Heat transfer system applying boundary later penetration

Abstract

A heat transfer system is disclosed incorporating a passive pump utilizing bubble technology to cycle a coolant through associated channels. The system includes a housing and channels containing a slurry consisting of liquid having a low boiling point and microspheres formed of metallic foam introduced into said liquid. The microspheres are caused to flow onto a heat source and penetrate the coolant boundary layer and thereby provide an efficient and fast transfer of heat from the source onto the microspheres and the coolant. The microspheres further provide and efficient and fast transfer of heat through the slurry to a heat dissipating component.

Description

This application claims the benefit of the earlier filing date of the provisional application Ser. No. 61/628,982 filed on Nov. 10, 2011 of the same title and of the same inventor, Troy W. Livingston.

BACKGROUND OF THE INVENTION

The present invention relates to a system and method for removing and dissipating heat from heat generating components such electronic chips, electronic circuit board and power components in computers.

This provisional patent application is related to U.S. Patent Application Ser. No. 61/575,946 filed on Aug. 31, 2011 titled “Heat Transfer Bridge” in the name of Troy W. Livingston. Said provisional application is being filed as a regular utility application concurrently herewith and is incorporated herein by this reference thereto. The Ser. No. of said utility application will be provided to the USPTO as available.

SUMMARY OF INVENTION

A heat transfer system is disclosed incorporating a passive pump utilizing bubble technology to cycle a coolant through associated channels. The system includes a housing and channels containing a slurry consisting of liquid having a low boiling point and microspheres formed of metallic foam introduced into said liquid. The microspheres are caused to flow onto a heat source and penetrate the coolant boundary layer and thereby provide an efficient and fast transfer of heat from the source onto the microspheres and the coolant. The microspheres further provide a fast transfer of heat through the slurry to associated heat dissipating components.

The foregoing features and advantages of the present invention will be apparent from the following more particular description of the invention. The accompanying drawings, listed herein below, are useful in explaining the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a section view of the inventive system depicting the formation of bubbles in a slurry comprising microspheres in a fluid wherein the bubbles are generated by a heat source and the interaction of the bubbles with microspheres to drive the slurry including the microspheres to and through the coolant outlet;

FIG. 2 is a highly enlarged view of a microsphere useful in describing the penetration of the fluid boundary layer to provide an efficient transfer of heat from the microsphere to the bounding metal surface;

FIG. 3 is useful in further explaining the efficient transfer of heat through the microspheres which effectively form a series of rapid heat transfer zones;

FIGS. 4A and 4B show a copper panel that is a material from which the microspheres are formed;

FIG. 5 shows the initial operation for cutting the panel of FIG. 4A into rectangles to initiate the operation to make the microspheres;

FIGS. 6A, 6B and 6C show the succeeding operations for forming the microspheres from the rectangle into a oval or circular form; and

FIG. 7 depicts an alternative embodiment of the invention wherein air is provided as the microsphere carrying medium rather than a liquid.

DESCRIPTION OF INVENTION

As cited above, the present application is related to U.S. provisional patent application Ser. No. 61/575,946 filed on Aug. 31, 2011 titled “Heat Transfer Bridge” in the name of Troy W. Livingston. The content of said Heat Transfer Bridge application is incorporated herein by this reference and cites the need for systems and methods for cooling electronic chips, electronic circuits, computers. Further discussions of the need for cooling electronic components is discussed in a multitude of U.S. patents including for example the recent U.S. Pat. No. 8,011,424 issued to Mark M. Murray and titled “Method for Convective Heat Transfer Utilizing a Particulate Solution in a Time Varying Field”.

The afore cited Livingston patent application Ser. No. 61/575,946 discloses cooling systems utilizing heat pumps and bubble technology to provide cooling for electronic circuits, IC chips and computers. Patent application Ser. No. 61/575,946 also discloses the provision of a coolant comprising a slurry including formed metal particles, and this application incorporates by reference thereto the disclosure and drawings of said application. The present invention provides improvement to said application Ser. No. 61/575,946.

