Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

屯兰矿选煤厂浮选煤浆准备器药剂雾化装置改造

改造前屯兰矿选煤厂浮选煤浆准备器药剂雾化装置故障率高,加药效率低,为检修和操作带来很大困难。废弃使用后又造成浮选药耗升高,浮选效果变差。通过优化改进原药剂雾化装置的结构、部件、油管给入位置,改进后的药剂雾化装置故障率低,能有效雾化浮选药剂,达到降低药耗,改善浮选效果,节约配件消耗,减轻检修作业负荷的优良效果。     

Undersizing of droplets from a vented nebulizer caused by aerosol heating during transit through an anderson impactor

The use of Anderson cascade impaction to measure droplet sizes from a vented nebulizer connected directly to the impactor was examined by performing two sets of impactor measurements. In the first set, the impactor was operated in room temperature air. In the second set, the impactor was immersed in a cooled water bath at the same temperature as the aerosol exiting the nebulizer (10°C). Normal saline was nebulized in five Pari LC Jet+nebulizers driven by a single Pulmo-Aide compressor, operating under ambient conditions of 36% RH and 22°C. Impaction was done once steady temperatures were reached. When the impactor was operated in room temperature air, the air travelling through the impactor warmed from 10°C at the entrance to the impactor to room temperature at the exit of the impactor. This heating resulted in significant droplet shrinkage due to humidification by evaporation from the droplets, since the impactor immersed in the cooled water bath gave an MMAD that was on average 70% larger than was obtained when the impactor was operated in room air (3.4 μm vs 2.1 μm). These results emphasize the need for caution when using impactors to measure nebulized hygroscopic aerosols, since even if these aerosols enter the impactor in vapor pressure equilibrium with their surrounding air, significant size changes can occur during transit through the impactor if the temperature of the aerosol differs significantly from that surrounding the impactor.     

温压炸药爆炸火球的特征

用红外热成像仪对温压炸药和常规炸药的火球特征参数进行了测量,发现温压炸药的热辐射远大于普通炸药.用高速摄像记录了温压炸药的二次爆炸现象,通过与B炸药的爆炸过程对比,发现二次爆炸对温压炸药的爆炸火球具有一定的增强作用.     

微通道内铜离子反萃取过程

考察了油相铜离子负载浓度、硫酸浓度、油水两相体积比和温度对微通道内铜离子反萃取过程的影响.实验过程中水油两相表观速率分别为0.014～0.560 m/s和0.014～0.230 m/s,最高反萃取效率可达0 87,表观总体积平均传质系数为0.02～0.12 s-1.因反萃取时间短未达到平衡,故微通道内整个反萃取过程由传质过程与化学反应共同控制.     

Filtration Characteristics of a Miniature Electrostatic Precipitator

This study investigates the filtration characteristics of a miniature dual saw-like electrodes electrostatic precipitator (ESP). Parameters such as particle size, rate of airflow through the ESP, voltage of charge electrode, and discharge polarity were considered to study their influence on aerosol penetration through the ESP. Polydisperse and monodisperse particles with sizes ranging from 30 nm to 10 w m were used as the challenge aerosols. Experimental results indicated that the aerosol penetration through the ESP decreased (from 96% to 15% for 0.3 w m) as the voltage of the discharge electrode increased (from + 4 kV to +8 kV) at a flow rate of 30 L/min. At a fixed electrode voltage (+8 kV), aerosol penetration increased from 15% to 69% for 0.3 w m particles as the flow rate increased from 30 to 120 L/min. The most penetrating particle size was in the range of 0.25 w m to 0.5 w m depending on the discharge voltage and the flow rate. In general, the most penetrating particle size of the ESP decreased with decreasing discharge voltage or with increasing flow rate. At the same voltage level but opposite polarity, the aerosol penetration through the ESP with negative corona was lower than that with positive corona. The difference in aerosol penetration was a factor of about 2 between the negative and positive coronas for 0.3 w m particles, and this difference was found to be independent of discharge voltage. Regarding energy conservation, use of a negative-polarity ESP was more economical if the same efficiency was required. However, the ozone generated by the ESP with negative polarity was about five times greater than that generated with positive polarity. Therefore when using an ESP as an indoor air cleaner, the search for an optimum balance between ozone production and aerosol collection efficiency should be considered.     

Fracture Resistance Characteristics of a Metal-Toughened Ceramic

The fracture characteristics of an Al₂O₃/Al composite are examined. Measurements of resistance curves and work of rupture are compared with predictions of a micromechanical model, incorporating the effects of crack bridging by the Al reinforcements. The bridging traction law is assumed to follow linear softening behavior, characterized by a peak stress, σ_c, and a critical stretch-to-failure, u _c. The values of σ_c and u _c inferred from such comparisons are found to be broadly consistent with independent measurements of stretch-to-failure, along with the measured flow characteristics of the Al reinforcement. The importance of large-scale bridging on the fracture resistance behavior of this class of composite is also demonstrated through both the experiments and the simulations.     

