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71.
Palut JM Montarnal P Gautschi A Tevissen E Mouche E 《Journal of contaminant hydrology》2003,61(1-4):203-218
A long-term single borehole diffusion experiment using tritiated water as tracer was carried out in Opalinus clay, an argillaceous rock formation that is accessible at the Mont Terri Underground Research Laboratory, situated in the Swiss Jura. The tracer was diluted in reconstituted formation water and introduced into a packed-off section of a borehole located in saturated rock. Pressure in this interval was maintained equal to the pore pressure of the surrounding rock in order to prevent any hydraulic gradient around the borehole and to avoid advective transport processes. The evolution of the tracer concentration in the injection system was monitored over time. After 1 year of diffusion, the claystone surrounding the interval was retrieved by overcoring the whole borehole and packer system, and by an adjacent oblique borehole. Compressed air was used as drilling fluid to reduce rock disturbances. The recovered overcore was sampled along profiles perpendicular to the borehole wall with a view to determining the tracer-concentration profiles in the rock. To avoid further evaporation of tritiated water, subsamples were immediately transferred into polyethylene bottles and disaggregated by adding a known amount of tracer-free water. Fifteen profiles were determined and showed a decreasing tracer concentration with distance into the rock. The pore-water contents were constant along those profiles, confirming that only very little water was lost during overcoring operations. The evolution of tritium-tracer concentration in the injection system over time and in situ profiles were interpreted with a 3-D numerical simulation of the experiment. That allowed for the identification of the transport parameters (orthotropic diffusion tensor and porosity) by minimising the relative quadratic error between the experimental and simulated data. The fitting is good and the results are consistent with data obtained on drill-core samples. The result of tritiated water is discussed regarding (1) the potential effect of mechanical and/or chemical disturbances around the injection borehole and (2) the specific behaviour of tritiated water. 相似文献
72.
Numerical simulation tools have been used to study the dominating processes during transport of aromatic hydrocarbons in the unsaturated soil zone. Simulations were based on field observations at an experimental site located on a glacial delta plain with pronounced layered sedimentary structures. A numerical model for transport in the unsaturated zone, SWMS-3D, has been extended to incorporate coupled multispecies transport, microbial degradation following Monod kinetics and gas diffusive transport of oxygen and hydrocarbons. The flow field parameters were derived from previous work using nonreactive tracers. Breakthrough curves (BTC) from the hydrocarbon field experiment were used to determine sorption parameters and Monod kinetic parameters using a fitting procedure. The numerical simulations revealed that the assumption of homogeneous layers resulted in deviations from the field observations. The deviations were more pronounced with incorporation of reactive transport, compared with earlier work on nonreactive transport. To be able to model reasonable BTC, sorption had to be reduced compared to laboratory experiments. The initial biomass and the maximum utilisation rate could be adjusted to capture both the initial lag phase and the overall degradation rate. Nevertheless, local oxygen limitation is predicted by the model, which was not observed in the field experiment. Incorporation of evaporation and diffusive gas transport of the hydrocarbons did not significantly change the local oxygen demand. The main cause of the observed discrepancies between model and field are attributed to channelling as a result of small-scale heterogeneities such as biopores. 相似文献
73.
Preliminary 3-D site-scale studies of radioactive colloid transport in the unsaturated zone at Yucca Mountain,Nevada 总被引:1,自引:0,他引:1
The U.S. Department of Energy (DOE) is actively investigating the technical feasibility of permanent disposal of high-level nuclear waste in a repository to be situated in the unsaturated zone (UZ) at Yucca Mountain (YM), Nevada. In this study we investigate, by means of numerical simulation, the transport of radioactive colloids under ambient conditions from the potential repository horizon to the water table. The site hydrology and the effects of the spatial distribution of hydraulic and transport properties in the Yucca Mountain subsurface are considered. The study of migration and retardation of colloids accounts for the complex processes in the unsaturated zone of Yucca Mountain, and includes advection, diffusion, hydrodynamic dispersion, kinetic colloid filtration, colloid straining, and radioactive decay. The results of the study indicate that the most important factors affecting colloid transport are the subsurface geology and site hydrology, i.e., the presence of faults (they dominate and control transport), fractures (the main migration pathways), and the relative distribution of zeolitic and vitric tuffs. The transport of colloids is strongly influenced by their size (as it affects diffusion into the matrix, straining at hydrogeologic unit interfaces, and transport velocity) and by the parameters of the kinetic-filtration model used for the simulations. Arrival times at the water table decrease with an increasing colloid size because of smaller diffusion, increased straining, and higher transport velocities. The importance of diffusion as a retardation mechanism increases with a decreasing colloid size, but appears to be minimal in large colloids. 相似文献
74.
