APPARATUS THEREFOR

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an apparatus and a method for filling a heat pipe with working fluid, and more particularly to the apparatus and method, which can charge a fine heat pipe having a small diameter with the working fluid.

2. Description of the Prior Art

Recently, it is a general trend that a high dense packaging of parts and systems is performed in all electronic industries including electronic/communication devices. So, dispersing and radiating heat from a system and cooling the system become very important. Where heat generated from the electronic devices is neglected, it becomes the main source that causes degradation of performance and reduction of the lifetime of the devices and systems. Therefore, a cooling method for effectively radiating heat is required. Especially, as electronic devices have become miniaturized and are increasingly thinned, cooling devices applied to the electronic devices also have to be fine and small, keeping step with them. Conventionally, a heat sink or a fan attached to the heat

sink is used as a cooling system in order to disperse and radiate heat generated in electronic devices. However, if the heat sink is reduced in its size, the performance of radiating heat becomes deteriorated in proportion to the reduction in size of the heat transferring area. Further, there is a limitation to manufacture a fan having a small size and to reduce noise generated by the fan. As a solution of the problems of the conventional cooling system, recently, the cooling system using a heat pipe has been discussed. The Heat pipe is a heat exchanging device which can efficiently transfer heat under a little temperature difference using latent heat caused by vaporization of working fluid therein without using power. FIG. 1 shows the operation principle of a general heat pipe. A body 101 of the heat pipe includes an evaporation section 102 (a heat absorbing section) , an adiabatic section

103 (a heat transferring section) , and a condensation section

104 (a heat discharging section) . Working fluid absorbs heat at the evaporation section 102 contacting a heat source, is diffused in vapor inside the body 101 of the heat pipe, travels along the heat transferring section 103, and dissipates the heat at the condensation section 104. The vaporized working fluid dissipating the heat is condensed at the condensation section 104, and then to be in turn changed into the liquid phase again. Then, the working fluid returns along a wall of

the wick of the heat pipe to the evaporation section 102. The working fluid inside the heat pipe repeatedly carries out the condensation and evaporation processes such as, so as to transfer the heat. The temperature of the evaporation section 102 and the heat transferring section 103 is higher than that of the condensation section 104. The vapor pressure at each section is a saturated vapor pressure. The pressure of the evaporation section 102 and the heat transferring section 103 is higher than that of the condensation section 104. As a result, the vapor travels through the heat transferring section 103 from the evaporation section 102 to the condensation section 104. The heat transfer is very rapidly performed at a speed similar to the speed of sound.

The performance of the heat pipe can be influenced by various parameters such as the wick structure circulating the working fluid, the nature of the working fluid, the filling amount of the working fluid, the degree of vacuum and the cleanness in the body of the heat pipe, and the like. Specially, as the heat pipe becomes fine, it becomes important to charge the heat pipe with the working fluid in the process of manufacturing the heat pipe.

FIG. 2 is a view illustrating a conventional steam blowing process of filling the heat pipe with the working fluid.

Referring to FIG. 2, the working fluid is first injected into the heat pipe and then the heat pipe is sealed (FIG. 2a) .

The sealed heat pipe is heated. Accordingly, gas (including air and inert gases such as argon gas) contained in the heat pipe before sealing are mixed with the vapor of the working fluid and the inside of the heat pipe is filled up with the mixed gas (FIG. 2b) . At this time, if small opening at one end of the heat pipe is opened, while the mixed gas containing impurities is being discharged off because of pressure difference between inside and outside of the heat pipe, and only low density and high temperature vapor gas only remains in the heat pipe (FIG. 2c) . When the opening of the heat pipe is sealed after a predetermined time lapses, the vapor of low density and high temperature becomes liquefied in accordance with cooling, so that the inside of a heat pipe becomes vacuum with the inside thereof filled with a desired amount of the working fluid filled therein (FIG. 2d) .

