objects are compressed to increase the volume of each of the plurality of channels and passages.
In a further separate aspect of the invention, an apparatus for preventing cracking of a liquid system is provided. The system preferably includes one or more pumps and one or more heat exchangers. The apparatus comprises an enclosure, wherein a size and volume occupied by fluid within the enclosure is minimized. The pump can be an electro-osmotic pump.
The enclosure is preferably capable of contracting and expanding between a minimum size and volume condition and a maximum size and volume condition.
In a second separate aspect of the invention, an apparatus for preventing cracking of a liquid system is disclosed. The apparatus comprises a housing having at least one inlet chamber and at least one outlet chamber, wherein a size and volume occupied by fluid within the inlet and outlet chambers is minimized.
The inlet and outlet chambers are preferably capable of contracting and expanding between a minimum size and volume condition and a maximum size and volume condition. The inlet and outlet chambers can be separated by a pumping structure or mechanism.
In a further separate aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The system includes at least one pump and at least one heat exchanger. The method comprises the steps of providing an enclosure and minimizing a size and volume occupied by fluid within the enclosure.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing a housing having at least one inlet chamber and at least one outlet chamber; and minimizing a size and volume occupied by fluid within the inlet and outlet chambers.
In a further aspect of invention, an apparatus for preventing cracking of a liquid system is provided. The system includes at least one pump and at least one heat exchanger. The apparatus comprises an enclosure and one or more compressible objects immersed in the enclosure.
The objects preferably accommodate a predetermined level of fluid expansion. The predetermined level of fluid expansion is preferably between 5 to 25 percent. The objects preferably have a size and volume proportion to an amount of fluid in the enclosure. The objects can be a hydrophobic foam. Alternatively, the objects can be hydrophobic sponges. Also, the objects can be balloons in hydrophobic bags. The objects can be made of rubber, plastic, foam, sealed foam or rubber, or vacuum laminated foam or rubber. The objects may be enclosed in vacuum laminated bags.
In a further aspect of the invention, an apparatus for preventing cracking of a liquid system is provided. The apparatus comprises a housing having at least one inlet chamber and at least one outlet chamber and one or more compressible objects immersed in the inlet and outlet chambers. The objects preferably have a size and volume proportional to an amount of fluid in the chambers.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing an enclosure and immersing one or more compressible objects in the enclosure.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing a housing having at least one inlet chamber and at least one outlet chamber and immersing one or more compressible objects in the inlet and outlet chambers.
In a further aspect of the invention, an apparatus for preventing cracking of a liquid system is disclosed. The apparatus comprises an enclosure and one or more air pockets disposed in the enclosure. The air pockets are preferably positioned farthest away from a location where liquid begins to freeze in the enclosure.
The air pockets preferably have a volume proportional to an amount of fluid in the enclosure. The air pockets preferably accommodate a predetermined level of fluid expansion. The predetermined level of fluid expansion is preferably between 5 to 25 percent.
In a further aspect of the invention, an apparatus for preventing cracking of a liquid system is disclosed. The apparatus comprises a housing having at least one inlet chamber and at least one outlet chamber and an one or more air pockets disposed in the inlet and outlet chambers. The air pockets are preferably positioned farthest away from a location where liquid begins to freeze in the chambers. The air pockets preferably have a volume proportion to an amount of fluid in the chambers.
In a further aspect of the invention, a method of preventing cracking of a liquid system is provided. The method comprises the steps of providing an enclosure and disposing one or more air pockets in the enclosure. The air pockets are positioned farthest away from a location where liquid begins to freeze in the enclosure.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing a housing having at least one inlet chamber and at least one outlet chamber and disposing one or more air pockets in the inlet and outlet chambers. The air pockets are positioned farthest away from a location where liquid begins to freeze in the chambers.
In a further aspect of the invention, an apparatus for preventing cracking of a liquid system is provided. The apparatus comprises an enclosure for holding liquid having a plurality of walls and at least one flexible object coupled to form a portion of at least one wall of the enclosure such that pressure exerted on the flexible objects increases a volume of the enclosure.
The flexible objects preferably accommodate a predetermined level of fluid expansion. The flexible objects can be spaced apart a predetermined distance. The flexible objects are preferably capable of contracting and expanding between a minimum volume condition and a maximum volume condition. The flexible objects are preferably secured within the enclosure and deformable under pressure. The flexible objects can be made of rubber. Alternatively, the flexible objects can be made of plastic or foam.
In a further aspect of the invention, an apparatus for preventing cracking of a liquid system is provided. The apparatus comprises a housing having at least one inlet chamber and at least one outlet chamber and at least one flexible object coupled to form a portion of at least one of the inlet and outlet chambers such that pressure exerted on the flexible objects increases a volume of the housing. The flexible objects preferably accommodate a predetermined level of fluid expansion.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing an enclosure and disposing at least one flexible object to form a portion of at least one wall of the enclosure such that pressure exerted on the flexible objects increases a volume of the enclosure. The flexible objects preferably accommodate a predetermined level of fluid expansion.
In a further aspect of the invention, a method of preventing cracking of a liquid system is disclosed. The method comprises the steps of providing a housing having at least one inlet chamber and at least one outlet chamber and disposing at least one flexible object to form a portion of at least one of the inlet and outlet chambers such that pressure exerted on the flexible objects increases a volume of the housing. The flexible objects preferably accommodate a predetermined level of fluid expansion.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic diagram of a conventional closed-loop cooling system, which includes an electro-osmotic pump and a heat exchanger.
FIG. 2 illustrates a schematic diagram of a housing having an inlet chamber and an outlet chamber.
FIG. 3 illustrates a schematic diagram of a housing having inlet and outlet chambers reduced in size and volume in accordance with the present invention.
FIG. 4 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.
FIG. 5 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.
FIG. 6A illustrates a schematic diagram of a housing having inlet and outlet chambers and a plurality of spaced apart flexible objects coupled to the chambers.
FIG. 6B 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.
FIG. 7A illustrates a schematic diagram of compressible objects coupled to inlet and outlet ports within a heat exchanger.
FIG. 7B illustrates a schematic diagram of compressible objects disposed along a bottom surface of a heat exchanger within adjacent microchannels.
FIG. 8A illustrates a schematic diagram of compressible objects coupled to walls of fluid filled tubing within a heat rejector.
FIG. 8B illustrates a schematic diagram of compressible objects disposed along a length of fluid filled tubing within a heat rejector.
FIG. 9 illustrates a schematic diagram of compressible objects disposed within fluid filled channels of a plate within a heat rejector.
FIG. 10 illustrates a schematic diagram of compressible objects disposed in fluid segments of a cooling loop.
FIG. 11 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.
FIG. 12 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.
FIG. 13 illustrates a flow chart illustrating steps of a preferred method of one embodiment of the present invention.
FIG. 14 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 PREFERRED EMBODIMENT
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.
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 may 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) within the pump 30 by electroosmotic forces, 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.
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 thermometers in the heat exchanger 20, or from thermometers 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.
As fluid temperature drops below freezing, ice forms into a blockage. 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.
In one embodiment, shown in FIG. 2, 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.
Still referring to FIG. 2, 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 prevents bending, stretching, or cracking of the chambers 62 and 64.
As shown in FIG. 3, the volume of inlet and outlet chambers 72 and 74 is substantially reduced compared to the chambers 62 and 64 in FIG. 2. 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).
In another embodiment, as shown in FIG. 4, 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.
Still referring to FIG. 4, 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 occuppied by the air pockets 85 and 87, and a 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 proportion 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.
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.
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 heat 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, reducing the size and volume of the chamber or reducing package insulation in the chamber could also work. 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. 4.
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. 5, one or more compressible objectss 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.
Still referring to FIG. 5, the one or more compressible objectss 95 and 97 are immersed and coupled to inlet and outlet chambers 92 and 94. The objects 95 and 97 can be a 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.
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.
In a further embodiment, as shown in FIG. 6A, 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.
Still referring to FIG. 6A, 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 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. Alternatively, the flexible objects 105 and 107 are secured within the chambers 102 and 104.
FIG. 7A 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 the outlet port 135, as shown by arrows. The compressible objects 132 and 134 are preferably designed and arranged such that it can be partially displaced to accommodate expansion of ice without cracking itself or other rigid elements of the inlet and outlet ports 131 and 135 in FIG. 7A.
FIG. 7B 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. 7B, 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. 7A and 7B, 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. 8A. 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.
FIG. 8A 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. 8B, 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.
FIG. 9 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. 9, 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.
In addition to the use of size and volume reducing means, air pockets, compressible objects, and compressible 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. 10, compressible elements 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 and compressible objects to design a system for which that 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 eliminate these volumes of fluid, thereby reducing the reservoirs at their source. 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.
In another embodiment, shown in FIG. 11, 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.
Still referring to FIG. 11, the housing 208 can be designed to withstand expansion of the fluid when freezing occurs. A plurality of flexible objects 210 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 210. The flexible objects 210 can be fastened to the plates. The flexible objects 210 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. 12. The flexible objects can be elastomer hinges or any suitable polymer hinge, so long as it can alter its shape when met by force.
In an alternative embodiment, as shown in FIG. 13, 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 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.
The predetermined level of fluid 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.
In another embodiment, shown in FIG. 14, 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.
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 a 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.
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.
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 modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention.

