SINTERED WICK STRUCTURE HEAT PIPE WITH PARALLEL PIPED HOLES AND MANUFACTURE METHOD THEREOF TECHNICAL FIELD The present invention relates, in general, to a heat pipe with various wick structures and method for producing the same and, in particular, to a heat pipe with various wick structures, in which metal powders or superfine metal fibers are deposited on a metal plate in a predetermined thickness, sintered, and shaped into a cylinder, a sintered metal powder wick is attached to an inner wall of the heat pipe, and movement of the working fluid is increased by capillary action because at least one of pipe type continuous air holes longitudinally positioned in the pipe are inside of the wick, and method for producing the heat pipe.

PRIOR ART Generally, a capillary type heat pipe has a structure in which a dense and thin net yarn is attached to an inner wall of the pipe or fine grooves are formed on the wall, or grooves are formed on the wall as well as the net yarn is attached to the wall, and a working fluid such as methyl alcohol, acetone, water (distilled water) is charged into the capillary type heat pipe and the pipe is sealed.

When one end of the pipe is heated by an exterior heat source, gas vaporized from a working fluid in the heated part of the pipe is moved to the non heated part of the pipe to be condensed while evaporation heat of the gas is transferred to the outside of the pipe. A condensed liquid is returned to the heated part of the pipe through metal net yarn or grooves owing to capillary action and the liquid is again evaporated, thereby heat transfer continuously occurring.

Conventionally, the heat pipe with the dense net yarn has been widely. used.

However, the heat pipe has disadvantages in that the heat pipe should have the dense metal net yarn attached to the inner wall thereof, so that when the heat pipe is thin or

long, the metal net yarn is hard to produce and production cost becomes high.

Furthermore, when the metal net yarn attached heat pipe is bent, the metal net yarn on a bent part of the heat pipe is damaged, and so the heat transfer does not sufficiently occur, and a mobility of the working fluid owing to capillary action is reduced.

To avoid the above disadvantages, a heat pipe, to which a wick is partially attached, was developed, but the heat pipe has an operational problem when a heated portion of the heat pipe is positioned at a higher level than the heat emitting portion of the heat pipe.

Additionally, a heat pipe with fine grooves has excellent mobility of liquid in the longitudinal direction thanks to the capillary action of the fine grooves, but is inferior in terms of the mobility of liquid in the circumferential direction. Thus, when evaporation or condensation occurs, the condensed liquid is not uniformly distributed over the circumference of the heat pipe because liquid does not sufficiently flow in the direction of circumference.

To avoid the above disadvantages, another type of heat pipe is used, in which a dense metal net yarn is covered on fine grooves. This heat pipe with grooves and metal net yarn has a good performance; however, the heat pipe has disadvantages in that its production process is very complicated and the production cost is high.

DISCLOSURE OF THE INVENTION Therefore, it is an object of the present invention to provide a heat pipe with good thermal conductivity, which has a wick structure with fine air holes in a metal powder and pipe type continuous air holes.

It is another object of the present invention to provide the heat pipe, in which fine air holes and pipe type continuous air holes are in contact with an inner wall of the pipe, or fluid can be moved quickly by capillaries positioned in a longitudinal and circumferential direction of the pipe.

It is still another object of the present invention to provide a method for producing the heat pipe, in which there is no need to separately produce a wick

because a tool, wires, and a metal powder are simultaneously inserted into the pipe and the resulting structure is sintered, thereby the production process is simple and the production cost is low.

It is yet another object of the present invention to provide a method for producing the heat pipe, in which mass production of the heat pipe and production of the long heat pipe can be easily accomplished by depositing metal powder on a metal plate in a predetermined thickness, sintering the resulting plate, and shaping the sintered plate into a cylinder; and furthermore, a pipe with a large diameter can be drawn to produce various shapes of heat pipes with a small diameter.

