Patent Publication Number: US-2019178583-A1

Title: Thermosyphon-type heat dissipation device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 62/598,130 filed Dec. 13, 2017, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a thermosyphon-type heat dissipation device, and more particularly to a liquid cooling heat dissipation device that is operated according to a thermosyphon mechanism. 
     BACKGROUND OF THE INVENTION 
     A conventional water-cooling heat dissipation device comprises a heat-absorbing head, a radiator, a fan and a pump. These components are connected with each other through a piping system. A liquid working medium is filled in a circulation path. During operation of the water-cooling heat dissipation device, the heated working medium is transferred from the heat-absorbing head to the radiator. In addition, the working medium is cooled down by the fan and fins. Afterwards, the working medium is returned back to the heat-absorbing head by the pump. 
     In case that the water-cooling architecture is able to undergo the liquid-gas transformation like a thermosyphon-type heat dissipation device, more heat from the heat source can be removed. In other words, the conventional water-cooling heat dissipation device needs to be improved. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, there is provided a thermosyphon-type heat dissipation device. The thermosyphon-type heat dissipation device includes a heat-absorbing head and a radiator. The heat-absorbing head includes a first outlet, a first inlet, an evaporation chamber and a liquid return chamber. The first outlet is connected with the evaporation chamber. The first inlet is connected with the liquid return chamber. The evaporation chamber and the liquid return chamber are in communication with each other through a gap. An inner space of the evaporation chamber is larger than an inner space of the liquid return chamber. The radiator includes a second inlet and a second outlet. The second inlet is in communication with the first outlet. The second outlet is in communication with the first inlet. 
     In an embodiment, the thermosyphon-type heat dissipation device further includes a pipe. The pipe is connected with the first outlet and the second inlet, and the pipe is connected with the second outlet and the first inlet. 
     In an embodiment, the pipe is a hard conduit or a flexible tube. 
     In an embodiment, the pipe is made of a plastic material or a non-plastic material. 
     In an embodiment, the thermosyphon-type heat dissipation device further includes a pump. The pump is connected between the second outlet and the first inlet. 
     In an embodiment, the heat-absorbing head comprises a top cover and a base, and the liquid return chamber and the evaporation chamber are defined by the top cover and the base collaboratively. A bottom surface of the base is in thermal contact with a heat source. The shortest distance between the gap and the bottom surface of the base is smaller than the shortest distance between the first outlet and the bottom surface of the base. 
     In an embodiment, the top cover has a guiding slant. When a working medium is heated, the working medium is guided to the first outlet by the guiding slant. 
     In an embodiment, the radiator includes a first compartment, a second compartment, a third compartment and a fourth compartment. The first compartment is in communication with the second inlet. The fourth compartment is in communication with the second outlet. The first compartment and the second compartment are in communication with each other through a first fluid channel group. The second compartment and the third compartment are in communication with each other through a second fluid channel group. The third compartment and the fourth compartment are in communication with each other through a third fluid channel group. A flowing direction of the first fluid channel group is reverse to a flowing direction of the second fluid channel group. The flowing direction of the second fluid channel group is reverse to a flowing direction of the third fluid channel group. 
     In an embodiment, the first compartment and the third compartment are located at a first side of the radiator, the first compartment is located over the third compartment, the second compartment and the fourth compartment are located at a second side of the radiator, and the second compartment is located over the fourth compartment. 
     In an embodiment, the radiator includes plural compartments and plural fluid channels in communication with the plural compartments. Moreover, one of the plural compartments is in communication with the second outlet and has the smallest inner space among the plural compartments. 
     In an embodiment, the radiator includes plural compartments and plural fluid channels in communication with the plural compartments. A first compartment of the plural compartments is in communication with the second outlet. The first compartment is in communication with a second compartment of the plural compartments through a first fluid channel group. An inner space of the second compartment is larger than an inner space of the second compartment. 
     Preferably, when the thermosyphon-type heat dissipation device is installed in an electronic device, the second inlet is at a level higher than the second outlet. 
     Preferably, when the thermosyphon-type heat dissipation device is installed in an electronic device, the first outlet is at a level higher than the first inlet. 
