厌氧迁移式污泥床反应器的水力特性研究

采用脉冲示踪法以NH4Cl作示踪剂,通过其在反应器中的停留时间分布来研究厌氧迁移式污泥床反应器(AMBR)的水力特性。反应器的结构决定了反应器的流态,从而控制着可能达到的处理效率。为优化设计反应器结构研究了反应器的构型、导流板与器壁间距对水力特性的影响。研究发现,反应器的流态介于推流式和完全混合式之间,带有导流板的反应器推流程度更大一些,而底部有孔的反应器推流程度弱,反应器的水力死区较小,均小于20%;导流板与器壁间距为8 mm时最佳。     

北京市典型交通道路CO的污染现状

于春季、秋季和冬季分别对北京市3类典型道路(开阔型、十字路口型、峡谷型)空气中CO污染进行了现场监测,对CO时空分布和影响因素进行分析。结果表明:十字路口CO平均浓度最高,为2.81mg/m3,CO日变化幅度较小,在中午上下班时间出现高峰,峡谷型道路次之,为2.55mg/m3,CO日变化呈单峰型,在中午前出现爬坡,下午有所降低,学院路CO污染最轻,CO平均浓度为2.39mg/m3,CO浓度日变化呈多峰型,早中晚高,其他时段较低;冬季CO污染最严重,平均浓度明显高于春季和秋季,分别为3.18mg/m3、2.49mg/m3,和2.45mg/m3;风向对CO的分布也有很大影响,背风面的CO浓度明显高于迎风面的CO浓度。     

Turbulence characteristics within sparse and dense canopies

Boundary layer interactions with canopies control various environmental processes. In the case of dense and homogeneous canopies, the so-called mixing layer analogy is most generally used. When the canopy becomes sparser, a transition occurs between the mixing layer and the boundary layer perturbed by interactions between element wakes. This transition has still to be fully understood and characterized. The experimental work presented here deals with the effect of the canopy density on the flow turbulence and involves an artificial canopy placed in a fully developed turbulent boundary layer. One and two-component velocity measurements are performed, both within and above the canopy. The influence of the spacing between canopy elements is studied. Longitudinal velocity statistical moments and Reynolds stresses are calculated and compared to literature data. For spacings greater than the canopy height, evidences of this transition are found in the evolution of the skewness factor, shear length scale and mixing length.     

Mass-based depth and velocity scales for gravity currents and related flows

Gravity driven flows on inclines can be caused by cold, saline or turbid inflows into water bodies. Another example are cold downslope winds, which are caused by cooling of the atmosphere at the lower boundary. In a well-known contribution, Ellison and Turner (ET) investigated such flows by making use of earlier work on free shear flows by Morton, Taylor and Turner (MTT). Their entrainment relation is compared here with a spread relation based on a diffusion model for jets by Prandtl. This diffusion approach is suitable for forced plumes on an incline, but only when the channel topography is uniform, and the flow remains supercritical. A second aspect considered here is that the structure of ET’s entrainment relation, and their shallow water equations, agrees with the one for open channel flows, but their depth and velocity scales are those for free shear flows, and derived from the velocity field. Conversely, the depth of an open channel flow is the vertical extent of the excess mass of the liquid phase, and the average velocity is the (known) discharge divided by the depth. As an alternative to ET’s parameterization, two sets of flow scales similar to those of open channel flows are outlined for gravity currents in unstratified environments. The common feature of the two sets is that the velocity scale is derived by dividing the buoyancy flux by the excess pressure at the bottom. The difference between them is the way the volume flux is accounted for, which—unlike in open channel flows—generally increases in the streamwise direction. The relations between the three sets of scales are established here for gravity currents by allowing for a constant co-flow in the upper layer. The actual ratios of the three width, velocity, and buoyancy scales are evaluated from available experimental data on gravity currents, and from field data on katabatic winds. A corresponding study for free shear flows is referred to. Finally, a comparison of mass-based scales with a number of other flow scales is carried out for available data on a two-layer flow over an obstacle. Mass-based flow scales can also be used for other types of flows, such as self-aerated flows on spillways, water jets in air, or bubble plumes.     

Numerical analysis of the effects of fluctuations of discharge capacity on transient flow field in gas well relief line

Transient gas flow in relief line is computed to determine the effects of fluctuations of discharge capacity on flow field. Based on the theories of computational fluid dynamics and aerodynamics, the solution and the analysis were carried out using finite volume CFD solver FLUENT 13.0. Flow fields in seven working conditions were simulated in the numerical investigation and their results were compared. The results showed that the fluctuations of discharge capacity, including extent and period, exert obvious effects on transient gas flow field in relief line. The larger the fluctuation extent and the shorter the fluctuation period, the more significant is the effect. The application method of simulation results is provided to guide the laying and fixing of pipelines, which is verified by filed measurement.     

