Improvement of porous cellulose acetate reverse osmosis membranes by change of casting conditions

The effects of temperature of casting solution in the range ?10° to 15°C, that of casting atmosphere in the range 10° to 30°C, relative humidity of casting atmosphere in the range 35% to 75%, and solvent evaporation period in the range 0.5 to 3 min were studied on shrinkage temperatures, solute separations, and product rates of Loeb-Sourirajan-type cellulose acetate membranes in reverse osmosis experiments. The composition of casting solution used was as follows: cellulose acetate, 17; acetone, 69.2; magnesium perchlorate, 1.45; and water, 12.35 wt-%. Best performance was obtained with membranes cast under the following conditions: temperature of casting solution, 10°C; temperature of casting atmosphere, 30°C; relative humidity of casting atmosphere, 65%; and solvent evaporation period, 1 min. For a 90% level of solute separation, the productivities of the above type of membranes were 22.9, 61.4, and 64.5 gallons/day-ft² at 250, 600, and 1500 psig using 3500 ppm NaCl–H₂O, 5000 ppm NaCl–H₂O, and 28395 ppm NaCl–H₂O feed solutions, respectively. In all cases, the feed flow rates corresponded to a mass transfer coefficient of 45 × 10^?4 cm/sec on the high-pressure side of the membrane. The general specifications of the above type of membranes are given for the operating pressures of 250, 600, and 1500 psig. The effects of the above casting condition variables on the surface pore structure during film formation are discussed.     

Time dependent voiding mechanisms in polyamide 6 submitted to high stress triaxiality: experimental characterisation and finite element modelling

Double notched round bars made of semi-crystalline polymer polyamide 6 (PA6) were submitted to monotonic tensile and creep tests. The two notches had a root radius of 0.45 mm, which imposes a multiaxial stress state and a state of high triaxiality in the net (minimal) section of the specimens. Tests were carried out until the failure occurred from one of the notches. The other one, unbroken but deformed under steady strain rate or steady load, was inspected using the Synchrotron Radiation Computed Tomography (SRCT) technique. These 3D through thickness inspections allowed the study of microstructural evolution at the peak stress for the monotonic tensile test and at the beginning of the tertiary creep for the creep tests. Cavitation features were assessed with a micrometre resolution within the notched region. Spatial distributions of void volume fraction (\(\mathit{Vf}\)) and void morphology were studied. Voiding mechanisms were similar under steady strain rates and steady loads. The maximum values of \(\mathit{Vf}\) were located between the axis of revolution of the specimens and the notch surface and voids were considered as flat cylinders with a circular basis perpendicular to the loading direction. A model, based on porous plasticity, was used to simulate the mechanical response of this PA6 material under high stress triaxiality. Both macroscopic behaviour (loading curves) and voiding micro-mechanisms (radial distributions of void volume fraction) were accurately predicted using finite element simulations.     

Unipolar charging of cylindrical insulating particles nearelectrode surfaces

Numerous papers have discussed the ionic charging of insulating spheres in uniform electric fields. However, in certain electrostatic technologies, such as separation and flocking, the particles are often cylindrical in shape, and they get charged on the surface of an electrode or in its proximity, so that existing formulas cannot be used. This paper addresses this problem from both a computational and an experimental point of view. The charge acquired by cylindrical particles of various dielectric constants was evaluated with an original computer program, based on the boundary-element method of field analysis. The computed results show that the position of the particle with respect to the electrodes changes the value of the saturation charge. The experimental setup simulated the charging conditions in a roll-type electrostatic separator. The unipolar space charge was generated by a needle-type electrode. An electrometer was used to measure the charge acquired by millimeter-size calibrated cylinders of polyethylene and polyvinyl chloride on a rotating roll electrode. The experimental results, which were in good agreement with the theoretical predictions, put forward a particle self-discharge effect, at field intensities beyond a well-defined threshold. This kind of information may guide the design of the electrostatic technologies based on the corona charging of granular matter     

Modeling of conductive particle behavior in insulating fluidsaffected by DC electric fields

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, or biological cell manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids by means of relatively high DC electric fields. This paper is aimed at characterizing the behavior of such particles by numerical modeling of two aspects: (1) particle motion under the action of electric field forces and (2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behavior are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impact with the electrodes. The conclusions regarding the behavior of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment     

Unipolar charging of insulating spheres in rectified AC electricfields

Nonfiltered rectifiers and pulsed power supplies are often used for the energization of the high-voltage electrodes in various electrostatic installations. The aim of this paper is to investigate the ionic charging of insulating particles in the pulsatory electric fields specific to such applications. In a first set of numerical simulations, the space charge was considered constant in time, which means that the ion generation is not related to the voltage drop between the electrodes. A second set of simulations was carried out using the assumption that the space charge is generated by the pulsed corona from one of the electrodes. The computed results, which were found in good agreement with the experimental data, show that the amount of charge acquired by a particle depends on the following factors: (1) particle transit time through the electric field zone; (2) space charge density; and (3) ratio between the corona onset voltage and the amplitude of the variable voltage applied to the electrodes. These factors are discussed in correlation with the operating parameters of roll-type corona-electrostatic separators, but the conclusions are valid for a wider group of industry applications     

