通风管道结构形式对颗粒物沉积的影响

在矩形断面通风管道无因次颗粒物沉积速率计算结果与相关实验数据验证的基础上,对弯头、变径、三通等通风管道结构内的颗粒物沉积进行了数值模拟. 管道流动采用RSM湍流模型,并应用拉格朗日随机轨道模型描述气固两相流动中颗粒运动. 结果表明,直管段内无因次颗粒物沉积速率与相关研究结果变化趋势相近,直管段侧壁、顶面无因次颗粒物沉积速率在无因次松弛时间大于1时(粒径约10 mm)呈下降趋势. 弯头、变径及三通管段内颗粒物沉积率随斯托克斯数(St)增加而升高,当St<0.1时,3种管段结构内颗粒物沉积率均较小且相差较小;当St>0.1时,相同St下弯头内颗粒物沉积率最高,其次为三通和变径. 直管段内小粒径颗粒物(<10 mm)主要受湍流扩散作用而沉积,对于大颗粒的沉积则主要受重力影响;弯头、变径及三通管段内颗粒St>0.1时,颗粒物的沉积主要受惯性碰撞影响.     

工业环管反应器结构对非均匀流动的影响

工业环管反应器的结构参数对管内液固两相流动及装置的平稳高效运行具有重要的影响。对工业聚丙烯环管反应器进行CFD模拟,发现环管反应器中存在明显的非均匀流动现象——弯管处的颗粒偏析和直管处的颗粒带。进而引入非均匀度定量表征非均匀流动,研究直管段长度和直管段数量对非均匀流动的影响。研究发现,对直管段数量为2的环管反应器,当直管段高径比超过43时,出口截面上颗粒分布的非均匀度不随高径比增加而变化;对直管段数量为4的环管反应器,直管段高径比越大,出口截面上颗粒分布越均匀;对直管段长度为39 m、高径比为65的环管反应器,直管段数量越多,出口截面上颗粒分布越均匀;与直管段数量相比,直管段长度(高径比)对出口处非均匀度的影响更显著。研究结果可为工业环管反应器的设计和优化提供指导。     

工业环管反应器结构对非均匀流动的影响

工业环管反应器的结构参数对管内液固两相流动及装置的平稳高效运行具有重要的影响。对工业聚丙烯环管反应器进行CFD模拟，发现环管反应器中存在明显的非均匀流动现象--弯管处的颗粒偏析和直管处的颗粒带。进而引入非均匀度定量表征非均匀流动，研究直管段长度和直管段数量对非均匀流动的影响。研究发现，对直管段数量为2的环管反应器，当直管段高径比超过43时，出口截面上颗粒分布的非均匀度不随高径比增加而变化；对直管段数量为4的环管反应器，直管段高径比越大，出口截面上颗粒分布越均匀；对直管段长度为39 m、高径比为65的环管反应器，直管段数量越多，出口截面上颗粒分布越均匀；与直管段数量相比，直管段长度（高径比）对出口处非均匀度的影响更显著。研究结果可为工业环管反应器的设计和优化提供指导。     

电动车冷系统低压橡胶软管

正由浙江峻和橡胶科技有限公司申请的专利(公开号CN 202992431U,公开日期2013-06-12)"电动车冷系统低压橡胶软管",涉及的电动车冷系统低压橡胶软管的胶管本体经穿模硫化成型,由前管段、弧形过渡段、直管段和内外扩径的后管段组成,前管段、弧形过渡段和直管段的内孔径为16mm,后管段的扩孔内径为24mm,前管段的中心轴线与直管段中心线间的倾斜夹角大于105°而小于     

花岗岩水膜除尘器在我厂的应用

为满足尿素生产用汽的需要 ,我厂启用了闲置的ＳＺＦ1 0 - 1 3型沸腾炉。经 2年运行 ,沸腾炉的锅炉效率很好 ,但烟尘经一级重力沉降除尘后 ,外排的烟尘量超过国家排放标准 70多倍 ,对周围的环境造成了严重污染。由于沸腾炉排放的烟尘量大 ,致使每 2 0ｄ左右就必须更换引风机叶轮 ,严重影响生产。为解决上述问题 ,我厂新安装了1台花岗岩水膜除尘器 (以下简称水膜除尘器 ) ,除尘灰水经沉淀后循环使用。水膜除尘器的投用 ,彻底解决了烟尘污染 ,取得了良好的效果。1　工艺情况水膜除尘器直立安装在重力沉降除尘器之后 ,作为二级除尘器。烟尘由除…     

