| Space nuclear reactor has the advantages of high energy density,high specific power,free from complex space environment,and long life cycle.It is an ideal energy source for long-term and far-reaching exploration missions in the future.Liquid lithium is a commonly used coolant in space reactors.Its thermophysical properties are critical primary data for the thermal-hydraulic design of cold lithium reactors.In order to improve the accuracy of the thermal system model,it is necessary to improve the existing thermophysical properties of liquid lithium.In this paper,we systematically study the variation of the thermophysical properties of liquid lithium,such as density,surface tension,viscosity,specific heat capacity,and thermal conductivity with temperature in the temperature range of 200℃～650℃ by experimental means.At the same time,the main influencing factors are analyzed to explore the critical thermal properties of liquid lithium from the mechanism level,and the experimental data obtained can improve and enrich the thermodynamic fundamental frontier physical parameters of liquid lithium metal.The research results of this paper can provide a reference for the testing methods and techniques of the fundamental physical properties of liquid metals,especially lithium.They can provide a basis for the study of the flow and heat transfer characteristics of liquid metals in a space environment and provide data support for the thermal-hydraulic design of megawatt-class space reactors.The main research work of this paper is as follows:(1)A measurement device that simultaneously measures liquid metals’ density and surface tension at high temperatures was developed using the maximum bubble pressure method as the experimental principle.The device was used to conduct experiments on liquid lithium using five different capillary tube diameters.The results showed that the average deviation of density experimental results was 0.47%,and the average deviation of surface tension results was 0.93%.Both density and surface tension decreased linearly with the increase in temperature,and the linear fitting equation was given in the temperature interval.The bubble interval during the experiment should be controlled at 10～15s for accurate measurement of surface tension.Use capillary tubes with an inner diameter of 2.0 mm to 2.5 mm and a large inner and outer diameter ratio.(2)An oscillating cup viscosity experimental device for measuring high-temperature liquid metal was developed using the damping torsional oscillation method and the Shvidkovskiy calculation method.The device was used to test liquid lithium with different diameter molybdenum wires,and the influence of different diameter molybdenum wires on viscosity measurement was analyzed.The results show that the average deviation of the kinematic viscosity experiment is 1.82%,the average deviation of kinetic viscosity is 1.70%,the kinetic viscosity decreases with the temperature increase,and the fitting formula is given in the temperature interval.The experimental deviation using 0.15 mm diameter molybdenum wire is 1/2 of that of 0.18 mm diameter molybdenum wire.(3)The laser flash method measured the specific heat capacity and thermal conductivity of liquid lithium.The results show that the average experimental deviation of thermal conductivity is 1.68%.The specific heat capacity of liquid lithium is relatively stable with the temperature change,and the thermal conductivity increases with the temperature increase.The quadratic fitting formula of thermal conductivity with temperature in the experimental range is given.When calculating this paper’s thermal conductivity and kinetic viscosity,the literature reference values of liquid lithium density and the experimental values were used.The comparison revealed that the maximum deviation of the results calculated using the two data sets was 0.5%,which verified the reliability of the method and experimental setup of the density study in this paper. |
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