不同收光方式下煤粉流的等离子体信号探测

针对煤粉流组分分布的不均匀性, 研究不同收光方式对煤粉流的激光诱导等离子体的光谱信号收集效果的影响.选用电厂常用燃煤神木混为实验对象,利用自行搭建的气固两相流实验台架产生稳定煤粉流,对比同向收光方式和侧向收光方式下煤的特征谱线信号探测的强度和稳定性.研究结果表明,相同实验条件下,中间穿孔反射镜使同向收光方式下探测的光谱信号强度较弱,而等离子体信号源位置沿激光束轴线的变化、等离子体信号本身沿空间分布的不均匀性及煤粉流的阻挡作用使侧向收光方式下探测的光谱信号稳定性较弱.     

煤粉颗粒流在不同焦点位置条件下的激发特性

将激光诱导击穿光谱技术应用到煤粉颗粒流测量中,分析激光与样品流相互作用,并考察不同的聚焦焦深对等离子体激发特性的影响。在自行搭建的两相流的实验台架上,在大气环境条件下,利用激光器分别对1.0,0.5,0,-0.5, -1.0 mm焦深作用条件下的煤粉颗粒流进行击穿,同时利用光谱仪对等离子体信号进行采集。在相同的激光能量以及收光角度等条件下,改变聚焦激光的焦深,分析对比不同焦深下的等离子体温度、电子密度以及对煤元素分析中关注的C, Si和Al三个代表元素的光谱强度的变化规律。结果表明,不同的激光聚焦焦深对等离子体温度、电子密度和元素光谱强度的影响规律较为明显,三个参数整体变化规律是一致的,最优点为0 mm,其次为1.0,0.5,-0.5 mm,最劣点为-1.0 mm。     

空气环境下煤粉流LIBS多元素同时检测中激光能量研究

考察了大气环境下激光诱导击穿光谱适用于煤粉流多元素同时检测的激光能量范围,分析了造成煤粉流测量谱线信号波动的原因,得到了适用于煤粉流多元素同时检测的激发区域功率密度范围和最佳功率密度。实验选取能量范围为20～160 mJ,粒径小于200 μm煤粉颗粒经下料口自由下落形成煤粉流束,通过螺杆式给粉机控制流量,波长1 064 nm脉冲激光聚焦后作用于下降的煤粉流束上,产生等离子体,光谱仪采集等离子体发射光谱信号,分析结果表明：实验台架下适于煤粉流LIBS检测的能量范围为30～60 mJ,对应激发前沿功率密度选取范围14.4～34.4 GW·cm-2,最佳测量功率密度19.5 GW·cm-2。     

脉冲等离子体推力器羽流沉积薄膜的结构与光学性质研究

为了研究脉冲等离子体推力器羽流污染特性,把握脉冲等离子体推力器羽流沉积薄膜性质,利用质谱仪对推力器羽流残余气体成分进行了分析,利用红外傅里叶光谱、光电子能谱及紫外可见光分光光度计对推力器羽流区阴极侧不同方位角处沉积薄膜的结构及光学性质进行了诊断研究结果表明,推力器羽流中主要存在C,F,CF,CF2和CF3气体分子;在各方位角处脉冲等离子体推力器羽流沉积生成了低氟碳比碳氟薄膜;沉积薄膜微观结构以30°角为界在羽流不同区域中具有不同的变化趋势;羽流沉积薄膜具有对波长小于500 nm的光低透射率及增强反射率的光学特性,受薄膜性质的影响,其光学特性具有极大的角度依赖性.     

激光能量对飞灰颗粒流中未燃碳LIBS检测影响研究

飞灰含碳量是评价锅炉燃烧效率的重要指标之一,对其进行在线测量有助于实时进行燃烧优化调整,从而提高整个机组的经济性和安全性。利用螺杆式给粉机搭建飞灰颗粒流含碳量测量台架,将脉冲激光直接作用于飞灰颗粒流,形成等离子体,利用激光诱导击穿光谱技术测量飞灰颗粒流中的含碳量信息。重点研究了激光能量对飞灰颗粒流中未燃碳有效激发和测量的影响规律。研究结果显示,在40～130 mJ能量的脉冲激光作用下,碳谱线强度随着激光能量的增大线性增强,而其信噪比则先增加后趋于稳定,无效光谱的剔除率则呈下降趋势。本实验条件下,激光能量在90～100 mJ之间,可得到较强的等离子体发射信号和较优的光谱数据利用率。因而激光能量与颗粒流的激发状态、碳元素特征谱线强度等密切相关。合理的激光能量有利于保证飞灰颗粒流的有效稳定激发,并获得具有良好信噪比的等离子体光谱信号。     