However, the conventional steam blowing process has a disadvantage that it cannot be applied to a micro heat pipe having a small diameter or a flat plate micro heat pipe. In the case of the micro heat pipe, its small diameter makes it difficult to inject the working fluid into the heat pipe. As well, although the working fluid is injected into the heat pipe, all of the working fluid is blown off through the opening of the heat pipe in an instant when the opening of heat pipe heated is opened(see FIG. 2c) . Therefore, it is almost impossible to charge the heat pipe with the working fluid at a

predetermined amount.

Korean patent laid-open publication no. 2003-0053424 discloses fine heat pipes having polygon-sectional shapes, which are made by using extruding and drawning processes. In the fine heat pipe, capillary force occurring at each corner of the polygon-sectional shape allows the working fluid to move, thereby permitting the heat pipe to be minute. The conventional heat pipe has a mesh type of wick structure formed of a copper net, or a sintered type of wick structure in which fine copper particles are sintered in order to circulate the working fluid. Since the conventional heat pipe has to have such wick structure inside the body thereof, there is a limitation to reduce the diameter of the heat pipe.

Meanwhile, in the fine heat pipe, the corners of the polygon sectional shape play the role of the wick structure. Thus, the fine heat pipe may have a wickless type wick structure, thereby reducing the diameter of the heat pipe below 3mm. However, in the case of the fine heat pipe, it is impossible to charge the heat pipe with the working fluid using the conventional steam blowing process as described above. Therefore, the method for filling the heat pipe with working fluid using a vacuum pump and an injector has been proposed.

In the method for filling the heat pipe with the working fluid using a vacuum pump and an injector, the vacuum pump is

connected to the fine heat pipe in order to make the inside thereof vacuum. Next, the working fluid is injected up into the heat pipe by vacuum sucking pressure. Then, some of the working fluid is removed by using the injector so that a predetermined amount of the working fluid remains in the heat pipe. Continuously, the remained working fluid is frozen by using liquefied nitrogen. Then, the heat pipe is made to be evacuated by using the vacuum pump. At this time, since the remained working fluid in the heat pipe is frozen, it does not get out accompanying the vacuum sucking pressure of the vacuum pump while making the heat pipe vacuum inside. Finally, when the opening of the heat pipe is sealed, the internal portion of the heat pipe becomes vacuum state filled partially with working fluid at a predetermined amount. However, the method for filling the heat pipe with working fluid like using the vacuum pump and the injector has complicated processing steps including the step of removing some of the injected working fluid while leaving a predetermined amount of the working fluid, a freezing step, and the like. Further, considering an aperture of a needle of the injector, it is difficult to leave the adequately predetermined amount of the working fluid. Furthermore, while the vacuum pump makes the internal portion of the heat pipe vacuum as leaving the frozen working fluid, some of the working fluid can be lost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and a method for filling a heat pipe with working fluid, which can charge a fine heat pipe having a small diameter with the working fluid.

In order to accomplish the object of the present invention, according to an aspect of the present invention, there is provided a method for filling working fluid within a heat pipe, which comprises; a steam injecting step of injecting a working vapor into the heat pipe through a lower end thereof, the lower end of the heat pipe being opened and the upper end of the heat pipe being closed; a blowing step of opening the upper end of the heat pipe to discharge a mixed gas containing air and the working vapor; a working vapor filling step of closing the upper end of the heat pipe to fill the inside of thereof with working vapor after the blowing step; and a sealing step of closing the lower end of the heat pipe. In order to accomplish the object of the present invention, according to another aspect of the present invention, there is provided an apparatus for filling a heat pipe with working fluid, which comprises: a pressure vessel containing working fluid and working vapor vaporized from the working fluid, and having an opening through which the working vapor can be communicated with the outside and a control valve

mounted near the opening in order to control the closing and the opening of the working vapor to flow through the opening; a connection tube for connecting the opening of the pressure vessel to the inside of heat pipe so that the working vapor in the pressure vessel can flow along the connection tube into the heat pipe; and a heating coil for overheating the pressure vessel.

