适用于固定工业源泄放的扩散模型-AERMOD

本文就适用于固定工业源泄放的扩散模型-AERMOD模型的特点及基本公式进行了介绍。AERMOD模型是高斯扩散模型,其应用范围相当广泛。AERMOD模型较显著的特点有:1)以行星边界层湍流结构及理论为基础;2)对地面源和高架源的情形都适用;3)对简单地形和复杂地形进行了一体化的处理。     

复杂地形上大气污染物扩散研究

对复杂地形上大气污染物扩散进行模拟的先决条件 ,是对湍流风场做出准确的预测。本文对复杂地形上大气污染物扩散以及湍流风场的研究分别作了介绍 ,同时列出了求解湍流风场和污染物扩散的基本方程组 ,为解决此类问题提供参考     

优化能源结构 改善宣城市大气环境质量

通过对宣城市能源结构和大气环境质量现状的分析,提高了天然气、电能和太阳能等清洁能源在能源结构中的比例,并运用城市多源扩散模式进行浓度预测.结果表明:采取清洁能源替代措施以后,大气中的二氧化氮和二氧化硫按功能区划分均可达到相应的国家标准.     

換热的流体动力学理論(續完)

4.卡門的湍流换热理论卡門的湍流换热理论从他的湍流一般速度分布线出发,考虑到所謂滯流层实际上由二部分構成:滯流层内部靠近壁面的地方,流体几乎作单純层流运动,叫做滯流内层;滯流层的外部,靠近湍流层或湍流主体的流体作既非层流又非完全湍流的运动,叫做过渡层。在滯流内层的动量传递主要靠分子扩散,在湍流层或湍流主体主要靠对流扩散,而在过渡层分子扩散与对流扩散则处于同样重要的地位;相当地热量的传递在滯流内层主要靠传导,在湍流层或湍流主体主要靠对流扩散,而在过渡层则传导与对流扩散同样重要。一般速度分布綫的特点,是与雷諾准数无关。它常被标繪在对数坐标紙上(图3),其縱軸为速度参数u~ ,橫     

汞源附近地区大气汞的流通量沉降模式研究

通过对汞矿附近大气汞测定以及生物监测分析 ,提出汞的湿沉降中流通量与大气中的SO2 的数学模式为y =2 938.7x - 60 .80 8(R =0 .7432 ) ;用MossBag监测大气汞湿沉降与大气汞总沉降之间的关系式为 :HgDep=KDry .HgPrec .Prec ;汞源距离与汞的沉降模式为 :HgHist =KE .E .exp(-R/R0 ) /(2πR0 2 )。以上模式的参数与实验测定数据相吻合。     

液化天然气水平连续泄漏重气的扩散过程

结合SLAB稳态烟羽模型,针对液化天然气(LNG)连续泄漏、水平喷射源的重气扩散过程进行了模拟研究,分析了液化天然气泄漏后混合云团扩散形成的浓度场、温度场和其它特征参数。利用MATLAB语言编制液化天然气连续泄漏扩散模拟程序,对两种试验环境条件(不同风速、大气温度、大气稳定度、相对湿度和地表粗糙度等环境参数)下扩散云团的特性参数进行模拟计算,得到各云团参数随下风向距离的变化规律。     

边界层方程求解传热传质复合自然对流的偏差分析

引　言动量、能量及质量的边界层方程是Naveir Stokes完整方程的简化形式 ,自上世纪初提出以来 ,应用极广 .传热传质复合自然对流是自然界和工业过程中常见的现象 ,由于存在热与物质扩散两种浮力相对大小及方向的差异以及Prandtl数和Schmit数的影响 ,使该问题颇为复杂 .Bottema     

烟囱的环保设计简述

水泥厂烟囱高度的计算,已不单纯从满足工艺生产的需要,还应满足环保的要求进行计算确定。文章着重阐述了烟囱高度的计算模式(其计算方法分为二步:第一步,烟囱抬升高度;第二步,依照大气扩散的数学模式以保证大气质量为标准来确定必要的烟囱高度。)以及计算模式中输入参数(大气质量控制标准、大气风速、大气稳定度等)的讨论。通过实例(以水泥厂5000t/d熟料生产线为例)演示计算出窑尾烟囱和冷却机烟囱的高度。生产实践表明,严格按照国标规定的要求进行设计计算烟囱的高度,是能满足环保要求的。     

年均大气扩散因子在厂址选择中的应用

年均大气扩散因子是胡二邦、高占荣、张茂栓等人提出的。采用年均大气扩散因子预测建设项目大气污染和气载污染物在各种环境条件下浓度在空间及时间上的分布．可以较客观的评价项目，优化厂址选择。本文具体分析了年均大气扩散因子的涵义、影响因素、计算方法及应用条件，将其结果有效地应用于建设项目待建厂址的选择之中。     