75.
根据非稳定热传导基本方程式积分得到离散化方程式,编写出计算程序,利用计算机求出复合板在热处理过程中各结点随时间而变化的温度,绘出等温线,以研究复合板经升温固化处理后的理想冷却方法. 相似文献
76.
77.
Effect of dissolved oxygen on methane production from bottom sediment in a eutrophic stratified lake
《环境科学学报(英文版)》2023,35(3):61-72
Clarifying the role of sulfate and dissolved oxygen (DO) in methane production may allow for precise and accurate modeling of methane emissions in eutrophic lakes. We conducted field observations of sulfate, methane, and DO concentrations in Lake Abashiri, a typical brackish and eutrophic lake in a cold region, to develop a DO-based method for quantitively estimating methane production in a eutrophic lake and analyzed the results. We found that sulfate concentrations decreased rapidly from 900.0 mg/L in water overlying the sediments to nearly 0.0 mg/L in the bottom sediment. Methane production was almost uniform across sediment depths of 0.05 to 0.25 m, ranging from 1400 to 1800 µmol/m2/day. Also, methane production was found to be a function of DO concentrations in water overlying the bottom and could be modeled by a logistic function: constant production at 1,400 µmol/m2/day for DO concentrations of 0.0 to 3.0 mg/L, rapidly decreasing to 0 µmol/m2/day for DO concentrations of 3.0 to 6.0 mg/L. This methane model was verified using a simple one-dimensional numerical model that showed good agreement with field observations. Our results thus suggest that the proposed methane model reduces uncertainty in estimating methane production in a eutrophic lake. 相似文献
78.
顶棚下方最高温度是隧道火灾发展蔓延时的重要参数。针对火焰撞击顶棚并受到顶棚侧墙限制的强羽流驱动的顶棚射流,利用FDS模拟了18种缩尺寸隧道火灾工况,研究了顶棚下方最高温度随着火源功率、火源与顶棚距离的变化规律。结果表明:火焰撞击区域附近顶棚下方温度随着火源功率的增大而降低,随火源与顶棚距离的增大而升高;相反,在远离火源区域顶棚下方的温度随火源功率增大而升高,随火源与顶棚距离增大而降低;同时,通过分析隧道中心面上顶棚下方温度分布规律,提出了火焰撞击受限顶棚时顶棚下方最高温升的预测模型,研究结果能为实际的隧道消防提供一些参考。 相似文献
79.
Jeffrey R. Brook Leiming Zhang Franco Di-Giovanni Jacob Padro 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):1
This paper describes the development of a detailed dry deposition model for routine computation of dry deposition velocities of SO2, O3, HNO3 and fine particle SO42− across much of North America. Four different dry deposition/surface exchange sub-models have been combined with the current Canadian weather forecast model (Global Environmental Multiscale model) with a 3 h time resolution and a horizontal spatial resolution of 35 km. The present model uses the US Geological Survey North American Land Cover Characteristics data to obtain fourteen different land use and five seasonal categories. The four sub-models used are a multi-layer model for gaseous species over taller canopy land-use types, a big-leaf model for gaseous species over lower canopies (including bare soil and water) and for HNO3 under all surface types and, two different models for SO42−, one for tall canopies and the other for short canopies. All necessary parameters for each sub-model, chemical species, land-use and seasonal categories have been selected from available data libraries or from the values reported in the literature. The purpose for developing this model (referred to as the Routine Deposition Model (RDM)), when coupled with air concentration data, is to provide estimates of seasonal dry deposition, which can be combined with wet deposition to produce total deposition estimates. Model theory is discussed in this paper and model sensitivity tests and results will be presented in a companion paper. 相似文献
80.