Design Characteristics of Single Hub Paddle Wheel Aerator

Aeration experiments, based on dimensional analysis, were conducted in brick masonry tanks of dimensions 2.9×2.9×1.6?m3 and 5.9×2.9×1.6?m3 to study the design characteristics of a single hub paddle wheel aerator. A generalized equation has been developed to estimate the optimum volume of water to be aerated at a given paddle wheel diameter (d) and speed (N). A simulation equation with E [nondimensional number characterizing standard aeration efficiency (SAE)] and P* (nondimensional number characterizing power input per unit volume) provided a correlation better than that with E and F (Froude number) and E and R (Reynolds number) only. A simplified generalized equation correlating E and P* was developed which can be used to predict aeration efficiency for P* ? 6.56. Similarly, a simulation equation with Ne [(power number)(nondimensional number charcterizing power consumption)] and P* provided a correlation better than that with Ne and F and Ne and R only. The optimum dynamic condition at which maximum SAE is produced has also been presented. All the above results are valid subject to 1.47 ? P* ? 15.54.     

Hydraulic Performance of Step Aerator

The step aerator for stepped chutes was recently introduced. Its purpose is to preaerate the zone between the spillway crest and the point of incipient bottom aeration to counter cavitation damage for relatively large unit discharges. The shape of the step aerator is optimized herein by hydraulic modeling to design the air supply and to indicate the aerator blockage characteristics. The shape and the performance of the improved step aerator are described in terms of air supply and the development of air-water flow on the stepped chute. Further, step insets are considered to reduce the spray formation on stepped chutes for small unit discharges, in combination with the step aerator. The performance of the step insets was investigated and their effect on the spray formation analyzed. The step aerator generally increases the maximum spray height at smallest discharges as compared to the standard stepped chute without step aerator. Insets over the first five steps significantly reduce spray relative to standard stepped chutes.     

Water-Circulating Aerator: Optimizing Structure and Predicting Water Flow Rate and Oxygen Transfer

Thermal stratification is a common phenomenon in deep lakes and reservoirs, which often results in water-quality deterioration, including such problems as hypolimnetic anoxia, the release of pollutants from sediments, and algal blooms. Hypolimnetic oxygenation and destratification are the two commonly used methods for resolving these water-quality problems. A new water-quality improvement device, the water-circulating aerator, was designed to destratify lakes and reservoirs, by circulation and oxygenation of upper and lower layers of water. The design of the structure of the water-circulating aerator is detailed. Three mathematical models were built to optimize this structure, estimate the rate of water flow in the aerator, and calculate the rate of oxygen transfer from air bubbles to water in the aerator. These models were verified by experiments. The water-circulating aerator system has been successfully applied in a stratified reservoir to increase dissolved oxygen to reduce the releasing of ammonia-nitrogen from sediments under anoxic conditions.     

Case Study of Aeration Performance under Changing Process Conditions

Off gas analyses of oxygen transfer efficiency (OTE) at Terminal Island Treatment Plant of Los Angeles document changing performance of fine-pore diffusers in an activated sludge plant from 1991 to 1998. Although the plant treats a challenging waste stream, the aeration tanks are little different from other plants. Recent sessions provided improved time and space resolution, compared to previous work. Samples were more closely spaced, and some samples were taken in the intervals between the aeration grids, at the ends of the tanks, and near the edges of the grids. Very short term fluctuations in the data were assessed by leaving the hood in the same position for 1–2 h. The 1998 efficiencies were low. Analysis of the measurements since 1991 shows effects expected from fouling, and there was also extensive deterioration of the air distribution system that has now been remedied by a refurbishment program. These measurements show the degree to which efficiency losses may grow unrecognized if OTE measurements are not done. Hence, this study may serve as a prototype for similar measurement programs at other plants.     

Modeling and Control of Oxygen Transfer in High Purity Oxygen Activated Sludge Process

A dynamic mathematical model for the high purity oxygen activated sludge process, which incorporates structured biomass, gas–liquid interactions and control systems, was developed. The model was calibrated using pilot plant data associated with the development of the West Point Treatment Plant near Seattle, Wash. The calibrated model was used to simulate oxygen transfer rates for various operating conditions. Simulations showed that an optimal control system can reduce aerator power by 33% as compared to a conventional design, and reduce average oxygen feed gas by as much as 18%. Vent gas purity control dramatically reduced the peak aerator horsepower required to maintain set point dissolved oxygen concentration during high loadings. Step feed operation reduced the stag-to-stage variation in aerator horsepower and also reduced the required peak power. Predicted power savings for a 605,000?m3/day plant were $500,000 per year at current power costs.     

