Research On Surface Wettability Gradient Enhanced Ultra-thin Loop Heat Pipe

The electronics industry is developing rapidly.According to market demand,electronic chips are also developing towards miniaturization.The miniaturization,high performance and high integration of chips have led to the increasing heat flux density of chips.At the same time,the heat dissipation space of electronic equipment is getting smaller and smaller,the operating temperature is an important factor that affects the performance of the chip,so how to effectively carry out thermal management in a limited space is a key problem that needs to be solved urgently.The loop heat pipe is a phase-change heat transfer,Due to its advantages of long heat transfer distance,small influence by gravity,thermal diode,and high heat transfer capacity,it is considered to be an effective way to solve the above situation.As the loop heat pipe shrinks,its heat transfer performance is also limited by many aspects.One of the important limitations is the circulating power inside the loop heat pipe,that is,the capillary suction provided by the wick inside the loop heat pipe may be shortage,in order to increase the power of the working circulation in the loop heat pipe.We introduce wettability gradient in the design of loop heat pipe to provide an extra driving force for circulating the working fluid.The hydrophobic surface treatment in the gas path can reduce the thermal resistance of the gas flow,and the hydrophilic gradient treatment in the liquid path can provide the liquid driving force to increase the power for the internal circulation of the loop heat pipe.Based on the above research purposes,this paper studied the preparation of copper-based gradient wettability surface.Under different reactions,the wettability and reaction time of the copper-based surface were explored.Finally,the copperbased gradient wettability surface with driving effect on the droplets was prepared by combining the above reaction and lift method or injection method.The design and welding of the loop heat pipe were studied.In this paper,the loop heat pipe is designed as a plate structure and the wick is designed as a rake structure.In this paper,copper foam is selected as the material for preparing the wick,and the performance of the prepared wick is characterized and tested.The capillary suction value of the wick after hydrophilic treatment is 2621.8 N/m2.After the preparation of the wick is completed,the copper welding is studied in this paper,and the soldering is selected to weld the loop heat pipe.A new degassing and filling method is proposed and used in this paper.This kind of degassing and filling method can accurately control the amount of filling,and only one assembly can complete the degassing and filling of the loop heat pipe.After the degassing,filling and sealing of the loop heat pipe,the performance test of the loop heat pipe was carried out.The temperature of each point of the loop heat pipe was collected,processed and analyzed.Finally,the loop heat pipe prepared in this paper was started when the temperature is around 43?,the performance of the surfacetreated loop heat pipe is improved compared with the surface-treated loop heat pipe;when the heating power is 3.6 W,the thermal resistance is reduced by 13.2%,and the surface-treated loop heat pipe has better temperature uniformity.