Thermal transfer device and working fluid therefor including a kinetic ice inhibitor

Abstract

A kinetic ice inhibitor is added to water in very small quantities (0.5 to 1.0 wt. %) to inhibit the nucleation and growth of ice crystals when the water is used as a working fluid in a heat transfer device, such as a vapor chamber heat sink. The preferred type of kinetic ice inhibitor is a water soluble polymer or copolymer, such as polymers, copolymers of polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCAP) and terpolymers VC-713. These polymers kinetically delay or inhibit the formation and growth of ice crystals in the water and significantly reduce the chances of expansion damage to the heat transfer device when subjected to below freezing temperatures potentially encountered during shipment and storage.

Description

BACKGROUND OF THE INVENTION

[0001] The instant invention relates to a water-based working fluid for use in thermal transfer applications. More specifically, the present working fluid is particularly suited for use in vapor chamber heat sinks that will be subjected to large temperature fluctuations during shipment and storage. In this regard, the water-based working fluid includes a kinetic ice inhibitor that inhibits ice nucleation and/or ice crystal growth in cold environments, and prevents the damage of device.

[0002] Vapor chamber heat sinks are well known in the heat transfer arts. A vapor chamber comprises a vacuum sealed space or chamber in which a small amount of a two-phase working fluid is present. In many applications, water is used as the working fluid because it inexpensive, has good thermal properties, and functions effectively through a wide range of operating temperatures. During manufacture, a small amount of working fluid is added to the chamber in a liquid phase. The chamber is then vacuum sealed. The result is an enclosed chamber having the equilibrium state water within the interior thereof. During use, this environment allows the liquid water to quickly absorb heat from its surroundings, change phase, i.e. change to a vapor phase, and transfer heat by rapid movement of the vapor particles within the interior of the chamber. Liquid water in the evaporation portion of the vapor chamber, absorbs heat from the heat source disposed beneath the vapor chamber. The heated water boils to vapor phase and rises and spreads to the condensation portion of the vapor chamber, transferring heat to the upper surfaces thereof. As the water vapor releases heat in the upper surfaces of the vapor chamber, it condenses on the upper surface of the chamber and returns by surface tension with the help of wicking materials to the evaporation portion of the vapor chamber.

[0003] Vapor chambers have been used in the prior art to provide high performance thermal management for semiconductor microprocessor electronics. In normal temperatures, as found in almost every personal computer, a conventional finned heat sink is placed in direct thermal contact with the heat source, i.e. CPU package. Heat generated by the CPU is absorbed by the heat sink, transferred to the fins by direct thermal conduction, and dissipated to ambient environment by blowing air over the surface the fins. In higher temperature applications, such as described above, a vapor chamber is interposed between the CPU and the heat sink to act as a high efficient heat spreader. The vapor chamber is thus in direct contact with the CPU and absorbs the heat directly from the CPU. The heat is then dissipated through the vapor chamber to the heat sink and further dissipated to the ambient environment. Because the vapor chamber is a more efficient thermal transfer device, heat is transferred from the CPU more quickly, and the CPU remains cooler and thus performs better and longer. Accordingly, the combined use of a vapor chamber and a heat sink has been found to provide better thermal performance in dissipating heat from the CPU than a heat sink alone and provides a more effective thermal solution for high end applications.

[0004] As indicated above, vapor chambers were previously used only in special high speed microprocessor applications requiring high performance thermal management. However, the ever-increasing speed of semiconductor microprocessors commonly used in personal computers and network servers has recently prompted an interest in the application of vapor chamber heat sinks to a wider variety of higher-volume, consumer semiconductor products. This wide-spread adoption of vapor chamber technology, will require that vapor chambers conform to the standards and environmental conditions encountered by personal computers rather than specialized high-end computers. There is thus a perceived need in the industry for a robust, highly stable and rugged vapor chamber that can withstand the environmental conditions encountered by electronic devices that are produced, shipped and stored in everyday commerce.

