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首页> 外文期刊>International Journal of Heat and Fluid Flow >Experimental study of external characteristics of a flashing water jet in water
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Experimental study of external characteristics of a flashing water jet in water

机译：水中闪水喷射外部特性的实验研究

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External characteristics of a flashing water jet released in water were studied using Particle Image Velocimetry and Shadowgraphy techniques for different pressure ratios and nozzle diameters. The flow dynamics of such a jet are dominated by vapor bubble formation due to thermal non-equilibrium and phase change processes. In order to gain insights into the physics of such complex flows, experiments were performed and measurements on velocity distribution and turbulence statistics were obtained. The bubble size distributions were also recorded to characterize the bubble disintegration mechanism. Flashing jet emanating from two different nozzle diameters, D = 5 mm and 2 mm, and at three different pressure ratios, P-R = 1.5 bar, 2 bar and 2.5 bar, were studied, at a fluid inlet temperature of T-0 = 380 K. The results revealed that the maximum value of centerline velocity occurs far downstream, at x = 0.02 m from the nozzle exit, due to the presence of vapor bubble formation that leads to an interaction between the liquid and gaseous phases. This is in contrast to a canonical water jet (i.e., without phase change), where the centerline velocity attains a maximum at the nozzle exit. For D = 5 mm, the turbulent kinetic energy (TICE) was higher and the decay rate was slower as compared to D = 2 mm for P-R = 2 bar. From the centerline velocity and TKE measurements, a critical injection pressure ratio, P-R 1.5 bar was documented, beyond which the external flow dynamics of the jet is governed primarily by the flashing mechanism. These observations were verified from the bubble size distribution measurements and can be attributed to thermal non-equilibrium and phase change process. Lastly, the presence of coherent structures in the flow reveals that the entrainment dynamics of a flashing jet is dominated by vorticity.
机译：使用颗粒图像速度和喷嘴直径的颗粒图像速度和影像技术研究水中释放在水中的闪蒸水射流的外部特性。这种喷射的流动动力学由由于热非平衡和相变过程引起的蒸气泡形成为主。为了进入这种复杂流的物理学的洞察，获得了实验，并获得了对速度分布和湍流统计的测量。还记录了气泡尺寸分布以表征泡沫崩解机制。从两个不同的喷嘴直径发出的闪光喷射，D = 5 mm和2 mm，并在三个不同的压力比下进行了PR = 1.5巴，2巴和2.5巴，在T-0 = 380 k的流体入口温度下。结果表明，由于存在蒸气泡形成，从喷嘴出口处，在X> =0.02μm处，在X> = 0.02m处发生的最大值。导致液相和气态相之间的相互作用，从喷嘴出口处发生在x> =0.02μm。这与规范水射流（即，没有相位变化）相反，其中中心线速度在喷嘴出口处达到最大值。对于D = 5mm，湍流动能（Tice）较高，与D = 2mm相比，衰减率较慢，对于P-R> = 2巴。从中心线速度和TKE测量，记录了临界注射压力比，P-R> 1.5巴，超出了喷射器的外部流动动态主要由闪光机构控制。这些观察结果从气泡尺寸分布测量验证，并且可以归因于热非平衡和相变过程。最后，流动中的相干结构的存在揭示了闪光射流的夹带动力学以涡流为主。

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