CROSS REFERENCE TO RELATED APPLICATION
This application also claims priority to Taiwan Patent Application No. 101145061 filed in the Taiwan Patent Office on Nov. 30, 2012, the entire content of which is incorporated herein by reference.
TECHNICAL FIELD
The disclosure relates to a heat conduction technology, and in particular, to a heat pipe and a processing method thereof.
RELATED ART
With the evolution of the integrated circuit package technology and process, internal circuits are becoming more intensified and miniaturized, so that the processing speed and frequency of electronic components are rapidly improved. However, when the miniaturized electronic components are running with a high frequency, the heat generation per unit area of the components is significantly increased, resulting in the problem that the hotspot on the chip. The statistical result shows that, up to 55% of damages to electronic products are caused by overheat. According to the research, every 10° C. of temperature decrease improves the efficiency of the processing chip by 1 to 3%. Therefore, during operation, the electronic components require a set of effective heat dissipation design to solve the problem of excessively centralized heat source, thereby ensuring the reliability, stability and service life of the electronic device in long-term use.
Heat pipe products (such as a heat pipe or a plate heat pipe) are featured in rapidly conduction of heat generated by a heat source to a heat dissipation end, and therefore are widely applied to current components that produce highly exhaust heat and require rapid heat dissipation, for example, electronic components, light emitting diodes (LEDs), and solar panels. The internal of a heat pipe is a low-pressure sealed space, and has a capillary structure and a working fluid filled therein. The internal low-pressure state greatly decreases the vaporization temperature of the working fluid. During the operation, the working fluid evaporates in an evaporation area upon being heated, taking away a lot of latent heat. The vapor of working fluid flows to a condensation area due to a local high pressure in the evaporation area, and condenses in the condensation area upon being cooled. The capillary structure enables the condensed working fluid to flow back to the evaporation area, so that the evaporation area is continuously provided with the working fluid, thereby maintaining a closed circulating system with one end for evaporation and one end for condensation.
In application, the maximum allowable heat flux of the heat pipe is restricted by different limitations. Typically, the copper-water heat pipe used in common electronic heat dissipation is usually restricted by the capillary limit. As the heat flux increases, the evaporation rate and the mass flow rate of the working fluid increase; if the evaporation rate and mass flow rate of the working fluid exceeds the maximum amount of working fluid that the capillary force is capable of carrying back to the evaporation area, the evaporation area will dry out, and as a result, the heat pipe operation fails.
SUMMARY
The disclosure is directed to a heat pipe and a processing method thereof, where a feature of a capillary structure surface of an existing heat pipe or vapor chamber is changed through a chemical reaction, so that a working fluid in the heat pipe and a modified capillary structure of an inner wall of the heat pipe have different wettability, thereby improving a capillary pressure difference that is used for driving the working fluid to flow and provided by the capillary structure in the pipe, hence significantly improving the maximum heat transfer rate of the heat pipe.
In an embodiment, the disclosure provides a heat pipe processing method, which includes steps of: providing a metal tube with openings at two ends, where an inner wall of the metal tube has a capillary structure surface; and oxidizing the capillary structure surface so as to form an oxidized structure surface.
In another embodiment, the disclosure provides a heat pipe, which includes a metal tube having a first area on an inner wall thereof; a working fluid, filled in the metal tube; and a first oxidized structure, formed on the inner wall defined by the first area, where the working fluid on the first oxidized structure surface has a first contact angle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic flow chart of a first embodiment of a heat pipe processing method according to the disclosure;
FIG. 2 is a schematic side sectional view of an end of a metal tube according to the disclosure;
FIG. 3A to FIG. 3C are schematic views of a contact angle;
FIG. 4A and FIG. 4B are schematic views of oxidizing an inner wall of a metal tube by using a mixed reaction solution according to the disclosure;
FIG. 5A is a schematic sectional view of the metal tube in FIG. 2 after an oxidization process in Step 21;
FIG. 5B is a schematic structural view of an oxidized structure with a long chain formed after a chemical modification procedure in Step 22;
FIG. 5C is a schematic sectional view of a heat pipe formed through a first embodiment of a heat pipe processing method;
FIG. 6A is a schematic flow chart of a second embodiment of a heat pipe processing method according to the disclosure;
FIG. 6B is a schematic sectional view of a heat pipe formed through a second embodiment of a heat pipe processing method;
FIG. 7A and FIG. 7B are schematic flow charts of other embodiments of a heat pipe processing method according to the disclosure;
FIG. 8 is a schematic flow chart of another embodiment of a heat pipe processing method according to the disclosure;
FIG. 9A is a schematic sectional view of a metal tube; and
FIG. 9B is a schematic sectional view of a heat pipe formed through the heat pipe processing method in FIG. 8.
