Effect of Free-fall Nozzle Channel Dispersion Angle on TC4 Discontinuous Droplets Pre-breakup in EIGA

The effect of the inlet gas pressure,supplementary gas pressure and nozzle channel dispersion angle on the pre-breakup behavior of Ti-6Al-4V(TC4)discontinuous droplets during EIGA was investigated by combining numerical simulation with experiments.The results show that the axial velocity at the recirculation zone before the stagnation location was first increased and decreased then increased significantly after the peak value,while the pressure of the recirculation zone increased with the increase in inlet pressure.With the supplementary pressure increasing,the velocity magnitude and range of the recirculation zone gradually decreased.As the dispersion angle of the nozzle channel increased,the pre-breakup efficiency of droplets gradually decreased,but the adhesion phenomenon of droplets on the inner wall surface of the nozzle channel(IWSNC)gradually weakened.Under the inlet pressure of 4 MPa,a supplementary pressure of 0.05 MPa,and the dispersion angle of 15°,the uniform and spherical TC4 powders with diameter of 70μm were prepared,which was consistent with the simulation results.The optimized process parameters is a balance between the size of the pre-atomized particles and the back-spraying and bonding phenomenons of droplets.

Experimental study on the dispersion behavior of a microemulsion collector and its mechanism for enhancing low-rank coal flotation

As the poor dispersion of oily collectors and the inferior hydrophobicity of the mineral surface, the lowrank coal has an unsatisfactory flotation performance when using traditional collectors. In this paper, an ionic liquid microemulsion was used as a collector to enhance its floatability. Flotation test results demonstrated the microemulsion collector exhibited a superior collecting ability. A satisfactory separation performance of 78.66% combustible material recovery was obtained with the microemulsion collector consumption of 6 kg/t, which was equivalent to the flotation performance of diesel at a dosage of25 kg/t. The dispersion behavior of the microemulsion collector was investigated using the CryogenicTransmission Electron Microscopy. The interaction mechanism of the microemulsion collector on enhancing the low-rank coal flotation was elucidated through the Zeta potential and contact angle measurements, the Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis.The microemulsion collector exhibited superior dispersibility, which was dispersed into positively charged oil droplets with an average size of 160.21 nm in the pulp. Furthermore, the nano-oil droplets could be more efficiently adsorbed on the low-rank coal surface through electrostatic attraction, resulting in the improvement of its hydrophobicity. Thus, the microemulsion collector shows great application potential in improving the flotation performance of low-rank coal.

A Preliminary Numerical Investigation of Airborne Droplet Dispersion in Aircraft Cabins

The emergence of the novel coronavirus has led to a global pandemic which has led to the airline industry facing severe losses. For air travel to recover, airlines need to ensure safe air travel. In this paper, the authors have modeled droplet dispersion after a single breath from an index patient. Computational Fluid Dynamics (CFD) simulations are conducted using the k-ωSST turbulence model in ANSYS Fluent. The authors have taken into consideration several parameters such as the size of the mouth opening, the velocity of the cabin air as well as the number of droplets being exhaled by the index patient to ensure a realistic simulation. Preliminary results indicate that after a duration of 20 s, droplets from the index patient disperse within a 10 m2 cabin area. About 75% of the droplets are found disperse for up to 2 m axially behind the index patient. This could possess an enhanced risk to passengers sitting behind the index patient. Ultimately, this paper provides an insight into the potential of CFD to visualise droplet dispersal and give impetus to ensure that necessary mitigating measures can be taken to reduce the risk of infection through droplet dispersal.

Spectral dispersion of cloud droplet size distributions and radar threshold reflectivity for drizzle

From first principles, we find that the radar threshold reflectivity between nonprecipitating clouds and precipitating clouds is strongly related to not only the cloud droplet number concentration but also the spectral dispersion of cloud droplet size distributions. The further investigation indicates that the threshold value is an increasing function of spectral dispersion and cloud droplet number concentration. These results may improve our understanding of the cloud-precipitation interaction and the aerosol indirect effect.

