Investigation of Electric Discharges in the Vicinity of a Charged Aerosol Cloud and Their Interaction with a Laser-Induced Spark

It is experimentally demonstrated that an extended laser-induced spark developed in the vicinity of a grounded electrode and having a structure in the form of separate spherical plasma formations may intercept the channel of a leader discharge developing from the grounded electrode to an artificially charged aerosol cloud. The interception occurs with the electric field intensity in the vicinity of the electrode being close to the value required for an upward positive leader. It is registered that the presence of a laser-induced spark in the vicinity of the electrode causes a manifold reduction of the time of stable leader formation. It is found that the emergence of an extended laser-induced spark of a CO₂ laser in the vicinity of the boundaries of a highly charged aerosol cloud does not provoke a discharge to ground from the cloud.     

用MLP法求强非线性保守系统的次谐共振周期解

在两种改进的LP解法的基础上，将它们结合起来，用于求强非线性保守系统的次谐共振周期解。研究了Dufling方程的1／3亚谐共振周期解和2次超谐共振周期解，结果表明本方法既可求得一类强非线性保守系统的次谐共振周期解又能提高解的计算精度。     

环形溶蚀器大气颗粒物采集系统条件实验研究

为确定环形溶蚀器大气颗粒物采集系统的最优化条件,于2008年夏季与冬季在北京市进行了关于优化环形溶蚀器涂渍溶液浓度的条件实验。结果表明:为保障大气中酸碱性气体的去除效率达到95%以上,环形溶蚀器中柠檬酸涂渍溶液的优化浓度在夏季和冬季分别为6%与3%;环形溶蚀器中碳酸钠涂渍溶液的优化浓度在夏季和冬季分别为2%与4%。讨论说明在特定地点特定时间利用环形溶蚀器大气颗粒物采集系统采样前,确定环形溶蚀器涂层溶液优化浓度的必要性。     

HC290含油工质在水平微肋管内沸腾换热特性及压降的实验研究

实验测试了HC290-Suniso 3GS混合工质在含油浓度为0.43%～5.28%、质量流率为40kg/m2*s～220kg/m2*s,蒸发温度分别为-5℃、0℃、 5℃时在水平微肋管内的沸腾换热特性及压降.蒸发试验段为一套管蒸发器,有效长度为2.0m,内管为内肋强化管,其外径为12.7mm,最大内径为11.44mm,T型肋高0.25mm,螺旋角20°,肋数为60;外套管是一光滑铜管,其内径为19mm.实验结果表明含油工质沸腾平均换热系数随工质质量流率、干度的增大而增加,随含油率的增大而降低,蒸发温度对其影响不大;压降随其质量流率的增大而增大,与光管相比其压降随质量流率的增大要更快,润滑油的加入对压降影响不大.通过测试沸腾换热特性所得的40多个实验数据点,回归出了适用于本实验条件的经验关联式.     

R134a通过短管流动的试验研究

短管机构在汽车空调、家用空调和热泵系统中得到越来越广泛的应用。目前，关于提供通过短管机构ＣＦＣ替代物性能研究方面的数据很少。本文给出了ＣＦＣ替代物Ｒ１３４ａ通过短管机构的流动特性试验研究。在很宽的操作条件下，通过试验研究了Ｒ１３４ａ流过短管机构的性能参数变化。长径比在７￣２０范围内，冷凝温度为３５℃￣５４℃时，过冷度可达１３．９℃，短管入口干度可达１０％左右。对进入短管的两相流和过冷液体性能进行了     

“沸腾法气溶胶发生和静电采样法”在扫描电镜表征超细粉体中的应用

该文介绍了一种为扫描电镜表征超细粉体制备样品的新方法—“沸腾法气溶胶发生和静电采样法”。将粉体悬浮在分散剂中,沸腾产生高浓度的气溶胶,利用静电沉积原理,将气溶胶状态的粉体粒子均匀收集至样品台,由扫描电镜进行表征。此法能打破由于存放或运输过程中因挤压、吸潮等引起的粒子团聚,较为真实的反映粉体原貌。该文也给出TTiO2超细粉末表征的实例。     

行波热声发电系统自激振荡的非线性动力学研究

利用非线性热声网络模型建立了一种行波热声发电系统的简化动力学演化方程,考察了系统自激振荡过程。重点探究非线性热声效应的影响,并与仅考虑线性热声效应的情况进行对比。结果表明,当仅考虑线性热声效应时,振荡曲线不断增大,无法达到稳定值;而考虑非线性热声效应时,自激振荡最后达到稳定幅值。进一步研究得出,系统电机的非线性阻尼系数越大,系统稳定后的振荡幅值越小。对不同电机非线性阻尼系数时系统产生的振荡曲线作频谱分析,计算结果和实际情况相近。最后考察了回热器未达临界温度梯度时系统的自激振荡过程。     

Analysis of the Internal Pressure in Tube Hydroforming and Its Experimental Investigation

The internal pressure of the process was studied theoretically and experimentally. The external load character and internal stress character of tube hydroforming were discussed first. Then, according to the characters, the function and classification of internal pressure were presented in general. Base on the stress analysis, its effect on the yield criterion and calculation formula were also researched and derived. To verify the correction of the theoretical analysis and derived formula, experiments with different internal pressures were carried out and the result was compared and discussed. It demonstrates that internal pressure plays an important role in tube hydroforming and theory and formula discussed and derived by this paper are feasible in practice.     

