Hybrid-Cells-in-Series Model for Solute Transport in Streams and Relation of Its Parameters with Bulk Flow Characteristics

The conceptualized hybrid-cells-in-series model, consists of a plug flow zone and two thoroughly mixed unequal reservoirs, all connected in series, has three time parameters, namely: (1) residence time of solute in the plug flow zone; and (2) residence times of solute in the two thoroughly mixed reservoirs. The model simulates closely advection-dispersion solute transport in natural streams. The resident time parameters are related to the velocity of flow, width of water surface, and depth of flow in the stream. Through the Péclet number, defined as Pe = (Δxu)/DL (in which Δx=process unit size; u=mean flow velocity; and DL=longitudinal dispersion coefficient), the relations of the model parameters with the longitudinal dispersion coefficient and with the bulk stream flow characteristics have been established. For a given reach of a stream, the parameters are inversely proportional to the flow velocity. By decoupling of pure advection by the plug flow component and dispersion of tracer by the two thoroughly mixed reservoir components, a robust fitting to the observed concentration-time data in natural streams was achieved.     

气体搅拌用透气砖阻力系数的测试

在实验室测定了工业用的狭缝型透气砖进出口压力差及气体出口速度,得出透气砖的阻力系数近似为44/Re,流动状态可近似认为呈层流,阻力系数与相对粗糙度无关,仅是雷诺数的函数,阻力损失与出口速度成正比。从而可计算出透气砖阻力损失,进而确定透气砖气体进口压力。在工业应用中,正常吹氩的压力差不大时,透气砖阻力系数≈0.07。     

Dispersion in Sediment-Laden Stream Flow

A theory is developed to demonstrate the effects of sorptive exchange on the transport of a chemical in a sediment-laden open-channel flow. Based on the multiple-scale method of homogenization, a depth-averaged transport equation is deduced up to a long time-scale. The dispersion coefficient is the sum of a modified Taylor dispersion coefficient and a dispersion coefficient due to a finite rate of mass exchange between dissolved phase in the water column and sorbed phase on suspended particles. These coefficients are functions of the suspension number and the bulk solid-water distribution ratio. It is shown that, for sufficiently large particles and solid fractions, enhancement of the longitudinal dispersion coefficient due to the sorptive exchange can be significant and should be included in a comprehensive model.     

底吹氩钢包内钢液流动与合金扩散的数值模拟

运用商业软件Ansys-Fluent,建立了1t钢包底吹氩与合金熔化扩散数值模型,其中钢包吹氩模型通过Wood′s Metal物理试验验证,吻合很好。研究采用数值模拟与现场试验相结合的方法分析了钢包内流场与合金加入的位置及方式对合金在钢包内扩散的影响。结果表明:260L/min吹氩流量过大,且吹氩时间过长(120s),建议使用100L/min的吹氩流量,加合金前吹氩时间30s,使Al块熔化与混均,保护合金,加合金后吹氩30s,降低合金的烧损。合金采用加入棒固定,在吹氩口上方加入后保持3~5s,熔化时间能由6.2s降低至2.0s,混匀时间能由35s降低至23s。另外,在降低烧损的同时,减少吹氩量和温降,起到节能减排的作用。     

带搅拌管式反应器中的流动特性

以NaCl溶液为示踪剂,采用脉冲示踪法考察了搅拌转速、流量及液位对带机械搅拌装置的管式反应器内停留时间分布（RTD）曲线的影响．用Peclet操作准数表征轴向扩散特性．结果表明：增加搅拌装置后,反应器内的流动型态仍接近活塞流;随流量的减小和液位的升高,流体流动愈向活塞流靠近,即减小流量或者升高水位有利于减小返混;当搅拌转速超过100r／min时,搅拌转速对停留时间分布的影响不大．     

Plume characteristics and liquid circulation in gas injection through a porous plug

