TECHNICAL FIELD

The invention relates to improvements in heat transfer materials. More particularly, this invention relates to the use of sintered diamond material for heat exchangers and regenerators.

BACKGROUND

Heat exchangers are used in many applications including heating units, cooling units, engines and many other applications. For example, heat exchangers are used in Stirling engines such as those found in, by way of example only, U.S. Patent No. 7,076,941, Such Stirling engines also use regenerators which are specialized heat exchangers. Typically, such engines use heat transferring materials in their heat exchangers and regenerators such as aluminum, copper, brass, or stainless steel. While these heat exchanges are adequate for some uses, an improved heat exchanger is needed which has a higher thermal conductivity. Higher thermal conductivity results in more efficient heat transfer and reduced energy loss, In addition, heat transferring materials are needed with a high thermal diffusivity for the efficient transfer of heat energy. There remains a need for improved heat exchangers and regenerators which have higher thermal conductivity than heat exchangers and regenerators of the past.

SUMMARY OF THE INVENTION

The present invention relates to the use of heat exchanging material constructed of sintered natural or synthetic diamond powder or particles. Synthetic diamonds have been manufactured for over half a century. In one manufacturing process, a natural diamond sliver is placed in a chamber under 58,000 atmospheres of pressure at 1500 degrees Celsius. The sliver of natural diamond is bathed in a molten solution of graphite and a catalyst. Carbon precipitates onto the diamond sliver. Using this process, a three carrot diamond can be grown in just a few days. Through this and otter methods, over 100 tons of synthetic diamonds are manufactured each year, These synthetic diamonds are used for various industrial and commercial applications, For example, synthetic diamonds are used in drill bits, cutting blades and grinding wheels.

Diamond particles such as natural or synthetic diamond dust are a byproduct of some of these applications and the diamond dust is readily available in many different sizes. This dust could be a byproduct of processes using natural or synthetic diamonds. The sintered diamond dust can be made of particles of various sizes from extremely fine powder to more coarse particles. For example the diamond dust can be found from commercially available sources in particle sizes ranging from .025 microns to 100 micions. For example, diamond dust can be purchased in these size ranges from

Advanced Abrasives Corporation of Pennsauken, New Jersey. The cost of diamond dust generally depends on the size of the diamond particles, and the finer the powder, the less expensive it is. Thus, fine powder can be used to form many desired shapes and configurations. Diamonds have one of the highest coefficients of thermal conductivity of any material. Sintered diamonds have a coefficient of thermal conductivity of nearly 8 watts/cm°C, maldng it an ideal heat exchanging medium. The use of irregularly shaped particles increases the surface area of the formed or finished sintered diamond heat exchanging material. The process of sintering diamond involves placing the'fine powder or particles in a mold. The mold is then placed in an ultra high temperature press and heated to a temperature in the range of 2000 degrees Fahrenheit under a pressure in the range of hundreds of pound per square inch. At this temperature and pressure, the diamond powder is fused together. It is within the scope of the present invention to mix the diamond powder with other materials such as boron carbide, silicon carbide or other materials before sintering. As used herein, sintered diamond can refer to pure sintered diamond, or sintered diamond which also includes other materials mixed with the diamond powder. The diamond could be natural or synthetic.

The sintered diamond material can be formed into many desired shapes including tubes, screens, mesh, disks, granules, or other possible shapes. Where necessary, passages can be formed in the finished sintered diamond heat exchanging materials to allow fluid to flow through. For example, if the sintered diamond is formed into a disk, fluid passages can be formed directly in the disk. The sintered diamond can be formed into various shapes depending on the required application. For example, the sintered diamond can be adapted to be used with a regenerator of a Stirling engine. A regenerator is a temporary repository of heat during certain cycles of the Stirling engine. Heated fluid flows through in one direction, and heat is transferred to the regenerator material. Relatively colder fluid flows through the regenerator in the other direction and picks up the heat energy left behind when the heated fluid flowed through.