SUMMARY OF THE INVENTION

[0005] The problem addressed by the present invention was discovered in connection with the shipment of microprocessor devices in cold environments. In the normal operation of a computer in a standard office environment, the computer may be subjected to a temperature range of anywhere between 20° C. and 70° C. Within this range, a water-based working fluid can function properly. However, during the transportation and storage of computers, the temperature range could be between −40° C. and +70° C. While the upper end of this temperature range does not pose a problem, the lower end creates a fundamental problem with the use of water as the working fluid in the vapor chamber. Once the temperature drops below the freezing point (0° C.), the water begins to form ice crystals and to expand. As well known in the art, the expansion of water in a closed container causes, at a minimum, physical deformation of the container, and worst case, causes a rupture of the container walls. The same is true in a closed container environment (with water in equilibrium state). The expansion of water within the vapor chamber can cause tremendous physical deformation of the vapor chamber walls, and in turn can damage the semiconductor devices to which it is mated.

[0006] The instant invention addresses this freezing problem by providing a working fluid for a heat transfer device, such as a heat pipe or vapor chamber heat sink, comprising water and a kinetic ice inhibitor as an additive to the water. The kinetic ice inhibitor preferably comprises a water-soluble polymer that can be added to the water in very small amounts so as not to affect the wicking and/or thermal performance of the water as a working fluid. In this regard, the working fluid of the present invention preferably comprises water and about 0.1 percent to about 1.5 percent by weight, and more preferably 0.5 percent to 1.0 percent by weight, of a substantially water soluble polymer having pendant groups such as a lactam ring, as generally represented by the following formula: 1

[0007] wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1. Some preferred water soluble polymer compounds which can be used to practice the invention include, but are not limited to polymers, copolymers and terpolymers, such as polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VP/VC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713).

[0008] As indicated above, one of the preferred applications of the working fluid is for use in a thermal transfer device, such as a heat pipe, or vapor chamber heat sink. In this regard, a preferred embodiment of the invention comprises a vapor chamber heat sink comprising a vacuum sealed vapor chamber having an evaporator section and a condenser section, wicking materials, and the working fluid of the present invention contained within the vapor chamber. As described hereinabove, the working fluid comprises water, and a kinetic ice inhibitor in an amount effective to kinetically inhibit the nucleation and growth of ice crystals within said working fluid when said working fluid is subjected to temperatures below 0° C. Preferable, the kinetic ice inhibitor comprises the water-soluble polymers as described hereinabove. In connection with the preferred application, the evaporator section of the vapor chamber is in thermal communication with a semiconductor device to remove heat from the semiconductor device. A finned heat sink structure can be mounted on the upper section of the vapor chamber to remove heat from the vapor chamber.

[0009] Accordingly, among the objects of the instant invention are: the provision of a working fluid for a heat transfer device wherein the working fluid is water and includes a kinetic ice inhibitor that inhibits the nucleation and growth of ice therein; the provision of a kinetic ice inhibitor comprising a water-soluble polymer compound; the provision of a vapor chamber construction (container and wicking materials) that can withstand the harsh environmental and temperature changes encountered during the shipping and storage of consumer goods; the provision of such a vapor chamber having a working fluid that resists the formation of ice crystals; the provision of such a vapor chamber having a working fluid as described herein.

[0010] Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.

DESCRIPTION OF THE DRAWINGS

[0011] In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

[0012] FIG. 1 is a side elevation view of a semiconductor/vapor chamber heat sink assembly including a vapor chamber heat sink constructed in accordance with the present invention;

[0013] FIG. 2 is a cross-sectional view of the vapor chamber;

[0014] FIG. 3 is a graph of temperature change versus time of various samples during a single temperature cycle of +25° C. to −40° C.;

[0015] FIG. 4 is a graph of temperature change versus time of the same samples during a single temperature cycle of −40° C. to +40° C.

[0016] FIG. 5 is a graphical table identified as Table 1 within the Specification showing the results of Experiment 1 as defined herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring now to the drawings, a heat transfer device including a working fluid in accordance with the teachings of the present invention is illustrated and generally indicated at 10 in FIGS. 1 and 2. As will hereinafter be more fully described, the heat transfer device 10 includes a working fluid 12 including a kinetic ice inhibitor additive that inhibits ice nucleation and changes ice growth patterns to effectively avoid or delay the freezing of the working fluid.

[0018] In the preferred embodiment of the heat transfer device 10 as described herein, the device 10 comprises a special form of heat pipe known as a vapor chamber or heat pipe lid. Generally speaking, heat pipes are a class of heat transfer device that transfer heat in a single dimension, i.e. along the length of the pipe. Vapor chambers are a special type of heat pipe having a much larger planar surface area. The larger surface area of the chamber spreads heat in two dimensions and provides for a highly efficient heat transfer mechanism. For purposes of the present invention, the term “heat transfer device” is not intended to be limited by any preferred embodiment as described herein, but rather should be broadly interpreted to include, but not be limited to heat pipes, heat pipe lids, heat spreader assemblies, heat sink assemblies, vapor chambers, and vapor chamber assemblies, and any other type of related heat transfer device that utilizes or includes as part of an assembly a working fluid in a chamber.

