Search results for "dynamics"
showing 10 items of 9782 documents
A simulation tool for ion exchange membrane crystallization of magnesium hydroxide from waste brine
2021
Abstract Increasing attention is nowadays paid to the management and valorisation of industrial waste brines aiming also at the recovery of raw materials. Magnesium has been listed as a Critical Raw Material by EU, prompting researchers to investigate novel routes for its recovery. Within this framework, a novel Crystallizer with Ion Exchange Membrane (CrIEM), is proposed as an innovative way to recover magnesium from industrial waste brines exploiting low-cost alkaline reactants. In the present work, a novel mathematical model of the CrIEM process is proposed to provide a useful tool for its design in different working conditions. Batch and feed & bleed continuous configurations have been …
Effect of different aqueous solutions of pure salts and salt mixtures in reverse electrodialysis systems for closed-loop applications
2018
Abstract Reverse Electrodialysis (RED) in a closed-loop arrangement is a viable way to convert low-grade heat into electric power. The present work experimentally investigates the use of pure salt- and equimolar two salts-water solutions as feeds in a lab-scale RED unit. RED performances were analysed in terms of Open Circuit Voltage (OCV), stack resistance and corrected power density. The pure salts and the mixtures employed were chosen via a computational analysis. Effect of feed solution velocity and concentration was investigated. Results concerning the pure salt-water experiments show that NH4Cl is the most performing salt in the concentration range probed, while higher power density v…
Solid–Liquid Suspensions in Top-Covered Unbaffled Vessels: Influence of Particle Size, Liquid Viscosity, Impeller Size, and Clearance
2014
Particle suspension in liquids is a unit operation commonly encountered in the process industry. Although it is usually carried out in baffled stirred tanks, there are some specific applications where the presence of baffles may be undesirable. In the present work solid-liquid suspensions are investigated in a radially stirred unbaffled tank provided with a top cover. The minimum impeller speed at which all solid particles get suspended (Njs) and the relevant power requirements (Pjs) are assessed. The dependence of these two parameters on physical properties (liquid viscosity, particle concentration, and size) and system geometrical configurations (impeller diameter and clearance) is invest…
Determination of limiting current density and current efficiency in electrodialysis units
2018
Abstract A crucial parameter for the design and operation of electrodialysis (ED) units is the limiting current density (LCD). This is often identified with the diffusion-limited current density, which corresponds to the complete solute depletion in the layer adjacent to the membrane. Current-voltage curves obtained from measurements with electrodes in contact with the solution (i.e. without membranes) are consistent with this interpretation and exhibit a horizontal plateau identifying LCD. However, real ED systems show more complex behaviours, with a reduced-slope tract instead of a plateau and a third region in which the current increases more markedly (overlimiting current). The phenomen…
On the bubbling dynamics of binary mixtures of powders in 2D gas-solid fluidized beds
2012
Abstract The bubbling behavior of fluidized beds has been thoroughly investigated in the last decades by means of several techniques (e.g. X-ray, Inductance, Resistance and Impedance based techniques). In recent years, Digital Image Analysis Techniques have shown their potential for accurate and cost effective measurements. Most of the works related to the experimental analysis of bubble behavior in the field of gas-solid fluidization actually deal with monodispersed particles although almost all industrial equipments operate with mixtures of particles. Among the works available in literature dealing with mixtures of particles having different diameters and/or densities, most of them aim at…
Membrane distillation heat transfer enhancement by CFD analysis of internal module geometry
2011
Module geometry optimisation can be a crucial matter in all separation processes using selective or hydrophobic membranes, e.g. reverse osmosis (RO) and membrane distillation (MD). In fact the choice of suitable channel shape and size can dramatically affect the performance of the process. With reference to the membrane distillation process, temperature polarization phenomena and pres¬sure drops along the channels largely affect the process efficiency (i.e. the efficient use of temperature driving force for the passage of vapour through the membrane) as well as pressure distribution, module mechanical resistance and pumping costs. Several works have been presented so far in literature on th…
Spectral and temperature sensitivity of area de-coupled tandem modules
2015
- Area de-coupling is a recently suggested method for current- or voltage-matching two-terminal tandem modules. It has previously been shown that under standard conditions, area de-coupled modules have the same theoretical efficiency as four-terminal tandem cells for any combinations of band gaps. In this work, the spectral and temperature sensitivity of ideal area de-coupled modules is investigated by detailed balance modeling. Voltage-matched area de-coupled modules are found to be considerably less sensitive to changes in the spectrum than current-matched modules. Current-matched modules are, on the other hand, found to be less sensitive to changes in the temperature. Under normal condit…
About the reliability, efficiency, and meaning of the error estimates of a LAOCOON3-type NMR analysis system
1977
Abstract The statistical error estimates of a LAOCOON3-type system are tested. The analyzabilities of a spectrum and spectral parameters are described by a new measure. The variation in the uncertainties of the parameters can be explained by correlation coefficients. According to the calculations made, the error estimates are normally quite reliable if the accuracy of the observed spectrum is known. In some cases the Newton-Raphson type of iteration does not converge or the confidence limits of the parameters are enormous or both; an example is discussed. It seems clear that one cannot avoid differing uncertainties of the parameters by changing the method of analysis, or that one can avoid …
Spinodal lines and Flory-Huggins free-energies for solutions of human hemoglobins HbS and HbA
1991
Gelation of deoxygenated solutions of sickle-cell human Hemoglobin (HbS) is of high theoretical interest and it has serious pathological consequences. For this reason HbS is probably the most studied protein capable of self-organization. This notwithstanding, the location in the T, c plane of the region of thermodynamic instability of solutions of deoxy-HbS (as bounded by the spinodal line and as distinct from the gelation region) has remained unknown, along with related values of Flory-Huggins enthalpies and entropies. In the present work this information is derived from experiments for the two cases of (deoxy) HbS and of human adult hemoglobin (HbA). Experiments also show critical exponen…
Crystallization of hard spheres revisited. II. Thermodynamic modeling, nucleation work, and the surface of tension
2018
Combining three numerical methods (forward flux sampling, seeding of droplets, and finite-size droplets), we probe the crystallization of hard spheres over the full range from close to coexistence to the spinodal regime. We show that all three methods allow us to sample different regimes and agree perfectly in the ranges where they overlap. By combining the nucleation work calculated from forward flux sampling of small droplets and the nucleation theorem, we show how to compute the nucleation work spanning three orders of magnitude. Using a variation of the nucleation theorem, we show how to extract the pressure difference between the solid droplet and ambient liquid. Moreover, combining th…