再生器烟道气氧量分析仪采样系统的改进

一、问题的提出我厂催化裂化装置再生器烟气氧量分析仪采样系统,原安装管路如图一所示。取样点(三个)设在双动滑阀之前,其标高为39.7米,采样管线选用φ27×3不锈钢管。由于采样气中催化剂粉沫含量大,采样管线长(全长40多米)部分管段又是水平敷设,经常造成催化剂粉沫堵塞采样导管的故障。我     

冷热原油顺序输送管内混油特性数值模拟

针对冷热原油顺序输送工艺,在已有混油理论基础上,建立了冷热原油顺序输送混油计算的数学模型,采用有限容积法进行了数值求解,对水平和竖直管内的混油特性进行了数值模拟和分析研究。结果表明,在水平管段,重力方向与管道轴向垂直,导致混油浓度在径向分布不对称;在竖直管段,重力方向与管道径向垂直,重力作用不会使得混油浓度在径向分布不对称,但在竖直管段,密度大的油品在上方时,混油量相对较大。     

管道弯头焊缝超声相控阵检测技术研究

受施焊条件限制,直管和弯管连接处焊缝内很容易产生缺陷;同时,由于结构的特殊性,连接处的受力情况比直管段复杂,容易产生新的缺陷。受检测条件影响,常规无损检测手段具有较大的局限性。制作了含根部未焊透、条渣、气孔等常见自然缺陷的弯头试块,采用超声相控阵检测技术对该试块进行检测。结果表明,对于弯头内的缺陷,超声相控阵检测技术具有较好的检测效果,能够满足实际检测需求,同时为后期弯头检测奠定了一定的基础,为压力管道的安全评价提供依据。     

水平井冲砂工艺技术探讨

水平井与直井冲砂的主要区别在水平井段,由于重力作用,砂粒在水平井段内自由沉降方向与液流方向近乎垂直,所以水平井冲砂是否成功,冲砂液排量大小已不是主要因素,关键是冲砂液要具有很好的悬浮和携带能力。本文主要简要的分析了水平井的冲砂技术。     

桡足类生物死体进入供水管网后的分布规律研究

对穿透水厂但经有效灭活的桡足类进入供水管网后的分布规律进行了研究。选择了水力沿程点、二次水池（箱）、用户龙头点、死水管段等代表性点位,经过长达一年半的监测研究,总结出桡足类在供水管网中的基本分布规律：由于重力沉降作用．桡足类死体在供水管网中的密度分布主要受水流速度影响,总体上表现为距离水厂管道沿线越远,其密度越高;在死水管段大量沉积;二次水池（箱）对桡足类死体有截留作用。     

Transport and deposition of inertial aerosols in bifurcated tubes under oscillatory flow

The transport and deposition of aerosol particles in a single bifurcation tube under oscillatory airflow condition are investigated via experiments and numerical simulations. In the experimental study, a novel stabilized laser-photodiode measurement technique is used to quantify the effects of frequency of oscillatory airflow and airflow rate on surface deposition of particles within the bifurcation tube. Surface deposition in the parent and daughter tubes is measured by orientating the laser-photodiode device parallel and perpendicular to the bifurcation plane and calculated using a transmission loss model. In the numerical simulation study, the same bifurcation tube is constructed using a two- and three-dimensional computer mesh in COMSOL^® to model particle mobility and deposition characteristics, considering the simultaneous effects of inertial impaction, gravitational settling and interception. The effects of frequency of oscillatory airflow, airflow rate and particle size on the particle trajectory and spatial deposition pattern are examined.     

A Computational Fluid Dynamics Study of Particle Penetration through an Omni-Directional Aerosol Inlet

Computational fluid dynamics (CFD) was used to study aerosol penetration through the entrance section of a bell-shaped omni-directional ambient aerosol sampling inlet. The entrance section did not include either an insect screen or a large-particle pre-separator. Simulations of the flow field were carried out for wind speeds of 2, 8, and 24 km/h and a fixed exhaust flow rate of 100 L/min; and, particle tracking was performed for 2 to 20 μ m aerodynamic diameter particles. Penetration calculated from CFD simulations was in excellent agreement with experimental results from previous studies with the root mean square relative error between simulation and experimental data being 3.8%. CFD results showed that the most significant regional particle deposition occurred on the upwind side of a curved flow passage between two concentric axisymmetric shells of the inlet housing and that deposition at the leading edges of the shells and within the exhaust tube was far less significant. At a wind speed of 2 km/h, penetration was affected by gravitational settling, e.g., penetration of 20 μ m particles was 71.9% when gravity was included and 80.4% without gravity. At higher wind speeds gravity had little effect. An empirical equation was developed to relate aerosol penetration to a Stokes number, a gravitational settling parameter, and a velocity ratio. Good fits of the correlation curves to experimental data and numerical results were obtained.     