Numerical analysis of phase behavior during rapid decompression of rich natural gases

The effect of the condensation process on the gas and liquid phase behavior during rapid decompression of rich natural gases is studied in the paper numerically. A one-dimensional mathematical model of transient thermal two-phase flow of compressible multi-component natural gas mixture and liquid phase in a shock tube is developed. The set of mass, momentum and enthalpy conservation equations are solved for the gas and liquid phases. The approach to model a liquid condensation process during rapid decompression of rich natural gas mixture is proposed. The mass transfer between the gas and the liquid is taken into account by introducing the appropriate terms into the governing equations. Thermo-physical properties of multi-component natural gas mixture are calculated by solving the Equation of State (EOS) in the form of the Soave–Redlich–Kwong (SRK-EOS) model. The proposed liquid condensation model is integrated into the GDP model. A simple case of GDP model, where the liquid was not considered, was extensively validated on base and dry natural gases. The proposed two-phase model is validated against the experiments where the decompression wave speed was measured in rich natural gases at low temperature. It shows a good agreement with the experimental data.     

能源资源流动的研究视角、主要内容及其研究展望

通过对能源资源流动研究成果的梳理和总结,从各相关学科不同研究视角出发阐述了能源资源流动研究的内容、着重点及其特色,指出经济地理学、交通地理学、物流学、产业经济学和产业生态学是能源流研究最为密切的学科。从能源流动特征、流动机制、流动效应以及流动的优化调控等4 个方面阐述了能源流研究的主要内容,并籍此认为各学科对于能源流研究的开展丰富和发展了资源流动的研究内容和方法。在对能源流动形式研究的探讨中,指出能源流动形式研究与资源流动的纵横向解析模式具有一致性,其纵横向研究各自独立展开,形成了两种截然不同的研究风格,但目前的相关研究缺乏将纵横向分析有效衔接的联系机制。最后,根据能源资源流动研究现状提出今后该领域相关研究建议。     

控制ORP实现连续流反应器部分亚硝化稳定运行

利用ORP在线监控设备,研究了控制ORP值实现连续流部分亚硝化反应器稳定运行的可行性,并使出水水质满足厌氧氨氧化需求.结果表明,在亚硝氮与氨氮比值、温度和pH值恒定的条件下,反应器内ORP值波动主要由于DO浓度波动引起.在稳定的亚硝化系统中,当ORP值大于250mV左右时,反应器出水亚硝氮与氨氮比值大于2.1;当ORP值控制在150mV左右时,反应器出水亚硝氮与氨氮比值稳定在1.2~1.3之间.ORP值控制在120mV时,反应器出水亚硝氮与氨氮浓度比值为0.9~1.06.将ORP值控制在150mV时,随着进水氨氮浓度由300mg/L提高至813mg/L,反应器出水亚硝氮与氨氮比值基本维持在1.1~1.3之间.但随之增加的游离氨浓度易导致亚硝化菌活性抑制.因此,在低氧环境下ORP作为连续流部分亚硝化反应器亚硝化程度的控制指标,其灵敏度和精度明显优于DO监测设备.     

混凝过程中絮体形貌的PIV成像观测与表征

采用粒子成像速度场仪(PIV)对Taylor-Couette反应器内的混凝过程中絮体的微观形貌进行了观测与表征.结果表明,内筒转速在20～60r/min范围内,生成的絮体颗粒较大,粒径分布均匀,絮凝沉淀效果最好.由于内筒旋转速度的变化直接导致混凝流场形态的变化,所以混凝过程中流场形态的变化对絮体生长过程有重要影响,进而直接影响到混凝效果.混凝过程中流场的周期性变化、涡间存在液体传递的波状涡结构有利于絮体颗粒的结合生长,并导致较高的絮凝沉淀去除率.这也说明PIV技术能够在测量流场的同时较好地反映混凝过程中微絮体的形貌变化特征,从而实现对絮凝过程的原位观测与表征.     

露天堆场防风抑尘网后湍流结构及抑尘效率的数值模拟

建立了开放性露天堆场周围空气流动的三维数学物理模型,选择应用标准k-ε紊流模型进行了静态流场的数值模拟;分析了典型棱形堆迎风面、平顶面和背风面周围空气的湍流结构和表面受力特性;基于流场数据揭示了防风抑尘网不同孔隙率下空气动力学结构的分布规律.结果显示:物料堆平顶面剪切力随孔隙率增大而增大;料堆迎风面在孔隙率较小时出现局部涡流,表面剪切力方向向下,孔隙率较大时,网后空气垂直方向压差作用显著,表面剪切力方向向上;背风面始终处于回流区,表面剪切力和回流点数随孔隙率大小变化不显著.综合流场结构和受力分布可得最佳孔隙率为0.2~0.4.该研究中对物料堆逐个表面进行空气动力学模拟可以避免由于剪切力方向不同产生矢量抵消而带来的计算失真.