气溶胶粒子在裂隙中穿透特性实验研究

为研究气溶胶颗粒通过房屋裂隙进入室内的穿透特性,用铁质矩形裂隙在实验室进行模拟实验研究。结果表明:气溶胶粒径、气体流速和裂隙高度对气溶胶的穿透率影响比较显著;流速和裂隙高度增加会增大气溶胶的穿透率;不同粒径的气溶胶在相同实验条件下穿透率存在明显差异,最易穿透的是粒径在0.5μm左右的粒子,小粒子和大粒子分别在Brownian扩散作用和重力沉降作用下穿透率低。     

洞室气溶胶穿透率测量实验研究

为评价某洞室对气溶胶粒子的封堵特性,利用电子低压碰撞器(ELPI)对洞室气溶胶穿透率进行实验测量,得到气溶胶渗透进入洞室的穿透率,初步建立评价洞室气溶胶穿透率的方法。结果表明:该洞室气溶胶的穿透率为0~0.32,对应粒径为0.08~3μm,显著低于一般居所的气溶胶穿透率。通过两次实验测量对比发现,洞室的整体穿透率由少数较大裂隙决定,有效封堵大裂隙可以显著减小气溶胶的穿透率。     

颗粒床过滤中最难过滤粒子粒径及最具穿透率流速研究

研究了颗粒床过滤中4种机理联合作用下的最具穿透率粒子粒径及最具穿透率气体流速特性。当气体流速、过滤介质粒径均不变时,得到了计算最难过滤粒子粒径的理论方程;当气溶胶粒子粒径、过滤介质粒径均不变时,得到了计算最具穿透率流速的理论方程。通过实验数据验证了理论的正确性。     

西北戈壁地区气溶胶的浓度及粒度分布特征

为了获取西北戈壁地区气溶胶随着粒径变化的概率分布函数,对该地区的2次现场取样进行调查。结果表明,采样点气溶胶的质量浓度为0.03~0.1 mg/m3;气溶胶的粒径分布遵循双峰分布的规律,第1个峰值出现在约0.5μm处,第2个峰值出现在约3μm处,其差异主要表现在第2个峰值的面积大小;大多数采样点气溶胶粒子数量中位粒径小于1μm,质量中位粒径位于2~5μm之间。     

管内Cu-水微米颗粒流湍流强化传热研究

传统光管在高雷诺数下的传热效果不理想,因此提出在水介质中添加微米Cu颗粒作为工作介质来强化管内换热的方法。建立了Cu-水微米流的多相流传热物理模型,采用基于颗粒动力学的欧拉-欧拉双流体模型,对粒径分别为10μm、50μm、100μm和500μm,流速分别为1 m/s、1.5 m/s、2 m/s和2.5 m/s,颗粒体积分数分别为5%、10%、15%和20%进行了传热Nu和阻力损失f数值计算,结果表明:Cu-水微米流的努塞尔数Nu随雷诺数Re和颗粒体积分数的增大而增大,而随粒径的增大而总体趋势减小;摩擦因子f随颗粒体积分数的增大而增大,而随雷诺数Re增大而增小;传热综合性能评价因子η随颗粒体积分数的增大而增大,随着粒径的增大而总体趋势减小。粒径10μm的传热综合性能在研究的粒径范围内最佳,η达到1.1~2.3。     

气溶胶对远红外激光辐射的衰减规律研究

计算分析了10.6μm波长远红外激光辐射在不同能见度条件下的大气气溶胶中水平传输的衰减系数、有效传输距离以及斜程传输时的透过率变化规律,对比分析了远红外激光辐射在1.0g/m3的高浓度酸雾和油雾气溶胶中的传输能力。根据Mie理论计算了直径为0.5～40μm的水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光的散射效率因子、吸收效率因子和消光效率因子。结果表明:气溶胶的消光系数越大、大气能见度越低,大气气溶胶对远红外激光辐射的衰减越严重;在1.0g/m3的高浓度酸雾和油雾气溶胶中远红外激光辐射的有效传输距离只有20～50m。水溶性大气气溶胶和尘状气溶胶粒子对10.6μm激光辐射的衰减机理基本相同,其中散射作用居于主导地位并且平均直径大于5μm的气溶胶粒子对10.6μm远红外激光辐射具有显著的衰减作用。     

PM2.5细颗粒物分离技术的数值模拟和性能改进

旋风切割器是分离细颗粒物的主流技术,为了提高其分离效率并减少能耗,本文分析了切割器参数对粒子分离的影响.基于计算流体动力学数值模拟的方法,分析了VSCC型旋风切割器的内部湍流流场,比较15~25L/min范围内不同流速下的涡流变化情况;基于"逃逸率"概念,模拟1~6μm内不同粒径的细小粒子逃逸率随流速的变化曲线,考察临界粒径dc并结合气溶胶实验进行验证,分析流速对分离性能的影响程度;之后考察了流速对压降的影响,提出一种几何参数改进方案,在避免压降升高的前提下提高分离性能.研究表明:流速影响旋风切割器内的湍流分布,随着流速增大,临界粒径变小,分离性能得到提升,模拟结果在16 L/min的流速下,临界粒径约为2.5μm,与实验结果基本一致,并且利用曲线给出计算总分离效率的思路;调节几何参数可以实现在低能耗的前提下,将临界粒径进一步降低为1.1μm,收集效率更高.研究结果可为PM2.5切割器的商业选择或工程设计提供理论参考.     

