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In many temperate oligotrophic lakes, algal accumulations can form below the mixing zone. However, Deep Chlorophyll Maxima (DCM) have also been found in some eutrophic, tropical lakes and in this paper we aim to identify if they are recurrent features in these kinds of lakes and to recognize the factors that favor their formation. We analyzed 5 years of thermal stratification, water quality, and chlorophyll a concentrations in a tropical eutrophic lake in Central Mexico. Thermal stratification patterns were characteristic of warm monomictic lakes. Full water column deoxygenation during winter mixing was recorded in 3 of the analyzed years, and an increase of ~ 1 °C in the hypolimnion was detected between 2011 and 2015. DCM were detected in 4 out of the 5 studied years, at the top of the hypolimnion when the water column was stratified (spring–summer). This study is the first report of recurrent DCM formation in the northern limit of the Neotropics. It confirms that high light penetration is a necessary condition for DCM. Stratified nutrients with epilimnetic P depletion are also factors favoring DCM formation.

This study reviews 87Sr/86Sr depth profiles of formation waters sampled by Sr residual salt analysis (Sr RSA) from >100 oil/gas wells and research sites, including reservoirs with clastic and carbonate host rocks and with gas, oil and water as the continuous fluid phase. Globally, the water data form a smooth trend between low seawater-like 87Sr/86Sr ratios (~0.706) at shallow depths and high (~0.724) ratios in deeply buried rocks, where water-rock interaction dominates. We test the hypothesis that 87Sr/86Sr depth profiles in individual wells could be influenced by diffusional mixing processes by developing 1D diffusion mixing equations to simulate compositional patterns through time and comparing them with observed profiles. Different combinations of boundary and initial conditions generate various patterns characteristic of diffusion, including non-steady-state curves relating to incomplete mixing and steady-state patterns (such as vertical or inclined straight lines) where initial heterogeneities have fully mixed. The dataset yielded 193 occurrences of these patterns. Steady-state patterns are more common and longer in water zones, while non-steady-state patterns are more common and longer in oil and gas zones. The detection of diffusional mixing patterns in hydrocarbon-saturated rocks suggests that diffusion is active, although on average a factor of ~13–18 slower, than in comparable water-saturated rocks. Pattern generation and equilibration times were modelled for each non-steady-state pattern and compared with the time since reservoir filling with oil/gas, revealing that 90% of them could have been generated since filling, but 60% of them would already have mixed to steady state had the initial compositional heterogeneities arisen during or before reservoir filling. This is critical evidence that at least some of the initial heterogeneities must have arisen, and subsequently partially mixed, after filling; these patterns tend to be short (

Lake Bolsena, the fourth Italian lake for volume (9.2âEUR?×âEUR?109âEUR?m3), must be considered as highly sensitive to eutrophication for its extremely long water renewal time. In this paper, temperature and chemical characteristics of the lake measured in the period 2003-2017 are used to discuss the mixing pattern and the variation in the oxygen and algal nutrient concentrations, as indicators of the trophic level. In the analysed period the lake showed oligomictic characteristics, reaching the full overturn, with homogenization of the chemical profile over the whole water column, only in 4 out of the 15 considered years. A regular decrease of oxygen and increase of phosphorus concentrations in the deepest layers has been observed in the non-circulating multi-year periods. The mean total phosphorus concentration showed a regular increase, reaching values close to 16âEUR?μgâEUR?P Lâ^'1 in early spring 2017, mostly because of the urban discharge from the watershed, not adequately collected from an existing sewage pipe. Chemical and mixing patterns are discussed in relation with a previous study, carried out in 1966-1971, confirming the recent increase of phosphorus concentrations and the lower frequency of full circulation. The progressive deterioration of lake water quality indicates the need of prompt actions to reduce the external nutrient load and of further studies on the physical and biological characteristics of the lake, still strongly missing.

Increasingly more data have indicated that the 40Ar/39Ar crushing technique provides a very useful approach to determine the mineralization ages of hydrothermal ore deposits. In this study novel gas mixing lines are proposed based on the data of two quartz samples by 40Ar/39Ar crushing. Electron microprobe analyses indicate that the quartz grains contain K-rich silicate microlites. Both quartzs by crushing yield two mixing lines with ages corresponding respectively to those of K-feldspar or sericite (post-mineralization fluids) and muscovite samples (ore-forming fluids). This is the first report that both ages of secondary and primary fluid inclusions (SFIs and PFIs) are confirmed correspondingly by those of the K-rich minerals. This study strongly indicates that the 40Ar/39Ar crushing technique is very useful to determine the ages of geofluid activities. The newly proposed gas mixing patterns are shown on the inverse and normal isochron diagrams, indicating: (1) the mixtures are in different proportions of the PFIs and SFIs in different crushing steps; (2) the gas mixing lines yield PFI ages with low initial 40Ar/36Ar ratios; (3) an intermediate age between PFI and SFI ages cannot be obtained because the progressive crushing technique never release gas mixtures with a constant PFI/SFI proportion for each step. The gas mixing lines are thus interpreted to yield significant geological ages. The mixing patterns will help us better understand the 40Ar/39Ar dating results and be used for references to other isotopic mixing isochron systems.

In this study, we examined the efficiency of mixing due to liquid jets in a model anaerobic digester. Xanthan Gum Keltrol T (XGKT) solution which is transparent and has similar rheological characteristics to those of digested sludge was selected as the model liquid. Experiments were carried out using 0.15 and 0.4 wt% XGKT solutions. Four different liquid jet orientations were used in a cylindrical vessel, namely vertical-downward, vertical-upward, tangential 45° upward and tangential 45° downward. A decolourisation method involving an acid–base reaction was used for flow visualisation. A fluorescent dye was used as the tracer to observe the mixing patterns in the vessel. Video images of flow visualisation experiments were analysed to investigate the changes in the volume of well-mixed regions as a function of mixing time. The results from flow visualization were compared with those from both computational flow dynamics (CFD) simulations and electrical resistance tomography (ERT). Results showed that well mixed region volume decreases with increasing liquid apparent viscosity. Complete mixing was achieved in 0.15 wt% XGKT solution, which has rheology similar to that of digested sludge with 2.3% solids, with all four different jet arrangements. For 0.4 wt% XGKT solution, which has rheology similar to that of digested sludge with 5% solids, mixing efficiency with jet arrangement changes in the following order: upward > 45° upward > 45° downward > downward jet arrangement. The results suggested that we can use transparent materials to study rheological behaviours of sludge and visualize the dynamics of mixing. Results from both ERT and CFD agreed well with those from flow visualization experiments.