Relationships between Cloud Droplet Spectral Relative Dispersion and Entrainment Rate and Their Impacting Factors

Cloud microphysical properties are significantly affected by entrainment and mixing processes.However,it is unclear how the entrainment rate affects the relative dispersion of cloud droplet size distribution.Previously,the relationship between relative dispersion and entrainment rate was found to be positive or negative.To reconcile the contrasting relationships,the Explicit Mixing Parcel Model is used to determine the underlying mechanisms.When evaporation is dominated by small droplets,and the entrained environmental air is further saturated during mixing,the relationship is negative.However,when the evaporation of big droplets is dominant,the relationship is positive.Whether or not the cloud condensation nuclei are considered in the entrained environmental air is a key factor as condensation on the entrained condensation nuclei is the main source of small droplets.However,if cloud condensation nuclei are not entrained,the relationship is positive.If cloud condensation nuclei are entrained,the relationship is dependent on many other factors.High values of vertical velocity,relative humidity of environmental air,and liquid water content,and low values of droplet number concentration,are more likely to cause the negative relationship since new saturation is easier to achieve by evaporation of small droplets.Further,the signs of the relationship are not strongly affected by the turbulence dissipation rate,but the higher dissipation rate causes the positive relationship to be more significant for a larger entrainment rate.A conceptual model is proposed to reconcile the contrasting relationships.This work enhances the understanding of relative dispersion and lays a foundation for the quantification of entrainment-mixing mechanisms.

An experimental study of immiscible liquid–liquid dispersions in a pump–mixer of mixer–settler

Drop size distribution(DSD) or mean droplet size(d32) and liquid holdup are two key parameters in a liquid–liquid extraction process. Understanding and accurately predicting those parameters are of great importance in the optimal design of extraction columns as well as mixer–settlers. In this paper, the method of built-in endoscopic probe combined with pulse laser was adopted to measure the droplet size in liquid–liquid dispersions with a pump-impeller in a rectangular mixer. The dispersion law of droplets with holdup range 1% to 24% in batch process and larger flow ratio range 1/5 to 5/1 in continuous process was studied. Under the batch operation condition, the DSD abided by log-normal distribution. With the increase of impeller speed or decrease of dispersed phase holdup, the d32 decreased. In addition, a prediction model of d32 of kerosene/deionized system was established as d32/D = 0.13(1 + 5.9φ)We-0.6. Under the continuous operation condition, the general model for droplet size prediction of kerosene/water system was presented as d32/D = C3(1 + C4φ)We-0.6. For the surfactant system and extraction system, the prediction models met a general model as d32/D = bφnWe-0.6.

Droplet characteristics in the multi-staged high speed disperser with single inlet

Droplet characteristics in the cavity zone of a multi-staged high speed disperser with single inlet were studied in this paper. The influences of both the operating and structural parameters on the mean droplet diameter, size distribution and liquid flux distribution were quantitatively analyzed. The result showed that the mean droplet diameter decreased with the increase of rotational speed and the number of rotors;whilst there is little influence on the inlet flow rate. In the experimental range, the minimum value of mean droplet diameter is 0.57 mm, 0.48 mm, 0.41 mm in the two-staged, three-staged and four-staged rotors, respectively. The Rosin–Rammler(R–R) distribution could describe the droplet size distribution appropriately, and it became uniform with the increase of rotational speed and the number of rotor, while the inlet flow rate had little effect on the droplet size distribution. The liquid flux distribution curves were always unimodal. With the increase of rotational speed, the location of maximum liquid flux ratio moved from zone 3 to zone 4 and this value decreased from 22.1% to 18.1%. Using Coefficient of Variation(CV) to indicate the uniformity of liquid flux distribution, it was found that the CV decreases from 47.5% to 22.7%when the number of rotor increased from 2 to 4.

散水式喷头水滴特性试验研究

为了掌握散水式喷头的水力性能,探究其水滴直径、水滴速度和水滴动能的规律.采用2DVD视频雨滴谱仪对散水式喷头在2种出水口当量直径D e、5种工作压力的工况下进行水力性能试验.结果表明:D e为4.88和5.98 mm的水滴平均直径分别集中分布在0.73~1.38和0.85~1.53 mm内,说明出水口当量直径越小,水滴分布可能更集中,且水滴平均直径随着距喷头距离增大而增大,并呈指数分布.水滴速度随压力和距喷头距离增大而增大,D e为4.88 mm的水滴平均速度大于D e为5.98 mm的.在相同的工作压力下,D e为5.98 mm的喷头其单个水滴动能、单位体积动能和动能强度均大于D e为4.88 mm的.单个水滴动能和水滴平均直径呈指数关系,单位体积动能与距喷头距离呈指数分布,动能强度在距喷头距离0.1~0.6 m内波动幅度较小.

