CdTe探测器能量刻度与探测效率的模拟计算

在实现对单能平行光子源的绝对测量之前,需要对CdTe探测器进行刻度。利用已知点源对CdTe探测器进行能量刻度,得到刻度曲线和能量分辨率,利用工业CT对CdTe探测器进行精确扫描,得到CdTe探测器内部结构,并以此为基础,利用MCNP5蒙特卡罗模拟程序建立CdTe探测器物理模型;计算20～150keV能量段,能量间隔为1keV每个能量点的探测效率,得到CdTe探测器的效率曲线图。发现CdTe探测器在低能段探测效率较高,但Te元素在27keV和32keV处产生了逃逸峰,探测效率有所下降,之后探测效率曲线呈现先上升后下降的趋势。     

热水解法制备Fe2O3纳米粒子及其在Si表面的分散

用快速热水解的方法,制备直径小于10 nm的单分散Fe(OH)3胶体粒子。X射线衍射(XRD)和透射电镜(TEM)衍射分析表明:Fe(OH)3胶体粒子脱水后转变为Fe2O3纳米粒子。用离心分散的方法,胶体粒子在干燥过程中避免了团聚现象,实现其在Si表面的单层均匀分散覆盖。研究了胶体溶液浓度对胶体粒子尺寸及表面覆盖度的影响:改变胶体溶液的浓度,可以调节胶体粒子在Si表面的覆盖度,但对胶体粒子尺寸的影响不明显。     

纳米粒子气溶胶分析系统的建立

纳米粒子气溶胶分析系统对粒径测量的量值可溯源到标准粒子,可进行单分散、多分散样品的测量以及电子分级筛选。该文介绍纳米粒子气溶胶分析系统的基本原理、测量方法和系统组成,总结了所进行的实验研究。并展望了良好的应用前景。     

低剪切应力下纳米炭黑在聚丙烯中的分散规律

使用低剪切应力下纳米复合材料的制备方法制备炭黑填充聚丙烯纳米复合材料,采用扫描电子显微镜等方法对复合材料进行观察和分析。以剥蚀机理为主要理论依据,对低剪切混合时间与炭黑分散的关系进行定量分析。结果表明纳米CB在PP中的最可几粒径随分散时间的延长而减小,混合时间超过140 s后纳米CB的粒径趋于极限值。得到纳米CB粒子在PP基体中的分散模型,为通过控制加工条件以获得纳米粒子在聚合物中的良好分散提供了理论指导。     

《二氧化硅孔材料的模板合成》化学综合实验的建设

化学综合实验"二氧化硅孔材料的模板合成"是为大学化学专业本科生开设的一个实验教学课程。其实验的主要内容是,首先合成制备单分散的聚苯乙烯乳胶粒子,然后以此单分散的聚苯乙烯乳胶粒子为初始材料,利用胶体晶模板法制备二氧化硅三维有序孔材料。利用透射电子显微镜和扫描电子显微镜对所制备的各级样品进行表征。教学实践发现,当作为初始材料的聚苯乙烯乳胶粒子尺寸较大时,三维有序孔材料的制备成功率高。文中介绍了此实验的建立以及对其进行改进的过程。     

热水解法制备Fe2O3纳米粒子及其在Si表面的分散

用快速热水解的方法，制备直径小于10nm的单分散Fe(OH)3胶体粒子。X射线衍射(XRD)和透射电镜(TEM)衍射分析表明：Fe(OH)3胶体粒子脱水后转变为Fe2O3纳米粒子。用离心分散的方法，胶体粒子在干燥过程中避免了团聚现象。实现其在Si表面的单层均匀分散覆盖。研究了胶体溶液浓度对胶体粒子尺寸及表面覆盖度的影响：改变胶体溶液的浓度。可以调节胶体粒子在Si表面的覆盖度，但对胶体粒子尺寸的影响不明显。     

微观图像技术在超细材料粒度分析中的应用

应用计算机微观图像采集分析系统建立了一套对超细材料进行形状表征和粒度测量的方法。该方法克服以往图像法测量样本小 ,得不到正确粒度分布的弊端。通过对SiO2 标准物的粒度测定表明 :均匀、单分散的测量样片的制备是图像法准确测量和分析的关键。当测量图片在 6张以上 ,累积测量颗粒总数在 2 0 0个左右时 ,测量结果具有代表性。该系统用于测量的粒度范围为 0 .5 μm～ 1cm的粒子时 ,长度测量误差小于 5 % ,颗粒等面积直径测量偏差小于12 %。     