This research studied the effect of mixing patterns for the bio-cement in the pilot test. The bio-cementation process initiated the crystal forms of calcium carbonate (CaCO3) to bind soil particles. Formation of CaCO3 was useful for the stabilization of earth structures. Soil samples were mixed with the solution containing 250mM of CO(NH2)2, 250mM of Ca2+ (by CaCl2), and urease concentrations of 20 % (v/v). For clay, there were three types of mixing blades; the rectangle, the spiral and the comb blades. The research found that firstly the sample mixed by the comb blade showed the highest value of shear wave velocity of 210.5 m/s. Secondly, the sample mixed by the rectangle blade showed the shear wave velocity of 167.3 m/s. Lastly, the sample mixed by the spiral blade showed the lowest value of the shear wave velocity of 150.6 m/s. For sand, there were 4 injection methods; (a) pour all the solution at one time (b) continuous drop (c) period drop and (d) period injection. The research found that the method (a) was a disadvantage method since it improved the ground only at the bottom area. In the same way, the method (b) was also a disadvantaged method because it improved the ground only at the top area. The most recommended methods were the methods (c) and (d) which improved the ground strength continuously along the depth.

This paper reports an analysis of the influence of fuels on the stabilization of turbulent piloted jet flames with inhomogeneous inlets. The burner is identical to that used earlier by the Sydney Group and employs two concentric tubes within the pilot stream. The inner tube, carrying fuel, can be recessed, leading to a varying degree of inhomogeneity in mixing with the outer air stream. Three fuels are tested: dimethyl ether (DME), liquefied petroleum gas (LPG), and compressed natural gas (CNG). It is found that improvement in flame stability at the optimal compositional inhomogeneity is highest for CNG and lowest for DME. Three possible reasons for this different enhancement in stability are investigated: mixing patterns, pilot effects, and fuel chemistry. Numerical simulations realized in the injection tube highlight similarities and differences in the mixing patterns for all three fuels and demonstrate that mixing cannot explain the different stability gains. Changing the heat release rates from the pilot affects the three fuels in similar ways and this also implies that the pilot stream is unlikely to be responsible for the observed differences. Fuel reactivity is identified as a key factor in enhancing stability at some optimal compositional inhomogeneity. This is confirmed by inference from joint images of PLIF-OH and PLIF-CH 2 O, collected at a repetition rate of 10 kHz in turbulent flames of DME, and from one-dimensional calculations of laminar flames using detailed chemistry for DME, CNG, and LPG.

The Amazon delivers a fifth of the global continental runoff and riverine dissolved organic carbon (DOC) to the ocean. Intensified biogeochemical processes are expected at the junction of the Amazon's major blackwater tributary, the Rio Negro, and its parent, the Rio Solimbes, due to large gradients in pH, conductivity, DOC and particle load. Dissolved organic matter (DOM) plays a major role in aquatic biogeochemical processes which are poorly understood on the molecular level. To gain insights into the potential role of DOM in non-conservative processes, we assessed dynamics of Cu, Fe and DOM by ultrahigh resolution mass spectrometry in: (1) endmembers, (2) regional samples and (3) laboratory mixing experiments under presence/absence of natural particles (>0.2 p.m). The relative abundances of 3600 DOM molecular formulae were interpreted via multivariate statistics which revealed major dynamics in the DOM molecular composition. >40% of molecular formulae displayed conservative behavior even in the presence of natural particles, agreeing with bulk DOC behavior, but opposing the oftenpresumed non-conservative behavior of DOM. Another 16-27% of formulae fluctuated in FT-ICRMS signal intensity during mixing, but did not show consistent non-conservative behavior. Both rivers left a clear molecular imprint within the DOM of the Amazon, each being linked to >800 molecular formulae. Characteristic for the Rio Negro was a dominance of phenolics with a wide molecular mass range (centered at similar to 400 Da), and for the Rio Solimbes more saturated but lower-molecular mass compounds (centered at similar to 300 Da). Both Fe and Cu showed distinct non-conservative mixing patterns under particle presence. In the controlled mixing experiments including original particles at natural concentration, up to 0.5 ttg/L Cu was released from the particles into solution at 20-40% blackwater contribution. Our molecular analysis revealed distinct DOM compositional changes in polyphenol- and nitrogencontaining formulae paralleling this release, suggesting links to desorption of potential ligands and charge-induced effects at particle surfaces caused by pH and conductivity changes in the course of mixing. (C) 2019 Elsevier Ltd. All rights reserved.

Methane (CH4), a potent greenhouse gas, is produced in and emitted from lakes at globally significant rates. The drivers controlling the proportion of produced CH4 that will reach the atmosphere, however, are still not well understood. We sampled a small eutrophic lake (Soppensee, Switzerland) in 2016–2017 for CH4 concentrations profiles and emissions, combined with water column hydrodynamics to investigate the fate of CH4 produced in hypolimnetic sediments. Using a mass balance approach for the periods between April and October of both years, net CH4 production rates in hypolimnetic sediments ranged between 11.4 and 17.7 mmol m−2 d−1, of which 66–88% was stored in the hypolimnion, 13–27% was diffused to the epilimnion, and 6–7% left the sediments via ebullition. Combining these results with a process‐based model we show that water column turbulent diffusivity (K z) had a major influence on the fate of produced CH4 in the sediments, where higher K z values potentially lead to greater proportion being oxidized and lower K z lead to a greater proportion being stored. During fall when the water column mixes, we found that a greater proportion of stored CH4 is emitted if the lake mixes rapidly, whereas a greater proportion will be oxidized if the water column mixes more gradually. This work highlights the central role of lake hydrodynamics in regulating CH4 dynamics and further suggests the potential for CH4 production and emissions to be sensitive to climate‐driven alterations in lake mixing regimes and stratification.

Despite the increasing importance of air-lift reactors, very little published information is available on how the ratio of aerated to non-aerated cross-sectional areas ( A d / A r ) of the reactor, and the aerating system affect the oxygen mass transfer and other performance characteristics. The influence of the ratio of cross-sectional areas of downcomer to riser ( A d / A r ), and the type of gas-distributor on volumetric oxygen mass-transfer coefficient, gas holdup, and liquid circulation velocity were investigated in a 114 L rectangular air-lift reactor with motile baffle, separating aerated from non-aerated compartments. The results indicated that the oxygen mass transfer characteristics of rectangular air-lift reactor are better at A d / A r of 2.0; the gas holdup and liquid circulation time showed maximum values at the same ratio. A new empirical model for the effects of the aeration rate and A d / A r ratio was proposed to account for the observed changes of volumetric oxygen mass transfer coefficient. The model took into account the different mixing patterns in the reactor for both cases: A d / A r ≤1 and A d / A r >1 using a wide range of these ratios.