[0019] More specifically, the vapor chamber (heat transfer device 10) includes a continuous outer wall structure 14 that is vacuum sealed to provide an internal vapor chamber 16 in which the working fluid 12 is disposed. The vapor chamber 10 includes a evaporator section generally indicated at 18, which is in thermal communication with at least one heat source, such as a semiconductor device, generally indicated at 20 and mounted on printed circuit board 22. In connection with the illustrated embodiments, the circuit board 22 includes a semiconductor device 20, such as a CPU. The evaporator section 18 is mounted in thermal communication with the upper surface of the semiconductor device 20. Thermal communication between the upper surface of the semiconductor device 20 and the lower surface of the evaporator portion 18 of the vapor chamber 10 is enhanced by the use of a thermal interface material, such as a thermal grease or thermally conductive adhesive sheet generally indicated at 28. Thermal interface materials of the type contemplated are well known in the art, and are commercially available from a variety of different manufacturers. The vapor chamber assembly 10 further includes an upper surface plate 30 that is in thermal communication with a finned heat sink structure 32. Thermal communication between the upper surface of the vapor chamber 10 and the lower surface of the heat sink 32 is enhanced by the use of a thermal interface material 34, such as a thermal grease or thermally conductive adhesive sheet as described above. It is noted that the heat sink 32 and the vapor chamber 10 are separate elements in the illustrated embodiment. However, this should not be interpreted to limit the assembly or combination of elements in any way. Other configurations of vapor chamber and heat sinks are contemplated and should be considered within the scope of the invention.

[0020] Contained within the vapor chamber 16 is a small volume of working fluid 12. In this regard, the working fluid 12 is preferably present within the vapor chamber 16 in an amount between about 5% and about 25% by volume of the total volume of the vapor chamber 16, and more preferably about 15%-20% by volume. Also present within the vapor chamber are wicking materials generally indicated at 24. The wicking materials 24 help condensed water vapor 26 to return to evaporator section 18 by surface tension along the inner surfaces of the vapor chamber. Wicking materials 24 of the type contemplated are well known in the heat transfer art and will not be described further herein. The working fluid 12 is found in a liquid state within the evaporator section 18 of the chamber 16, as dictated by surface tension. In the evaporator section 18, the working fluid 12 quickly absorbs heat and boils to vapor phase. The water vapor (see large arrows 36 in FIG. 2) rises and spread to the condensation portion 40 of the vapor chamber 16, transferring heat to the upper surfaces thereof. As the water vapor 36 releases heat in the cooler upper portion of the vapor chamber, it condenses (see small arrows 38 in FIG. 2) on the upper surface of the chamber and returns by surface tension with the help of wicking materials 24 to the evaporation portion 18 of the vapor chamber 16. The detailed operational characteristics of a working fluid 12 within a vapor chamber 10 are well known in the art as described hereinabove, and will not be described further in connection with the present invention.

[0021] The working fluid 12 preferably comprises water and includes a kinetic ice inhibitor that is present in an amount effective to kinetically inhibit the nucleation and formation of ice crystals when the working fluid is subjected to below freezing temperatures.

[0022] A kinetic ice inhibitor is distinguished from a thermodynamic ice inhibitor in the manner in which the formation of ice is prevented. Thermodynamic ice inhibitors fall into two broad categories: 1) alcohols and glycols (high vapor pressure), and 2) salt compounds (low vapor pressure). These categories of ice inhibitors mix with the water and shift the actual freezing point of water to a very low level. In some cases, −40° C. is possible with glycols. However, these compounds have distinct disadvantages when used in connection with electronics. With regard to alcohols and glycols, these compounds require a very high percentage (30%-50%) of the total volume of water. This high percentage dramatically increases the vapor pressure in the vapor chamber at high temperatures and will influence the vapor chamber thermal performance. In contrast, salt compounds become over-saturated at high temperatures. In addition, alcohols, glycols and salts may adversely react with copper (Cu), which is used on the interior of the vapor chamber, and wicking materials, causing corrosion.