抚顺市气象和地形因素与大气污染扩散的研究

大气污染物、气象因素和地形条件有机结合在一起构成了大气污染物扩散系统。通过对抚顺市气象和地形因素的分析，揭示了三者之间的内在联系，为大气污染物扩散模型的应用提供依据。     

Dynamic simulation of a 2D bubble column

The present paper demonstrates how 2D, dynamic simulations of a flat bubble column are feasible, applying state-of-the-art dynamic turbulence models, when an appropriate turbulent dispersion term is applied in the conservation equation for the gas volume fraction. The kω turbulence model yielded a better qualitative prediction of the bubble plume than the kε model, due to the low-Reynolds number treatment of the former model. The simple mixing length turbulence model gave the best prediction of the meandering plume, without any dispersion term. The mixing length model is, however, almost identical to a Large-Eddy simulation when run time-dependent on a fine mesh, and should be applied with care due to the use of a constant turbulence length scale and the inherent 3D nature of turbulence. By refining the mesh to the extreme end, it was shown that an apparently grid independent numerical solution was really grid-dependent, even when dynamic turbulence models were applied. The apparently grid independent solution was computed with an increment in the computational mesh that was of the same size as an equilibrium Kolmogorov length scale.     

DROP DISPERSION IN SUSPENSION POLYMERIZATION

Four models, two based on laminar shear and two based on turbulent flow, are proposed to describe drop dispersion in non-coalescing systems. The models predict the largest surviving drop size _dmax as a function of geometry, speed and physical property variables.

Laboratory data including suspension polymerization runs support the boundary layer laminar shear model for drops larger than approximately 200 microns. Smaller drops support a turbulence model.

The boundary layer shear model was confirmed in scale-up suspension polymerization runs aimed at producing 1000 micron maximum bead sizes. Five approximately geometrically similar polymerizers were used, varying in size from 7.5 to 15000 liters.     

Ausbreitung von Abgasfahnen

The dispersion of pollutant plumes . Experimental methods for the determination of plume characteristics and basic mathematical diffusion models with particular emphasis on Gaussian models are reviewed. The most important process in the dispersion of air pollutants is turbulent diffusion in the atmosphere. Equidensitometric measurements of oil refinery plumes in North Germany show that the Gaussian plume model is applicable. The fundamental plume concentration standard deviations and eddy diffusivity coefficients are determined. The equidensitometric model of the eddy structure of plumes explains the time-averaged properties of the plume.     

DROP DISPERSION IN SUSPENSION POLYMERIZATION

Four models, two based on laminar shear and two based on turbulent flow, are proposed to describe drop dispersion in non-coalescing systems. The models predict the largest surviving drop size _dmax as a function of geometry, speed and physical property variables.

Laboratory data including suspension polymerization runs support the boundary layer laminar shear model for drops larger than approximately 200 microns. Smaller drops support a turbulence model.

The boundary layer shear model was confirmed in scale-up suspension polymerization runs aimed at producing 1000 micron maximum bead sizes. Five approximately geometrically similar polymerizers were used, varying in size from 7.5 to 15000 liters.     

鼓泡塔内气泡羽流周期性摆动的数值模拟

以二维和三维鼓泡塔内气液二相流动的动态特性为研究对象,寻找各自合适的湍流模型和边界条件设置。二维鼓泡塔的进口气速采用2种不同的方法:①实际进口速度法;②均值修正法。湍流模型选用标准k-ε湍流模型、RNG k-ε湍流模型。结果显示二维模拟使用RNG k-ε湍流模型、三维模拟使用标准k-ε湍流模型能够得到周期性的羽流摆动,且二维鼓泡塔的进口气速采用均值修正法能够得到较合理的摆动周期。     

Heat and mass transfer and stabilization of combustion in the boundary layer behind a rib and a backward-facing step

A comparison of the characteristics of the boundary layer with combustion with flame stabilization by a rib and a backward-facing step is performed. Data on the thermal boundary layer, the flame blow-off velocity, and the rate of ethanol evaporation into an air flow with a turbulence intensity of up to 26% are obtained. It is shown that the temperature of the outer region of the boundary layer and the flame blow-off velocity behind the rib are higher than those behind the backward-facing step. With both methods of flame stabilization, the intensity of evaporation corresponds to transient mass transfer.     

