Experimental System Design And Heat Transfer Characteristics Research On A Vapor-liquid Separated Flat Loop Heat Pipe Evaporator

As we all known, cooling device of high heat flux density components is extremely critical to promote runtime reliability, optimize performance and extend lifetime of the product. With the continuous development of large application servers, data processing centers and aerospace equipment make thermal management become more and more stringent, requiring thermal solutions with both high efficient heat dissipation performance and low manufacture cost. As a part of traditional LHP evaporator, wick plays a key role in driving liquid medium at condenser section flow back to evaporation section to maintain the operation process. However, low heat and mass transfer efficiency always accompany with LHP operation process due to the existence of vapor-liquid interface in the wick. More specifically, increasing penetration resistance in the wick resulting from the vapor partial pressure makes it difficult for the working medium to transport in LHP. In the meantime, it’s hard to maintain a single phase change process in LHP with traditional structural design, so vapor-liquid two-phase flow forming in the LHP lower its heat transfer efficiency.An excellent overall LHP performance is contributed by the good start-up and operational performance and lower thermal resistance. In this paper, a phase change space was placed between wick and the heating surface to eliminate vapor-liquid interface from wick, utilizing phase change force to drive working medium circulation. As liquid continually drop in the heating surface and vapor get away from phase change space, high efficiency heat transfer was realized through relative separation of heat and mass transfer in the wick.A visualization vapor-liquid separated flat loop heat pipe evaporator system was built base on the new heat transfer mechanism introduced above. Besides that, the visualization of evaporator is designed to observe the evaporation and flow in the evaporator, and start-up and power increasing experiment were studied and thermal resistance was also analyzed. Three main experimental stages, pre-boiling, boiling and steady stage were experimentally observed during start-up process. Meanwhile, the experimental results showed that steam drive head resulted from vapor-liquid interface separated from the wick helped to improve its thermal performance when the wick, vapor-liquid interface and the bottom of the evaporator arrived at a reasonable situation. And 0.5mm EC height condition is the best choice in the four experimental conditions.