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451.
Peter Grindrod Mark S. Edwards Jenny J. W. Higgo Geoffrey M. Williams 《Journal of contaminant hydrology》1996,21(1-4)
We consider the dispersion and elution of colloids and dissolved nonsorbing tracers within saturated heterogeneous porous media. Since flow path geometry in natural systems is often ill-characterized macroscopic (mean) flow rates and dispersion tensors are utilized in order to account for the sub-model scale microscopic fluctuations in media structure (and the consequent hydrodynamic profile). Even for tracer migration and dispersal this issue is far from settled.Here we consider how colloid and tracer migration phenomena can be treated consistently. Theoretical calculations for model flow geometries yield two quantitative predictions for the transport of free (not yet captured) colloids with reference to a non-sorbing dissolved tracer within the same medium: the average migration velocity of the free colloids is higher than that of the tracer; and that the ratio of the equivalent hydrodynamic dispersion rates of colloids and tracer is dependent only upon properties of the colloids and the porous medium, it is independent of pathlengths and fluid flux, once length scales are large enough.The first of these is well known, since even in simple flow paths free colloids must stay more centre stream. The second, if validated suggests how solute and colloid dispersion may be dealt with consistently in macroscopic migration models. This is crucial since dispersion is usually ill-characterized and unaddressed by the experimental literature. In this paper we present evidence based upon an existing Drigg field injection test for the validity of these predictions.We show that starting from experimental data the fitted dispersion rates of both colloids and non-sorbing tracers increase with the measured elution rates (obeying slightly different rules for tracers and colloids); and that the ratio of colloid and nonsorbing tracer elution rates, and the ratio of colloid and nonsorbing tracer dispersion rates may be dependent upon properties of the colloids and the medium (not the flow regime).It is important to realize that even for unretarded species, an earlier peak in the breakthrough curve does not necessarily correspond to a faster mean elution rate, or vice versa. But rather that a colloid may elute faster but disperse less than an equivalent tracer. Hence its peak may be retarded compared to that of the tracer, even assuming no retardation. Hence one must consider a combination of mean elution rate and mean dispersion rate, and not rely on “peak times” to corroborate chromatographic effects. The importance of this lies in the fact that these processes are not independent and yet upscale differently. Thus realistic estimates of effective colloid dispersion rates should be upscaled in a way consistent with that adopted for tracers within the same system. 相似文献
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454.
新型湿式湍流除尘器及在电厂输煤系统中的应用 总被引:1,自引:0,他引:1
介绍了针对火电厂输煤系统作业环境粉尘治理而研制开发的新型湿式湍流除尘器的设计思路、设备结构、技术特点及在电厂输媒系统的应用情况。 相似文献
455.
Xiaodong Zou Zhemin Shen Tao Yuan Shan Yin Jingping Cai Liping Chen Wenhua Wang 《Atmospheric environment (Oxford, England : 1994)》2006,40(40):8068-8073
In this paper, a shifted power-law model, based on the wind profile model, had been supposed to simulate concentration gradient of nitrogen dioxide (NO2) with distance from a highway. Field experiments were performed for NO2 gradients from a highway in Shanghai by using passive samplers. The shifted power-law model was fitted well with experimental results of field experiments both in this study and in the literature. The results not only verified the validity of shifted power-law relationship between NO2 concentration and the distance from a highway, but also partially demonstrated that there were some significant similarities between wind profile and air pollutants concentration profile near highway. With known concentration of chosen reference point and appropriate value of the parameter k, the model could be practically applied for predicting the NO2 distributions near a highway. The methods of determining the parameter k were also discussed for further detailed studies. 相似文献
456.
在空气气氛下,对医疗废物中几种有代表性的有机质进行非等温热解实验。分析实验结果发现,热解失重曲线与N2气氛下不同,出现多个DTG峰。利用Freeman—CarroⅡ法求出了各有机质的表观动力学参数,并建立了能较好反映各物料失重过程的表观多步反应动力学模型。针对混合物料无法直接求出表观动力学参数,建立了多组分反应动力学模型。 相似文献
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空气中挥发性有机物监测技术的研究进展 总被引:13,自引:0,他引:13
讨论了空气中挥发性有机化合物(VOCs)的监测分析方法研究进展。重点介绍了空气中VOCs的采集、分析和测定;简要叙述了样品前处理的新方法--固相微萃取法(SPME)与其它前处理方法的研究概况。 相似文献
460.
深层过滤理论与技术的研究进展 总被引:7,自引:0,他引:7
深层过滤是水处理工艺中的重要单元操作。近年来 ,在滤料、过滤工艺的研究开发及过滤理论研究方面有了新的发展。本文评述了一些主要研究进展 相似文献