     In an embodiment, a working medium is filled in the thermosyphon-type heat dissipation device, and the working medium is an engineered fluid with low boiling point or water. During a process of heating or cooling the working medium, the working medium undergoes a two-phase liquid-gas or gas-liquid transformation. 
     In accordance with another aspect of the present invention, there is provided a thermosyphon-type heat dissipation device. The thermosyphon-type heat dissipation device includes a heat-absorbing head and a radiator. The heat-absorbing head includes a first outlet, a first inlet, a top cover, a base, an evaporation chamber, a liquid return chamber and a gap. The liquid return chamber and the evaporation chamber are defined by the top cover and the base collaboratively. The first outlet is connected with the evaporation chamber. The first inlet is connected with the liquid return chamber. The evaporation chamber and the liquid return chamber are in communication with each other through the gap. A working medium is filled in the heat-absorbing head. When the working medium in the evaporation chamber is heated, the working medium is transformed from a liquid state into a gaseous state and the gaseous working medium is outputted from the first outlet. The working medium in the liquid return chamber is in the liquid state and transferred to the evaporation chamber through a capillary action of the gap. The radiator includes a second inlet and a second outlet. The second inlet is in communication with the first outlet, the second outlet is in communication with the first inlet. The working medium is transformed from the gaseous state into the liquid state by the radiator. 
     In an embodiment, the thermosyphon-type heat dissipation device further includes a pipe. The pipe is connected with the first outlet and the second inlet, and the pipe is connected with the second outlet and the first inlet. 
     In an embodiment, the thermosyphon-type heat dissipation device further includes a pump. The pump is connected between the second outlet and the first inlet. 
     In an embodiment, a bottom surface of the base is in thermal contact with a heat source, and the shortest distance between the gap and the bottom surface of the base is smaller than the shortest distance between the first outlet and the bottom surface of the base. 
     In an embodiment, the top cover has a guiding slant. When a working medium is heated, the working medium is guided to the first outlet by the guiding slant. 
     In an embodiment, the radiator includes a first compartment, a second compartment, a third compartment and a fourth compartment. The first compartment is in communication with the second inlet. The fourth compartment is in communication with the second outlet. The first compartment and the second compartment are in communication with each other through a first fluid channel group. The second compartment and the third compartment are in communication with each other through a second fluid channel group. The third compartment and the fourth compartment are in communication with each other through a third fluid channel group. A flowing direction of the first fluid channel group is reverse to a flowing direction of the second fluid channel group. The flowing direction of the second fluid channel group is reverse to a flowing direction of the third fluid channel group. 
     In an embodiment, the first compartment and the third compartment are located at a first side of the radiator, the first compartment is located over the third compartment, the second compartment and the fourth compartment are located at a second side of the radiator, and the second compartment is located over the fourth compartment. 
     In an embodiment, the radiator includes plural compartments and plural fluid channels in communication with the plural compartments. Moreover, one of the plural compartments is in communication with the second outlet and has the smallest inner space among the plural compartments. 
     In an embodiment, the radiator includes plural compartments and plural fluid channels in communication with the plural compartments. A first compartment of the plural compartments is in communication with the second outlet. The first compartment is in communication with a second compartment of the plural compartments through a first fluid channel group. An inner space of the second compartment is larger than an inner space of the second compartment. 
     Preferably, when the thermosyphon-type heat dissipation device is installed in an electronic device, the second inlet is at a level higher than the second outlet. 
     Preferably, when the thermosyphon-type heat dissipation device is installed in an electronic device, the first outlet is at a level higher than the first inlet. 
     In an embodiment, the working medium is an engineered fluid with low boiling point or water. During a process of heating or cooling the working medium, the working medium undergoes a two-phase liquid-gas or gas-liquid transformation. 
     In accordance with a further aspect of the present invention, there is provided a heat-absorbing head. The heat-absorbing head includes an inlet, an outlet, an evaporation chamber and a liquid return chamber. The outlet is connected with the evaporation chamber. The inlet is connected with the liquid return chamber. When the heat-absorbing head is in horizontal placement and attached on a heat source, the inlet is located at a lateral side of the heat-absorbing head. When the heat-absorbing head is in vertical placement and attached on the heat source, the inlet is located at a lower position of the heat-absorbing head. 
