Flow And Heat Transfer Enhancement Mechanism Of Oscillating Heat Pipe With Binary Fluid Of Liquid Metal

The problem of efficient thermal management of high-power and high-heat-flux electronic devices has become the bottleneck restricting the development of advanced electronic devices.As a new type of efficient two-phase heat transfer element,oscillating heat pipe(OHP)is considered as one of the most effective means to solve the high power and high heat flux heat dissipation.The research shows that the OHP mainly relies on sensible heat transfer,and when the liquid plug oscillating flows at high frequency or flows in one direction at high speed,the heat absorption and release speed of the working fluid plays a key role in the heat transfer performance of OHP.However,due to the low thermal conductivity of conventional working fluid,the heat absorption and release capacity of working fluid in high-speed flow is insufficient,which leads to the deterioration of heat transfer performance of OHP.At the same time,the existing two-dimensional OHP structure has limited heat transfer capacity.It limits the development of OHP under the conditions of high power and high heat flux.Therefore,using liquid metal with high thermal conductivity to improve the thermal conductivity of working fluid is proposed in this work.The heat transfer performance of OHP is further enhanced through structural improvement,thus improving the applicability of OHP in high power and high heat flux places.In this thesis,a lot of experimental and theoretical research has been carried out around the flow and heat transfer of OHP with binary fluid of liquid metal.The main research contents and conclusions are as follows.The flow type and heat transfer performance of a two-dimensional oscillating heat pipe filled with binary fluid of liquid metal are visualized and tested,and the influence of liquid metal on liquid plug oscillation is analyzed.Based on the viscosity of mixed working fluid,a theoretical model for oscillating motion of binary fluid of liquid metal was developed,and the influence mechanism of liquid metal on liquid plug oscillation was revealed.By increasing the structure dimensional from two-dimensional to three-dimensional,a three-dimensional OHP with liquid metal and ammonia was fabricated,and its heat transfer performance was studied by experiments.In addition,the heat transfer model of OHP with binary fluid of liquid metal is established under the unidirectional circulating flow of working fluid,and the flow and heat transfer characteristics of OHP are studied theoretically.At the same time,the mechanism of liquid metal strengthening heat transfer of OHP is revealed.Finally,according to the force analysis of liquid plug movement,a new type of three-dimensional OHP with liquid metal vapor cushion is proposed,which further enhances the heat transfer performance of three-dimensional OHP.The results show that the flow patterns of working fluid in OHP with binary fluid of liquid metal are mainly oscillating and unidirectional circulating flow.It is found that there are liquid film and vapor bubble between liquid metal and tube wall.It is also found that the higher density of liquid metal increases the inertia force of the working fluid,increases the oscillating amplitude of the liquid plug,and is beneficial to the circulating flow of the working fluid.However,the higher density of liquid metal will reduce the frequency of oscillation.At the same time,the higher viscosity of liquid metal will reduce the flow speed of liquid plug,thus deteriorating the start-up and heat transfer performance of OHP at low power.Liquid metal promotes unidirectional flow of working fluid and enhances heat transfer performance of OHP.The new liquid metal-ammonia three-dimensional OHP can realize heat transfer with heating power of 1000W and heat flux of 111W/cm~2,and its heat transfer capacity is obviously higher than that reported in the existing literature.Through theoretical analysis,it is found that the liquid metal can increase the macroscopic convective heat transfer coefficient of the working fluid and thus enhance the sensible heat transfer,which is the main reason for liquid metal to enhance the heat transfer performance of OHP.The liquid metal will increase the flowing friction resistance of the working fluid and reduce the velocity of unidirectional flow,and then the proposed liquid metal vapor-cushion three-dimensional OHP has better heat transfer ability in a certain power range.In addition,increasing the cooling water temperature can further improve the heat transfer performance of the liquid metal vapor-cushion three-dimensional OHP.