Coalescence dynamics of two droplets of different viscosities in T-junction microchannel with a funnel-typed expansion chamber

The coalescence behavior of two droplets with different viscosities in the funnel-typed expansion chamber in T-junction microchannel was investigated experimentally and compared with droplet coalescence of the same viscosity.Four types of coalescence regimes were observed:contact non-coalescence,squeeze non-coalescence,two-droplet coalescence and pinch-off coalescence.For droplet coalescence of different viscosities,the operating range of non-coalescence becomes narrowed compared to the droplet coalescence of same viscosity,and it shrinks with increasing viscosity ratioηof two droplets,indicating that the difference in the viscosity of two droplets is conducive to coalescence,especially when1<η<6.Furthermore,the influences of viscosity ratio and droplet size on the film drainage time(Tdr)and critical capillary number(Ca)c)were studied systematically.It was found that the film drainage time declined with the increase of average droplet size,which abided by power-law relation with the size difference and viscosity ratio of the two droplets:Tdr~(ld)^(0.25±0.04)and Tdr~(η)^(﹣0.1±0.02).For droplet coalescence of same viscosity,the relation of critical capillary number with two-phase viscosity ratio and dimensionless droplet size is Cac=0.48λ^(0.26)l^(﹣2.64),while for droplet coalescence of different viscosities,the scaling of critical capillary number with dimensionless average droplet size,dimensionless droplet size difference and viscosity ratio of two droplets is Cac=0.11η^(﹣0.07)ls^(﹣2.23)l^(0.16)_(d).

Effect of injection angle,density ratio,and viscosity on droplet formation in a microfluidic T-junction

The T-junction microchannel device makes available a sharp edge to form micro-droplets from biomaterial solutions. This article investigates the effects of injection angle, flow rate ratio, density ratio,viscosity ratio, contact angle, and slip length in the process of formation of uniform droplets in microfluidic T-junctions. The governing equations were solved by the commercial software. The results show that contact angle, slip length, and injection angles near the perpendicular and parallel conditions have an increasing effect on the diameter of generated droplets, while flow rate, density and viscosity ratios, and other injection angles had a decreasing effect on the diameter.

Determining the Charge-to-Mass Ratio of the Electron

The aim of this lab was to determine an experimental value for the charge-to-mass ratio e/me of the electron. In order to do this, an assembly consisting of Helmholtz coils and a helium-filled fine beam tube containing an electron gun was used. Electrons were accelerated from rest by the electron gun at a voltage of 201.3 V kept constant across trials. When the accelerated electrons collided with the helium atoms in the fine beam tube, the helium atoms entered an excited state and released energy as light. Since the Helmholtz coils put the electrons into centripetal motion, this resulted in a circular beam of light, the radius of which was measured by taking a picture and using photo analysis. This procedure was used to test currents through the Helmholtz coils ranging from 1.3 A to 1.7 A in increments of 0.1 A. Using a linearization of these data, the experimental value for the charge-to-mass ratio of the electron was found to be 1.850 × 1011 C/kg, bounded between 1.440 × 1011 C/kg and 2.465 × 1011 C/kg. This range of values includes the accepted value of 1.759 × 1011 C/kg, and yields a percent error of 5.17%. The rather low percent error is a testament to the accuracy of this procedure. During this experiment, the orientation of the ambient magnetic field due to the Earth at the center of the apparatus was not considered. In the future, it would be worthwhile to repeat this procedure, taking care to position the Helmholtz coils in such a way to negate the effects of the Earth’s magnetic field on the centripetal motion of electrons.

Experimental study on fusion and break-up motion after droplet collision

The interactions between droplets have an important influence on the atomization of liquid fuel,the combustion efficiency,and the reduction of particulate matter emissions for an engine.For this reason,this paper presents results from an experimental study on the coalescence and break-up of droplets after collision.According to the shape and parameters of the droplets at different times after the collision of the droplets was captured by a high speed camera,analysis was done for the following effects of droplet collisions:the collision-coalescence motion for the collision between the droplets,the change history of the dimensionless length-to-width ratio of the oscillation motion,the critical size ratio of the breakup motion,and the liquid physical properties of the particles.The results show that the droplets collide and exhibit two forms of coalescence oscillation and break-up:for oscillating motion,at higher droplet collision velocities and dimensionless size ratios,there will be a larger dimensionless length-to-width ratio for the droplet oscillation;for the break-up motion,at higher collision velocities,there will be lower dimensionless size ratios,and lower liquid surface tension,shorter times over which the droplet breaks,and facilitated droplet break-up.The research results presented here can be used for atomization in engine cylinder,increasing the gas/liquid contact area and enhancing the combustion efficiency of gas/liquid heat transfer to improve the combustion efficiency of the engine.