In one example embodiment of the present invention, the diamond material can be formed into circular disks resembling mesh material. It will be understood by those of . ordinary skill in the art that the disks need not be circular, but can take many different . shapes. The material could be made into thin disks which resemble wire mesh heat exchanging material, In this case, the mesh-like disks would be separated by thin insulating layers (with holes for fluid flow) that would keep heat from being conducted firom one end of the regenerator to the other. In one example embodiment, the disks would be on the order of 1/8 inch thick.

In another embodiment, the sintered diamond material can be formed into small, irregular pieces of sintered diamond material. These irregular pieces can be packed into a space between insulating disks, and.the fluid flow would be between and around these pieces. When used for a heat exchanger, the diamond particles can be formed- into shapes having two flow passages therethrough. The use of two sets of passages is well known in heat exchangers. As fluid flows through one set of passages, heat is transferred to the heat exchanger material. The heat is then transferred to the fluid flowing through the other set of passages. The two sets of passages are isolated from one another so that the two streams of fluid do not mix with one another. hi one example embodiment, a regenerator includes a housing. The housing includes a plurality of sintered diamond elements having a fluid passage therethrough. A plurality of insulating elements are spaced between the sintered diamond elements and also have a fluid passage therethrough. The fluid passages of the insulating elements are k fluid communication with the fluid passages of the sintered diamond elements. The sintered diamond elements can comprise irregularly shaped diamond dust particles sintered together such that the sintered diamond elements are porous. Alternatively, or in addition, the sintered diamond elements can include a plurality of disks placed adjacent one another between the insulating elements. The sintered diamond elements can be made ftom diamond particles of between 0.001 and 500 microns, for example. In one example embodiment, the sintered diamond elements axe made by placing the particles in a mold and subjecting the particles to high temperature and pressure as is known in the diamond sintering art.

In some example embodiments, each of the sintered diamond elements and each of the insulating elements have an opening therethrough, for example through the center of the sintered diamond elements and the insulating elements. Insulating material can be placed within each of the openings of the sintered diamond elements and each of the insulating elements.

In another example embodiment of the invention, a heat exchanger includes a housing containing a plurality of sintered diamond elements. The plurality of sintered diamond elements have first and second fluid passages associated therewith which are isolated from one another. The sintered diamond elements could be, for example mesh constructed of sintered diamonds. Alternatively, or in addition, the sintered diamond elements could be made as disks of sintered diamonds having passages therethrough.

In another embodiment, the sintered diamond elements include a plurality of tubes of sintered diamond. One fluid flow is through the tubes and a second fluid flow is between the plurality of tubes. Iti another example embodiment, the sintered diamond elements include a first plurality of tubes and a second plurality of tubes. The first plurality of tubes forms a first fluid passage and me second plurality of tubes forms a second fluid passage.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and applications of the invention are illustrated by the attached non-limiting drawings. The attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale.

Figure 1 is an exploded perspective view of one embodiment of the present invention; Figure 2 is another exploded perspective view of the invention of Figure 1;

Figure 3 is a perspective view of another embodiment of the present invention;

Figure 4 is a front elevation view of the invention of Figure 3 ;

Figure 5 is a perspective view of another embodiment of the present invention; Figure 6 is an end view of another embodiment of the present invention; Figure 7 is a front elevation view of the invention of Figure 6;

Figure 8 is a cross-sectional view of another embodiment of the present invention;

Figure 9 is a cross-sectional view of another embodiment of the present invention;

Figure 10 is a cross-sectional view of another embodiment of the present invention; Figure 11 is an end view of the invention of Figure 10;

Figure 12 is an end view of another embodiment of the present invention;

Figure 13 is a cross-sectional view of the invention of Figure 12;

Figure 14 is an end view of another embodiment of the present invention;

Figure 15 is a cross-sectional view of the invention of Figure 14; Figure 16 is a simplified representation of a sintered diamond molding apparatus ;

Figure 17 is a simplified representation of a sintered diamond top mold;

Figure 18 is a simplified representation of a sintered diamond bottom mold;

Figure 19 is a simplified representation of another sintered diamond top mold;

Figure 20 is a simplified representation of another sintered diamond bottom mold; Figure 21 is a simplified representation of a side cross-sectional view of sintered diamond top and bottom molds shown separated from one another;

Figure 22 is a simplified representation of a side cross-sectional view of sintered diamond top and bottom molds shown together;

Figure 23 is a simplified representation of a side cross-sectional view of sintered diamond tubes after molding has taken place; and

Figure 24 is a simplified representation of the process of molding sintered diamond. DETAILED DESCRIPTION

Throughout the following description specific details are presented to provide a • more thorough understanding to persons skilled in the art. However, well-known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rattier than a restrictive, sense.