DETAILED DESCRIPTION
In order to enable the examiner to further understand the features, objectives and functions of the disclosure, related detailed structures and design concepts and principles of the equipment of the disclosure are described in detail below, so that the examiner can understand the features of the disclosure. The detailed description is provided as follows:
Referring to FIG. 1, FIG. 1 is a schematic flow chart of a first embodiment of a heat pipe processing method according to the disclosure. In this embodiment, the method 2 includes Step 20, in which a metal tube with openings at two ends is provided. Referring to FIG. 2, FIG. 2 is a schematic side sectional view of an end of a metal tube according to the disclosure. The metal tube 80 is a column-shaped hollow tube with a certain length. An inner wall thereof has a capillary structure surface 81. In this embodiment, the capillary structure surface 81 is a groove structure formed on the inner wall of the metal tube. In another embodiment, the capillary structure surface 81 may also be a mesh structure formed on the inner wall or a porous metal structure formed through sintering, and the mesh or pores of the sintered metal are used as a capillary structure. The method for forming the capillary structure surface 81 is well known to persons skilled in the art, so the disclosure is not limited to the forms of the capillary structure surface 81 described above. The metal tube 80 may use a material with a good heat conduction property, for example, copper or aluminum. In this embodiment, the metal tube 80 is a copper tube. It should be noted that, the section shape of the metal tube 80 in the disclosure may be a circle, but is not limited thereto.
Referring to FIG. 1 again, Step 21 is then performed, in which the capillary structure surface is oxidized so as to form an oxidized structure surface. A first contact angle exists between the oxidized structure surface and a working fluid (such as water, but is not limited thereto). Referring to FIG. 3A to FIG. 3C, FIG. 3A to FIG. 3C are schematic views of a contact angle. The contact angle is defined as an included angle when a surface of the working fluid contacts a surface. FIG. 3A to FIG. 3C show contact angle relationships between the working fluid 91 and different surfaces 90a, 90b, and 90c, where θ1<θ2<θ3. A smaller contact angle indicates that the surface has a higher wettability, and more specifically, when the working fluid is water, the surface having a smaller contact angle belongs to a hydrophilic surface, while a greater contact angle indicates that the wettability of the surface is poorer than that of a surface with a smaller contact angle, and more specifically, when the working fluid is water, the surface having a greater contact angle belongs to a hydrophobic surface.
Referring to FIG. 1 again, the oxidization in Step 21 may be performed in many manners. In an embodiment, with two ends of the metal tube having the capillary structure unclosed, as shown in FIG. 4A, the metal tube 80 is soaked in a mixed reaction solution 92 (oxidizing solution) formed of ammonium persulfate and an alkaline solution. Alternatively, as shown in FIG. 4B, guided by a pipeline 93 and a pump 94, the mixed reaction solution 92 flows into the metal tube 80 and contacts the capillary structure, so that the mixed reaction solution 92 oxidizes the inner wall of the metal tube 80. The alkaline solution may be sodium hydroxide or potassium hydroxide, but is not limited thereto. The ammonium persulfate may also be substituted by potassium persulfate or sodium persulfate. Taking a mixed reaction solution of ammonium persulfate and sodium hydroxide as an example, when the solution reacts with the inner wall of the metal tube, by adjusting parameters such as the concentration, concentration ratio, reaction time and reaction temperature of the sodium hydroxide and the ammonium persulfate, the capillary structure surface on the inner wall of the metal tube may be modified to be an oxidized structure surface. Taking copper as an example, the concentration of the sodium hydroxide may range from 0.25 to 5M, the concentration ratio of the sodium hydroxide to the ammonium persulfate ranges from 4 to 50 (NaOH/(NH4)2S2O8=4˜50), the reaction time ranges from 0 to 12 hours, and the reaction temperature ranges from 0 to 70° C., so that the oxidized structure surface is a surface formed of a blue copper hydroxide microstructure. A reaction equation thereof is shown in Equation (1) below. It should be noted that, the sodium hydroxide may be substituted by potassium hydroxide.
