共查询到19条相似文献,搜索用时 125 毫秒
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对水蒸气超音速非平衡凝结流动进行了数值模拟,研究了水蒸气超音速流动过程中的非平衡相变及凝结激波现象,揭示了压缩激波与核化凝结流动之间相互作用的非平衡流动规律.发现了激波的耗散效应对非平衡相变的影响,探讨了激波发生时,波阵面处核化凝结、液滴生长的变化规律. 相似文献
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高温熔融液滴的破碎特性研究 总被引:2,自引:0,他引:2
本文采用高速摄影和数字图像处理技术对高温熔融液滴与冷却水作用时的破碎现象进行了研究,用图像技术对高速摄影(1000 fps,512×512象素)照片进行处理,识别液滴破碎后所形成的碎片,并统计出碎片的数目及尺寸分布;还对液滴温度、冲击速度、水温等因素对液滴破碎过程的影响进行了实验研究和分析。研究结果表明,随着实验条件的改变,液滴破碎后的碎片有三种典型形态,冷却水温度对碎片形态有重要影响;碎片的当量直径符合累积高斯分布,分布曲线可用Sigmoid函数表示;冷却水温度越高,冲击高度越大,液滴温度越高,液滴的破碎过程进行得越彻底。 相似文献
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《工程热物理学报》2017,(11)
为了深入研究闪急沸腾喷雾二次破碎即大尺度液滴的破碎机理,本课题以甲醇和乙醇两种燃料为研究对象,利用特殊设计的过热液滴发生器,通过显微阴影成像技术捕捉并分析处于闪沸状态过热液滴的宏观形态、内部空隙率及其破碎特性,研究表明:甲醇及乙醇两种燃料的过热液滴形态主要受液滴温度和过热度影响,而当过热度增加时,液滴内空隙率逐渐增加,从而显著降低了液滴的表面张力。此外,当过热度达到250C时,过热液滴内部空隙率超过50%从而发生剧烈破碎,伴随产生大量小尺度液滴,标志着闪沸喷雾二次破碎模式由传统的机械破碎模式向热力学破碎模式的转变。同时结果表明对于两种实验燃料,过热液滴破碎的临界过热度及对应的空隙率数值基本不变。 相似文献
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Hiroaki Watanabe Akiko Matsuo Ashwin Chinnayya Ken Matsuoka Akira Kawasaki Jiro Kasahara 《Proceedings of the Combustion Institute》2021,38(3):3709-3716
Two-dimensional numerical simulations are conducted based on the Eulerian-Lagrangian method to model a gaseous detonation laden with monodispersed water droplets. The premixed mixture is a slightly diluted stoichiometric hydrogen oxygen mixture at low pressure. The outcome of the interactions of the droplet breakup with the cellular instabilities and the non-uniform flow behind the leading front is analyzed. The simulation results are also analyzed using instantaneous flow fields and Favre average profiles for water droplets. Breakup occurs mainly near the detonation front. The mean final diameter of the water droplets at the end of the breakup process is the same regardless of the initial strength of the leading shock or whether it is lower or greater than the Chapman-Jouguet value. The polydispersity comes from local phenomena behind the leading shock, such as forward jets coming from triple point collisions, transverse waves and a combination of both. The total breakup time is longer than that estimated from post-shock conditions and the present finding is in line with the previous experimental results on spray detonation. 相似文献
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The breakup of an uncharged electrically conducting liquid dropet placed in a uniform electrostatic field into two daughter droplets caused by strong nonspheroidal deformation is qualitatively analyzed by applying the principle of minimum potential energy under spontaneous virtual variations of the droplet’s state. It is shown that the breakup mechanism involves asymmetric mass distribution among the daughter droplets, which are found to be stable with respect to their respective intrinsic charges. 相似文献
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《Physics letters. A》2014,378(5-6):539-548
Experiments involving heating of liquid droplets which are acoustically levitated, reveal specific modes of oscillations. For a given radiation flux, certain fluid droplets undergo distortion leading to catastrophic bag type breakup. The voltage of the acoustic levitator has been kept constant to operate at a nominal acoustic pressure intensity, throughout the experiments. Thus the droplet shape instabilities are primarily a consequence of droplet heating through vapor pressure, surface tension and viscosity. A novel approach is used by employing Legendre polynomials for the mode shape approximation to describe the thermally induced instabilities. The two dominant Legendre modes essentially reflect (a) the droplet size reduction due to evaporation, and (b) the deformation around the equilibrium shape. Dissipation and inter-coupling of modal energy lead to stable droplet shape while accumulation of the same ultimately results in droplet breakup. 相似文献
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基于体积分数法建立了Y型微通道中双重乳液流动非稳态理论模型,数值模拟研究了Y型微通道内双重乳液破裂情况,详细分析了双重乳液流经Y型微通道时的流场信息以及双重乳液形变参数演化特性,定量地给出了双重乳液流动破裂的驱动以及阻碍作用,揭示了双重乳液破裂流型的内在机理.研究结果表明:流经Y型微通道时,双重乳液受上游压力驱动产生形变,形变过程中乳液两端界面张力差阻碍双重乳液形变破裂,两者正相关;隧道的出现将减缓双重乳液外液滴颈部收缩速率以及沿流向拉伸的速率,并减缓了内液滴沿流向拉伸的速率,其对于内液滴颈部收缩速率影响不大;隧道破裂和不破裂工况临界线可以采用幂律关系式l~*=βCa~b进行预测,隧道破裂和阻塞破裂工况临界线可以采用线性关系l~*=α描述;与单乳液运动相图相比,双重乳液运动相图各工况的分界线关系式系数α和β均相应增大. 相似文献
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WooTae Kim SushantaK. Mitra Xianguo Li L.A. Prociw T.C.J. Hu 《Particle & Particle Systems Characterization》2003,20(2):135-149
The distribution of sizes and velocities of droplets initially formed in sprays is an important piece of information needed in the spray modelling, because it defines the initial condition of the spray droplets in the predictive calculations of the downstream two‐phase flow fields. A predictive model for the initial droplet size and velocity distributions in sprays is formulated in this study. The present model incorporates both the deterministic and the stochastic aspect of spray formation process. The deterministic aspect takes into account of the unstable wave motion before the liquid bulk breakup through the linear and nonlinear instability analysis, which provides information for the liquid bulk breakup length, the mass‐mean diameter and a prior distribution for the droplet sizes corresponding to the unstable wave growth of various wavelengths. The stochastic