Mixing Cell Research Articles

Vapor–Liquid Equilibrium, Excess Molar Enthalpies, and Excess Molar Volumes of Binary Mixtures Containing Methyl Isobutyl Ketone (MIBK) and 2-Butanol, tert-Pentanol, or 2-Ethyl-1-hexanol

Phase equilibrium and calorimetric measurements provide complementary data that are vital for process models. The combined use of vapor–liquid equilibrium (VLE) data and excess enthalpies (HE) makes the thermodynamic model more reliable in extrapolation outside the conditions of the measurement. This is important during the tight time schedule of process development. In this work, phase equilibrium and excess enthalpies of binary mixtures were measured by using three apparatuses. Two types of VLE runs were conducted by using a circulation still of the Yerazunis-type and by using Agilent headspace sampler with a gas chromatograph (HS-GC). A SETARAM C80 calorimeter equipped with a flow mixing cells was taken into use for excess enthalpy measurements. New data of phase equilibrium, excess molar enthalpy, and excess molar volume were obtained for industrially relevant binary mixtures of methyl isobutyl ketone (MIBK) with alcohols (2-butanol, tert-pentanol, 2-ethyl-1-hexanol). Excess enthalpy data at 298.15 K are well in line with equilibrium data obtained in the range of (294 to 368) K. Azeotropic behavior was observed in the MIBK + tert-pentanol system. The experimental data were used for the optimization of Wilson and Redlich–Kister equation parameters.

Dual-tracer, non-equilibrium mixing cell modelling and uncertainty analysis for unsaturated bromide and chloride transport

A model is presented for simulating one-dimensional advective dispersive solute transport in the vadose zone. The finite-volume, mixing-cell model uses drainage flux intervals as the index variable, which are calculated by a soil water balance model. The modelling approach considers solute transport from two different regions as well as a slow and a fast transport domain in each region as parallel transport processes. The model is applied to breakthrough curves of Cl− and Br− measured at different locations and different depths in the volcanic vadose zone of the Tutaeuaua subcatchment of Lake Taupo, New Zealand, following a dual tracer application. Estimates of transport parameter and model predictive uncertainty were derived using the differential evolution adaptive metropolis, DREAMZS adaptive Markov chain Monte Carlo algorithm, a formal Bayesian likelihood function, observed leachate volumes, and Cl− breakthrough curves. The model was subsequently evaluated using Br− breakthrough curves from the dual tracer experiment and a previously conducted Br− tracer-only experiment. Uncertainty bounds derived by this MCMC method simultaneously capture the observed Br− and Cl− breakthrough curves and corresponding drainage volumes. Results suggest that the slow transport domain properties are relatively similar for different locations in the vadose zone and that the variability in contaminant fluxes is predominantly driven by structural variability of the vadose zone causing lateral flow.

What is Janssen's length doing in an agglomerator?

Abstract In a wet agglomeration process occuring in a low shear mixer, the function of the blade is to promote emergence of stable agglomerates and to homogenize the liquid sprayed on the powder surface. The design of the bowl and the mixing blade along with the values of the process parameters (load, rotation speed, etc.) contribute to the agglomeration mechanisms. In this work a preliminary approach is conducted to study the mechanical input during agglomeration through the analysis of static and dynamic stress distributions (by force measurements) and particles' motions (by visualizations through a transparent wall) in the powder bed, using an experimental mixing cell. A characteristic depth is identified as a representative parameter of the static state of a laterally confined semolina bed. This characteristic depth is implied when the granular medium is submitted to a vertical mechanical stress. For wet agglomerates, the static distribution of vertical stresses can be approximated by the Janssen's model. Under dynamic conditions, a correlation is found between the mechanical resistance of agglomerates and the maximum vertical stress according to the water content. In the context of wet agglomeration in a mixing device, these results allow to consider the role of the characteristic length in the mixing bowl.

