航天器用低温多层隔热性能计算方程

Thermal performance equation of multilayer insulator for spacecraft

航天器常用有效发射率表征多层的隔热性能,其经验值范围为0.02~0.04,经验值仅与多层单元数有关,不随温度变化。有效发射率经验值的适用条件是多层的热面温度约-10℃~50℃,多层的冷面不照太阳。使用条件偏离得越多,有效发射率的经验值导致的计算偏差就越大。针对该问题,提出采用辐射项加导热项的混合传热模型,取代传统的纯辐射模型,并给出了方程中导热项系数和辐射项系数的计算方法。以国产10单元多层为例,给出了方程系数的详细计算过程,该系数已用于工程实际。用多种工况验证了该方程的准确性,并阐述了纯辐射模型导致较大偏差的问题根源。采用混合传热模型使高温/低温区的计算偏差从20℃降低至5℃。混合传热模型比纯辐射模型更适于描述多层的传热过程。最后,研究了选取多层隔热性能热平衡试验工况的原则。

The effective emissivity of multilayer insulator(MLI)is widely used in spacecraft thermal analysis and thermal design,and the empirical range of effective emissivity is 0.02 to 0.04 which is only related to numbers of layers and has nothing to do with temperature.The working condition of empirical range of effective emissivity is that the hot side temperature of MLI is within-10℃to 50℃and that the cold side is without solar heat flux.More condition deviation led to larger calculation deviation made by empirical range of effective emissivity.In order to solve the problem,the thermal performance equation of MLI normal heat transfer was proposed.The equation was made up of thermal radiation item and heat conduction item,and the acquisition method for the coefficient of radiation item and conduction item was described.As an example,the native 10-layer MLI was discussed,and the coefficients of the MLI were obtained,which was useful in engineering.The equation was examined in many working conditions.By using the equation,the cause of the problem was obtained,and the deviation was dropped from 20℃to 5℃in high and low temperature zone.The blade radiation model was well replaced by hybrid heat transfer model.Finally,the problem of how to design the operating conditions of MLI thermal balance test was briefly discussed.