The heat pipe transfers heat under even a little temperature difference condition by using a latent vapor heat of the working fluid therein without using power. The performance of the heat pipe is greatly influenced by filing of the working fluid. That is, the performance of the heat pipe is influenced by accurate injection of the working fluid, a filling amount of the working fluid, the degree of a vacuum, and a chemical reactivity between the working fluid and the heat pipe, and so on.

Where the working fluid chemically is responsive to materials of the heat pipe, even when the working fluid is filled under the sustained vacuum at a predetermined degree, the working fluid circulates in the heat pipe while reacting to the heat pipe, to generate inert gases. These inert gases prevent the circulation of the working fluid, thereby causing degradation of the performance and the lifetime of the heat pipe. Therefore, the heat pipe and the working fluid are preferably selected from materials which do not chemically

react to each other. If the heat pipe is made of copper, pure water is used as the working fluid. If the heat pipe is made of aluminum, acetone is used as the working fluid.

The present invention uses a steam injection process to make it possible to inject the working fluid into the heat pipe having a smaller diameter than 3mm. The steam injection process uses characteristics of fluid and gas in which a volume of fluid greatly increase by vaporization, a density of gases increases according to the increase of the gas pressure under a constant temperature condition, and various gases are easily and uniformly mixed under a normal condition.

According to the present invention, working vapor can be injected into the fine heat pipe having a 1.5mm ~ 3.0mm diameter by the steam injection. The working vapor of a high density injected into the heat pipe is uniformly mixed with air and inert gases contained in the heat pipe, and then some of the working vapor capturing the air and the inert gases is discharged outside. The heat pipe is sealed in the state of the pure working vapor filled in the heat pipe. The working vapor is fully filled in the heat pipe when it is in vapor state. However, when the working vapor is cooled and liquefied, its volume is greatly reduced. Thus, all spaces in the heat pipe become vacuum state, excepting for the space the working fluid occupies. As a result, the steam injection process can make it accomplished to evacuate the inside of the heat pipe and to

fill the inside of the heat pipe with the working fluid.

Furthermore, the present invention uses characteristics of gas: identical gases regularly change depending on the three values of the pressure, temperature and volume thereof, while one of physical properties is dependent on the other two physical properties. Therefore, it is possible to control a pressure of a gas by determining a temperature of the gas limited under a constant volume condition. Further, if the pressure, the temperature, and the volume of the filled gas are determined, the molar amount of the gas can be calculated by using an equation of state, i.e. PV=nRT, in an ideal state. This means that the filling amount of the working fluid can be accurately controlled. The vapor of high temperature has a characteristic similar to that of an ideal gas so as to satisfy the equation of state for the ideal gas. However, in commercial production process, there may be a correction value for working vapor determined by experiments. Since the correction values determined by the experiment are influenced by the performance of equipments, the present invent will be described assuming that the working vapor satisfies the equation of the state for the ideal gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of

the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a conventional heat pipe; FIG. 2 is a view illustrating a conventional steam blowing process;

FIG. 3 is a view showing the structure of an apparatus for filling a heat pipe with working fluid, according to the present invention; FIG. 4 is a view illustrating a method for filling a heat pipe with working fluid, according to the present invention;

FIG. 5 is a block diagram illustrating the method for filling a heat pipe with working fluid, according to the present invention; FIG. 6 is a block diagram illustrating a process of filling a pressure vessel with the working vapor, according to the present invention; and

FIG. 7 is a graph showing a characteristic for a method of filling a heat pipe with working fluid, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

Referring to FIG. 3, an apparatus for filling a heat pipe with working fluid includes a pressure vessel 10, a connection tube 20, and a heating coil 30.

The pressure vessel 10 may contain the working fluid and working vapor vaporized from the working fluid. The pressure vessel 10 has an opening 12 through which the working vapor flows. Further, the pressure vessel 10 has a control valve 15 mounted near the opening 12 in order to control the flow of the working vapor through the opening 12 of the pressure vessel 10 by closing and opening the opening 12.