Effect of storage time on the pressure oxidation enthalpy of pyrite

The information on heat of oxidation–reduction reactions is important for the heat balance and optimization of the autoclave design in the hydrometallurgical industry in ore processing. Pyrite (FeS2) is a gangue mineral that presents with nickel-containing pentlandite, and copper-containing chalcopyrite minerals. The presence of pyrite impacts to the overall heat of leaching process. This study has been performed on a differential scanning calorimeter (DSC80, Setaram) with a commercial mixing cell to study the thermal behaviour of pure pyrite FeS2 (Valdenegrillos, Spain) mineral particles during oxidative pressure leaching at 150 °C and partial oxygen pressure of 3.4 MPa. A calorimetric method for determining the enthalpy of leaching of sulphide minerals at high temperatures and oxygen pressures has been used to evaluate the enthalpies of oxidation of freshly ground pyrite and pyrite stored for a year in contact with air (stored pyrite) under conditions relevant to pressure oxidation operations. Ground pyrite stored over time has long since been known to result in greater heat evolution during oxidative leaching. A likely mechanism for this phenomenon was uncovered: formation of ferrous sulphate and sulphuric acid during storage in contact with air influencing greater heat evolution at the outset of the reaction. Two mass loss steps on TG curve of stored pyrite, attributed to the elimination of atmospheric moisture and H2O molecule from FeSO4·H2O, is absent on TG curve of freshly ground pyrite.

High pressure rheometer for in situ formation and characterization of methane hydrates

We present a novel setup for a high pressure rheometer operating with concentric cylinders geometry for in situ studies of hydrate formation and rheological characterization. The apparatus uses an external high pressure mixing cell to saturate water-in-oil emulsions with methane gas. The capability of mixing combined with a true rheometer design make this apparatus unique in terms of setup and sample formation. We have used the apparatus to form gas hydrates in situ from water-in-oil emulsions and characterize suspension rheological properties such as yield stress and shear-thinning behavior.

Paste Residence Time in a Spouted Bed Dryer. IV: Effect of the Inert Particle Size Distribution

The residence time distribution and mean residence time of a 10% sodium bicarbonate solution that is dried in a conventional spouted bed with inert bodies were measured with the stimulus-response method. Methylene blue was used as a chemical tracer, and the effects of the paste feed mode, size distribution of the inert bodies, and mean particle size on the residence times and dried powder properties were investigated. The results showed that the residence time distributions could be best reproduced with the perfect mixing cell model or N = 1 for the continuous stirred tank reactor in a series model. The mean residence times ranged from 6.04 to 12.90 min and were significantly affected by the factors studied. Analysis of variance on the experimental data showed that mean residence times were affected by the mean diameter of the inert bodies at a significance level of 1% and by the size distribution at a level of 5%. Moreover, altering the paste feed from dripping to pneumatic atomization affected mean residence time at a 5% significance level. The dried powder characteristics proved to be adequate for further industrial manipulation, as demonstrated by the low moisture content, narrow range of particle size, and good flow properties. The results of this research are significant in the study of the drying of heat-sensitive materials because it shows that by simultaneously changing the size distribution and average size of the inert bodies, the mean residence times of a paste can be reduced by half, thus decreasing losses due to degradation.

Characterizing slurry hydrodynamic transport in a large overflow tubular ball mill by an improved mixing cell model based on tracer response data

Overflow tubular ball mills are depicted by an intrinsic pool of slurry at the toe of the ball charge, which facilitates the discharge of fine progenies (finished product) from the mill. To ensure that adequate slurry removal capacity is achieved while keeping the ball charge well saturated with slurry at all times (for efficient grinding), good knowledge of slurry transport inside the mill is essential. Most existing ball mill simulation models either inadequately account for the continuous exchange of slurry between the ball charge and the slurry pool or do not consider the realities such as back-mixing or bypasses in the system thereby leading to inaccurate prediction of slurry transport. To close that gap, a model is proposed here, in which both axial and radial flow parameters as well as a short-circuit component are incorporated as an improvement to the simple mixing cell model to correctly describe the inherent in-mill slurry transport dynamics. The model fits adequately to the experimental data for all conditions tested. Further, the model results show that the slurry axial back-mixing and the radial exchange rate are both affected by slurry solids concentration and ball load volume. Also, the model reveals that under conditions of low slurry solids concentration (< 37 vol.%), a part of the feed slurry may simply short-circuit to the exit. These results just serve as a priori indication that, having correct knowledge of in-mill slurry transport dynamics would enable mill operational variables to be appropriately tuned to achieve desirable mill behavior that corresponds to maximum milling and energy efficiencies.