It is a further object of the present invention to provide a light heat pipe with a good bent-up property and capillary performance, which can be easily produced by depositing non-woven superfine metal fibers on a metal plate in a predetermined thickness, sintering the resulting plate, shaping the sintered metal plate into a cylinder, charging a working fluid into the cylindrical metal pipe under vacuum, and sealing the metal pipe.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view of a heat pipe produced by inserting a tool and wires and removing them according to the present invention; Fig. 2 is a sectional view of the heat pipe, into which a tool and wires are inserted, according to the present invention; Fig. 3 is a sectional view of the heat pipe produced by inserting the tool and removing it according to the present invention; Figs. 4a and 4b are fragmentary sectional views of Fig. 1 ; Figs. 5a and 5b are fragmentary sectional views of Fig. 2; Figs. 6a and 6b illustrate various shapes of wires;

11. The method according to claim 10, wherein the metal plate has unevenness, V or U shaped-groove formed in a longitudinal direction of pipe.

12. The method according to claim 10 or 11, wherein the metal powder is coated on unevenness, V, or U shaped-grooves on the metal plate, and the resulting metal plate is sintered.

13. The method according to claim 10, wherein said metal powder consists of copper, and copper-tin alloy powder containing 1 to 10 % tin or copper-zinc alloy powder containing 1 to 10 % zinc is used to promote sintering of the metal powder.

14. A heat pipe, comprising: a sealed hollow metal pipe, both sides of which are sintered under vacuum; a porous wick attached to the inner wall of the metal pipe, said porous wick forming a mat of superfine metal fibers with a diameter of 20 to 80 czm in a shape of non-woven fabric; and a working fluid filled in the heat pipe, said working fluid being selected from the group consisting of ammonia, freon, methanol, water, and acetone.

15. The heat pipe according to claim 14, wherein the wick consisting of non- woven superfine metal fiber is sintered in conjunction with a metal net yarn.

16. The heat pipe according to claim 14, wherein the sealed hollow metal pipe is sintered at 700 to 1500°C under a reducing gas selected from the group consisting of nitrogen, hydrogen, and a mixture of 70 to 90 % hydrogen and 10 to 30 % argon gas.

Figs. 7a to 14b illustrate various shapes of wick structures; Fig. 15a is a side view of sintered metal plate, on which metal powder or superfine metal fiber is coated; Fig. 15b is a front view of cylindrical pipe produced by connecting both side of the metal plate of Fig. 15a ; and Fig. 16 is a longitudinal sectional view of the heat pipe of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION Based on the present invention, the above objects can be accomplished by a provision of a heat pipe with a wick structure containing pipe type continuous air holes, produced by positioning a tool at a center of the pipe and multiple wires in contact with an inner wall of the pipe, respectively; charging metal powder between the inner wall of the pipe and the tool; sintering the resulting structure in a furnace under a reducing atmosphere at 700 to 1000 °C for 10 to 180 min to attach a sponge type wick with fine air holes to the inner wall of the pipe; removing the tool and wires to form the wick structure with pipe type continuous air holes; charging a working fluid into the inside of the pipe under vacuum ; and sealing the pipe.

Various shapes of wick structures may be formed by using various shapes of tools, and various shapes of wires are positioned in such a way that wires contact with the inner wall of the pipe or wires are positioned between the inner wall of the pipe and the tool. In another heat pipe of the present invention, the multiple wires are not inserted into the pipe, but the tool is positioned at a center of the pipe and sintered.

In addition, the present invention provides a method for producing a heat pipe with a wick structure containing pipe type continuous air holes, comprising the steps of positioning a tool at a center of the pipe and multiple wires at a position attached to an inner wall of the pipe, respectively ; charging metal powder between the inner wall of the pipe and the tool; sintering the resulting structure in a furnace under a reducing atmosphere at a temperature for a predetermined length of time to attach a sponge type wick with fine air holes to the inner wall of the pipe; removing the tool and wires to

form the wick structure with pipe type continuous air holes ; and charging a working fluid into the inside of the pipe under vacuum and sealing the pipe.

The heat pipe is characterized in that multiple wires are positioned between the tool and the inner wall of the pipe, and sintered in a furnace under a reducing atmosphere at 700 to 1000 °C for 10 to 180 min.

The wick has a shape of pipe type continuous air holes selected from the group consisting of circle, lozenge, and ellipse.

The tool is made of one selected from the group consisting of A1203, stainless steel, and silicon nitride, and the wires are made of stainless steel of 0.1 to 1 mm thickness. For example, when the diameter of the wire is less than 0.1 mm, the wire is not suitable to be used because the wire is too thin. On the other hand, when the diameter is more than 1 mm, heat transfer performance and capillary force of the heat pipe are reduced because a path for moving evaporated gas becomes narrow.

