Thermal insulation materials with micro/nano porous structure are widely used in aerospace field. Gas permeation has a marked impact on thermal insulation properties of insulation materials. Most investigations on gas permeation measurement are based on one-dimensional Darcy's law by measuring the pressure gradients and the volume flow of the two sides of the materials. However, the two-dimensional diffusion that usually occurred in the materials will result in errors for evaluating the permeability by the one-dimensional Darcy's law. In this paper, the two-dimensional isothermal seepage equation is derived to describe the gas diffusion in micro/nano porous materials and an experimental device is designed to measure the transient permeability of the materials. By the control volume method and the Peaceman-Rachford alternating direction implicit (ADI) algorithm (PR-ADI), the two-dimensional isothermal seepage equation is discretized and solved numerically to give the pressure distribution in the material. And the genetic algorithm is employed to identify the permeability based on the pressure varying with time obtained by the experiment. A computer code is developed based on the above model and numerical method to simulate the seeping process and identify the permeability. The transient seeping experiment is conducted for a kind of silica aerogel and its permeability varying with the pressure is obtained by the two-dimensional solution.

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获得微/纳米多孔材料压力相关渗透率的反分析

具有微米/纳米多孔结构的绝热材料被广泛用于航空航天领域。气体渗透对隔热材料的隔热性能有显着影响。气体渗透率测量的大多数研究都是基于一维达西定律，即通过测量材料两侧的压力梯度和体积流量。然而，通常在材料中发生的二维扩散将导致通过一维达西定律评估渗透率的误差。本文推导了二维等温渗流方程来描述气体在微/纳米多孔材料中的扩散，并设计了一个实验装置来测量材料的瞬态渗透率。通过控制体积法和Peaceman-Rachford交替方向隐式（ADI）算法（PR-ADI），离散二维等温渗流方程，并对其进行数值求解，以得出材料中的压力分布。并采用遗传算法，根据实验得到的随时间变化的压力识别渗透率。基于以上模型和数值方法，开发了计算机代码，以模拟渗流过程并识别渗透率。对一种二氧化硅气凝胶进行了瞬态渗流实验，通过二维解求得了其渗透率随压力的变化。并采用遗传算法，根据实验得到的随时间变化的压力识别渗透率。基于以上模型和数值方法，开发了计算机代码，以模拟渗流过程并识别渗透率。对一种二氧化硅气凝胶进行了瞬态渗流实验，通过二维解求得了其渗透率随压力的变化。并采用遗传算法，根据实验得到的随时间变化的压力识别渗透率。基于以上模型和数值方法，开发了计算机代码，以模拟渗流过程并识别渗透率。对一种二氧化硅气凝胶进行了瞬态渗流实验，通过二维解求得了其渗透率随压力的变化。