单分散纳米Pd的简易加热合成及对甲醛的电催化氧化

以PdCl2为金属前驱体,在水-乙醇混合体系内,添加微量的CTAB,简易加热合成单分散纳米Pd粒子,用XRD和TEM等技术进行了表征,考察了PdCl2/CTAB组成对纳米粒子形貌和尺寸的影响,通过循环伏安法对纳米Pd粒子修饰玻碳电极对甲醛的电催化活性进行了研究。结果表明,通过改变PdCl2/CTAB组成可以调控纳米Pd粒子的粒径和形貌;当PdCl2与CTAB的物质的量之比为1∶21、于(70±1)℃反应3h时,得到呈单分散性的多边形纳米钯粒子,粒径为(8±1)nm,它对甲醛有较高的电催化活性。     

标称值1μm粒度标准物质的研制

为了完善我国粒度测量溯源及传递体系,满足粒度仪检定校准需求,本文中采用分散聚合的方法制备得到了单分散交联聚苯乙烯标准粒子,所得到的标准粒子球形度好、粒径分布标准偏差为1.5%。利用扫描电子显微镜和图像分析系统对其进行了定值研究,结果表明,该粒度标准物质的量值为1.28μm,定值不确定度为0.9%。     

基于膜计算与粒子群算法的盲源分离方法

为了解决盲源分离方法收敛速度慢、分离性能不高的问题,提出一种基于膜计算(Membrane Computing,MC)和粒子群算法(Particle Swarm Optimization,PSO)的盲源分离方法。算法以分离信号负熵作为粒子群的适应值函数,将粒子均匀分布到各基本膜中,将各基本膜内最优位置输出到表层膜并选择适应值最小的最优位置作为群体最优位置,通过粒子自身最优位置和群体最优位置对种群粒子进行速度和位置的更新。粒子群最优解调整盲源分离的步长函数,进行信号的分离。提出的算法简化了惯性权重取值问题,保证了PSO算法局部搜索的精度,满足了全局搜索的多样性。仿真实验和实例应用表明,提出的算法可以很好地分离混合信号,并且能避免PSO算法的早熟收敛问题,具有更快的收敛速度和更优异的分离性能。     

Design and Evaluation of Four-Stage Low-Pressure Cascade Impactor Using Electrical Measurement System

The low-pressure cascade impactor has been used to collect ultrafine particles that cannot be measured by conventional cascade impactors. Low-pressure cascade impactors resemble ordinary impactors, but are operated at reduced pressures of 0.05 ～ 0.4 atm. Many kinds of low-pressure impactors have been developed by different researchers. However, it is still difficult to accurately design and evaluate the low-pressure cascade impactor.

In this study, a four-stage low-pressure cascade impactor for measuring the size distribution of submicron aerosol particles was designed and evaluated. To evaluate particle collection efficiency of each stage, an electrical measurement system was used. The cut-point diameters of Stages 1 through 4 were 0.238, 0.173, 0.111, and 0.063 μm in aerodynamic diameter. Stage 2 showed poor steepness of the collection efficiency curve and larger cut-point Stokes number than theory, which may be attributed to high nozzle velocity. The fluorometric method for particle collection efficiency measurement was shown to be unreliable for ultrafine particles.

The solid particle collection efficiency of the designed impactor was examined with different substrate conditioning methods. Porous metal substrate and silicon-coated substrate were tested with NaCl particles. It was shown that silicon coating did not effectively reduce the particle bounce because of high nozzle velocity, whereas the porous metal substrate considerably enhanced the particle collection efficiency.     

Design and Evaluation of Four-Stage Low-Pressure Cascade Impactor Using Electrical Measurement System

The low-pressure cascade impactor has been used to collect ultrafine particles that cannot be measured by conventional cascade impactors. Low-pressure cascade impactors resemble ordinary impactors, but are operated at reduced pressures of 0.05 ∼ 0.4 atm. Many kinds of low-pressure impactors have been developed by different researchers. However, it is still difficult to accurately design and evaluate the low-pressure cascade impactor.

