Theoretical study of liquid droplet dispersion in a venturi scrubber

The droplet concentration distribution in an atomizing scrubber was calculated based on droplet eddy diffusion by a three-dimensional dispersion model. This model is also capable of predicting the liquid flowing on the wall. The theoretical distribution of droplet concentration agrees well with experimental data given by Viswanathan et al. for droplet concentration distribution in a venturi-type scrubber. The results obtained by the model show a non-uniform distribution of drops over the cross section of the scrubber, as noted by the experimental data. While the maximum of droplet concentration distribution may depend on many operating parameters of the scrubber, the results of this study show that the highest uniformity of drop distribution will be reached when penetration length is approximately equal to one-fourth of the depth of the scrubber. The results of this study can be applied to evaluate the removal efficiency of a venturi scrubber.     

Mathematical Modeling of SO2 Absorption in a Venturi Scrubber

Abstract

A three-dimensional mathematical model was used to predict the removal efficiency of a venturi scrubber for SO₂ absorption into a water and alkaline solution. In order to obtain better results, nonuniform droplet concentration distribution was considered. The results of the model with nonuniform droplet concentration distribution are compared with several sets of experimental data, as well as with prediction data of a mathematical model with uniform droplet concentration distribution. Without exception, all comparisons indicated that including nonuniformity of droplet concentration distribution in the model will significantly improve the agreement between the experimental data and predicted values.     

基于剪切乳化机的采油污水再现配置与分散相破碎乳化行为

以剪切乳化机为主体,设计、加工了一套采油污水室内再现配置装置,探讨了含油量、剪切强度(与流量同比变化,下同)等不同配置条件下的再现采油污水粒度分布、乳化度、Zeta电位和粘度等性能参数以及乳化机前后的压力损失.结果表明,该采油污水再现配置装置,能满足不同性质采油污水的配置要求,剪切乳化机的压力损失随着剪切强度的增大而明显升高,而随含油量增大没有明显的变化趋势,呈现出基本稳定的状态.较大的剪切强度创造了湍流流体条件,强化了分散相颗粒之间的碰撞聚结行为,因而再现采油污水的乳化度随剪切强度增大而降低,这种降低的程度又受含油量的影响:低含油量时剪切强度的影响明显,高含油量时这种影响逐渐减弱并趋于平缓.鉴于高含油量时趋于形成大粒径油珠,再现采油污水的乳化度随含油量增大而呈现略微的下降趋势,这种下降趋势的程度同时受剪切强度的影响:低剪切强度时含油量的影响较为明显,而高剪切强度时的剪切条件削弱了含油量的影响.Zeta电位随着剪切强度增大而不断增大,使得分散相颗粒带电绝对值降低,乳化体系有脱稳的趋势,导致颗粒间的碰撞聚结机会变大,与乳化度降低的趋势相吻合.剪切强度和含油量对再现采油污水粘度的影响不大.     

旋风除尘器流场及浓度场实验与模拟

在研究旋风除尘器内气固两相的运动状况及分离机理方面,计算机模拟替代部分实验的方法能够优化设计旋风除尘器结构参数,提高其对微细颗粒的捕集效率,减少运行压力损失。本研究采用RSM模型和随机轨道模型对旋风除尘器内流场及浓度场进行模拟及实验。研究表明,旋风除尘器压力损失模拟结果与实验结果吻合较好,对于大于5μm的颗粒其捕集效率模拟结果与实验结果基本吻合;旋风除尘器外壁的颗粒浓度呈螺旋带状分布;如将排气管管径减少至原直径0.8倍,可使其对2μm颗粒捕集效率提高6.6%,但压力损失提高36.5%;颗粒的凝并作用有利于提高旋风除尘器微细颗粒的捕集效率。     

Scaling of spontaneous imbibition data with wettability included

Wettability is a dominant parameter governing spontaneous imbibition. However less attention has been paid to the effect of wettability on the scaling of spontaneous imbibition data. Actually few models can include wettability in scaling of spontaneous imbibition data. To this end, a scaling model has been developed for NAPL (oil)-saturated porous media with different wettability based on the fluid flow mechanisms in porous media. Relative permeability, capillary pressure, initial water saturation, and wettability are considered in the scaling model. Theoretically this scaling model is suitable for both cocurrent and countercurrent spontaneous imbibition. The experimental data of countercurrent spontaneous water imbibition at different wettability cannot be scaled using the frequently used scaling model but can be scaled satisfactorily using the scaling model developed in this study. An analytical solution to the relationship between recovery and imbibition time for linear spontaneous imbibition has also been derived in the case in which gravity is ignored. The analytical solution predicts a linear correlation between the recovery by spontaneous water imbibition and the square root of imbibition time, which has been verified against experimental data.     