基于光学薄膜的LED光谱调制技术

针对白光LED光谱与自然光谱的不同,讨论了采用光学薄膜改善白光LED光谱的可行性,同时提出了一种利用光学薄膜消除白光LED发光光谱中蓝光成份的方法,设计了光学薄膜的透过率曲线,并分析了其可行性.针对单色LED光谱随温度不同发生变化的特点,根据分析样品在4.9°、24°和49°三种环境温度下的光谱分布,设计了一种光学薄膜的透过率曲线,分析利用该设计薄膜改善单色LED光谱温度稳定性的可行性及结果.研究结果表明,在保证白光LED出光效率的前提下,仅靠在发光芯片上镀制光学薄膜的方式并不能改善光谱的结构,而使之与自然光中的可见光谱相似.采用设计的光学薄膜,可以消除白光LED发光光谱中的蓝光波段,提高光谱的舒适性.在4.9°、24°和49°三种环境温度下,利用设计的薄膜可将分析LED的发光光谱的中心波长稳定在700 nm附近,相对发光强度稳定在0.2附近,不同温度时光谱分布的相似性也有了较大的改善,研究结果有助于LED照明光源的进一步应用.     

激光等离子体软x光辐射的时间分辨测量

采用透射光栅和软x光条纹相机测量了铜激光等离子体软x光发射的时间分辨光谱。通过比较时间分辨谱和时间积分光谱,从实验上考查了条纹相机在软x光区域的响应特性。文中也给出了激光等离子体软x光不同谱带及波长发射的时间过程。     

基于无序纳米颗粒的光子晶体有机薄膜

无序光子晶体有机物薄膜的制备是实现光阻隔材料量产的关键。设计了无序多级光子晶体结构有机物薄膜，以热塑性聚氨酯作为膜材基质，将二氧化钛颗粒作为反射隔光材料填入基质中。采用时域有限差分法进行了模拟，结果表明，增加填充因子导致了反射峰和光谱禁带的蓝移，而增加颗粒直径造成了光谱禁带红移。将单一直径均匀分布的阵列作为对比，分析了粒径多级性和结构聚结性对光谱的影响。对于横电波和横磁波，在0°～70°的宽入射角范围内实现了高效禁带效应。这种无序光子晶体结构的有机薄膜为宽角度光阻隔材料提供了参考。     

激光等离子体光丝中太赫兹频谱的调控

研究了双色激光场激发空气成丝产生太赫兹辐射频谱的变化规律.实验观察到随驱动光功率和光丝长度增加,太赫兹光谱主要发生红移的现象.分析表明,由于等离子体密度的增加,太赫兹辐射的趋肤深度减小,等离子体吸收主导了红移的发生.在光丝足够短的条件下,趋肤深度远大于光丝长度,从而产生等离子体振荡主导的太赫兹辐射光谱蓝移.本研究为超快宽带太赫兹辐射的频谱调控提供了新思路.     

不同角度包层光剥离的理论与实验研究

光纤激光器中存在传输角度不同的包层光,为研究腐蚀型包层光剥离器(CLS)对各角度包层光的剥离效果,实验测量了光纤腐蚀段的散射系数,仿真分析了不同传输角度下包层光的剥离度与腐蚀长度的关系。为提供角度分布不同的包层光,搭建两套剥离器测试系统,分别对双包层光纤和无芯光纤制作的包层光剥离器进行实验。在双包层光纤实验中,两系统包层光的最大传输角由10°和8°变为3°12'和3°1',接近芯中光的最大传输角度为2°27';在无芯光纤实验中,两系统包层光的最大传输角由11°和8°变为2°9'和2°12',且随剥离度的增加,最大传输角度趋近于0°,即腐蚀型包层光剥离器能够基本剥离包层光。最后在波长为1 018 nm的同带泵浦激光器上对双包层光纤制作的腐蚀型包层光剥离器进行测试,在输入功率为1 136 W情况下,其剥离度为18. 3 d B。     

激光诱导煤粉等离子体的特性研究

本文研究了煤粉形态对于激光诱导煤粉等离子体特性的影响,以指导应用激光感生击穿光谱进行煤质测量时最佳样品形态的选择.建立了一套激光诱导击穿光谱的实验台架,对同一煤种的4个不同粒径范围的粉状样品进行激光激发与光谱分析,利用钙原子不同跃迁能级发射谱线的强度分布计算了0.3～0.5μs区间内的等离子体温度,并依据谱线Stark展宽与电子密度的关系得到了等离子体的电子密度.再对激发不同粒径煤粉样品产生的等离子体温度与电子密度进行了对比.实验证明,煤粉粒径越小,等离子体温度越高且电子密度越大,也即样品的等离子化程度越高,越有利于煤中元素的定量分析.     