高气液比水平井临界携液流量预测新模型

明确气井积液机理和携液规律对于掌握井下流体的流动状态至关重要。目前现场应用的临界携液流量模型较多,但是不同模型计算结果差异较大,Turner等模型计算的长北区块气井携液流量偏大,不利于指导生产。通过开展水平井流动模拟正交实验,捕捉典型流态,发现管斜角在45°~60°出现过渡流,通过编制流态识别程序进一步确定管斜角为46°时开始出现过渡流,此时携液最困难。基于液滴理论,引入井斜修正系数,建立了新的临界携液流量模型,新模型在长北区块气井中具有良好的适用性。新模型敏感性分析结果表明,由强到弱影响气井携液能力的因素依次为油管内径、井底流压、井斜角、井底温度。绘制的临界携液流量图版为后期开展停喷井治理措施的时机提供了依据。

基于工程应用的CW-GMAW熔滴过渡形态表征

综述了涉及工程应用的冷丝熔化极气体保护焊(Cold wire gas metal arc welding,CW-GMAW)熔滴过渡形态特征。结果表明,在大电流、强规范、富氩混合气体保护下,CW-GMAW工艺的熔滴过渡形态呈喷射过渡;当电流较小、电弧电压较低时,可能为滴状过渡,甚至在弧压很低时,呈现短路过渡形态。该工艺电弧发生偏向冷丝的位移,弧长变短甚至发生短路,与冷丝送进速率比增高及冷丝在电弧中产生大量金属蒸气时弧柱电阻下降有关。在具有富氩混合保护气体的相同工艺参数下,CWGMAW转变电流比GMAW降低了4%~7%。焊接工艺参数对CW-GMAW和GMAW工艺熔滴过渡形态的影响规律大致相近,但前者因涉及冷丝送进速率比和电极焊丝送进速度,以及它们的匹配等,使焊接电流的影响更为复杂。

不同侧风和静电电压对静电喷雾飘移的影响

为研究不同侧风和静电电压对静电喷雾雾滴飘移的影响规律,设计不同侧风(恒速风1、2、4 m/s及0~4 m/s变化的模拟自然风)及静电电压(0,2,4,6,8 k V),进行喷杆式静电喷雾机的雾滴飘移试验,测定不同静电电压下的雾滴粒径与荷质比,并对比分析雾滴飘移质量中心距和飘失率。结果表明:随着静电电压的增大,雾滴粒径减小,雾滴荷质比增大,0~8 k V电压下电极干燥和电极打湿对雾滴荷质比没有显著影响。在侧风风速为1 m/s时,0~8 k V静电喷雾的雾滴飘移中心距小于0.55 m,雾滴飘失率低于15%。在侧风风速2 m/s时,非静电喷雾的雾滴飘失率为11.9%,6~8 k V静电喷雾的雾滴飘失率超过20%,其中静电电压8 k V的雾滴飘失率(23.9%)比非静电喷雾增加100.8%。在侧风风速4 m/s时,4~8 k V静电喷雾的雾滴飘移中心距在0.9 m以上,雾滴飘失率在30%以上,其中静电电压8 k V下的雾滴飘移中心距为967.2 mm比非静电喷雾下增加了13.7%,雾滴飘失率为35.4%比非静电喷雾下增加了59.5%。相同静电电压下,2 m/s的恒速风和0~4 m/s变化的模拟自然风之间对雾滴飘失率无显著差异。该研究为优化喷雾技术参数和提高雾滴抗飘移的能力提供参考。

背负式静电喷雾器设计与试验

为改善传统背负式施药器械的喷雾效果,运用高压静电喷雾技术,设计了背负式静电喷雾器。该喷雾器由蓄电池、隔膜泵、高压静电发生器、喷枪、直射喷头和药箱组成,采用直接充电的方式对雾滴进行充电。为考察该喷雾器的性能,用网状目标法对荷质比进行了测量,用Oxford激光粒子图像分析测试系统测试了雾滴粒径及速度,最后用纸卡法测试了雾滴覆盖度。测试结果表明:荷质比随喷嘴压力的加大基本呈线性增长,因而在保证零部件及系统可靠的前提下,设计静电喷雾器时可适当增加喷嘴压力;静电促进雾滴吸附于作物表面、使雾滴粒径细小且分布均匀、改善了雾滴的速度分布均匀性,从而使雾滴能够均匀吸附于作物表面各部位,并显著提高了雾滴的覆盖度。