GRAVITATIONAL SETTLING OF SUSPENDED PARTICLES FROM A FULLY DEVELOPED FLOW IN A CURVED TUBE

The gravitational settling of monodisperse particles from fully developed laminar flow in a horizontal curved tube is considered. The particle size is small compared with the tube radius, and their concentration is small so that they do not interact with each other or affect the flow. It was found that for sufficiently heavy particles, or for tubes with very small curvature, or for very small flow Reynolds numbers, the settling to the tube surface versus axial distance is much the same as that for a straight tube. However, for the opposite size of these parameters, the settling behavior becomes much different than that of a straight tube. Particles are maintained in the flow in helical spiral motions and do not settle to the tube surface.     

Aerosol Deposition in Sampling Probes

Deposition of aerosol particles on the inner walls of sampling probes is of concern in many aerosol sampling applications. Only inertial and gravitational effects have been considered in previous studies of the aerosol deposition; however, the lift force on particles is also of significance. In this investigation, experiments have been conducted to construct a database for aerosol deposition in Willeke-type sampling probes. An empirical correlation has been made between wall losses and the depositional forces of drag, gravity, inertia, and particle lift through the use of dimensionless parameters. Inclusion of the lift effect in this correlation not only helps to better predict particle behavior in the sampling inlet, but it also provides a basis for understanding of the intrinsic deposition phenomenon. The correlation has a geometric standard deviation of 1.13 and a 0.93 correlation coefficient relative to the experimental data.     

Gravitational deposition of aerosol particles from a developing flow in a horizontal circular tube

Aerosol particle deposition due to gravitational settling in a horizontal circular duct is examined for steady laminar flow, which develops from a uniform velocity profile at the entrance to a parabolic velocity profile downstream. Numerical calculation methods, based on the analysis of the limiting trajectories of the particles, are used to determine the deposition efficiency as a function of the duct entrance length. The results show that the deposition for the limiting cases of very large or small settling approach the solutions for deposition in a slug or a Poiseuille flow, respectively. In addition, particle inertial effects were included and for relatively large inertia, the deposition rate was significantly affected.     

水平双管程液=固循环流化床中颗粒分布和压降

为促进流化床换热防垢节能技术在水平双管程换热器中的应用,设计和构建了一套冷模透明水平双管程液-固循环流化床换热装置。以水和聚甲醛颗粒为工质,利用电荷耦合器件（CCD）图像测量和处理系统及压差传感器,考察了颗粒加入量（0.50%~1.25%）和循环流量（6~11 m³·h^-1）对颗粒分布和压降的影响。结果表明：上管程的颗粒分布更为均匀,下管程内存在“死区”,上、下管程的固含率均沿重力方向增大。上管程的颗粒分布不均匀度随循环流量的增加而波动,下管程则先迅速增大再逐渐减小。上、下管程的颗粒分布不均匀度均随颗粒加入量的增加而波动。压降比率随循环流量和颗粒加入量的增加而波动,在实验范围内的最大值为18.3%。绘制了操作参数对颗粒分布和压降影响的三维图,以确定较适宜的操作参数范围。     

Experimental Study of Particle Losses Close to the Entry of Thin-Walled Sampling Probes at Varying Angles to the Wind

This article summarizes the results of an extensive experimental study of sampling losses in thin-walled probes at various values of velocity ratio R and the probe orientation with respect to the freestream. The purpose of this study was to gain insights into the complex interaction of various parameters that influence sampling losses and the consequent effect on the overall sampling efficiency. A 0.635 cm diameter sharp-edged tube was mounted in a small wind tunnel where the freestream velocity could be varied over a wide range of values. Polydispersed spherical glass beads were used as the test aerosol. The number concentration and the particle size distribution were measured using the aerodynamic particle sizer (APS 3310). The sampling efficiency was determined as a function of orientation for a range of particle sizes (or Stokes number). By using an existing model to predict the aspiration efficiency for thin-walled probes, the sampling losses could be isolated from the sampling efficiency. In this manner a new empirical model was developed to predict the losses as a complex function of Stokes number, sampler orientation, and velocity ratio. The losses appear to be influenced by particle inertia, impaction, gravitational settling in the boundary layer developing inside the thin-walled probe, and vena contracta or flow recirculation loss near the entry. It was evident from the results that these losses are strongly influenced by the Stokes number and sampler orientation. The losses also increased strongly with increasing value of velocity ratio for all orientations.     