To form various types of wick structure, the metal powder is sintered at a temperature of 700 to 1000 °C, preferably 850 to 950 °C. For example, when the temperature is lower than 700°C, time required to sufficiently sinter the metal powder is too long. On the other hand, when the temperature is higher than 1000°C, copper powder may be melted, and so the wick structure is hard to form. To prevent oxidation of the metal powder, the powder is sintered in a furnace under a reducing atmosphere for 10 to 180 min. When the powder is sintered for less than 10 min, the powder cannot be sufficiently sintered. On the other hand, the powder is sintered for 180 min or more, the copper powder is melted, and so fine air holes are hard to form.

Furthermore, the metal powder consists of copper and has a particle diameter of 40 to 1000 gin, preferably 100 to 400 am. Sometimes, copper-tin alloy powder containing 1 to 5 % tin or copper-zinc alloy powder containing 1 to 5 % zinc is used to promote sintering of the metal powder.

Examples of the working fluid include liquid with a good thermal conductivity such as water, methyl alcohol, and acetone.

Additionally, the present invention provides a method for producing a heat pipe, comprising the steps of : depositing metal powder of 100 to 250 mesh on a metal plate

in a thickness of 0.2 to 2 mm; sintering the resulting metal plate in a furnace under a reducing gas selected from the group consisting of nitrogen, hydrogen, and a mixture of 70 to 90 % hydrogen and 10 to 30 % argon gas at 700 to 1500°C for 10 to 180 min; shaping the metal plate into a cylinder; and charging a working fluid into the cylindrical pipe with a wick structure under vacuum and sealing the pipe.

Because a heat transfer of the heat pipe is conducted through a wall of the metal pipe, the metal plate is made of metals with an excellent thermal conductivity, which can endure a pressure in the sealed heat pipe and be used for a long time, such as copper, iron, aluminum, and stainless steel. Preferably, the metal plate is made of copper.

The metal plate with grooves may be used to ensure rapid flow of the working fluid, and the metal plate with V or U shaped grooves, which are dug in a longitudinal direction of the pipe, may be used to ensure rapid flow of the working fluid and enlarge a heat transfer area.

The metal powder may be made of copper, iron, aluminum, or stainless steel.

Preferably, the powder is made of copper. A spherical particle diameter of the powder may be 100 to 250 mesh, preferably 150 mesh. To rapidly sinter the powder, copper-tin alloy powder containing 1 to 10 % tin, or copper-zinc alloy powder containing 1 to 10 % zinc may be used.

It is preferable to sinter the metal powder at a temperature of 850 to 950 °C.

For example, when the temperature is 850°C or lower, it takes a long time to sufficiently sinter the metal powder. On the other hand, when the temperature is higher than 950°C, copper powder may be melted, and so the wick structure is hard to form.

To prevent oxidation of the copper powder, the powder is sintered in a furnace under a reducing atmosphere for 10 to 180 min. When the powder is sintered for less than 10 min, the powder cannot be sufficiently sintered. On the other hand, the powder is sintered for 180 min or more, the copper powder is melted, and so fine air holes are hard to form.

The working fluid is a liquid such as ammonia, freon, methanol, water, and organics (e. g. acetone), which can be easily vaporized, and working fluids suitable to be used according to a working temperature and a material of pipe are described in Table 1.

Table 1 Working Working Compatibility of fluid with pipe material Temperature (C) Fluid Iron Copper Aluminum Stainless steel - 60 to 50 Ammonia O X O O - 40 to 120 Freon O O O 10 to 200 Methanol O X X 30 to 200 Water X O X X 150 to 300 Organics O O O

O : compatible, X: non-compatible The heat pipe may be sealed with a metal or plastic cap, PVC, bakelite, or teflon.

In addition, the heat pipe of the present invention may have the wick structure, in which a non-woven fabric type superfine metal fiber mat is attached to the metal plate.

The resulting metal plate is sintered at 700 to 1500 °C under reducing gas such as nitrogen, hydrogen, or a mixture of 70 to 90 % hydrogen and 10 to 30 % argon gas, and then both sides of the plate are connected to each other to produce a cylindrical heat pipe.

The working fluid is charged into the heat pipe under vacuum, and the heat pipe is sealed.