Spatial distribution of odors in simulated benthic boundary layer flows

Many animals orient to odor sources in aquatic habitats where different flows and substrates affect the hydrodynamics of benthic boundary layers. Since the dispersal of chemicals is due to the fluid mechanics of a particular environment, we quantified the changes in the fine structure of an odor plume under different hydrodynamic conditions in the benthic boundary layer of a laboratory flume. We sampled turbulent odor plumes at 10 Hz using a microchemical sensor (150 µm diameter) under two flow speeds: 3.8 and 14.4 cm/sec, and at 1, 8, 50 mm above the substrate. These distances above the substrate occur within different flow regions of the boundary layer and correlate with the location of crustacean chemosensory appendages within boundary layer flows. The high flow velocity exhibited a greater level of turbulence and had more discrete odor pulses than the low flow velocity. In general, odor signals showed a high level of temporal variation in fast flow at heights 1 and 8 mm above the substrate. In slow flow, temporal variation was maximal at 50 mm above the substrate, exhibiting more variance than the same height at the fast flow. These patterns of odor signals resulted in part from differences in the height above the substrate of the main axis of the odor plume at the two flow speeds. Our results imply that animals chemically orienting to an odor source will need to compensate for varying hydrodynamic properties of odor transport and dispersal. The method by which animals extract spatial information from odor plumes will need to account for changing flow conditions, or else it will not be equally efficient in extracting information about chemical spatial distributions.     

Experimental and numerical investigation of liquid circulation induced by a bubble plume in a baffled tank

Bubble induced liquid circulation is important in applications such as bubble columns and air-lift reactors. In this work, we describe an experimental and numerical investigation of liquid circulation induced by a bubble plume in a tank partitioned by a baffle. The baffle divides the tank into two compartments. Liquid can flow from one compartment to the other through openings at the top and the bottom of the baffle. Gas (air) was injected in the riser section in the form of bubbles at one corner of the tank. The temporal and spatial variation of velocity field in the liquid as a function of the gas flow rate was measured using particle image velocimetry (PIV). At a constant gas flow rate, the liquid flow field is unsteady due to the interaction with the bubbles. The time scales associated with the velocity-time series and the bubble plume thickness variation were calculated. The time averaged-velocity field was used to quantify the variation of the liquid circulation rate with gas flow rate. The turbulence in the liquid was measured in terms of turbulent intensities. These were calculated from the experimental data and were observed to be less than 3 cm/s. A 2-d Euler-Euler two-fluid model with buoyancy and drag as the interaction terms was used to simulate the flow. The parameters chosen for the simulations were selected from literature. It is shown that inclusion of turbulence model such as k-ε is necessary to capture the overall flow behavior. Good agreement was observed between experimentally obtained velocity profiles and the recirculation rates with the simulation results.     

Fractal and turbulence characteristics of aerodynamic fields of swirl burners

Turbulence intensities at the exit of a centrally fuel rich (CFR) burner were measured employing a probe with hot-film sensors. In addition, using glycol as a smog tracer, optical images of the highlighted primary airflow were taken with a CCD camera and contrast-enhanced by computer. Profiles of the interface between primary and secondary air were obtained from which fractal dimensions (FDs) of the primary air boundary were estimated. Results indicate that FDs of this air boundary are in the range of 1.10–1.30 depending on burner conditions. As the FD and mean turbulence intensities of the primary air boundary have uniform distributions, they can be used to analyze coal combustion and NO_x formation characteristics of the burner. When either decreasing the outer secondary air vane angle or increasing either the inner secondary air vane angle or total mass flow rate of the secondary air, the burner swirl number increases which subsequently shows up as an increase in the FD and mean turbulence intensities of the primary air boundary. Increasing the ratio of the mass flow rate of inner to outer secondary air decreases the burner swirl number, but increases the FD and mean turbulence intensities of primary air boundary.     

Development of a reactive puff model for simultaneous consideration of plume dispersion and plume chemistry

To comprehensively assess and understand the environmental impacts of air pollutants emitted from large-scale point sources, the complex, non-linear photochemistry inside the plumes should be considered together with atmospheric turbulent dispersion of the air pollutants. For this purpose, a reactive puff model that can consider both atmospheric turbulent dispersion and photochemical reactions was developed in this study. The model’s performance was evaluated by comparing the model-predicted concentrations with the ship-plume chemical concentrations measured from the Intercontinental Transport and Chemical Transformation (ITCT) 2K2 field campaign. This comparison study confirmed the ability of the developed reactive puff model to capture the major characteristics of both plume dispersion and photochemical reactions. Based on these findings, the reactive puff model was applied to a Korean power plant (Hadong) as a case study. This article is dedicated to Professor Chang Kyun Choi for celebrating his retirement from the School of Chemical and Biological Engineering, Seoul National University.