Functional genomics unique to week 20 post wounding in the deep cone/fat dome of the Duroc/Yorkshire porcine model of fibroproliferative scarring.

BackgroundHypertrophic scar was first described over 100 years ago; PubMed has more than 1,000 references on the topic. Nevertheless prevention and treatment remains poor, because 1) there has been no validated animal model; 2) human scar tissue, which is impossible to obtain in a controlled manner, has been the only source for study; 3) tissues typically have been homogenized, mixing cell populations; and 4) gene-by-gene studies are incomplete.Methodology/Principal FindingsWe have assembled a system that overcomes these barriers and permits the study of genome-wide gene expression in microanatomical locations, in shallow and deep partial-thickness wounds, and pigmented and non-pigmented skin, using the Duroc(pigmented fibroproliferative)/Yorkshire(non-pigmented non-fibroproliferative) porcine model. We used this system to obtain the differential transcriptome at 1, 2, 3, 12 and 20 weeks post wounding. It is not clear when fibroproliferation begins, but it is fully developed in humans and the Duroc breed at 20 weeks. Therefore we obtained the derivative functional genomics unique to 20 weeks post wounding. We also obtained long-term, forty-six week follow-up with the model.Conclusions/Significance1) The scars are still thick at forty-six weeks post wounding further validating the model. 2) The differential transcriptome provides new insights into the fibroproliferative process as several genes thought fundamental to fibroproliferation are absent and others differentially expressed are newly implicated. 3) The findings in the derivative functional genomics support old concepts, which further validates the model, and suggests new avenues for reductionist exploration. In the future, these findings will be searched for directed networks likely involved in cutaneous fibroproliferation. These clues may lead to a better understanding of the systems biology of cutaneous fibroproliferation, and ultimately prevention and treatment of hypertrophic scarring.

Dynamic Analysis of Drug-Induced Cytotoxicity Using Chip-Based Dielectrophoretic Cell Immobilization Technology

Quantification of programmed and accidental cell death provides useful end-points for the anticancer drug efficacy assessment. Cell death is, however, a stochastic process. Therefore, the opportunity to dynamically quantify individual cellular states is advantageous over the commonly employed static, end-point assays. In this work, we describe the development and application of a microfabricated, dielectrophoretic (DEP) cell immobilization platform for the real-time analysis of cancer drug-induced cytotoxicity. Microelectrode arrays were designed to generate weak electro-thermal vortices that support efficient drug mixing and rapid cell immobilization at the delta-shape regions of strong electric field formed between the opposite microelectrodes. We applied this technology to the dynamic analysis of hematopoietic tumor cells that represent a particular challenge for real-time imaging due to their dislodgement during image acquisition. The present study was designed to provide a comprehensive mechanistic rationale for accelerated cell-based assays on DEP chips using real-time labeling with cell permeability markers. In this context, we provide data on the complex behavior of viable vs dying cells in the DEP fields and probe the effects of DEP fields upon cell responses to anticancer drugs and overall bioassay performance. Results indicate that simple DEP cell immobilization technology can be readily applied for the dynamic analysis of investigational drugs in hematopoietic cancer cells. This ability is of particular importance in studying the outcome of patient derived cancer cells, when exposed to therapeutic drugs, as these cells are often rare and difficult to collect, purify and immobilize.