Figures 1 through 11 illustrate various embodiments of the present invention. Referring to Figures 1 and 2, an exploded view of a heat exchanger 10 illustrating one embodiment of the present invention is shown. The heat exchanger 10 includes a housing 12. The housing 12 is shown as cubic in configuration for illustration purposes only. It will be understood by those skilled in the art that the housing 12 can be made in many possible shapes. The housing 12 has walls 14, 16, 18 and 20, shown again in the particular configuration for illustration purposes. Sintered diamond tabes 22 are placed within the housing 12. The length and diameter of sintered diamond tubes 22 are a matter of design choice, depending on the heat transfer and flow and pressure and temperature requirements for a particular application. The tubes 22 are held in position by faceplates 24 and 26 which have holes 28 through which the tubes 22 extend. Fluid (not shown) can flow through the tubes 22 in the direction of wow 30. Walls 14 and 18 have fluid holes 32 and 34 respectively. Fluid can flow into and out of holes 32 and 34 in the direction of arrow 36. As fluid flows through tubes 22, heat is transferred to or from the tubes 22, A second isolated fluid flow through holes 32 and 34 travels around and between tubes 22. This fluid flow either picks up or delivers heat to the tubes 22 depending on the relative temperatures of the fluid flowing within and around the tabes 22. Because the tubes 22 are made of sintered diamond, a highly efficient heat exchanger is created.

Figures 3 and 4 show another example embodiment of a heat exchanger 50. A housing 52 is shown as cubic in configuration for illustration purposes only. The housing 52 can be made in many possible shapes. The housing 52 has walls 54, 56, 58, and 60, again shown in the particular configuration for illustration purposes. Sintered diamond tubes 62 are placed within the housing 52. The length and diameter of sintered diamond tubes 62 are a matter of design choice, depending on the heat transfer requirements for a particular application. The tubes 62 are held in position by walls 56 and 60 which have holes 68 through which the tubes 62 extend. Fluid (not shown) can flow through the tubes 62 in the direction of arrow 70. Ends 74 and 78 have fluid holes 82 and 84 respectively. Fluid can flow into and out of holes 82 and 84. As fluid flows through tubes 62, heat is transferred to or from the tubes 62. A second isolated fluid flow through holes 82 and 84 travels around and between tubes 62. This fluid flow either picks up or delivers heat to the tubes 62 depending on the relative temperatures of the fluid flowing through and around the tubes 62. Figure 5 shows another example embodiment of a heat exchanger 150. A housing

152 is shown, as cubic in configuration for illustration purposes only. It will be understood by those of skill in the art ihat the housing 152 can be made in many possible ^' shapes. The housing 152 has walls 154, 156, 158 and 160, shown again in the particular configuration for illustration purposes, Sintered diamond tubes 162 and 163 are placed within the housing 152. The length and diameter of sintered diamond tabes 162 and 163 are amatter of design choice. The tubes 162 are held in position by walls 156 and 160 which have bores 168 through which the tubes 162 extend. Similarly, tubes 163 extend through ends 174 and 178 which have bores 169 therethrough. Fluid (not shown) can flow through the tubes 162 in the direction of arrow 170. A second) isolated flow of fluid ^' flows through tubes 163 in the direction of arrow 171. If the fluid flowing through tubes 162 has a higher temperature than the fluid flowing through tubes 163, heat is transferred to the fluid flowing through tubes 163. If the fluid flowing through tubes 163 has a higher temperature than the fluid flowing through the tubes 162, heat is transferred to the fluid flowing through tubes 162, Because the tubes 162 and 163 and the housing are made of sintered diamond, the heat is transferred very efficiently.