The metal plate is made of metals with excellent thermal conductivity, which can endure a pressure in the sealed heat pipe and be used for a long time, such as copper, iron, aluminum, and stainless steel. Preferably, the metal plate is made of copper.

The superfine metal fiber mat consisting of 20 to 80 um thin fibers has a good absorptivity and capillary force owing to many air holes connected to each other, and thus allows the working fluid to easily flow. The superfine fiber is made of metals having good processability, such as copper, iron, aluminum, stainless steel, and titanium.

Preferably, the superfine fiber is made of copper or copper alloy.

The working fluid is a liquid such as ammonia, freon, methanol, water, and organics (e. g. acetone), which can be easily vaporized.

The hollow metal pipe may be sealed with a metal or plastic cap, PVC, bakelite, or teflon.

The wick may be longitudinally attached to the whole heat pipe or to a portion of the heat pipe the according to a use of the heat pipe. For example, when a whole length of the heat pipe is 1 m, the wick may be attached to only a portion of the heat pipe, which is positioned within a range from a heated portion to a position of 10 to 220 mm, because when one end of the metal pipe is at a lower position than the other end, heat transfer can be accomplished by a natural convection of an evaporated working fluid.

On the other hand, when a heat source is positioned at an upper part of the heat pipe, which stands vertically, or the heat pipe is lain horizontally, the wick is attached to the whole heat pipe.

In addition, the wick consisting of superfine metal fiber may be sintered in conjunction with a metal net yarn. That is to say, even though the metal net yarn has a lower absorptivity and capillary force than the superfine metal fiber, and so mobility of fluid is reduced, the wick comprising the metal net yarn can be used because the metal net yarn has a excellent tensile force.

The application of the preferred embodiments of the present invention is best understood with reference to the accompanying drawings, wherein like reference numerals are used for like and corresponding parts, respectively.

With reference to Fig. 1, a sectional view of heat pipe is illustrated, in which sintered metal powder is attached to the pipe and a wick has pipe type continuous air holes. The sintered metal powder wick 2 and fine void holes 3 in the sintered metal powder wick are extended from an evaporation part of the pipe to a condensation part of the pipe. 4 is a path for moving evaporated gas.

Referring to Fig. 2, a sectional view of the heat pipe is illustrated, into which a tool and wires used to sinter metal powder are inserted. The tool 5 is made of ceramic materials such as A1203 or steel materials such as stainless steel, to which metal powder is not attached during sintering metal powder. The metal powder is charged between the pipe and the tool, which are standing vertically, sintered, then the tool 5 and wires 6 are removed, thereby the pipe of Fig. 1 with pipe type continuous air holes 3 and 4 is produced and the sponge type metal powder is attached to an inner wall of the pipe by sintering of the powder.

Turning now to Fig. 3, a sectional view of a heat pipe with the simple structure produced by inserting the tool 5 and removing it without using wires 6 is illustrated.

Furthermore, when various shapes of tool are inserted into the heat pipe, various shapes of wick structures can be formed as shown in Figs. 7a to 14b.

Wires 6 may be positioned in such a way that wires contact the inner wall of the pipe or wires are inside of the powder wick, as shown in Figs. 4a to 5b.

A portion of the pipe, from which wires are removed, forms pipe type continuous air holes, and various type wires may be used according to the number, diameter, and shape of wire. Referring to Figs. 6a and 6b, various shapes of air hole such as circle, quadrangle, lozenge, and triangle may be formed in the wick, and positioned in such a way that holes contact the inner wall of the pipe or holes are positioned between the tool and the inner wall of the pipe.

Production cost and time are necessary to produce the tool, but the heat pipe can be produced at low cost during mass production of the heat pipe because the tool can be repeatedly used. Also, the heat pipe of the present invention has a higher heat transfer effect than the conventional heat pipe because a sponge type wick formed by sintering has a more improved capillary force than other types of wicks.

A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit the present invention.

EXAMPLE 1 An A1203 tool with a diameter of 8 mm and twelve stainless steel wires with a diameter of 0.5 mm were positioned at a center of an anoxic copper pipe with an outer diameter of 13 mm and a length of 30 cm. Between the pipe and the ceramic tool, copper powder with a diameter of 100 to 400, am was charged, sintered in a furnace under a reducing atmosphere at 850 to 950 °C for 30 to 120 min, then the resulting ceramic tool and wire were removed. The resulting pipe had pipe type continuous

air holes 3 and 4 as shown in Fig. 1, and a sintered sponge type wick containing about 50 % copper attached to the inner wall of the pipe. The pipe with the wick was vacuumed, charged with a working fluid, and sealed to produce a heat pipe with a wick structure of pipe type continuous air holes.

