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Mixture Composition (mixture + composition)

Distribution by Scientific Domains

Engineering	50%
Chemistry	25%
Polymers and Materials Science	12%

Selected Abstracts

Effects of dilution on the exposure in sediment toxicity tests,buffering of freely dissolved concentrations and changes in mixture composition

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2007
Thomas L. ter Laak
Abstract Some sediment toxicity tests, such as the Microtox® test, are conducted by diluting either contaminated sediment or an aqueous phase with clean water. The present study aims to clarify how the dilution procedure affects the exposure of organisms. It is shown that freely dissolved concentrations of hydrophobic compounds are buffered by desorption from the sediment matrix when sediment is diluted with water. The buffering depends on the properties of the sediment matrix and contaminant. Consequently, the composition of a contaminant mixture changes with dilution, and the exposure in a sediment dilution toxicity test is poorly defined. This questions the application and subsequent assessments of such tests. Additionally, the often-observed higher toxicity in sediment dilution tests relative to elutriate dilution tests is not sufficient to claim direct contact exposure, because the enhanced sensitivity in sediment dilution tests also can be explained by buffering from the sediment matrix. In applying these tests, one should be aware of the fundamental differences between the sediment dilution strategy and the dilution of an aqueous phase and of the consequences it has for the outcome of the test. [source]

Comparison of low temperature mixed refrigerant cycles for separation systems

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2009
M. Mafi
Abstract Numerous mixed refrigerant cycles (MRCs) were developed in the past several decades in different applications. In this paper, two sets of low temperature MRCs are developed and simulated for a typical olefin plant utilizing a mixture of methane, ethane, propane and nitrogen as cycle working fluid to replace the pure ethylene refrigeration cycle that is used in conjunction with propylene refrigeration cycle in conventional plants. The key parameters of the cycles including mixture compositions and operating pressure levels are optimized to meet the objective of minimum shaftwork in compressor. The results show that different cycle configuration has different optimal mixture composition and low and high operating pressures. The results of exergy analysis reveal that the main location of the exergy loss in the cycles is the heat exchanger system. Also, the Carnot factor versus heat flow diagram is provided to identify the distribution of inefficiencies in the heat exchangers for each cycle. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system using the optimal working fluid mixture composition, optimal high and low operating pressures and optimal arrangement of the cycle components. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Behaviour of refrigerant mixtures with gas/liquid injection

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2003
Samuel M. Sami
Abstract In this paper, the impact of gas/liquid injection on the behaviour of new alternative refrigerant mixtures such as; R-410A, R-507, R-407C, and R-404A are discussed, analysed and presented. The test results were obtained using an air,source heat pump set up with enhanced surface tubing heat exchanger under various gas/liquid injection ratios. Performance tests were conducted according to the ARI/ASHRAE Standards. The performance data demonstrated that as gas/liquid injection increases compressor head pressure and discharge temperature decrease and this has a positive effect in protecting the compressor. The effect of gas/liquid injection on mixture behaviour varies from mixture to another depending upon the mixture composition. Furthermore, hot gas injection appears to have a significant and positive influence on the COP. The performance of refrigerants R-407C and R-404A has been enhanced with 5% gas injection and mix of gas and liquid 5% injection, respectively. The data presented in these figures also show that other hot gas injection ratios and gas/liquid mix degrade the heat exchanger performance. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Mechanistic Insights into Copper(I)-Catalyzed Azide-Alkyne Cycloadditions using Continuous Flow Conditions

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010
Michael Fuchs
Abstract The copper-catalyzed azide-alkyne cycloaddition (CuAAC, "click chemistry") was studied employing copper-in-charcoal (Cu/C) and a variety of copper metal sources as "heterogeneous" catalysts. The type and pretreatment conditions of the different copper sources on the CuAAC were investigated. In addition, the effect of copper leaching from the catalyst over time and in dependence on the reaction mixture composition was studied by ICP-MS analysis in the continuous flow mode. These investigations confirm a "homogeneous" mechanism and suggest surface layer copper(I) oxide as the catalytically active species in CuAAC chemistry involving zerovalent copper metal. [source]

Aromatic nitro substitution reaction between 4-nitro- N - n -butyl-1,8-naphthalimide and n -heptanethiol in water,methanol binary mixtures