Periodic event‐triggered observation and control for nonlinear Lipschitz systems using impulsive observers

In this paper, we investigate the observation and stabilization problems for a class of nonlinear Lipschitz systems, subject to network constraints, and partial state knowledge. In order to address these problems, an impulsive observer is designed, making use of the event‐triggered technique in order to diminish the network communications. Sufficient conditions are given to ensure a milder version of the separation principle for these systems, controlled via an event‐triggered controller. The proposed observer ensures practical state estimation, while the corresponding dynamic controller ensures practical stabilization. The sampling and the data transmission are carried out asynchronously. The dynamic controller is tested in simulation on a flexible joint. Copyright © 2017 John Wiley & Sons, Ltd.     

Maintenance of Response Readiness in Patients With Parkinson's Disease: Evidence From a Simple Reaction Time Task.

The authors explored the effect of Parkinson's disease (PD) on the generation and maintenance of response readiness in a simple reaction time task. They compared performance of idiopathic PD patients without dementia, age-matched controls, and younger controls over short (1-, 3-, and 6-s) and long (12- and 18-s) foreperiod intervals. After each trial, the authors probed memory for visual information that also had to be maintained during the trial interval. Patients and controls did not differ overall in their ability to maintain readiness over long delays. However, within the PD group only, errors in maintaining visual information were correlated with difficulty in maintaining readiness, suggesting that systems impaired in PD may facilitate the maintenance of processing in both motor and cognitive domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization of electrostatic separation Processes using response surface modeling

The efficiency of electrostatic separation processes depends on a multitude of factors, including the characteristics of the granular mixtures to be sorted, the feed rate, the configuration of the electrode system, the applied high voltage, and the environmental conditions. The possibility of optimizing the operation of industrial electrostatic separators using rather simple computed-assisted experimental design techniques has already been demonstrated. The aim of the present work is to analyze the peculiarities of application of a more sophisticated group of response surface experimental design techniques that make use of quadratic functions for modeling the electrostatic separation process. One unique contribution to this work is to consider the economic value of the process in addition to the technical result. The 11 electrostatic separation tests, corresponding to a central composite design, were carried out on samples of chopped electric wire wastes. The CARPCO laboratory roll-type electrostatic separator employed for this study enabled a rigorous control of two factors: the applied high-voltage level and the speed of the rotating roll electrode. The objective was to maximize the benefits from the recycling of both constituents of the binary copper-polyvinyl chloride granular mixture. The optimum operating conditions computed with the quadratic model derived from the experimental results were in good agreement with the data of pilot-plant tests. Thus, the highest extraction of useful materials was obtained at high voltage and low speed, while the optimum conditions for greatest economic value were found to be high voltage and high speed. The response surface methodology can be easily applied to most of the industrial applications of electrostatic separation technologies.     

Electrostatic separation of muscovite mica from feldspathic pegmatites

This paper aims at evaluating several electrostatic separation techniques that could be effective for the recovery of mica flakes from pegmatite ores characterized by grain sizes <0.5 mm: 1) triboadhesive separation; 2) dc electric field separation; 3) ac electric field separation; 4) corona field separation using a grounded metallic roll electrode and thermal conditioning; and 5) corona field separation using a grounded metallic roll electrode covered with an insulating layer. The experiments have been carried out on samples containing about 50% mica, 25% feldspar, 15% quartz, 10% iron oxides and hydroxides, as well as iron silicates, with grain sizes ranging between 0.16-0.4 mm. The experimental data confirmed the theoretical predictions: all four separation techniques using high-intensity electric fields improved the grade of muscovite mica concentrate to levels that fulfill the requirements of several industry applications such as welding wire manufacturing. The best results [46.11% SiO/sub 2/, 33.64% Al/sub 2/O/sub 3/, and 11.1% (K/sub 2/O+Na/sub 2/O)] were obtained when performing a three-stage separation using method 5).     

Charging and discharging of insulating particles on the surface of a grounded electrode

The aim of the present paper is to analyze the corona charging of millimeter-size insulating disks, as well as their discharging when they are no longer exposed to the action of an external electric field. The experiments were carried out on a roll-type electrostatic laboratory separator, equipped with a wire-type corona electrode, simulating the actual charging/discharging conditions in an industrial unit. Disks of various sizes were charged on the surface of the roll electrode, then the high voltage supplied to the corona electrode was turned off and the particles were collected in a Faraday pail, connected to an electrometer. The charge measurements were performed at various time intervals from high-voltage turn-off. In this way, the charge decay could be recorded and the discharge process fully characterized. The measured data show that the discharge process depends on the nature, size, and shape of the particles, as well as on the contact conditions between the particles and the grounded roll electrode. These data could guide the design of the electrostatic separation experiments that precede any new industrial application of this technology.