| Special microchromatography is an analytical device used for hydrogen isotopes separation and analysis.With the improvement of separation technology and the development of high-performance and low-cost stuffing,special microchromatography separation and quantitative analysis of hydrogen isotopes technology will be further developed,and the application will be more extensive.However,chromatographic separation column,the key component of special microchromatography,needs to work alternately under the temperature of liquid nitrogen and 300?.Currently,there is no mature product in the market,which needs to be customized and developed.How to design a kind of low temperature liquid nitrogen device which meets the working requirements of chromatographic column with small volume and saving is a key technology of special microchromatography,and it is also the main research content of this subject.In this paper,through the combination of theoretical calculation,simulation analysis and experimental measurement,the structure design,checking and testing of the low temperature liquid nitrogen unit of the low temperature unit are carried out,two kinds of low temperature liquid nitrogen devices are developed to meet the demand of special microchromatography.Through literature review and theoretical calculation,a device prototype is designed,which uses light calcium Silicon insulation plate with low thermal conductivity as insulation layer and another vacuum insulation method as insulation layer,according to the design input,stainless steel is chosen as the structure material of the inner and outer wall,and the thickness of the insulating layer and inner wall is calculated through the design load theory.The thickness of the outer wall is 50 mm,1mm and 1.5mm respectively;choose the flaky Evia heater and the stainless steel spiral heater as the heating methods of two structures to ensure that the heater can be used for a long time under the conditions of liquid nitrogen and 300?;in the control system,the RS485 bus structure and PLC automatic control module are adopted to realize the automatic filling of liquid nitrogen in the low temperature liquid nitrogen unit,the control of liquid level,the control of heater,the temperature of program and the collection of data,etc.The heat transfer module of COMSOL Multiphysics simulation software is adopted to analyze the heat effect of the two designed liquid nitrogen units under the conditions of low temperature and high temperature.The analysis results show that,two devices with different design structures can meet the temperature requirement of the chromatographic column heating activation,and the heat preservation performance is good under high temperature condition;when working under liquid nitrogen,the heat preservation effect of the heat preservation layer can ensure that the outer layer is not condensation,the simulation analysis results are in good accordance with the design scheme.The liquid nitrogen consumption of the two devices under static state is 1.54L/d and 7.92L/d respectively through experiments,which meets the design requirement of <10L/d;the heating functions of the two devices can provide the temperature needed for the high-temperature activation of the chromatographic column;the test results of sample separation performance on the special microchromatography show that,the developed device can provide low temperature and high temperature environment requirements for analysis and realize the separation of samples on the chromatographic column. |
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