Novel measurement system for respiratory aerosols and droplets in indoor environments

The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier.     

Analysis of Direct Contact Condensation of Flowing Steam onto Injected Water with Multifluid Model of Two-Phase Flow

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.     

Study on stable delivery of charged uniform droplets for freeform fabrication of metal parts

Electrostatic delivery of charged uniform metal droplets is a novel method to deposit metal parts with short process period and low cost. But the delivery process is unstable and delivery accuracy of charged droplets deteriorates because of actions of mutual interactions of closely charged droplets. A droplet generator with droplet charging and deflecting system has been established to find out the way for stably and accurately deflecting droplets. The parameters for generating uniform droplets were first s...     

微滴式数字PCR中低浓度荧光微滴分类

数字PCR检测过程中,确定微滴是否为阳性直接影响最终浓度,也是影响仪器准确度的重要因素之一。目前的自动分类方法并未考虑到数字PCR技术中浓度对结果误差的影响,导致在低浓度下自动设置的方法与实际结果偏差较大。本文设计了一种基于广义帕累托分布的荧光微滴分类方法,讨论了不同浓度下误分类对结果可能的影响,据此确定了分布模型参数,并在自行研制的微滴式数字PCR仪上进行验证。实验结果显示:经本文方法分类后,样品中目标拷贝数在5~5 000的范围内线性回归的r_2=0.995 6,这意味着广义帕累托分布较好地拟合了微滴荧光强度边界分布,本文提出的荧光微滴自动分类方法在低浓度下取得了较好的效果。     

双旁路耦合电弧MIG焊熔滴过渡受力分析

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。     

Caustic imaging of gallium droplets using mirror electron microscopy

We discuss a new interpretation of mirror electron microscopy (MEM) images, whereby electric field distortions caused by surface topography and/or potential variations are sufficiently large to create caustics in the image contrast. Using a ray-based trajectory method, we consider how a family of rays overlaps to create caustics in the vicinity of the imaging plane of the magnetic objective lens. Such image caustics contain useful information on the surface topography and/or potential, and can be directly related to surface features. Specifically we show how a through-focus series of MEM images can be used to extract the contact angle of a Ga droplet on a GaAs (001) surface.     

切削液油雾形成机制及影响因素的实验研究

对切削液油雾产生的机制进行理论分析,并对切削液油雾形成的影响因素进行实验研究。实验在密闭的车床内进行,利用车床的供液系统采用浇注式供给磨削液,在油雾产生密集区域内安装有磨削液雾滴粒径的测量装置,该装置中的共聚焦显微镜可观察切削液雾滴在空气中的分布,精确扫描单颗雾滴的形态轮廓,通过计算机可计算出雾滴的分布和直径尺寸。分别控制主轴转速和切削液流量,探究对所形成的油雾浓度和平均直径的影响。实验结果表明:金属加工过程中主轴转速和切削液流量对切削液油雾特性的影响显著,随着主轴转速的增加,油雾的平均直径减小,而油雾浓度却呈上升趋势;随着切削液流量的增加,油雾的平均直径变大,并且油雾浓度同样呈上升趋势。     

液滴在双轨亲水轨道上的运动特性研究

目的 探究重力驱动液滴在双轨亲水轨道上的运动特性,揭示其力学机理。方法 采用喷涂法制备不锈钢超疏水表面,然后采用激光刻蚀法在超疏水表面上加工出不同类型的亲水轨道。研究液滴在不同轨道上的运动行为,讨论液滴运动状态与轨道参数之间的关系,并对液滴运动的力学特性进行分析。结果 液滴在平行双轨轨道上的运动阻力约为在单轨轨道上的1.6~2.4倍,其与轨道宽度呈正相关,与轨道间距呈负相关,且液滴运动终止时呈现出轨道中途停滞、轨道末端停滞、脱离轨道末端三种状态;液滴在非平行双轨轨道上的运动阻力与运动方向有关,由宽端至窄端的运动阻力较由窄端至宽端更小,前者约为后者的90.7%。结论 液滴在轨道上的运动阻力主要受液滴与亲水轨道的接触面积影响。当平行双轨轨道的间距增大时,液滴在垂直轨道的方向上拉伸效果增强,液滴将沿平行轨道的方向收缩,铺展长度减小,由此液滴与亲水轨道的接触面积减小,从而降低了液滴运动阻力;而液滴在非平行轨道不同运动方向上的阻力差异与液滴的表面张力有关。     

基于BP神经网络的液滴图像识别方法

通过CCD监测白酒和掺入50％水的白酒两种不同液体液滴的生长过程,针对最大的液滴提取特征参数,利用主成分分析技术对特征参数进行优化,确定了5项有效的特征参数。最后采用BP神经网络识别不同的液滴。结果表明：不同液体液滴的轮廓特征参数是有区别的。因此,结合模式识别的图像液滴分析技术可以应用于分析和鉴别液体。