多孔型石英复合材料受热脱水特性的研究

Study on Heat-Induced Dehydration Characteristics of Porous Quartz Composites

针对含湿多孔型石英复合材料受热脱水影响透波性能的问题,建立了热湿耦合传递高温脱水数值模型,开展了关键参数对脱水过程影响的分析,获得了受热脱水过程中材料温度、湿分及介电损耗的分布。建立了多孔型石英复合材料热湿耦合传递高温脱水数值模型,为获得模型的关键参数水蒸气阻力系数,按照2016年ISO12572标准规定的杯法开展了实验测试;同时,设计并开展了多孔型石英复合材料高温加热实验,验证了数值模型的可靠性。依据建立的数值模型,探究了实际应用过程中,受热温度、材料初始含湿量、水蒸气阻力系数对多孔型石英复合材料热湿传递及透波性能的影响,并分析了不同工况下材料内部温度、体积含湿量及介电损耗随加热时间的变化规律。研究表明,较高的受热温度及较低的初始含湿量有利于多孔型石英复合材料中湿分的脱除,水蒸气阻力系数的增大会明显抑制气态水逃逸,材料在523 K受热下的脱水速度约为423 K下的3倍;303 K、90%相对湿度饱和吸湿工况脱水时间约为303 K、30%相对湿度工况的2倍;水蒸气阻力系数小于200时,对材料的高温脱水过程影响有限。因此,考虑到飞行器在实际存储过程中应采取隔湿外涂层处理减少其吸潮,并在低空飞行阶段充分加速提高气动加热的温度及时间以快速脱除湿分,减小高空飞行中湿分对无线电通信的影响。

This paper constructs a numerical model for coupled heat-moisture transfer during high-temperature dehydration to eliminate the influences of dehydration on the wave-transmitting performance of porous moisturized quartz composites.The influences of key parameters on the dehydration process are analyzed,and the distributions of material temperature,moisture content and dielectric loss during heat dehydration are obtained.Specifically a numerical model for high temperature dehydration of porous quartz composite is established an experiment is carried out according to the cup method stipulated in the standard ISO 12572:2016 to obtain the key parameter vapor resistance coefficient of the model.At the same time,the high temperature heating test of porous quartz composites is designed and carried out,which verified the reliability of the numerical model.Based on the established numerical model,the influences of the heating temperature,the initial moisture content and the vapor resistance coefficient on the heat and moisture transfer and wave transmission performance of porous quartz composites are investigated in practical application.The variations of the internal temperature,the volumetric moisture content and the dielectric loss with heating time under different working conditions are analyzed.The results show that higher heating temperature and lower initial moisture content are beneficial to the removal of moisture in porous quartz composites.The increase of vapor resistance coefficient can obviously inhibit the gaseous water escape.Specifically,the dehydration rate of materials heated at 523 K is about 3 times that at 423 K.The dehydration time under 303 K and 90% relative humidity(saturated hygroscopic condition)is about twice that under 303 K and 30% relative humidity.When the vapor resistance coefficient is less than 200,the influence on the high temperature dehydration process is limited.Therefore,the aircraft should be treated with external coatings to reduce its moisture absorption in the actual storage process,and should fully speed up in the low-altitude flight stage to increase the temperature and time of aerodynamic heating,thus quickly removing moisture and reducing the influence of moisture on radio communication during high-altitude flight.The research results can provide guidance for the practical application of the porous quartz composites.