The head-on collision, merging and internal mixing dynamics of two unequal-sized droplets were experimentally studied and interpreted, using water, $n$-decane and $n$-tetradecane to identify the distinguishing effects of surface tension and liquid viscosity on the merging and mixing patterns. It is shown that, upon merging of water and $n$-decane droplets, mushroom-like jets of dissimilar characteristics develop within the merged mass for small and large values of the impact Weber number (We), and that such jets are not developed for intermediate values of We. Furthermore, such jet-like mixing patterns were not observed for droplets of $n$-tetradecane, which has smaller surface tension and larger viscosity as compared to water. A regime nomogram relating the Ohnesorge and symmetric Weber numbers is constructed, providing a unified interpretation of the internal mixing patterns. Numerical simulations based on an improved volume-of-fluid method and an adaptive mesh refinement algorithm provide auxiliary diagnoses of the flow fields and the observed phenomena.

The effect of wave baffles inclination angle on the behavior of a packed bed operating under liquid up-flow was experimentally investigated. The system has been widely used in biotechnology due to the large surface area available for the microorganisms attachment. The results of different flow rates showed that the reactor “e” at $$\theta = 180^{\circ }$$ behaves as a plug flow distorted by a constant axial dispersion. At low flow rates, the mean residence time (MRT) and variance residence time (VRT) are high. However, both parameters increase with increasing the height of the sand bed for all reactors “a”, “b”, “c”, “d” and “e” (i.e. $$\theta = 0^{\circ }, 15^{\circ }, 30^{\circ }, 45^{\circ }$$ and $$180^{\circ }$$ ), respectively, and the flow patterns lie between plug flow and perfectly mixed. Other results of residence time distribution (RTD) obtained from all reactors showed that these reactors do not have segregations or dead volumes and the reactor “c” at $$\theta = 30^{\circ }$$ presents a uniform dispersion, high N-tanks number and a low MRT compared with the reference reactor at flat baffles.

The Wahiba Sand Sea is a large dune system composed of northern and southern zones. The dunes receive sand from multiple sources including two fluvial systems draining mountain basins, older underlying dunes, and a large coastline. Although the sand sea is distinctly divided into geomorphic regions with different dunes types, ages, and bulk mineral compositions, the ubiquitous presence of carbonate grains throughout the dune field has led to models that suggest the coast and shallow shelf is the direct and primary source of sediment for the entire sand sea. This study uses a novel method which couples selective, grain-by-grain analysis using laser-induced breakdown spectroscopy (LIBS) of a single mineral species with the classification method of Soft Independent Modeling of Class Analogy (SIMCA). The analysis of carbonate grains using the LIBS method reveals that the carbonates are comprised of several sub-populations that are well mixed throughout the dune field. Individual sources of carbonate grains are also composed of multiple sub-populations creating further complexity. Sand in the Northern Wahiba is predominantly, and directly, derived from wadi systems that lie on the west and northeast sides of the dunes and once bordered the southern end of the dunes. The Southern Wahiba is composed of a more complex mixture of sand derived from the coast; however, the coastal sediments themselves were dominantly derived from the fluvial systems in the region, along with sediment of unknown original source. The new LIBS/SIMCA method of grain-by-grain analysis shows promise for unraveling complex mixing patterns in sedimentary deposits.

The temporal and spatial variability of the upper ocean hydrochemistry in the Black Sea is analysed using data originating from profiling floats with oxygen sensors and carried out with a coupled three-dimensional circulation-biogeochemical model including 24 biochemical state variables. Major focus is on the dynamics of suboxic zone which is the interface separating oxygenated and anoxic waters. The scatter of oxygen data seen when plotted in density coordinates is larger than those for temperature, salinity and passive tracers. This scatter is indicative of vigorous biogeochemical reactions in the suboxic zone, which acts as a boundary layer or internal sink for oxygen. This internal sink affects the mixing patterns of oxygen compared to the ones of conservative tracers. Two different regimes of ventilation of pycnocline were clearly identified: a gyre-dominated (cyclonic) regime in winter and a coastal boundary layer (anticyclonic eddy)-dominated regime in summer. These contrasting states are characterized by very different pathways of oxygen intrusions along the isopycnals and vertical oxygen conveyor belt organized in multiple-layered cells formed in each gyre. The contribution of the three-dimensional modelling to the understanding of the Black Sea hydro-chemistry, and in particular the coast-to-open-sea mixing, is also demonstrated. Evidence is given that the formation of oxic waters and of cold intermediate waters, although triggered by the same physical process, each follow a different evolution. The difference in the depths of the temperature minimum and the oxygen maximum indicates that the variability of oxygen is not only just a response to physical forcing and changes in the surface conditions, but undergoes its own evolution.

This work focuses on the study of bulk flows accompanying the coalescence of two aqueous drops, one containing surfactant and the other surfactant-free, in silicone oils of various viscosities. It is observed that the surfactant-free drop intrudes into the surfactant-laden drop in the form of a penetrating jet whose speed increases and average radius decreases with increasing outer phase viscosity. Mixing patterns within the coalescing drops are due to the force imbalance caused by capillary pressure difference and surfactant-induced Marangoni stresses. The driving force for mixing associated with the difference in interfacial tension between the drops is considerably stronger than that related to the drop size. The long timescale mixing of the drops is driven by rapid interior convection, and the subsequent, slow, diffusive process. Three-dimensional numerical simulations show excellent qualitative and quantitative agreement with the experimental results. The implications of our results to formulation strategies of complex microstructures in practical applications are also discussed.

Biphasic calcium phosphate (BCP) bioceramics, the mixture of hydroxyapatite (HA) and beta- tricalcium phosphate (β-TCP), are widely used as bone repair materials. Optimization of its composition and mixing pattern is crucial for its design and preparation. A series of BCP structures with a HA/β-TCP mass ratio of 0/100, 30/70, 50/50, 70/30, and 100/0 were constructed and studied with a simulated annealing molecular dynamics method. On the basis of equilibrated BCP structures, their elastic constants and moduli were computed and analyzed. With increasing HA content, the elastic moduli of BCP increase. Under the same mass ratio (50/50), the elastic moduli have no distinct changes for different mixing patterns. Calculations on the uniaxial extension of BCP reveal a sophisticated nonlinear and loading-path dependent behavior. The maximum stress decreases with increasing β-TCP content and mixing level.

This article presented the effect of mixing patterns for the bio-cement in two different soils (Kaolin clay and Bangkok sand). Bio-cementation process initiated the crystal forms of calcium carbonate (CaCO3) to bind the soil particles. Soil samples were mixed with the solution containing 250 mM of CO(NH2)2, 250 mM of Ca2+ (by CaCl2) and 20% (v/v) of urease. In simulated deep mixing of Kaolin clay, the research found that blades used in solution mixing affected the strength development of Kaolin clay after bio-cementation. The V s of 210 m s−1 was found in comb blade mixer. In simulated deep mixing of Bangkok sand, the research found that solution injecting method affected the V s of Bangkok sand. The period drop and the period injecting methods provided better V s results than the one time pouring and the continuous injecting methods.

