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首页> 外文期刊>International Journal of Heat and Mass Transfer >Detailed chemical equilibrium model for porous ablative materials
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Detailed chemical equilibrium model for porous ablative materials

机译：多孔烧蚀材料的详细化学平衡模型

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摘要

Ablative materials are used in thermal protection systems for atmospheric re-entry vehicle heat shields. A detailed chemical equilibrium heat and mass transport model for porous ablators is presented for the first time. The governing equations are volume-averaged forms of the conservation equations for gas density, gas elements, solid mass, gas momentum, and total energy. The element (gas) fluxes are coupled at the surface of the material with an inlet/outlet boundary condition, allowing modeling either atmospheric gases entering the porous material by forced convection or pyrolysis gases exiting the material. The model is implemented in the Porous material Analysis Toolbox based on OpenFOAM (PATO). The thermodynamics and chemistry library Mutation++ is used as a third party library to compute equilibrium compositions, gas properties, and solve the state-of-the-art boundary layer approximation to provide the ablation rate and the element mass fractions at the surface of the material. The model is applied to the detailed analysis of boundary layer and pyrolysis gas flows within a porous carbon/phenolic ablator characterized in a state-of-the-art arc-jet test. The selected configuration consists of an iso-flux ellipsoid-cylinder sample submitted to a 2.5 MW/m~2 heat flux with a decreasing pressure gradient from the stagnation point to the cylinder's side. During the first tenths of a second of the test boundary layer gases percolate through the sample. Then, as the sample heats up, the internal pressure increases inside the sample due to pyrolysis-gas production. The resulting pressure gradient blocks the boundary layer gases and leads to a pyrolysis gas flow that separates into two streams: one going towards the upper surface, and one going towards the lower pressure side under the shoulder of the sample. We show that the temperature profile is modified when using the detailed mass transport model. The sample's sub-shoulder zone is significantly cooled down while a temperature increase is observed in-depth. Implementing the model of this study in space agency codes will allow improving ground-test analyses and help provide more accurate material properties for design.
机译：烧蚀材料用于大气可折返车辆隔热板的热保护系统中。首次提出了详细的多孔烧蚀机化学平衡传热和传质模型。控制方程是气体密度，气体元素，固体质量，气体动量和总能量的守恒方程的体积平均形式。元素（气体）通量通过入口/出口边界条件耦合到材料表面，从而可以模拟通过强制对流进入多孔材料的大气或离开材料的热解气体。该模型在基于OpenFOAM（PATO）的多孔材料分析工具箱中实现。热力学和化学库Mutation ++用作第三方库，用于计算平衡成分，气体性质，并解决现有技术的边界层近似问题，以提供材料表面的烧蚀率和元素质量分数。该模型适用于边界层和热解气体在多孔碳/酚烧蚀器中的流动的详细分析，其特征在于最新的电弧喷射测试。选定的配置包括一个等通量椭圆形圆柱体样品，该样品经受2.5 MW / m〜2的热通量，并且从停滞点到圆柱体侧面的压力梯度减小。在测试边界层的十分之一秒内，气体会渗透穿过样品。然后，随着样品加热，由于产生热解气体，内部压力增加。所产生的压力梯度会阻塞边界层气体，并导致热解气流分离为两股流：一股流朝向上表面，另一股流朝向样品肩部下方的低压侧。我们显示当使用详细的传质模型时，温度曲线被修改。样品的副肩区显着冷却，同时观察到温度升高。在航天局代码中实施本研究的模型将有助于改进地面测试分析，并有助于为设计提供更准确的材料特性。

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