More general capillary pressure and relative permeability models from fractal geometry

More general capillary pressure and relative permeability models were derived theoretically from fractal modeling of a porous medium. It was found that the new capillary pressure model could be reduced to the frequently-used Brooks–Corey capillary pressure model and the Li–Horne imbibition model when the fractal dimension of a porous medium takes specific values. This also demonstrates that the Brooks–Corey model and the Li-Horne model have a further confirmed theoretical basis. Capillary pressure data measured using mercury intrusion techinque were used to verify the model. The results demonstrated that the new capillary pressure model could represent the capillary pressure curves in those rocks with fracures or with great heterogeneity while the existing models cannot. The new relative permeability models can be reduced to the Brooks–Corey relative permeability model in a specific case. It has been proved theoretically that the relative permeability of each phase in a smooth fracture is only a linear function of its own saturation. Relative permeability data were calculated using the new models and the model results were compared with experimental data measured using a steady-state technique. The comparison demonstrated that the relative permeability models and experimental results were consistent with each other.     

The effects of drop size and formulation upon the spread of pesticide droplets impacting on water‐sensitive papers

Abstract

The effects of drop size and formulation upon the spread of pesticide droplets impacting on water‐sensitive papers (WSPs) was investigated. Droplets of diameter 70–350 μm, of four permethrin formulations, were produced using a monosize droplet generator. The droplets were collected on WSPs and in Dow Corning fluid and their diameters measured using a binocular microscope. Spread factors, upon the WSPs, for each dropsize/formulation combination were then calculated. Spread factors varied with both formulation and droplet size and for droplets of 200 and 300 μm diameter spread was significantly correlated with the dynamic surface tension of the formulation. The results suggest that proper calibration of WSPs is necessary for effective droplet sizing.     

湿法烟气脱硫系统中折板式除雾器性能的数值模拟

采用CFD软件对湿法烟气脱硫系统中广泛使用的折板式除雾器的主要性能进行了数值模拟。建立了数学模型,对气体相采用基于雷诺时均方程的SST ｋ-ω湍流模型封闭N-S方程,对液滴相采用基于Euler-Lagrange的DPM方法。通过调节除雾器的结构参数和工作参数,揭示了气液两相流动的流场,分析了结构参数对除雾器分离效率和工作压力降的影响,可用于湿法烟气脱硫系统中折板式除雾器的设计和优化。     

新型离心式脱硫塔气液两相流数值模拟

利用FLUENT软件和SIMPLE算法对新型旋流脱硫塔的气液两相流场进行了数值模拟。计算中气相采用了RSM湍流模型,颗粒相采用了Lagrange坐标系下的随机轨道模型。分析结果表明,气相流场具有强旋流特性;喷射液滴的直径、喷淋量和烟气流速影响其在塔内的分布:喷射液滴粒径越大、喷射量越小、烟气流速越大,入口段降温越少;塔体上方截面平均浓度随液滴粒径的增加而降低,随液气比的增加而增加,随烟气流速的增加会先增加至最高值然后降低。喷淋液滴在其他运行参数不变时,平均粒径范围为0.5～1 mm,会对进口烟气起到较好的净化与降温的作用,并使塔体上方喷淋液滴在截面z=4.15 m处浓度分布均匀且覆盖率高;在保证液滴粒径较小时,通过降低烟气流速或增加喷淋量可提高液滴喷淋覆盖率,使得烟气与喷淋充分接触。计算得到的气相流场分布与实测值吻合较好,证明了数学模型的合理性,为进一步优化分离器结构提供了可靠依据。     