FIG. 1 depicts a heat transfer system 12 including a liquid container 14 having a bubble forming chamber 16 all essentially indistinguishable from the embodiment shown in FIG. 30 of application Ser. No. 61/575,946. The formation, and initial function, of the bubbles 32 (and the subsequent coalesced bubbles) is to provide a pumping action to power the flow of a fluid as disclosed in said application 61/575,946. For purposes of the present description only the bubble chamber 16 and the outlet tube/channel 18 and return tube/channel 20 are shown in FIG. 1. The other section of the heat transfer system are shown and described in the afore cited Ser. No. 61/575,946. A liquid slurry 30 that comprises microspheres 26 that are introduced into a fluid 24 to provide an enhanced and rapid transfer of heat are basic concepts of the invention.

Container 14 is mounted over a heat source 22 comprising, for example, an IC chip. The adjacent sections of the overall system 12 including container 14 and outlet tube 18 and return tubes 20 are disclosed and described in the referenced patent application, Ser. No. 61/575,946. The improvements provided by the present invention can be fully described using the relatively simplified drawings of FIGS. 1-3.

As disclosed in said prior application, a fluid such as for example methylene chloride 24 is contained in container 14 and in tubes 18 and 20. Methylene chloride (dichloromethane) is a volatile fluid that has a low boiling point of 39.6 degrees C. (103 degrees F.). Note that other fluids having a low boiling point could also be utilized. Microspheres 26 are introduced into the fluid 24 to form a slurry 30 that can flow in the tubes 18 and 20. As will be explained in more detail hereafter, in a preferred embodiment the copper microspheres are approximately 0.020 inches in diameter and are formed of copper foam material. Note that in the cited application Ser. No. 61/575,946 metal particles are employed in the slurry 30, whereas but in the present application comprises formed foam copper microspheres 26 are introduced into the liquid 24 to constitute the slurry 30.

Refer now briefly to the bubble function in chamber 16. When the heat source becomes hot and the dichloromethane fluid 24 reaches its boiling point of 103 degrees F., the fluid will start to produce bubbles 32 on the interior surface 34 of chamber 16 which is adjacent the heat source 22. The small originating bubbles 32 will rise and coalesce continuously to form larger bubbles 36, and the still larger bubbles indicated at 38. The coalescing function indicated in FIG. 1 may occur several times and is dependent on the fluid parameters, the temperature, the size of chamber 16, etc. Chamber 16 is shaped to guide the bubbles upwardly toward outlet tube 18. It has been found that all the bubbles 32, 36 and 38 push the hot slurry 30 including the hot fluid 24 and microspheres 26 upwardly toward outlet tube 18, as indicated by the arrow lines generally labeled 17. Tube 18 is 3.5 mm in diameter which is approximately the same diameter of the larger bubbles 38 in chamber 16. Since the larger bubbles 38 are approximately the same diameters as the tube 18, these bubbles effectively pump (push) the slurry 30 including the microspheres 26 through tube 18 (as indicated by the arrow line 21) and to the other sections of heat transfer system 12 as shown in FIG. 30 of said application Ser. No. 61/575,946. As described in said cited application, the heated slurry 30 flows to and through a heat absorbing (heat dissipating) structure which may include radiating fins enabling the slurry to transfer heat to the heat absorbing structure and dissipate heat energy in that region. The cooled slurry 30 than flows back through return tube/channel 20, as indicted by arrow line 40 in FIG. 2, and returns to the bubble chamber 16 to be recycled.

FIG. 2 depicts a microsphere 26 of FIG. 1 in a highly enlarged view. FIG. 2 is useful in explaining the interaction of the microsphere with an associated heat source of heat dissipating (cooling) surface 34. For description purposes, microsphere 26 is shown in an instantaneous supported position on surface 34. Note of course, that the slurry 30 including the liquid 24 and microspheres 26 are in a continuous flow mode during the operation. Importantly, the microsphere 26 is shown as penetrating the fluid coolant boundary layer 42. The action of the microspheres 26 to pierce the fluid coolant boundary layer is a basic feature of the present invention.

A fluid boundary layer is a known phenomena in fluid mechanics and is a layer of substantially static fluid liquid 24 in the intermediate the flowing liquid and a bounding surface. The bounding surfaces shown in FIG. 1 comprise the interior surface of chamber 16, the interior surfaces of the tubes 18 and 20. For present purposes, the boundary layer comprises a static thin film of liquid that is next to the surface walls of the liquid containment surface and acts as an insulator thus preventing the heat energy in the bounding surface to efficiently transfer heat to the flowing liquid through the heat conducting surface. This reduction in the heat transfer is detrimental in both the absorption of heat from the heat source and the dissipation of heat to the heat radiating components. Fluid viscosity and fluid flow rate affect the boundary layer thickness and the resulting heat insulating effect. Prior liquid cooling systems depend on liquid flow to provide the cooling medium are subject to a loss in efficiency due to the effects of the liquid boundary layer phenomena. The present invention solves the problem.