Energy Concept for Predicting Hydraulic Jump Aeration Efficiency

Hydraulic jumps, plunging jets and stepped channels are generally used as energy dissipators and self-aerators. Accordingly, it is expected to find a positive correlation between the aeration efficiency and energy dissipation. For this purpose, hydraulic jump self-aeration efficiency has been investigated with the function of energy dissipation rate per unit width. The hydraulic jump data revealed a positive linear relationship between the aeration efficiency and energy dissipation rate. This new procedure could have practical implications for predicting hydraulic jump aeration efficiency.     

Effect of Aeration on the Quality of Effluent from UASB Reactor Treating Sewage

The treatment of effluent of pilot- and full-scale upflow anaerobic sludge blanket (UASB) reactors operating at steady state was studied in an aeration-settling system. The fine pore submerged diffusers were used to aerate the effluent of UASB reactors under different operating conditions. Forty to 55% of the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) removal efficiencies were achieved by the direct aeration of the UASB effluent in the laboratory. The maximum removal efficiencies were achieved at 30?min hydraulic retention time (HRT) and a dissolved oxygen (DO) of 5–6??mg/L or high KLa (vigorous aeration). Batch experiments on nitrogen purging and the aeration of sulfides, volatile organic compounds (VOCs), and nonpurgeable organic carbons (NPOCs) were performed to ascertain the mechanism of BOD/COD removal. During aeration, BOD and COD were reduced by the stripping of H2S and VOCs and by the chemical oxidation of total sulfides and organic carbon. The stripping and chemical oxidation depended on the HRT and DO. The performance of a full-scale surface aeration system was compared to the performance of a pilot-scale diffused aeration system. Final sedimentation was effective only in removing the solids from the effluent of the aeration system. The results were confirmed by organic mass balance.     

Modeling VOC Emissions in the High-Purity Oxygen Activated Sludge Process

Mass balances for volatile organic compounds (VOCs) were added to a structured mathematical model of the high-purity oxygen activated sludge (HPO-AS) process. The model was sized to correspond to two large existing HPO-AS treatment plants. The stripping of ten different VOCs was modeled and compared to stripping from conventional air activated sludge process. The results show that the covered aeration tanks can reduce stripping by more than 90%, depending on the specific VOC. If biodegradation is considered, the HPO-AS process degrades more than the conventional process due to the higher liquid-phase concentrations that result because of reduced stripping. The increase in biodegradation depends on the VOCs degradability but should increase to nearly 100% for highly volatile but biodegradable VOCs.     

Oxygen Transfer in High-Speed Surface Aeration Tank for Wastewater Treatment: Full-Scale Test and Numerical Modeling

Oxygen transfer is one of the key processes in the bioreactor. Herein a computational fluid dynamics model for the oxygen transfer in high-speed surface aeration tank has been developed and validated through a full-scale aeration test. The test results indicate that the oxygen transfer mainly comes from the spray water in air and that the gas entrainment by the plunging of spray water and the surface reaeration in the aeration tank contribute little to the total oxygen transfer in high-speed surface aerator. A simple method was proposed to measure the oxygen transfer rate for high-speed surface aerator.     

Dimensional Analysis of Reaeration Rate in Streams

Atmospheric reaeration at the free surface of lakes and streams is a relevant process for water quality, thus the amount of oxygen transferred to the water body should be carefully estimated. Recent studies have demonstrated that available equations for estimation of the reaeration rate offer a poor fit with field data different from those for which each equation was originally developed. Thus, none of the available equations is applicable to all stream hydrodynamic conditions; on the contrary, they remain stream-specific, probably since some parameters involved in the process have been neglected in their formulation and their expressions are too simplistic. This paper proposes a comprehensive approach to the mass-transfer process at the air-water interface that is based on dimensional analysis. Careful inspection of equations in the literature shows that the mass-transfer process at the air-water interface has been affected by 14 different parameters. The application of dimensional analysis produces, for a wide rectangular section if wind speed is negligible, a dimensionless equation for the mass-transfer rate, where this rate is a function of the Froude number, channel slope, Reynolds number, Sherwood number, Weber number, and relative roughness. This expression is further developed to address the reaeration process in streams and rivers. As a result, at a fixed temperature, the dimensionless reaeration rate KaND (where ND denotes nondimensional) is finally a function of only the Froude number, channel slope, Reynolds number, and relative roughness. Moreover, the application of the Darcy-Wiesbach equation allows this dimensionless rate KaND to be considered as a function of only three of the aforementioned parameters. This result provides a comprehensive approach to the reaeration process that can also explain the unreliability of the literature equations available up to now.     