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2009
Eduardo Rezende Triboni
Abstract The second-order rate constants of thiolysis by n -heptanethiol on 4-nitro- N - n -butyl-1,8-naphthalimide (4NBN) are strongly affected by the water,methanol binary mixture composition reaching its maximum at around 50% mole fraction. In parallel solvent effects on 4NBN absorption molar extinction coefficient also shows a maximum at this composition region. From the spectroscopic study of reactant and product and the known H-bond capacity of the mixture a rationalization that involves specific solvent H-donor interaction with the nitro group is proposed to explain the kinetic data. Present findings also show a convenient methodology to obtain strongly fluorescent imides, valuable for peptide and analogs labeling as well as for thio-naphthalimide derivatives preparations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Specific and non-specific solvent effects on aromatic nucleophilic substitution.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2002
6-dinitrobenzene, Kinetics of the reaction of 1-fluoro-, homopiperidine in binary solvent mixtures
Abstract This paper presents a comparative study of the solvent effects on the kinetics of the reactions between 1-fluoro-2,6-dinitrobenzene and hexahydro-1H -azepine in ethyl acetate,+,chloroform or acetonitrile and acetonitrile,+,chloroform binary solvent mixtures. The purpose was to asses the contribution of each molecular-microscopic solvent property to the overall solvation effect of the reaction critical state. The influence of the dipolarity/polarizability, hydrogen-bond donor acidity and hydrogen-bond acceptor basicity of the solvent mixtures on the reaction rate was analyzed by the application of the multiparametric approach of Kamlet, Abboud and Taft. The evaluation of the correlation coefficients shows that the solvation effects are dominated by the non-specific interactions. Moreover, the incidence of the hydrogen-bond acceptor solvent ability is more important than that corresponding to the hydrogen-bond donor character, except for the reactions that manifest kinetic retarding effects. The influence of the solvation effects on the base catalysis was analyzed, describing the response patterns of the partial rate coefficients to the mixture composition and also to each solvent property. The application of a preferential solvation model to the kinetic results yields information on the preferential solvation of the reaction critical state by any of the pure solvents, or by the hydrogen-bonded complexed media. Copyright © 2002 John Wiley & Sons, Ltd. [source]

The interrelation of changes in oxygen content and product quality in modified atmosphere packages of peanuts

PACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2001
Marzena Ucherek
Abstract The aim of this work was to examine the effect of changes in oxygen content in different types of packages for snacks (multilayer laminated materials, cans) and analyse the changes in the sensorial and physicochemical characteristics of the stored products. Roasted and salted peanuts produced by one of the well-known companies, packed in modified atmosphere packages (MAP) were the object of this investigation. The interdependence of the changes in oxygen content and product quality was examined in relation to the storage period and type of package used. From the results it can be said that changes in oxygen content in packages of peanuts produce similar effects irrespective of the packaging material used. The correlation observed during storage of peanuts, between changes in oxygen content in different packaging materials and changes of the separate sensorial and physicochemical parameters of the product, especially of the peroxide value, may be a basis for validity forecasting and determination of the optimum composition of gas mixture. This study indicates that evaluation of the quality of packages integrally related to their content should consider both product examination and the package and gas mixture composition, as there may exist an interdependence between quality features of the product and oxygen content in a package. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Heating rate effects on the TL characteristics of hot filament CVD diamond film

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010
E. Cruz-Zaragoza
Abstract The thermoluminescence (TL) glow curve of polycrystalline chemically vapor deposited (CVD) diamond is strongly dependent on the heating rate used. In the present work, we report results about the heating rate effects on a 500,µm hot filament (HF) CVD diamond film grown on silicon substrate using a precursor gas mixture composition of CH4(5,sccm),CO(10,sccm),H2(400,sccm). The irradiations were performed with 60Co source. The TL measurements were carried out at different heating rates in the 2,30,K/s range. As the heating rate increases, the maximum TL peak intensity decreases and shifts to higher temperature. The shift was from 578 to 669,K for heating rates of 2 and 30,K/s, respectively. The kinetics parameter and its dependence on the heating rate were evaluated using the Chen's peak shape method and a computerized glow curve deconvolution (CGCD) method. [source]

Structured Ti/Hydrocarbon Plasma Polymer Nanocomposites Produced By Magnetron Sputtering with Glancing Angle Deposition

PLASMA PROCESSES AND POLYMERS, Issue 1 2010
Andrei Choukourov
Abstract Structured Ti/hydrocarbon plasma polymer nanocomposite films are deposited at a glancing angle by magnetron sputtering of titanium in an Ar/hexane mixture and by sequential magnetron sputtering of titanium and polypropylene. The surface chemistry of such films is tuned by adjusting the gas mixture composition. The structure of the substrate may convert the morphology of organic films deposited at a glancing angle from continuous to nanostructured thin films. [source]