In this study, a four-stage low-pressure cascade impactor for measuring the size distribution of submicron aerosol particles was designed and evaluated. To evaluate particle collection efficiency of each stage, an electrical measurement system was used. The cut-point diameters of Stages 1 through 4 were 0.238, 0.173, 0.111, and 0.063 μm in aerodynamic diameter. Stage 2 showed poor steepness of the collection efficiency curve and larger cut-point Stokes number than theory, which may be attributed to high nozzle velocity. The fluorometric method for particle collection efficiency measurement was shown to be unreliable for ultrafine particles.

The solid particle collection efficiency of the designed impactor was examined with different substrate conditioning methods. Porous metal substrate and silicon-coated substrate were tested with NaCl particles. It was shown that silicon coating did not effectively reduce the particle bounce because of high nozzle velocity, whereas the porous metal substrate considerably enhanced the particle collection efficiency.     

液压冲击器流场分析

通过流体力学的相关理论分析了压力反馈式液压冲击器的整体流场,建立了液压冲击器流场的基本方程;对冲击器的力学模型进行了简化,并求解了流场中的速度分布和流动损失情况。为了形象地得出冲击器流场的参数变化规律,文章利用Catia软件和Fluent的前处理器Gambit对冲击器的流场进行了建模,并利用Fluent软件对液压冲击器的瞬态流场进行了模拟求解。对比CFD模拟的结果和求解基本方程的结果,结果比较吻合。对瞬态流场的分析表明,在进油口截面突然变化的部位流速变化较大,远离这一区域后开始趋于平稳,而冲击过程中的中腔出油口存在速度较大的区域。另外,随着进油速度增大,流场的紊流情况加剧,流动的损失量呈抛物线增加。     

Observation Evaluation of Nozzle Clogging in a Micro-orifice Impactor Used for Atmospheric Aerosol Sampling

A micro-orifice impactor uses micro-orifice nozzles to extend the cut sizes of the lower stages to as small as 0.18 μm in diameter without resorting to low pressures or creating excessive pressure drops across the impactor stages. In this work, the phenomenon of nozzle clogging caused by particle deposition was investigated experimentally for a commercial micro-orifice uniform deposit impactor (MOUDI, MSP model 100). Using an optical microscope, we observed that the micro-orifice nozzles of the lower three stages were partially clogged due to particle deposition during the atmospheric aerosol sampling. To examine the effect of nozzle clogging on the performance of the impactor, the pressure drop and the particle collection efficiency were evaluated for the lower three stages. The pressure drops across the clogged nozzles were higher than the nominal values given by the manufacturer. The particle collection efficiency of each stage was evaluated by using an electrical method for fine particles with diameters in the range of 0.1-0.6 μm. Monodisperse liquid dioctyl sebacate (DOS) particles were used as test aerosols. A Faraday cage was employed to measure the low-level current of the charged particles upstream and downstream of each stage. The collection efficiency curves shifted to correspondence to smaller orifice sizes, and the 50% cutoff sizes were much smaller than those given by the manufacturer for the three stages with nozzles less than 400 μm in diameter.     

Influence of clean air and inlet configuration on the performance of slit nozzle virtual impactor

A two-partitioned horizontal inlet was developed for improving the collection efficiency and minimizing the wall loss problem in slit virtual impactor. The two-partitions were provided to simultaneously supply both aerosol and clean air to the virtual impactor. Both numerical and experimental investigations were carried out on the developed inlet configuration by considering different flowrate ratios of aerosol to clean air. The horizontal inlet was helpful in reducing the cutoff diameter, whereas the clean air prevented the particle deposition on the virtual impactor walls. The performance of two-partitioned horizontal inlet was compared with the conventional vertical inlet configuration for PM_2.5, PM₅ and PM₁₀ virtual impactors. All the operating conditions and geometric parameters, such as the inlet flowrate; the width of collection nozzle; the width, length and span of acceleration nozzle; and the distance between collection and acceleration nozzles, were kept the same and only the inlet configuration was changed. The major-to-total flowrate ratio was kept at 0.9 and minor-to-total flowrate ratio at 0.1. It was observed that by using the two-partitioned horizontal inlet configuration, the cutoff diameters for PM_2.5, PM₅ and PM₁₀ virtual impactors, were reduced by 16%, 10% and 11%, respectively, while the wall loss of particles near the cutoff size in all three cases were reduced from 16% to about 1%.     

