PM Motors for High Efficiency Applications

PM motors are suitable for nearly all applications, like pumps, elevators, compressors, blowers, extruders, generators, electric vehicles, servodrives, cooling towers, household appliances, etc. This paper will present some applications where the use of PM motors allowed for enhancements in energy efficiency and process quality

Motores de ímans permanentes para aplicações de alta eficiência

Motores de ímans permanentes (motores PM) podem ser utilizados em praticamente todas as aplicações, tais como bombas, elevadores, compressores, ventiladores, extrusoras, geradores, veículos elétricos, servoacionamentos, torres de refrigeração, eletrodomésticos, etc. Este artigo apresenta algumas aplicações para evidenciar que o uso de motores PM traz melhorias em eficiência energética e qualidade do processo

Perspectives on the environmental implications of sustainable hydro-power: comparing countries, problems and approaches

Perspectives on the Environmental Implications of Sustainable Hydropower gathers scientific papers from three of the worlds most important hydropower producers to discuss aspects of sustainable hydropower and the means by which it can be studied and achieved. The papers examine the application and use of new technologies and protocols for studying hydropower, adaptive management and the implications and use of long-term data sets for minimizing hydropower impacts on fish populations. The papers include a cross section of biological and hydrological experts. The implicit among country comparisons highlight a number of common hydropower themes, particularly the need to expand from single species studies to include broader consideration of the ecosystem, the importance of maintaining habitat, trait and species diversity and the need for consistently collected long-term data sets. Hydropower Sustainability Long-term studies Brazil Canada NorwaypublishedVersio

Probing the Structure of Liquids with 129Xe NMR Spectroscopy: n-Alkanes, Cycloalkanes, and Branched Alkanes

The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129Xe as a NMR probe. 129Xe chemical shifts have been experimentally determined for xenon dissolved in a total of 21 alkanes. In order to allow the comparison of the different solvents at similar thermodynamic conditions, the measurements were performed over a wide range of temperatures, from the melting point of the solvent up to 350 K. The results were rationalized in terms of the density, nature, and organization of the chemical groups within xenon’s coordination sphere. Additionally, molecular dynamics simulations were performed using established atomistic force fields to interpret and clarify the conclusions suggested by the experimental results. The analysis is able to interpret previous results in the literature for ethane and propane at very different experimental conditions

Alkane coiling in perfluoroalkane solutions: a new primitive solvophobic effect

In this work, we demonstrate that n-alkanes coil when mixed with perfluoroalkanes, changing their conformational equilibria to more globular states, with a higher number of gauche conformations. The new coiling effect is here observed in fluids governed exclusively by dispersion interactions, contrary to other examples in which hydrogen bonding and polarity play important roles. FTIR spectra of liquid mixtures of n-hexane and perfluorohexane unambiguously reveal that the population of n-hexane molecules in all-trans conformation reduces from 32% in the pure n-alkane to practically zero. The spectra of peffluorohexane remain unchanged, suggesting nanosegregatiori of the hydrogenated and fluorinated chains. Molecular dynamics simulatiOns support this analysis. The new solvophobic effect is prone to have a major impact on the structure, organization, and therefore thermodynamic properties and phase equilibria of, fluids involving mixed hydrogenated and fluorinated chains.Fundacao para a Ciencia e Tecnologia [UID/NAN/50024/2013, UID/QUI/0100/2013, SFRH/BPD/81748/2011

On the Behavior of Solutions of Xenon in Liquid n-Alkanes: Solubility of Xenon in n-Pentane and n-Hexane

The solubility of xenon in liquid n-pentane and n-hexane has been studied experimentally, theoretically, and by computer simulation. Measurements of the solubility are reported for xenon + n-pentane as a function of temperature from 254 to 305 K. The uncertainty in the experimental data is less than 0.15%. The thermodynamic functions of solvation such as the standard Gibbs energy, enthalpy, and entropy of solvation have been calculated from Henry’s law coefficients for xenon + n-pentane solutions and also for xenon + n-hexane, which were reported in previous work. The results provide a further example of the similarity between the xenon + n-alkane interaction and the n-alkane + n-alkane interactions. Using the SAFT-VR approach we were able to quantitatively predict the experimental solubility for xenon in n-pentane and semiquantitatively that of xenon in n-hexane using simple Lorentz−Berthelot combining rules to describe the unlikely interaction. Henry’s constants at infinite dilution for xenon + n-pentane and xenon + n-hexane were also calculated by Monte Carlo simulation using a united atom force field to describe the n-alkane and the Widom test particle insertion method

Liquid Mixtures Involving Hydrogenated and Fluorinated Chains: (p, ρ, T, x) Surface of (Ethanol + 2,2,2-Trifluoroethanol), Experimental and Simulation

The effect of mixing hydrogenated and fluorinated molecules that simultaneously interact through strong hydrogen bonding was investigated: (ethanol + 2,2,2-trifluoroethanol) binary mixtures were studied both experimentally and by computer simulation. This mixture displays a very complex behavior when compared with mixtures of hydrogenated alcohols and mixtures of alkanes and perfluoroalkanes. The excess volumes are large and positive (unlike those of mixtures of hydrogenated alchools), while the excess enthalpies are large and negative (contrasting with those of mixtures of alkanes and perfluoroalkanes). In this work, the liquid density of the mixtures was measured as a function of composition, at several temperatures from 278.15 to 353.15 K and from atmospheric pressure up to 70 MPa. The corresponding excess molar volumes, compressibilities, and expansivities were calculated over the whole (p, ρ, T, x) surface. In order to obtain molecular level insight, the behavior of the mixture was also studied by molecular dynamics simulation, using the OPLS-AA force field. The combined analysis of the experimental and simulation results indicates that the peculiar phase behavior of this system stems from a balance between the weak dispersion forces between the hydrogenated and fluorinated groups and a preferential hydrogen bond between ethanol and 2,2,2-trifluoroethanol. Additionally, it was observed that a 25% reduction of the F−H dispersive interaction in the simulations brings agreement between the experimental and simulated excess enthalpy but produces no effect in the excess volumes. This reveals that the main reason causing the volume increase in these systems is not entirely related to the weak dispersive interactions, as it is usually assumed, and should thus be connected to the repulsive part of the intermolecular potential