Various forms of plumes have been identified following the injection of air at different rates through a porous plug into water contained in a ladle-shaped vessel. Discrete bubbles form at the plug and rise uniformly through the column of liquid at gas flow rates up to 14 cm³/s cm² of plug surface; at higher flow rates, groups of bubbles increasingly coalesce into larger gas pockets, and beyond about 40 cm³/s cm², the gas globes are large enough to cover the entire plug surface before detachment and gradual disintegration as they rise through the body of liquid. The gas fraction, as well as bubble frequency, bubble velocity, and bubble size, have been measured in the various dispersion regimes by means of an electroresistivity probe. The radial distributions of gas fraction and bubble frequency are approximately bell-shaped about the axis of flow, and the reduced values are close to Gaussian functions of the reduced radial distance from the axis. The gas fraction along the axis has been correlated to the reduced height of the plume; it increases with decreasing distance above the plug and with increasing gas flow rate. The axial bubble frequency shows a decrease in the vicinity of the plug with the onset of bubble coalescence, but the values of the frequencies at all gas injection rates converge to about 12 s⁻¹ toward the surface of the bath. The mean bubble velocity increases with increasing flow rate but drops once coalescence is fully established. Conversely, there is a sudden increase in the mean bubble diameter with the onset of coalescence. The axial and radial components of the velocity of the liquid surrounding the plume have been measured by means of a Laser-Doppler Velocimeter (LDV), and the results show that the circulation patterns are identical, irrespective of the dispersion regime. The axial flow which is upward in the vicinity of the plume decreases in magnitude with increasing radial distance, ultimately reversing to an in-creasing downward flow beyond a certain distance from the plug axis. Similarly, the radial flow which is outward from the plume near the liquid surface decreases steadily with depth and eventually reverses to an inward flow at a depth independent of the gas injection rate. The profiles of the axial velocities are almost sigmoidal, except in the coalescence regime, where the effect of turbulence is profound at the upper liquid layers. The radial liquid velocities are generally small relative to the axial components, only about one-fifth as large, considering the maximum average values.     

Extension of Preissmann Scheme to Two-Dimensional Flows

A numerical solution to the finite difference of two-dimensional (2D) depth-averaged equations on nonstaggered grid points is proposed in this technical note. Following a locally one-dimensional procedure, the basic equations are split into a pair of one-dimensional equations. Therefore, the solution of a 2D problem is reduced to the solution of a sequence of two one-dimensional problems. The discretization of the split one-dimensional equations is obtained with the use of the original Preissmann operator. Using Fourier’s classic linear analysis, stability, dissipation and dispersion with frictional resistance are investigated for the variations of the Courant number and weighting time factor.     

Physically Based Coupled Model for Simulating 1D Surface–2D Subsurface Flow and Plant Water Uptake in Irrigation Furrows. I: Model Development

Physically based modeling of the interacting water flow during a furrow irrigation season can contribute to both a sustainable irrigation management and an improvement of the furrow irrigation efficiency. This paper presents a process based seasonal furrow irrigation model which describes the interacting one-dimensional surface–two-dimensional subsurface flow and crop growth during a whole growing period. The irrigation advance model presented in a previous study is extended to all hydraulic phases of an irrigation event. It is based on an analytical solution of the zero-inertia surface flow equations and is iteratively coupled with the two-dimensional subsurface flow model HYDRUS-2. A conceptual crop growth model calculates daily evaporation, transpiration and leaf area index. The crop model and HYDRUS-2 are coupled via its common boundaries, namely (1) by the flux across the soil-atmosphere interface; and (2) by the flux from the root zone, which is associated with the plant water uptake. We assume the water stress is the only environmental factor reducing crop development and hence final crop yield. The model performance is evaluated with field experimental data in the companion paper, Part II: Model Test and Evaluation (W?hling and Mailhol 2007).     