Figures 6 and 7 illustrate a regenerator 210 in accordance with an example embodiment of the present invention. It will be understood by those of skill in the art that the particular configuration of the regenerator 210 is shown for illustration purposes only and that various other configurations of the regenerator are possible, An outer housing 212 is provided with flanges 214 and 216. Depending on the particular application, the housing could be made from metal, such as, for example, aluminum;, brass, or steel. In this example embodiment, the flanges 214 and 216 include bolt holes 218 for attaching tie regenerator 210 to otter parts of a system. The regenerator 210 includes an insulating layer 220 made of any suitable insulating material. The choice of insulating material will depend on the application in which the regenerator 210 is used and could include a polymer or ceramic material for example, A sintered diamond heat exchanging medium 230 is provided. In this illustrated embodiment, the sintered diamond heat exchanging medium 230 is shown as a series of rings 232. The rings 232 axe separated by insulating material 234 to prevent heat transfer in the direction of fluid flow illustrated by line 240. Because the sintered diamond heat exchanging medium 230 has such a high coefficient of thermal conductivity, heat would rapidly spread from one end 242 of the regenerator 210 to the opposite end 244 without insulating material 234. The sintered diamond heat exchanging medium 230 and the insulating material 234 are porous such that fluid (not shown) can flow in the direction of line 240. As is known to those of sldll in the art, a regenerator works by heated fluid flowing in one direction, for example direction 240A. The heated fluid flows through the sintered diamond heat exchanging medium 230 and transfers its heat to the sintered diamond heat exchanging medium 230. In another cycle, relatively cooler fluid flows in the direction 240B. The relatively hotter sintered diamond heat exchanging medium transfers heat to the cooler fluid flowing in direction 240B. In some applications, an insulating core 250 is provided such that the diameter of the regenerator matches other components in the system without providing excess regeneration capacity.

Figure 8 illustrates another embodiment of a regenerator 310 using sintered diamond heat exchanging medium 330. An outer housing 312 is provided with flanges 314 and 316. Again, depending on the particular application, the housing could be made ftom, for example, metal, such, as aluminum, brass, or steel. The regenerator 310 includes an insulating layer 320 made of any suitable insulating material. The choice of insulating material will depend on the application in which the regenerator 310 is used and could include a polymer or ceramic material for example. A sintered diamond heat exchanging medium 330 is provided. In this illustrated embodiment, the sintered diamond heat exchanging medium 330 is shown as a quantity of granules 332 packed between insulating material 334 to prevent heat transfer in the direction of fluid flow illustrated by line 340. The granules 332 axe sized such that spaces 336 are present between granules 332. The spaces 336 allow for fluid to flow between and around the granules 332. The insulating material 334 is porous to allow fluid to flow through the insulating material 334. An insulating core 350 is provided for use in some applications. ^' Figure 9 illustrates another embodiment of a regenerator 410 in accordance with an example embodiment of the present invention. An outer housing 412 is provided with flanges 414 and 416. The regenerator 410 includes an insulating layer 420 made of any suitable insulating material. A sintered diamond heat exchanging medium 430 is provided. Jh this illustrated embodiment, the sintered diamond heat exchanging medium ' 430 is shown as multilayered sintered diamond mesh 432. The mesh 432 is separated by insulating material 434 to prevent heat transfer in the direction of fluid flow illustrated by line 440. Because the sintered diamond heat exchanging medium 430 has such a high coefficient of thermal conductivity, heat would rapidly spread from one end 442 of the regenerator 410 to the opposite end 444 without insulating material 434. An insulating core 450 is provided to adjust the capacity of the regenerator 410.

