Research On Key Technology For Guarded Hot-plate High Temperature Thermal Conductivity Measuring Apparatus

Thermal conductivity is one of the important parameters to measure the thermal properties of the insulation material,its accurate acquisition is closely related to the research and development of aerospace,building energy conservation and other fields.The guarded hot plate(GHP)method is the most accurate method for measuring the thermal conductivity of insulation material,but the measurement temperature range of domestic instruments based on this method is near room temperature,high temperature demand is obvious,so our laboratory developed the first and second generation of high-temperature thermal conductivity measuring instruments.The first generation realized the measurement function,the second generation solved some problems of mechanical structure and proposed a calibration method based on different thickness,but had insufficient understanding on the temperature distribution of test stack and the interaction of different components,the temperature control precision need to be improved,and the measurement efficiency is still relatively low.Research on key technologies involved in these issues is of great significance.Based on the second generation high temperature thermal conductivity measuring instrument,the temperature distribution of test stack and the interaction of different components were simulated and analyzed by the finite element ANSYS software,so the mechanical structure could be improved;designed the temperature acquisition module and thermocouple calibration furnace,so accurate temperature control and calibration could be achieved;proposed a method based on dynamic periodic identification to determine the system steady-state,and the measurement efficiency is improved obviously.The major work of this thesis is as the following:1.This paper introduced the basic concepts and the main measuring method of thermal conductivity;described the development status and trends of GHP thermal conductivity measuring instrument at home and abroad,then pointed out the key technologies of high temperature GHP and problems of the second generation laboratory prototype;proposed the purpose and the contents of this research.2.Introduced the Fourier one dimensional heat transfer law and the calculation formula of thermal conductivity,then the GHP measurement principle and design of mechanical structure.Improved the key mechanical structure using ANSYS finite element simulation,including the temperature distribution of test stack and the interaction of different components3.The temperature acquisition module of the instrument is designed,including the scheme selection,cold junction compensation,analog front end design,AD sampling circuit,communication interface,software design and temperature sampling experiment.4.Design of multi-thermocouple calibration furnace.Including the mechanical design of multi-thermocouple jack block,the heating wire and sheet metal,E5 CC temperature control and heating circuit design,thermocouple calibration experiment.5.Study on the method of rapid measurement of instrument.Introduced the Kalman filter theory and algorithm,and the PID temperature control based on Kalman filter.Then described the method to determine system steady-state based on dynamic periodic identification,interactive software and measurement experiment.6.Conclusions and prospects,the main conclusions of this paper are summarized,and the remaining problems are pointed out,so the effort direction is cleared.