[0023] A kinetic ice inhibitor physically interacts with the water molecules and ice crystals to prevent ice crystal growth. At temperatures below 0° C., the inhibitor binds to or absorbs on the ice crystal face to block ice crystal growth and prevent small ice crystals from progressing to larger crystal species. The inhibitor thus maintains the ice crystals as small crystal formations and inhibits growth to larger stages. In other words, with kinetic inhibition ice crystal growth slows dramatically, or sometimes stops.

[0024] The preferred kinetic ice inhibitors of the present invention comprise compounds belonging to a group of water-soluble polymers, copolymers and terpolymers having at least one pendant group, such as a lactam ring, containing an amid group (—N—C═O) at the top of each pendant ring adjacent to the polymer backbone. Another variation of polymer within the scope of the invention contains the amid group as a pendant group without a ring. These polymers are generally depicted as follows: 2

[0025] wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1.

[0026] Copolymers of the type contemplated herein are depicted as follows: 3

[0027] wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and x and y are whole numbers greater than 1.

[0028] Terpolymers of the type contemplated herein are depicted as follows: 4

[0029] wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R3 is a third pendant group having a amino group (O—C═O) adjacent the polymer backbone, and x, y, and z are whole numbers greater than 1.

[0030] It is well understood by those skilled in the art that a given polymer composition is comprised of polymers having variable chain lengths, and that (n), (x), (y) and (z) in the depictions above represents an average number of repeating units of the compound.

[0031] Without limiting the scope of the invention, and for the purpose of illustrating the invention, various water soluble polymeric inhibitors were evaluated including polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly (vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713). These structures are depicted below. 5

[0032] The above-noted polymers and copolymers are commercially available through a variety of chemical manufacturers. Accordingly, their synthesis will not be described herein.

[0033] In contrast to the high volume of thermodynamic inhibitor required in the prior art, kinetic polymer inhibitors of the type contemplated herein are preferably added to the water in an amount between about 0.1 percent by weight to about 1.5% by weight, and are found to be highly effective in a range from between about 0.5% by weight to about 1.0% by weight.

[0034] EXPERIMENT 1

[0035] Without limiting the scope of the invention for the purpose of illustrating the invention, various polymer inhibitors were evaluated and tested in comparison to glycol and pure water as working fluids. In all, 60 different samples were tested and the results of testing are shown in the TABLE 1 (FIG. 5).

[0036] The objective of Experiment 1 was to check the candidate polymer additives impact on the working fluid freezing, and to verify the concept of kinetic ice inhibition in a heat pipe or vapor chamber application.

[0037] Experiment Input

[0038] Polymer Materials

[0039] 1) VC-713

[0040] 2) Inhibex501 ISP

[0041] 3) Inhibex 101 ISP

[0042] 4) PVCAP

[0043] 5) VP/VC

[0044] 6) EP-1

[0045] Comparison Materials

[0046] 7) Ethylene Glycol

[0047] 8) Water

[0048] Polymer Additives' Concentration

[0049] Two concentrations of working fluid have been used in this experiment. They are 0.5% and 1%, which are very dilute compared to Ethylene Glycol's 30% and 50% (Thermal dynamic inhibition).

[0050] Experiment Unit

[0051] Instead of using a vapor chamber, which would have been expensive for experimental study, ▪ 4mm (Thickness 0.5mm) and ▪ 6mm (0.6 mm) tubes have been used to verify the idea. The tubes were crimped to avoid water leakage and evaporation during experiment.

[0052] Working Fluid Volume

[0053] In order to clearly see the impact of additives on the freezing, the volume used in this experiment is approximately 5 times higher than normal heat pipe's

[0054] Unit Orientation

[0055] Tubes have been put in vertical position in the experiment, since this is the most severe position for failure.

[0056] Experiment Output

[0057] Tube diameter changes during the experiment

[0058] Two position diameters have been measured in the experiment, see sketch in Table 2 (below).

[0059] Working Fluid Volume Changes

[0060] Leakage was checked frequently to see the impact of freezing or sample defect.

[0061] Experiment Method

[0062] The freezing inhibition experiment has been performed using special temperature cycle test unit. The temperature cycle is from −40° C. to 60° C. See the sketch in Table 2.

[0063] 0 cycle, 5 cycles and 10 cycles' output data has been measured using micrometer and weight balance.

SUMMARY OF RESULTS (EXPERIMENT 1)

[0064] a) VC 713

[0065] After 5 cycles, the maximum weight change is 2.2% and diameter change is 2.82%. No blister happening in all samples.

