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排序方式: 共有446条查询结果,搜索用时 62 毫秒
81.
《Journal of Nuclear Science and Technology》2013,50(12):1006-1022
When subcooled water in accumulator tanks is injected during a loss-of-coolant accident of a pressurized water reactor, violent condensation takes place in cold legs because of direct contact of steam with water. A flow model based on the multifluid model of the two-phase flow has been developed to formulate the condensation and mixing processes in the injection region. The measured liquid film temperature and pressure profiles in the injection region have been explained quantitatively with the model which includes (a) drop generation arising from atomization of injected water, (b) condensation of steam on the drops, (c) flow contraction resulting from the formation of the dead water region, and (d) deposition of the drops. The calculated results show that the condensation rate depends mostly on the drop diameter generated near the water injection nozzle and the maximum drop mass fraction in the injection region. The present model can predict the effect of inlet thermal-hydraulic conditions on the condensation rate qualitatively, and then it has been confirmed that higher condensation rate with initial steam mass velocity is caused by the formation of finer drops and the higher drop mass fraction in the injection region. 相似文献
82.
The dispersion characteristics of respiratory droplets are important in controlling transmission of airborne diseases indoors.
This study investigates the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets
within the range of 1.0 − 10.0μm in an office room with three air distribution methods, specifically mixing ventilation (MV),
displacement ventilation (DV), and under-floor air distribution (UFAD). The diffusion, gravitational settling and deposition
mechanism of particulate matter were accounted by using an Eulerian modeling approach with one-way coupling. The simulation
results indicate that exhaled droplets up to 10μm in diameter from normal human respiration are uniformly distributed in MV.
However, they become trapped in the breathing zone by thermal stratifications in DV and UFAD, resulting in a higher droplet
concentration and an increased exposure risk to other room occupants. Sneezed/coughed droplets are more slowly diluted in
DV/UFAD than in MV. Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the
breathing zone. 相似文献
83.
双旁路耦合电弧MIG焊熔滴过渡受力分析 总被引:2,自引:0,他引:2
针对双旁路耦合电弧熔化极惰性气体保护(Metal inert gas,MIG)焊过程,使用高速摄像采集不同旁路电流下的熔滴过渡图像,通过图像处理提取熔滴过渡数据信息,并对熔滴所受的主要作用力进行定量计算。根据计算结果对比分析不同参数下熔滴受力的动态变化情况,研究旁路电弧对熔滴过渡的促进机理。结果表明,在焊接总电流较大的情况下电磁力对双旁路耦合电弧MIG焊熔滴过渡的影响最显著,旁路电弧可以促进熔滴上弧根面积的扩展和熔滴缩颈的形成,通过增加向下的电磁力来促进熔滴过渡,且旁路电流越大旁路电弧对熔滴过渡的促进作用越明显;在焊接总电流不变的情况下,随着旁路电流的增加熔滴过渡频率随之增加,熔滴尺寸随之减小,熔滴过渡形式逐渐由大滴过渡转变为喷射过渡。 相似文献
84.
《分离科学与技术》2012,47(7):991-1002
This work investigated the effects of breakage and coalescence on de-oiling hydrocyclone performance utilizing Computational Fluid Dynamics (CFD). It was found that an increase in the entrance flow rate with low entrance oil concentration not only did not increase the separation performance of the hydrocyclone but it also decreased the separation efficiency. On the contrary, the hydrocyclone performance was enhanced with increasing the inlet velocity. Furthermore, a comparison between the standard design and the conical inlet chamber design was drawn in terms of separation efficiency for low entrance oil concentration; the results depicted that the conical design had higher separation efficiency. 相似文献
85.
以简单线性剪切流为背景,采用VOF模型及若干自定义子程序进行模拟分析,探讨物性对油滴变形和破碎的影响关系。模拟表明:粘度对变形起到抑制作用,粘度越大,变形越难,更能耐受剪切流动;表面张力越小,油滴越容易发生变形和破碎,稳定性越差,表面张力阻止了油滴的变形;油滴粒径越大,越易变形、破碎,越不稳定。 相似文献
86.
87.
Winston Duo Wu Sean Xuqi Lin Xiao Dong Chen 《American Institute of Chemical Engineers》2011,57(6):1386-1392
In this article, a glass nozzle driven by piezoceramics is used to experimentally study the continuous generation of a stream of monodisperse droplets from the breakup of a liquid jet. The approach is demonstrated by examining the breakup dynamics of three distinct liquids. The droplet formation process has been found to be highly controllable and reproducible. The dependence of nozzle performance on liquid properties, flow rate, and disturbance frequency has been investigated. The ratio between the actual disturbance frequency and Reynolds number, ω, is employed at first to represent the operating range that facilitates monodisperse droplet formation. Then, the dimensionless quantity ω*, obtained by multiplying ω by the viscous characteristic time, r/(μ/ρ), has been shown to collapse the data for the lower and higher bounds of the actual disturbance frequency ranges that secure monodispersity of the droplets of all the samples tested. The impacts of liquid flow rate and disturbance frequency on the monodisperse droplet size and spacing between two neighboring droplets have been investigated and discussed. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
88.
Static mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
89.
90.
Arshad Khan D. Sen P. Kothalkar B. K. Sapra S. Mazumder Y. S. Mayya 《Drying Technology》2013,31(6):679-686
This work discusses the design, development, and performance of an indigenous laboratory spray dryer with a relatively slow drying rate. The drying time of droplets of colloidal silica (5 wt%) and sodium chloride solution (20 wt%) in this spray dryer was nearly 10 s. The present system was composed of a four-jet compressed air nebulizer that generates a droplet size of 2–5 µm with a nebulization rate of nearly 60 mL/h. The generated powder can be collected using a cyclone or a wire mesh collector. Design and characterization of this system as well as characterization of the micrometric self-assembled powder grains obtained by this spray dryer are discussed. 相似文献