## Claims

1. An apparatus for preventing cracking in a pump, comprising:
a housing having at least one inlet chamber and at least one outlet chamber, the inlet and outlet chambers having a relatively narrowed central portion and substantially identical expanded end portions; and
means for initiating freezing from the narrowed central portion to the expanded end portions.

2. The apparatus of claim 1, wherein the means for initiating comprises at least one metallic insert mounted at a location in at least one of the inlet and outlet chambers.

3. The apparatus of claim 2, wherein the metallic insert is made of one of the following: copper, gold, silver, or a material of high thermal conductivity, such as silicon, aluminum, or a metal.

4. The apparatus of claim 2, wherein the metallic insert is coated with nickel or copper.

5. A method of preventing cracking in a pump, the method comprising the steps of:
providing a housing having at least one inlet chamber and at least one outlet chamber, the inlet and outlet chambers having a relatively narrowed central portion and substantially identical expanded end portions; and
providing means for initiating freezing from the narrowed central portion to the expanded end portions.

6. The method of claim 5, wherein the step of providing means for initiating comprises disposing at least one metallic insert at a location in at least one of the inlet and outlet chambers.

7. The method of claim 6, wherein the metallic insert is made of one of the following: copper, gold, silver, or a material of high thermal conductivity, such as silicon, aluminum, or a metal.

8. The apparatus of claim 6, wherein the metallic insert is coated with nickel or copper.