A simple experiment designed to study mixing of a material of complex rheology in a stirred tank is described. Non-Newtonian suspensions of blue maize flour that naturally contain anthocyanins have been chosen as a model fluid. These anthocyanins act as a native, wide spectrum pH indicator exhibiting greenish colors in alkaline environments, blue tones in neutral conditions, and pink–violet colors in acid environments. Students used a continuous injection of a basic solution in an initially acidic environment to reveal mixing patterns and flow structures and to follow their evolution over time in a typical stirred tank configuration. These experiments aim to demonstrate, in a laboratory setting, basic concepts related to mixing: (i) the existence of mixing pathologies in laminar-stirred tanks; (ii) the complex rheology of some real suspensions; (iii) the effect of tank geometry on mixing performance; and (iv) the quantitation of mixedness and mixing evolution using digital color analysis.

Through experiment and numerical modeling, this study investigated the establishment of moderate or intense low-oxygen dilution (MILD) combustion in a laboratory-scale furnace when fuel and air are fully premixed (FP), partially premixed (PP), or non-premixed (NP). Experiments were carried out at firing rates from 7.5 to 15 kW and equivalence ratios (Φ) ranging from 0.5 to 1. The furnace thermal fields and exhaust NOx emissions for the three mixing patterns were compared. Validated computational fluid dynamics was used to aid in better understanding the flow and compositional structures in the furnace. Natural gas was used as the fuel. The eddy dissipation concept (EDC) model and the GRI-Mech 3.0 mechanism were used. Additional chemical kinetics calculations were also performed to examine reaction pathways under the MILD combustion regime. Moreover, the characteristics of the reaction regime of MILD combustion were examined and are discussed in detail. Estimation of the initial jet momentum rate (J) showe...

In this paper, a thermodynamic analysis of non-isothermal mixing's influence on the energy target of water-using network is presented. Firstly, water streams in the network are divided into two categories, and then based on the classification all the non-isothermal mixing patterns between two streams are defined. Through thermodynamic analysis from energy composite curve of hot and cold water streams, the influences of non-isothermal mixing on the energy target of water-using network are explored and some mixing rules are obtained, which can be used to simplify the heat exchanger network of a given water-using system and improve the system's energy performance through identifying the beneficial non-isothermal mixings. The applicability of these rules is illustrated by an example in the paper and the result is very encouraging.

This study was conducted to build up the inventories of Pb isotopic compositions of major Pb pollution sources in South Korea. Since non-ferrous metal smelters are one of major anthropogenic sources, two smelters for zinc, each one of smelter for lead and copper were selected for the study. The Pb concentrations and isotopic compositions of metal ores, wastewater, sludge, metal rod and produced sulfuric acid were analysed to understand the Pb isotopic patterns in environment. The isotopic ratio, , of zinc ores from zinc smelter were in the range of 1.179~1.198 and the ratio of waste, flue gas and products samples were 1.105~1.147. This results implied that the isotopic patterns of output samples showed mixing patterns between two distinct metal ore soerces. In 2011, major importing countries of zinc ore were Australia, Peru and Mexico. Thus Pb isotopic patterns from zinc smelter is originated from the mixing patterns between less radiogenic Australian ores and more radiogenic South America`s ores. Lead smelters also showed the same mixing patterns with those of zinc smelters. However copper smelter showed same Pb isotopic patterns with more radiogenic South America`s ores.

Mechanical properties and material mixing patterns of friction stir spot welded (FSSW) joints of dissimilar aluminum alloys were investigated. Two aluminum alloys typically used in automotive applications, 5052-H32 and 6061-T6, were selected. During the experiment, the process parameters including the z-axis force and torque histories were measured as a function of the tool displacement. The mechanical properties were investigated by microhardness measurements of the joint, and the material mixing in the stir zone was investigated by EPMA. The experimental results illustrate different process parameter histories, material mixing in the stir zone and material properties including microhardness distributions for FSSW joints of dissimilar aluminum alloys, likely due to different mechanical behaviors of the selected aluminum alloys in the FSSW process temperature range.

A comparison of the performance of four full-scale aerated horizontal flow constructed wetlands was conducted to determine the efficacy of the technology on sites receiving high and variable ammonia loading rates not yet reported in the literature. Performance was assessed in terms of ammonia and solids removal, hydraulic conductivity and mixing patterns. The capability of systems to produce ammonium effluent concentrations

Water samples were collected for 23 different stations along a cross section profile of an estuary extending over to adjacent sea. The collected water samples were filtered and analyzed for major–minor ions and strontium isotope using the standard procedure to understand the geochemical behaviors of major and minor elements. The normalized values indicated that all riverine elements were entering to adjacent coastal sea with some significant variations at the estuary. The seawater dilution and regression lines explain about the overall patterns for seven elements. Removal processes were detected on calcium, magnesium, strontium and sulfate in the estuarine region. No significant mineral precipitation observed to release magnesium with respect to calcium. Minor variations of strontium and sulfate ions could be attributed to the presence of organic matter in the study area. Comparing seven elements with total suspended matters revealed that the total suspended matters played crucial role in either adsorption or absorption of all the elements in estuary before it reaches to coastal sea. Mixing patterns of strontium isotope showed minimal non-conservative with an evidence of active geochemical process in the estuary.

A comprehensive study on the liquid mixing with/without instantaneous reactions was conducted using planar laser induced fluorescence (PLIF) technique, where a novel reactive PLIF technique was adopted to quantitatively visualize the dynamic variation of the concentration of fluorescence dye due to signal quenching by a Fenton reaction. The factors (e.g., tracer injection direction, tracer injection position, impeller speed) influencing the reactive and non-reactive mixing processes were investigated, and the mixing performances were characterized by non-reactive mixing times (τ95 and τ99), and reactive mixing time (θ99), respectively. The experimental results from the 2-D measurements of liquid mixing behavior emphasized the significance of the understanding on the spatio-temporal mixing patterns: not only did the tracer injection position affect the mixing performances in the stirred tank, but also the sampling position to monitor the mixing status would lead to a large difference in evaluating the mixing performance. For the stirred tank with fast reactions, the reactive mixing performance had a strong interplay with the non-reactive mixing.

