液-液水力旋流器两相湍动流数值模拟研究进展

对水力旋流器内的单相流场和液．液水力旋流器轻相浓度场两个方面的数值模拟研究进行了论述,通过分析国内外近二十年的重要研究成果,提出了今后液-液水力旋流器内两相湍流场数值研究的重点和发展方向。     

液液水力旋流器流场特性与分离特性研究（五）—压降比的影响因素分析

对液液水力旋流器的降比影响因素进行了简单的分析，分别研究了液液水力旋流器大，小锥角变化对其压降比的影响，并对其影响程度进行了细致的分析。     

液液水力旋流器流场特性与分离特性研究(五)──压降比的影响因素分析

对液液水力旋流器的压降比影响因素进行了简单的分析，分别研究了液液水力旋流器大、小锥角变化对其压降比的影响，并对其影响程度进行了细致的分析。     

液液旋流器中粒径、流量和效率的关系

在固液旋流器中 ,流量和粒径被孤立地看作是影响分离的两个参数。本文以除油旋流器的实验结果为基础 ,阐述了液液水力旋流器中流量的作用机理 ,以及液滴和流量之间的联系 ,综合分析了粒径和流量对分离的影响 ,定性地给出了液液水力旋流器的粒径 -流量 -效率曲线 ,并为液液旋流器的深入研究提供了新思路     

液液水力旋流器流场数值模拟技术研究

深入研究了液液水力旋流器的流动机理 ,用流体力学原理和方法建立了液液水力旋流器的物理模型并给出了修正的 k- ε模型 ,即 RNG k- ε模型。根据该模型 ,以 SIMPLER算法为基础 ,研究了数值计算方法并对具体实例作了计算。通过数值计算得到了液液水力旋流器内流体流动的速度矢量图和流线图。计算结果与理论分析一致 ,证明了模型和算法的正确性 ,为进一步研究旋流器的结构优化、粒子跟踪和旋流器特性参数对分离效率的影响等打下了基础。     

液液水力旋流器流场特性与分离特性研究(四)──锥角变化对压力损失的影响

对液液水力旋流器的压力损失分布情况进行了简单的介绍,分别研究了液液水力旋流器大、小锥角变化对其底流压力损失及溢流压力损失的影响,并对其影响程度进行了分析。     

液液水力旋流器场特性与分离特性研究（四）——锥角变化对压力损失的影响

对液液水力旋流器的压力损失分布情况进行了简单的介绍，分别研究了液液水力旋流器大、小锥角变化对其底流压力损失及溢流压力损失的影响，并对其影响程度进行了分析。     

液液水力旋流器流场特性与分离特性研究（四）—锥角变化对压力损失的影响

对液液水力旋流器的压力损失分布情况进行了简单的介绍，分别研究了液流水力旋流器大，小锥角变化对其底流压力损失及溢流压力损失的影响，并对其影响程度进行了分析。     

液-液旋流分离器内流场的数值模拟研究

用计算流体动力学(CFD)的数值方法,采用RSM模型对油水分离用液一液水力旋流器的流场进行了数值模拟。单相流场的模拟结果表明,旋流器内的流场结构是强旋转和非对称的三维结构,因而对旋流器的研究(无论是数值模拟还是实验测量)必须是基于三维的;旋流器上游区内流体紊流现象严重,两侧有循环流存在,这都对两相分离不利,应改进结构以改变这种流动形式;其模拟结果与他人实验结果吻合较好,说明该湍流模型和算法是可靠的。另外还对油一水两相流场进行了研究,初步揭示了液一液两相分离的现象,这都为进一步研究旋流器特性参数对分离效率的影响和旋流器的结构优化提供了参考。     

液—液分散雾化形成液滴的模式

基于图像采集与处理方法实验研究了水喷入非相溶油中的液液分散雾化过程.结果表明,通过改变操作条件使水破碎形成3种水滴模式:滴流、层流射流和湍流射流,揭示了其演变规律及其形成机理,获得了分散液体破碎强度、射流长度脉动和液滴粒径分布参数随雷诺数Re、韦伯数We的变化规律.随Re和We增加,分散液体破碎强度持续增强,在Re=467,We=8.6时液滴形成模式由滴流向层流射流发展,在Re=3169,We=241时演变为湍流射流,且液滴的粒径均匀性和最小平均粒径均出现在湍流射流模式下;在滴流模式下,液滴的形成、长大与脱离喷嘴均由液滴受力的平衡机制控制;在层流射流模式下,射流柱破碎形成液滴主要由两相界面的表面波扰动引起,且射流长度的脉动具有随机和非周期的特点;在湍流射流模式下,射流柱表面出现拟序涡结构,其在射流起始段失稳,在射流扩散段大量形成较小粒径的液滴.     