According to the present invention, the connection tube 20 is bridged between the opening 12 of the pressure vessel 10 and the heat pipe 1. A fill tube is used as the connection tube 20 and the end of the heat pipe is connected to one end of the fill tube. More specifically, one end of the fill tube 20 is connected to the opening 12 of the pressure vessel 10 and the other end of the fill tube 20 is connected to the lower end of heat pipe 1.

The working fluid contained in the pressure vessel 10 is that fluid to be filled within the heat pipe 1. Therefore, if the heat pipe is made of copper material, water is used as the working fluid. If the heat pipe is made of aluminum material, acetone is used as the working fluid.

Since the pressure vessel 10 provides the working fluid to an internal portion of the heat pipe 1, the working fluid

contained in the pressure vessel must not contain inert gases. Therefore, the pressure vessel is made of the material which does not chemically react with working fluid in order to prevent inert gases from being generated. Considering that water or acetone is commercially available as the working fluid, the pressure vessel 10 is preferably made from stainless steel.

The present invention includes a heating coil 30 in order to heat the pressure vessel 10. The heating coil 30 is installed in one body with the pressure vessel 10 to heat the pressure vessel 10. The internal temperature of the pressure vessel 10 is capable of being controlled at a required temperature through the control of the caloric value of the heating coil 30. The present invention also includes a temperature sensor 40 which senses the temperature in the pressure vessel 10 and a pressure sensor 50 which senses the pressure in the pressure vessel 10. The values of the temperature sensor 40 and the pressure sensor 50 are displayed respectively on a display 45, 55.

The internal temperature of the pressure vessel 10 can be checked through the temperature sensor 40 to control the caloric value of the heating coil 30 so that the heating coil heats the pressure vessel 10 to be overheated and maintains the internal temperature constantly.

According to the present invention, the heating coil 30 can be connected to a wattmeter 62 and a variable transformer (a slidacs) 64 for the control of the caloric value. The wattmeter 62 displays an amount of electric power provided to the heating coil 30 and the variable transformer 64 controls the electric power provided to the heating coil 30. Therefore, it is possible to control the electric power by means of the variable transformer 64 with taking a view of values displayed on the wattmeter 62 in order to maintain the internal temperature of the pressure vessel 10 at the required temperature.

Preferably, the apparatus for filling a heat pipe with the working fluid can be constructed to have automatic controlling system which controls the operation of the following apparatuses, including controller (not shown in Figs.)

Referring to FIGS. 4 through 6, the operation of the apparatus, and the method for filling a heat pipe with the working fluid according to the present invention will be described. The method for filling a heat pipe with the working fluid according to the present invention includes a steam injection step S30, a blowing step S40, a the working vapor filling step s50, and a sealing step S60. Preferably, a injection the working vapor of the steam injection step s30 is performed after performing a pressure vessel connecting step slO and a

fluid communication step s20. The pressure vessel 10 is filled with the working vapor through performing a working fluid injection step sllO, a mixed gas filling step sl20, a mixed gas discharging step sl30 and a working vapor filling step 140. The steam injection step S30 according to the present invention is to inject the working vapor into the inside of the heat pipe 1 through the lower end of the heat pipe. The working vapor means the working fluid vaporized by heating.

According to the present invention, the work vapor injected into the heat pipe is provided from the pressure vessel 10. Referring to FIG. 6, the process of filling the pressure vessel 10 with the working vapor will be described.

The working fluid is injected into the pressure vessel 10 in the step sllO. The control valve 15 disposed near the opening 12 is closed after the injection of the working fluid so as to stop fluid communication with the outside of the pressure vessel and isolate the inside of the pressure vessel 10 from the outside of the pressure vessel 10. Then, the variable transformer 64 is operated to supply the electricity to the heating coil 30, so as to allow the heating coil 30 to heat the pressure vessel 10. The heating coil 30 heats the pressure vessel 10 to be overheated. In a case where the working fluid is water, the pressure vessel 10 is heated to a temperature of 110 ⁰ C ~ 130°C above the evaporation point. Then, the mixed gas filling step 120 is performed.