基于Mie光散射理论的尾流气泡前向散射光特性研究

实验中利用CMOS图像传感器代替传统的光电探测器接受前向散射光,由几何光学和图像处理分析得出不同散射角的散射光与采集图像中的光环相对应.通过计算各个光环的所有像素值的总和就可以得到前向散射光光强的相对值,进而可以得出前向散射光光强变化规律.根据米氏（Mie）光散射理论可以计算出气泡各个方向的散射光光强,通过比较实验结果和Mie理论计算结果可以看出,采用CMOS图像传感器探测和图像处理技术可以准确地得出散射光强度的变化规律.     

Spherical turbulent flame propagation of pulverized coal particle clouds in an O2/N2 atmosphere

The present study aims to clarify the effects of turbulence intensity and coal concentration on the spherical turbulent flame propagation of a pulverized coal particle cloud. A unique experimental apparatus was developed in which coal particles can be dispersed homogeneously in a turbulent flow field generated by two fans. Experiments on spherical turbulent flame propagation of pulverized coal particle clouds in a constant volume spherical chamber in various turbulence intensities and coal concentrations were conducted. A common bituminous coal was used in the present study. The flame propagation velocity was obtained from an analysis of flame propagation images taken using a high-speed camera. It was found that the flame propagation velocity increased with increasing flame radius. The flame propagation velocity increases as the turbulence intensity increases. Similar trends were observed in spherical flames using gaseous fuel. The coal concentration has a weak effect on the flame propagation velocity, which is unique to pulverized coal combustions in a turbulent field. These are the first reports of experimental results for the spherical turbulent flame propagation behavior of pulverized coal particle clouds. The results obtained in the present study are obviously different from those of previous pulverized coal combustion studies and any other results of gaseous fuel combustion research.     

形体细胞的MCEM模型及其光散射分布特征

针对光散射细胞微粒测量中真实形体细胞的取向对测量结果的影响问题，基于Rayleigh-Debye-Gans理论和双椭球核式(CEM)模型在应用中的差异，建立了CEM的修正模型(MCEM)，根据此模型系统讨论了细胞在不同入射角变化情况下其光散射强度分布所产生的变化，得到了不同入射角下有核细胞光散射强度分布与有核细胞相关物理特征量的动态响应关系；此外，对有核细胞光散射强度分布进行拟合，得到了有核细胞光散射强度分布函数。误差分析表明：拟合结果可有效地应用于真实细胞光散射测量中的数值反演计算。     

激光诱导煤粉发射光谱的基体效应研究

激光诱导发射光谱分析技术是目前正被广泛发展的一种元素定量检测手段,其分析结果的准确性与精度和分析基体的物理化学特性紧密相关.本文采用波长为1064nm的激光烧蚀煤样,以中阶梯光谱仪和ICCD分析诱导产生的等离子体发射光谱.通过试验基体的不同形态特性对各种元素定量分析特征光谱的强度、稳定性以及元素分析探测限的影响,研究激光诱导煤粉发射光谱的基体效应规律,并从激光等离子体形成的理论机制上进行实验分析.研究表明,适中的煤粉颗粒尺寸与样品密度更有利于激光诱导煤粉发射光谱的定量分析.     

MR angiography with pulsatile flow.

To achieve acceptable scan times, current multiple thin slice and 3D MR angiography (MRA) methods usually are based on continuous data acquisition, without ECG-synchronization. The purpose of this work is to study consequences of pulsatile blood flow for the 2D inflow method. Arterial blood flow and blood signal intensity versus cardiac phase were studied by a 2D phase based method with retrospective cardiac synchronization. Such studies were performed in different parts of the body and with different excitation flip angles. As expected, a clear relation between intensity enhancement and time dependent flow can be demonstrated. The raw data of these multiphase studies was used to simulate alternative inflow MRA data acquisition strategies to improve image quality, without the excessive increase in scan time implied by standard cardiac triggering. The alternatives investigated were data collection during part of the cardiac cycle and cardiac-ordered phase encoding. Simulation results indicate that the best results are obtained by a combination of both strategies. This method was implemented on Philips Gyroscan systems to compare it with standard nontriggered 2D inflow in practical MRA studies. For highly pulsatile flow, much better MR angiograms were obtained in this way.     