On the Behaviour of Solutions of Xenon in Liquid Cycloalkanes: Solubility of Xenon in Cyclopentane

The solubility of xenon in liquid cyclopentane has been studied experimentally and theoretically. Measurements of the solubility of xenon in liquid cyclopentane are reported as a function of temperature from 254.60Kto 313.66 K. The imprecision of the experimental data is less than 0.3%. The thermodynamic functions of solvation of xenon in cyclopentane, such as the standard Gibbs energy, enthalpy, entropy and heat capacity of solvation, have been calculated from the temperature dependence of Henry’s law coefficients. The results provide further information about the differences between the xenon + cycloalkanes and the xenon + n-alkane interactions. In particular, interaction enthalpies between xenon and CH2 groups in nalkanes and cycloalkanes have been estimated and compared. Using a version of the soft-SAFT approach developed to model cyclic molecules, we were able to reproduce the experimental solubility for xenon in cyclopentane using simple Lorentz-Berthelot rules to describe the unlike interaction

Diffusion coefficients of perfluorinated n-alcohols in water and heavy water: experiment and computer simulation

Fluorinated surfactants find nowadays many industrial applications due to their enhanced ability to lower surface tension in aqueous solutions [1]. As a result of their extensive use, emissions of fluorinated surfactants became frequent and, because of their persistent character, have been increasingly found in the environment [2]. Both the development of theoretical models to study the environmental fate of those pollutants and the design of unit operations (e.g. adsorption) used for their removal require the knowledge of some key properties such as the diffusion coefficients in water. n-alcohols with perfluorinated carbon chains can be regarded as the most simple fluorinated surfactants, being suitable to be used as model substances that can make easier the molecular interpretation and the theoretical treatment of fluorinated surfactants in a systematic way. On the other hand, the smallest perfluorinated n-alcohols find applications in many fields, such as the pharmaceutical industry, polymer production and refrigerant technology as components of working fluids. We have recently reported intra-diffusion coefficients of 2,2,2-trifluoroethanol in water for dilute solutions as a function of composition and temperature, obtained both experimentally (NMR spin-echo) and by computer simulation (molecular dynamics) [3]. The results obtained by molecular dynamics closely reproduce the experimental ones, which has encouraged us to attempt predicting the dynamic properties of aqueous solutions of the higher fluorinated alcohols and other fluorinated surfactants. In this work, the intra-diffusion coefficients of 2,2,3,3,3-pentafluoropropan-1-ol, 2,2,3,3,4,4,4-heptafluorobutan-1-ol and 2,2,3,3,4,4,5,5,5-nonafluoropentan-1-ol in water and heavy water were measured experimentally by NMR spin-echo technique and compared with results obtained from computer simulation (molecular dynamics). The comparison that can be done between experimental and simulation results is used to test the theoretical models for this chemical family of substances and enriches the molecular interpretation of the results, which can be useful to anticipate trends for more complex fluorinated surfactants. [1] Buck, R. C.; Franklin, J.; Berger, U.; Conder, J. M.; Cousins, I. T.; de Voogt, P.; Jensen, A. A.; Kannan, K.; Mabury, S. A.; van Leeuwen, S., Integr. Environ. Assess. Manage 2011, 7, 513−541 [2] D’Hollander, W.; de Voogt, P.; De Coen, W.; Bervoets, L., Rev. Environ. Contam. Toxicol. 2010, 208, 179–215 [3] Pereira, L. A. M.; Martins, L. F. G.; Ascenso, J. R.; Morgado, P.; Prates Ramalho, J. P.; Filipe, E. J. M., submitted to publicatio

Viscosity of Liquid Perfluoroalkanes and Perfluoroalkylalkane Surfactants

As part of a systematic study of the thermophysical properties of two important classes of fluorinated organic compounds (perfluoroalkanes and perfluoroalkylalkanes), viscosity measurements of four n-perfluoroalkanes and five perfluoroalkylalkanes have been carried out at atmospheric pressure and over a wide range of temperatures (278–353 K). From the experimental results the contribution to the viscosity from the CF2 and CF3 groups as a function of temperature have been estimated. Similarly, the contributions for CH2 and CH3 groups in n-alkanes have been determined using literature data. For perfluoroalkylalkanes, the viscosity results were interpreted in terms of the contributions of the constituent CF2, CF3, CH2, and CH3 groups, the deviations from ideality on mixing hydrogenated and fluorinated chains, and the contribution due to the formation of the CF2–CH2 bond. A standard empirical group contribution method (Sastri–Rao method) has also been used to estimate the viscosities of the perfluoroalkylalkanes. Finally, to obtain molecular level insight into the behavior of these molecules, all-atom molecular dynamics simulations have been performed and used to calculate the densities and viscosities of the perfluoroalkylalkanes studied. Although both quantities are underestimated compared to the experimental data, with the viscosities showing the largest deviations, the trends observed in the experimental viscosities are captured