Simulating the Feasibility of Using Liquid Micro-Jets for Determining Electron–Liquid Scattering Cross-Sections

The extraction of electron–liquid phase cross-sections (surface and bulk) is proposed through the measurement of (differential) energy loss spectra for electrons scattered from a liquid micro-jet. The signature physical elements of the scattering processes on the energy loss spectra are highlighted using a Monte Carlo simulation technique, originally developed for simulating electron transport in liquids. Machine learning techniques are applied to the simulated electron energy loss spectra, to invert the data and extract the cross-sections. The extraction of the elastic cross-section for neon was determined within 9% accuracy over the energy range 1–100 eV. The extension toward the simultaneous determination of elastic and ionisation cross-sections resulted in a decrease in accuracy, now to within 18% accuracy for elastic scattering and 1% for ionisation. Additional methods are explored to enhance the accuracy of the simultaneous extraction of liquid phase cross-sections.     

水介质对超声空蚀纳米生成物形貌的影响

为探究水介质下超声空蚀纳米结构的生成机制,研究不同水介质条件下超声空蚀纳米生成物的形貌特征。利用超声振动空蚀实验装置,在4种不同水介质中分别对45钢样品进行超声空蚀实验,通过激光共聚焦显微镜、扫描电子显微镜对实验后样品表面空蚀纳米生成物形貌进行分析。结果表明:45钢在不同水介质中空蚀生成的纳米微结构有很大差异;在去离子水和Na Cl溶液中空蚀坑环状区域纳米结构呈现为不规则絮状结构,在自来水和Na₂SO₄溶液中生成的空蚀坑周围形成了纳米多层片状结构;在自来水中,随着超声时间的增加,纳米单层片状结构先是长度方向尺寸增大,后逐渐叠加成纳米多层片状结构,总厚度增大。45钢在自来水中超声空蚀生成的纳米多层片状结构的尺寸,与实验时间和介质中离子有关,源于空蚀-腐蚀耦合作用产生;自来水中的SO₄^2-等离子也为片状纳米层间的组装起到促进作用。     

压电膜片式微喷的多场耦合仿真模型及其应用

基于自行设计制造的压电驱动膜片式微喷装置的实际结构,建立了一个多场耦合的数值模型,用来研究压电驱动的膜片式微滴喷射过程中的参数作用和变化规律。在模型的建立过程中,对流体部分的湍流判定和表面力作用的关键技术问题进行了分析研究。该模型能较好地模拟微喷装置工作过程。利用该模型研究了驱动波形对液滴属性的决定关系,以及液体腔中一个工作周期内压力的变化规律等问题。     

Comparison of pneumatic jets and tabs for Active Aerodynamic Load Control

A fast, efficient way to control loads on utility scale wind turbines is important for the growth of the wind industry. Microtabs and microjets are two Active Aerodynamic Load Control devices, which address this need. Both act perpendicular to the surface of the airfoil, and these actively controlled devices are used to mitigate changes in aerodynamic loading experienced by wind turbine rotors due to wind gusts, wind shear, or other atmospheric phenomena. This work explores the aerodynamic effects of microjets and then compares them to those of microtabs. Flow around an airfoil with an activated microjet at the trailing edge has been simulated using the Reynolds‐averaged Navier–Stokes solver OVERFLOW‐2. Using a Chimera overset grid topology, a microjet has been placed near the trailing edge of the lower surface of a NACA 0012 airfoil. For a jet velocity about half of the freestream velocity, the microjet can change the lift up to ΔC_L = 0.2, but the amount of change varies with the momentum coefficient of the jet. The change in lift is not symmetric for positive and negative angles of attack due to changes in the boundary layer thickness with angle of attack. Increasing the Reynolds number reduces the effectiveness of the microjet only slightly. The effects of jet velocity, jet activation time, and airfoil angle of attack on airfoil lift, drag, and pitching moment are compared with previous work, which illustrates the deployment of a microtab at the 95% chord location of a NACA 0012 airfoil. This study shows that microjets and microtabs have very similar responses in lift and pitching moment, but the drag for the microjet is noticeably lower. Copyright © 2013 John Wiley & Sons, Ltd.     