Multiple Linear Regression Model Approach for Aerosol Dispersion in Ventilated Spaces Using Computational Fluid Dynamics and Dimensional Analysis

Aerosol dispersion in living spaces especially bioaerosols, due to accidents or deliberate acts, is of significant current interest. Computational fluid dynamics (CFD) provides an accurate and detailed platform to study the influence of different parameters on aerosol distribution in indoor spaces. The simulations however are time consuming and site-specific. The work here introduces an approach toward addressing this challenge. During emergencies, an accurate, quicker, and more general model is required to give rapid answers to first responders. Significant parameters influencing aerosol behavior in an office room were identified and through dimensional analysis, nine dimensionless groups were developed. Fractional factorial design was used to build sixteen scenarios to explore the design space. These scenarios were then simulated using a comprehensive CFD model. Large eddy simulation with the Smagorinsky subgrid scale model was applied to compute the airflow. Aerosols were modeled as a dispersed solid phase using the Lagrangian treatment. The influence of the dimensionless groups on the temporal variation of the number of aerosols in the room and the spatial distribution of the particles in the room was analyzed. The results showed that all the identified dimensionless groups were significant. Multiple linear regression models were developed for the prediction of the number of aerosols in the room and their spatial distribution as a function of the significant parameters influencing aerosol transport. The linear models accurately predicted the data on which they were based but did not predict the results of the independent tests as well. The limited predictive ability of the model showed that the relationships between the dimensionless groups are nonlinear and a higher level of experimental design will have to be applied to better explore the design space.     

Evaluation of Preaeration with V-Notch Weir and Cascade Structures in Clarifiers

Hydraulic structures, such as stepped cascades and weirs, involve air entrainment (aeration) and oxygen transfer. Therefore, they can increase dissolved oxygen levels. Weir aeration occurs in rivers, fish hatcheries, and wastewater treatment plants. A stepped cascade aerator is another type of aeration structure. A stepped cascade consists of a series of steps or drops, built into the face of the chute. Often, the hydraulic head is naturally available and incurs no operating cost. For the preaeration process, weir and stepped cascade structures can be previously designed for clarifiers where weirs can be used as an aid to aeration process of treatment plants. Therefore, this paper aims to review the design considerations of circular clarifiers with combined weir and stepped cascade structures as a new approach and alternative preaeration system without energy requirement before aeration tank units. The detailed example for preaeration in circular clarifiers with combined weir and stepped cascade structures is presented. Thus, the circular clarifiers with weir and stepped cascade structures as effluent and preaeration strucures can be effectively redesigned with given new design considerations.     

Evaluation of Peak Ground Velocity as a “Good” Intensity Measure for Near-Source Ground Motions

This paper investigates the “goodness” of peak ground velocity as a dependable intensity measure for the earthquake shaking of civil structures. The paper stresses the importance of distinguishing between acceleration pulses and velocity pulses, and identifies two classes of near-source ground motions: those where the peak ground velocity is the integral of a distinguishable acceleration pulse and those where the peak ground velocity is the result of a succession of high-frequency, one-sided acceleration spikes. It is shown that the shaking induced by the former class is in general much more violent than the shaking induced by the latter class of motions even when motions that belong to the former class may be generated by significantly smaller-magnitude earthquakes. Building on the dimensional analysis introduced in the companion papers this paper shows that both linear and nonlinear structural responses from a variety of records which exhibit distinguishable pulses scale better with the peak pulse acceleration than with the peak pulse velocity, indicating that the peak pulse acceleration is a more representative intensity measure of the earthquake shaking. This conclusion is further supported from the response analysis of linear and bilinear single-degree-of-freedom oscillators subjected to selected records from the 1999 Chi-Chi Taiwan earthquake that exhibit unusually high and long period velocity pulses. The paper shows that these high velocity pulses alone do not impose unusual demands on most civil structures. What is more detrimental are local, distinguishable acceleration pulses that override the long period velocity pulses.     