Comparative Study of Pressure Reducers for Aerosol Sampling from High Purity Gases

A performance evaluation and comparative study has been conducted with six pressure-reducing devices suitable for particle sampling from high pressure gas systems. Pressure-reducing devices are used to reduce the gas pressure from that existing in the high-purity compressed gas system to ambient conditions for subsequent measurement of particulate contaminants by particle counters. Six pressure-reducing devices, including designs based on the orifice plate, orifice design with expansion cone, and capillary tube designs, have been evaluated experimentally to determine their particle penetration characteristics and contribution to background particle.

Studies showed that particle loss in pressure reducers depended upon the pressure-reducing geometry, gas pressure and particle size. Particle penetration through orifice type devices was found to be superior to that found for capillary tube type devices. The 50% penetration through orifice type pressure reducers was found to be at a particle diameter of approximately 3.0 μ while for the capillary tube designs at a particle diameter less than 1.0 μ. For the orifice-type pressure reducers the particle background concentration was less than 0.05 particles/ft³ (1.77 particles/m³). Significantly higher particle background levels were found for the capillary tube type devices which is believed to result from particle reentrainment from the capillary tube wall.     

Respiratory Deposition of Fibers in the Non-Inertial Regime—Development and Application of a Semi-Analytical Model

A semi-analytical model describing the motion of fibrous particles ranging from nano- to micro scale was developed, and some important differences in respiratory tract transport and deposition between fibrous particles of various sizes and shapes were elucidated. The aim of this work was to gain information regarding health risks associated with inhalation exposure to small fibers such as carbon nanotubes. The model, however, is general in the sense that it can be applied to arbitrary flows and geometries at small fiber Stokes and Reynolds numbers. Deposition due to gravitational settling, Brownian motion and interception was considered, and results were presented for steady, laminar, fully developed parabolic flow in straight airways. Regarding particle size, our model shows that decrease in particle size leads to reduced efficiency of sedimentation but increased intensity of Brownian diffusion, as expected. We studied the effects due to particle shape alone by varying the aspect ratios and diameters of the microfibers simultaneously, such that the effect of particle mass does not come into play. Our model suggests that deposition both due to gravitational settling and Brownian diffusion decreases with increased fiber aspect ratio. Regarding the combined effect of fiber size and shape, our results suggest that for particles with elongated shape the probability of reaching the vulnerable gas-exchange region in the deep lung is highest for particles with diameters in the size range 10–100 nm and lengths of several micrometers. Note that the popular multi-walled carbon nanotubes fall into this size-range.     

Diffusional Particle Loss Upstream of Isokinetic Sampling Inlets

Isokinetic sampling, in which a subsample is extracted from the center of laminar aerosol flow, is routinely used to collect representative particles for analysis. Isokinetic sampling minimizes wall effects, including particle loss due to Brownian diffusion to the tube wall. This particle diffusion is analogous to the heat transfer problem originally posed by Graetz in 1883. Analytical solutions to the Graetz problem have been applied to calculate particle loss averaged over the entire main flow. However, these solutions overestimate diffusional particle loss near the center of the main flow. In the present solution, confluent hypergeometric functions are used to solve analytically for particle concentration as a function of radius. The solution is integrated near the center of the main flow to determine particle loss for isokinetically sampled aerosols. Sampling efficiencies valid down to nanometer-sized particles are presented in terms of dimensionless parameters. Diffusional particle loss for isokinetically sampled aerosol can be 1.8 times less than that from the main flow aerosol. The present results can be used to design isokinetic sampling systems and to assess particle loss in these systems. For 5 nm diameter particles sampled isokinetically from a laminar flow tube (0.318 cm tube radius, 10 m length) into an ultrafine condensation particle counter, sampling efficiency is strongly affected by main flow Reynolds number, Re; sampling efficiency increases from 4.9%at Re=100 to 99%at Re=1500.