基于注入锁模光纤激光器的OTDM时钟提取技术实验研究

提出了一个新的全光时钟提取方案 :用非均匀复用后的OTDM信号去驱动主动锁模光纤环行激光器中的调制器件 ,得到复用前的单路时钟光脉冲 ,并且成功地从 2×10Gb/sOTDM信号中提取出 10GHz的单路时钟光脉冲     

气溶胶微喷射曲面共形打印影响因素的仿真分析与实验研究

目的 探究气溶胶微喷射曲面共形打印过程中的影响因素,并研究这些因素对打印线条最小特征线宽及形貌的影响规律。方法 针对微喷射曲面共形打印的影响因素,构建基于数值模拟及实验验证的研究模式。基于计算流体力学的数值模拟,对微喷射曲面共形打印过程中喷印头内气溶胶流束喷射的运动过程进行仿真分析。采用控制变量法研究气体流量、工作距离以及喷嘴大小对打印过程及打印线条的影响规律,并在此基础上设计单因素实验加以验证。结果 实验结果表明,最小特征线宽随鞘气流量的增大而逐渐减小,随载气流量、工作距离以及喷嘴直径的增大而逐渐增大。当载气流量为100 mL/min、鞘气流量为400 mL/min、工作距离为3 mm、喷嘴直径为500 μm时,打印线条的最小特征线宽可达43 μm,且未出现明显卫星液滴、沉积空洞及颗粒过喷等缺陷。结论 载气流量、鞘气流量、工作距离与喷嘴直径等因素显著影响了微喷射曲面共形打印柔性电路的最小特征线宽及微观形貌。实验结果与仿真数据具有相同的变化规律,验证了微喷射曲面共形打印仿真的可行性,为微喷射曲面共形打印的研究奠定了基础。     

参激非线性振子不稳定区域的实验研究

对一端固定、一端滑动、受轴向简谐激励的屈曲梁的非线性动力学行为进行了实验研究。对固定的参数激励频率和阻尼，当参数激励幅值较小时梁的运动是周期的，但大幅值激励会使运动通过倍周期分岔变为混沌。实验得到了动态响应在参数平面上的分布，并研究了阻尼对分布区域的影响。实验结果为全面了解系统解的分布及该类结构的动力学设计提供了有价值的资料。     

R134a臣卧式螺旋管内流动沸腾换热特性实验研究

对R134a在水平直管和螺旋管内的沸腾换热特性进行了实验研究.在三个不同的蒸发温度(5℃、10℃和20℃),工质R134a的质量流量范围为100～400kg/(m~2·s)和干度范围为0.1～0.8的条件下,实验得到了R134a在水平直管和螺旋管内的沸腾换热系数随其质量流量和干度的变化关系,将水平直管和螺旋管内的沸腾换热特性数据进行了比较,结果显示,在实验条件下,卧式螺旋管的传热系数比直管的平均增加13.7%.     

液体CO2冷藏车制冷系统的毛细管长度与厢体冷负荷匹配的实验研究

分析了绿色制冷剂--液体CO2在毛细管中的流动特征,对液体CO2在外径为2.18mm、内径为1.20mm,在一定进、出口压力下,对不同长度、不同曲直程度的毛细管内的质量流量进行了实验研究.同时对制冷系统中使用了毛细管的冷藏车的保温性能进行了测试,从而获得了与冷藏车厢体冷负荷相匹配的最佳毛细管长度.     

水平管外R404A降膜蒸发传热的实验研究

搭建了降膜蒸发实验台,研究了水平单管外的降膜蒸发传热特性。测试管为外径19mm、有效实验长度为2500mm的光滑管和强化管。实验采用R404A作为管外降膜蒸发工质,与管内热水进行换热。布液采用喷嘴喷淋的方式,通过21个喷口当量直径为2mm的喷嘴完成。分别在变饱和温度(0、5、10、15℃)、变热流密度(从8到30kW/m2)和变喷淋量(从0.07到0.11kg/(m·s)时进行实验,研究了降膜蒸发换热性能相应的变化情况,得到R404A的管外降膜蒸发换热的一些规律,这对降膜蒸发器的设计及应用具有一定的参考作用。     

激光粒子计数器校准中气溶胶稀释方法的研究

为了解决无法通过直接比较法实现激光粒子计数器对凝结核粒子计数器的溯源问题,根据伯努利气体流动原理和气溶胶稀释比例的计算方法,分析了气溶胶在稀释过程中,存在随着补充气体流量的增加,稀释器腔体内压力不恒定的问题,提出了一种新的气溶胶稀释方法,可满足激光粒子计数的溯源问题。实验结果表明,该方法解决了补充气体对气溶胶出气口流量的干扰问题,同时能够对高浓度气溶胶中不同粒径的0～90倍范围内稀释比例保持较好的一致性,测量数据与理论计算值的最大相对误差不超过4.4%。     

The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

Dental healthcare workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients'' mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of airflow, energy and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the airflow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs'' exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and the DHCW are important considerations for reducing DHCWs'' exposure to droplets/aerosol particles emitted from the patient''s mouth during treatments.     

Experimental and Numerical Investigation of the Fracture of Obstacles by Groups of High-Speed Bodies

The processes of high-speed interaction of several compact bodies with obstacles of finite thickness are studied experimentally and numerically in a three-dimensional statement of the problem. In experiments, the number of particles in a homogeneous flow varied from two to seven. The density of flow (distance between the particles) was also variable. In numerical calculations, we simulated the collisions of four particles with an obstacle for the cases of frontal impacts and asymmetric impacts separated in time. We present the numerically determined configurations of the bodies, the distributions of the specific volume of microdefects in the obstacle, and the experimental data on changes in the area and the mass of backside cleavage fragments. We also study the distinctive features of the processes of deformation and fracture of obstacles depending on the intensity of interaction between the particles.