桨式搅拌器的功率计算

搅拌设备的设计除应保证工艺要求外,以最小功率消耗达到搅拌目的亦是设计目标之一,本文就桨式搅拌器在不同桨叶倾斜角度工况下的功率进行计算,可以作为搅拌设备结构设计的参考依据。     

Pressure-Impulse Diagram for Blast Loads Based on Dimensional Analysis and Single-Degree-of-Freedom Model

Characteristics of a pressure-impulse diagram for blast loads are studied based on a dimensional analysis and a single-degree-of-freedom model. Structural behavior is dominated by the fundamental elastic response mode and the structural damage is controlled by the maximum structural deflection. The blast loading is simplified into a descending pressure pulse. A characteristic curve in nondimensional loading parameter space is used to define an isodamage critical diagram, pressure-impulse diagram, to distinguish damaged and undamaged ranges in the loading parameter space. Three damage regimes on a pressure-impulse diagram, i.e., (I) impulse-controlled damage, (II) peak load and impulse-controlled damage, and (III) peak load-controlled damage, exist respectively for impulsive, dynamic and quasistatic structural response regimes determined by the ratio between loading time and the response period of a structure. It is observed that there is a noticeable loading shape influence on the pressure-impulse diagram in Regime-II when both peak load and impulse are important for dynamic structural response. A unique effective pressure-impulse diagram is proposed to eliminate the pulse loading shape effect on a pressure-impulse diagram.     

150t转炉5孔氧枪喷头的设计与应用

阐述了安钢150t转炉氧枪喷头重要参数设计,并通过冷态测试和实际运用对氧枪喷头的使用效果进行了分析和讨论。     

Evaluation of Oxygen Sag Equation for Second-Order Biochemical Oxygen Demand Decay

In this work we present a new reliable analytical evaluation of the oxygen sag equation for second-order biochemical oxygen demand reaction. A single series expansion relation is derived for dissolved oxygen sag equation in terms of binomial coefficients. The convergence of the series is tested by the concrete cases of parameters. The formulas obtained are numerically stable for k3L0t<1. Numerical results are presented, and compared with results using alternative evaluation schemes.     

Evaluation of Performance of Bridge Deck Expansion Joints

The bridge deck expansion joint is an important element in the functioning of bridge structures. When joints fail to function properly, they can create problems out of proportion to their size. Selection of a good joint for use can create fewer bridge maintenance problems. The purpose of the study was to evaluate the performance of several types of joints currently in use on Indiana highway bridges. The types of joints investigated are compression seal, strip seal, integral abutment, poured silicone, and polymer modified asphalt. The research was accomplished through questionnaire surveys, analysis of Indiana Department of Transportation roadway management data, and expert interviews. The questionnaire survey identified the problems and their causes and the merits and potential improvements of each type of joint. The analysis of Indiana roadway management data ranked the performance of different types of joints based on the deterioration rates estimated by the regression coefficients. The expert interviews investigated the practices of Indiana and its surrounding states regarding the selection and maintenance of joints. Based on the research results, several suggestions were proposed to ensure the longer service life of expansion joints.     

Dimensional Analysis of the Earthquake Response of a Pounding Oscillator

In this paper, the dynamic response of a pounding oscillator subjected to pulse type excitations is revisited with dimensional analysis. The study adopts the concept of the energetic length scale which is a measure of the persistence of the distinguishable pulse of strong ground motions and subsequently presents the dimensionless Π products that govern the response of the pounding oscillator. The introduction of Buckingham’s Π theorem reduces the number of variables that govern the response of the system from 7 to 5. The proposed dimensionless Π products are liberated from the response of an oscillator without impact and most importantly reveal remarkable order in the response. It is shown that, regardless the acceleration level and duration of the pulse, all response spectra become self-similar and, when expressed in the dimensionless Π products, follow a single master curve. This is true despite the realization of contacts with increasing durations as the excitation level increases. All physically realizable contacts (impacts, continuous contacts, and detachment) are captured via a linear complementarity approach. The proposed analysis stresses the appreciable differences in the response due to the directivity of the excitation (toward or away the stationary wall) and confirms the existence of three spectral regions where the response of the pounding oscillator amplifies, deamplifies, and equals the response of the oscillator without pounding.     

不同搅拌桨形式对稀土萃取槽内搅拌效果的影响模拟分析

搅拌桨是稀土萃取搅拌反应器最重要的辅助设备之一,不同搅拌桨类型对搅拌效果有不同影响.利用计算流体力学模拟软件--MIXSIM,对圆盘式四直叶涡轮搅拌桨及开式45 ℃折叶涡轮搅拌桨的搅拌情况进行模拟分析,得出了2种搅拌桨的搅拌混合特点及应用范围.