Study on lactose attrition inside the mixing cell of a laser diffraction particle sizer using a novel attrition index

Attrition is the general term that describes the breakdown of crystals due to collisions with each other or some other body, or by a shearing fluid. These interactions produce new crystals from the parent crystals and are likely to be a major source of secondary nucleation in industrial crystallizers. However, these collision interactions are difficult to devolve because they occur simultaneously. This work studies lactose monohydrate attrition within the small sample presentation unit of a laser diffraction particle sizer (Malvern Mastersizer, 2000, UK). Stirrer speed, particle concentration and initial crystal size were varied and particle size distributions (PSDs) were recorded every 2 min for 1 h. From these, three basic attrition mechanisms were recognizable: shattering, chipping and abrasion. The degree of attrition was quantified using indices: the shattering index (SI) and attrition index (AI), which are both typical of literature indices; and the differential attrition index (DAI) proposed here. All indices show similar trends although the DAI is more sensitive to subtle changes in PSDs. Of the three variables studied, particle concentration least affects attrition. Experiments with low initial crystal size and low impeller speed produce fines in the < 10-μm range, indicating that abrasion is the dominant attrition mechanism. In contrast, when the initial crystal size is large and impeller speed is high, crystal fragments are produced across all size ranges indicating that all three attrition mechanisms occur. This variation across the results indicates that the three mechanisms are differentiated by the collision energy intensity, which is a function of both crystal size and impact velocity. These experimental observations were found to closely follow theoretical predictions for crystal–impeller impacts (Synowiec et al. Chem. Eng. Sci. 48 (1993) 3485–3495 and Mersmann et al. Chem Eng & Technol. 11 (1988) 80–88). When applied to industrial crystallizers, this work demonstrates that careful selection of pumps and impellers is needed to control secondary nucleation.

Regional transport modelling for nitrate trend assessment and forecasting in a chalk aquifer

Regional degradation of groundwater resources by nitrate has become one of the main challenges for water managers worldwide. Regulations have been defined to reverse observed nitrate trends in groundwater bodies, such as the Water Framework Directive and the Groundwater Daughter Directive in the European Union. In such a context, one of the main challenges remains to develop efficient approaches for groundwater quality assessment at regional scale, including quantitative numerical modelling, as a decision support for groundwater management. A new approach combining the use of environmental tracers and the innovative ‘Hybrid Finite Element Mixing Cell’ (HFEMC) modelling technique is developed to study and forecast the groundwater quality at the regional scale, with an application to a regional chalk aquifer in the Geer basin in Belgium. Tritium data and nitrate time series are used to produce a conceptual model for regional groundwater flow and contaminant transport in the combined unsaturated and saturated zones of the chalk aquifer. This shows that the spatial distribution of the contamination in the Geer basin is essentially linked to the hydrodynamic conditions prevailing in the basin, more precisely to groundwater age and mixing and not to the spatial patterns of land use or local hydrodispersive processes. A three-dimensional regional scale groundwater flow and solute transport model is developed. It is able to reproduce the spatial patterns of tritium and nitrate and the observed nitrate trends in the chalk aquifer and it is used to predict the evolution of nitrate concentrations in the basin. The modelling application shows that the global inertia of groundwater quality is strong in the basin and trend reversal is not expected to occur before the 2015 deadline fixed by the European Water Framework Directive. The expected time required for trend reversal ranges between 5 and more than 50 years, depending on the location in the basin and the expected reduction in nitrate application. To reach a good chemical status, nitrate concentrations in the infiltrating water should be reduced as soon as possible below 50 mg/l; however, even in that case, more than 50 years is needed to fully reverse upward trends.

Application of the Hybrid Finite Element Mixing Cell method to an abandoned coalfield in Belgium

The Hybrid Finite Element Mixing Cell (HFEMC) method is a flexible modelling technique particularly suited to mining problems. The principle of this method is to subdivide the modelled zone into several sub-domains and to select a specific equation, ranging from the simple linear reservoir equation to the groundwater flow in porous media equation, to model groundwater flow in each sub-domain. The model can be run in transient conditions, which makes it a useful tool for managing mine closure post-issues such as groundwater rebound and water inrushes. The application of the HFEMC method to an abandoned underground coal mine near the city of Liege (Belgium) is presented. The case study zone has been discretised taking advantage of the flexibility of the method. Then, the model has been calibrated in transient conditions based on both hydraulic head and water discharge rate observation and an uncertainty analysis has been performed. Finally, the calibrated model has been used to run several scenarios in order to assess the impacts of possible future phenomena on the hydraulic heads and the water discharge rates. Among others, the simulation of an intense rainfall event shows a quick and strong increase in hydraulic heads in some zones coupled with an increase in associated water discharge rates. This could lead to stability problems in local hill slopes. These predictions will help managing and predicting mine water problems in this complex mining system.