The inventive cooling system disclosed herein provides microspheres of foamed metal that are introduced into a cooling liquid to form a slurry. The microspheres are formed into round balls and compressed to match the density of the liquid to provide an almost neutral buoyancy to provide a unique heat transfer slurry. The microspheres penetrate the boundary layer as will be described herein to improve the heat transfer rate and the heat transfer efficiency. As alluded to above, the heat transfer rate and as well as the heat transfer efficiency are improved both when transferring heat to the microspheres from a hot source and when transferring heat from the microspheres to a heat dissipating source.

In a preferred embodiment, microspheres 26 are formed from copper foam. Copper is an excellent conductor of heat. The microspheres are introduced into a methylene chloride liquid 24 to form the coolant slurry 30. In one embodiment, the slurry 30 comprises forty percent by volume of methylene chloride 24 and forty percent by volume of foam copper microspheres 26; other fluids having a low boiling point may be used. The boundary layer as specifically related to the present invention will now be described with reference to FIG. 2.

For purposes of description and clarity FIG. 2 depicts a highly enlarged view of a single microsphere 26 positioned on the liquid bounding surface 40 of a heat source 34. The quantity of microspheres 26 in the liquid 24 is determined by various factors such as the thickness and flow rate of the slurry 30 desired, the heat transfer rate desired, etc. The coolant boundary layer 42 is depicted as a thin film and the thickness thereof is dependent on various factors including the viscosity of the coolant and the flow rate.

It is a function of the microspheres 26 to absorb heat from the heat source 34; however as described above, the coolant boundary layer 42 acts as an insulator tending to prevent heat transfer from the hot surface 34 to the liquid slurry 30. Refer now to both FIGS. 1 and 2. The slurry 30 containing the microspheres 26 flows back or returns to the bubble chamber 16 as indicated by the arrow line 40. The textured surfaces 46 of the copper microspheres 26 flow onto, engage, rub and scrape the bounding surface layer 42 and penetrate the boundary layer to provide direct or full/good copper microsphere 26 to metal 34 contact as depicted in FIG. 2. The thickness of the coolant boundary layer (the insulator) is thus breached and effective metal to metal contact for heat transfer is thus accomplished. These actions results in an efficient and maximal high rate of heat transfer from the heat source 34 directly to the microsphere s 26. The microspheres further transfer heat energy to the surrounding liquid 24 and other microspheres in slurry 30.

Another important aspect of the invention is the improved rate of heat transfer provided by the copper microspheres in the slurry liquid as compared to the rate of heat transfer in a clear liquid. As is known, the rate of heat conduction through a metal is much higher than in liquid. For comparison, thermal conductivity charts show that the heat transfer rate of copper given as 385 (W/mK) as compared to that of water which given as 0.6 (at 20 degrees C.). As stated above the microsphere 26 is formed from foamed copper material. The foamed copper is compressed to the density of the coolant liquid, and since the microsphere 26 is not solid copper, but rather a foam composite, the rate of heat transfer through the microsphere can be considered to change (as a rough approximation) to about 100 times the rate of heat transfer through the coolant liquid.

Refer now also to FIGS. 1 and 3. As evident from the drawings of FIGS. 1 and 3 there is a multitude of microspheres in the slurry 30. FIG. 3 pictorially and simplistically depicts the increased rate of heat transfer through the slurry 30 comprised of microspheres 26 and the liquid 24. Assume for description purposes a steady state and momentary condition and that the boundary layer 42 of heat source 34 has just been penetrated by the microsphere 26A and the microsphere 26A rapidly absorbs the heat energy. As stated above, there is a fast rate of heat transfer through microsphere 26A that is about 100 times the rate of heat transfer through the liquid 24. Next the heat energy from microsphere 26A exits upwardly into the liquid 24. There is a slower rate of transfer of heat energy through the liquid 24 to the microsphere 26B. Next there is a rapid transfer of heat through microsphere 26B which is 100 times faster (indicated as 100×) than the transfer through the liquid. Microsphere 26B transfers energy to the surrounding liquid 24. There is a slower rate of transfer of heat energy through the liquid 24 to microsphere 26C. Next, there is a rapid transfer of energy through microsphere 26C to the surrounding liquid 24. The surrounding liquid than conveys the heat to the dissipating surface 48. Accordingly a series of rapid heat transfer zones are formed in the coolant. The rate of heat transfer and the efficiency of heat transfer are thus significantly enhanced as compared to that provided by a clear liquid.