降低分散相破碎的低剪切阀技术路线及研发进展

阀门作为应用于石化等行业的关键设备之一,通过调整阀门开度调节液流流量。在多相流分离领域,位于分离器上游的阀门容易造成分散相剪切破碎,形成更加细小的液滴,甚至出现乳化现象,增加了分离难度。文章聚焦于降低分散相破碎的低剪切阀,从影响液滴破碎及最大稳定液滴直径的关键物理因素出发,包括单位质量平均能量耗散率、液流能量耗散体积等,对降低液滴破碎的可行性路径进行总结,具体包括减小流经阀门液流的流场紊乱、增加油滴聚结结构,以及增大液流能量耗散体积。在此基础上,分析了多种典型低剪切阀门的结构特点及实际性能,并总结了低剪切阀的发展趋势,为新型低剪切阀开发及优化设计,以及规模化推广应用提供理论及技术支撑。

Preparation of Microcapsules with Liquid Droplet Coalescence Method Followed by Phase Separation

Novel preparation method of microencapsules was developed on the basis of the liquid coalescence method followed by phase separation. Oil droplets of limonene dissolving expanded polystyrene as a shell material were forced to collide and coalesce with the Isopar oil droplets of core material in the continuous wates phase. When two kinds of oil droplets are collided and coalesced with each other, expanded polystyrene dissolved in the limonene oil may be phase-separated in the oil droplets newly formed to form the microcapsule shell, because the Isopar oil was a poor solvent for expanded polystyrene but a good solvent for the limonene oil. In the experiment, the diameter (or number) of limonene oil droplets dissolving expanded polystyrene was mainly changed, because the coalescence frequency between the droplets is strongly dependent on the number of droplets. Favorable core shell types of microcapsules with the shell thickness from 1.0 to 5.0 μm were able to be prepared under all the experimental conditions adopted here.

Downstream pressure and elastic wall reflection of droplet flow in a T-junction microchannel

This paper discusses pressure variation on a wall during the process of liquid flow and droplet formation in a T-junction microchannel. Relevant pressure in the channel, deformation of the elastic wall, and responses of the droplet generation are analyzed using a numerical method.The pressure difference between the continuous and dispersed phases can indicate the droplet-generation period. The pressure along the channel of the droplet flow is affected by the position of droplets, droplet-generation period, and droplet escape from the outlet. The varying pressures along the channel cause a nonuniform deformation of the wall when they are elastic. The deformation is a vibration and has the same period as the droplet generation arising from the process of droplet formation.

Mass transfer area in a multi-stage high-speed disperser with split packing

In this study, the mean droplet diameter in the cavity zone and the total mass transfer area of a multi-stage highspeed disperser(HSD) reactor with different packing combinations were measured and evaluated. The effects of rotational speed and packing radius, as well as the packing ring radius and numbers, on the mean droplet diameter and the total mass transfer area were evaluated. A model was established to calculate the mass transfer area in the cavity zone in the HSD reactor, and it was found that the packings contribute 61%–82% of the total mass transfer area. A correlation for predicting the mass transfer area in the packing zone was regressed by the dimensionless analysis method. An enhancement factor based on the mass transfer area in the packing zone was proposed to evaluate the effect of packing combination on mass transfer area. Two optimum packing combinations were proposed in consideration of the mean droplet diameter and the enhancement factor.

不同污染背景下云滴谱离散度对云降水模拟影响的个例研究

云滴谱离散度是云雨自动转化过程参数化中不可忽视的重要参数,对地面降水有着重要的影响。本文利用WRF-Chem(Weather Research and Forecast coupled with Chemistry)模式,对发生在2019年1月3~6日长江中下游地区的一次降水过程进行了模拟。在清洁和污染的气溶胶背景下,设定不同的云滴谱离散度的数值(0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9和1.0),研究云降水微物理的变化。结果表明,该个例降水主要来源于云雨自动转化以及云雨碰并过程。在清洁条件下的地面累计降水量大于在污染条件下的累计降水量,这是因为在清洁条件下云滴数浓度小,有利于云雨自动转化以及云雨碰并过程。虽然云雨自动转化以及云雨碰并过程占主导,但导致地面累计降水量随云滴谱离散度增大而增大的主要原因是:随着云滴谱离散度的增大,冰粒子质量浓度增大,导致融化过程增强,产生更多的雨滴,从而增强地表降水。所得结果将提高我们对云降水对气溶胶和离散度响应过程的理论认识。

