气液喷射反应器内液滴粒径分布PLIF研究

气液喷射反应器是一种高强度反应器,反应器内部液滴粒径大小和分布对反应收率和选择性具有决定性影响。本文建立了气液喷射反应器内液滴粒径分布测量实验装置,并利用面激光诱导荧光（PLIF）技术对气液喷射反应器内液滴粒径分布进行了研究,得到不同气液流率情况下的液滴粒径的分布规律,结果显示：液相流率不变时,随气相流率的增大,反应器内液滴平均粒径逐渐减小,分布范围变小; 气相流率不变时,随液相流率的增大,液滴平均粒径逐渐减小,粒径分布趋于集中。     

Remote measurement of the aerosols size distribution by lidar

The purpose of this paper is the remote and spatially resolved measurement of the aerosols size distribution in the atmosphere and in particular of water droplets in clouds and fogs. The technique is based on the well-known backscattering LIDAR (LIght Detection and Ranging) [1] technique, using different wavelengths (598.8 nm, 299.4 nm) and a stochastic based inversion algorithm.     

压力旋流喷嘴雾化滴径分布的模型预测和实验

利用激光片光荧光诱导技术（PLIF）测得不同液体流量下的压力旋流喷嘴雾化滴径分布,用平均粒径约束的三参数最大熵模型对雾化滴径分布进行预测。将理论预测分布与实验结果进行拟合,得到广义伽玛参数α随着液体流量变化的一般表达式。用拟合模型对粒径分布的特点和规律进行总结,结果表明：拟合模型能很好地预测粒径的数量分布,且不受小液滴的影响;随着液体流量的增加,液滴粒径分布范围逐渐变窄,峰值液滴粒径呈线性减小趋势,峰值液滴百分数呈线性增加趋势。     

甘露醇喷雾干燥过程中液滴粒度分布变化的群体粒数衡算模拟和实验研究

利用群体粒数衡算（population balance，PB）计算机模拟和实验研究了甘露醇水溶液的喷雾干燥过程中液滴的粒度分布的变化规律。液滴干燥过程中的颗粒粒度的萎缩速率，在群体粒数衡算模型中描述为液滴的逆（或负）生长项，通过单个液滴反应动力学方法（reaction engineering approach，REA）获得。基于单个液滴干燥的反应工程方法模型REA和群体粒数衡算模型PB集成建立了PBREA模型。PBREA 模型的求解是通过高分辨率数值方法。本文模拟研究了不同工况下，不同粒径液滴的干燥时间、液滴平均含湿量以及液滴粒度分布随时间的变化。结果显示，液滴粒径越大，干燥时间越长，模型预测的颗粒平均粒径为实验值的1.0~1.5倍，粒度分布跨度是实验值的0.61~0.89倍。模拟误差主要来源于液滴及颗粒粒径分布统计精度、单个静止液滴与群体运动液滴干燥的差异、热导率及扩散系数是经验值3个方面。在使用Buchi 290 小型喷雾干燥仪进行的实验中，使用了图像采集和分析方法得到了液滴及颗粒的数密度分布，并和模拟结果做了对比。结果表明该模型可以有效地预测喷雾干燥过程中干燥颗粒的平均粒度及分布跨度。     

Measurement of the size distribution of fat crystals using a laser particle counter

A new method that uses a laser particle counter has been developed to measure the size of fat crystals. The fat crystals were suspended in isobutanol in the ratio of 1∶25,000. The solid and liquid fat recovery after being in contact with isobutanol for 24 hr, fatty acid composition of the solid and liquid fractions, DSC melting behavior and polarized light microscopy proved that isobutanol did not affect the structural integrity of the fat crystals. The mean crystal size of commercial shortenings ranged from 5 to 9 μm. The isobutanol suspension method makes it possible to quantitatively separate the solid and liquid components of a fat. It also provides a convenient way of preparing fat crystals for scanning electron microscopy.     

同轴双通道喷嘴雾化滴径沿轴向分布特性

Experiments were performed on the breakup of water droplets in a coaxial twin-fluid air-blast atomizer by a high-speed gas stream.With the measurements of Sauter mean diameter（SMD）distributions at a downstream distance of the atomizer,the droplet size was found first to decrease,reaching a minimum,and then to increase monotonically with the downstream distance.Correlation of L_c where the minimum droplet size appeared as a function of aerodynamic Weber number and liquid Reynolds number was analyzed.The growth rate of droplet size passes by L_c downstream increased with increasing water velocity,and the relationship between SMD and x/D_g accurately reflected the increasing trend of droplet size.     