Refer now to FIGS. 4A-4B that depict a procedure for forming the copper microspheres of the invention. While other metals such as aluminum can be used in the inventive system, copper has been found to be the preferred metal because of its better heat conductivity properties. FIGS. 4A and 4B show a copper sheet/panel 50 that is a material from which the microspheres 26 are formed. FIG. 5 shows the initial operation such as a steel rule die 54 for cutting a sheet 50 of FIG. 4A into rectangular pieces/cubes 56 see FIG. 6A, to initiate forming the microspheres 26. FIGS. 6A, 6B and 6C show the succeeding operations for trimming the rectangular/cube 56 to form oval or circular microsphere 26 and to compress the foam microspheres to a desired density for use as described above. It should also be understood that microspheres of differing sizes can be employed in the same slurry.

FIG. 7 depicts an alternative embodiment of the invention wherein air is provided as the microsphere carrying medium rather than a liquid. As depicted in FIG. 7 microspheres 26 are fed through a tube 60 to exit adjacent and air nozzle 62. The air 64 from nozzle 62 has previously passed adjacent a heat source and is hot. The hot air 64 from the nozzle drives the microspheres 26 onto a heat dissipating surface 66. The heated microspheres 26 penetrate the air boundary layer 68 of the heat dissipating surface and 66 and efficiently transfer heat to surface 66. The microspheres 26 which have dissipate their heat energy are then returned to a containing chamber as depicted by arrow line generally labeled 69 for reuse.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A heat transfer system comprising in combination

a) a container for a flowing fluid slurry, said container having a panel with an interior bounding surface for said slurry and an exterior surface for receiving heat wherein a fluid boundary layer comprising a thin film of fluid formed on said bounding surface effectively comprises a heat transfer insulator;

b) an outlet channel and an inlet channel for said container;

c) a slurry comprising a fluid having a low boiling point and metal microspheres;

d) a heat source positioned to be thermally coupled to said container;

e) said fluid generating bubbles in response to heat received from said heat source;

f) said bubbles providing a pumping action to drive said heated slurry upwardly through said outlet channel

e) a large quantity of said metal microspheres in said slurry being moved over and engaging said interior bounding surface thereby penetrating said fluid boundary layer to obtain an efficient metal to metal heat transfer.

2. A fluid flow system for transferring heat from a heat source to a heat dissipating region, said system comprising in combination

a) a container inclosing a flowing liquid slurry;

b) a heat source mounted to provide heat to said container and said slurry;

c) said slurry containing a plurality of foamed copper microspheres that are substantially of the same density as said liquid;

d) said fluid generating bubbles in response to heat received from said heat source and said bubbles providing a pumping heated slurry to flow from said heat source toward said heat dissipating region and said microspheres to transfer heat generally upwardly and away from said heat source;

e) said copper microspheres in said flowing providing a fast rate of heat transfer through the spheres to adjacent liquid, said liquid slurry providing a slower rate of heat transfer to adjacent microsphere which next provides a fast rate of heat transfer to adjacent microspheres and liquid whereby a series of zones of fast heat transfer are provided to thereby in total effect a fast efficient transfer of heat from said heat source to said heat dissipating region.

3. A heat transfer system comprising in combination

a) a source of metallic microspheres;

b) a source of heated air;

c) a heat dissipating surface;

d) a chamber region into which said microspheres are introduced;

e) a nozzle for jetting said heated air into said chamber region and to impinge on said heat dissipating surface;

f) said jetted heated air driving said microsphere onto said heat dissipating surface and penetrating the air (fluid) boundary to provide a fast rate of heat transfer from said heated air to said dissipating surface.

4. A heat transfer system as in claim 1 wherein

a) a portion of said flow path is angled causing said microspheres to strike against said interior boundary layer surface.

5. A heat transfer system as in claim 1 providing a relatively enlarged heating chamber enabling said bubbles to coalesce to the size of said outlet channel to drive said bubbles through said channel.