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Mixing Zone (mixing + zone)
Selected AbstractsMapping the geochemistry of the northern Rub' Al Khali using multispectral remote sensing techniquesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2001Kevin White Abstract Spatial variations in sand sea geochemistry relate to mixing of different sediment sources and to variations in weathering. Due to problems of accessibility, adequate spatial coverage cannot be achieved using field surveys alone. However, maps of geochemical composition produced from remotely sensed data can be calibrated against limited field data and the results extrapolated over large, inaccessible areas. This technique is applied to part of the Rub' Al Khali in the northern United Arab Emirates. Trend surface analysis of the results suggests that the sand sea at this location can be modelled as an east,west mixing zone of two spectral components: terrestrial reddened quartz sands and marine carbonate sands. Optical dating of these sediments suggests that dune emplacement occurred rapidly around 10 ka BP, when sea level was rising rapidly. The spatial distribution of mineralogical components suggests that this phase of dune emplacement resulted from coastal dune sands being driven inland during marine transgression, thereby becoming mixed with rubified terrestrial sands. Copyright © 2001 John Wiley & Sons, Ltd. [source] A novel microfluidic mixer utilizing electrokinetic driving forces under low switching frequencyELECTROPHORESIS, Issue 9 2005Lung-Ming Fu Abstract This paper presents a novel technique in which low-frequency periodic electrokinetic driving forces are utilized to mix electrolytic fluid samples rapidly and efficiently in a double-T-form microfluidic mixer. Without using any additional equipment to induce flow perturbations, only a single high-voltage power source is required for simultaneously driving and mixing the sample fluids which results in a simple and low-cost system for the mixing purpose. The effectiveness of the mixer as a function of the applied electric field and the periodic switching frequency is characterized by the intensity distribution calculated downstream from the mixing zone. The present numerical and experimental results confirm that the proposed double-T-form micromixer has excellent mixing capabilities. The mixing efficiency can be as high as 95% within a mixing length of 1000 ,m downstream from the secondary T-junction when a 100 V/cm driving electric field strength and a 2 Hz periodic switching frequency are applied. The results reveal that the optimal switching frequency depends upon the magnitude of the main applied electrical field. The rapid double-T-form microfluidic mixer using the periodic driving voltage switching model proposed in this study has considerable potential for use in lab-on-a-chip systems. [source] Numerical modelling of the potential effects of a dam on a coastal aquifer in S. SpainHYDROLOGICAL PROCESSES, Issue 9 2009M. L. Calvache Abstract This study presents the results of a three-dimensional variable-density numerical modelling of the Motril-Salobreña coastal aquifer and the possible effects of the entry into service in May 2005 of the Rules Dam, located just 17 km from the coast. Present parameters of the Motril-Salobreña aquifer show that the system's conditions are very similar to a natural regime. The dam will substantially alter aquifer recharge, as the entry flow through the alluvial sediments of the Guadalfeo River will be entirely cut off or drastically reduced. Different scenarios reproducing the possible evolution of the aquifer under operation of the Rules Dam have been modelled. In most cases, results indicate that the conditions of the aquifer would worsen, with a general advance of the freshwater,saltwater interface. The area with most risk of saltwater intrusion is the old mouth of the Guadalfeo River, where the mixing zone could advance 1200 m inland. It is proposed that maintaining a 5,6 Mm3 year,1 ,ecological flow' in the Guadalfeo River could prevent this saline advance. This application demonstrates that variable-density models are potentially useful tools for estimating the effects of dams on the hydrodynamic and hydrochemical conditions of a coastal aquifer. Copyright © 2009 John Wiley & Sons, Ltd. [source] Analysis of the effect of mixing vane geometry on the flow in an annular centrifugal contactorAICHE JOURNAL, Issue 9 2009Kent E. Wardle Abstract The annular centrifugal contactor is a compact mixer/centrifuge developed for solvent extraction processes for recycling used nuclear fuel. This research effort couples computational fluid dynamics (CFD) modeling with a variety of experimental observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the volume-of-fluid method combined with large eddy simulation of turbulence was found to have very good agreement with the experimental measurements. A detailed comparative analysis of the flow and mixing with different housing vane geometries (four straight vanes, eight straight vanes, and curved vanes) was performed. Two additional variations on the eight straight vane geometry were also simulated. This analysis determined that at the simulated moderate flow rate the four straight mixing vane geometry has greater mixing and fluid residence time as compared to the other mixing vane configurations. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Development of an Industrial Multi-Injection Microreactor for Fast and Exothermic Reactions , Part IICHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2008D. M. Roberge Abstract A Grignard reaction performed in a microreactor is presented. The reaction is of type A (highly exothermic and very rapid) and has a low yield which is attributed to a hot spot formed in the mixing zone of the reactor. The reaction yield could be significantly increased by applying the multi-injection principle, leading to better thermal control in the microreactor. Nevertheless, the microreactor plays a major role in reducing the magnitude of the hot spot. Knowing this, it was possible to design and construct an industrial microreactor with significant advantages such as modularity, high flow rate operation, and low investment expenditure (pumps and flow controller minimization). [source] Predicting the Displacement of Yoghurt by Water in a Pipe Using CFDCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007M. Regner Abstract A numerical scheme based on the volume of fluid (VOF) method for predicting the displacement of one liquid by another has been verified versus electrical resistance tomography (ERT) and ultrasonic velocity profile (UVP) measurements for the displacement of yoghurt by water. The scheme using the VOF method predicts the skewed phase distribution as measured using ERT and the global structure of the velocity profile as measured using UVP. The phase distribution using the VOF method was compared with the results using the species transport model which allows for mixing between the phases. The species transport model was found to be less suitable for predicting the displacement of yoghurt by water since the turbulence model was unable to accurately predict the turbulent viscosity in the mixing zone between yoghurt and water, which resulted in a too high rate of mixing. [source] | ||||||||||