[0066] Concentration Impact 6

[0067] From the results, we can understand that a higher concentration results in a smaller tube expansion.

[0068] Tube Diameter Impact 7

[0069] Generally speaking, with the increase of tube diameter, the possibility of expansion increases.

[0070] After 10 cycles, the maximum weight change is 10.43% (we assume this includes weight balance error or a badly crimped tube) and biggest diameter change is 1.35%. Again, there is no blister happening in the samples. The biggest diameter changes come from 6mm tube with 0.5% additive working fluid.

[0071] b) Inhibex 501

[0072] After 5 cycles, just one 4mm tube (with 1%) left, all other samples were broken. After 10 cycles the left one also was broken.

[0073] c) Inhibex 101

[0074] After 5 cycles, 5 among 8 samples survived, however the tube expansions are very big for survivors (from 1.39% to 3.72). After 10 cycles all other samples were broken.

[0075] d) PVP

[0076] Almost the same results with Inhibex 101

[0077] e) PVCAP

[0078] 5 samples survived after 5 cycles test, and among those, 2 samples survived after 10 cycles test. The left ones were in pretty good shape.

[0079] f) EP-1

[0080] Samples almost failed after 5 cycles test.

[0081] g) Ethylene Glycol

[0082] Almost no any change for the both 30% and 50% fluids, the info can be feedback to new additive development.

[0083] h) Water

[0084] Two 6 mm tubes were broken after 5 cycles test. Although there is no blister in the two 4 mm tubes after 10 cycles, the expansions are pretty big.

[0085] Conclusion

[0086] VC-713 has the best overall performance in the test. Furthermore, from the experiment 1, we can understand that the intent of kinetic inhibition is to prolong the period prior to catastrophic growth of ice. Time is very important issue in this kind of application. However, it is possible for us to find proper combinations of polymer or other additive materials and prevent catastrophic growth of ice for each application case. 1 TABLE 2 Experiment Parameters Temp. Cycle [−40° · 60°] Measurement Position Diameter i) Tempe Cycle +60 C. (30 min) 8 ii) Tube Orentation and Fluid Volume 9 iii) Measurement Position 10 iv) Tube Info a. Type 1 Diameter = 4.00 mm Thickness = 0.50 mm Length = 116 mm b. Type 2 Diameter = 6.00 mm Thickness = 0.6 mm Length = 130 mm v) Diameter Measurement Orentation 11 12 vi) Definition of Sample Name 13 vii) Material Type

[0087] EXPERIMENT 2

[0088] Based on the results of Experiment 1, selected samples were further tested to monitor the mechanism of kinetic inhibition and to graph temperature change profiles over time. The results of Experiment 2 are graphically shown in FIGS. 3 and 4 of the drawing Figures. The tested samples are as follows:

[0089] 1) FTE-01-0.5 (VC-713 0.5% concentration)

[0090] 2) FTE-01-1.0 (VC-713 1.0% concentration)

[0091] 3) FTE-07-50 (Glycol 50% concentration)

[0092] 4) FTE-08 (Pure water)

[0093] 5) Ambient temperature

[0094] The working fluids were placed in an open beaker, and subjected to a temperature range from room temperature 25° C. to −40° C. (maintained for 2 hours), and then from −40° C. to +40° C. (maintained for 2 hours). The samples were subjected to only one cycle of temperature change. K-type thermocouples were inserted into each backer to take the measurement of temperature. The experimental output comprises readings of temperature over time resulting in the downside temperature change profile shown in FIG. 3 and the upside temperature change profile shown in FIG. 4.

[0095] From the results of Experiment 2 it can be concluded that the additive VC-713 (polymer) helps to delay the ice formation process compared to pure water. It can also be concluded that the higher concentration is more effective by comparing curves 1 and 2 of FIGS. 3 and 4. We also note from curve 3 (Glycol) that the temperature change is smooth, which means that the freezing point is totally shifted. From FIG. 4. (upside temperature change), we note that the temperature change of curve 3 is very sharp, which is not good for thermal performance. Further noted from FIG. 4 is that the curves of slopes 1 (VC-713) and 4 (water) are similar, which means that a working fluid with VC-713 as an additive should have similar thermal performance to pure water.

