气凝胶纳米绝热材料耦合导热微观机理研究

Due to the size effect, the movement of gas molecule in nano pore and phonon in nano skeleton for insulating nanomaterials will be restricted, and the super insulation is shown. The conduction coupling of skeleton and the pore gas in insulating nanomaterials have a large influence on the effective thermal conductivity, especially the gas contact layer in the surface of solid making the effect is more significant. So the project will establish the computation model of lattice Boltzmann method (LBM) for phonon heat transport in nanograins for the microscopic mechanism of heat conduction in it. Furthermore, the scattering of molecules and phonons in the gas-solid interface will be numerically simulated by LBM. Based on it, the gas-solid coupling conduction computation model that can take into account of the scattering of phonon in solid and phonon-molecule in gas –solid interface and molecule in gas will be built. So the research of all scatting of microscopic particles in solid, gas and gas –solid interfaces will be systematically and deeply investigated. Meanwhile, the heat conduction experiments for insulating nanomaterials would be done. The more precise theoretical prediction results will be provided for the performance optimization design and development of insulating nanomaterials.

由于尺度效应，纳米绝热材料孔隙内气体分子及固体骨架内声子输运受到抑制，使其具有极佳的绝热性能。纳米绝热材料的固体骨架和孔隙内气体导热的耦合作用很大程度上影响气凝胶材料的有效热导系数,尤其是在固体表面处气体接触层的存在，使得这种影响更为显著。本项目从纳米颗粒导热微观机理着手，首先建立颗粒内声子输运的格子玻尔兹曼法(LBM)计算模型。在此基础上，进一步采用LBM数值模拟气固界面分子-声子间散射行为。进而建立能同时描述远处固体声子散射、气固界面分子-声子散射及远处气体分子散射的纳米绝热材料气固耦合导热计算模型。实现对固体、气体及气固界面处所有微观粒子散射机制深入系统地研究。同时，开展纳米绝热材料导热的实验研究。为纳米绝热材料性能优化设计及开发生产提供更为精确的理论预测结果。

本项目建立了纳米多孔材料气凝胶的气固耦合LBM导热模型，利用区域分裂理论的LBM方法数值模拟了纳米气凝胶的气固耦合传热特性，并考虑了接触层对气固耦合导热特性的影响。模拟结果表明：不考虑接触层作用时，气固耦合导热系数随着气相尺度的增加而增大，变化幅度随着气相尺度的增大而逐渐减小，气固耦合的导热系数随着固相尺度的增加而增大，增大幅度比较均匀。考虑接触层作用时，不同孔隙尺度对应的气固耦合导热系数均减小，在孔隙尺度较小时，减小幅度较大，随着孔隙尺度的增大，减小幅度逐渐减小。这是由于随孔隙尺度的增大，接触层所占比例相对减小，因此对气固耦合导热系数的影响逐渐减小。最后采用瞬态热线法测量了五种不同孔隙率气凝胶的导热系数，并与数值模拟结果进行比较，结果表明：考虑接触层作用时的数值模拟结果与实验结果更为接近。