BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the present apparatus and method can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus and method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is a longitudinal cross-sectional view of a heat pipe in accordance with a first embodiment of the present invention;
FIG. 2 is a radial cross-sectional view of the heat pipe in accordance with the first embodiment, taken along line II-II of FIG. 1;
FIG. 3 is a longitudinal cross-sectional view of a heat pipe in accordance with a second embodiment of the present invention;
FIG. 4 is a longitudinal cross-sectional view of a heat pipe in accordance with a third embodiment of the present invention; and
FIG. 5 is a longitudinal cross-sectional view of a heat pipe in accordance with a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a heat pipe in accordance with a first embodiment of the present invention. The heat pipe comprises a casing 100 and a composite capillary wick 200 arranged to attach on an inner wall of the casing 100. A column-shaped vapor passage 300 is enclosed with an inner surface of the composite capillary wick 200 in a center of the casing 100. The casing 100 comprises an evaporating section 400 at one end and a condensing section 600 at an opposite end thereof, and a central section (i.e. adiabatic section) 500 located between the evaporating section 400 and the condensing section 600. The casing 100 is made of highly thermally conductive materials such as copper or copper alloys and filled with a working fluid (not shown), which acts as a heat carrier for carrying thermal energy from the evaporating section 400 to the condensing section 600. Heat that needs to be dissipated is first transferred to the evaporating section 400 of the casing 100 to cause the working fluid to evaporate. Then, the heat is carried by the working fluid in the form of vapor to the condensing section 600 where the heat is released to ambient environment, thus condensing the vapor into liquid. The condensed liquid is then brought back via the composite capillary wick to the evaporating section 400 where it is again available for evaporation.
The composite capillary wick 200 comprises a first type of capillary wick 250 which is a folded-type wick and a second type of capillary wick 240 which is one of a sintered-type wick and mesh-type wick. The first type of capillary wick 250 is defined on the inner wall of the casing 100 at the central and condensing sections 500, 600. Referring to FIG. 2, the first type of capillary wick 250 is formed by a plurality of metal sheets 222 tightly stacked together along a radial direction of the casing 100 with an outer metal sheet being attached to the inner wall of the casing 100. Each metal sheet 222 is folded with a cross-sectional configuration having a plurality of serrations disposed along a circle so as to form the first type of capillary wick 250 with a beehive-shaped structure in a radial direction of the casing 100. The metal sheet 222 can be stamped to define a plurality of pores or form a plurality of protruding portions. The capillary pore size and rate of the first type of capillary wick 250 is accurately controlled during manufacturing of the metal sheets 222. The first type of capillary wick 250 has a large pore size to make the condensed liquid return to the evaporating section 400 quickly and simultaneously lowers a flow resistance caused by adverse contact between the vapor and liquid at the central section 500 of the casing 100. The second type of capillary wick 240 is arranged on the inner wall of the casing 100 at the evaporating section 400 and has a high pore rate and a small pore size; as a result the liquid at the evaporating section 400 is then rapidly evaporated and the condensed liquid is rapidly drawn back to the evaporating section 400. The capillary pore size of the first type of capillary wick 250 is larger than that of the second type of capillary wick 240 so that the first type of capillary wick 250 at the central section 500 can provide a smaller flow resistance than the second type of capillary wick 240 at the evaporating section 400 for the condensed liquid as the condensed liquid is brought back to the evaporating section 400 via the central section 500.
In this embodiment, the composite capillary wick 200 has different types of capillary wick disposed in different sections of the heat pipe. The first type of capillary wick 250 has a relatively large average capillary pore size and therefore provides a relatively low flow resistance to the condensed liquid to flow therethrough, and meanwhile, the second type of capillary wick 240 has a relatively small average capillary pore size and accordingly develops a relatively large capillary force to the liquid. As a result, the first type of capillary wick 250 reduces the flow resistance that the condensed liquid encounters when flowing through the condensing and central sections 600, 500, and the second type of capillary wick 240 has a large capillary force and therefore the liquid is then rapidly drawn back to the evaporating section 400 from the central section 500 as the liquid reaches to a position adjacent to the evaporating section 400. The condensed liquid is returned back from the condensing section 600 in an accelerated manner. After the condensed liquid is returned back to the evaporating section 400, a next phase-change cycling will then begin. Thus, as a whole, the cycling of the working fluid is accelerated and therefore the total heat transfer capacity of the heat pipe is enhanced.
FIG. 3 illustrates a heat pipe in accordance with a second embodiment of the present invention. Main differences between the first and second embodiments are that in the second embodiment the composite capillary wick 210 comprises a second capillary wick 241 similar to the second type of capillary wick 240 in the first embodiment, a first type of capillary wick 251 similar to the first type of capillary wick 250 in the first embodiment and a third capillary wick 261. The second capillary wick 241 is arranged at the evaporating section 400 of the casing 100. The first type of capillary wick 251 is located at the central section 500 of the casing 100. The third capillary wick 261 is disposed at the condensing section 600 of the casing 100. The third capillary wick 261 is a sintered-type wick and has a larger capillary pore size than that of the second type of capillary wick 241 in the second embodiment so as to provide a high pore size and a low flow resistance for the condensing section 600 of the casing 100.
FIG. 4 illustrates a heat pipe in accordance with a third embodiment of the present invention. Main differences between the third and first embodiments are that in the third embodiment the thickness of the composite capillary wick 220 from the condensing section 600 to the evaporating section 400 via the central section 500 is gradually increased. The thickest point of the composite capillary wick 220 is received at the evaporating section 400 of the casing 100 so as to provide a large capillary wick force and absorb more of the working fluid at the evaporating section 400. The vapor passage 310 enclosed by the composite capillary wick 220 has a gradually decreasing radial cross-sectional area along a longitudinal direction of the casing 100 from the condensing section 600 toward the evaporating section 400. The other structure of the heat pipe of the third embodiment is similar to that of the first embodiment. Heat exchange between the working fluid and the inner wall of the casing 100 is greatly improved and the heat transfer efficiency of the heat pipe is improved as a result.
FIG. 5 illustrates a heat pipe in accordance with a fourth embodiment of the present invention. Main differences between the fourth and second embodiments are that in the fourth embodiment the thickness of the composite capillary wick 230 from the condensing section 600 to the evaporating section 400 via the central section 500 is gradually increased. The thickest point of the composite capillary wick 230 is received in the evaporating section 400 of the casing 100 so as to provide a large capillary wick force and absorb more of the working fluid at the evaporating section 400. The vapor passage 320 enclosed by the composite capillary wick 230 has a gradually decreasing radial cross-sectional area along a longitudinal direction of the casing 100 from the condensing section 600 toward the evaporating section 400. The other structure of the heat pipe of the third embodiment is similar to that of the second embodiment.
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.
Patent Application
20070246194
