共查询到20条相似文献,搜索用时 328 毫秒
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A kinematic mixing model has been developed to predict far field effluent distributions for ocean discharges. The model allows for complex outfall configurations and time varying discharge rates to be simulated. The model can use field observations or the output from a proven near field mixing model as input to this far field mixing model. The model uses observed or simulated horizontal currents at one location to advect the effluent plume and a scale-dependent “diffusion velocity” submodel to account for horizontal diffusive processes. To collect data to calibrate and verify the model, long-term continuous dye release experiments were conducted at two New Jersey ocean outfalls. Based upon the results of the dye release experiments, appropriate values for the diffusion velocity were determined for each outfall. Simulations using these diffusion velocities provided reasonable predictions of plume width and of average dye concentration at each transect for each outfall. This work demonstrates that an Eulerian velocity observed at one location in the coastal ocean off New Jersey may be used to predict Lagrangian transport over a distance of several kilometers. 相似文献
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Octavio Olivares Adolfo Elias Rocío Snchez Manuela Díaz‐Cruz Rodolfo D. Morales 《国际钢铁研究》2002,73(2):44-51
Fluid dynamics of gas‐liquid interactions in a LD converter to refine steel was physically and mathematically simulated. Using a water model three cases of gas supply were considered, top blowing, bottom injection and combined process top blowing‐bottom injection. Mixing time in top blowing increases with bath height and the distance between the lance of the gaseous jet and the bath surface. The jet penetration was found to be dependent on the modified Froude number. The unstable and unsteady behaviour of the bath topography, as affected by the gaseous jet, was well simulated through a multiphase momentum transfer model. In top blowing, three zones of liquid splashing were found, penetration with low splash, heavy splash and dimpling with low splash intensity. These zones depend on the gas flow rate and the distance from the lance to the bath surface. During bottom injection mixing times decrease with the number of tuyères, increases of bath height and gas flow rate. In a combined process mixing time decreases considerably due to the recirculating flow formed by the action of the top jet and the submerged jets. When a submerged jet is located just below the top jet the mixing time does not decrease as compared with the separated processes either top blowing or bottom stirring. 相似文献
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Young Do Kim Il Won Seo See Whan Kang Byung Cheol Oh 《Canadian Metallurgical Quarterly》2002,128(8):753-760
The mixing processes of a buoyant jet discharged from a submerged single port were analyzed using a three-dimensional hybrid model. In the proposed hybrid model, the initial mixing was simulated by a jet integral method, and the advection-diffusion process was simulated using a particle tracking method. Laboratory experiments were conducted for various flow conditions in order to verify the proposed model. The simulated horizontal concentration distributions and minimum dilutions at the water surface were generally in agreement with the observations. The vertical concentration distributions for coflowing jets were well simulated by both the jet integral and the particle tracking methods of the hybrid model. Trajectories simulated by the jet integral module of the hybrid model were in agreement with the measured trajectories when the velocity ratio was low. For cases where the velocity ratio was high, the hybrid model in which the vortex-pair distribution was used gave better results than the hybrid model with only Gaussian velocity distribution. 相似文献
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根据相似理论,以钢厂80 t单嘴精炼炉1:4的水模型模拟了单嘴精炼炉内气泡行为,分析了吹气流量(2~10 L/min)、吹气塞直径(15~30 mm)对气泡行为、混匀时间的影响。水模拟结果表明,随吹气流量增加,混匀时间减少,但吹气流量≥6 L/min,混匀时间没有显著变化;在相同吹气量下,吹气塞直径增加,混匀时间减少。实验研究基础上,在80 t单嘴精炼炉上进行了超低碳钢的生产试验,结果表明单嘴精炼炉在18 min脱碳时间内,钢中碳含量可降到10×10-6;脱硫剂消耗4 kg/t的情况下,成品钢中S含量为(20~30)×10-6,脱硫率平均达49%;吹氩强度平均为4 L/(t·min),是相同吨位RH的25%。 相似文献
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This paper describes a simple model for the desorption and transport of soluble reactive phosphorus (SRP) to subsurface drains. The model assumes first-order kinetically rate-limited desorption in a soil surface mixing layer over a soil profile layer that rests on an underlying, shallow restricting layer. Input data include precipitation, soil hydraulic properties, drain outflow, free water surface fluctuation, sorbed P concentrations for the mixing layer and profile, desorption rate and equilibrium soil-SRP partitioning. Model results are compared to data on flow and SRP concentrations in drain outflow collected during natural rainfall events under field conditions. The concentration time series simulated follow the sharp rise, peak, and gradual recession of the observed field data. Predicted event mass loads resulting from observed and simulated tile discharges differ from the observed load by +8.2% and ?9.7%, respectively. Sensitivity analysis indicate that equilibrium assumptions would not provide satisfactory results and that mass transfer limits SRP release to the tile drain. 相似文献
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The flow field characteristics and stirring abilities of five kinds of bottom-blowing arrangements on the molten bath were researched in a 3t electrical arc furnace (EAF) with regular shape. The mixing time was measured by water experiment under different flow rates. Flow field characteristics of three-phase flow were simulated by numerical simulation. The average mixing time decreased with the flow rate and the radius of circle coincide increasing for the EAF with regular shape. Moreover, weakening counteracting force of counter-swirls could efficiently reduce mixing time than weakening impeding forces of sidewall with concentric circle arrangements at the tested conditions. Compared with 6R bottom-blowing arrangement at industrial application research, the 7R bottom-blowing arrangement, which was determined by the water model experiments and the simulations, could stir molten better in nitriding process, which agreed well with the experimental results of the water experiment and the numerical simulation. 相似文献