Cu+(NH4)2S2O8+NaOH→Cu(OH)2+2Na2SO4+2NH3+2H2O (1)
In another embodiment, in the oxidized structure surface, the blue copper hydroxide microstructure may further be dehydrated to form a black copper oxide microstructure, and a reaction equation thereof is shown in Equation (2) below.
Cu+(NH4)2S2O8+NaOH→Cu(OH)2+2Na2SO4+2NH3+2H2O
Cu(OH)2→CuO+H2O (2)
Another embodiment of the oxidization in Step 21 is basically similar to the method in above Equations (1) and (2), and the difference lies in that, in this embodiment, the copper surface is oxidized to be the blue copper hydroxide microstructure by adjusting the composition of the mixed reaction solution, the concentration, ratio, reaction time, and reaction temperature of the solution of potassium persulfate and potassium hydroxide, as shown in Equation (3) below. It should be noted that, the potassium persulfate may be substituted by sodium persulfate, and the potassium hydroxide may also be substituted by sodium hydroxide.
Cu+K2S2O8+2KOH→Cu(OH)2+2K2SO4 (3)
In another embodiment, in the oxidized structure surface, the copper hydroxide microstructure may further be dehydrated to form a black copper oxide microstructure, and a reaction equation thereof is shown in Equation (4) below.
Cu+K2S2O8+2KOH→Cu(OH)2+2K2SO4
Cu(OH)2→CuO+H2O (4)
In addition, another embodiment of the oxidization in Step 21 is to perform oxidization through temperature processing, that is, the oxidization in this embodiment does not require any reaction solution; instead, the oxidizing effect is achieved by controlling the temperature and time. In an embodiment, with two ends unclosed, a metal tube having a traditional capillary structure is placed into a high-temperature oven in an aerobic environment (such as an atmosphere environment), after an oxidizing temperature and an oxidizing time, the capillary structure on the inner wall of the metal tube is modified to be a metal oxide. Taking copper as an example, the copper may be reacted for 0.5 to 6 hours under a temperature ranging from 250 to 450° C., so that the surface of the inner wall of the copper tube is modified to be copper oxide, and the reaction equation is shown in Equation (5) below.
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A contact angle between the oxidized structure surface formed according to foregoing Equation (1) to Equation (5), in which copper is taken as an example, and the oxidized microstructure formed by water and copper on the surface is close to zero degree, which improves the hydrophilicity of the modified oxidized capillary structure.
Referring to FIG. 1 again, after Step 21, Step 22 is further performed, in which a second oxidization reaction is performed on partial area of the inner wall of the metal tube or a first oxidized structure surface in the partial area is modified so as to form a second oxidized structure surface. The working fluid on the second oxidized structure surface has a second contact angle. In this embodiment, the second contact angle is greater than the first contact angle. Referring to FIG. 5A, FIG. 5A is a schematic sectional view of the metal tube in FIG. 2 after Step 21. An area having a plurality of dots in FIG. 5 represents a first oxidized structure 82 on the inner wall. Taking a copper tube as an example, in Step 22, in an embodiment of oxidization, after a first oxidization reaction manner is performed according to foregoing Equation (1) to Equation (5), and a second oxidization reaction manner is then performed. In the second oxidization reaction manner, partial area 800 of the metal tube 80 is soaked into a chemical solution such as a diluted solution of fluoroalkylsiloxane [CF3(CF2)n(CH2)2Si(OCH2CH3)3 or CF3(CF2)n(CH2)2Si(OCH3)3], fluoroalkyltrichlorosilane [CF3(CF2)n(CH2)2SiCl3], fluoroalkyldimethylchlorosilane [CF3(CF2)n(CH2)2SiCl(CH2)2], alkylsiloxane [CH3(CH2)nSi(OCH2CH3)3 or CH3(CH2)nSi(OCH3)3], alkyltrichlorosilane [CH3(CH2)nSiC13], alkyldimethylchlorosilane [CH3(CH2)nSiCl(CH2)2] or alkyl mercaptan [CH3(CH2)nSH] (for example, an ethanol solution with the concentration of 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane being 1 w.t. %) for a reaction that lasts 0 to 1 hour, and is then taken out of the solution, washed, and placed into an oven for drying (at a temperature of 25 to 150° C.), so that the first oxidized structure surface 82 is modified to be the second oxidized structure surface 83 having a long chain structure 830 shown in FIG. 5B. The long chain structure 830 may be long chain fluoroalkyl group or long chain alkyl group. In addition, a second contact angle is exists between the oxidized structure surface 83 and the working fluid (such as water), and the second contact angle is greater than the first contact angle.
