| As a mobile power,micro nuclear power plants featured with small size,high power density,and high reliability,has promising applications in the fields of ocean and island development,ship and aerospace vehicle power.Therefore,it is the focus of competition among western countries.The super high temperature heat pipe using lithium as the working fluid can replace the primary loop heat transfer process of traditional nuclear power plants,and it is an important way to realize the miniaturization of nuclear reactors.It can not only greatly reduce the volume of nuclear reactors,but also increase the outlet temperature of the nuclear reactors to improve energy conversion efficiency.However,our country's research on lithium super high temperature heat pipes started relatively late,and there is a lack of basic research on packaging process and precise design of high-performance wicks.In this paper,niobium is used as the shell material of lithium super high temperature heat pipes.In order to realize the forming of the inner grooves with high aspect ratio in niobium tubes with different diameters,a set of integral forming equipment for spinning and drawing processes is designed using the rotation and feed motion of a lathe.In the equipment,the distance between a rotating die and a compression die is adjusted to suit the spinning of heat pipes with different diameter;a drawing fixture is designed and installed on the lathe tool post to draw the spinning tube axially;and a positioning fixture is designed on the spindle to realize the positioning of the mandrel.And the effect of the device was verified.In order to analyze the forming mechanism of the grooves,a finite element model of the grooved tube spinning and drawing processing was constructed and numerical simulation analysis was performed.The stress and strain,deformation characteristics and flow features of niobium during the machining process are obtained.It was found that the front and rear tooth surfaces were unevenly formed,the bottom of the groove has large deformation and small displacement,and the center of tooth has large displacement and small deformation.In order to study the influence of parameters on the formation of the inner grooves,the results of spinning and drawing processing experiments were analyzed,and it was found that the increase in feed ratio,rotation speed and depth of ball spinning would increase the spinning force and make the formed groove deeper.When the feed ratio,rotating speed,depth of ball spinning and the position of mandrel are greater than or equal to 0.62mm/r,360r/min,0.5mm and 0mm respectively,the groove can be formed completely.A high-temperature capillary pressure test device was designed to observe the phenomenon and study the performance of liquid lithium wicking the grooved wick with different structural parameters.It was found that the temperature at which the capillary rise occurred must be greater than 380°C.Both the wetting form and the wetting speed have a certain randomness,and the change of the contact angle caused by the oxide film is the main reason for the randomness;There are three types of wetting forms: fully wetting to the highest,partially wetting to the highest and individually wetting to the highest.Similarly,the wetting speed can be divided into three states: fast-slow,slow-fast-Slow and uniform-fast-slow.Changes in the depth and width of the rectangular groove will cause vary in capillary pressure and viscous friction resistance,and ultimately lead to its influence on the capillary height not monotonous.When the effects of capillary pressure and viscous frictional resistance changes are balanced,the capillary height reaches the maximum.When the depth of the rectangular groove is 350?m or the width is 250?m,and the aspect ratio is between 1.35-1.52,the capillary pressure reaches the highest.The capillary pressure of the rectangular grooved wick is better than that of trapezoidal and V-shaped grooves. |
PDF Full Text Request