[0096] It can therefore be seen that the present invention provides a working fluid for use in a thermal transfer device, such as a heat pipe, or vapor chamber heat sink that is uniquely suited for use in low temperature applications. The addition of a small amount of a kinetic polymer ice inhibitor to water for use as the working fluid effectively inhibits the nucleation of ice crystals and thereafter inhibits further growth of the ice crystals to larger formations. The effect of the inhibitor in the water is a significant delay in time during which ice crystals will form. The polymer ice inhibitor is added to the water in very small quantities and is not believed to affect either the thermal performance of the working fluid or the wicking performance upon surface tension. In particular, the use of a water-soluble lactam group polymer as the ice inhibitor provides a unique and effective alternative to conventional thermodynamic ice inhibitors without sacrificing much in the way of performance and effectiveness. For these reasons, the instant invention is believed to represent a significant advancement in the art, which has substantial commercial merit.

[0097] Although the present invention is described and associated with thermal transfer devices in the field of semiconductor electronics, it is contemplated that the working fluid as described herein could have other applications in other industries, such as automotive, heating and ventilation and still other applications requiring a cooling feature. In this regard, the term “heat transfer device” is intended to define any type of device that includes a vapor chamber and has a working fluid disposed therein. The term is not intended to limit the present disclosure to semiconductor applications and/or heat pipes or vapor chamber heat sinks.

[0098] While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

Claims

1. A working fluid for use in a thermal transfer device comprising:

water; and

a kinetic ice inhibitor in an amount effective to kinetically inhibit the nucleation and growth of ice crystals within said water when said working fluid is subjected to temperatures below 0° C.

2. The working fluid of claim 1 wherein said kinetic ice inhibitor comprises a substantially water-soluble polymer.

3. The working fluid of claim 2 wherein said polymer is present in an amount of from about 0.01 percent to about 1.5 percent by weight relative to the total fluid weight.

4. The working fluid of claim 3 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

5. The working fluid of claim 2 wherein said polymer has the following formula

14

wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1.

6. The working fluid of claim 5 wherein said pendant group is a lactam ring.

7. The working fluid of claim 2 wherein said polymer is a copolymer having the following formula

15

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and x and y are whole numbers greater than 1.

8. The working fluid of claim 2 wherein said polymer is a terpolymer having the following formula

16

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R3 is a third pendant group having a amino group (O—C═O) adjacent the polymer backbone, and x, y, and z are whole numbers greater than 1.

9. The working fluid of claim 2 wherein said polymer is selected from the group consisting of: polymers, copolymers and terpolymers of polyvinylcaprolactam (PVCAP) and polyvinylpyrrolidone (PVP).

10. The working fluid of claim 2 wherein said polymer is selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713).

11. A heat transfer device comprising:

a vacuum sealed vapor chamber having an evaporator section and a condenser section;

a working fluid contained within said vapor chamber, said working fluid comprising:

water; and

a kinetic ice inhibitor in an amount effective to kinetically inhibit the nucleation and growth of ice crystals within said working fluid when said working fluid is subjected to temperatures below 0° C.

12. The heat transfer device of claim 11 wherein said kinetic ice inhibitor comprises a substantially water-soluble polymer.

13. The heat transfer device of claim 12 wherein said polymer is present in an amount of from about 0.01 percent to about 1.5 percent by weight relative to the total fluid weight.

14. The heat transfer device of claim 13 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

15. The heat transfer device of claim 12 wherein said polymer has the following formula

17

wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1.

16. The heat transfer device of claim 15 wherein said pendant group is a lactam ring.

17. The heat transfer device of claim 12 wherein said polymer is a copolymer having the following formula

18

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and x and y are whole numbers greater than 1.

18. The heat transfer device of claim 12 wherein said polymer is a terpolymer having the following formula

19

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R3 is a third pendant group having a amino group (O—C═O) adjacent the polymer backbone, and x, y, and z are whole numbers greater than 1.

19. The heat transfer device of claim 2 wherein said polymer is selected from the group consisting of: polymers, copolymers and terpolymers of polyvinylcaprolactam (PVCAP) and polyvinylpyrrolidone (PVP).

20. The heat transfer device of claim 12 wherein said polymer is selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713).

21. A semiconductor assembly comprising:

a semiconductor device;

a vapor chamber heat sink having a vacuum sealed vapor chamber,

said vapor chamber having an evaporator section in thermal communication with said semiconductor device and further having a condenser section;

a working fluid contained within said vapor chamber, said working fluid comprising:

water; and

a kinetic ice inhibitor in an amount effective to kinetically inhibit the nucleation and growth of ice crystals within said working fluid when said working fluid is subjected to temperatures below 0° C.