废水液滴在低温烟气中的蒸发特性数值研究

建立了液滴在低温低速烟气中运动和蒸发的数学模型,数值研究了液滴在不同的烟气速度和烟气温度环境中的蒸发特性,获得了液滴速度、温度和直径随时间的变化规律,以及烟气速度和温度对液滴蒸发特性的影响。计算结果表明：气相速度越大,液滴初速度对液滴运动速度的影响越小,液滴速度越容易达到烟气速度。对于初始直径和速度一定的液滴,气液初始相对速度越大,液滴达到临界蒸发温度所需的时间越短,完全蒸发时间也越短。在文中研究的烟气速度范围内,整体上气相速度的改变对液滴完全蒸发时间的影响很小。气相温度的改变对液滴达到临界蒸发温度的时间以及完全蒸发时间的影响很大。烟气从较高温度和较低温度分别下降相同幅度的温度时,液滴在烟气中的完全蒸发时间按不同的倍数在增加,烟气温度越低,液滴完全蒸发时间增加的越多。对于文中研究的液滴,无量纲完全蒸发时间随烟气温度变化呈指数递减规律。     

Development of a measuring technique for simultaneous in situ detection of nanoscaled particle size distributions and gas temperatures

Point measurements of time-resolved LII signals have been performed in sooting premixed low pressure flames. Soot particle size distribution and gas temperature in these flames are known from independent measurements. This data is used to validate parameters of an improved LII model, where special emphasis is taken on the accurate modelling of mass and heat transfer rates. Using this model particle size distributions and gas temperatures can be estimated from time-resolved LII signals using non-linear regression. Standard numerical methods are applied. An experimental setup is presented, which allows measuring one-dimensional maps of particle size distribution and gas temperature. The technique is based on the one-dimensional and time-resolved detection of LII signals using a Streak camera.     

Modelling dispersion of traffic pollution in a deep street canyon: Application of CFD and operational models

In this study, numerical modelling of the flow and concentration fields has been undertaken for a deep street canyon in Naples (Italy), having aspect ratio (i.e. ratio of the building height H to the street width W) H/W = 5.7. Two different modelling techniques have been employed: computational fluid dynamics (CFD) and operational dispersion modelling. The CFD simulations have been carried out by using the RNG k–? turbulence model included in the commercial suite FLUENT, while operational modelling has been conducted by means of the WinOSPM model. Concentration fields obtained from model simulations have been compared with experimental data of CO concentrations measured at two vertical locations within the canyon. The CFD results are in good agreement with the experimental data, while poor agreement is observed for the WinOSPM results. This is because WinOSPM was originally developed and tested for street canyons with aspect ratio H/W ≌ 1. Large discrepancies in wind profiles simulated within the canyon are observed between CFD and OSPM models. Therefore, a modification of the wind profile within the canyon is introduced in WinOSPM for extending its applicability to deeper canyons, leading to an improved agreement between modelled and experimental data. Further development of the operational dispersion model is required in order to reproduce the distinct air circulation patterns within deep street canyons.     

多孔孔板水力空化反应器的水力特性

设计不同孔分布的孔板空化反应器,通过测定空化数及.OH产生量,研究多孔孔板水力空化反应器空化特性,为高性能多孔孔板水力空化反应器的设计奠定基础。实验结果表明,空化数随孔板孔径的增加、入口压力的减小和溶液温度的升高而增大;.OH产生量随孔板孔径的减小和运行时间的增加而增加,随入口压力和溶液温度的升高先增加后减小。结果表明,多孔孔板水力空化反应器的水力空化效果与孔板结构及操作条件有关。     

滤袋数目对翼形上进风袋式除尘器内流场影响的数值模拟研究

针对实际运行过程中,袋式除尘器滤袋使用寿命短,压力损失过大的问题,本文以翼形上进风袋式除尘器为研究对象,采用CFD(computational fluid dynamics)技术模拟分析不同滤袋数(分别为92、88、84、80、76和72)时袋式除尘器内气流分布和压力损失规律。主要考察了流量分配系数、最大流量不均幅值、气流迹线、滤袋表面速度分布与压降等指标。结果表明,滤袋数为76个时,气流分布最为均匀,各滤袋负载均衡;相同过滤速度下,装置的压降随滤袋数目的增加而上升,即压降大小顺序为9288847672;与72个滤袋相比,76个滤袋的可用过滤面积更大。综合考虑,袋式除尘器的最优滤袋数目为76个。模拟结果为袋式除尘器的设计和优化提供了依据。     