     In an embodiment, the evaporation chamber and the liquid return chamber are in communication with each other through a gap, and the gap includes plural slits. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic perspective view illustrating a thermosyphon-type heat dissipation device in a horizontal placement according to an embodiment of the present invention; 
         FIG. 1B  is a schematic perspective view illustrating a thermosyphon-type heat dissipation device in a vertical placement according to an embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view illustrating the heat-absorbing head of the thermosyphon-type heat dissipation device as shown in  FIG. 1A  and taken along the line  2 - 2 ; 
         FIG. 3  is a schematic cutaway view illustrating the heat-absorbing head of the thermosyphon-type heat dissipation device according to an embodiment of the present invention; 
         FIG. 4  is another schematic cutaway view illustrating the heat-absorbing head of the thermosyphon-type heat dissipation device according to an embodiment of the present invention; 
         FIG. 5  is a schematic cross-sectional view illustrating the radiator of the thermosyphon-type heat dissipation device as shown in  FIG. 1A  and taken along the line  5 - 5 ; and 
         FIG. 6  schematically the fluid channel design of another radiator used in the thermosyphon-type heat dissipation device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1A  is a schematic perspective view illustrating a thermosyphon-type heat dissipation device in a horizontal placement according to an embodiment of the present invention.  FIG. 1B  is a schematic perspective view illustrating a thermosyphon-type heat dissipation device in a vertical placement according to an embodiment of the present invention.  FIG. 2  is a schematic cross-sectional view illustrating the heat-absorbing head of the thermosyphon-type heat dissipation device as shown in  FIG. 1A  and taken along the line  2 - 2 . In an embodiment of the present invention, a thermosyphon-type heat dissipation device  1  is provided. The thermosyphon-type heat dissipation device  1  comprises a heat-absorbing head  11  and a radiator  12 . The heat-absorbing head  11  comprises an outlet  111  and an inlet  112 . The radiator  12  comprises an outlet  121  and an inlet  122 . The outlet  111  of the heat-absorbing head  11  is in communication with the inlet  122  of the radiator  12 . The outlet  121  of the radiator  12  is in communication with the inlet  112  of the heat-absorbing head  11 . In some embodiments, the outlet  111  of the heat-absorbing head  11  and the inlet  122  of the radiator  12  are integrated with each other or directly coupled to each other. In some embodiments, the outlet  121  of the radiator  12  and the inlet  112  of the heat-absorbing head  11  are integrated with each other or directly coupled to each other. Moreover, the thermosyphon-type heat dissipation device  1  is equipped with a piping system to connect the heat-absorbing head  11  and the radiator  12 . For example, the outlet  111  of the heat-absorbing head  11  and the inlet  122  of the radiator  12  are connected with each other through a pipe  13 , and the outlet  121  of the radiator  12  and the inlet  112  of the heat-absorbing head  11  are connected with each other through a pipe  14 . The pipes  13  and  14  are hard conduits (e.g., plastic hard conduits or flexible metallic conduit) or flexible tubes. According to the practical requirements or applications, the pipes  13  and  14  are made of a plastic material or a non-plastic material (e.g., a metallic material). The materials of the pipes  13  and  14  are not restricted. 
     In some other embodiments, the heat-absorbing head  11  has an additional outlet, and the radiator  12  has an additional inlet. The additional outlet of the heat-absorbing head  11  and the additional inlet of the radiator  12  are connected with each other through an additional pipe  13 . Similarly, the heat-absorbing head  11  has an additional inlet, and the radiator  12  has an additional outlet. The additional inlet of the heat-absorbing head  11  and the additional outlet of the radiator  12  are connected with each other through an additional pipe  14 . 
     Please refer to  FIG. 1A ,  FIG. 1B  and  FIG. 2  again. The heat-absorbing head  11  of the thermosyphon-type heat dissipation device  1  may be horizontally or vertically attached on a heat source  15 . For example, the heat source  15  is mounted on a PCB  16  within an electronic device  18 . Consequently, the space utilization flexibility of the electronic device with the thermosyphon-type heat dissipation device  1  will be enhanced. 