Modeling of Nonequilibrium Bromide Transport through Alluvial Gravel Vadose Zones

Understanding solute transport and flux through the vadose zone is important for predicting potential contaminant loading to groundwater systems. Two dual‐permeability models: mixing cell (MC) and HYDRUS 1D (H1DDP) were used to simulate long‐term nonequilibrium Br− leaching using data derived from suction cup samples at two field sites (sampled to 7‐ and 4‐m depths) on the Canterbury Plains, New Zealand. Effective model parameters were derived by inverse methods to represent average transport processes through the heterogeneous profiles. Suction cup samples indicated rapid initial movement of solute through the profiles followed by a long tail. The “management type” MC model results were comparable to the more complex HYDRUS model, providing similar overall fits to the observed data (similar RMSE ∼ 0.05–0.1). Modeling indicated that macropore flux was significant in transporting solute through the profile (MC range 5–59%; H1DDP range 15–54% of total fluxes) and simulations of cumulative fluxes from both models were similar. The MC model results indicated macropore transporting water contents of ∼0.003 (v/v) and matrix domain transporting water contents of around 0.1 to 0.15 (v/v) for the two field sites. These estimates suggest that only 3 mm of bulk drainage is required to transport solutes 1 m through the macropore domain, whereas approximately 100 to 150 mm of drainage is required to transport solutes the same distance through the matrix domain. More accurate representation of boundary conditions, texture spatial distributions, and hydraulic interactions is important for obtaining a better understanding of flux dynamics in future studies.

Environmental exposure of 2LiBH4+MgH2 using empirical and theoretical thermodynamics

It has been shown that the consequence of environmental exposure can be qualitatively predicted by modeling the heat generated as a result of environmental exposure of reactive hydrides along with heat loss associated with conduction and convection with the ambient surroundings. To this end, an idealized finite volume model was developed to represent the behavior of dispersed hydride from a breached system. Semi-empirical thermodynamic calculations and substantiating calorimetric experiments were performed in order to quantify the energy released, energy release rates and to quantify the reaction products resulting from water and air exposure of a lithium borohydride and magnesium hydride combination. The hydrides, LiBH4 and MgH2, were studied in a 2:1 “destabilized” mixture which has been demonstrated to be reversible. Liquid water hydrolysis reactions were performed in a Calvet calorimeter equipped with a mixing cell using pH-neutral water. Water vapor and gaseous oxygen reactivity measurements were performed at varying relative humidities and temperatures by modifying the calorimeter and utilizing a gas circulating flow cell apparatus. The results of these calorimetric measurements were used to develop quantitative kinetic expressions for hydrolysis and air oxidation in these systems. Thermodynamic parameters obtained from these tests were then incorporated into a computational fluid dynamics model to predict both the hydrogen generation rates and concentrations along with localized temperature distributions. The results of these numerical simulations can be used to predict ignition events and the resultant conclusions will be discussed.

Physical constraints in the deep hypolimnion of a subalpine lake driving planktonicBacteriaandArchaeadistribution

The study of the hydrodynamics of the hypolimnion of a deep holo-oligomictic lake (Lake Maggiore, Northern Italy, z max = 370 m) during the last 28 years showed that hypolimnetic waters remained isolated, not exchanging with the mixing zone even in winter when the full overturn conditions are most likely. The thickness of the isolated layer can range from 100 to 300 m. Thus, water masses of variable size reside in the lake for many years, and their physical and chemical conditions remain relatively unaffected by seasonal variability and epilimnetic imputs. In the hypolimnetic waters prokaryote abundance is three times lower than in the mixing layer but cell size is significantly higher. In addition, the relative abundance of Archaea and Crenarchaeota increases with depth in respect to that of Bacteria. The heterogeneous distribution of the two domains within the habitat can be attributed to the existence in the same environment of isolated water masses.

