护热板法测量高温下材料导热系数的研究

Study on Measuring Thermal Conductivity of Materials at High Temperature by Guarded-hot-plate

中国计量科学研究院(NIM)新研制了单样品高温防护热板法装置,设计工作温度范围从室温至500℃、导热系数测量范围0.02~0.5 W/(m·K)。通过新的温度控制技术,有效抑制了系统热惯性引起的热振荡,在长达2 h的热平衡期内,各部件的温度波动可控制在0.005℃以内;采取上防护板温度补偿,抑制了上防护板的漏热。新装置测量导热系数的不确定度为1.2%(k=2)。在平均温度30~70℃范围,与美国国家标准技术研究院的导热系数标准参考物质NIST SRM 1450d标准值相对偏差为0.2%~1.9%。测量了有机玻璃的导热系数,与PTB测量值的相对偏差为-0.8%~-1.5%。在40~400℃温度范围,测量了高温岩棉的导热系数,测量不确定度为4.7%(k=2)。

Guarded-hot-plate(GHP)method plays the primary procedure for measurements of the thermal conductivity of insulators.The method has important applications in the fields of new material explorations and industrial energy savings.The National Institute of Metrology(NIM)has newly developed a single sample high temperature protection hot plate method device,the design working temperature ranges from room temperature to 500℃,and the thermal conductivity measurement range is 0.02~0.5 W/(m·K).We developed a new controlling scheme that effectively suppressed the thermal oscillation caused by the thermal inertia of the big equipment ensemble.The temperature of each component of the device is continuously stablized within 0.005℃in a period up to 2 hours.The heat leak from the upper guarded plate is a specific question with the GHP devices of the single sample type.The phenomenon become serious with increasing temperatures.We studied the temperature compensation procedure that effectively suppresses the heat leak through the upper guarded plate.We applied the device measuring the standard reference material for thermal conductivity of SRM1450d of NIST,in the sample average temperature from 30℃to 70℃,the relative deviation from the reference values falls in the range of 0.2%~1.9%with the measurement uncertainty of 1.2%(k=2).We used the device measuring the thermal conductivity of cast polymethyl methalcylate,and observed the relative deviation of-0.8%to-1.5%from the publication data by the PTB.We then measured the thermal conductivity of mineral wool in the temperatures ranging from 40~400℃with the measurement uncertainty of 4.7%(k=2).