     Please refer to  FIG. 2 . The heat-absorbing head  11  comprises a top cover  113  and a base  114 . A bottom surface  1142  of the base  114  is in thermal contact with the heat source  15 . For example, the base  114  is directly attached on the heat source  15 , or an intermediate medium (a thermal grease, an adhesive or a soldering material) is clamped between the base  114  and the heat source  15 . Moreover, a liquid return chamber  115  and an evaporation chamber  116  are defined by the top cover  113  and the base  114  of the heat-absorbing head  11  collaboratively. The inlet  112  is connected with the liquid return chamber  115 . The outlet  111  is connected with the evaporation chamber  116 . Preferably, the vacuum state of the heat-absorbing head  11  is previously created, and a working medium is filled in the heat-absorbing head  11 . When the working medium in the evaporation chamber  116  absorbs heat, the working medium is transformed into the gaseous working medium. The gaseous working medium is ejected toward the outlet  111 . There is a gap  117  between the evaporation chamber  116  and the liquid return chamber  115 . The evaporation chamber  116  and the liquid return chamber  115  are in communication with each other through the gap  117 . Due to the gap  117 , the gaseous working medium in the evaporation chamber  116  is not returned back to the liquid return chamber  115 . Moreover, because of the capillary action of the gap  117 , the working medium in the liquid return chamber  115  can be continuously moved (or transferred) to the evaporation chamber  116 . In the heat-absorbing head  11 , the inner space of the evaporation chamber  116  is larger than the inner space of the liquid return chamber  115 . Consequently, the possibility of returning the gaseous working medium in the evaporation chamber  116  back to the liquid return chamber  115  will be largely reduced. 
     In this embodiment, the gap  117  is formed in a stopping wall  1131  that is extended downwardly from the top cover  113 . Preferably, the gap  117  runs through the stopping wall  1131 . The position or the structure of the gap  117  is not restricted. In another embodiment, the gap  117  is formed in a stopping wall that is extended upwardly from the base  114 . Alternatively, a portion of the top cover  113  and a portion of the base  114  at the junction region are not connected with each other or partially connected with each other to define the gap  117 . That is, the way of defining the gap  117  is not restricted. Preferably, the installation position of the gap is specially designed. For example, the shortest distance D 117  between the gap  17  and the bottom surface  1142  of the base  114  is smaller than the shortest distance D 111  between the outlet  111  and the bottom surface  1142  of the base  114 . Consequently, after the working medium is heated and evaporated, the working medium is moved toward the outlet  111  at the higher position because of the structural and pressure relationships. That is, the gaseous working medium is not moved toward the gap  117 , which is located at the lower position and full of the liquid working medium. 
     Please refer to the cross-sectional view of  FIG. 2  and the cutaway view of the heat-absorbing head  11  of  FIG. 3 . The heat-absorbing head  11  further comprises a boiling enhancement structure  1141 . The boiling enhancement structure  1141  is formed on the base  114  for facilitating boiling the working medium. For example, the boiling enhancement structure  1141  comprises plural skived fins that are closely and densely arranged, or the boiling enhancement structure  1141  is another three-dimensional structure with a large surface area. When the bottom surface  1142  of the base  114  is in contact with the heat source  15 , the boiling enhancement structure  1141  absorbs the heat from the heat source  15  at a faster rate. Consequently, the working medium is vaporized into the gaseous state more quickly. Moreover, since the structure of the evaporation chamber  116  is specially designed, the gaseous working medium is ejected toward the outlet  111   
     During the operation of the thermosyphon-type heat dissipation device  1 , the working medium is filled in the thermosyphon-type heat dissipation device  1 . In accordance with the present invention, the working medium is water or an engineered fluid with low boiling point. For example, the working medium is 3M Fluorinert FC-72 (boiling point is 56° C.), 3M Novec Fluids 7000 (boiling point is 34° C.) or 3M Novec Fluids 7100 (boiling point is 61° C.). The example of the working medium is not restricted as long as the working medium flowing through the boiling enhancement structure  1141  is transformed into the gaseous state. Moreover, during the expanding and pressuring process, a great deal of heat is removed. 
