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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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将瞬态团簇尺寸分布模型引入蒸汽冷凝体系,通过求解描述团簇增长的动力学方程,模拟研究了特定冷凝条件下团簇及微小液滴尺寸分布的演化特征。模型结果表明,核化过程中,团簇/微液滴尺寸分布迅速从单调递减式分布转变为近似正态分布特征。随着时间延长,尺寸分布的峰值向团簇/微液滴尺寸增加的方向移动。在壁面冷凝过程中,核化生成的最小液滴也具有一定分布,进一步完善了经典冷凝理论中对初始冷凝过程液滴分布和演化过程的描述。同时模拟结果与文献报道的微米级液滴生长演化趋势相似,表明较大尺寸液滴分布特征是核化阶段团簇/微液滴尺寸分布特征进一步演化的结果,揭示了冷凝过程液滴尺寸分布演化的微观物理本质。 相似文献
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低压蒸汽滴状冷凝过程中液滴生长特性 总被引:1,自引:0,他引:1
研究了低压条件对滴状冷凝过程液滴生长特性的影响。首先,研究了超疏水表面上空气环境和蒸汽环境中附着液滴的接触角,发现蒸汽环境中的接触角比空气环境中的小,而蒸汽压力对接触角没有显著影响。第二,实验研究了冷凝过程中的液滴的生长周期和脱落尺寸,液滴的脱落半径随压力的降低而增大,生长周期也随之延长。第三,实验研究了液滴合并生长速率,并结合理论分析直接冷凝长大的生长速率,直接冷凝生长速率随压力的减小而减小,并随过冷度的减小而下降,而实验范围内合并生长速率不受压力影响。第四,根据滴状冷凝液滴分布的时间序列模型,分析了不同压力下液滴生长的临界尺寸,随着压力的降低,液滴生长方式的临界尺寸增大。 相似文献
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为了更加深入了解超燃冲压发动机燃烧室中的燃料雾化机理,对来流Mach数为1.94的超声速气流中液体横向射流的雾化过程进行了数值模拟研究.计算采用Euler-Lagrange方法,液滴二次破碎模型采用K-H/R-T模型.计算结果表明:考虑液滴二次破碎时,采用雾化锥模型获得的射流穿透深度以及液滴速度分布与实验结果符合得很好;初始液滴直径对射流穿透深度和液滴分布的影响很小;随着初始雾化锥角的增加,相同横截面上的射流穿透深度逐渐减小.当不考虑液滴二次破碎时,液滴穿透深度及分布与所选的初始液滴直径有很大关系. 相似文献
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Shiro Yoshida 《Zeitschrift für Physik A Hadrons and Nuclei》1982,308(2):133-143
The exciton model is applied to a multi-nucleon emission process after fusion caused by heavy-ion collisions. The master equations for the probability distribution are successively solved by assuming an initial distribution calculated by using a simple Fermi gas model. The equilibration process is discussed, and the results are compared with those of the equilibrium statistical theory and experimental data. 相似文献
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A. V. Andriyash S. A. Dyachkov V. V. Zhakhovsky D. A. Kalashnikov A. N. Kondratev S. E. Kuratov A. L. Mikhailov D. B. Rogozkin A. V. Fedorov S. A. Finyushin E. A. Chudakov 《Journal of Experimental and Theoretical Physics》2020,130(3):338-357
The results of photon Doppler velocimetry of ejecta from shock-loaded metal samples are reported. The experiments have been performed with tin and lead samples of a given thickness and a given surface roughness. The direct numerical simulation of the process of mass ejection from the surface of shock-loaded samples is performed for conditions close to experimental by the smoothed particle hydrodynamics method. The areal density and initial velocity distribution of the volume density of ejecta are determined. Using these results, we calculate the time dependence of the profile of the volume density at the expansion of the formed dust cloud to air. Applying an approach based on the transport equation for the correlation function of the scattered field, the main parameters of the velocity distribution of ejecta, areal density of ejecta, etc. are reconstructed from spectral photon Doppler velocimetry data. The experimentally observed temporal dynamics of spectra, which is caused by the drag of dust in air, is described at an appropriately chosen size dispersion of dust particles. The masses of ejecta reconstructed from experimental data are in agreement with the smoothed particle hydrodynamics results. 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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This paper presents experimental and simulation results of cold spray coating deposition using the mask placed above the plane substrate at different distances. Velocities of aluminum (mean size ~ 30 μm) and copper (mean size ~ 60 μm) particles in the vicinity of the mask are determined. It was found that particle velocities have angular distribution in flow with a representative standard deviation of 1.5–2 degrees. Modeling of coating formation behind the mask with account for this distribution was developed. The results of model agree with experimental data confirming the importance of particle angular distribution for coating deposition process in the masked area. 相似文献
