Thermal management is an issue which is essential in all kinds of categories, such as permafrost stabilization, electronic equipment cooling, and aerospace, etc. Heat pipe is a common application means in plenty of thermal management methods. Heat pipe is a two-phase heat conduction device, which can conduct heat with high efficiency and effectively.
Please refer to FIG. 1, which is a structural diagram showing a traditional heat pipe device in accordance with the prior art. In FIG. 1, the heat pipe 1 is mainly configured by the tube 11, the wick structure 12 and the end caps 13. The interior of the heat pipe 1 is maintained in a low-pressured situation, and the adequate amount of the low-boiling point liquid 181 is injected in the interior thereof. The liquid evaporates easily because of its low boiling point. The wick structure 12 is configured by a capillary porous material, and is attached in the internal sidewall of the tube 11. One end of the heat pipe 1 is the evaporating end 151, and the other end thereof is the condensing end 152. When one end of the heat pipe 1 is heated, the liquid in the capillary tube evaporates quickly as the high-pressured vapor 182. The vapor 182 flows to the other end of the heat pipe 1 under the pressure gradient, and releases the heat to condense as the liquid 181 de novo. Then the liquid 181 flows to the evaporating end 151 along the capillary porous material by the action of the capillary force again. The circulation repeats infinitely, and the heat can be transported from one end of the heat pipe 1 to the other end thereof. The circulation proceeds fast, and the heat can be conducted continuously.
The wick structure of the traditional heat pipe is distributed in the inner surface of all the heat pipe, and the cell size of the wick structure thereof is limited. Although the capillary force can be increased because of the small cell size, at the same time, the resistance of liquid flow is also increased. This contradictory causes a barrier in increasing the performance of the traditional heat pipe. Meanwhile, the limitation of the capillary force also causes the limitation of the length of heat pipe. In addition, since the wick structure of the traditional heat pipe is configured in the inner surface of all the heat pipe, the vaporization is formed in the inner surface thereof when the heat pipe is heated. When the applied heat load or the wall temperature becomes excessively, boiling of the liquid in the wick structure may occur. The vapor bubbles generated inside the wick structure may block the liquid return paths and the wick can dry out.
In order to overcome the drawbacks of the abovementioned traditional heat pipe, a modified loop heat pipe is developed in recent years. The vapor line and the liquid line are designed as a loop. Please refer to FIG. 2(A) and FIG. 2(B), which are structural diagrams showing a loop heat pipe device in accordance with the prior art. In FIG. 2(A), the heat pipe 2 includes the evaporator 21, the condenser 23, the compensation chamber 25, the vapor line 231 and the liquid line 233. Among these, the evaporator 21 is a cylinder tube, and the interior of the evaporator 21 includes a sidewall 210, the primary wick structure 211, the secondary wick structure 212 and the non-wick flow path 214. The sidewall 210 toward inside is a grooved shape, and the axial vapor channel 213 is formed in the linkage between the primary wick structure 211 and the sidewall 210. The liquid line 233 is referred to as the bayonet, which directs the liquid all the way to the closed end of the evaporator 21. After the liquid exits the bayonet into the evaporator core, most of the liquid wets the primary wick structure 211 and the secondary wick structure 212. The excess liquid goes back to the compensation chamber 25 through the non-wick flow path 214. The condenser 23 is connected to or near to a heat sink 93 such as cooling sheet.
When the evaporator 21 is connected to or closed to an external heat source 91, the evaporator 21 will absorb the heat from the external heat source 91 and causes the internally-stored condensate 262 to evaporate as the vapor 261. Furthermore, the vapor 261 flows along the vapor line 231 because of the pressure gradient. When reaching the condenser 23, the vapor emits the heat because of the influence of the heat sink 93, and condenses as the condensate 262 again. When the loop heat pipe (LHP) is operating, the flow in the LHP is driven by surface tension developed in the capillary of the primary wick structure 211. Menisci form at the outer surface of the primary wick structure 211. The capillary action draws the liquid at the inner surface of the primary wick structure 211 to the outer surface of the primary wick structure 211. The liquid is then vaporized across the meniscus and gains the pressure, required as the pumping force to drive the whole system. The compensation chamber 25 is used for storing the excess condensate 262, and for adjusting the amount of the working fluid under the different intensities of the external heat source 91 in all circulation system.
The above heat pipe evaporators in the prior art are all cylinders. With regard to the plate heat source such as electronic chips, etc., the heat pipe evaporator needs the switching element to switch a cylinder to a plate benefit for the heat dissipation design of the plate heat source. Such a design increases the uncertainty of the switching element, and increases the thermal resistance so as to influence the efficiency of heat conductivity.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.