凝聚式单分散气溶胶发生技术的探讨

实现高效空气过滤器计数法的首要任务就是选择合适的气溶胶发生器。本文中首先介绍了凝聚式单分散气溶胶发生器的工作原理、构造形式、发生流程以及国内外研究进展,然后详细分析了其发生气溶胶粒子粒径和浓度的影响参数;作者认为凝聚式单分散气溶胶发生器能够快速地发生浓度可调的、适用于高效空气过滤器效率测试的单分散亚微米气溶胶粒子,可以满足国家标准《高效空气过滤器性能试验方法》的修订对气溶胶发生装置的要求。     

自配流型液压冲击器建模与仿真

液压冲击器是工程施工中常用的液压设备。其工作过程中运动部件的高加速度及惯性工作油压的特性,使得其与常规液压设备工作状况有很大区别。在液压冲击器的研究过程有必要快速准确地建立计算仿真模型。在AMESIM系统中基于功率键合原理搭建的液压冲击器仿真系统,综合考虑了液压冲击器主要功能和特点,可快速实现对冲击器主要仿真参数的计算。利用现有的YYG250型液压凿岩机的冲击器设计参数进行仿真后,计算结果与实测工况参数之误差在5%之内,说明了仿真模型的正确性和可靠性。该模型对不同系列的冲击器的参数设计和冲击特性研究提供了良好的平台。     

Tuning the dye aerosol impaction and TiO2 nanoparticle stacking structures for High-Efficiency Dye-Sensitized solar cells

The rapid manufacturing of high-efficiency dye-sensitized solar cells (DSSCs) is limited by the slow dye adsorption on TiO₂ nanoparticles (NPs)-accumulated photoelectrode using conventional dip-coating process. Therefore, we aim to accelerate the adsorption of dyes that are attached on TiO₂ NPs by employing an aerosol impactor. Herein the aerosolized dyes are designed to get deposited rapidly on the TiO₂ NPs-accumulated photoelectrode. In addition, to effectively trap the irradiated sunlight in DSSCs, we assemble the photoelectrodes incorporated with bilayered TiO₂ thin films comprising small TiO₂ NPs-based underlayer and large TiO₂ NPs-based overlayer as dye-supporting and light-scattering mediums, respectively. Furthermore, the effects of dye aerosol impaction and TiO₂ stacking structures on the efficiency of DSSCs are examined. The power conversion efficiency (PCE) of DSSCs comprising a N719 dye-supporting layer treated with dip-coating process was determined as ～ 5.67%; however, when the bilayered TiO₂ thin films with an optimized thickness ratio of light-scattering overlayer and dye-supporting underlayer were coated with N719 dyes using dye aerosol impactor, the resulting PCE increased to ～ 7.46%. This suggests that the photovoltaic characteristics of DSSCs can be enhanced considerably using the effective TiO₂ NP stacking structures coated with rapid, uniform, and strong aerosol dye adsorption throughout the TiO₂-based photoelectrodes.     

多级冲击器压强分布计算及实验验证

本文以SPAL型多级冲击器为例，给出了冲击器各级压强分布的理论计算方法，设计加工了压强测试装置，测量了多级冲击器在不同工作条件各级实际压强，并与理论计算值进行对比分析。     

Development of electric virtual impactor with variable sampling particle size range

An electric virtual impactor with a capability of sampling fine and ultrafine particles was developed and its performance was evaluated both numerically and experimentally. The electric virtual impactor was provided with metallic electrodes, to which electric voltage in the range of 75–9000 V was applied for creating an electric field within the virtual impactor. Particle electric mobility was utilized to sample ultrafine particles at the major outflow section, while particle inertia was employed to collect fine particles at the minor outflow section. Silver nanoparticles with known charge level and Arizona test dust were used to experimentally validate the performance of the electric virtual impactor. Numerical and experimental outcomes agreed well with each other. The upper cutoff size of the electric virtual impactor was fixed at about 2.6 μm, while the lower cutoff size varied from 7 nm to 110 nm depending on the applied electric voltage. As a result, the proposed electric virtual impactor was able to sample both fine and ultrafine particles of a desired particle size range.