确定喷雾干燥中雾滴粒度分布的轨迹分析法

由于喷雾干燥中雾滴的运动较复杂，所以目前多是通过实验测量来确定雾滴粒度分布，有限多不便因素。通过模拟粒子受力情况以及与空气的传质传热，采用时间增量法和拖动坐标系逐步跟踪粒子的运动轨迹，建立数学模型，再结合实验中样板取样所得到的数据，即可确定喷雾干燥中雾滴粒度分布。     

Spray characterization: Numerical prediction of Sauter mean diameter and droplet size distribution

A simplified equation of the Nukiyama-Tanasawa type for droplet size distribution in sprays is obtained from the synergetic concept of entropy information, assuming spherical droplets and zero and infinity as their limit sizes. The introduction of Sauter mean diameter (SMD) definition in that equation yields a new distribution function dependent solely on SMD, which is calculated from available correlations for pressure-jet and pre-filming airblast atomizers. For plain-jet airblast atomizers a new and dimensionally consistent correlation is determined. Several droplet size distributions are then predicted. Experimental data are compared with predictions of SMD; the agreement is satisfactory.     

Measurement of aerosol size distribution function using Mie scattering—Mathematical considerations

This paper analyzes the applications of Mie scattering to measure the size distribution function (SDF) of aerosols. Measurement of SDF by Mie scattering usually involves solving the Fredholm integral equations of the first kind based on discrete inputs with uncertainties (e.g., extinction measurements at multiple wavelengths or at multiple angles). A set of inputs which are not mutually independent within the measurement error implies that redundancy exists in the measurements and not all the measurements provide useful information for solving the integral equations. To avoid such redundancy, this paper develops a method to analyze the dependency among the kernel functions associated with Mie scattering. Applications of this method are demonstrated and the results provide valuable insights into the optimization of SDF measurement based on Mie scattering, in terms of minimizing the number of measurements needed and revealing the optimal wavelengths and angles to perform the measurements.     

Prediction of droplet size distribution in sprays of prefilming air-blast atomizers

Droplet size distribution is a crucial parameter of atomization process besides droplet mean diameter. In this paper, the finite stochastic breakup model (FSBM) of prefilming air-blast atomization process has been proposed according to the self-similarity of droplet breakup. There are four parameters in FSBM, which are the initial droplet diameter D₀, the maximum stable droplet size D_c, the minimum mass ratio of a sub-droplet to the mother droplet a, and the droplet breakup probability P(D). The simulation results of droplet size distribution with this model agreed well with the experimental results of prefilming air-blast atomizers. With this model, the nonlinear relationship between the mean droplet diameters and droplet size distribution of the air-blast atomization process can be predicted exactly.     

A water droplet size distribution dependent modeling of hydrate formation in water/oil emulsion

Experimental data on chord length distributions and growth rate during methane hydrate formation in water‐in‐oil emulsions were obtained in a high pressure stirring reactor using focused beam reflectance measurement and particle video microscope. The experiments were carried out at 274.2 K for 10–30% water cuts and agitation rates ranging from 200 to 500 rpm initially at 7.72 MPa. Rapid growth was accompanied by gradually decrease in rate. Free water was observed to become depleted during rapid growth while some water remained encapsulated inside hydrate layers constituting a mass transfer barrier. The apparent kinetic constants of methane hydrate formation and free‐water fractions were determined using a newly developed kinetic model independent of the dissolution rate at the gas–oil interface. It was illustrated that continued growth depends on distribution and transfer of water in oil‐dominated systems. This perception accords with observations of hydrate film growth on suspended water droplet in oil and clarifies transfer limits in kinetics. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1010–1023, 2017     

Measurement of particle size distribution by image analyser

Image analysis provides a very useful method for the measurement of the size distribution of granular materials. The method is very useful when the grains to be measured are very small (1 ? 25 μm), or are imbedded in a solid matrix. The techniques of measurement are described and the analytical methods for the transformation of random chord measurements made on section to three-dimensional size are provided in a convenient form. An example is given using data obtained from a modern automatic image analyser. Traditionally, this technique is applicable only to spherical particles, but the method presented in this paper can be used for particles of irregular shape which enhances its utility considerably.     

On fog formation in a coronal discharge: effects of the discharge on droplet growth

The effect of a coronal discharge on the growth of small cloud droplets was studied in a 1 m³ cloud chamber. Evidence was found that the discharge creates large numbers of nuclei for condensation, possibly as a reaction between NO and NO₂, formed by the discharge, and the SO₂, Aitken nuclei and H₂O in the chamber air. The rate of droplet growth using these nuclei was also studied. The major effect upon the droplet growth process appears to be due to increased competition for vapor due to the nucleation of new droplets.     