Residence Time Distribution Characterization of the Flow Structure in Dissolved Air Flotation

A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks (Ncstr) in a series model are calculated. The variance is found to relate to the flow structure and the Ncstr is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by DAF. The result shows a significant difference in RTD depending on expected flow structure. Analytically, a conceptual model is defined by dividing the DAF tank into an upper and a lower layer. In the upper layer, the water flow is horizontal and in the lower the water flow is vertical. The hypothesis is that mixing of the tracer takes place in the upper layer and that there is no significant mixing in the lower layer. Two simple mixing models are evaluated for the upper layer; the completely mixed tanks in series model, characterized by the number of tanks, and the dispersed plug flow model, characterized by the Peclet number. The models show good agreement with the experiments when the stratified flow structure is expected, but less agreement when the flow deviates from the stratified flow structure. The dispersed plug flow model shows the best fit with the experiments. The completely mixed tanks in series model is less sensitive, generating greater changes to the modeled RTD curve, which makes it more difficult to fit the model to the experiments.     

Coupled Large Strain Consolidation and Solute Transport. I: Model Development

The development of a numerical model, CST1, for coupled large strain consolidation and solute transport in saturated porous media is presented. The consolidation algorithm is one-dimensional and includes the capabilities of a previous code, CS2, with the addition of time-dependent loading, unload/reload effects, and an externally-applied hydraulic gradient. The solute transport algorithm is two-dimensional and accounts for advection, longitudinal and transverse dispersion, first-order decay reactions, and linear equilibrium sorption. Solute transport is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating layer. The key to the transport model is the definition of two Lagrangian fields of elements that follow the motions of fluid and solid phases separately. This reduces numerical dispersion and simplifies transport calculations to that of dispersion mass flow between contiguous fluid elements. The effect of relative numerical resolution of fluid and solid elements on the accuracy of sorption/desorption is also discussed. This paper presents the theoretical and numerical development of the CST1 model. A companion paper presents verification checks of CST1 and the results of simulations that illustrate the significance of consolidation-induced solute transport for some interesting numeric examples.     

铝合金装配式机油滤清器开发设计

针对目前市场上钢制滤清器存在使用寿命短、环境污染重等缺陷,设计开发铝合金机油滤清器,主要包括3D数模、二维图纸、强度模拟分析、工艺流程等内容.该铝合金机油滤清器具有使用寿命长、可拆卸、散热性好、绿色环保等优点,且回收残值大,为企业降低成本,与传统钢质滤清器相比具有很大的市场竞争力.     

五流连铸中间包结构优化的水模型实验

以国内某钢厂五流连铸中间包为研究对象,根据相似原理建立了1：3的中间包水模拟系统,考察不同内部结构对中间包流体流动特性的影响．研究结果表明：原型中间包内部结构不合理,各流水口之间的流体流动特性差异很大,存在较大死区．通过内部结构优化设计,使中间包流场得到明显改善,其中方案Ⅵ效果最佳,平均停留时间离散度最小,活塞区体积达23．84％,死区体积为10％,比原型下降了71．70％．     

水口吹氩工艺板坯结晶器内气泡运动行为的物理模拟

以1300 mm × 230 mm板坯连铸结晶器的相似比0.4的物理模型,研究了拉速1.1 m/min、水口插入深度160 mm、水口吹气量0～15 L/min时连铸结晶器内气泡的运动行为,及其对钢液流股冲击深度、液面波动和液面裸露的影响。实验结果表明,随水口吹气量增加,结晶器内气泡的数量和尺寸都有所增加,气泡在钢液内水平方向扩散范围增大,且气泡最大穿透深度亦增加;当水口吹气量增大到5 L/min时,气泡逸出后在液面由全部向水口方向运动变为以集中逸出位置为中心的四散运动。     

Solvent extraction of La（III） with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester （EHEHPA） by membrane dispersion micro-extractor

The conventional rare earth solvent extraction equipments have many problems such as long mixing time, low processing capacity, large factory area occupation, high energy consumption and so on. In order to solve the problems, many types of equipments were brought out. In this work, studies were carried out on the La（III） extraction process with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester （EHEHPA） by membrane dispersion micro-extractor. Equilibrium studies showed that the initial aqueous pH value 4.15 with the saponification rate 40%was the optimal operation condition. The effects of membrane dispersion micro-extractor operational conditions such as dispersion mode, bulk flow rate and organic phase flow rate on the extraction efficiency were studied. The results showed that when the organic solution was the dispersed phase, the extraction efficiency was higher than that of others. Increasing bulk flow ratio could enhance the extraction efficiency greatly. When the ratio of organic phase flow rate to that of aque-ous phase was 80：80, the extraction efficiency was over 95%. The effect of stripping phase acidity on the La（III） recovery was studied. The results showed that when the stripping phase pH was 2.0, organic phase flow rate to stripping phase flow rate was 20：80;the re-covery efficiency of La（III） can reach 82%.     

