Development Of A Low-temperature High-precision Thermal Conductivity Factor Measuring Instrument

The way of heat transfer includes radiation, convection and the heat conduction. Heat conduction means heat passing from the one object with high temperature to another which has lower temperature or one part to another in certain object. It is a way to save energy by using thermal isolation materials; meanwhile, thermal conductivity factor of a material is an important parameter to specify the property of thermal isolation materials. Precision measurement of thermal conductivity factor plays an important role in development and production for thermal isolation materials. The hot plate protection method based on the Fourier one-dimensional stable state heat conduction principle for thermal conductivity factor measuring is wildly used, with the advantages of broadly measuring range and high precision.Problems still existing in the previous instrument, especially for the measured thermal conductivity factor which greatly influenced by temperature difference between cold and hot plate, thee average temperature, the change of room temperature, the thickness of test sample and the uncontrolled clamping force of sample. The new instrument in terms of double plate protection hot plate method was developed with lower temperature and high precision. The instrument has the controlling structure of pre-clamping force controller, meanwhile it could reduce the effect of various factors mentioned above by the optimized hardware and software. Furthermore, it could work below room temperature (approach to absolute Zero at lowest). The results calculated by the new one are more precise than former, with the measurement error dropping from 5% to 1.5% and working time span decreasing to 2/3 compared with previous instrument.1. Analysis of recent research of thermal conductivity instrument and problems of plate method were discussed and then the characters of new instrument were presented with aim and meaning of our study.2. Though the analysis of one-dimensional stable state heat conduction principle, formulas of thermal conductivity were deduced as well as factors of effect on thermal conductivity were discussed. Basic principle of measurement of thermal conductivity instrument based on discussion above was defined.3. Clamping force controlling structure was designed including machinery and electronic part in order to satisfy the national standards of clamping force for instrument. This optimization greatly improved the measurement repeatability and the precision.4. The connection way of guard shield and the hot plate in thermal conductivity instrument was improved, then consider the influence of loss heat and resistance, the equation of principle was updated.5. Liquid loop unit was added to body case, algorithm for controlling was improved and the impact of temperature around on measurement was reduced. The range of instrument could be enlarged from -250℃to -100℃in a shorter working time.6. The summarization and future plan were presented.