When the working fluid is heated, the working fluid changes into the working vapor and the pressure in the pressure vessel 10 gradually increases by the working vapor. Since the volume of the working fluid increases highly in the vaporization of the working fluid and the density increases when the pressure increases under an identical temperature condition, the inside of the pressure vessel 10 comes in a state of high temperature and high density due to the working vapor continuously supplied thereto and having highly increased volume. Since the gases have a characteristic of being uniformly mixed with one another, the working vapor is uniformly mixed with air and inert gases existing in the pressure vessel 10 and the inside of the pressure vessel 10 is filled up with the mixed gas of high temperature and high density.

Then, the mixed gas discharging step sl30 is performed. The control valve 15 is operated to open the opening 12 of the pressure vessel 10 and to discharge the mixed gas out of the pressure vessel 10. Since the pressure vessel 10 is overheated, the working vapor is continuously supplied from the working fluid. Further, the pressure in the pressure vessel 10 decreases slightly because the opening 12 is opened. However, as the pressure of the inside of the pressure vessel 10 still is higher than the pressure of the outside of the pressure vessel 10, and as the working vapor is continuously supplied by

the vaporization of the working fluid, the pressure difference between the inside and outside of the pressure vessel 10 allows the discharge of the mixed gas from the pressure vessel 10, but does not permit the introduction of outer air into the pressure vessel 10. Therefore, the mixed gas in the inside of the pressure vessel 10 gradually is replaced by pure working vapor.

Continuously, as the working vapor filling step 140, if it is determined that the discharge of the mixed gas is completed; the control valve 15 is closed to stop discharging gas through the opening 12. The pressure vessel 10 is filled with only pure working vapor vaporized from the working fluid.

Preferably, the caloric value is uniformly controlled so that the internal portion of the pressure vessel 10 is fully filled with the working vapor in a constant temperature and pressure. In the pressure vessel, the volume of the pressure vessel is determined and the pressure of gases in the pressure vessel changes with relation to the temperature. Therefore, when the temperature of the pressure vessel 10 is controlled by governing the caloric value of the heating coil 30, the pressure of the pressure vessel can be controlled constantly during filling the working vapor within the pressure vessel.

Referring to FIG. 5, after the pressure vessel 10 is filled with the working vapor, the pressure vessel connecting step slO is performed in which the fill tube 20 connects the opening 12 of the pressure vessel 10 to the lower end of the

heat pipe 1 of which the lower end is open and the upper end is closed.

Generally, the closing of the heat pipe 1 is performed by cool welding such as a pinch-off junction. The pinch-off junction is generally referred to as the cool welding, in which the heat pipe is pinched with a nipper and bent due to a grip of the nipper. The bent portions of the heat pipe are in line contact with each other and adhered to each other. The pinch- off junction is performed under a normal temperature and a certain pressure, so it is referred to as the cool welding in order to distinguish the pinch-off junction from the general welding. The closing of the heat pipe made of material which has a sufficient ductility, such as aluminum or copper, can be performed by using the cool welding such as the pinch-off junction. Therefore the closing and sealing of the heat pipe can be reliably performed by the cool welding so as to intercept the flowing of the fluid. Of course, the closing of the heat pipe according to the present invention may be realized by using another method. As used herein, a closing or sealing process refers to a process of the junction of the end of the heat pipe in order to close and seal the end of the heat pipe.

When the end of heat pipe closed by the pinch-off junction is opened, the welded surface of the heat pipe is cut by using a high speed cutter or the folded portion of the heat pipe is

unfolded by using the nipper.

After the heat pipe is connected to the pressure vessel 10, the fluid communication step s20 is performed. The control valve 15 is open so that the working vapor in the pressure vessel is communicable to the inside of the heat pipe of which the upper end is closed and the lower end is open. The working vapor can be injected from the inside of pressure vessel 10 into the inside of the heat pipe 1 because of the pressure difference between the inside of the pressure vessel and the heat pipe.

In the steam injection step s30 in winch the working vapor is injected inside the heat pipe, as the working vapor is provided to the inside of heat pipe, the working vapor is uniformly mixed with air existing within the heat pipe and the inside of the heat pipe becomes filled with a mixed gas of the high temperature and high density.