Electrohydrodynamic flow patterns and collection efficiency in narrow wire-cylinder type electrostatic precipitator

Recently, narrow electrostatic precipitators (ESPs) have become a subject of interest because of their possible application for the cleaning of the exhaust gases emitted by diesel engines. Diesel engines emit fine particles, which are harmful to human and animal health. There are several methods for decrease particulate emission from a diesel engines, but up to now, these methods are not enough effective or very expensive. Therefore, an electrostatic precipitation was proposed as an alternative method for control of a diesel particulate emission.In this work, results of electrohydrodynamic (EHD) secondary flow and particle collection efficiency measurements in a narrow wire-cylinder type ESP are presented. The ESP was a glass cylinder (300 mm × 29 mm) equipped with a wire discharge electrode and two collecting cylinder-electrodes. A 0.23 mm in diameter and 100 mm long stainless-steel discharge wire electrode was mounted in the center of the cylinder, parallel to the main flow direction. The collecting electrodes were made of stainless steel cylinders, each with a length of 100 mm and inner diameter of 25.5 mm. An air flow seeded with a cigarette smoke was blown along the ESP duct with an average velocity of 0.9 m/s.The EHD secondary flow was measured using 2-dimensional particle image velocimetry (PIV) method. The PIV measurements were carried out in the wire electrode mid-plane, perpendicularly to the wire and the collecting electrodes. The results show similarities and differences of the particle flow in the wire-cylinder type ESP for a negative and a positive DC voltage polarity.The collection efficiency was calculated from the fractional particle concentration. The fractional particle concentration was measured using the optical aerosol spectrometer. The results of the fractional collection efficiency confirmed the common view that the collection efficiency of fine particles in the ESP increases with increasing voltage and it is higher for negative voltage polarity and decreases when decreasing particle diameter.     

强声波作用下煤颗粒周围气体的振荡流动特性

根据二维非稳态层流的质量和动量守恒方程,研究强声波作用下煤颗粒周围气体的振荡流动特性.入射波的振幅远大于颗粒特征长度,声雷诺数小于20.根据通用微分方程的解,详细分析不同声雷诺数与斯特劳哈尔数下,颗粒壁面的流场分布、轴向压力梯度、切向应力及分离角的分布,发现在低频（~50 Hz）时,颗粒壁面轴向压力梯度、切向应力及流动分离角的分布主要受曲率效应影响,其变化规律与振荡速度的幅值变化相对应;在高频时（~5 000 Hz）,颗粒壁面轴向压力梯度、切向应力及流动分离角的分布同时受到曲率效应和流动加速度的影响.为进一步研究强声波强化煤颗粒燃烧提供理论基础.     

Evaluation of steady and pulsatile flow with dynamic MRI using limited flip angles and gradient refocused echoes

Magnetic resonance imaging sequences utilizing limited flip angles and gradient echoes yield rapid (less than 2 min) dynamic images of the cardiovascular system. These images contain both accurate anatomical and functional information. Using a gradient refocused acquisition in the steady state (GRASS) in the CINE mode, we studied the relationship between gradient echo signal intensity and velocity of steady and pulsatile flow in a phantom simulating medium to large vessels. Images were acquired on a 1.5 Tesla system (repetition TIME = 21 ms, echo TIME = 12 ms, flip ANGLE = 30 degrees). Data from each pulse interval were sorted in 16 images. Signal intensities from flow tube lumina and surrounding stationary water jacket were used to calculate contrast ratios which were compared to velocity measurements made with electromagnetic (EM) flow probes outside the magnet room. During steady flow, signal intensity contrast ratios increased with increasing flow and in a 10 mm thick slice, reached a peak at 48 cm/s, and declined for velocities up to 90 cm/s. Changes in instantaneous velocity during pulsatile flow correlated well (r > .88) with signal intensity changes up to a maximum mean velocity of 17 cm/s. Total signal intensity from the lumen for an “R to R” interval correlated extremely well (r > .97) with mean pulsatile flow velocities up to 30 cm/s. The excellent correlation between gradient echo signal intensity and actual flow velocities suggests that this imaging sequence might be useful for evaluating normal and pathologic flow phenomena.