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的动力学数值模拟

开放性露天堆场的散尘是大气颗粒物的重要来源. 来流空气在棱形物料堆的上部绕流,使其表面的空气流动结构逐点不同,而料堆表面的空气动力学结构又决定着堆场的散尘机理及散尘量. 分析了典型单一棱形料堆周围空气湍流结构,并应用三维标准k-ε紊流模型对其流场进行了数值模拟;计算了来流方向抑尘网前后不同断面处风速的垂直分布;分析了不同孔隙率(0、0.2、0.3、0.4、0.5、0.6和1.0)抑尘网后料堆迎风面和背风面沿高度方向、平顶面沿水平方向的剪切应力特性和分布规律. 结果表明:抑尘网前3倍网高距离处的风速较无网工况(孔隙率为1.0)略有减小,降幅随孔隙率增大而减小, 孔隙率为0时最大降幅为5.1%;网前2倍网高距离处与抑尘网之间区域的风速廓线与无网工况相差甚远,孔隙率为0时近网区域风速最高降幅达92.8%. 抑尘网和料堆迎风面之间区域,从地面至网顶高度,不同孔隙率抑尘网工况下的风速均较无网工况小,最小处为无网工况风速的18.5%;抑尘网以上区域的风速较无网工况的大,最大处为无网工况风速的128.0%,并且差距随抑尘网孔隙率的减小而增大. 料堆剪切力分布显示,其迎风面和平顶面为主要散尘面,背风面被涡旋卷起的扬尘量较前两者小得多. 防风抑尘网的设置改变了料堆周围空气的流动结构和受力分布,对不同孔隙率的抑尘网数值模拟结果可知,0.2和0.3为最佳孔隙率.      

Responses of the earthworm Eisenia andrei exposed to sublethal aluminium levels in an artificial soil substrate

Industrial discharges of Al are increasingly common. In this study, the activities of three antioxidases, malondialdehyde (MDA) content and changes in coelomocytes were investigated in earthworms (Eisenia andrei) exposed to different concentrations of aluminium chloride (range 0–200 mg Al kg^?1 dry soil) in artificial soils for 32 days. Within the first 16 days of Al exposure, catalase activity was elevated in most treatments, while the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were inhibited in all treatments. After 16 days exposure, SOD and GSH-Px activities returned to normal at lower Al concentrations, but were still inhibited at higher concentrations, hence the inhibition of SOD and GSH-Px showed some exposure-level dependence during the late exposure phase. MDA content was significantly elevated from 16 days after initial exposure. Neutral Red retention time of coelomocytes decreased at the highest exposure concentrations after 32 days, and an increased proportion of cells showing membrane damage was also observed at this time using flow cytometry. We conclude that excessive Al in soils can cause oxidative stress and cell damage in earthworms. Hence, Al accumulation in the environment may present an ecological hazard through suppression of the important functions of earthworms in soil ecosystems.     

烧结车间抽尘风管尘垢防治探讨

钢铁厂的铁矿烧结车间用抽风系统将生产过程混入空气中的粉尘和有害气体抽走。烧结热量作用使抽尘气流温度较高且含水汽偏大,风管外面的冷气作用使风管内表面累积一层粘结强度高的尘垢,影响正常生产。探讨尘垢生成机理,介绍采用夹层风管预防内表面累积尘垢。     

上流式厌氧污泥反应器在石化高浓度废水预处理中的应用

为了更加有效地处理己内酰胺高浓度废水,在原A/O处理系统前采用上流式厌氧污泥反应器先对高浓度己内酰胺废水进行预处理.工业应用结果表明:由于己内酰胺高浓度废水中含有大量的硫酸盐、磷酸盐和硝酸盐等无机酸盐,因此必须严格控制反应系统进水的pH值在5.5～6.5之间,以有效保证系统平稳运行,防止酸化;当COD控制在8000～12000mg/L时,COD的去除率可达到55%以上,达到了处理后的水质要求.