As shown in 5C, a slash area inside the tube wall defined by the area 800 represents the second oxidized structure 83 formed on the inner wall. After Step 21, the oxidized structure formed in the area 801 may be regarded as a hydrophilic oxidized structure. After Step 22, compared with the oxidized structure in the area 801, the oxidized structure formed in the area 800 may be regarded as a hydrophobic oxidized area. Referring to FIG. 1 again, finally in Step 23, a processing procedure is performed on the metal tube so as to form a heat pipe. In Step 23, the processing procedure is divided into several stages. In the first stage, an end of the metal tube is closed; in the second stage, the metal tube is vacuumized; then in the third stage, the working fluid such as water is filled into the metal tube with one end being closed; subsequently, in the fourth stage, another end of the metal tube is closed, so as to form a structure with both ends being closed. Finally, surface processing and cleaning are performed on the heat pipe, so as to finish the heat pipe. After Step 23, in another embodiment, molding processing is performed on the heat pipe, so as to form different shapes of heat pipes, for example: U-shaped pipe, L-shaped pipe or ring-shaped pipe.
Referring to FIG. 6A, FIG. 6A is a schematic flow chart of another embodiment of the disclosure. In this embodiment, the capillary structure on the inner wall of the metal tube is modified to be an oxidized structure mainly through heating. In the method 3, through Step 30, a metal tube with two ends unclosed is also provided, where features of the metal tube is the same as those of the metal tube in the foregoing Step 20, and are not described herein again. Then in Step 31, the metal tube is placed in an aerobic environment with a first oxidizing temperature, and the first oxidized structure surface is obtained after a first oxidizing time. Taking copper as an example, the first oxidizing temperature is 80° C. to 150° C., and the first oxidizing time is 0 to 10 hours. A first contact angle exists between the first oxidized structure formed in Step 31 and the working fluid. In this embodiment, the metal tube is a copper tube, so the first oxidized structure is cuprous oxide. Then Step 32 is performed, in which another oxidizing processing is performed on partial area of the metal tube having the first oxidized structure surface, so as to form a second oxidized structure surface. As shown in FIG. 6B, in this embodiment, the manner for oxidizing processing is to place the first oxidized structure surface in an area 802 of the metal tube 80 into an aerobic environment with a second oxidizing temperature, and the second oxidized structure is obtained after a second oxidizing time. In this embodiment, the second oxidizing temperature is 250° C. to 450° C., and the second oxidizing time is 0.5 to 6 hours. The second oxidized structure surface 85 obtained through Step 32 has a second contact angle, and the second contact angle is smaller than the first contact angle of the first oxidized structure surface 84 (an area having a plurality of dots shown in FIG. 6B) in another area 803. It should be noted that, if the second oxidized structure 85 (such as a slash area inside the tube wall shown in FIG. 6B) is formed through heating, in order to prevent the heat conduction effect from affecting the area 803 that originally has the first oxidized structure, the area 803 may be cooled while the area 802 is heated. For example, the area 803 is cooled by means of ice-bath or liquid gas, so that a heat conduction effect when the area 802 is heated does not affect the area 803. In addition, apart from the heating manner, the oxidization in Step 32 may also be manners according to foregoing Equation (1) to Equation (4), namely, the soaking manner, in which the mixed reaction solution is enabled to contact the first oxidized structure surface in the area 802 of the metal tube 80, so that the metal tube having the first oxidized structure is modified by the mixed reaction solution, thereby forming a second oxidized structure surface 85. The second oxidized structure surface 85 may be a metal oxide or a metal hydroxide, for example, copper oxide or copper hydroxide. Referring to FIG. 6A again, after Step 32, similarly, in Step 33, a processing procedure is performed on the metal tube so as to form a heat pipe. The processing procedure is divided into several stages. In the first stage, an end of the metal tube is closed; in the second stage, the metal tube is vacuumized; then in the third stage, the working fluid such as water is filled into the metal tube with one end being closed; subsequently, in the fourth stage, another end of the metal tube is closed, so as to form a structure with both ends being closed. Finally, surface processing and cleaning are performed on the heat pipe, so as to finish the heat pipe. After Step 33, in another embodiment, molding processing is performed on the heat pipe, so as to form different shapes of heat pipes, for example: U-shaped pipe, L-shaped pipe or ring-shaped pipe.
