酚醛树脂基复合材料传热-热解模型构建与试验研究

Research on Construction and Experimental Verification of Heat Transfer-Pyrolysis Model for Phenolic Resin-Based Composite Materials

针对现有酚醛树脂基复合材料传热-热解模型忽略产物气体渗流可压缩效应的问题,建立了考虑热解气体可压缩流动的酚醛树脂基复合材料传热-热解模型。通过可压缩压力耦合方程组半隐式方法,求解完整的Navier-Stocks方程,以实现对热解气体可压缩流动的模拟,而非现有模型普遍采用的不可压缩Darcy方程;改进了热解度的计算方式,提高了孔隙动态演化时热解区域材料物性插值的准确性。以一种酚醛树脂基复合材料——酚醛气凝胶复合材料为例,通过热质量试验数据,推导了热解动力学模型。测量了完全热解前后材料的关键计算输入参数。通过10 kPa低气压热试验测得了1000℃加热下材料的背温。结果表明:酚醛气凝胶复合材料存在200~550℃、550~800℃、800~1200℃共3个主要热解区间;完全热解前、后,材料孔隙率分别为0.568、0.484,渗透率分别为10^(-13)、10^(-12) m^(-2)。计算模型与试验结果吻合较好,最大相对误差为9.2%;热解气体向舱内渗流形成富集区域的现象对材料隔热有负面影响,但低导热系数和产物气体热阻塞作用仍使材料具备优异的防隔热性能。

A heat transfer-pyrolysis model considering the compressible flow of pyrolysis gas was established for phenolic resin-based composite materials to address the issue of neglecting the compressible effect of product gas permeation in the existing models.In order to simulate the compressible flow of pyrolysis gas,the compressible semi-implicit method for pressure linked equations(SIMPLE)was employed to solve the complete Navier-Stocks equations,rather than the incompressible Darcy equation commonly used in the existing models.The calculation method of pyrolysis degree was improved to enhance the accuracy of material property interpolation in the pyrolysis region during the dynamic evolution of pore structure.A phenolic resin-based composite material,phenolic aerogel composite material,was taken as an example.The pyrolysis kinetics model was derived from thermogravimetric experimental data.Key calculation input parameters of the material are measured before and after complete pyrolysis.The back temperature of the material under heating at 1000℃ was measured through a 10 kPa low-pressure thermal test.The results indicated that the phenolic aerogel composite material had three main pyrolysis intervals:200—550℃,550—800℃,and 800—1200℃.Before complete pyrolysis,the porosity was 0.568,and the permeability was 10^(-13) m^(-2).After complete pyrolysis,these values were 0.484,and 10^(-12) m^(-2) respectively.The calculation model showed good agreement with experimental results,with a maximum relative error of 9.2%.The phenomenon of pyrolysis gas permeating into the cabin and forming enrichment areas negatively affected the thermal insulation of the material.However,the low thermal conductivity and the thermal blocking effect of product gas still endowed the material with excellent thermal insulation performance.