Patent Application
20070062036
The present invention relates generally to heat-dissipating devices, and more particularly to a method of filling and sealing a predetermined quantity of working fluid within a heat-dissipating device such as a heat pipe or a vapor chamber-based heat spreader or the like.
Vapor chamber-based heat spreaders and heat pipes are highly efficient devices for dissipating heat from heat-generating components such as central processing units (CPUs) of computers. As a common characteristic, these heat-dissipating devices contain therein a small quantity of working fluid and are capable of dissipating a large amount of heat by using a phase change mechanism of the working fluid. Vapor chamber-based heat spreaders generally have a plate-type configuration and therefore are particularly advantageous in transferring heat from a concentrated heat source uniformly to a large heat-dissipating surface such as a large heat sink base. When a vapor chamber-based heat spreader is maintained in thermal contact with the heat source, the working fluid contained in the heat spreader vaporizes into vapor. The vapor then runs quickly to be full of an inner chamber defined in the heat spreader, and when the vapor comes into contact with the cooler heat sink base attached to the heat spreader, it releases its latent heat of vaporization to the heat sink base and then turns into condensate; thus, the working fluid transfers the heat of the concentrated heat source evenly to the large heat sink base. Thereafter, the condensate returns back to the contacting region between the heat source and the heat spreader for being available again for evaporation.
As with heat pipes, they generally have an elongated configuration and therefore are particularly advantageous in bringing heat from a heat source to a distant region where the heat is dissipated. A heat pipe generally consists of a vacuum casing defining a chamber, a wick structure lining an inner wall of the casing and a working fluid filled in the chamber. The heat pipe is vacuumed and then hermetically sealed. The heat pipe has an evaporating end for receiving heat from the heat source and a condensing end for releasing the heat absorbed by the evaporating end. As heat generated by the heat source is inputted into the heat pipe via its evaporating end, the working fluid contained therein absorbs the heat and turns into vapor. Due to the difference of vapor pressure between the two ends of the heat pipe, the generated vapor moves, with the heat being carried, towards the condensing end where the vapor is condensed into condensate after releasing the heat into ambient environment by, for example, fins thermally contacting the condensing end. Afterwards, the condensate resulted from the vapor in the condensing end is drawn back by the wick structure to the evaporating end where it is again available for evaporation. This continuous cycle transfers a large quantity of heat with a very low thermal gradient.
For transferring heat, the heat pipe is expected to have a low thermal resistance (R), which is affected by the maximum heat transfer capacity (Qmax) of the heat pipe and the temperature difference (ΔT) between the evaporating end and the condensing end of the heat pipe. The three parameters are related, based on the relationship: R=ΔT/Qmax. As can be seen from the equation, the thermal resistance (R) of the heat pipe decreases as the temperature difference (ΔT) between the two ends of the heat pipe decreases and the maximum heat transfer capacity (Qmax) of the heat pipe increases. Specifically, the parameters Qmax and ΔT of the heat pipe are closely related with the quantity of working fluid and the vacuum condition sealed within the heat pipe. The larger amount of working fluid the heat pipe contains, the higher maximum heat transfer capacity (Qmax) the heat pipe has. Meanwhile, a higher vacuum degree inside the heat pipe is helpful in lowering the temperature difference (ΔT) between the two ends of the heat pipe. A major factor affecting the vacuum degree inside the heat pipe is the amount of undesirable air retained in the heat pipe, including the air contained in the working fluid, the air retained in the pores of the wick structure and the air left in the chamber of the heat pipe.
A conventional method for sealing within a heat pipe with a predetermined amount of working fluid relates to the use of a vacuum pump to evacuate the heat pipe. Typically, a suction tube of the vacuum pump extends into an interior of the heat pipe through an open end thereof and the vacuum pump operates to extract the air contained in the heat pipe. Thereafter, the heat pipe is filled with the predetermined amount of working fluid and the open end of the heat pipe is sealed. However, by this method, the air contained in the heat pipe cannot be effectively extracted and removed. Ultimately, a certain amount of air will inevitably be still left within the heat pipe. Furthermore, the air retained in the pores of the wick structure arranged inside the heat pipe also cannot be sufficiently drawn out of the heat pipe by the vacuum pump. In addition, in most cases, the open end of the heat pipe is previously shrunk to have a diameter (typically about 2 millimeters), which is much smaller than that of the vacuum casing of the heat pipe, in order to facilitate sealing the heat pipe subsequently. In this situation, pumping the undesirable air out of the heat pipe becomes a time-consuming work. Meanwhile, it becomes more difficult to draw the air out of the heat pipe through such a narrow outlet.
Therefore, it is desirable to provide a method of filling and sealing a predetermined quantity of working fluid within a heat pipe (or a vapor chamber-based heat spreader or the like), which overcomes the foregoing disadvantages.
The present invention relates to a method of filling and sealing a predetermined quantity of working fluid within a hollow metal casing of a heat-dissipating device. The method includes the following steps: (1) filling a working fluid into the hollow metal casing through an open end thereof until the hollow metal casing is full of the working fluid; (2) pumping a portion of the working fluid out of the hollow metal casing until the predetermined quantity of working fluid is left in the hollow metal casing; and (3) sealing the open end of the hollow metal casing.
In accordance with one aspect of the present method, the air contained in the working fluid is previously removed before the working fluid is filled into the hollow metal casing. In accordance with another aspect of the present method, a wick structure is disposed inside the hollow metal casing and the hollow metal casing is heated after the working fluid is filled into the hollow metal casing but before the portion of the working fluid is pumped out of the hollow metal casing, so as to remove the air retained in the pores of the wick structure.
In the present method, a vacuum condition is formed in the hollow metal casing, by pumping the originally filled working fluid out of the casing until the predetermined quantity of working fluid is left therein. The undesirable air originally contained in the heat pipe, including that in the working fluid and in the wick structure, is effectively removed.
Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which:
In the heat pipe 10, a working fluid 16 is required. Typically, the working fluid 16 is water, although other liquids such as methanol or the like may also be suitable. Before filled into the heat pipe 10, the working fluid 16 is heated to a boiling temperature thereof so as to extract and remove the undesirable air contained in the working fluid 16 (step 101).
With the undesirable air contained in the working fluid 16 being removed, the working fluid 16 is then filled into the heat pipe 10 through the open end 12 of the casing 11 by using a filling tube 20, until the chamber 14 of the casing 11 is full of the working fluid 16 (step 102), as shown in
After the chamber 14 of the casing 11 is full of the working fluid 16, the casing 11 is disposed into a heating device 30 in which heating elements 32 are arranged, as shown in
The casing 11 then is placed in an upside-down manner, as shown in
To draw the working fluid 16 out of, and retain the predetermined quantity of working fluid in, the casing 11, the suction tube 72 of the pump 70 may also extend into a large portion of the interior of the casing 11, as shown in
In the present method 100, the air contained in the working fluid and the air retained in the pores of the wick structure 15 are previously removed. The vacuum condition in the casing 11 is formed, by pumping the originally filled working fluid 16 out of the casing 11 until the predetermined quantity of working fluid is left therein. As a result, the undesirable air contained in the heat pipe 10, including that in the working fluid 16 and in the wick structure 15, is effectively removed.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200510037444.3 | Sep 2005 | CN | national |