Although the flows shown in FIG. 1 and FIG. 6A are methods for making oxidized structures of different contact angles in the same metal tube, in fact, two stages of the oxidizing procedure are not necessarily used at the same time. In an embodiment, as shown in FIG. 7A, in Step 40, a metal tube having a capillary structure and with two ends being unclosed is provided, for example, a copper pipe. Then in Step 41, the capillary structure on an inner wall defined by a specific area of the metal tube is oxidized, so as to form a hydrophilic area. The manner of Step 41 is the same as that of Step 21, and is not described herein again. Then, an end of the metal tube is closed, the metal tube is vacuumized, and a working fluid such as water is filled into the metal tube that has one end closed. Subsequently, another end of the metal tube is closed so as to form a structure with both ends being closed. Finally, surface processing and cleaning are performed so as to form a heat pipe. In another embodiment, as shown in FIG. 7B, in Step 50, a metal tube having a capillary structure and with two ends unclosed is provided, for example, a copper pipe. Then in Step 51, a capillary structure in a specific area of the metal tube is oxidized so as to form a hydrophobic area. The manner of Step 51 is the same as that of Step 31 or the process of Step 21 to Step 22, and is not described herein again. If the oxidization is performed through heating the metal tube as described in Step 31, an area not expected to be oxidized through heating may be cooled, for example, cooled by means of iced-bath or liquid gas, so as to prevent other areas from being affected by a heat conduction effect when the specific area is heated and oxidized into an oxidized structure. Then, an end of the metal tube is closed, the metal tube is vacuumized, and a working fluid such as water is filled into the metal tube with one end being closed. Subsequently, another end of the metal tube is closed so as to form a structure with both ends being closed. Finally, surface processing and cleaning are performed so as to form a heat pipe. Generally, taking a copper material as an example, when the internal of the heat pipe is purely the capillary structure, a contact angle thereof with the working fluid such as water is from 70 to 80 degrees. However, in the oxidized structure formed in an oxidizing manner according to the disclosure, a contact angle between the oxidized structure in the hydrophilic area and water may be less than 70 degrees, so the hydrophilic area can also be used as an evaporation area of the heat pipe; the contact angle between the oxidized structure in the hydrophobic area and water may be more than 80 degrees, so the hydrophobic area can also be used as a condensation area of the heat pipe.
Referring to FIG. 8, FIG. 8 is a schematic flow chart of another embodiment of a heat pipe processing method according to the disclosure. In this embodiment, the method 6 includes Step 60, in which a metal tube with two ends unclosed is provided. Referring to FIG. 9A, FIG. 9A is a schematic sectional view of a metal tube. An inner wall of the metal tube 70 has a capillary structure 71 (an area having a plurality of dots shown in FIG. 9A). The inner wall of the metal tube 70 may be divided into an evaporation area 700, a condensation area 701 and a heat insulating area 702. Then, in Step 61, the capillary structure 71 in the evaporation area 700 is oxidized, so as to modify the capillary structure 71 into a first oxidized structure, where the working fluid on the first oxidized structure surface has a first contact angle. In Step 62, an oxidized structure with desirable hydrophilicity may be formed through the tree oxidizing manners disclosed in the foregoing Step 21. In an embodiment, the first contact angle is less than 70 degrees. Then, in Step 62, the capillary structure 71 in the condensation area 701 is oxidized, so as to modify the capillary structure 71 into a second oxidized structure, where the working fluid on the second oxidized structure surface has a second contact angle. In Step 62, the hydrophobic oxidized structure may be formed through the oxidizing manner disclosed in Step 31 or the oxidizing manner disclosed in Step 21 and Step 22. In an embodiment, the second contact angle of the hydrophobic oxidized structure is more than 80 degrees. Then, in Step 63, a processing procedure is performed on the metal tube so as to form a heat pipe. The processing procedure is divided into several stages. In the first stage, an end of the metal tube is closed; in the second stage, the metal tube is vacuumized; then in the third stage, the working fluid such as water is filled into the metal tube with one end being closed; subsequently, in the fourth stage, another end of the metal tube is closed, so as to form a structure with both ends being closed. Finally, surface processing and cleaning are performed on the heat pipe, so as to finish the heat pipe. Referring to FIG. 9B, FIG. 9B is a schematic sectional view of a heat pipe formed in Step 63. The oxidized structure surface 72 (a slash area in the tube wall of the evaporation area 700 shown in FIG. 9B) in the evaporation area 700 is a hydrophilic oxidized structure, and can generate a contact angle less than 70 degrees. The oxidized structure surface 73 (the slash area in the tube wall of the condensation area 701 shown in FIG. 9B) in the condensation area 701 is a hydrophobic oxidized structure, and can generate a contact angle greater than 80 degrees.