Medication nebulizer performance. Effects of diluent volume, nebulizer flow, and nebulizer brand

BACKGROUND: Medication nebulizers are commonly used to delivery aerosolized medications to patients with respiratory disease. We evaluated output and respirable aerosol available to the patient (inhaled mass) for 17 medication nebulizers using a spontaneous breathing lung model. METHODS: Three nebulizer fill volumes (3, 4, and 5 mL containing 2.5 mg of albuterol) and 3 oxygen flows (6, 8, and 10 L/min) were evaluated using the 17 nebulizers. A cotton plug at the nebulizer mouthpiece was used to trap aerosol during simulated spontaneous breathing. Following each trial, the amount of albuterol remaining in the nebulizer and the amount deposited in the cotton plug were determined spectrophotometrically. Aerosol particle size was determined using an 11-stage cascade impactor. RESULTS: Increasing fill volume decreased the amount of albuterol trapped in the dead volume (p < 0.001) and increased the amount delivered to the patient (p < 0.001). Increasing flow increased the mass output of particles in the respirable range of 1 to 5 microns (p = 0.004), but the respirable mass delivered to the patient was affected to a greater extent by nebulizer brand (p < 0.001) than flow. Although 2.5 mg of albuterol was placed into the nebulizers, less than 0.5 mg in the respirable range of 1 to 5 microns was delivered to the mouthpiece. CONCLUSIONS: The performance of medication nebulizers is affected by fill volume, flow, and nebulizer brand. When they are used for research applications, the nebulizer characteristics must be evaluated and reported for the conditions used in the investigation.     

Treatment of Stagnant Zones in Riverine Advection-Dispersion

Advection-dispersion in streams encounters pockets of stagnant or dead zones in the flow, which trap the injected tracer. Treatment of stagnant or dead zones for dispersion is presented using one-dimensional advection-dispersion equation. A method is suggested for simultaneous estimation of dispersion coefficient, apparent (or effective) velocity, and effective injected mass of tracer, from a temporal concentration profile observed at a downstream section. The method is robust and uses a nonlinear optimization. Using the method procedure for estimation of adsorption coefficient for riverine advection-dispersion has also been suggested. The effective velocity is related to the stagnant zone fraction (average fraction of cross-sectional area attributed to stagnant zones) and adsorption. The application of the method on published data sets show that the parameter-estimates are reliable and the observed concentration profiles are closely reproduced. The analytical procedure described for the treatment of stagnant zones may have a wide application in civil engineering as well as other fields. The amount of chemicals released from the industrial units or by an accident can be estimated.     

Pinning Force during Closure Process at Blocked Pipe Entrance

The high design standards for the preservation of the urban water environment result in more detention basins in residential areas. The steep channel and outfall pipe from a detention basin can be hazardous to children and small animals. During an event, a trapped person may flow with water toward the outfall entrance. When the outfall pipe is gradually blocked, the flow force acting on the blocking body can be pinning at the beginning to eventually deadly. It is not clear as to how to quantify the pinning force on the block during the closure of flow because the number of unknown forces is greater than the number of equations for force balance. This paper presents a new approach using the method of superposition to calculate the pinning force with and without a blockage at the culvert entrance. The analysis conducted in this paper verifies that the pinning force on the clogging block is dominated by the flow dynamic force until the flow becomes discontinued. As soon as the hydrostatic force is developed, the pinning force can be lethal. This study confirms that an outfall pipe shall be protected by a trash rack with its surface area 4 times the culvert opening area. As long as the continuity of flow is sustained by the blocked rack, the hydrostatic force will not be developed or a chance for survival remains.     