自由旋片除雾器脱水性能实验研究

提出一种新型除雾装置——自由旋片除雾器。在实验室条件下,从除雾效率、压力损失两方面研究了自由旋片除雾器的性能。实验结果表明,风速在11 m/s左右时,自由旋片除雾器的除雾效率达到最大值。对比实验发现,自由旋片除雾器的除雾效率远高于固定叶片除雾器的除雾效率,二者的除雾效率最大值相差约10%。自由旋片除雾器的除雾效率变化曲线在6~13 m/s的流速范围内相当平滑,说明自由旋片除雾器对含雾气流流速的波动有很好的适应性。另外,增加液气比和雾滴粒径会提高自由旋片除雾器的除雾效率。自由旋片除雾器压力损失系数仅为4.3,而固定叶片除雾器压力损失系数为6.6。所以,自由旋片除雾器的阻力特性远优于固定叶片除雾器。     

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The AFBC ash must be treated as a special case for fabric filters, and careful selection of cleaning method and fabric must be made to minimize the inherently high pressure drop characteristics of this ash.     

基于GT-Power柴油机颗粒捕集器捕集性能的仿真研究

利用GT-Power软件建立了柴油机颗粒捕集器(DPF)仿真模型,进行了仿真计算。研究了颗粒捕集器本身结构参数对其捕集效率与压降的影响。结果表明,影响颗粒捕集器捕集效率的主要参数有通道密度(CPSI)、过滤体孔隙率、过滤体微孔直径以及过滤壁厚度;影响颗粒物压降的主要参数有通道密度、过滤体渗透率、过滤体孔隙率以及过滤壁厚度。     

Direct field observation of the relative humidity effect on the beta-gauge readings

The effect of ambient relative humidity (RH) on hourly particulate matter (PM10) readings of beta-gauge monitors has been studied using two collocated monitors in the field. The inlet air of monitor 1 was conditioned with water vapor to increase its RH, whereas monitor 2 operated normally in ambient conditions. Experimental data showed that PM10 readings of monitor 1 were nearly the same as monitor 2, as long as the RH of its conditioned incoming air did not exceed approximately 80-85%. However, when the RH exceeded approximately 80-85%, PM10 readings of monitor 1 became higher than monitor 2, and the difference increased with increasing RH. The measurement of pressure drop across the filter was also conducted, and the data revealed that the increase of pressure drop per unit of PM10 concentration decreased when RH was higher than approximately 80-85%, as compared with the case when RH was lower than 80-85%. This is perhaps because of more porous structure of deposited particles in the beta-gauge monitor when RH is greater than approximately 80-85%. The theoretical calculation using an evaporation model and a thermodynamic model has been conducted to simulate the beta-gauge readings. The results show that the theoretical PM10 concentrations using the evaporation model are in better agreement with the actual beta-gauge readings than those using the thermodynamic equilibrium model.     

并流旋转床气体出口压降数值分析

气体出口是旋转床的重要组成部分,对旋转床流场与气相压降有着重要的影响。研究并流旋转床结构、构建气体出口物理模型,利用RNG k-ε湍流模型,探索不同气体出口结构对并流旋转床流场的影响。模拟结果表明:具有4个切向气体出口的DCRPB3615型旋转床有利于旋转床内速度分布均匀、降低湍动能,减小气相压降。模拟与实验对比表明,DCRPB3615压降比单一径向出口的CRPB3615型旋转床降低10%左右。     

Modeling of dispersion near roadways based on the vehicle-induced turbulence concept

A mathematical model is developed for dispersion near roadways by incorporating vehicle-induced turbulence (VIT) into Gaussian dispersion modeling using computational fluid dynamics (CFD). The model is based on the Gaussian plume equation in which roadway is regarded as a series of point sources. The Gaussian dispersion parameters are modified by simulation of the roadway using CFD in order to evaluate turbulent kinetic energy (TKE) as a measure of VIT. The model was evaluated against experimental carbon monoxide concentrations downwind of two major freeways reported in the literature. Good agreements were achieved between model results and the literature data. A significant difference was observed between the model results with and without considering VIT. The difference is rather high for data very close to the freeways. This model, after evaluation with additional data, may be used as a framework for predicting dispersion and deposition from any roadway for different traffic (vehicle type and speed) conditions.