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Visual characteristics and initial growth rates of round cryogenic jets at subcritical and supercritical pressures

机译:亚临界和超临界压力下圆形低温射流的视觉特征和初始增长率

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Cryogenic liquids initially at a subcritical temperature were injected through a round tube into an environment at a supercritical temperature and at various pressures ranging from subcritical to supercritical values. Pure N-2 and O-2 were injected into environments composed of N-2, He, Ar, and various mixtures of CO+N-2. The results were photographically observed and documented near the exit region using a CCD camera illuminated by a short duration backlit strobe light. At low subcritical chamber pressures, the jets showed surface irregularities that amplified downstream, exhibiting intact, shiny, but wavy (sinuous) surface features that eventually broke up into irregularly shaped small entities. A further increase of chamber pressure at constant jet initial and ambient temperatures caused the formation of many small droplets to be ejected from the surface of the jet similar to what is observed in the second wind-induced jet breakup regime. As the chamber pressure was further increased, the transition to a full atomization regime was inhibited near but slightly below the critical pressure. The jet structure at this point changed and began to resemble a turbulent gas jet with no detectable droplets. The reason was attributed to the reduction of the surface tension and enthalpy of vaporization as the critical pressure of the injectant is approached. The initial divergence angle of the jet was measured at the jet exit and compared with the divergence angle of a large number of other mixing layer flows, including atomized liquid sprays, turbulent incompressible gaseous jets, supersonic jets, and incompressible but variable density jets. The divergence angle for all these cases was plotted over four orders of magnitude in the gas-to-liquid density ratio, the first time such a plot has been reported over this large a range of density ratios. At and above the critical pressure of the injectant, the jet growth rate measurements agreed quantitatively with the theory for incompressible but variable density gaseous mixing layers. This is the first time a quantitative parameter has been used to demonstrate that the similarity between the two flows extends beyond a mere qualitative physical appearance. Finally, as the pressure is reduced to progressively more subcritical values, the spreading rate approaches that measured by others for liquid sprays. (C) 2002 American Institute of Physics. [References: 29]
机译:将最初处于亚临界温度的低温液体通过圆管注入到处于超临界温度和从亚临界到超临界值的各种压力的环境中。将纯净的N-2和O-2注入由N-2,He,Ar和CO + N-2的各种混合物组成的环境中。使用CCD相机以短时间背光频闪灯照明,对结果进行照相观察并记录在出口区域附近。在低亚临界腔室压力下,喷射流显示出表面不规则性,并向下游放大,表现出完整,发亮但呈波浪形(弯曲)的表面特征,最终分解为不规则形状的小实体。在恒定的喷嘴初始温度和环境温度下,腔室压力的进一步增加导致许多细小液滴的形成从喷嘴的表面喷射出来,这类似于在第二种风引起的喷嘴破裂状态中观察到的情况。随着腔室压力的进一步增加,在接近临界压力但略低于临界压力的情况下,抑制了向完全雾化状态的过渡。此时的射流结构发生了变化,开始类似于湍流的气体射流,没有可检测到的液滴。原因归因于随着接近喷射器的临界压力,表面张力的降低和汽化焓的降低。在射流出口处测量射流的初始发散角,并将其与大量其他混合层流的发散角进行比较,这些混合流包括雾化液体喷雾,湍流不可压缩气体射流,超音速射流以及不可压缩但可变密度的射流。所有这些情况的发散角在气液密度比上绘制了四个数量级,这是第一次在如此大的密度比范围内报道这种图。在喷射器的临界压力及以上时,射流生长速率的测量与不可压缩但密度可变的气态混合层的理论定量吻合。这是第一次使用定量参数来证明两个流之间的相似性超出了单纯的定性物理外观。最后,随着压力逐渐降低到亚临界值,散布速率接近其他喷雾剂测得的散布速率。 (C)2002美国物理研究所。 [参考:29]

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