Performance Characteristics of a Laser Initiated Microdetonator

The test results of 320 units of a laser initiated microdetonator are summarized. The commercially fabricated units used a lead styphnate/lead azide/HMX (1 mg/17.5 mg/13.5 mg) explosive train design contained in a miniature aluminum can that was capped with a glass-metal seal window. The test parameters were the laser energy, temperature, laser pulse duration, laser wavelength and nuclear radiation (5 × 10⁶ rad of 1 MeV gamma rays). The performance parameters were the laser energy for ignition and the actuation response time.     

Aerosol Characteristics in a Subway Environment

This paper presents an attempt to characterize biological and nonbiological aerosols in a subway environment. This opportunity to study a subway station atmosphere was approached as a collaboration of different organizations within the Department of Defense (DoD) and a suite of instruments was assembled for real-time monitoring, sample collection, and subsequent sample analysis. Based on ultraviolet (UV) fluorescence, aerosols of a biological nature were found to comprise a small fraction of the total aerosols (typically <1%). The total number concentration of aerosols exhibits a diurnal cycle that depends on the station usage. Several bacterial species were identified using polymerase chain reaction (PCR) analysis. The most common element in the aerosols is iron. Sodium chloride is also prevalent in the aerosol mass.     

Flow Characteristics in a Vortex Chamber

In this article we examine confined swirling flows using the integral equations of continuity and energy, along with the minimum pressure criterion. The pressure drop and the core size have been studied in the swirling confined vortex chamber. Both the n = 2 vortex model, with reverse and non‐reverse flow, and the free vortex model have been used at the vortex chamber exit plane. The influence of vortex chamber geometry, such as contraction ratio, inlet angle, area ratio, aspect ratio, and Reynolds number, on the flow field has been analyzed and compared with the present experimental data. The pressure drop across the vortex chamber differs from that in pipe flow, due to the mechanism of swirl flow that depends mainly on the intensity of tangential velocity. If the chamber length is increased, the vortex decays producing a weaker tangential velocity (less centrifugal force) that leads to less pressure drop. Based on the present theory, a new approach to determine the tangential velocity and radial pressure profiles inside the vortex chamber is developed and compared with the available experimental data. It shown that the n = 2 vortex model with reverse flow gives better results for strongly swirling flow.     

Characteristics of YSZ synthesized with a glycine-nitrate process

The amount of glycine addition was optimized for synthesizing (Y₂O₃)_0.08(ZrO₂)_0.92 (YSZ) powders with a glycine-nitrate process. The effect of glycine quantity was investigated on the phase structure, sintering behavior, electrical performance and microstructure of the resulted YSZ powders. With the increase of glycine addition, the crystallite size of the YSZ powder increased, the specific surface area decreased, and the density of the sintered YSZ pellets decreased when they were fired at the same temperature. Thermodynamic calculation showed that the flame temperature of the glycine-nitrate combustion reaction was much higher when more glycine was used. A highly loose powder was thus obtained with low quantity of glycine addition. When 70% of stoichiometric amount of glycine was used, YSZ powder had the highest densification rate. AC impedance spectroscopy showed that the amount of glycine had effects not only on total conductivity, but also on grain boundary and bulk contributions. The highest conductivity attained a value of 0.027 S cm⁻¹ at 800 °C for YSZ prepared with 80% of stoichiometric amount of glycine.     

Moisture-Expansion Characteristics of a Fired Kaolinite-Hydrous Mica-Quartz Clay

The natural and autoclave moisture expansions of a fired clay containing kaolinite, hydrous mica, and quartz were studied. A relation was established between the two expansions, which, together with a moisture-expansion peak at about 1000°C, is explained in terms of the poorly crystalline and noncrystalline phases developed during firing. When low-fired specimens that were exposed to moisture were desorbed by re-firing, the shrinkage that accompanied the loss of moisture was interrupted by an expansion at about 5OOOC. This expansion depended on the firing temperature and probably was caused by the dehydroxylation of hydrous mica regenerated from mica anhydride by moisture sorbed after firing. In the case of specimens fired above the moisture-expansion peak, the moisture responsible for expansion must be held in much the same way in the natural and in the autoclaved specimens. A study of the kinetics of moisture expansion showed a linear relation between the magnitude of expansion and the log of time for the period during which the specimens were exposed to moisture in the air. A similar relation existed for specimens fired from 1000° to 1150°C and autoclaved from 2 to 200 hours. It is further shown that it was possible, using preexisting data, to estimate, from the magnitude of expansion after a short period, the expansion to be expected at any time within the period to which the preexisting data referred.     