This research was initiated to investigate associations between flour breadmaking traits and mixing and empirical dough rheological properties under thermal stress. Thirty hard spring wheat flour samples were analyzed by a Mixolab standard procedure. Mixolab profiles were divided into six different stages, and torque measurements of individual stages were modeled by nonlinear curve fitting using a compound of two solution searching procedures, multidimensional unconstrained nonlinear minimization and genetic algorithm. Mixing patterns followed exponential equations. Dough torque patterns under heat constraint, specifically dough thermal weakening and pasting profiles, were described by a sigmoid logistic equation as a function of time. Dough stability during heating appeared important for bread loaf volume increase from significant correlations between bread loaf volume and parameters generated from models of a dough thermal weakening stage. Multivariate continuum regression was employed to calib...

Behavior of the solid phase in fluidized beds was studied by a 2D CFD-DEM approach to obtain more information on the solid mixing and circulation. Hydrodynamic parameters, including solid diffusivity, and internal and gross circulations were considered in this study. To validate the simulation, time-position data obtained by the Radioactive Particle Tracking (RPT) technique were used. It was shown that the 2D model can satisfactorily predict the axial diffusivity, while the radial diffusivity calculated based on the model is an order of magnitude smaller than the experimental one in 3D. The influence of aspect ratio of the bed, type of distributor, and inlet gas velocity on solids mixing pattern were also studied. The solids flow pattern in the bed changed considerably by increasing the aspect ratio. Different solid circulations were captured by numerical model for the two types of distributors, namely porous and injection types. The results suggested that increasing the superficial gas velocity caused rigorous internal and gross circulations, which in return, improved solids mixing and decreased deviations from well mixed state.

During unidirectional solidification of multicrystalline (mc) silicon, the adjustment of controllable mixing patterns with high stirring efficiency can be obtained by application of a double-frequency travelling magnetic field (TMF). It is assumed that such Lorentz force mode is generated within KRISTMAG ® heater magnet modules (HMM) positioned around a rectangular crystallization container with silicon melt. The induced flow distributions were studied numerically by 3D magnetic and transient flow calculations. The electromagnetic interference due to the presence of two frequencies and its effect on the resulting Lorentz force density have been estimated analytically. The results show that the flow can be intentionally intensified in the bulk volume without generation of hazardous high velocities in the peripheral region, i.e. near container walls. No considerable resonance effect has been found. As a result the TMF penetration and, hence, the melt mixing level within the central region is enhanced. Additionally, a general improvement of the process purity can be predicted.

The riser of a Circulating Fluidised Bed (CFB) is the key-component where gas-solid or gas-catalytic reactions occur. Both types of reactions require different conditions of operating velocities (U), solids circulation fluxes (G), overall hydrodynamics and residence times of solids and gas. The solids hydrodynamics and their residence time distribution in the riser are the focal points of this paper. The riser of a CFB can operate in different hydrodynamic regimes, each with a pronounced impact on the solids motion. These regimes are firstly reviewed to define their distinct characteristics as a function of the combined parameters, U and G. Experiments were carried out, using Positron Emission Particle Tracking of single radio-actively labelled tracer particles. Results on the particle velocity are assessed for operation in the different regimes. Design equations are proposed. The particle velocities and overall solids mixing are closely linked. The solid mixing has been previously studied by mostly tracer response techniques, and different approaches have been proposed. None of the previous approaches unambiguously fits the mixing patterns throughout the different operating regimes of the riser. The measured average particle velocity and the velocity distribution offer an alternative approach to determine the solids residence time distribution (RTD) for a given riser geometry. Findings are transformed into design equations. The overall approach is finally illustrated for a riser of known geometry and operating within the different hydrodynamic regimes. (C) 2010 Elsevier B.V. All rights reserved.

Slow granular flows play an important role in industries ranging from food to pharmaceuticals to ceramics. This subject has received much attention in recent literature; however, heat transfer in even the simplest particle flows is poorly understood. Heat transfer depends on the flow of granular materials: the bed conductivity is a function of the (changing) micro-structure; heat redistribution also depends on particle mixing/segregation. In this work, a multi-scale, multi-physics modeling technique, thermal particle dynamics (TPD), is used to examine the interplay between transient heat transfer and particle mixing in rotating tumblers. We study the effect of the mixing rate on the heating rate of the granular material by changing the tumbler cross-sectional shape and operation parameters—rotation rate and tumbler filling level. We use the Peclet number in the granular bed to determine the dominant heating mechanism—conduction or convection—and to predict conditions that will favor more rapid flow of thermal energy in the granular bed. The rate of heat transport is characterized using the Nusselt number and a fluids-inspired relationship correlating this quantity with the Peclet values is attempted. Finally, we use a continuum model to study the relationship between the mixing patterns and temperature contours.

Basic experiments on the mixing of horizontally injected high-density calcium chloride water solution in vertically upward low-velocity water flow have been performed in a small-scale apparatus. Mixing patterns observed in the experiments have been classified into complete mixing and incomplete mixing, or complete entrainment and incomplete entrainment. In complete mixing, the injected high-density solution is completely mixed with or entrained into the vertically upward water flow. On the other hand, in incomplete mixing, the high-density solution is partly mixed with or entrained into the vertically upward water flow and partly falls down or stays there even in the upward water flow. Numerical calculations have been conducted by solving the continuity equation and the momentum equations for the total fluid together with the mass transfer equation for the solute, taking density change into account. The numerical calculations have predicted approximately the increase in mixing efficiency, which is defined as the fraction of the injected solute mass that actually leaves the test section, and the calculations also have estimated approximately the boundary flow rates between the complete and incomplete mixing processes observed in the experiments.

A new type of demountable plate static mixer composed of σ-shaped elements was developed, which was designed to perform multi-lamination of two fluids through systematic splitting and inverse recombination. Its flow and mixing characteristics have been investigated by conducting the decolourisation reaction of iodine with sodium thiosulfate and CFD analysis. Visualized mixing patterns demonstrate that splitting and inverse recombination progress as designed in the flow of Re less than 10, where the number of mixing elements required for complete mixing increases with Re. At Re > 10, secondary flows are generated due to the two- and three-dimensionally curved portion in the mixer, distorting the systematic splitting and recombination. They contribute to accelerating mixing progress through the deformation and elongation of the interfaces between the fluids to be mixed. The number of elements for complete mixing becomes maximum at Re of 10-20 and then decreases with further increasing Re. Mixing progress in the flow direction and cross-sectional mixing patterns obtained by CFD analysis show that splitting and inverse recombination do not perform satisfactorily in a shallow channel, which suggests that the aspect ratio of the mixer channel should be set around one if heat transfer is simultaneously taken into account. Based on the CFD velocity data, fluid particles disposed on the inlet cross-section at a time were traced in the mixer with the aspect ratio of one. Distributions of travelling or residence time of fluid particles reveal that the overall flow behaviour in the mixer approaches the plug flow with increasing Re as well as the number of mixing elements. The friction factor, which was obtained by applying the calculated pressure loss to the Fanning's equation, varies in inverse proportion to Re at Re < 10 and its variation becomes smaller with further increasing Re.

