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首页> 外文期刊>International Journal of Heat and Mass Transfer >Effect of vibrational degrees of freedom on the heat transfer in polyatomic gases confined between parallel plates
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Effect of vibrational degrees of freedom on the heat transfer in polyatomic gases confined between parallel plates

机译：振动自由度对平行板间多原子气体中传热的影响

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摘要

Conductive stationary heat transfer through rarefied nonpolar polyatomic gases, confined between parallel plates maintained at different temperatures, is investigated. It is assumed that gas molecules possess both rotational and vibrational degrees of freedom, described by the classical rigid rotator and quantum harmonic oscillator models, respectively. The flow structure is computed by the Holway kinetic model and the Direct Simulation Monte Carlo method. In both approaches the total collision frequency is computed according to the Inverse Power Law intermolecular potential. Inelastic collisions in DSMC simulations are based on the quantum version of the Borgnakke-Larsen collision model. Results are presented for N_2, O_2, CO_2, CH_4 and SF_6 representing diatomic as well as linear and nonlinear polyatomic molecules with 1 up to 15 vibrational modes. The translational, rotational, vibrational and total temperatures and heat fluxes are computed in a wide range of the rarefaction parameter and for various ratios of the hot over the cold plate temperatures. Very good agreement, between the Holway and DSMC results is observed as well as with experiments. The effect of the vibrational degrees of freedom is demonstrated. In diatomic gases the vibrational heat flux varies from 5% up to 25% of the total one. Corresponding results in polyatomic gases with a higher number of vibrational modes show that even at low reference temperatures the contribution of the vibrational heat flux may be considerably higher. For example in the case of SF_6 at 300 K and 500 K the vibrational heat flux is about 67% and 76% respectively of the total heat flux. Furthermore, it is numerically proved that the computed solutions are in agreement with the Chapman-Enskog approximation in a central strip of the computational domain even at moderately large values of the rarefaction parameter, as found in previous investigations. This property has been used to compute the gas thermal conductivity predicted by the adopted models.
机译：研究了通过稀有非极性多原子气体的传导性固定传热，该气体被限制在保持不同温度的平行板之间。假设气体分子同时具有旋转和振动自由度，分别由经典的刚性转子模型和量子谐波振荡器模型描述。流动结构通过Holway动力学模型和直接模拟Monte Carlo方法计算。在两种方法中，总碰撞频率都是根据逆幂定律的分子间电势来计算的。 DSMC模拟中的非弹性碰撞基于Borgnakke-Larsen碰撞模型的量子形式。给出了N_2，O_2，CO_2，CH_4和SF_6的结果，它们代表具有1至15个振动模式的双原子以及线性和非线性多原子分子。平移，旋转，振动和总温度以及热通量是在稀疏参数的宽范围内以及针对热板与冷板温度的各种比率计算的。在Holway和DSMC结果之间以及实验中都观察到非常好的一致性。证明了振动自由度的影响。在双原子气体中，振动热通量从总量的5％到25％不等。具有更高数量的振动模式的多原子气体的相应结果表明，即使在低参考温度下，振动热通量的贡献也可能更高。例如，在SF_6处于300 K和500 K的情况下，振动热通量分别约为总热通量的67％和76％。此外，从数值上证明，计算的解与计算域中心带中的Chapman-Enskog逼近一致，即使在稀疏参数的值较大的情况下也是如此（如先前的研究所示）。此属性已用于计算采用的模型预测的气体导热系数。

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