Mathematical model for mixing index in gas,solid fluidized bed: an analysis

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010
Abanti Sahoo
Abstract An available theoretical model for mixing index in gas-solid fluidized bed has been analyzed for further modification and improvement. Assumption of 50% bed material moving in the upward direction and rest 50% in the downward direction considered for the above model (the counter-flow circulation model) has been analyzed for optimum result. A computer program was run for different bed conditions by varying operating parameters, namely, the mixture composition, fractions of bed materials, minimum fluidization velocity of the jetsam particles and that of the bed materials (i.e. mixture of the jetsam and the flotsam particles). The developed model was solved by finite difference (central differencing). Fraction of the bed material moving in the upward direction was varied from 0 to 100% and the minimum fluidization velocity was varied within the Umf of the flotsam to that of the jetsam particles (i.e. 0.465,1.0335 m/s). Optimum fraction of bed materials with respect to its distribution (as per the earlier proposed model) in the upward and downward streams during the fluidization process was found to be 20 and 80%, respectively. The modified model was validated by conducting experiments on fluidization and studying the mixing characteristics of regular homogeneous materials (sago) in a 15 × 100 cm cylindrical column. Fairly good agreement was observed between the values of mixing index obtained from the proposed modified model and the experimental observations. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Comparison of low temperature mixed refrigerant cycles for separation systems

In situ monitoring of reaction-induced phase separation with modulated temperature DSC

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Steven Swier
Abstract A linearly polymerizing and network forming epoxy-amine system, DGEBA-aniline and DGEBA-MDA, respectively, will be modified with 20 wt% and 50 wt% of a high- Tg thermoplastic poly(ether sulphone) (Tg=223°C), respectively, both showing LCST-type demixing behavior. Reaction-induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES-rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature-conversion-transformation diagram unambiguously shows the LCST-type demixing behavior of this system, while the relation between the composition/glass transition of the PES-rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non-isothermal post-cures. [source]

Influence of magnetic field on two-phase flow convective boiling of some refrigerant mixtures

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2005
Samuel M. Sami
Abstract In this paper, an experimental study on the influence of magnetohydrodynamic (MHD) on heat transfer characteristics of two-phase flow boiling of some refrigerant mixtures in air/refrigerant horizontal enhanced surface tubing is presented. Correlations were proposed to predict the impact of MHD on the heat transfer characteristics such as average heat transfer coefficients, and pressure drops of R-507, R-404A, R-410A, and R-407C in two-phase flow boiling inside enhanced surface tubing. In addition, it was found that the refrigerant mixture's pressure drop is a weak function of the mixture's composition. It was also evident that the proposed correlations for predicting the heat transfer characteristics were applicable to the entire heat and mass flux, investigated in the present study. The deviation between the experimental and predicted value using new and improved correlations for the heat transfer coefficient and pressure drop were less than ±20%, for the majority of data. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Behaviour of new refrigerant mixtures under magnetic field

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2005
Samuel M. Sami
Abstract The behaviour of some new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point and consequently on the thermophysical properties. Furthermore, the use of magnetic field appears to have a positive influence on the thermal capacities of the condenser and the evaporator depending upon the refrigerant mixture's thermophysical properties. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Effect of magnetic field on the performance of new refrigerant mixtures

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2003
Samuel M. Sami
Abstract Performance test results of new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various magnetic field conditions. Performance tests were conducted according to the ARI/ASHRAE Standards. The test results demonstrated that as magnetic field force increases, compressor head pressure and discharge temperature slightly increase as well as less liquid refrigerant is boiling in the compressor shell. This has a positive effect in protecting the compressor. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point. Furthermore, the use of magnetic field appears to have a positive influence on the system COP as well as thermal capacities of condenser and evaporator. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Study of liquid injection impact on the performance of new refrigerant mixtures

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2003
Samuel M. Sami
Abstract In this paper, the test results of liquid injection impact on the performance of new alternative refrigerant mixtures such as: R-410A, R-507, R-407C and R-404A are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various liquid injection ratios. Performance tests were conducted according to the ARI/ASHRAE standards. The performance data demonstrated that as liquid injection ratio increases, compressor head pressure and discharge temperature decrease. This has a positive effect in protecting the compressor. The effect of liquid injection on mixture behaviour varies from one mixture to another depending upon the mixture's composition. Furthermore, liquid injection appears to have a significant influence on R-410A behaviour compared to the other mixtures in question. Copyright © 2002 John Wiley & Sons, Ltd. [source]