       FIG. 3  is a schematic cutaway view illustrating the heat-absorbing head of the thermosyphon-type heat dissipation device according to an embodiment of the present invention. The design of the evaporation chamber  116  of the heat-absorbing head  11  can be seen from  FIG. 1A ,  FIG. 2  and  FIG. 3 . As shown in these drawings, the evaporation chamber  116  is gradually widened in the direction from the liquid return chamber  115  (or the gap  117 ) to the outlet  111 . As shown in the cross-sectional view of the heat-absorbing head  11  of  FIG. 2 , an inner surface of the top cover  113  has a guiding slant  1132 . The guiding slant  1132  is located over the base  114  (or especially over the boiling enhancement structure  1141 ). Due to the guiding slant  1132 , the gaseous working medium (or the heated mixture of the gaseous working medium and the liquid working medium) is guided in the direction A toward the outlet  111  of the heat-absorbing head  11 . 
     Please refer to  FIG. 1A  and  FIG. 1B . The thermosyphon-type heat dissipation device  1  is specially designed to allow the working medium to be stably transferred in one direction. For example, the height H 122  of the inlet  122  of the radiator  12  is higher than the height H 111  of the outlet  111  of the heat-absorbing head  11 , and the height H 122  of the inlet  122  of the radiator  12  is higher than the height H 121  of the outlet  121  of the radiator  12 . Consequently, during the operation of the thermosyphon-type heat dissipation device  1 , the gaseous working medium is vaporized upwardly and fed into the inlet  122  of the radiator  12 . After the gaseous working medium is transferred through the radiator  12 , the gaseous working medium is transformed into the liquid state through condensation. The working medium flows to the outlet  121  of the radiator  12  along the gravity direction. Then, the working medium is returned to the liquid return chamber  115  of the heat-absorbing head  11  through the pipe  14 . Consequently, the self-circulation efficacy is achieved. 
     For allowing the working medium to be smoothly transferred from the heat-absorbing head  11  to the radiator  12  or returned from the radiator  12  to the heat-absorbing head  11 , the thermosyphon-type heat dissipation device  1  is additionally equipped with a pump. In an embodiment, the pump is connected between the outlet  121  of the radiator  12  and the inlet  112  of the heat-absorbing head  11 . As shown in  FIG. 1A , the pipe  14  is additionally connected with a pump  17 . After the working medium is cooled down, the working medium can be smoothly moved from the radiator  12  to the heat-absorbing head  11  by the pump  17 . Consequently, the backflow problem is avoided. In another embodiment, the pump is connected between the outlet  111  of the heat-absorbing head  11  and the inlet  122  of the radiator  12 . For example, the pipe  13  is additionally connected with a pump (not shown). Due to the pump, the working medium can be smoothly moved from the heat-absorbing head  11  to the radiator  12 . As mentioned above, the working medium used in the present invention is able to undergo the two phase transformation. Consequently, the selection of the pump is important. Preferably, the pump is capable of withstanding the cavitation effect, the formation of vapor cavities or the formation of the bubbles. Moreover, the number of the pump is not restricted. For example, plural pumps  17  are connected with the pipe  13  or the pipe  14  in series. In case that the thermosyphon-type heat dissipation device  1  comprises plural pipes  13  or  14 , plural pumps  17  are connected with the pipes in parallel. That is, the arrangement of the pumps is not restricted. 
     Please refer to  FIG. 1A  and  FIG. 1B  again. As mentioned above, the heat-absorbing head  11  of the thermosyphon-type heat dissipation device  1  may be in the horizontal placement or the vertical placement. In case that the heat-absorbing head  11  is horizontally placed (see  FIG. 1A ), the inlet  112  of the heat-absorbing head  11  is located at a lateral side of the heat-absorbing head  11 . In case that the heat-absorbing head  11  is vertically placed and attached on the heat source (see  FIG. 1B ), the inlet  112  of the heat-absorbing head  11  is located at a lower position of the heat-absorbing head  11 . Under this circumstance, the height H 111  of the outlet  111  of the heat-absorbing head  11  is higher than the height H 112  of the inlet  112  of the heat-absorbing head  11 . In addition, the height H 112  of the inlet  112  of the heat-absorbing head  11  is lower than the height H 121  of the outlet  121  of the radiator  12  or lower than the height H 17  of the pump  17 . In this context, the heights of the outlets, the inlets and the pump indicate the vertical distances from the same horizontal plane (e.g., a bottom plate or a casing of the electronic device). In case that the thermosyphon-type heat dissipation device  1  is equipped with the pump  17 , the influence of the gravity force on the thermosyphon-type heat dissipation device  1  will be reduced. Under this circumstance, the heights of the outlets, the inlets and the pump are not restricted. 