动态旋流器液滴破碎研究

本文介绍了动态旋流器的分离原理和结构特点，结合前人对液滴破碎的研究成果，分析了动态旋流器液滴破碎机理。通过对旋流器中湍动能的分析研究，总结出动态旋流器内液滴破碎的主要原因和部位。     

导叶式旋流器内油滴的聚结破碎及影响因素

利用流场测试实验和模拟计算对导叶式旋流器的内部流场和湍流性能进行研究,得到导致旋流场中油滴发生聚结破碎现象的内因为时均速度梯度引起的黏性剪切力和湍流流动引起的高剪切应力及湍动能,并分析了油滴破碎的主要发生部位。同时为宏观考察导叶式旋流器内油滴聚结与破碎相对作用强弱,验证了旋流器的分离性能作为表征量的可行性,并在此基础上,利用导叶式旋流器的分离性能实验结果对油滴聚结破碎发生的外因进行研究,结果表明导向叶片的结构参数（叶片数和叶片出口角）和旋流器的操作参数（入口流速、溢流率、分散相入口浓度和操作温度）均会影响到油滴在旋流器中的存在和运动形态。     

A model for drop and bubble breakup frequency based on turbulence spectra

In this article, a new Eulerian model for breakup frequency of drops induced by inertial stress in homogeneous isotropic turbulence is developed for moderately viscous fluids, accounting for the finite response time of drops to deform. The dynamics of drop shape in a turbulent flow is described by a linear damped oscillator forced by the instantaneous turbulent fluctuations at the drop scale. The criterion for breakup is based on a maximum value of drop deformation, in contrast with the usual critical Weber criterion. The breakup frequency is then modeled as a function of the power spectrum of Weber number (or velocity square), based on the theory of oscillators forced by a random signal, which can be related to classical statistical quantities, such as dissipation rate and velocity variance. Moreover, the effect of viscosities of both phases is included in the breakup frequency model without resorting to any additional parameter. © 2018 American Institute of Chemical Engineers AIChE J, 65: 347–359, 2019     

Transformation of single drop breakup from binary to ternary and multiple in turbulent jet flows

By releasing liquid drops in turbulent jet flows,we investigated the transformation of single drop breakup from binary to ternary and multiple.Silicone oil and deionized water were the dispersed phase and con-tinuous phase,respectively.The probability of binary,ternary,and multiple breakup of oil drops in jet flows is a function of the jet Reynolds number.To address the underlying mechanisms of this transfor-mation of drop breakup,we performed two-dimensional particle image velocimetry(PIV)experiments of single-phase jet flows.With the combination of drop breakup phenomenon and two-dimensional PIV results in a single-phase flow field,these transformation conditions can be estimated:the capillary number ranges from 0.17 to 0.27,and the Weber number ranges from 55 to 111.     

激波与亚毫米液滴相互作用的二维和三维数值模拟研究

为了研究激波与亚毫米液滴相互作用过程,基于现有的实验结果,利用Fluent平台,采用VOF (Volume of Fluid)多相流模型和k-ε 湍流模型,通过二维数值模拟分析了不同韦伯数(We)对亚毫米液滴变形演化过程的影响规律,通过三维数值模拟揭示了亚毫米液滴爆炸式破碎机理。结果表明,韦伯数对液滴变形有促进作用,韦伯数越大,液滴在压缩变形阶段所需要的时间越短;在气动力不变的条件下,相同液滴直径条件下,马赫数越大,液滴所受的气动力越大,液滴质心位移的无量纲加速度越大,低韦伯数下液滴的横向展开速率随韦伯数增大而减小,而高韦伯数下液滴的横向展开速率随韦伯数增大而增大。数值模拟结果与对比实验结果相近,有效阐明了韦伯数对亚毫米液滴变形的作用。     

Numerical simulation of two-phase flow and droplet breakage of glycerin-water mixture and kerosene in the cyclone reactor

A liquid-liquid cyclone reactor(LLCR)was designed to achieve mixing-reaction-separation integration during isobutane alkylation catalyzed by ionic liquids.However,studies of the droplets deformation and breakage in the kind of reactors are lacking.In this work,the research studied the velocity distribu-tion,pressure field,and turbulent field to investigate the flow pattern and the main energy loss location in the LLCR through the computational fluid dynamics(CFD)method.The simulation results were verified by experiemnts to prove the correctness of the model.Then the deformation and breakage process of dro-plets,and the influencing factors of droplets breakage were studied by remodeling which was based on the tangential velocity distribution result of the three dimensional model.The three dimensional simu-lation results clearly showed that the pressure of the LLCR was mainly concentrated in the cone section and fluid turbulent motion was the most intense near the lateral wall,The reconstruct the results of the two dimensional model clearly showed that the deformation and breakage location of droplets were mainly occurred in the velocity boundary layer,while it was difficult to break in the mainstream region.In addition,low surface tension and high Weber number had a positive effect on droplet breakage.     