Then, in the blowing step s40, the upper end of the heat pipe is opened to discharge the mixed gas out of the heat pipe due to the pressure difference, the mixed gas consisting of the working vapor and the air gases filled in the heat pipe. At this time, the working vapor is continuously provided through the lower end of the heat pipe 1 from the pressure vessel 10.

Then, in the working vapor filling step s50, when discharging out all of the mixed gas from the heat pipe 1 is completed, the heat pipe is closed again at its upper end and

filled with the working vapor. It is possible to maintain the internal pressure and temperature of the pressure vessel 10 at a constant state when capable of controlling the caloric amount of the heat coil 30 even if the internal pressure of the pressure vessel 10 is reduced slightly due to opening the upper end of the heat pipe 1.

that the pressure in the pressure vessel 10 decreases slightly because the upper end of the heat pipe is opened and the inside of the heat pipe is in fluid communication with the inside of the pressure 10. However, the temperature and pressure in the pressure vessel 10 can be governed uniformly through controlling the caloric value of the heat pipe 30. That is, since the inside of the heat pipe 1 and the inside of the pressure 10 are fluid-movably connected to each other to come under the condition of the same temperature and pressure, maintaining the inside of the pressure vessel 10 at a constant temperature and pressure through the heating coil 30 leads the heat pipe 1 to be filled at the state of the constant temperature and pressure. Since the filling amount of the working vapor contained in the heat pipe 1 is determined based on the temperature and the pressure of the inside of the heat pipe 1, if the temperature and the pressure in the heat pipe 1 is controlled uniformly during filling the heat pipe with the working vapor in a mass production process, the filling amount

of the working fluid contained in the heat pipe 1 can be controlled uniformly.

Further, according to the present invention, the amount of the working fluid contained in the heat pipe 1 can be determined precisely. Under the condition as to an equation of the state of the ideal gas, the volume condition is determined constantly according to the heat pipe and the pressure is changed in proportion to the temperature.

Therefore, it is possible to control the internal pressure properly through the caloric value of the heating coil 30. In other words, it means that by controlling the P and T at the same time in the condition of n=PV/RT it is possible to decide the molar amount of working fluid which is to be filled in the heat pipe 1, thereby making it possible to decide the filling amount of working fluid.

In the sealing step S60, the heat pipe 1 is closed at its lower end and sealed at the state of the working vapor being filled inside the heat pipe at a predetermined amount.

When the heat pipe is cooled to normal temperature, the working vapor becomes liquefied to reduce its volume, resulted in that all the rest of the space the working vapor occupies become vacuum state. Namely, the present invention can accomplish the filling of working fluid simultaneously with the vacuum state.

FIG. 7 is a graph showing a characteristic of the method for filling a heat pipe with working fluid according to the present invention.

Referring to FIG. 7, it is understood that the fine heat pipe can be charged precisely with a selected amount of working fluid, based on the change of parameters of the temperature and the pressure of the pressure vessel. Specifically, in comparison with the conventional methods of filling the heat pipe with the working fluid by using a vacuum pump and an injector, in the conventional methods, as the filling amount of the working fluid is measured in a solution state before a vacuum step, the amount of the working fluid may be changed in the vacuum step, thereby making it difficult to accurately control the amount of the working fluid filled within the heat pipe. Meanwhile, in the present invention, the amount of the working fluid injected into the heat pipe can be directly controlled, thereby filling a heat pipe with working fluid more precisely.

The present invention does not require the conventional process of filling inside each heat pipe with a predetermined solution to reheat it for gas removal or cooling quickly the heat pipe for making it vacuum again. However in the present invention, once pressure vessel is filled with the working vapor, the working vapor can be continuously provided to the heat pipes, thereby improving the productivity. Further, the

present invention can control accurately the amount of the working fluid filled within the heat pipe.

Furthermore, in the present invention, the steam injection allows the working vapor to flow into the heat pipe due to the pressure difference, thereby filling the fine heat pipe with the working fluid.