Research On Phase Change Characteristic Of Miniature Fixed-points

The space thermal infrared remote sensing is an important observation means for space to earth observation system.And the high precision spaceborne calibration system(onboard blackbody)plays a decisive role in maintaining high stability and high precision of the infrared observation.Now,the calibration accuracy of the spaceborne blackbody of China is not high.After the launch,the accuracy of the measurement will gradually change with the working time,and it can’t be calibrated periodically.To solve the above problems and meet the demand of high precision measurement,it is proposed that the fixed point as the temperature standard is applied in the satellite borne black body.Considering the special circumstances of the application,the volume,quality and power consumption of the fixed-points applied in the on-orbit calibration need to be as small as possible.Therefore,compared with the traditional benchmark on an international scale of fixed-points,the quality of miniature fixed-points used in spaceborne blackbody temperature calibration is very small(about 5 g).So in the process of phase change,the miniature fixed-points will be more sensitive to the influence factors,such as impurities,environmental temperature,heating power and so on.In order to improve the level of infrared remote sensing quantitative on-orbit calibration system,high purity phase change materials(99.99999%)are chose,including miniature Ga,miniature Ga-In,miniature phenyl salicylate and miniature water,to research the phase change characteristic of these miniature fixed-points in quasi-adiabatic environment and small power heating.The results show that the temperature fluctuations of miniature Ga,miniature Ga-In and miniature water are 5 m K,3m K and 5 m K respectively.The replicability of the melting points of miniature Ga and miniature Ga-In both are 2 m K.While the foreign reproducibility of miniature Ga and miniature Ga-In are 2.3 m K and 2.2 m K respectively.The replicability of the melting points of miniature water is 3 m K.The replicability of the run-off point of Ga,Ga-In both are 2 m K.The replicability of the run-off point of water is 6 m K.The results can meet the precision requirements of the space scale,and the repeatability of miniature Ga and miniature Ga-In both are better than foreign measurement level.Through the method of increasing the volume of crucible and the purity of phenyl salicylate,the melting curves of the phenyl salicylate can be improved.Three different accessor methods of the run-off points are discussed in this paper,such as the second order differential method,the tangent intersection method and the average method.The result that the run-off point has strong linear relationship with the heating power is obtained for the first time.These results can provide experimental data support for the research on orbit calibration of spaceborne blackbody radiation source in the future.The first chapter mainly introduces the background and significance of the study,the main contents on the miniature fixed-points at home and abroad and the main content of this paper.The second chapter mainly introduces the theoretical basis,including the theory of metal phase change,fixed-point and interpolation formula.The third chapter mainly introduces the design,cleaning and pollution prevention perfusion for the miniature stainless steel crucible and graphite crucible.The fourth chapter mainly introduces the quasi-adiabatic system,including temperature control parts,the phase change temperature transmission parts and temperature measurement parts.The fifth chapter mainly introduces the testing results for the miniature gallium fixed-point,miniature gallium-indium fixed-point,miniature phenyl salicylate fixed-point and miniature water triple point.The sixth chapter is mainly about the summary of the work and the introduction of the following research content.