aspect deals with the final stage of droplet formation after the liquid bulk breakup by statistical means through the maximum entropy principle based on Bayesian entropy. The two sub‐models are coupled together by the various source terms signifying the liquid‐gas interaction, the mass mean diameter and the prior distribution based on the instability analysis. The initial droplet size and velocity distributions are measured experimentally by phase‐Doppler interferometry for sprays generated by a planar research nozzle and a practical gas turbine airblast nozzle. For the two nozzles, the liquid bulk sheet is formed before its breakup in a coflowing air stream. It is found that the model predictions are in satisfactory agreement with the experimental data for all the cases measured. Hence the present model may be applied to a variety of practical sprays to specify the initial conditions for the spray droplets formed in practical spray systems. 相似文献
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Using lattice Boltzmann approach, a phase-field model is proposed for simulating droplet motion with soluble surfactants. The model can recover the Langmuir and Frumkin adsorption isotherms in equilibrium. From the equilibrium equation of state, we can determine the interfacial tension lowering scale according to the interface surfactant concentration. The model is able to capture short-time and long-time adsorption dynamics of surfactants. We apply the model to examine the effect of soluble surfactants on droplet deformation, breakup and coalescence. The increase of surfactant concentration and attractive lateral interaction can enhance droplet deformation, promote droplet breakup, and inhibit droplet coalescence. We also demonstrate that the Marangoni stresses can reduce the interface mobility and slow down the film drainage process, thus acting as an additional repulsive force to prevent the droplet coalescence. 相似文献
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《中国物理 B》2020,(5)
On the basis of a volume of fluid(VOF) liquid/liquid interface tracking method, we apply a two-dimensional model to investigate the dynamic behaviors of droplet breakup through a splitting microchannel. The feasibility and applicability of the theoretical model are experimentally validated. Four flow regimes are observed in the splitting microchannel, that is, breakup with permanent obstruction, breakup with temporary obstruction, breakup with tunnels, and non-breakup. The results indicate that the increase of the capillary number Ca provides considerable upstream pressure to accelerate the droplet deformation, which is favorable for the droplet breakup. The decrease of the droplet size contributes to its shape changing from the plug to the sphere, which results in weakening droplet deformation ability and generating the nonbreakup flow regime. 相似文献
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The paper presents the experimental research findings for the integral characteristics of processes developing when two-phase liquid droplets collide in a heated gas medium. The experiments were conducted in a closed heat exchange chamber space filled with air. The gas medium was heated to 400–500 °C by an induction system. In the experiments, the size of initial droplets, their velocities and impact angles were varied in the ranges typical of industrial applications. The main varied parameter was the percentage of vapor (volume of bubbles) in the droplet (up to 90% of the liquid volume). The droplet collision regimes (coalescence, bounce, breakup, disruption), size and number of secondary fragments, as well as the relative volume fraction of vapor bubbles in them were recorded. Differences in the collision regimes and in the distribution of secondary fragments by size were identified. The areas of liquid surface before and after the initial droplet breakup were determined. Conditions were outlined in which vapor bubbles had a significant and, on the contrary, fairly weak effect on the interaction regimes of two-phase droplets. 相似文献
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A combined experimental and numerical study is undertaken to investigate the hydrodynamic characteristics of single-phase droplet collision in a shear flow. The passing-over motion of interactive droplets is observed, and the underlying hydrodynamic mechanisms are elucidated by the analysis of the motion trajectory, transient droplet deformation and detailed hydrodynamic information (e.g., pressure and flow fields). The results indicate that the hydrodynamic interaction process under shear could be divided into three stages: approaching, colliding, and separating. With the increasing confinement, the interaction time for the passing-over process is shorter and the droplet processes one higher curvature tip and more stretched profile. Furthermore, the lateral separation Δy/R1 exhibits larger decrease in the approaching stage and the thickness of the lubrication film is decreased during the interaction. As the initial lateral separation increases, the maximum trajectory shift by the collision interaction is getting smaller. During the collision between two droplets with different sizes, the amplitude of the deformation oscillation of the larger droplet is decreased by reducing the size ratio of the smaller droplet to the bigger one. 相似文献