复虹现象的实验研究

彩虹是一种常见的大气光学现象,在一定天气条件下,在彩虹的附近还会出现附加的弧形彩色条纹,这就是复虹。目前关于复虹的实验研究还十分有限。本文从集体散射与单体散射两方面对复虹现象进行了实验研究。通过水雾光散射再现了复虹现象,并测量统计了水滴尺寸及其分布对复虹的影响。然后通过单水滴光散射实验,研究了不同照明波长、不同水滴尺寸下的复虹现象,从微观上解释了复虹的形成机理。我们还利用散射理论计算研究了水滴尺寸及其统计分布对复虹效果的影响,计算结果进一步证实了实验结论的正确性。

云滴谱离散度的理论、观测和数值模拟研究进展

云滴谱离散度(ε)作为衡量云滴粒子尺度分布以及离散程度的参数,在气溶胶-云-降水过程中有着重要作用。其中ε与云滴(N_(c))或背景气溶胶数浓度(N_(d))的相关关系是描述云内微物理和动力过程,以及量化气溶胶对云和降水影响的重要因子之一。很多气溶胶间接效应的研究中,未考虑云滴谱离散度带来的影响,这使得相关理论研究和模式模拟仍然具有一定的局限性。本文基于云滴谱离散度的概念,从多个方面回顾了近年来云滴谱离散度相关理论、观测和数值模拟研究进展,包括ε与N_(c)或N_(d)的相关性,云滴谱离散度对云中微物理参量和动力过程的影响机制,以及由云滴谱离散度引起的气溶胶间接效应的估算及其不确定性等。从过往研究来看,影响ε的因素很多,不仅是云滴数浓度,还包括云中的上升速度、液水含量等,甚至气溶胶的理化特性、云中的凝结、碰并、夹卷和蒸发等过程都会对ε产生不同的影响。背景气溶胶浓度的变化一定程度上会改变云滴尺度和浓度分布进而影响ε。受地区差异和云条件影响,ε与N_(c)或N_(d)的相关性存在很大差别,既有正相关也有负相关,甚至不相关。即使针对同一云团,在云的不同部位甚至云的不同发展阶段,ε可呈现出不同程度的变化。ε可通过改变暖云的云水-雨水转化效率从而对降水即第二间接效应产生影响;又可通过影响云滴有效半径从而改变云的光学特性来影响第一间接效应。不同的ε-N_(c)参数化关系会导致全球模式中间接效应的估算出现不同程度的抵消或增强,由此可导致地面气象场和降水分布发生改变。总之,ε与云中相关参量之间的关系以及对间接效应产生的影响还存在很大的不确定性,需要对背后的机理进行更加深入的研究。本文归纳总结了当前云滴谱离散度相关研究面临的问题和存在的挑战,对未来的研究重点和工作方向进行展望,部分结论可为进一步认识云滴谱离散度在气溶胶-云相互关系中的作用提供参考。

旋流烟气下喷雾干燥脱硫塔中气液分布及混合特性的数值研究

针对喷雾干燥脱硫塔中的混合问题,采用离散颗粒相模型(DPM)对塔内液滴群径向位移、液滴群散布及气液混合进行数值分析,重点考察烟气入口旋流强度S和液滴群平均粒径d的影响。结果表明:烟气入口旋流强度从0增加到0.5时,液滴群径向位移先缓慢减小后迅速增大;液滴群平均粒径从65μm增加至150μm时,液滴群径向位移近似线性增大;随着烟气入口旋流强度和液滴群平均粒径增加,液滴群散布程度呈先增加后减小的趋势;合适的烟气入口旋流强度和液滴群平均粒径能有效减小气液混合度,显著改善气液混合效果;烟气入口旋流强度为0.3时,液滴群径向位移和气液混合度最小,与无旋流相比,分别平均减小了约20%和34.45%;液滴群平均粒径为150μm时,液滴群散布程度最大,气液混合度最小,与液滴群平均粒径65μm相比,气液混合度平均减小了约51.85%。