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本文用Lagrange方法结合起跳沙粒初始运动状态分布模拟了稳态风沙输运过程。根据已有的对地表沙粒撞击起跳现象的研究成果,列出四种典型的沙粒起跳初始运动状态分布形式。将在各分布形式下模拟得到的宏观量与风洞实验测量得到的宏观量的变化规律相比较,通过考察依据各分布形式所作数值模拟得到的风沙宏观运动的特征量与实验测量结果的一致程度,得到了其中较合理的分布形式。分析表明稳定风沙输运中起跳沙粒的初始速度和角度的分布曲线均应为一单调下降曲线,根据实验数据本文构造出由指数分布和正态分布组成的分段函数形式来描述这一曲线。并通过进一步的实验验证了这一分布形式的合理性。 相似文献
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We propose a branching process based on a dynamical scaling hypothesis relating time and mass. In the context of earthquake occurrence, we show that experimental power laws in size and time distribution naturally originate solely from this scaling hypothesis. We present a numerical protocol able to generate a synthetic catalog with an arbitrary large number of events. The numerical data reproduce the hierarchical organization in time and magnitude of experimental interevent time distribution. 相似文献
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Dong-Joo Kim Kyo-Seon Kim 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2003,31(2):227-235
The particle formation and growth combined with plasma chemistry in the pulsed corona discharge process (PCDP) to remove NO/sub x/ were analyzed by the discrete-sectional model. In the PCDP, most of the NO is converted into NO/sub 2/ and, later, into HNO/sub 3/ which reacts with NH/sub 3/ to form the NH/sub 4/NO/sub 3/ particle. In the beginning of the reactor, we have the high concentration of small size particles and, later, the particle size distribution in the reactor becomes bimodal with the large size and small size particles and, finally, becomes monodisperse with the large size particles. As the average electron concentration increases, it takes a shorter reactor length to remove the NO/sub x/. As the initial NO and H/sub 2/O concentrations decrease, the NH/sub 3/ is consumed more slowly to form the ammonium nitrates particles. As the averaged electron concentration and initial H/sub 2/O concentration increase, the large size particles grow more quickly and the particle size distribution becomes bimodal earlier. As the initial NO and NH/sub 3/ concentrations increase, the diameter of large size particles becomes larger by the faster coagulation between particles. The predicted NO/sub x/ conversion and particle size distribution were in close agreements with the published experimental results at the averaged electron concentration of 2/spl times/10/sup 5/ cm/sup -3/ in this study. 相似文献
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E. V. Lipnyagov S. A. Perminov G. V. Ermakov B. M. Smolyak 《Thermophysics and Aeromechanics》2009,16(4):627-633
Results of statistical measurement of n-pentane and n-hexane boiling-up expectancy time near the boundary of attainable superheating
are presented. Experiments were carried out in glass capillaries with various volumes of superheated liquid. Several samples
with the volume from 100 to 200 measurements of life time for preset metastable state have been obtained (p, T = const). Their histograms contain small empty initial section, maximum and long “tail” in the area of large times. Non-monotonous
dependence of probability distribution density on time proves non-stationary character of the random process resulting in
the production of supercritical embryo. Two simple approximations of non-stationary nucleation flow well describing experimental
data have been considered. For exponential distribution, the probabilities of experimentally found peculiarities of boiling-up
expectancy time distribution density have been evaluated; they prove incompatibility of this distribution with the experimental
one. 相似文献