一种新型高效率微阀的设计与实验研究

提出三肋式微型气动阀这一可用于流场主动控制领域的新型微阀,通过增大逆/正向气流的损失系数比来大幅提高效率。阐述了气动阀的设计原理,对其效率高的原因进行了解释;对三肋式气动阀的流场进行数值模拟以验证设计原理,并对三角阀、气动阀的流量与效率进行计算与分析。结果表明:三肋式气动阀的效率提高到三角阀的4倍。加工了3种微阀实验件,在不可压与可压两种状态下分别进行对比实验。结果表明:在不可压状态下,三角阀的效率为3%~4%,三肋式气动阀为17%~18%;在可压状态下,三角阀的效率接近2%,三肋式气动阀约为16%。     

Fluidization enhancement of agglomerates of metal oxide nanopowders by microjets

The quality of gas–solid fluidization of agglomerates of nanoparticles has been greatly enhanced by adding a secondary flow in the form of a high‐velocity jet produced by one or more micronozzles pointing vertically downward toward the distributor. The micronozzles produced a jet with sufficient velocity (hundreds of meters per second), turbulence, and shear to break‐up large nanoagglomerates, prevent channeling, curtail bubbling, and promote liquid‐like fluidization. For example, Aerosil R974, an agglomerate particulate fluidization (APF) type nanopowder, expanded up to 50 times its original bed height, and difficult to fluidize agglomerate bubbling fluidization (ABF) type nanopowders, such as Aeroxide TiO2 P25, were converted to APF type behavior, showing large bed expansions and homogeneous fluidization without bubbles. Microjet‐assisted nanofluidization was also found to improve solids motion and prevent powder packing in an internal, is easily scaled‐up, and can mix and blend different species of nanoparticles on the nanoscale. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

基于MEMS的医用雾化微喷研究

介绍了一种基于MEMS技术的雾化微喷的设计、仿真、加工和实验结果。该微喷以压电效应为驱动方式,通过压电片振动所产生的压力使液体从阵列微喷孔中喷出,所产生的液滴直径和速度分布集中,无热效应,不会破坏药液的物理和化学特性。通过有限元仿真分析了微喷液体腔内压力波的分布,并根据仿真结果优化了微喷孔的布置。实验结果表明,该微喷所产生的液滴平均直径15μm,平均速度3m/s。     

Surface modification of poly(dimethylsiloxane) for controlling biological cells’ adhesion using a scanning radical microjet

A scanning radical microjet (SRMJ) equipment using oxygen microplasma has been developed and successfully applied for controlling biological cells’ attachment on biocompatible polymer material, poly(dimethylsiloxane) (PDMS). The radical microjet has advantages in localized and high-rate surface treatment. Moreover, maskless hydrophilic patterning using SRMJ has been demonstrated to be applicable to patterned cell cultivation which is useful in emerging biotechnological field such as tissue engineering and cell-based biosensors. Since control of PDMS surface properties is an indispensable prerequisite for cells’ attachment, effects of oxygen flow rates and treatment time on localized hydrophilic patterning of PDMS surfaces were first investigated for controlling HeLa cells’ (human epitheloid carcinoma cell line) attachment. Relationships between surface conditions of treated PDMS films and attached cell density are also discussed based on surface properties analyzed using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).     

Experimental study on diffusion combustion of high-speed hydrogen round microjets

Experimental data on the phenomenon of nozzle choking at diffusion combustion of a high-speed hydrogen microjet at its ignition close to the nozzle are presented. As is found, such a phenomenon is due to the nozzle heating by the «bottleneck flame region» which is generated at the origin of microjet. This flow region persists up to transonic velocities of the microjet preventing from cooling of the nozzle and the transition to supersonic speed. In the case of hydrogen ignition far from the nozzle exit in supersonic conditions, the «bottleneck flame region» is suppressed, the flame becomes detached from the nozzle which is no longer heated so that the supersonic range is attained. The subsonic combustion of hydrogen microjet is stabilized by the «bottleneck flame region» while the supersonic one becomes more stable at the generation of shock cells. The results of the present study provide new details on the combustion of hydrogen microjets and could by useful for the operation of different burners.     

用于制作生物微阵列的压电超声聚焦微喷系统

研制了一种用于制作生物微阵列的超声聚焦微喷系统。与用以制作生物微阵列的其他微喷方法相比,超声聚焦喷射具有过程温和,无堵塞等优势。为了提高微阵列的整齐性,减少喷点的直径和昂贵试剂的用量,提出了向下隔离喷射的设计。实验证明,利用该系统可以制作出排列整齐、喷点直径小于100μm,大小均匀的微阵列。