Network Implementation of the Two-Component Pressure Approach for Transient Flow in Storm Sewers

The two-component pressure approach (TPA) is an alternative to the Preissman slot method (PSM) for modeling highly transient sewer flow, including transitions between free-surface and pressurized conditions. TPA and PSM resolve intralink wave action by discretizing sewers with numerous elements and solving one-dimensional flow equations in contrast to link-node models, such as the popular storm water management model, which resolve only interlink wave action. Here, improvements of TPA are reported to support storm sewer network modeling. These include a source term discretization to preserve stationarity, a wetting and drying scheme, and a local time-stepping scheme to coordinate solution updates across many links and enable coupling to a two-dimensional overland flow model. A unique variant of the Harten, Lax and van Leer (HLL) Riemann solver is also introduced, and a boundary solver is developed to accommodate the wide range of possible flow regimes and transitions. The boundary solver is explicit to facilitate the extension of TPA to large networks and coupling with an overland flow model. Promising results are obtained in a varied set of test problems involving simple sewer networks.     

The effect of heliox on nebulizer function using a beta-agonist bronchodilator

OBJECTIVE: To evaluate nebulizer performance when heliox was used to power the nebulizer. METHODS: Conventional and continuous nebulizer designs were evaluated. The conventional nebulizer was used with 5 mg albuterol and flows of 8 L/min air, 8 L/min heliox, and 11 L/min heliox; it was also used with 10 mg albuterol and a heliox flow of 8 L/min. The continuous nebulizer was set to deliver 10 mg of albuterol over 40 min at flows of 2 L/min air, 2 L/min heliox, and 3 L/min heliox; it was also used with 20 mg albuterol and a heliox flow of 2 L/min. A cotton plug at the nebulizer mouthpiece was used to trap aerosol during simulated spontaneous breathing. The amount of albuterol deposited on the cotton plug was determined spectrophotometrically. Particle size was determined using an 11-stage cascade impactor. RESULTS: For both nebulizer designs, particle size and inhaled mass of albuterol decreased significantly (p < 0.001) when the nebulizer was powered with heliox rather than air. When powered with heliox, the reduction in inhaled mass of albuterol was less for the conventional nebulizer (16%) than the continuous nebulizer (67%). The nebulization time, however, was more than twofold greater with heliox (p < 0.001). Increasing the flow of heliox increased the particle size (p < 0.05), inhaled mass of albuterol (p < 0.05), and inhaled mass of particles 1 to 5 microm (p < 0.05) to levels similar to powering the nebulizer with air at the lower flow. Increasing the albuterol concentration in the nebulizer and using the lower heliox flow increased the inhaled mass of albuterol (p < 0.05) while maintaining the smaller particle size produced with that flow. CONCLUSIONS: The use of heliox to power a nebulizer affects both the inhaled mass of medication and the size of the aerosol particles. The flow to power the nebulizer should be increased when heliox is used.     

Coupled 1D–Quasi-2D Flood Inundation Model with Unstructured Grids

A simplified numerical model for simulation of floodplain inundation resulting from naturally occurring floods in rivers is presented. Flow through the river is computed by solving the de Saint Venant equations with a one-dimensional (1D) finite volume approach. Spread of excess flood water spilling overbank from the river onto the floodplains is computed using a storage cell model discretized into an unstructured triangular grid. Flow exchange between the one-dimensional river cells and the adjacent floodplain cells or that between adjoining floodplain cells is represented by diffusive-wave approximated equation. A common problem related to the stability of such coupled models is discussed and a solution by way of linearization offered. The accuracy of the computed flow depths by the proposed model is estimated with respect to those predicted by a two-dimensional (2D) finite volume model on hypothetical river-floodplain domains. Finally, the predicted extent of inundation for a flood event on a stretch of River Severn, United Kingdom, by the model is compared to those of two proven two-dimensional flow simulation models and with observed imagery of the flood extents.