       FIG. 4  is another schematic cutaway view illustrating the heat-absorbing head  11  of the thermosyphon-type heat dissipation device  1  according to an embodiment of the present invention. In this cutaway view, the liquid return chamber  115  and the gap  117  are shown. After the liquid working medium is returned back to the heat-absorbing head  11  through the pipe  14 , the liquid working medium is not directly transferred to the evaporation chamber  116  of the heat-absorbing head  11 . That is, the liquid working medium is stored in the liquid return chamber  115  of the heat-absorbing head  11  and then transferred to the evaporation chamber  116  through the capillary action. In an embodiment, the gap  117  is composed of at least one slit or opening. In the embodiment of  FIG. 4 , the gap  117  is composed of plural slits. The distribution range of the plural slits is substantially equal to width of the liquid return chamber  115  or contacted with both ends of the liquid return chamber  115 . Consequently, even if the heat-absorbing head  11  is in the vertical placement (see FIG.  1 B), the working medium can be transferred to the evaporation chamber  116  through a portion of the gap  117 . 
       FIG. 5  schematically the fluid channel design of the radiator  12  used in the thermosyphon-type heat dissipation device  1  of this embodiment. As shown in this cross-sectional view of  FIG. 5 , the inner portion of the radiator  12  comprises a first compartment  123 A, a second compartment  123 B, a third compartment  123 C, a fourth compartment  123 D, three fluid channel groups and plural fins  125 . The fins  125  are arranged between the fluid channels. The first compartment  123 A and the third compartment  123 C are located at the same side with the inlet  122 . The first compartment  123 A is located over the third compartment  123 C. A partition wall  126  is arranged between the first compartment  123 A and the third compartment  123 C. The second compartment  123 B and the fourth compartment  123 D are located at the same side with the outlet  121 . The second compartment  123 B is located over the fourth compartment  123 D. Similarly, a partition wall  127  is arranged between the second compartment  123 B and the fourth compartment  123 D. 
     Please refer to  FIG. 5  again. The first fluid channel group  124 A is connected between the first compartment  123 A and the second compartment  123 B. Consequently, the first compartment  123 A and the second compartment  123 B are in communication with each other. After the gaseous working medium (or the mixture of the gaseous working medium and the liquid working medium) is fed into the first compartment  123 A through the inlet  122  of the radiator  12 , the gaseous working medium (or the mixture of the gaseous working medium and the liquid working medium) is split and transferred to the second compartment  123 B through the first fluid channel group  124 A. The second fluid channel group  124 B is connected between the second compartment  123 B and the third compartment  123 C. Consequently, the second compartment  123 B and the third compartment  123 C are in communication with each other. The flowing direction of the working medium in the second fluid channel group  124 B is reverse to the flowing direction of the working medium in the first fluid channel group  124 A. After the working medium is collected in the second compartment  123 B, the working medium is transferred to the third compartment  123 C through the second fluid channel group  124 B. The third fluid channel group  124 C is connected between the third compartment  123 C and the fourth compartment  123 D. Consequently, the third compartment  123 C and the fourth compartment  123 D are in communication with each other. The flowing direction of the working medium in the third fluid channel group  124 C is reverse to the flowing direction of the working medium in the second fluid channel group  124 B. After the working medium is collected in the third compartment  123 C, the working medium is transferred to the fourth compartment  123 D through the third fluid channel group  124 C. Due to the S-shaped fluid channels, the working medium is naturally moved from the higher level to the lower level along the gravity direction. Moreover, since the inner space of each compartment is larger than the diameter of each fluid channel, the working medium is continuously transferred in one direction without backflow. Finally, the working medium is outputted from the outlet  121  of the radiator  12 . 
     While the working medium is moved in the radiator  12 , the heat energy contained in the working medium is transmitted to the fins  125  through the fluid channels of the fluid channel groups  124 A,  124 B and  124 C. With the cooperation of a fan (not shown) or an airflow generation device to remove the heat, the working medium is transformed from the gaseous state to the liquid state and the working medium is cooled down. Then, the working medium is returned back to the liquid return chamber  115  of the heat-absorbing head  11 . Then, the next liquid-gas circulation process will be performed. 
