氩-碳-硅等离子体热力学性质和输运系数计算

Calculation of thermodynamic properties and transport coefficients of Ar-C-Si plasma*

计算了广温度范围(300—30000 K)和广压力范围(0.1—10 atm,1 atm=101.325 k Pa)下,不同混合物比例、碳和硅蒸气浓度的局域热力学平衡(LTE)和化学平衡(LCE)的氩-碳-硅等离子体组分、热力学性质和输运系数.等离子体气相平衡组分使用质量作用定律计算,同时凝聚相组分采用相平衡的方法计算.输运系数的计算包括黏度、电导率和热导率,使用拓展到高阶近似的Chapman-Enskog方法.采用文献中较新的数据得到了较为准确的碰撞积分,导出了Ar-C-Si等离子体的输运系数.结果表明,在相变温度以下,凝聚态物种的引入导致Ar-C-Si等离子体的热力学性质、输运系数与纯Ar等离子体接近,在相变温度点则会产生不连续点.压力、碳/硅蒸气浓度和比例对等离子体热力学性质和输运系数具有较大影响.最终计算值与文献数据对比符合良好,有望为氩-碳-硅等离子体传热流动数值模拟提供基础数据.

The compositions,thermodynamic properties and transport coefficients of the argon-carbon-silicon plasma at local thermodynamic equilibrium and local chemical equilibrium in temperatures range of 300-30000 K and pressure range of 0.1 to 10 atm and are different mixture ratios are investigated in this work.The condensed phases and Debye-Hückel corrections are both taken into account.The equilibrium component in gas phase is calculated by mass action law(Saha’s law and Gulberg-Waage’s law),Dalton’s partial pressure law,con-servation of the elements and charge quasi-neutral equation,and at the same time the condensed species is calculated under the assumption of local phase equilibrium.Thermodynamic properties including density,enthalpy and specific heat are evaluated through a classical statistical mechanics approach.The transport coefficient calculations including viscosity,electrical conductivity,and thermal conductivity are carried out by using a third-order approximation(second-order for viscosity)of the Chapman-Enskog method.Collision integrals are obtained by using the relatively new data.The results show that the concentration and ratio of blend of C vapor and Si vapor can greatly affect the properties of the Ar plasma owing to the introduced C and Si vapor’s own properties and their new reactions.While the pressure influences those properties through the shift of chemical equilibrium and the change of total number density.In addition,the introduction of condensed species leads the thermodynamic properties and transport coefficients of the lower temperature plasma to become almost the same as those of pure argon,and causes discontinuous points at phase-transition temperature.The final calculation results are in good agreement with those in the literature,and the slight difference in transport coefficient between them can be explained by the different selection of interaction potentials.The results are expected to provide reliable basic data for the numerical simulation of argon-carbon-silicon plasma.