Liquid-liquid mixing for the breakup of accelerating drops

Studies have been made on the fragmentation of liquid metal drops falling through a waterglycerine mixture containing small amounts of nitrogen bubbles owing to the passage of a strong shock wave. The apparent drop volume increased with lime, but neither stripping of small droplets nor misty wake formation was observed in the high-speed photographs. The drop flattened initially into a spherical cap which increased in radius, but remained smooth, within the time period of interest. Hence the Taylor instability is not the principal fragmentation mechanism at these Weber numbers (5-644). Entrainment of liquid into the drop was the cause of breakup, and was postulated to be due to turbulent mixing resulting from vorticity generation near the plane of separation. A hydrodynamic fragmentation model was developed which predicts the rale of drop volume increase reasonably well. The breakup time constant was presented, and drop trajectory can also be predicted from the model.     

Characterizations of Cloud Droplet Shatter Artifacts in Two Airborne Aerosol Inlets

Aircraft-based aerosol sampling in clouds is complicated by the generation of shatter artifact particles from aerodynamic or impaction breakup of cloud droplets and ice particles in and around the aerosol inlet. Aerodynamic breakup occurs when the Weber number of a droplet, which primarily depends on the droplet size and the magnitude of the relative motion of the droplet and the local air mass, exceeds a critical value. Impaction breakup of a droplet occurs when the droplet's impaction breakup parameter, K, which is a combination of Weber and Ohnesorge numbers, exceeds a critical value. Considering these two mechanisms, the critical breakup diameters are estimated for two aerosol inlets of different designs—a conventional forward-facing solid diffuser inlet (SDI) and a cross-flow sampling sub-micron aerosol inlet (SMAI). From numerical simulations, it is determined that cloud droplets of all sizes will experience impaction breakup in SDI, while only droplets larger than ～16 μm will experience impaction breakup in SMAI. The relatively better in-cloud sampling performance of SMAI is because of its cone design that slows the flow just upstream of the sample tube. The slowing upstream flow, however, causes aerodynamic breakup of drops larger than ～100 μm. The critical breakup diameters determined from analysis of field data largely validate numerical predictions. The cross-flow sampling design of SMAI is seen to ensure that shatter artifacts in the inlet are minimal even when there are a significant number of particles larger that the critical breakup size. The study results, thus, suggest that the SMAI design presents an effective approach to sample interstitial particles from aircraft.

© 2013 American Association for Aerosol Research     

Single drop breakup in turbulent flow

The breakup process of a single drop in homogeneous isotropic turbulence was studied using direct numerical simulations. A diffuse interface free energy lattice Boltzmann method was applied. The detailed visualization of the breakup process confirmed breakup mechanisms previously outlined such as initial, independent, and cascade breakups. High‐resolution simulations allowed to visualize another drop breakup mechanism, burst breakup, which occurs when the mother drop has a large volume, and the flow is highly turbulent. The simulations indicate that the type of the breakup mechanism is a strong function of mother drop size and energy input. Large mother drops in highly turbulent flow fields are more likely to burst, producing a large number of drops of the size close to the Kolmogorov length scale. Small drops in moderate turbulence tend to break only once (initial breakup). The interfacial energy of a drop was tracked as a function of time during drop deformation and breakage. The maximum energy level of the deformed mother drop was compared to commonly used estimates of critical energy necessary to break a drop. Our results show that these reference levels of critical energy are usually underestimated. Moreover, in some cases even if the critical energy level was exceeded, the drop did not break because the time of the interaction between the drop and the eddies was not enough to finish the breakup. The numerical insight presented here can be used as a guideline for the selection of assumptions and simplifications behind breakup kernels.     

Break-up of droplets in Karr reciprocating plate extraction column

The breaking rate of individual drops was investigated in a Karr type reciprocating plate extraction column. The binary systems used were: water-1,2-dichloroethane, water-toluene and water-n-butanol. The breakage probability and the conditional probability of breaking-up into a given number of daughter droplets, as well as the drop size distribution of daughter droplets, were the measured characteristics. Relations between the breakage probabilities and the breakage frequency were derived.A mathematical model of the frequency of breaking-up into > and more droplets developed was based on the assumption that collisions with turbulent eddies of the Kolmogoroff region of universal equilibrium are responsible for the process. A probabilistic model of daughter drop size distribution was also derived in the form of a β-distribution. The models were compared with experimental results and a good agreement was obtained.