Figures 10 and 11 illustrate another embodiment of a regenerator 510 in accordance with an example embodiment of the present invention. An outer housing 512 is provided with flanges 514 and 516. The regenerator 510 includes an insulating layer 520 made of any suitable insulating material. A sintered diamond heat exchanging medium 530 is provided. In this iHustrated embodiment, the sintered diamond heat exchanging medium 530 is shown as sintered diamond wire-like mesh 532. The wire- like mesh 532 is separated by insulating material 534 to prevent heat transfer in the direction of fluid flow illustrated by line 540. An insulating core 550 is provided if needed for the particular application. ■ Figures 12 and 13 illustrate another embodiment of a regenerator 610 in accordance with an example embodiment of the present invention. An outer housing 612 is provided to house the internal components of the regenerator 610. The regenerator 610 includes a sintered diamond heat exchanging medium 630. In this illustrated embodirnentj the sintered diamond heat exchanging medium 630 is shown as sintered diamond tubes 632. Sections of tubes 632 can be separated by insulating material (not shown) such as fiberglass insulation material, or other insulating material, to prevent heat transfer in the direction of fluid flow- illustrated by line 640. Fluid flows through the tubes 632 and through trie insulating material from one end of the regenerator 610 fo the other, as will be readily appreciated by one of ordinary skill in Hie art.

Figures 14 and.15 illustrate another embodiment of a regenerator 710 in accordance with an example embodiment of the present invention. An outer housing 712 is provided to house the internal components of the regenerator 710. The regenerator 710 includes a sintered diamond heat exchanging medium 730. In this illustrated embodiment, the sintered diamond heat exchanging medium 730 is shown as a sintered diamond spiral 732. Sections of the spiral 732 can be separated by insulating material. (not shown) such as fiberglass insulation material, or other insulating material, to prevent heat transfer in the direction of fluid flow illustrated by line 740. Fluid flows through the sections of the spiral 732 and through the insulating material from one end of the regenerator 710 to the other, as will also be readily appreciated by those of skill in the art, Figure 16 is a simplified representation of a sintered diamond molding apparatus 810. The molding apparatus 810 includes a top mold 812 mounted to a plate 813 and a bottom mold 814 mounted to a plate 815, which is in turn mounted to a base 824. The apparatus includes a means 820 for pressing the top mold 812 and the bottom mold 814 together, shown for representation purposes only as actuated by a handle 816. Those of ordinary skill in the art will readily appreciate that the pressures required to sinter the diamond are much greater than can be produced by hand. A heat source 818 is also provided for the sintering process. Again, those of ordinary skill in the art will readily appreciatethat the temperatures required for the process will necessitate a much more complex heating system than the one illustrated. In concept, the diamond material (not shown) is placed in the bottom mold 814, and 1he top mold 812 and the bottom mold 814 are brought together under pressure. The top mold 812 and bottom mold 814 are heated by the heat source 818 to sinter the diamond material.

Figures 17 and 18 illustrate the top mold 812 and the bottom mold 814. The top ' mold 812 has pins 830. The bottom mold has cylindrical cavities 832. The difference between the outside diameter of the pins and the inside diameter of the cavities determines the wall thickness of the sintered diamond tubes created by the molds 812 and 814. Figures 19 and 20 illustrate another embodiment of a- top mold 912 and a bottom mold 914. The top mold 912 lias pins 930. The bottom mold has cavities 932 in the shape of wire mesh. The difference between the size of the pins 930 and the size of the cavities 932 determines the wire size of the sintered diamond mesh created by the molds 912 and 914.

Figures 21 through 23 illustrate a schematic representation- of a cross-section of molds 812 and 814 of the present invention. The top mold 812 has pins 830. The bottom mold 814 has cylindrical cavities 832. The pins 830 are sized to fit within the cavities 832 such that tubes 834 are created after the sintering process. Figure 21 illustrates the top mold 812 separated from the bottom mold 814. Figure 22 illustrates Uie top mold 812 ^' nested inside the .bottom mold 814. Figure 23 illustrates the bottom mold 814 with the top mold 812 removed and the tubes 834 formed in the cavities 832.

Figure 24 represents a schematic of the molding process. Sintered diamond dust 870 and optionally a binding agent 872 are mixed using a mixing process represented by cylinder 874. The blended material 876 is injected into a bottom mold 878 through an injection molding apparatus 880/ The top mold 882 is forced down into the bottom mold 878 and the blended material 876 is heated while the pressure is applied. TMs sintering process is well lαiown in the art.

It is to be understood that the exemplary embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by one skilled in the art without departing from the scope of the invention.