Evaluating Henry's law constant of N-nitrosodimethylamine (NDMA)

N-Nitrosodimethylamine (NDMA), a potential carcinogen, may contaminate the groundwater when the reclaimed wastewater is used for irrigation and groundwater recharge. Henry's law constant is a critical parameter to assess the fate and transport of reclaimed wastewater-borne NDMA in the soil profile. We conducted a laboratory experiment in which the change of NDMA concentration in water exposed to the atmosphere was measured with respect to time and, based on the data, obtained the dimensionless Henry's law constant (K(H)') of NDMA, at 1.0 x 10(-4). The K(H)' suggests that NDMA has a relatively high potential to volatilize in the field where NDMA-containing wastewater is used for irrigation and the volatilization loss may be a significant pathway of NDMA transport. The experiment was based on the two boundary-layer approach of mass transfer at the atmosphere-water interface. It is an expedient method to delineate K(H)' for volatile or semi-volatile compounds present in water at low concentrations.     

阴离子有机改性膨润土吸附废水中甲基紫的热力学规律研究

采用十二烷基磺酸钠对膨润土进行改性,制得阴离子有机改性膨润土。通过静态吸附法探讨了改性膨润土对染料废水中甲基紫的吸附等温式和吸附热力学规律。结果表明,随着温度的升高,平衡吸附量增加;随着平衡浓度的增加,平衡吸附量不断增大,并趋于饱和。不同温度下吸附等温式与Langmuir方程拟合较好,热力学分析表明,吸附过程吸热,吸附焓变和熵变均为正值,吸附自由能变为负值。     

RE-AERATION LAW OF WATER FLOW OVER SPILLWAYS

1. INTUODUCTION Due to the strong turbulence of the flow over the spillway, air is entrained into water body making the oxygen content increased. It is important for river, especially for city-river to maintain favorable water quality and ecological envir…     

浓度及温度场问题三维数值模拟及应用

研究温度和污染物的扩散规律,对于健康河流具有十分重要的意义。在排水口附近,温度和污染物的扩散具有很强的三维性。在已开发的三维紊流水动力模型基础上,研制了浓度及温度场三维数学模型。在模型中,空度用来处理不规则边界,VOF用来处理自由面。另外,模型还采用了k-ε紊流模型和壁面函数。利用建立的模型,对水槽和天然的排水口附近的水位、流场、紊动能及其扩散率、温度场和浓度场的分布规律等进行了模拟和研究。通过研究进一步认识了排水口局部三维水流运动规律,浓度和温度扩散规律及分布。     

台阶坝面消能水气两相流数值模拟

 采用VOF法模拟自由表面,用非结构网格来处理复杂的边界形状,并根据边界形式进行适当的分区,利用k-ε气液两相流模拟光面和台阶溢流面的流场,得到了溢流面的流场、水面线以及消能率等相关水力参数。数值模拟试验结果表明,台阶溢流坝面水流紊动掺气充分,消能率较高,并与物理模型试验结果进行对比分析,二者吻合良好。     

二维非定常水跃湍流现象的数值模拟

通过求解时均N-S方程及K-ε湍流模型,数值模拟了典型水跃湍流由静止到最终稳定的全过程,采用VOF模型跟踪自由表面的变化.本文给出了水跃现象在不同时刻自由表面的变化情况,主要对水跃过程中自由表面的形状、内部流场结构、速度矢量场及压力场分布进行了分析.结果表明,VOF模型能够有效地描述水跃这类复杂自由表面流道的湍流特性,...     

波浪环境中垂向紊动射流的三维数值模拟

实验结果显示在持续的波浪环境中污染物稀释度比无波环境有显著提高,但是关于波浪要素与污染物浓度分布之间的关系的研究还不充分,结论还不统一,需要在实验及数值计算等方面对这个课题作更深入的研究.本文采用非线性紊流模型和VOF方法建立了波浪环境中垂向紊动射流的三维数值模型,通过改变波浪参数做了大量的数值模拟实验.基于数值模拟结果,重点分析了射流初始稀释阶段污染物浓度分布和波浪要素的关系.     

涌潮对钱塘江河道流场影响的三维数值模拟研究

利用实测的钱塘江地形数据建立了钱塘江三维河道的计算机几何模型,并根据已有的涨潮潮位等水文信息,采用VOF方法追踪模拟水和大气的自由交界表面,对钱塘江涌潮进行了三维非稳态数值模拟。数值模拟结果与不同时刻和不同测点所测得的水文数据的对比显示,模型能较好地模拟涨潮条件下河道内流场和潮位的变化。在此基础上进行了涌潮对河道内流场影响的规律的研究。     

Online headspace chromatographic method for measuring VFA in biogas reactor.