application/pdf, We measured the stable isotopic composition of hydrogen (δD) within atmospheric water vapor collected simultaneously at six sites in the vicinity of a lake (Lake Kasumigaura, Eastern Japan) to determine its spatial distribution characteristics and thereby diagnose sources and mixing of atmospheric moisture. The measured spatial distribution of δD showed no relation to distance from the lake, although it showed a correlation with the distribution of the water–vapor mixing ratio Q. For two of the three sampling days, we found a simple two-component (i.e., water vapor transpiring from local land surfaces and pre-existing vapor in the background atmosphere) mixing line in a Keeling plot (i.e., δ − 1/Q diagram). On a third day, however, contributions from lake evaporation were detected in addition to the above components. On this day, lake-derived vapor accounted for approximately 10–20% of atmospheric water vapor at the sites located leeward of the lake. The observed differences in mixing patterns among sampling days can be explained by a simple atmospheric moisture budget. Thus, it is likely that simultaneous isotopic measurements of atmospheric water vapor at multiple locations with aid of Keeling plot are capable of giving us useful information in diagnosing the sources and mixing pattern of the vapor.

The spatial and temporal variations of elemental and isotopic Sr in the Mississippi River (MR) mixing zone are examined in an attempt to address the extent to which estuarine environments modify the fluvial Sr flux on its way to the ocean. We collected samples from the MR delta and its outflow region during four cruises that took place from 1999 to 2002. MR discharge varied from about 7600–30,600 m3 s− 1. Mixing patterns revealed minimal non-conservative behavior of Sr in the dissolved pool. Monthly measurements of the Lower MR at an anchored site during 2000 shows that Sr input to the Gulf of the Mexico from the MR varies temporally in both elemental concentration and isotopic composition, and that the flux of Sr is largely a function of water discharge. The extent of the non-conservative geochemical behavior of Sr does not compromise the use of Sr isotope ratios for stratigraphic dating purposes.

A unique high-temperature apparatus was developed to trigger chaotic mixing at high-temperature (up to 1800 °C). This new apparatus, which we term Chaotic Magma Mixing Apparatus (COMMA), is designed to carry out experiments with high-temperature and high-viscosity (up to 10(6) Pa s) natural silicate melts. This instrument allows us to follow in time and space the evolution of the mixing process and the associated modulation of chemical composition. This is essential to understand the dynamics of magma mixing and related chemical exchanges. The COMMA device is tested by mixing natural melts from Aeolian Islands (Italy). The experiment was performed at 1180 °C using shoshonite and rhyolite melts, resulting in a viscosity ratio of more than three orders of magnitude. This viscosity ratio is close to the maximum possible ratio of viscosity between high-temperature natural silicate melts. Results indicate that the generated mixing structures are topologically identical to those observed in natural volcanic rocks highlighting the enormous potential of the COMMA to replicate, as a first approximation, the same mixing patterns observed in the natural environment. COMMA can be used to investigate in detail the space and time development of magma mixing providing information about this fundamental petrological and volcanological process that would be impossible to investigate by direct observations. Among the potentials of this new experimental device is the construction of empirical relationships relating the mixing time, obtained through experimental time series, and chemical exchanges between the melts to constrain the mixing-to-eruption time of volcanic systems, a fundamental topic in volcanic hazard assessment.

This paper is concerned with the mixing and residence time distribution behaviour of an experimental electrically enhanced column contactor in which electrically charged drops of water were fed into an organic liquid phase of sunflower oil across which a non-linear electrical field was maintained. The effects of electrical field strength upon mixing in the continuous phase were determined and a significant increase in mixing was observed as the field strength was increased. A quantitative theoretical development describing the observed behaviour is also presented. The mixing is described by simultaneous consideration of the movement of the drop phase and the continuous liquid phase. The drop motion, after formation at the charged nozzle and during the subsequent trajectory motion under the influence of the non-linear electric field, is analysed. The interaction between the drop motion and the velocity field of the continuous phase is thus described. The paper describes theoretical prediction of the interactions between charged drops and the electrodes. These interactions can exert a strong influence on the overall residence time of drops passing through the column, and potentially on the velocity profile of the continuous phase. Description of both sets of interactions is used to predict mixing patterns in the continuous phase as a function of applied field strength. The predicted mixing patterns are compared with experimentally recorded images of tracer movement in the continuous phase obtained under the same conditions. The calculated patterns compare favourably with those measured by experiment. The modelling methodology was used afterwards with success for predicting the residence time distribution in the form of the normalised concentration (proportional to the exit function) versus time.

The autoignition behaviour of hydrogen in a turbulent co-flow of heated air at atmospheric pressures was examined experimentally. Turbulent flows of air, with temperatures up to 1015 K and velocities up to 35 m/s, were set up in an optically accessible tube of circular cross-section. The fuel, pure or diluted with nitrogen, was continuously injected along the centreline of the tube, with velocities equal to or larger than those of the air, and temperatures that were lower. The fuel mixing patterns hence obtained were akin to diffusion from a point source or to an axisymmetric jet within a co-flow. For a relatively wide range of temperatures and velocities, a statistically steady condition of randomly occurring autoignition kernels was observed, whose axial location was measured by hydroxyl radical chemiluminescence. The probability density function of autoignition location was sharp enough to allow the accurate determination of a minimum autoignition length and smooth enough to allow the mean and variance to be calculated. It was found that both autoignition lengths increased with the air velocity and decreased with the air temperature, as expected. An estimate of the residence time up to autoignition showed that the autoignition delay times increased with the air velocity for the same temperature, suggesting a delaying effect of the turbulence on autoignition. The connection between these findings and previous experimental and direct numerical simulation studies is discussed.

We tested the hypothesis that the growth rate of Anabaena circinalis, under diurnally stratified conditions, would increase as flotation velocity increased owing to higher light availability. An in situ experiment compared the growth of diurnally stratified populations of A. circinalis with flotation velocities of 0.5 and 1.0 in h -1 , with neutrally buoyant populations that were exposed to either mixed or persistently stratified conditions. The experiment was conducted in the turbid lower Murray River in South Australia (vertical attenuation coefficient = 4.52 ± 0.36 m -1 ). To represent the mixing patterns, A. circinalis was contained in diffusion chambers that were moved to different positions in the water column throughout the day. Diurnal populations with flotation velocities of 1.0 and 0.5 m h -1 grew at 0.23 ± 0.01 and 0.15 ± 0.01 day -1 , respectively. Mixed populations grew at 0.19 ± 0.01 day -1 , whereas persistently stratified populations grew at 0.43 ± 0.01 day -1 . Results were used to extend a model that predicts growth of A. circinalis when exposed to the different mixing patterns. The model showed that blooms are unlikely to be formed when the period of diurnal stratification is 1 week, flotation velocity is important and a bloom may form depending on values assigned to the growth period and maximum mixed depth (Z m ).

