Incorporating layer- and local-scale heterogeneities in numerical simulation of unsaturated flow and tracer transport

This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport.     

Transport of volatile compounds in porous media in the presence of a trapped gas phase

The presence of an immobile gaseous phase in an otherwise-saturated porous medium affects the transport of volatile compounds. The linear theory of partitioning tracers suggests that a volatile tracer introduced into such a system should be retarded with a constant retardation factor. Using high concentrations, however, the saturation of the gaseous phase will change as an effect of the tracer test itself. Competitive gas transfer among all volatile compounds and the change of saturation may lead to tracer concentrations that are temporarily higher than those injected. We analyze the system in the framework of the coherence theory by Helfferich [Soc. Pet. Eng. J. 21 (1) (1981) 51]. The governing equations are formulated as functions of total concentration, i.e., the mass of solutes in all phases per pore volume. Neglecting dispersion and mass-transfer kinetics, we derive the characteristic form of the resulting system of hyperbolic equations. In a system with N volatile compounds, a variation of the concentrations splits up into N waves, each traveling with its own characteristic velocity. If the presence of a gaseous phase is sustained, one wave will be a standing one. We perform numerical model calculations for tracers with various Henry's law coefficients and show that the results agree with the semi-analytical solution obtained by coherence theory.     

基于PLIF的混合气温度和浓度测量及其应用

缸内混合气温度和浓度分布,对发动机稳定运行,保障行车安全、避免发生路上人身伤亡或财物损失有重要影响。为了测量发动机缸内混合气的温度和浓度分布,建立了利用单波长激光诱导双示踪剂产生双荧光的测试系统,并拍摄了不同混合气温度、压力和浓度下的荧光图像,获得了不同示踪剂的荧光强度及其比值随温度、压力和浓度的变化关系,并将标定结果用于光学发动机缸内混合气的温度和浓度测量。结果表明,荧光强度及荧光比值均受到环境的压力、温度和混合气浓度的影响。利用PLIF方法得到的片光源穿过的缸内水平截面内的平均温度与用气缸压力计算的同一曲轴转角下的缸内平均温度变化趋势相同,两者之间的差值随着活塞上行而逐步减小。     

基于能位测定和示踪检测法的地下煤火漏风状态研究

应用能位测定法和示踪检测技术联合检测了鸡西老二井火区地下漏风状态。通过测试计算相对总压值得出了火区范围内井巷系统与采空区的风流关系,进而定性确定了火区内老二井与胜利井之间存在的可能漏风路径。在此基础上,利用瞬时释放示踪气体法确定了胜利井和老二井间的漏风方向和漏风速度,计算得出了火区下采空区内平均直线漏风风速为0.13m/s,漏风量为776m3/min。研究结果为矿区采取针对性的防灭火措施提供依据,并为同类问题的解决提供参考。     

海洋环境中氧同位素示踪物技术

本文简要地介绍了在环境海洋学中的氧同位素示踪物技术，它有望成为大洋环流研究中一种新的可靠方法。以热带西太平洋和东海黑潮区等为例，文章对运用氧同位素示踪物技术以及氧同位素与盐度的相羞生描述海流的输运过程、水平和垂直扩散过程以及水团特征和混合过程等问题加以阐述。     

新疆尼勒克南部地区花岗斑岩锆石U-Pb年龄

对巴斯陶萨依、莫斯早特套花岗斑岩地质、地球化学特点,锆石的特征进行了详细的研究和单颗粒锆石U-Pb同位素年龄测定。获得巴斯陶萨依岩浆结晶锆石U-Pb同位素年龄为241.3±3.6 Ma,以及继承性锆石U-Pb同位素年龄为292.3±5.6 Ma。综合各方面因素认为这两个岩体侵位时代为早三叠世(印支早期)。     

Anthropogenic lead distribution in soils under arable land and permanent grassland estimated by Pb isotopic compositions

The role of land use on fate of metals in soils is poorly understood. In this work, we studied the incorporation of lead in two neighboring soils with comparable pedogenesis but under long-term different agricultural management. Distributions of anthropogenic Pb were assessed from concentrations and isotopic compositions determined on bulk horizon samples, systematical 5-10 cm increment samples, and on 24-h EDTA extracts. Minor amounts of anthropogenic lead were detected until 1-m depth under permanent grassland, linked to high earthworm activity. In arable land, exogenous Pb predominantly accumulated at depths <60 cm. Although the proximity between the two sites ensured comparable exposition regarding atmospheric Pb deposition, the isotopic compositions clearly showed the influence of an unidentified component for the cultivated soil. This work highlights the need for exhaustive information on historical human activities in such anthropized agrosystems when fate of metal pollution is considered.     

Numerical analysis of water and solute transport in variably-saturated fractured clayey till

This study numerically investigates the influence of initial water content and rain intensities on the preferential migration of two fluorescent tracers, Acid Yellow 7 (AY7) and Sulforhodamine B (SB), through variably-saturated fractured clayey till. The simulations are based on the numerical model HydroGeoSphere, which solves 3D variably-saturated flow and solute transport in discretely-fractured porous media. Using detailed knowledge of the matrix, fracture, and biopore properties, the numerical model is calibrated and validated against experimental high-resolution tracer images/data collected under dry and wet soil conditions and for three different rain events. The model could reproduce reasonably well the observed preferential migration of AY7 and SB through the fractured till, although it did not capture the exact depth of migration and the negligible impact of the dead-end biopores in a near-saturated matrix. A sensitivity analysis suggests fast flow mechanisms and dynamic surface coating in the biopores, and the presence of a plough pan in the till.     

活性污泥反应器流态研究中示踪剂的选择

针对活性污泥反应器中的流态研究需要,通过备选示踪剂氯化锂、亚甲蓝和氯化钠的污泥吸附试验以及曝气静沉试验,研究了活性污泥对这3种示踪剂的吸附作用,以及示踪剂浓度对污泥处理效果的影响情况。结果表明,亚甲蓝易被污泥吸附,对试验数据干扰较大,且吸附亚甲蓝后,水样中污泥对COD_Cr的处理效率下降幅度达50%以上;氯化锂和氯化钠是离子型示踪剂,本身不易被吸附,投加后的活性污泥对COD_Cr的处理效率基本不变,保持在70%以上。从示踪剂投加量以及出水水质控制方面考虑,确定氯化锂为3种示踪剂中的最佳示踪剂。     

同步进出水SBR设备最佳进水方式流态模拟

借助流体计算软件Fluent对某同步进出水SBR设备4种不同进水位置以及3种进水孔排布分别进行流态模拟,根据模拟结果得到最佳的进水方式;同时在该进水方式下对进水流量为0.5、0.7、1.0、1.3和1.5 m3/h时反应器内的流态分布情况进行了数值模拟,最后通过示踪剂实验与模拟结果对比验证。对于实验用SBR(长×宽×高为2 m×2 m×1.2 m),进水流量1.0 m3/h是最佳进水流量,此时反应器内流态稳定,进水区域主要分布于反应器中下部以及远离堰口的池壁附近,死水区面积较小,冲击负荷适中,进水对出水水质影响较小;当进水流量小于1.0 m3/h时,进水主要分布于反应器池底,对角线方向以及远离进水端池壁附近3个区域且彼此相对独立,池内死水区面积较大;当进水流量大于1.0 m3/h时,进水冲击负荷过大,迅速形成短流,影响出水水质。