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The process of alloying steel melts in ladles consists of the three partial steps alloy addition, alloy solution, and alloy mixing. Addition and dissolution together can be simulated approximately by continuous addition of a dissolved substance to be mixed. In this way, the mixing process during alloying can be captured separately. The process was studied in model experiments with continuous addition of NaCl solution to water in a 0.18 m3 cylindrical acrylic glass vessel. The water was stirred by air injection through an eccentrically positioned nozzle in the bottom. The added amount of NaCl was 40 cm3 of a 20% aqueous solution. The addition time was varied. The NaCI concentration in the water vessel was continuously measured with electrical conductivity probes at 12 different positions. From the thus obtained concentration-vs.-time curves, the mixing times were determined. They were studied for stirring gas rates between 100 and 700 cm3/min(STP) and for various addition times of the indicator. The measured mixing times depended on the gas stirring rate. They were also functions of the indicator addition time and decreased with increasing addition time until they became zero or negative. Trials where NaCI was added in form of a melting, NaCI containing ice sphere, yielded negative mixing times, which means that melting is slower than mixing. A theoretical model to describe mixing with continuous addition is presented. Besides the measurement of the mixing process, the three main flow directions of the indicator solution when it leaves the injection nozzle were documented by a video camera. They were associated to the concentration curves measured at the conductivity probes to which the flow was directed. It was found that concentration maxima occurred on the curves when the flow was directed to the respective measuring probe. The duration of the maxima coincided almost always with the duration of the flow directions. 相似文献
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Wind Mixing in Temperature Simulations for Lakes and Reservoirs 总被引:2,自引:0,他引:2
A one-dimensional mathematical formulation for simulating the wind mixing of the surface layers in reservoirs and lakes is developed. Emphasis is placed on the estimation of the net available wind-supplied energy for mixing by taking into consideration the variability of the wind in time. The formulation of the dynamics of the wind-mixed layer presented in this paper is implemented in a modified version of the one-dimensional Massachusetts Institute of Technology reservoir model. The model was used to predict the annual cycle of the thermal structure of Spada Lake in northwestern Washington State. A complete record of inflow and outflow water temperatures, temperature profiles in the reservoir, and meteorological data at the site over a 16-month period provided the basis for verifying the model. Special effort was made to screen and analyze these data to assure their quality. The application of the temperature model in Spada Lake produced good agreement between simulated and observed temperature profiles. Noticeable features of this application are the accurate simulation of the growth of the wind-mixed layer in the fall and the prediction of the exact time of formation and melting of the ice cover in the winter. These features could not have been predicted accurately without accounting for the variability of the wind pattern and its effect on the net available energy for mixing, as it was found in earlier simulations with simpler formulations of the wind-mixing effect. 相似文献
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The effects of varying hydraulic retention time (HRT) and associated upflow velocity on mixing and reactor performance were evaluated in five lab-scale upflow anaerobic sludge blanket (UASB) reactors treating real domestic wastewater. The mixing and transport studies were carried out with the help of tracer experiments at various HRTs using a pulse tracer input. A number of existing models were assessed for the analysis of the time series of observed tracer concentrations. The plug-flow reactor (PFR) model with two-zone dispersion better simulated the time series of tracer concentrations at all HRTs than other models, such as single compartment dispersion, completely mixed flow reactors (CMFRs) in series, and a combination of CMFR and PFR. The dispersion coefficients obtained from the two-zone dispersion model correlated well with the dispersion analysis expression for flow in a circular cylinder, and the correlation can be used for the prediction of dispersion in a UASB reactor. The analysis of reactor performance data indicated that reduction of dispersion owing to decrease in the upflow velocity resulted in increased sulfidogenic activity in the reactor. This was attributed to the inability of the sulfate reducers to colonize in the reactor at high upflow velocity and mixing condition. 相似文献
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A two-phase flow, three-dimensional, steady-state model is developed to study the flow field and volume fraction distribution
in a stirred tank used in the processing of silicon carbide-reinforced aluminum composites in the melt state. The aim is to
optimize the stirring to obtain a good mixing of SiC particles. The model is based on the general-purpose code PHOENICS. In
addition to the liquid-aluminum phase, the SiC particles are treated as a nonviscous second phase. Interphase momentum transfer
occurs through a drag force. Sedimentation is simulated by assigning a high viscosity to the second phase and removing the
gravity force when particle concentration reaches a critical value. The stirrers' blades impart a momentum on both phases,
proportional to their respective volume fractions. A water model is simulated first, followed by the real Al-SiC melt. The
study reveals the importance of particle size that affects the drag force applied on the particles and hence their motion
and distribution. The model can be used to study the effect on mixing of tank geometry and the stirrers' operation. 相似文献