Research On Temperature Source Performance Of High Temperature Heat Pipe

At present,countries around the world use the ITS-90 temperature scale to carry out the transmission of temperature measurements to ensure the uniform and accurate transmission of temperature measurements internally and the international equivalence of temperature measurements externally.The definition of fixed point,interpolation instruments and interpolation equations are the three elements of ITS-90 international temperature scale.The interpolation instrument in the temperature range from 13.8033 K to 961.78℃ is the standard platinum resistance thermometer,while the defined fixed point is the scale for assigning values to platinum resistance thermometers using the phase change point of pure substances.In order to improve the level of the defined fixed point assignment,heat pipes are often used internationally as isothermal furnace liners to improve the uniformity of the vertical temperature field of the fixed point temperature source,which in turn improves the level of realization of the defined fixed point.Silver freezing point(961.78 ℃)and aluminum freezing point(660.323 ℃)are very important definition fixed point of the ITS-90 international temperature standard.Metrology institutes in foreign developed countries such as the National Institute of Standards and Technology(NIST)、the Physikalisch-Technische Bundesanstalt(PTB)、the British National Physical Laboratory(NPL)and other developed countries use high-temperature sodium heat pipe to realize the silver and aluminum freezing point,while China benchmark has not yet adopted the heat pipe technology,only the use of three-stage temperature control technology.Therefore,there is a significant gap between Chinese technical indicators of the fixed point temperature source vertical temperature field uniformity and developed countries metrology institute.In addition,the comparative method of calibration is also an important means of temperature measurement value transfer.The homogeneous temperature block is usually used to improve the level of comparative method calibration,while a few countries use heat pipe technology to improve the performance of comparative temperature sources.In order to improve the level of high-temperature definition fixed-point realization and the comparative method temperature measurement transfer capability,this paper carries out the research of high-temperature heat pipe fixed-point temperature source and heat pipe comparative temperature source.In the study of fixed-point temperature source,a high-temperature heat pipe fixed-point temperature source that can realize the freezing point of silver and aluminum was developed by using three-stage temperature control and high-temperature heat pipe technology,and the uniformity of its vertical temperature field was studied.The experimental results show that when the furnace temperature is controlled at a temperature lower than the freezing point of silver and aluminum about 1 ℃,the uniformity of its vertical temperature field is 9.2m K、11m K respectively.In order to seek the best fixed point realization technique,the effect of different inducting methods on the zinc freezing plateau was investigated.It was found that: a satisfactory freezing plateau could be obtained by using quartz rod for multiple inductions.And using this method,the silver freezing point was successfully realized at the high temperature heat pipe fixed point temperature source.Meanwhile,a comparative temperature source study of cesium heat pipe and sodium heat pipe was carried out to study their thermal properties.In order to improve the technical index of the comparative temperature source of cesium heat pipe,homogeneous cylinders of different materials were installed respectively between the cesium heat pipe and the heating chamber to compare the technical index of the cesium heat pipe under different conditions.The experimental results show that: cesium heat pipe and sodium heat pipe comparative temperature source temperature stability were ±1.5m K and ±4.6m K,respectively,and the temperature uniformity were 65 m K and 8.7m K.Through the above research,the developed high temperature heat pipe fixed point temperature source can meet the needs of silver and aluminum freezing point realization and improve the realization level of ITS-90 international temperature standard in China.The comparative method temperature calibration capability and level can be improved with the placement of nickel homogeneous block in this high temperature heat pipe isothermal furnace.