Evolution of the droplet size distribution during a two-phase flow through a porous media: Population balance studies

Fibrous-bed coalescers are frequently used for separation of the suspension. The effectiveness of the process depends on the flow condition through the packed bed and its structure. The population balance equation was used for analysis of the evolution of the distribution of droplet diameter in the raw suspension due to the coalescence and breakage of droplets passing different sequences of the coalescer structures distinguished by the packing density of fibers in the layers of the coalescers. The results of calculations show the values of particular parameters, like droplet concentration, the mean diameter of the droplet and droplet size distribution in the population as the results of the process. The proposed model can be useful for the designing of the coalescer structures for their particular applications.     

Parametric study of droplet size in an axisymmetric flow-focusing capillary device

A conventional technique for microfluidic droplet generation is Co-axial Flow Focusing(CFF) in which a contraction zone is placed downstream of the dispersed phase nozzle. In this contraction zone, the dispersed-phase(dphase) fluid is pinched off by continuous-phase(c-phase) fluid to generate micro-droplets. Studying the influence of multiple parameters such as the fluids velocities and viscosities, the interfacial tension, and nozzle and orifice diameters on the droplet size is of great importance for the design and application of CFF devices. Thus,development of more complete numerical models is required. In this paper, we show our model is compatible with experimental data and then numerically investigate the effects of aforementioned parameters on the droplet generation in a CFF microfluidic device. Simulation results showed that the c–phase flow rate, viscosity and the interfacial tension had great impacts on the droplet size. The effect of the nozzle diameter on the generated droplet size was small compared to that of the orifice in a CFF device. Using the simulation results, a correlation was also developed and suggested which predicts the droplet size with less than 15% error in a wide range of the introduced dimensionless parameters.     

Measurement of air bubble size using densitometer

A simple mass-transfer model is derived which gives the initial air bubble size distributions in a dispersion of air bubbles in water from the density/time responses to a step increase of pressure. Bubble size distributions from the model showed reasonable agreement with direct optical measurements. This work is applicable to dilute dispersions of bubbles which experience a sufficiently large increase in pressure such that the resulting solution is unsaturated with air.     

Measurement methods of particle size distribution in emulsion polymerization

The particle size distribution of polymer always develops in emulsion polymerization systems, and certain key phenomena/mechanisms as well as properties of the final product are significantly affected by this distribution. This review mainly focuses on the measurement methods of particle size distribution rather than average particle size during the emulsion polymerization process, including the existing off-line, on-line, and in-line measurement methods. Moreover, the principle, resolution, performance, advantages, and drawbacks of various methods for evaluating particle size distribution are contrasted and illustrated. Besides, several possible development directions or solutions of the in-line measurement technology are explored     

Synthesis of silicon nanoparticles with a narrow size distribution: A theoretical study

This work presents a study of the processes involved in synthesis of narrowly distributed silicon nanoparticles from the thermal decomposition of silane. Two models are proposed, one which simultaneously solves the kinetic mechanism of Swihart & Girshick (1999, Journal of Physical Chemistry B 103, 64–76) while adjusting the sintering parameters; and another which adjusts the kinetic and surface growth mechanisms while neglecting coagulation and sintering. The models are applied to simulate the centreline of the hot-wall reactor and process conditions of Körmer et al. (2010, Journal of Aerosol Science 41, 998–1007). Both models are shown to give good agreement with experimental PSDs at a range of process conditions. However, it is reported that an unphysical sintering process is obtained when attempting to use Swihart & Girshick's kinetic mechanism, while solving for the sintering parameters. The model with adjusted gas-phase and surface growth processes gives better quantitative and qualitative agreement with experimental results. It is therefore recommended that further study into the kinetic and heterogeneous growth mechanisms be conducted in order to better understand the fundamental processes occurring in this hot-wall reactor.     

Effect of initial droplet size distribution on sulfur removal efficiency in FGD/SDA

Dry scrubbing with lime slurry in a spray dryer [spray dryer absorber (SDA)] has been an important technology for flue gas desulfurization (FGD). Mathematical models based on the heat and mass balances are used to predict SO₂ removal in the SDA as a function of initial size distribution of slurry droplets. Since the existence of moisture in the droplets appreciably enhances the SO₂ removal, its removal efficiency depends on the rate of drying as well as that of SO₂ removal itself, both depending on droplet diameter. With the increase in the geometric standard deviation (GSD) of the initial droplet size distribution, the efficiency of SO₂ removal first increases and then decreases, showing a maximum at a certain value of GSD. This trend is altered by the sorbent content of the droplets, expressed as stoichiometric ratio (SR). The decrease in SR makes the maximum move to higher GSD and reduces the variation in the efficiency with respect to GSD. For SR<0.73, a minimum efficiency also appears, ahead of the maximum. The results are well explained by the specific rates of both drying and SO₂ removal of the droplets.