固体火箭中低热载荷固体相变工质自适应热防护机理研究

Solid rocket is transformed from the inertial trajectory of reentry from the atmosphere to the whole flight in the atmosphere, and the thermal environment is also changing from low heat flux and high heat flux and short heating time in the boost section to medium heat load, long heating time and large total heating amount in the whole process. Facing large area and cabins where thermal environment remains 50~200 kW/m2, if the original passive thermal protection is still used, the thickness of thermal insulation and thermal insulation layer needs to be greatly increased, which seriously restricts the development of a new generation of solid rocket..A new adaptive active thermal protection method is proposed in this study: The porous metal matrix materials with high melting point were infiltrated by solid state refrigerant with high latent heat and suitable phase transition temperature. By establishing heat and mass transfer mechanisms including phase transition, heat exchange between working fluid and skeleton, and between external environment and internal structure, while analying the properties and preparation methods of high enthalpy phase change inorganic salt solid-state cooling refrigerants , it is possible to explore a lightweight, efficient, adaptive and promising active thermal protection method, which will provide a key technical reserve for the design of a new generation of solid rocket.

固体火箭装备由传统出大气层再返回的抛物线飞行向着全程大气层内高速飞行转变，面临的热环境也由过去的主动段低热流密度、再入段高热流密度短加热时间向全程中等热载荷、长加热时间、大总加热量转变。面对50~200kW/m2的大面积箭体和舱内热环境，如果还采用原先的被动热防护，需要极大提高防热、隔热层厚度，严重制约了新一代固体火箭的研制。.本课题提出一种新型的自适应主动热防护方法：利用相变潜热大、相变温度合适的固态冷却工质（盐类、包覆水分子的固化凝胶材料）熔渗入熔点更高的多孔金属基体骨架材料。通过建立包含相变、工质与骨架之间热交换、外部环境与内部结构之间的传热传质机理，针对性分析高焓值相变无机盐固态冷却工质的性质和制备方法，探索出一种轻质、高效、自适应、工程应用前景好的主动热防护方法，为新一代的固体火箭设计提供关键技术储备。

本项目针对飞行器（特别是固体火箭上升段）的防热需求，提出了利用分解温度及分解焓合适的固态盐类冷却工质熔渗入熔点更高的多孔金属基体骨架材料，从而在受到高速飞行过程中的气动加热后，冷却工质能够通过自生温度升高、分解、相变来吸热的主动热防护方法。. 本研究分析了26种无机盐工质，在其中重点针对碱金属硝酸盐和铵盐材料进行了分析和实验，最终确定了NH4Cl作为无机盐冷却工质；针对金属基体，经过不断尝试，最终确定了造孔剂体积分数30%，造孔剂粒径为75-150μm的多孔钛合金为基体，最终所制备的复合材料中NH4Cl冷却介质占复合材料总质量的6.5%，从而确定了一种NH4CL无机盐与钛合金多孔介质材料复合成型的热防护材料与结构，通过了150kW/m2热流密度、100s以上的热考核，金属材料温度始终保持在许用温度以下，证明了这样的自适应热防护材料和结构能够满足目前飞行热环境的使用需求，. 随着后续研究，如果能够形成规模化生产的工艺，可以将这一材料结构直接做成飞行器壁面壳体、热端部件等材料，在不改变飞行器外形的基础上，实现轻质、高效的自适应防热与结构一体化设计。