熔喷聚丙烯驻极体空气过滤材料对不同气溶胶的过滤性能及过滤机理研究

测定了熔喷聚丙烯驻极体空气过滤材料对离子型(KCl)、极性非离子型(DEHS)两种不同实验气溶胶粒子的过滤性能,研究了粒子的粒径、荷电特性及流动速率对过滤性能的影响,分析了惯性效应、扩散效应和静电效应对粒子捕获能力的贡献。结果表明,熔喷聚丙烯驻极体空气过滤材料对不同气溶胶粒子的捕获能力差别较大,对KCl气溶胶的捕获能力要优于DEHS气溶胶,其原因与驻极体空气过滤材料所具有的特殊的静电效应有关。KCl用作实验气溶胶时,不出现MPPS(最易透过粒径)现象,过滤机理以静电效应为主;DEHS用作实验气溶胶时,MPPS值在0.08μm附近,小于经典单纤维过滤值0.3μm,过滤机理以惯性效应、扩散效应为主,以静电效应为辅。     

合肥地区气溶胶光学特性的地基观测研究

利用自主研制的DTF-5型太阳辐射计观测合肥地区2008年10月—2010年5月的太阳直接辐射消光,反演合肥地区气溶胶光学厚度、Angstrom参数和沙尘天气过程中的粒子谱分布,并对结果进行分析。结果表明:合肥地区气溶胶光学厚度季节变化除气候因素外,受人为因素影响明显,季节变化规律复杂。总体上秋季较小,冬春季节持续增大,夏季较平稳。而Angstrom参数与气溶胶光学厚度大致呈反相关,秋冬上升,春季骤降,夏季平稳值较大。气溶胶光学厚度日变化大致可分为4种类型:日变化相对稳定;整体呈上升趋势;整体呈下降趋势;一日内出现一到多个峰值。其中第四种类型出现几率最大。沙尘天气过程中,气溶胶光学厚度和Angstrom参数分别呈现出"谷-峰-谷"、"峰-谷-峰"的变化规律,其中Angstrom参数在沙尘影响严重时甚至出现负值。半径为0.2~1.0μm的大粒子和大于1.0μm的巨粒子浓度在沙尘天气过程中大幅增加。     

石墨气溶胶粒度分布及远红外消光因子研究

在烟幕试验箱中测试了不同湿度条件下超细石墨气溶胶的粒子分布及其随时间变化的规律。根据Mie散射理论计算了石墨气溶胶粒子对8～14μm远红外的消光因子。分析表明,石墨气溶胶的粒度随着分散时间延长和空气相对湿度减小而变小。小尺度的石墨气溶胶粒子对8～14μm红外的消光效率因子非常小,但随着气溶胶粒子直径的增加,消光效率因子显著变大并趋于稳定。直径大于2.5μm的石墨气溶胶粒子均能够对8～14μm远红外产生良好的消光效果。     

Study of airflow induced by regular particles in freefall through tubes

Airflow induced by falling particles can be a significant factor in causing dust emission during the conveyance of bulk materials. Heretofore, there have been few experimental studies on the effect of the particle size and the diameter of the tubes through which they are falling on the induced airflow. This study involved the experimental analysis of the correlation between those two factors and the induced airflow. The results were as follows: within the range of the total drag coefficient (0.62–0.94) of the experimental setup, the induced airflow velocity increased with an increment of the mass flow rate of the particles and drop height, and the power exponents of a fitted curve were approximately 0.35 and 1.29, respectively. Within the particle diameter range of 3.247–9.223 mm, the power coefficients and power exponents of a fitted curve for induced airflow velocity increased from 0.224 and 0.269 to 0.458 and 0.384, respectively, with the increase in particle size. As the tube diameter decreased from 200 mm to 120 mm, both the induced airflow velocity and the quantity of specific induced airflow increased, while the quantities decreased when the tube diameter decreased from 120 mm to 75 mm. The semi-empirical equation of the induced airflow velocity was established to predict the quantity of induced airflow under various operation conditions.     