22. The semiconductor assembly of claim 21 wherein said kinetic ice inhibitor comprises a substantially water-soluble polymer.

23. The semiconductor assembly of claim 22 wherein said polymer is present in an amount of from about 0.01 percent to about 1.5 percent by weight relative to the total fluid weight.

24. The semiconductor assembly of claim 23 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

25. The semiconductor assembly of claim 22 wherein said polymer has the following formula

20

wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1.

26. The semiconductor assembly of claim 25 wherein said pendant group is a lactam ring.

27. The semiconductor assembly of claim 12 wherein said polymer is a copolymer having the following formula

21

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and x and y are whole numbers greater than 1.

28. The semiconductor assembly of claim 22 wherein said polymer is a terpolymer having the following formula

22

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R3 is a third pendant group having a amino group (O—C═O) adjacent the polymer backbone, and x, y, and z are whole numbers greater than 1.

29. The semiconductor assembly of claim 22 wherein said polymer is selected from the group consisting of: polymers, copolymers and terpolymers of polyvinylcaprolactam (PVCAP) and polyvinylpyrrolidone (PVP).

30. The semiconductor assembly of claim 22 wherein said polymer is selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-7 13).

31. A method of inhibiting the nucleation and growth of ice crystals in a water-based working fluid to be used in a heat transfer device, said method comprising:

treating said working fluid with a kinetic ice inhibitor comprising a substantially water-soluble polymer.

32. The method of claim 31 wherein said polymer is present in an amount of from about 0.01 percent to about 1.5 percent by weight relative to the total fluid weight.

33. The method of claim 32 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

34. The method of claim 31 wherein said polymer has the following formula

23

wherein R1 is a pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and n is a whole number greater than 1.

35. The method of claim 34 wherein said pendant group is a lactam ring.

36. The method of claim 31 wherein said polymer is a copolymer having the following formula

24

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, and x and y are whole numbers greater than 1.

37. The method of claim 31 wherein said polymer is a terpolymer having the following formula

25

wherein R1 is a first pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R2 is a second pendant group having an amid group (N—C═O) adjacent to the polymer backbone, R3 is a third pendant group having a amino group (O—C═O) adjacent the polymer backbone, and x, y, and z are whole numbers greater than 1.

38. The method of claim 31 wherein said polymer is selected from the group consisting of: polymers, copolymers and terpolymers of polyvinylcaprolactam (PVCAP) and polyvinylpyrrolidone (PVP).

39. The method of claim 31 wherein said polymer is selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713).

40. A working fluid for use in a thermal transfer device comprising:

between about 98.5 wt % and about 99.9 wt % water; and

between about 0.1 wt % and about 1.5 wt % of a kinetic ice inhibitor effective to kinetically inhibit the nucleation and growth of ice crystals within said water when said working fluid is subjected to temperatures below 0° C.,

said kinetic ice inhibitor comprising a substantially water-soluble polymer selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-7 13).

41. The working fluid of claim 40 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

42. A heat transfer device comprising:

a vacuum sealed vapor chamber having an evaporator section and a condenser section;

a working fluid contained within said vapor chamber, said working fluid comprising:

between about 98.5 wt % and about 99.9 wt % water, and between about 0.1 wt % and about 1.5 wt % of a kinetic ice inhibitor effective to kinetically inhibit the nucleation and growth of ice crystals within said water when said working fluid is subjected to temperatures below 0° C.,

said kinetic ice inhibitor comprising a substantially water-soluble polymer selected from the group consisting of: polyvinylpyrrolidone (PVP), polyvinylcaprolactam (PVCAP), poly(vinylpyrrolidone-vinylcaprolactam) (VPNC), and poly(vinylpyrrolidone-vinylcaprolactam-dimethylaminoethyl) (VC-713).

43. The heat transfer device of claim 41 wherein said polymer is present in an amount of from about 0.5 percent to about 1.0 percent by weight relative to the total fluid weight.

44. The heat transfer device of claim 42 further comprising a finned heat sink structure in thermal communication with said evaporator section of said vapor chamber.

45. The heat transfer device of claim 42 wherein said working fluid is present in said vapor chamber in an amount between about 5% and about 25% by volume of a total volume of said vapor chamber.