Physical constraints in the deep hypolimnion of a subalpine lake driving planktonic Bacteria and Archaea distribution

The study of the hydrodynamics of the hypolimnion of a deep holo-oligomictic lake (Lake Maggiore, Northern Italy, zmax¼370 m) during the last 28 years showed that hypolimnetic waters remained isolated, not exchanging with the mixing zone even in winter when the full overturn conditions are most likely. The thickness of the isolated layer can range from 100 to 300 m. Thus, water masses of variable size reside in the lake for many years, and their physical and chemical conditions remain relatively unaffected by seasonal variability and epilimnetic imputs. In the hypolimnetic waters prokaryote abundance is three times lower than in the mixing layer but cell size is significantly higher. In addition, the relative abundance of Archaea and Crenarchaeota increases with depth in respect to that of Bacteria. The heterogeneous distribution of the two domains within the habitat can be attributed to the existence in the same environment of isolated water masses.

Analysis of partial suspension in stirred mixing cells using both MRI and ERT

Abstract Magnetic resonance imaging (MRI) and electrical resistance tomography (ERT) are collectively used to examine partial suspension of various glass and nylon particles in the same stirred baffled mixing cell of inner diameter 50 mm. Virtually complete suspension is observed to occur at critical agitation rates considerably lower than expected. Radial and axial particle concentration profiles, as measured using MRI and ERT, compare reasonably well. The higher resolution of MRI is able to detect concentration variations adjacent to the vessel wall whilst fillet formation of unsuspended solids is imaged at the base of the cell. To the best of our knowledge, this study represents the first direct comparison of MRI against ERT.

Clinical Application by Flow Microcalorimeter Mixing Cell

Clinical Application by Flow Microcalorimeter Mixing Cell

Heats of Mixing Using an Isothermal Titration Calorimeter: Associated Thermal Effects

The correct determination of the energy generated or absorbed in the sample cell of an Isothermal Titration Calorimeter (ITC) requires a thorough analysis of the calorimetric signal. This means the identification and quantification of any thermal effect inherent to the working method. In this work, it is carried out a review on several thermal effects, studied by us in previous work, and which appear when an ITC is used for measuring the heats of mixing of liquids in a continuous mode. These effects are due to: (i) the difference between the temperature of the injected liquid and the temperature of the mixture during the mixing process, (ii) the increase of the liquid volume located in the mixing cell and (iii) the stirring velocity. Besides, methods for the identification and quantification of the mentioned effects are suggested.

Ungauged catchment contributions to Lake Tana's water balance

AbstractLake Tana's flow system is governed by four main components: the inflow from surrounding river catchments into the lake, the outflow at Bahir Dar through the Blue Nile, the direct rainfall on the lake and the direct evaporation from the lake. While recent studies applied simple pragmatic approaches to estimate runoff from ungauged catchments, here emphasis is placed on more advanced approaches based on regionalization and spatial proximity principles. In the regionalization approach, model parameters of the conceptual HBV (Hydrologiska Byråns Vattenbalansavdelning) rainfall‐runoff modelling of gauged catchments are transferred to ungauged catchments to allow runoff simulation. Parameter transfer was attempted through regression, proximity procedures and catchment size. This yielded 42, 47 and 46%, respectively, of the total river inflow for the three procedures. Lake areal rainfall is estimated by interpolation of the rain gauges around the lake, open water evaporation is estimated by the Penman‐combination equation while observed inflows and outflow data are directly used in the lake water balance. The water balance closure term was established by comparing the measured lake levels with the calculated levels. Results show that runoff from ungauged catchments is around 880 mm per year for the simulation period 1995–2001 with a water balance closure error of 5%. In addition, use is made of river and lake water chemistry to arrive at an estimate of the unknown inflow and outflow components through the mixing cell approach. The results obtained with this method also provide independent information with regard to the errors in the individual water balance components. Copyright © 2009 John Wiley &amp; Sons, Ltd.