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Probing free jet expansions of supercritical fluids

机译:探测超临界流体的自由射流膨胀

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摘要

Attempting to improve the comprehension of supersonic molecular beams at elevatedpressures we present a comparative study of thermodynamic descriptions of the terminal flowvelocity in free jet expansions. As model system we choose carbon dioxide due to itswidespread utilization in supercritical fluid technology. Numerical results for thethermodynamic quantities are obtained using a high accuracy equation of state explicit in theHelmholtz free energy. The influence of pressure and temperature on the beam velocity isinvestigated for a broad range of stagnation conditions. A consistent physical picture isobtained for calculations employing the initial and final molar enthalpies, while enormousdiscrepancies are found for descriptions based on the molar isobaric heat capacity or the heatcapacity ratio. The deviations are particularly pronounced at the gas—liquid phase transitionand in the vicinity of the critical point and can be related to the diverse assumptions of idealgas behavior. It is shown that computations using real fluid enthalpies permit to assess thefraction of condensation in supersonic jets.
机译:为了提高对超音速分子束在高压下的理解,我们对自由射流膨胀中的末端流速的热力学描述进行了比较研究。作为模型系统,我们选择二氧化碳是因为二氧化碳在超临界流体技术中的广泛利用。使用在亥姆霍兹自由能中显式表示的高精度状态方程获得热力学量的数值结果。对于广泛的停滞条件,研究了压力和温度对光束速度的影响。对于使用初始和最终摩尔焓的计算,可以获得一致的物理图像,而基于摩尔等压热容或热容比的描述,发现存在巨大差异。在气相-液相转变和临界点附近,这种偏差特别明显,并且可能与理想气体行为的各种假设有关。结果表明,使用实际流体焓的计算可以评估超声速射流中的冷凝分数。

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