喷雾器及施液量对水稻冠层农药雾滴沉积特性的影响

【目的】分析弥雾机和手动喷雾器在不同施液量条件下喷雾,农药雾滴在水稻冠层沉积分布特征,阐明农药剂量的沉积结构及空间分布对药剂防治效果的影响。【方法】以农药雾滴采集装置和水敏纸收集农药雾滴,通过DepositScan软件分析雾滴覆盖率和雾滴密度,并利用示踪剂估测农药沉积量。【结果】弥雾机和手动喷雾器不同施液量条件下喷雾,叶角45°和0°水稻叶片正面的雾滴覆盖率显著高于叶片反面。弥雾机在225、450、600 L·hm-2施液量条件下喷雾,叶角0°水稻叶片反面的雾滴密度均大于200个/cm2,施液量间差异显著。手动喷雾器在600、900、1 200 L·hm-2施液量条件下喷雾,叶角0°和45°水稻叶片反面的雾滴密度均小于15个/cm2,施液量间无显著差异。相同剂量,弥雾机在450 L·hm-2施液量条件下喷雾,水稻冠层各位点上的农药沉积量最高;而手动喷雾器不同施液量条件下喷雾,水稻冠层各位点上的农药沉积量无显著差异。手动喷雾器喷雾叶片反面的农药沉积量均低于弥雾机喷雾。用15 g a.i.·hm-2氯虫苯甲酰胺防治纵卷叶螟,弥雾机在施液量450 L·hm-2条件下喷雾的防治效果最高,手动喷雾器在施液量1 200 L·hm-2条件下喷雾的防治效果最差。【结论】弥雾机和手动喷雾器稻田喷雾,农药雾滴在水稻叶片正面的覆盖率均高于叶片反面。弥雾机喷雾时增加施液量,能提高水稻叶片反面的雾滴密度和覆盖率;手动喷雾器喷雾时增加施液量,无显著效应。与手动喷雾器相比,弥雾机喷雾显著增加了叶片反面的雾滴密度、雾滴覆盖率及农药沉积量,能显著提高药剂的防治效果。

喷雾液滴撞击大豆叶片表面研究

利用两台高速数码摄像机对喷雾液滴撞击大豆叶片表面过程和结果进行了测试与分析。研究结果表明，产生沉积和回缩破碎两种状态时，液滴K值均小于57．7；发生喷溅时，大部分液滴K值大于57．7，但由于叶片表面密被长柔毛使得液滴在低撞击角度下易于喷溅，因此液滴在撞击角度为28°和44°时K值小于57．7。液滴在沉积过程中，在相同粒径和撞击角度下，液滴撞击速度越高最大铺展越大，铺展时间也越长，但撞击速度高和撞击速度低的液滴最终铺展比接近。沉积部位对液滴铺展过程和结果有重要影响。液滴在回缩破碎过程中，在表面张力的回缩和叶片表面的粘滞作用下分离破碎，与沉积于叶片表面的液滴相比较，液滴收缩破碎后合计最终铺展比大大提高，均匀破碎的液滴其合计最终铺展比比不均匀破碎的液滴大。当撞击耽数较高时，喷溅液滴将呈现喷射成串小液滴的状态；当撞击耽数较低时，喷溅液滴将呈现喷射单独的2—3个大液滴的状态。喷射出成串小液滴后的液滴主体部分最终铺展比比喷射出单独大液滴后的液滴主体部分大。

双极性接触式航空机载静电喷雾系统荷电与喷雾效果试验

该文针对航空施药植保无人机设计了双极性接触式航空机载静电喷雾系统,分别对该系统喷施静电油剂和水的荷电与雾化效果进行了测试。将该航空静电喷雾系统搭载于3WQF120-12型油动单旋翼植保无人机喷施静电油剂,并使用该植保无人机自带喷雾系统分别喷施静电油剂和常规水基化药剂,对比了3种施药方式的沉积分布均匀性和对小麦蚜虫、锈病的防治效果。试验结果表明:当喷雾液为水时,静电喷雾系统的静电电压和极性不会改变水的雾滴谱;当喷雾液为静电油剂时,正电荷使雾滴粒径减小,负电荷使雾滴粒径增大,且静电喷头的雾滴相对粒谱宽度随静电电压的增加而增大;喷雾液的荷质比与静电电压正相关,相同静电电压和输出电极下水的荷质比大于静电油剂,同一静电电压下负输出雾化喷头药液的荷质比高于正输出。小麦大田试验表明:使用静电喷雾系统喷施静电油剂的雾滴沉积分布均匀性最好,其单位面积沉积量为0.048 6?g/cm2,沉积量的标准偏差为0.015?g/cm2,变异系数为30.43%;使用无人机自带喷雾系统喷施静电油剂和常规水基化药剂的单位面积沉积量分别为0.051 3和0.035 6?g/cm2,标准偏差分别为0.019和0.016?g/cm2,变异系数分别为42.57%和45.54%;喷施静电油剂的2个处理对麦蚜和锈病的防治效果和药效期均明显高于水基化药剂,使用静电喷雾系统的测试在药后7 d对蚜虫防治效果为87.92%,明显高于无人机自带喷雾系统喷施静电油剂76.43%的防治效果。该静电喷雾系统配合喷施静电油剂可提高沉积分布均匀性,增加防治的持效期和效果。

模拟油乳状液的制备及稳定性的研究

研究了煤油与原油配制模拟油乳状液的稳定性,应用显微镜测定了模拟油乳状液粒子的粒径.实验确定了配制模拟油乳状液的最佳原油与煤油比、乳化速度、乳化时间和油水比.对破乳剂OX-9354和OX-9351在模拟油与原油乳状液中的脱水情况进行了对比,表明脱水率变化趋势相同,模拟油可以用来评价破乳剂.