离心甩油盘径向喷雾破碎机理实验研究

本文发展了离心甩油盘高速旋转雾化的光学测试实验台,采用高速数字成像、高速阴影成像等可视化方法研究了在不同转速(8~20kr/min)和燃油流量(4~15g/s)下航空煤油的喷雾形态及燃油破碎过程,分析了喷雾特性变化规律,并采用激光粒度分析仪测量了不同工况下的燃油雾化粒径及其分布规律。实验结果表明,甩油盘雾化过程中,科氏力推动液膜聚积在与甩油盘旋转方向相反的喷口一侧,且甩油盘喷孔出口处的液体呈薄片状。随着燃油的进一步破碎雾化,实验中观察到三种不同的破碎形态:韧带破碎、袋状破碎和剪切破碎,跟转速和燃油流量有关,研究基于气动韦伯数和液气动量比给出了破碎模式图。研究表明甩油盘转速是影响雾化特性的主要因素,甩油盘转速越高,燃油粒径越小;离散度在气动韦伯数和液气动量比的综合作用下呈现不同的变化趋势。

大陆性浓积云云滴谱离散度影响因子的飞机观测研究

利用2020年7月30日山西省人工增雨防雷技术中心在山西省忻州地区开展的大陆性浓积云飞机探测资料,分析了积云微物理参量、云滴谱离散度随时间和高度的变化以及云滴谱离散度的影响因子。结果表明,该大陆性浓积云云滴谱离散度随高度的增加先递增后递减,但变化范围较小。云滴谱离散度随数浓度、含水量增大而逐渐收敛,呈弱正相关关系;离散度与体积平均半径的相关性随体积平均半径的增大由正转负,与垂直速度呈现正相关关系。云中碰并过程对云滴谱离散度及其影响因子影响较大,建议未来云滴谱离散度的参数化增加对碰并过程的考虑。

基于数据融合的油水分离效果预测研究

面向油气田开发中油水分离效果的智能预测,在考虑分离器结构参数、采出液物性参数、来液流动参数基础上,基于分离器中油水分散液滴沉降动力学分析,采用数据融合方法将油水分离的特征参数与支持向量机算法相耦合,通过分离器样本数据的机器学习训练,建立了基于数据融合的油水分离效果预测方法,并开展了脱水温度、脱水时间、原油物性参数(密度、黏度、界面张力)等影响因素对预测分离效果的系列分析,以期为油气田地面采出液智能分离技术的发展提供理论支持和研究基础。

A Study of Shallow Cumulus Cloud Droplet Dispersion by Large Eddy Simulations

Cloud droplet dispersion is an important parameter in estimating aerosol indirect effect on climate in general circulation models（GCMs）.This study investigates droplet dispersion in shallow cumulus clouds under different aerosol conditions using three-dimensional large eddy simulations（LES）.It is found that cloud droplet mean radius,standard deviation,and relative dispersion generally decrease as aerosol mixing ratio increases from 25 mg-1（clean case） to 100 mg-1（moderate case）,and to 2000 mg-1（polluted case）.Under all the three simulated aerosol conditions,cloud droplet mean radius and standard deviation increase with height.However,droplet relative dispersion increases with height only in the polluted case,and does not vary with height in the clean and moderate cases.The mechanisms for cloud droplet dispersion are also investigated.An additional simulation without considering droplet collision-coalescence and sedimentation under the aerosol mixing ratio of 25 mg-1 shows smaller values of droplet mean radius,standard deviation,and relative dispersion as compared to the base clean case.This indicates that droplet collision-coalescence plays an important role in broadening droplet spectra.Results also suggest that the impact of homogeneous mixing on cumulus cloud droplet spectra is significant under all the three simulated aerosol conditions.In weak mixing（strong updraft） regions where clouds are closer to be adiabatic,cloud droplets tend to have larger mean radius,smaller standard deviation,and hence smaller relative dispersion than those in stronger mixing（downdraft or weak updraft） regions.The parameterized cloud optical depth in terms of cloud liquid water content,droplet number concentration,and relative dispersion is only slightly smaller than the result calculated from detailed droplet spectra,indicating that current parameterization of cloud optical depth as used in many GCMs is plausible for low clouds.