A headspace chromatographic method has been applied to measure volatile fatty acids in anaerobic digesters using gas phase extraction at pH less than 2 and temperature higher than 65 degrees C. The concentration of volatile fatty acids in liquid and gas phase can be correlated in the form of Henry's coefficient. Analysis of different factors in the batch indicated that pH, temperature, and salt addition had a strong impact on apparent solubility, while liquid/gas volume ratio and organic acid concentration had little impact. Larger liquid volume had a positive impact on extraction efficiency, while increased gas headspace had a negative impact, indicating that the system was total mass-limited. The best conditions were at pH < 2.0, and temperatures above 75 degrees C. The advantage of an automated gas-extraction system for organic acid analysis, compared to an automated liquid system is that it contains no filter element, which is 4 susceptible to fouling in manure samples or samples with high solid content. An automated system which included a valerate pulse to the parent reactor was implemented, and operated for a short period.     

水电站进水前池三维数值模拟

建立水电站进水前池内流动的k-ε紊流数值模型,采用VOF方法,对高水头小流量引水式电站进水前池内流场进行了三维数值模拟。计算得出了冲击式水轮机在引用设计流量1．94m^3／S时前池内水流流态,底板压力分布,及压力钢管进口流速分布以及在针阀突然关闭时,前池内水面涌高时水面线形状。数值计算结果结合常规理论分析可以为工程设计提供参考。     

Adsorption kinetics, isotherms and thermodynamics of atrazine removal using a banana peel based sorbent

Atrazine removal from water by treated banana peels was studied. The effect of pH, contact time, initial atrazine concentration, and temperature were investigated. Batch experiments demonstrated that 15 g L(-1) adsorbent dosage removed 90-99% of atrazine from 1-150 ppm aqueous solutions. The removal was both pH and temperature dependent with the most atrazine removed between pH 7 and 8.2 and increased with increasing temperature. Equilibrium data fitted well to the Langmuir and Redlich-Peterson models in the concentration and temperature ranges investigated, with a maximum adsorption capacity of 14 mg g(-1). Simple mass transfer models were applied to the experimental data to examine the adsorption mechanism and it was found that both external mass transfer and intraparticle diffusion played important roles in the adsorption mechanisms. The enthalpy of atrazine adsorption was evaluated to be 67.8 ± 6.3 kJ mol(-l) with a Gibbs free energy of -5.7 ± 1.2 kJ mol(-1).     

尾坎位置对坎式阶梯溢洪道水力特性影响研究

〗坎式阶梯溢洪道具有较高的掺气效率,然而目前为止对其详细流场结构以及消能特性开展的研究尚不多见。为此结合VOF法,采用标准k-ε紊流模型对带尾坎的阶梯溢洪道进行了三维数值模拟,研究了不同尾坎位置对其水力特性的影响。结果表明：随着尾坎向上游移动,水面线和尾坎下游侧的旋涡大小均无明显变化,但尾坎上游侧的旋涡尺度逐渐减小;对于不同体型,同一台阶凸角上流速呈先增加后不变的规律,而对于同一体型,下游台阶凸角上流速大于上游的;台阶水平面上最大压强先增加后不变,台阶竖直面上最小压强逐渐减小,而尾坎下游侧竖直面上最小压强则呈增加的趋势;台阶面上最大紊动能耗散率逐渐增加,而尾坎上的则相反,总的消能率变化甚微。     

NUMERICAL SIMULATION OF THE ENERGY DISSIPATION CHARACTERISTICS IN STILLING BASIN OF MULTI-HORIZONTAL SUBMERGED JETS

3-D numerical simulation was carried out for the water flow in a stilling basin with multi-horizontal submerged jets by using two different turbulence models, namely, the VOF RNG k - ? and Mixture RNG k - ? turbulence models. The calculated water depth, velocity profile and pressure distribution are in good agreement with the data obtained in experiments. It indicates that the numerical simulation can effectively be used to study the water flow movement and the energy dissipation mechanism. The numerical simulation results show that the turbulent kinetic energy distribution obtained by using the Mixture turbulence model covers a region about 18% larger than that calculated by using the VOF turbulence model, and is in better agreement with the actual situation. Furthermore, the Mixture turbulence model is better than the VOF turbulence model in calculating the air entrainment.     