电子材料用球形超细银粉的制备

采用化学还原法,以抗坏血酸为还原剂,油酸为分散剂,将硝酸银溶液滴加到还原性溶液中制备电子材料用球形高纯超细银粉。对还原机理进行了分析,探讨了还原过程中各种因素如硝酸银溶液浓度、还原剂浓度、pH值、搅拌方式及速率以及反应温度等对银粉粒度大小及分布的影响。采用TEM、SEM、EDAX和XRD对所得银粉进行了表征。结果表明,通过改变反应条件可制备0.3￣1.0μm的不同粒径的球形高纯超细银粉。     

Use of the Electrostatic Classification Method to Size 0.1 μm SRM Particles—A Feasibility Study

The use of the electrostatic classification method for sizing monodisperse 0.1 μm polystyrene latex (PSL) spheres has been investigated experimentally. The objective was to determine the feasibility of using electrostatic classification as a standard method of particle sizing in the development of a 0.1 μm particle diameter Standard Reference Material (SRM). The mean particle diameter was calculated from a measurement of the mean electrical mobility of the PSL spheres as an aerosol using an electrostatic classifier. The performance of the classifier was investigated by measuring its transfer function, conducting a sensitivity analysis to verify the governing theoretical relationships, measuring the repeatability of particle sizing, and sizing NIST SRM 1691, 0.269 μm and NIST SRM 1690, 0.895 μm particles. Investigations of the aerosol generator’s performance focused on the effect of impurities in the particle-suspending liquid on the resulting particle diameter.The uncertainty in particle diameter determined by electrical mobility measurements is found to be −3.3% to +3.0%. The major sources of uncertainty include the flow measurement, the slip correction, and a dependence of particle size on the aerosol flow rate. It was found that the classifier could be calibrated to indicate the correct size to within 0.1% for both SRM particle sizes if the defined classification length is decreased by 1.9%.     

Control of electrostatic charge on particles by impact charging

The control of electrostatic charge on particles in gas–solids pipe flow has been studied experimentally and theoretically. Alumina particles of 3.3 μm in count median diameter were dispersed in airflow and pneumatically transported in the dilute phase. Five different materials were used for the transport pipes, and the relationships between the particle charge and the pipe length were obtained. The polarity and the amount of particle charge were found to depend on the pipe material and the length. In order to control the particle charge, a system combining two different pipe materials was proposed depending on the particle-charging characteristics. The charge controlled by this method was in good agreement with the theoretical calculation. Furthermore, it was found that the distribution of particle charge as well as the average can be controlled.     

Optical Probe for the In-Line Determination of Particle Shape, Size, and Velocity

A laboratory optical probe was developed to simultaneously determine the following particle characteristics: circularity, particle projection area, equivalent diameter of a circle, length of the particle outline or perimeter, maximum chord length, aspect ratio, and particle velocity. Using the projection area and the perimeter, the particle shape factor circularity can be determined. The aspect ratio was approximated by the ratio of the equivalent diameter to the maximum chord length. The basic measuring principle is multi-point scanning of the particle shadow image by a line of optical fibers. In addition, the particle velocity can be measured by a differential spatial filter of optical fibers. These fibers are step index fibers with a core diameter of 64 µm and cladding of 70 µm. The shadow image of a single particle was generated by a parallel laser beam. The uncertainty of the measured circularity and aspect ratio was investigated by using metal wires with diameters of 0.12 to 0.5 mm as test particles with known circularity and aspect ratio. The standard deviations were 1.9% for the circularity and 15.5% for the approximated aspect ratio. In addition, the optical probe system was investigated by measurements of solid particles with different shapes. As an example, the results of sand, marjoram seed, and metallic oxide particles are shown. Using 1000 sand particles, the correlation between equivalent diameter and particle velocity could be demonstrated. The presented configuration of the optical probe is applicable in the size range of 0.1 to 0.9 mm and up to a particle velocity of 5 m/s.     

Optical Probe for the In-Line Determination of Particle Shape,Size, and Velocity

A laboratory optical probe was developed to simultaneously determine the following particle characteristics: circularity, particle projection area, equivalent diameter of a circle, length of the particle outline or perimeter, maximum chord length, aspect ratio, and particle velocity. Using the projection area and the perimeter, the particle shape factor circularity can be determined. The aspect ratio was approximated by the ratio of the equivalent diameter to the maximum chord length. The basic measuring principle is multi-point scanning of the particle shadow image by a line of optical fibers. In addition, the particle velocity can be measured by a differential spatial filter of optical fibers. These fibers are step index fibers with a core diameter of 64 µm and cladding of 70 µm. The shadow image of a single particle was generated by a parallel laser beam. The uncertainty of the measured circularity and aspect ratio was investigated by using metal wires with diameters of 0.12 to 0.5 mm as test particles with known circularity and aspect ratio. The standard deviations were 1.9% for the circularity and 15.5% for the approximated aspect ratio. In addition, the optical probe system was investigated by measurements of solid particles with different shapes. As an example, the results of sand, marjoram seed, and metallic oxide particles are shown. Using 1000 sand particles, the correlation between equivalent diameter and particle velocity could be demonstrated. The presented configuration of the optical probe is applicable in the size range of 0.1 to 0.9 mm and up to a particle velocity of 5 m/s.