The mixing performance of a batch stirred tank with four Ekato Intermig® impellers is investigated in this paper by experimental and computational methods. We considered three impeller speeds corresponding to Reynolds numbers 37, 50 and 100, all in the laminar regime. For the purposes of model development and flow validation, Newtonian rheology is assumed, where the fluid density and viscosity is set to 1247.6 kg/m 3 and 0.4 kg/(m s) , respectively. The computed velocity field and mixing patterns are validated using Particle Image Velocimetry, acid-base visualization experiments and Planar Laser-Induced Fluorescence. All three techniques reveal excellent agreements between the experiments and computations. Also, detailed Lagrangian analysis of mixing, using particle tracking and stretching simulations, is presented for two flowrates in the laminar regime. It is shown that severe compartmentalization exists in the vessel and transport in the axial direction is very slow. Characterization of local micromixing intensities is presented by computing the distribution of intermaterial area density and striation thickness distribution (STD) from the stretching field. It is found that the STDs at both flowrates are identical despite significant differences in the stretching field, suggesting that at low stirring rates micromixing performance is independent of agitation speed.

We report a laser-induced fluorescence (LIF) experimental method that is able to quantify dye concentration in a laminar three-dimensional flow. The geometry of interest is a stirred tank reactor agitated by three impellers. The method is employed to reveal the spatial structure of the evolving mixing patterns and its statistical properties. For chaotic flow conditions, the statistics of the passive scalar reveals a non-Gaussian concentration probability density function with an exponential tail. We find that the concentration patterns, once established, do not change with time; i.e., they are self-similar. This LIF method also provides detailed flow structures that are of importance to the study of mixing. Flow structure varies considerably as a function of Reynolds number (Re). However, we find that the mixing patterns are structurally invariant and they slowly decay as a result of a nonequilibrium state between stretching and diffusion.

The purpose of this research was to further investigate the hydrodynamics of the United States Pharmacopeia (USP) paddle dissolution apparatus using a previously generated computational fluid dynamics (CFD) model. The influence of paddle rotational speed on the hydrodynamics in the dissolution vessel was simulated. The maximum velocity magnitude for axial and tangential velocities at different locations in the vessel was found to increase linearly with the paddle rotational speed. Path-lines of fluid mixing, which were examined from a central region at the base of the vessel, did not reveal a region of poor mixing between the upper cylindrical and lower hemispherical volumes, as previously speculated. Considerable differences in the resulting flow patterns were observed for paddle rotational speeds between 25 and 150 rpm. The approximate time required to achieve complete mixing varied between 2 to 5 seconds at 150 rpm and 40 to 60 seconds at 25 rpm, although complete mixing was achievable for each speed examined. An analysis of CFD-generated velocities above the top surface of a cylindrical compact positioned at the base of the vessel, below the center of the rotating paddle, revealed that the fluid in this region was undergoing solid body rotation. An examination of the velocity boundary layers adjacent to the curved surface of the compact revealed large peaks in the shear rates for a region within ~3 mm from the base of the compact, consistent with a "grooving" effect, which had been previously seen on the surface of compacts following dissolution, associated with a higher dissolution rate in this region.

Anabaena circinalis is common in the lower Murray River, Australia, and may compromise water quality due to the release of toxins. The water is turbid and thermal structure may significantly affect light availability. An in situ experiment was designed to represent complete mixing, diurnal stratification and persistent stratification and test the effect on growth of A. circinalis. To represent the mixing treatments, cells were incubated in diffusion chambers that were adjusted to different positions in the water-column throughout the day. Populations exposed to persistent stratification over six days grew significantly faster than the other treatments at a rate of 0.65 day−1. However, growth of the diurnally stratified populations was slower than (0.28 day−1), or similar to (0.40 day−1) the mixed population (0.40 day−1). Therefore, the growth of the subpopulations exposed to the euphotic zone was insufficient to counteract the slow growth of the majority that were confined to darkness during the stratified period. A relationship between growth rate (G) and average daily light dose (I) was constructed and growth rate at optimal light dose (Gmax), slope of linear section of G–I curve (α), and light dose where lines of Gmax and light-limited portion of G–I curve intersect (Ik) were solved as 0.66 day−1, 0.12 day−1 (mol−1 m−2 day−1)−1 and 5.4 mol m−2 day−1, respectively. Using these parameters, a model was developed to predict possible differences in growth between diurnal and mixed populations under varying conditions of vertical light attenuation, mixed depth and incubation time. Copyright © 2003 John Wiley & Sons, Ltd.

To prevent the recurrence of a disastrous eruption of carbon dioxide (CO2) from Lake Nyos, a degassing plan has been set up for the lake. Since there are concerns that the degassing of the lake may reduce the stability of the density stratification, there is an urgent need for a simulation tool to predict the evolution of the lake stratification in different scenarios. This paper describes the development of a numerical model to predict the CO2 and dissolved solids concentrations, and the temperature structure as well as the stability of the water column of Lake Nyos. The model is tested with profiles of CO2 concentrations and temperature taken in the years 1986 to 1996. It reproduces well the general mixing patterns observed in the lake. However, the intensity of the mixing tends to be overestimated in the epilimnion and underestimated in the monimolimnion. The overestimation of the mixing depth in the epilimnion is caused either by the parameterization of the k-epsilon model, or by the uncertainty in the calculation of the surface heat fluxes. The simulated mixing depth is highly sensitive to the surface heat fluxes, and errors in the mixing depth propagate from one year to the following. A precise simulation of the mixolimnion deepening therefore requires high accuracy in the meteorological forcing and the parameterization of the heat fluxes. Neither the meteorological data nor the formulae for the calculation of the heat fluxes are available with the necessary precision. Consequently, it will be indispensable to consider different forcing scenarios in the safety analysis in order to obtain robust boundary conditions for safe degassing. The input of temperature and CO2 to the lake bottom can be adequately simulated for the years 1986 to 1996 with a constant sublacustrine source of 18 l s−1 with a CO2 concentration of 0.395 mol l−1 and a temperature of 26 °C. The results of this study indicate that the model needs to be calibrated with more detailed field data before using it for its final purpose: the prediction of the stability and the safety of Lake Nyos during the degassing process.