Meanwhile, a structure of a heat pipe 10 according to another embodiment of the present invention is illustrated in Figs. 15 and 16. The heat pipe 10 consists of a hollow metal pipe 11 in which both ends lla and Ilb are sealed and the inside is a vacuum, the wick 12 attached to the inner wall of the metal pipe 11, and the working fluid charged in the hollow metal pipe 11.

As described above, the heat pipe 10 in Fig. 15b is produced by connecting both sides of a metal plate 13, to which the sintered wick 12 is attached, in Fig. 15a by welding. Both ends 11 a and lib of the pipe are sealed and the inside of the pipe is a vacuum, as shown in Fig. 16.

The metal plate 13 of Fig. 15a, to which the wick 12 is attached, is produced by depositing metal powder of 100 to 250 mesh in a thickness of 0.2 to 2 mm on the metal plate 13, and sintering the resulting metal plate in a furnace under a reducing atmosphere at 700 to 1500 °C under reducing gas such as nitrogen, hydrogen, or a mixture of hydrogen and argon gas for 10 to 180 min.

EXAMPLE 2 Copper powder with a size of 150 meshes was uniformly deposited on a copper plate with a width of 600 mm and a thickness of 0.7 mm in a thickness of 0.6 mm to give a copper-coated copper plate as shown in Fig. 15a, which was then sintered in a continuous type furnace under a reducing atmosphere at 800 to 1000 °C for 30 to 120 min and cut into rolls with a width of 38.7 mm, followed by soldering the rolls with copper phosphorous brazing metal in a pipe-manufacturing machine to afford pipes with a wick structure, which were 12.70 mm in diameter, as shown in Fig. 15b.

Phosphorous of the solder prevents the copper from being oxidized.

The resulting pipe was cut in a length of 300 mm, and both sides lla and

lib of the cut pipe were closed as shown in Fig. 16. Then, the resulting pipe was vacuumed, charged with a working fluid, and sealed to produce a heat pipe with a wick structure having continuous air holes.

EXAMPLE 3 In order to compare the heat pipe of the present invention, in which a superfine metal fiber was coated, with a conventional heat pipe, the heat pipe, in which a sintered superfine metal fiber wick was attached to an inner wall of copper pipe with an inner diameter of 110 mm and an outer diameter of 127 mm, and the conventional heat pipe, to which metal net yams were attached, were tested for a temperature and a heat transfer time. The working fluid occupied 6 % of total volume in the pipe, a length of pipe exposed to heat source was 10 cm, the heat pipe had scales indicating positions of 0.1 m, 0.5 m, and 1 m from the heat source and horizontally set, the heat source was water at 60 °C, and temperatures at each position were measured every second within a range of 5 to 30 sec. As a result, it was observed that temperatures of the heat pipe of the present invention are different from those of the conventional heat pipe, as shown in Table 2, and the heat pipe of the present invention has more excellent heat transfer performance than the conventional heat pipe.

Table 2 Graph showing temperature as a function of time for heat pipes according to conventional and present inventions

Time (sec) As described above, the present invention provides a heat pipe with various wick structures containing pipe type continuous air holes and a method for producing the heat pipe, in which the prepared wick is inserted into the pipe. The method comprises the steps of charging metal powder between an inner wall of the pipe and a tool (or wires), sintering the metal powder to attach it to the inner wall of the pipe, then removing wires to produce pipe type continuous air holes. The method of the present invention has advantages in that a process for producing the heat pipe is simple, and that heat can be sufficiently rapidly transferred because a flow velocity of a working fluid is increased owing to osmotic action and heat is transferred through the wick attached to the heat pipe.

Another advantages of the present invention are that the production method of the heat pipe becomes simple by producing the heat pipe after metal powder or superfine metal fiber is coated on the metal plate and sintered, and that a bent-up property is excellent because the wick is strongly attached to the metal plate by sintering, as well as heat transfer effect, workability, and production cost are excellent because movement of the working fluid is increased by the osmotic action.

The present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.