     For facilitating the operation of the pump  17 , the working medium has to be in the liquid state when the working medium is outputted from the outlet  121  of the radiator  12 . In order to achieve this purpose, the inner space of the compartment  123 D in communication with the outlet  121  of the radiator  12  is the smallest among the compartments. Alternatively, the inner space of the second last compartment  123 C is larger than the inner space of the last compartment  123 D. The diameter of the third fluid channel group  124 C connected between the compartment  123 C and the compartment  123 D is much smaller than the compartments  123 C and  123 D. Consequently, after the working medium is transformed into the liquid state, the working medium is transferred to the compartment  123 D and outputted from the outlet  121 . 
     The fluid channels in the radiator  12  are not restricted to the S-shaped configuration of  FIG. 5 . It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention.  FIG. 6  schematically the fluid channel design of another radiator  12 ′ used in the thermosyphon-type heat dissipation device of the present invention. The configuration of  FIG. 6  is substantially the image configuration of  FIG. 5 . As shown in this cross-sectional view of  FIG. 6 , the inner portion of the radiator  12 ′ comprises a first compartment  123 A′, a second compartment  123 B′, a third compartment  123 C′, a fourth compartment  123 D′, three fluid channel groups and plural fins  125 ′. The fins  125 ′ are arranged between the fluid channels. The first compartment  123 A′ and the third compartment  123 C′ are located at the same side with the inlet  122 ′. The second compartment  123 B′ and the fourth compartment  123 D′ are located at the same side with the outlet  121 ′. A partition wall  126 ′ is arranged between the first compartment  123 A′ and the third compartment  123 C′. Similarly, a partition wall  127 ′ is arranged between the second compartment  123 B′ and the fourth compartment  123 D′. The first fluid channel group  124 A′ is connected between the first compartment  123 A′ and the second compartment  123 B′. After the gaseous working medium (or the mixture of the gaseous working medium and the liquid working medium) is fed into the first compartment  123 A′ through the inlet  122 ′ of the radiator  12 ′, the gaseous working medium (or the mixture of the gaseous working medium and the liquid working medium) is split and transferred to the second compartment  123 B′ through the first fluid channel group  124 A′. The second fluid channel group  124 B′ is connected between the second compartment  123 B′ and the third compartment  123 C′. After the working medium is collected in the second compartment  123 B′, the working medium is transferred to the third compartment  123 C′ through the second fluid channel group  124 B′. The third fluid channel group  124 C′ is connected between the third compartment  123 C′ and the fourth compartment  123 D′. After the working medium is collected in the third compartment  123 C′, the working medium is transferred to the fourth compartment  123 D′ through the third fluid channel group  124 C′. Due to the S-shaped fluid channels, the working medium is naturally moved from the higher level to the lower level along the gravity direction and finally outputted from the outlet  121 ′ of the radiator  12 ′. While the working medium is moved in the radiator  12 ′, the heat energy contained in the working medium is transmitted to the fins  125 ′ through the fluid channel groups  124 A′,  124 B′ and  124 C′. With the cooperation of a fan (not shown) or an airflow generation device to remove the heat, the working medium is transformed from the gaseous state to the liquid state and the working medium is cooled down. 
     The inner fluid channel configurations as shown in  FIG. 5  and  FIG. 6  are presented herein for purpose of illustration and description only. In some other embodiments, the fluid channels allow the working medium to be transferred from left to right, from right to left, from top to bottom, from upper left to lower right or from the upper right to the lower left. The number of the compartments is not restricted. That is, the thermosyphon-type heat dissipation device may have more (e.g., 5 or 6) compartments or less (e.g., 3) compartments. The fluid channel configuration is not restricted as long as the inlet  122  of the radiator  12  is at the level higher than the outlet  121  of the radiator  12 . 
     In the thermosyphon-type heat dissipation device  1  of the present invention, the base  114  of the heat-absorbing head  11  is made of a metallic material with good thermal conductivity (e.g., silver, copper, gold, aluminum, iron or alloy of the above metallic materials) or a nonmetallic material with good thermal conductivity (e.g., graphite). The top cover  113  and the base  114  are made of the identical thermal conductive material or different thermal conductive materials. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all modifications and similar structures.