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首页> 外文期刊>The Journal of Chemical Physics >Widom line, dynamical crossover, and percolation transition of supercritical oxygen via molecular dynamics simulations
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Widom line, dynamical crossover, and percolation transition of supercritical oxygen via molecular dynamics simulations

机译：通过分子动力学模拟超临界氧的金属纸线，动态交叉和超临界氧的渗透过渡

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Supercritical oxygen, a cryogenic fluid, is widely used as an oxidizer in jet propulsion systems and is therefore of paramount importance in gaining physical insights into processes such as transcritical and supercritical vaporization. It is well established in the scientific literature that the supercritical state is not homogeneous but, in fact, can be demarcated into regions with liquid-like and vapor-like properties, separated by the "Widom line." In this study, we identified the Widom line for oxygen, constituted by the loci of the extrema of thermodynamic response functions (heat capacity, volumetric thermal expansion coefficient, and isothermal compressibility) in the supercritical region, via atomistic molecular dynamics simulations. We found that the Widom lines derived from these response functions all coincide near the critical point until about 25 bars and 15-20 K, beyond which the isothermal compressibility line begins to deviate. We also obtained the crossover from liquid-like to vapor-like behavior of the translational diffusion coefficient, shear viscosity, and rotational relaxation time of supercritical oxygen. While the crossover of the translational diffusion coefficient and shear viscosity coincided with the Widom lines, the rotational relaxation time showed a crossover that was largely independent of the Widom line. Further, we characterized the clustering behavior and percolation transition of supercritical oxygen molecules, identified the percolation threshold based on the fractal dimension of the largest cluster and the probability of finding a cluster that spans the system in all three dimensions, and found that the locus of the percolation threshold also coincided with the isothermal compressibility Widom line. It is therefore clear that supercritical oxygen is far more complex than originally perceived and that the Widom line, dynamical crossovers, and percolation transitions serve as useful routes to better our understanding of the superc
机译：超临界氧，低温流体广泛用作喷射推进系统中的氧化剂，因此在获得诸如跨临界和超临界蒸发的过程中的物理见解方面是至关重要的。在科学文献中，超临界状态不是均匀的，但实际上，可以划分为具有液体样和蒸气状的地区，由“国有线”分开。在本研究中，我们通过原子分子动力学模拟确定了由热力学响应函数（热容量，体积，热膨胀系数和等温可压缩性）的极值的基因座的氧气线。我们发现，来自这些响应函数的范围源于临界点附近，直到约25条和15-20 k，超出其等温可压缩线开始偏离的临界点。我们还获得了从液体状的交叉，以蒸汽的漫射系数，剪切粘度和超临界氧的旋转弛豫时间的蒸气状行为。虽然平移扩散系数和剪切粘度与光om线相吻合的交叉，但旋转弛豫时间显示了在很大程度上独立于国有线线的交叉。此外，我们表征了超临界氧分子的聚类行为和渗透转变，基于最大簇的分形维度确定渗透阈值以及找到跨越所有三个维度跨越系统的集群的概率，并发现轨迹渗透阈值也与等温可压缩性的太线线相吻合。因此，显然，超临界氧气比最初感知更复杂，并且金融线路，动态交叉和渗透过渡是有用的路线，以更好地了解超级级

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