Research On Internal Flow-Phase Change And Heat Transfer Enhancement Of High Temperature Heat Pipe

High-temperature heat pipes have broad application prospects in thermal protection of hypersonic vehicles,space nuclear reactor cooling,solar energy utilization,and so on.The lack of means to finely regulate the flow and phase change characteristics of high-temperature alkaline liquid-metal fluids inside heat pipes is the bottleneck that restricts high-temperature development heat pipe technology.In this paper,the flow-phase transformation of liquid metal inside a high-temperature heat pipe is studied.The critical dynamic wetting physical parameters of liquid metal inside a high-temperature heat pipe are measured,microscopic simulations and the constitutive relationships between flow-phase transformation and microstructure are constructed as an idea to break through the existing high-temperature heat pipe performance bottleneck and the limitation of not being able to fine-tune the design.In this paper,the synergistic mechanism of flow-phase change inside the high-temperature alkali heat pipe and the modulation mechanism of flow-phase change synergy by capillary core form are investigated using experiments and simulations.The new capillary core micro structure design is presented.New capillary core structure’s effectiveness full-scale heat pipe model and experiments demonstrate the new capillary core structure’s effectiveness.The effect of heat-flow-solid coupling characteristics on the heat transfer performance of high-temperature heat pipes caused by high temperature and external factors is analyzed using a flow-solid bi-directional coupling simulation method.The main research contents and results are as follows.(1)The phase change flow characteristics of the alkali metal in the micro-groove are analyzed at the micro-local level.The effects of three different shapes of trapezoidal,rectangular,and spherical grooves on the workpiece’s phase change flow are discussed.The unique heat transfer path of the high temperature liquid metal different from that of the conventional water workpiece is found,due to which a new capillary core design method is proposed.It is found that the trapezoidal groove is more suitable for heat pipes with a higher liquid filling rate than the rectangular groove.In comparison,the spherical groove is ideal for heat pipes with a higher liquid filling rate than the other two are not suitable for high-temperature metal heat pipes.(2)The overall performance model of heat pipe considering the high-temperature heat pipe’s internal flow and phase change characteristics is established.The internal flow and phase change characteristics of common types of absorbent cores,i.e.,sintered,grooved and combined absorbent cores,are compared.A new interphase combined absorbent core is designed on this basis,which has better overall performance.(3)To prepare sodium metal high-temperature heat pipe,we build a heat pipe performance test device and carry out experiments on the start-up characteristics,uniform temperature characteristics,and heat transfer characteristics of the heat pipe by different capillary core design,liquid filling rate,tilt angle,and heating method.(4)The study of high-temperature heat pipe flow-solid-thermal coupling characteristics based on the flow-solid bi-directional coupling model and the discussion of high-temperature thermal stress,local external force,and local deformation on the heat pipe performance characteristics.This study can provide theoretical guidance for understanding the flow phase change law of high-temperature liquid metal,the regulation of high-temperature heat pipe performance,and high-temperature heat pipes’ operating characteristics under extreme conditions.