Referring to Equation (6) below, Equation (6) is used for calculating a capillary pressure difference in the heat pipe.
ΔP is a capillary pressure difference; σ is a surface tension; θe is a contact angle between the working fluid and the capillary structure in the evaporation area; θc is a contact angle between the working fluid and the capillary structure in the condensation area; r is a capillary radius; evap represents the evaporation area; and cond represents the condensation area. In the conventional heat pipe, the amount of the filled working fluid is as high as the capillary structure; when the evaporation area is heated and the working fluid is volatilized, the contact angle of the working fluid in the evaporation area may be smaller than the contact angle in the condensation area, thereby generating a capillary pressure difference and driving the operation of the working fluid. Different capillary structures have different capillary radiuses. The design of changing the capillary structure may be used to improve the capillary pressure difference during operation. In addition, the capillary structure in a general heat pipe is made of a uniform material, so the contact angle between the working fluid and the capillary structure is a fixed value.
According to the manner in the disclosure, with the same radius of the capillary structure and with the surface tension of the working fluid being unchanged, the working fluid can have different wettability in the condensation area and the evaporation area through chemical surface modification, that is, the contact angle in the evaporation area and that in the condensation area are changed. After substitution into Equation (6), it is detected that the effect of improving the capillary pressure difference and generating the maximum heat conduction amount can also be achieved. Taking the embodiment shown in FIG. 9B of the disclosure as an example, in this embodiment, after the foregoing oxidizing process, the contact angle of the oxidized structure surface 72 in the evaporation area 700 may achieve 57 degrees approximately, while the contact angle of the oxidized structure surface 73 in the condensation area 701 may achieve 137 degrees approximately. Therefore, the working fluid (such as water) in the heat pipe 7 can have different wettability in the evaporation area 700 and in the condensation area 701 through chemical surface modification without changing the surface tension of the working fluid in the heat pipe, thereby achieving the effect of improving the capillary pressure difference and generating the maximum heat conduction amount.
For example, in an embodiment, the working fluid is water, the tube material of the heat pipe is copper, and the internal of the heat pipe is provided with a groove capillary structure. A total length of the pipe is 25 cm, a pipe diameter is 6 cm, a groove height is 0.34 cm, a groove width is 0.21 cm, and the total number of grooves is 55. Through the chemical surface modification processing, the contact angle between water and copper in the condensation area can be improved to 137 degrees. If the contact angle between water and copper is fixed at 78 degrees in the evaporation area, after the contact angles are substituted into the equation, the maximum heat conduction amount is calculated. The maximum heat conduction amount of the heat pipe is 128.3 W at this time. The maximum heat conduction amount of the conventional heat pipe is only 28.4 W. Upon comparison, the heat conduction amount of the capillary structure that undergoes the chemical oxidizing modification is significantly improved.
The exemplary implementations or embodiments of the technical solutions in the disclosure used for solving the problem are described above, which are not intended to limit the scope of the disclosure. Any equivalent change and modification made without departing from the content of the application scope of the disclosure or made according to the scope of the disclosure shall fall within the scope of the disclosure.
Patent Application
20140150997