背负式喷雾器雾滴分布特性的CFD模拟与试验

为了解决不同喷雾条件对背负式喷雾器雾滴分布的影响问题,采用CFD离散相粒子跟踪模拟方法,研究了距喷嘴垂直高度分别为0.4、0.55和0.7m,喷雾压力分别为0.15、0.2、0.3和0.35MPa,风速分别为0、1、2、3m/s情况下,雾滴沉积分布和粒径分布特性,并进行试验验证。结果表明:沉积率受风速影响显著,随风速增大而降低,但沉积率受喷雾压力影响不显著。模拟与试验结果回归决定系数R2和标准误差SE分别为0.9424、0.039,表明CFD离散相粒子跟踪模拟法可用于评估雾滴沉积分布。雾滴粒径分布模拟结果与试验结果相关性差,CFD模拟法不宜用于评估雾滴粒径分布情况。该研究为后续各类喷雾器数据测量提供参考。

Design of a Silicon Beam Resonator for a Novel Gas Sensor

A new silicon beam resonator design for a novel gas sensor based on simultaneous conductivity and mass change measurement is investigated. High selectivity and sensitivity in gas detection can be obtained by measuring the charge-to-mass ratio of gas molecules. Structures of silicon beam resonators are designed, simulated, and optimized. This gas sensor is fabricated using sacrificial layer microelectronmechanical system technology, and the resonant frequency of the microbeam is measured.

除油旋流器内油滴粒径的分布

The relationship between mean inlet drop size and separation efficiency of reducing section,tapered section,parallel section and the whole hydrocyclone is discussed in this paper.The effect of operation parameters such as feed flowrate, split ratio on mean oil drop size in the wall of each part in hydrocyclone is also investigated.The result suggests that separation efficiency of the reducing section,tapered section and the whole hydrocyclone increased with increasing inlet droplet size,whereas the separation efficiency of parallel section does not vary very much.When inlet flowrate is high enough,mean droplet sizes in the wall of hydrocyclone decreases with increasing feed flowrate.The split ratio has little influence on mean droplet sizes on the wall of hydrocyclone,and mean oil droplet diameters decreases along the axial direction under same operation condition.

石油磺酸盐与原油乳化影响因素研究

采用显微观测与乳状液析水率测定相结合的方法研究石油磺酸盐与原油乳化问题。通过正交实验,研究石油磺酸盐质量分数、油水体积比及振荡次数等因素对乳状液液滴结构及稳定性的影响。结果表明,油水体积比对乳状液液滴结构影响最大,随着油水体积比的增大,乳状液平均粒径和分散度先增大再减小。乳状液破乳前期,油水体积比对乳状液析水率的影响最大;乳状液破乳后期直至破乳结束,石油磺酸盐质量分数对乳状液析水率的影响最大;振荡次数对乳状液析水率的影响较小。

高钾空心玻璃微球的制备

以无机化合物为初始原料,选择合理的玻璃溶液配方和成球条件,用液滴法制备出直径200μm,壁厚2μm,K2O摩尔分数大于10%的空心玻璃微球(HGM)。利用扫描电镜X射线能量色谱仪对玻璃球壳的组分进行了分析。结果表明,所制备的高钾空心玻璃微球各项技术指标能基本满足神光-Ⅱ物理实验的要求,微球球壳成份实测结果与理论计算结果吻合。

气力式静电喷枪设计及其喷雾性能的测试

为了提高植保作业中喷雾器的喷雾效果,将高压静电喷雾技术与气力式喷雾技术结合,设计了气力式静电喷枪。该喷雾器由充电式镍氢电池、高压静电发生器、喷枪主体、静电喷头组成,采用感应充电的方式对雾滴进行充电。对喷枪的喷幅进行了测量,用法拉第筒法测量了荷质比,用PIV(particle image velocimetry)测速系统测量了雾滴运动速度分布,最后用浓度测试法测量了雾滴沉积率。结果表明:静电作用可使喷枪喷幅变宽;荷质比随气体压力的加大而增长;静电作用能提高雾滴运动速度且使雾滴运动速度分布更加均匀;静电作用能提高雾滴在叶片上的沉积率,尤其能提高叶片背面的沉积率,从而使雾滴能够均匀吸附于作物表面各部位。

喷雾冷冻法单个液滴冻结过程模拟

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