Performance Characteristics of a New Continuous-Flow Electrophoresis Instrument

Abstract

An instrument is described for the continuous separation of particles by means of electrophoresis. The effect of field strength, electrolyte flow rate, and sample flow rate on migration distance and particle band width were investigated. The interrelationships between the various operational parameters and particle band resolution are discussed.     

Ultraviolet Transmission Characteristics of a Fluorophosphate Laser Glass

Ultraviolet transmission characteristics of LG-810 fluorophosphate laser glass were investigated as a means of diagnosing transition metal contamination. Absorption bands normally exhibited by this glass were shown to derive primarily from metallic impurities. Uv-transparent glasses were produced having absorption cut-offs close to those reported for BeF₂-based glasses.     

Characteristics of a recuperative heat exchanger with a textile heat-transfer surface

The heat transfer coefficients in laminar flow of water in a recuperative heat exchanger with a textile heat-exchange surface were experimentally studied. The method of measurement is described and the experimental data are reported. It is shown that convective heat exchange as the liquid moves in the textile channels is significantly enhanced due to the discrete roughness of the fabric.     

蛇形微通道内泄漏流特性

微流体系统通常具备极大的比表面积、易于控制等优势,在气-液相传质、传热、反应等方面具有良好的应用前景。本文考察了6个气液相体系在矩形截面蛇形微通道中的气液两相泰勒流流动情况以及气泡和液弹的动态行为,以气泡截面形状的几何模型为基础,得到了微通道中净泄漏流的量化方程。同时发现在较大的操作区间内,蛇形微通道对泄漏流的可控性优于直形微通道。并且详细分析了不同气液相流量、液相物性（表面张力和黏度）和气泡长度对蛇形微通道主通道净泄漏流的具体影响。     

Hydrodynamic Characteristics of a Pilot-Scale Screw Conveyor Dryer

This article presents results of an experimental study on the flow characteristics of a pilot-size screw conveyor dryer (SCD). In particular, the effects of granular solids flow rate (15.2–206 kg/h) and screw speed (10.8–28 rpm) on the residence time distribution (RTD) were studied using sand as the model material. The RTD was measured using a dynamic step change in the solids flow rate. Parameters such as solids holdup, degree of fullness, mean residence time, and uniformity of the discharge flow were studied. The solids holdup and hence the degree of fullness was found to decrease with increase in the screw speed and decrease with the solids flow rate. The mean residence time was found to decrease with an increase in the screw speed, as expected. The screw speed and the solids flow rate strongly affected the discharge uniformity. An optimum value of the degree of fullness was observed with regard to the solids flow rate. Over the operating range examined, the solids flow pattern was close to plug flow, as indicated by high values of N and Pe number.     

Hydrodynamic Characteristics of a Pilot-Scale Screw Conveyor Dryer

This article presents results of an experimental study on the flow characteristics of a pilot-size screw conveyor dryer (SCD). In particular, the effects of granular solids flow rate (15.2-206 kg/h) and screw speed (10.8-28 rpm) on the residence time distribution (RTD) were studied using sand as the model material. The RTD was measured using a dynamic step change in the solids flow rate. Parameters such as solids holdup, degree of fullness, mean residence time, and uniformity of the discharge flow were studied. The solids holdup and hence the degree of fullness was found to decrease with increase in the screw speed and decrease with the solids flow rate. The mean residence time was found to decrease with an increase in the screw speed, as expected. The screw speed and the solids flow rate strongly affected the discharge uniformity. An optimum value of the degree of fullness was observed with regard to the solids flow rate. Over the operating range examined, the solids flow pattern was close to plug flow, as indicated by high values of N and Pe number.     

新型循环射流混合器湍流特性分析

采用Fluent SST k-w湍流模型,分别对新型循环射流混合器受限区域内喷嘴射流自相似性和挡板长度对射流轴线衰减规律进行了数值研究. 对自由湍动圆射流在不同轴向距离下数值模拟所得无量纲速度衰减曲线与理论曲线吻合较好. 通过三维湍流流场分析对混合器内流体流动进行分区,并利用涡量分布分析混合器内的流体循环流动情况. 结果表明,在z/H=0.25时,平均涡量达最大值áw?max=11.22. 相平面角度qp<20o时,áw?为正,其余为负. 特别是qp=16o时,áw?max=27.22;qp=20o时,áw?min=-100.66. 由剪切速率分布得出较大的剪切速率分布于尾涡的位置. 最后给出了强化混合效果应考虑的因素.     

延安某变电站黄土湿陷特性探讨

黄土在陕北地区广泛分布,黄土湿陷性问题这一地区的主要问题,本文结合延安某变电站勘察实例,通过对场地黄土湿陷前后微结构电镜扫描结果对变电站的黄土湿陷性特性进行了探讨。