NUMERICAL SIMULATION OF TWO-DIMENSIONAL OVERTOPPING AGAINST SEAWALLS ARMORED WITH ARTIFICIAL UNITS IN REGULAR WAVES

A new mathematical model for the overtopping against seawalls armored with artificial units in regular waves was established. The 2-D numerical wave flume, based on the Reynolds Averaged Navier-Stokes (RANS) equations and the standard k-ε turbulence model, was developed to simulate the turbulent flows with the free surface, in which the Volume Of Fluid (VOF) method was used to handle the large deformation of the free surface and the relaxation approach of combined wave generation and absorbing was implemented. In order to consider the effects of energy dissipation due to the armors on a slope seawall, a porous media model was proposed and implemented in the numerical wave flume. A series of physical model experiments were carried out in the same condition of the numerical simulation to determine the drag coefficient in the porous media model in terms of the overtopping discharge. Compared the computational value of overtopping over the seawall with the experimental data, the values of the effective drag coefficient was calibrated for the layers of blocks at different locations along the seawalls.     

扭曲型挑坎挑流的数值模拟

采用RNGK-ε湍流模型与VOF多相模型对扭曲型挑坎挑流进行水气两相流三维数值模拟,模拟了挑坎里的自由水面与挑流的空中轨迹线,得到计算域的速度、压强、湍动能K与湍动能耗散率ε的分布、内外挑距与水舌宽度,并与物理模型的试验结果进行比较,两者吻合良好,验证了该数值模拟方法的可靠性、合理性。     

三维宽顶堰紊流场数值模拟及分析

本文利用三雏标准k-ε紊流数学模型,选择VOF方法追踪自由表面,采用气液两相流计算模型对宽顶堰流场进行了数值模拟,计算结果与试验数据较为吻合.模拟结果表明,数值模拟能够广泛应用于数值模拟带有复杂自由表面的泄水建筑物紊流场.     

宽顶堰水流数值模拟分析

本文利用紊流模型模拟了带有曲线自由表面的宽顶堰流的紊流流场,采用VOF法来确定自由表面,采用气液两相流计算模型对宽顶堰流场进行了数值模拟,计算结果与试验数据较为吻合.模拟结果表明,数值模拟是作为研究水利工程中带有自由表面的水流结构的一个强有力的工具,其结果对物理试验也是一个很好的补充.     

带差动挑坎的溢洪道流场三维数值模拟

采用RNGκ-ε紊流模型和VOF方法对某工程带差动型挑坎的溢洪道流场进行了三维数值模拟研究,详细描述了差动坎处的流速、压强等水力参数的分布规律,得出了高低坎挑射水舌的挑距、入水角。将部分结果与试验对比,符合良好,验证了数值模拟是准确可靠的,可作为模型试验的有益补充,为挑坎设计提供重要的参考依据。     

Anisotropic diffusion of volatile pollutants at air-water interface

The volatile pollutants that spill into natural waters cause water pollution. Air pollution arises from the water pollution because of volatilization. Mass exchange caused by turbulent fluctuation is stronger in the direction normal to the air-water interface than in other directions due to the large density difference between water and air. In order to explore the characteristics of anisotropic diffusion of the volatile pollutants at the air-water interface, the relationship between velocity gradient and mass transfer rate was established to calculate the turbulent mass diffusivity. A second-order accurate smooth transition differencing scheme (STDS) was proposed to guarantee the boundedness for the flow and mass transfer at the air-water interface. Simulations and experiments were performed to study the trichloroethylene (C₂HCl₃) release. By comparing the anisotropic coupling diffusion model, isotropic coupling diffusion model, and non-coupling diffusion model, the features of the transport of volatile pollutants at the air-water interface were determined. The results show that the anisotropic coupling diffusion model is more accurate than the isotropic coupling diffusion model and non-coupling diffusion model. Mass transfer significantly increases with the increase of the air-water relative velocity at a low relative velocity. However, at a higher relative velocity, an increase in the relative velocity has no effect on mass transfer.     

浅层地热能不同开发方案对深层地下淡水咸化效应研究

为了保证浅层地热能可持续开发,同时控制深层承压淡水咸化,需评价浅层地热能开发对深层地下水咸化控制效应。基于地下水渗流、热量运移和溶质运移理论,以江苏省地质工程勘察院(南通分院)地下水源热泵系统为研究对象,建立松散孔隙地下水系统渗流—热量运移—溶质运移多场耦合数值模型,模拟预测了第Ⅰ承压含水层浅层地热能开发过程中地下水系统水位、温度、水化学浓度的演化规律,通过增大利用温差和减小夏季灌采比优化浅层地热能开发利用方案,定量评价增大利用温差和减小夏季灌采比对热贯通和深层地下淡水咸化的控制效应。结果表明：增大利用温差和减小夏季灌采比能有效缓解热贯通和深层淡水咸化的发展趋势,增大利用温差对深层地下淡水咸化的控制效应更为显著,减小夏季灌采比对热贯通的控制效应更为显著。