Steady flow and mixing in a model of an "arterialized" vein punctured by a cannula as occurs during hemodialysis has been investigated in vitro. The motivation is that a major cause of vascular access dysfunction is the development of venous stenoses. This phenomenon lacks physiological explanation. However, one may attribute this quick process to the chemical content of the dialyzed blood and its flow near the point of infusion. The interest in mixing of chemical compounds in the dialyzed blood supplied through the cannula is, therefore, genuine due to the clinical impacts of haemodyalysis. We are interested in understanding the mixing of the two streams; namely, the untreated blood through the vein and the treated blood through the cannula. This mixing affects the local pH, which in turn can affect the solubility of several salts used for dialysis. In addition, since the blood contains molecules of widely different diffusivity properties, the local composition of blood near the point of injection is of interest. The hypothesis is that concentration non-uniformities may lead to undesired chemical or bio-chemical reactions leading to the pathological processes in the region around the needle. The mixing of a high Schmidt number substance in the stream entering from the cannula with the base flow in the vein is studied by laser induced fluorescence (LIF). The investigations are performed for a range of typical Reynolds numbers in the cannula and the vein found during hemodialysis. The study shows complicated mixing patterns around the cannula, and that non-uniformities in the blood persist over long distances for the lower flow rates found in vivo. For the higher flow rates, the flow loses its stability and mixing is enhanced. The nature of this instability is shown, and quantitative data of concentration fluctuations are given. We have further considered the effect of rotating the cannula. This leads to a significant change in the mixing process. The significance of the non-uniformities in mixing of solvents in the blood for the development of venous stenoses should be further studied not only in fluid dynamical terms but also in terms of endothelial (cellular) effects. (C) 2002 Published by Elsevier Science Inc. (Less)

The interplay between diffusive and convective mixing processes may have a strong impact upon apparent reaction rates. This paper analyzes the interaction of convection and diffusion mechanisms by considering an infinitely fast irreversible reaction A + B → products, occurring in a two-dimensional chaotic flow. Attention is focused on the geometric properties of mixing patterns and on the overall reactant consumption. We show that the length of the reaction interface undergoes a transition from a kinematics-dominated exponential growth to a persistent oscillatory regime. This regime results from two competing mechanisms, namely, recursive stretching and folding of the interface caused by chaotic advection and merging of contiguous striations patterns owed to diffusive transport. In the case of globally chaotic flows, a singular transition is observed in the scaling of the dominant eigenvalue with the Peclet number. The geometric information arising from the analysis of the reaction interface is also explo...

Flow structures and gas mixing patterns establishing in the freeboard of a bubbling gas-fluidized bed have been investigated by means of a planar laser light scattering (PLLS) technique. Nondiffusive tracing of the flow structures has been accomplished by injection of an aerosol of micrometer-sized scattering particles at a preset axial position in the splash zone of the reactor. A digital image acquisition and analysis technique has been developed and used to characterize the macroscopic and microscopic features of the flow structures. Experiments have been carried out in the freely bubbling regime at gas superficial velocities ranging from incipient fluidization to U/U-mf = 2.6. Bed solids consist of glass beads of two different size ranges belonging to group B of the Geldart classification of powders. Results are analyzed with the aim of determining effective gas dispersion coefficients and characteristic time-scales for gas micromixing in the splash zone as a function of the excess gas superficial velocity.

More than a dozen indoor air quality studies have reported a large discrepancy between concentrations measured by stationary indoor monitors (SIMs) and personal exposure monitors (PEMs). One possible cause of this discrepancy is a source proximity effect, in which pollutant sources close to the respondent cause elevated and highly variable exposures. This paper describes three sets of experiments in a home using real-time measurements to characterize and quantify the proximity effect relative to a fixed distant location analogous to a SIM. In the first set of experiments, using sulfur hexafluoride (SF6) as a continuously emitting tracer pollutant from a point source, measurements of pollutant concentrations were made at different distances from the source under different air exchange rates and source strengths. A second set of experiments used a continuous point source of carbon monoxide (CO) tracer pollutant and an array of high time resolution monitors to collect simultaneous concentration readings at different locations in the room. A third set of experiments measured particle count density and particle-bound polycyclic aromatic hydrocarbon (PAH) concentrations emitted from a continuous particle point source (an incense stick) using two particle counters and two PAH monitors, and included human activity periods both before and during the source emission period. Results from the SF6 and CO experiments show that while the source is emitting, a source proximity effect can be seen in the increases in the mean and median and in the variability of concentrations closest to the source, even at a distance of 2.0 m from the source under certain settings of air exchange rate and source strength. CO concentrations at locations near the source were found to be higher and more variable than the predictions of the mass balance model. For particles emitted from the incense source, a source proximity effect was evident for the fine particle sizes (0.3 to 2.5 microm) and particle-bound PAH up to at least 1.0 m from the source. Analysis of spatial and temporal patterns in the data for the three tracer pollutants reveal marked transient elevations of concentrations as seen by the monitor, referred to as "microplumes," particularly at locations close to the source. Mixing patterns in the room show complex patterns and directional effects, as evidenced by the variable intensity of the microplume activity at different locations. By characterizing the spatial and temporal variability of pollutant concentrations in the home, the proximity effect can be quantified, leading to improved indoor monitoring designs and models of human exposure to air pollutants.

The effects of flow perturbations on the extent of mixing vs. time are examined in a cylindrical vessel partially filled with uniform-sized powder mixture. Mixtures produced by pure rotational motion are compared to those undergoing rotational motion supplemented by rocking. Characterization of the mixing experiments is conducted using solidification and image analysis methods, affording visual inspection of the internal mixing patterns and evaluation of the composition distributions. Pure rotational motion causes slow axial mixing. When rotational motion is supplemented by a rocking perturbation, mixing time is greatly accelerated.

An 8-plane 16-sensor ring electrical resistance tomography (ERT) system was designed and installed within a 1.5-m-dia. plant-scale stirred uessel. Results are reported for the unsteady dynamic macromixing of miscible liquids following a pulse addition of brine tracer. Acquired data, afier reconstruction, is conveniently represented as a stack of 2-D tomograms and 3-D solid body isosurjaces, thereby providing an equiualent of medical whole-body scanning for a chemical process unit. The results demonstrate the ability of ERT to distinguish the different mixing patterns from two types of impeller in 3-D and to monitor plant-scale miscible liquid mixing processes aperimentally, with good resolution in both space and time.

In this work, a model for simultaneous optimization of mixing patterns and feed distribution in LDPE (Low Density PolyEthylene) reactors is presented. The formulation is based on a a novel technique for optimizing mixing patterns in chemical reactors, resulting in an optimal control formulation which is solved as an NLP. The kinetic model is based on representing the molecular weight distribution by statistical moments.