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An experimental assessment of the enhancement of fuel droplet vaporization in a very high turbulence intensity environment
Proceedings of the Combustion Institute ( IF 5.3 ) Pub Date : 2020-11-28 , DOI: 10.1016/j.proci.2020.07.093
Cameron Verwey , Madjid Birouk

A zero-mean flow fan-stirred chamber is used to gather data on suspended fuel droplet evaporation at turbulence intensities, q1/2, approaching 4.30 m/s. This research is driven by the oft-cited but unconfirmed belief that the droplet evaporation rate, K, eventually plateaus with increasing turbulence kinetic energy. Further motivation comes from numerous real-world examples, including combustion systems, where droplets are exposed to turbulence intensities far beyond the experimental capabilities reported in the literature to date. Decane, ethanol, and heptane fuels are selected and grouped into two categories based on the similarity of their vapor pressures, Pv, and mass diffusivity coefficients, DAB, in an effort to discern which thermophysical properties are important to vaporization enhancement, or lack thereof, in high turbulence. Individual droplets with constant initial diameters, d0, of 500 µm are placed in the central region of a highly homogeneous and isotropic turbulent flow field using a novel multi-fiber intersection technique. Neither alkane fuel exhibits any sign of reduced effect of turbulence, as K/K0 remains a strongly linear function of turbulence intensity throughout the test conditions. Conversely, the normalized evaporation rate of ethanol begins to plateau at the higher levels of intensity. Although equalizing the vapor pressures of ethanol and heptane was sufficient to match K/K0 values at low intensity, their divergence as q1/2 increases implies that the thermodynamically-predicted vapor quantity at the droplet surface does not enforce an upper limit on turbulence effectiveness at moderately elevated temperatures. This is confirmed by decane, which has the lowest volatility and yet experiences the greatest improvement in evaporation rate at the highest levels of turbulence.



中文翻译:

在非常高的湍流强度环境中增强燃料滴蒸发的实验评估

零均流风扇搅拌室用于收集湍流强度q 1/2时接近4.30 m / s的悬浮燃料滴蒸发的数据。这项研究是基于经常被引用但未经证实的信念进行的,即液滴蒸发速率K最终随着湍流动能的增加而趋于平稳。进一步的动力来自许多现实世界的例子,包括燃烧系统,在这些系统中,液滴暴露于湍流强度之下,远远超出了迄今为止文献中报道的实验能力。根据癸烷,乙醇和庚烷的蒸气压P v和质量扩散系数D AB的相似性,选择癸烷,乙醇和庚烷燃料并将其分为两类。为了辨别哪种热物理性质对于在高湍流下增强或不增强汽化是重要的。使用新颖的多纤维相交技术,将具有恒定初始直径d 0为500 µm的单个液滴放置在高度均匀且各向同性的湍流场的中心区域。两种烷烃燃料都没有表现出降低湍流影响的迹象,因为在整个测试条件下,K / K 0仍然是湍流强度的强线性函数。相反,乙醇的标准化蒸发速率在较高强度下开始趋于平稳。尽管均衡乙醇和庚烷的蒸气压足以匹配K /K 0值在低强度下,随着q 1/2的增加而发散,这意味着在液滴表面进行热力学预测的蒸气量不会在温度适度升高时对湍流效率施加上限。癸烷证实了这一点,癸烷具有最低的挥发性,但在最高湍流水平下蒸发速率却得到最大改善。

更新日期:2020-12-01
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