中文摘要：

应用稀薄气体分子热运动理论，研究了真空层复合传热机理，提出了真空层当量导热系数计算方法，分析了不同真空层压力和热媒温度对真空层传热量的影响以及导热、对流和辐射传热量在真空层总传热量中所占比例和变化规律，提出优化真空保温管道保温性能的方法。试验结果与计算结果的最大偏差率为7．9％。真空层压力应控制在2kPa以下，以获得满意的保温效果。真空层压力高于101．3kPa时，真空层内传热以对流传热为主；当真空层压力降低到1kPa时，真空层内传热以辐射传热为主。真空层的对流传热不应被忽略。

英文摘要：

Based on the theory of aerothermodynamics for rarefied gas, discusses the principle of compound heat transfer in the vacuum layer. Presents a method for calculating the equivalent thermal conductivities for this layer. Analyses the effect of thermal characters on heat transfer in vacuum layer, such as vacuum pressure and temperature of steam, and discusses the percentages of conduction, convection and radiation in vacuum layer and their variability. Presents how to optimize the thermal performance of the pipelines. Results prove to be satisfactory for the maximum of deviation rate between calculated data and experimental data is 7.9%. The pressure in vacuum layer should be controlled under 2 kPa to achieve desirable insulating effects. The dominating way of heat transfer in vacuum layer is the convection when the vacuum pressure is above 101.3 kPa, and it is the radiation when the vacuum pressure is under 1 kPa. The convection in vacuum layer should not be neglected.