497 research outputs found
Chronicles of Oklahoma
No full textArticle examines the motivations behind the migration of black Americans from Arkansas to Oklahoma in the late nineteenth century, observing the political situation of the time and the results of the move. Lori Bogle also provides specific information about one homesteader, James A. Rouce, who settled near Hitchcock
Chemical Engineering Science Danckwerts special issue on Digitalisation
No full textDigitalisation is a hot topic everywhere. Chemical Engineers have been at the vanguard of applying digital approaches and algorithms to problems in manufacturing and environmental systems, and other systems where there is chemical and physical change. What is new today is the huge increase in compute power, the continued development of mathematical algorithmic approaches and in particular the developments in Artificial Intelligence and Machine Learning, in our ability to measure new properties in real time, and in the sheer volume of available data, both static and dynamic often as images as well as point values
Fidelity versus Vanguard: Comparing the Performance of the Two Largest Mutual Fund Families
No full textThis paper compares the risk and return of investing in equity mutual funds provided by the world's two largest mutual fund families: Fidelity and Vanguard over a long horizon. We believe this will help guide investors; this study is an example of the calculations that mutual fund companies should facilitate by being required to provide accurate, accessible and free data. Over the entire period 1977 through 2003 both Fidelity's (no load) and Vanguard's diversified U.S. funds out returned the Wilshire 5000 index; Fidelity's portfolio out returned Vanguard's portfolio by 0.62 % per year but under returned it by 0.39 % when risk adjusted.
Improving efficiency and discharge power of acid-base flow battery via a bi-objective optimisation
No full textThe implementation of effective storage systems is essential for a deeper market penetration of intermittent
renewable sources. One promising, environmentally friendly energy storage technology is the Acid-Base Flow
Battery (AB-FB). In the charge phase it stores electricity in the form of pH and salinity gradients via Bipolar
Membrane Electrodialysis, while in the discharge phase it applies the reverse process for the opposite conversion.
Despite the clear benefits over other osmotic batteries, the potential of the AB-FB has been poorly explored.
This study presents the first bi-objective optimisation of the AB-FB in terms of net round trip efficiency
(RTEnet) and average net discharge power density per membrane area (NPDd). A comprehensive mathematical
model previously developed by our research team was used to predict the battery performance. The ε-constraint
approach was used to build curves of Pareto optimal solutions under various scenarios by letting several operating
and design parameters to vary. Using current commercial membranes, optimal solutions yielded an RTEnet
ranging from 32 % to 64 %, while the corresponding NPDd ranged from 19.5 W m^-2 to 4 W m^-2. These results
highlight the great potential of the AB-FB, as well as the need of a proper design of experimental stacks.
Simulating hypothetical membranes with improved, yet realistic characteristics shifted the range of RTEnet and
NPDd to 59.1–76.3 % and 23.2–4.4 W m^-2, respectively, showing that the technological advancement in
membrane manufacturing is essential for the development of high-performance AB-FB systems. Although the ABFB
performs similarly to other batteries, it can be made of non-critical materials that are not subject to supply
disruptions or economic dependency, making the AB-FB a sustainability-friendly option and a good candidate for
the future energy storage systems scenario
Water desalination by capacitive electrodialysis: Experiments and modelling
No full textElectrodialysis-related technologies keep spreading in multiple fields, among which water desalination still plays a major role. A new technology that has not yet been thoroughly investigated is capacitive electrodialysis (CED), which couples the standard ED with capacitive electrodes. CED has a number of advantages such as removal of toxic products and system simplification. Little mention is made of this technology in the literature and, to the best of our knowledge, no modelling works have ever been presented. In this work, the CED process has been studied through experiments and modelling. A CED model is presented for the first time. With a simple calibration based on macroscopic membrane properties and the characterisation of electrode behaviour, the model is able to simulate the dynamics of simple as well as more complex layouts. An original experimental characterisation of electrodes is presented, showing how the collected data can be implemented into the model. After a successful validation with experimental data, dynamic simulations of a single pass CED unit have been performed with the aim of assessing the effect of different capacitive electrode properties on process performance. Results show how the impact of these properties is different depending on the number of cell pairs
A 2-D model of electrodialysis stacks including the effects of membrane deformation
No full textMembrane-based processes have gained a relevant role in many engineering applications. Much effort has been devoted to thoroughly understand the fundamental phenomena behind them. However, membrane deformation has been taken into consideration only recently, although much evidence has shown its impacts in many applications. This work presents a novel 2-D, multi-scale, semi-empirical process model able to predict the behavior and the performance of Electrodialysis (ED) systems in cross-flow configurations in the presence and absence of local membrane deformations. The model exploits the results and the simulation approaches of previous fluid-structure investigations performed by the authors. Low-scale numerical simulations are coupled with a high-scale model to predict the redistribution of channel height, flow rate, friction coefficient and Sherwood number in ED stacks caused by local membrane deformations. Finally, salt and water fluxes, mass balances and electrochemical quantities are computed to assess the performances of cross-flow ED stacks. Different test cases have been simulated for the desalination of seawater by two-stage ED. Interestingly, membrane deformation is found to reduce, albeit slightly, the energy consumption. More pronounced effects are expected if thinner or less stiff membranes are used
Modelling of Electrodialysis units by a multi-scale process simulator
No full textDrinking water production by desalination is an interesting alternative to face water scarcity issues. Electrodialysis (ED) is an electro-membrane process that is actually gaining attention as a competitive alternative for seawater and brackish water desalination due to recent developments in manufacturing of high performance ion exchange membranes (IEMs). In this context, a suitable process simulator can be a very effective tool in order to drive the design of optimized ED systems.
In this work a novel mathematical model of ED units was developed by a hierarchical simulation strategy of separation of scales, in order to address the full simulation problem. The model was implemented in PSE gPROMS Modelbuilder. In the lower-hierarchy model, transport phenomena of salt and water were simulated within the whole cell pair of an electrodialyser. Then, the higher-hierarchy model describes the behaviour of the stack. The model is based on mass balance equations and phenomenological expressions of fluxes that describe transport phenomena along channels and across IEMs. In addition, Kirchhoff’s law together with the Nernst’s law for the non-Ohmic voltage drop was used to determine the electrical behaviour of the equivalent circuit. Finally, the model makes use of CFD correlations from a lower scale as input data in order to predict the effect of concentration polarization and the contribution of pumping to the energy consumption.
Co-current, counter-current and crossflow configurations were simulated, by obtaining the distribution of current density/voltage and concentration along the channels. Finally, total resistance, total power consumption and specific energy consumption were computed. Several simulations were carried out by changing the operating conditions and the stack features. Simulation results showed a good agreement with experimental findings as obtained from the literature, demonstrating that the model is able to adequately capture the phenomenological description of the ED process
Electrodialysis with capacitive electrodes (CED): hierarchical process modelling for water desalination
No full textThe present work describes the development of the first dynamic model for CE
Hierarchical modelling of electrodialysis desalination process
No full textIn recent years, thanks to the development of ion exchange membranes (IEMs) manufacturing industry, Electrodialysis (ED) is spreading as a viable alternative to the more common membrane desalination processes. Therefore, many research efforts have been recently devoted to studying this process both via experimental and modelling activities.
In the present work a novel mathematical model for ED was developed using a multi-scale approach. This method allows to build a hierarchical simulation tool that is able to gauge the impact of all the phenomena involved in the process. The lower-hierarchy model describes the behaviour of the elementary unit of an ED stack, namely cell pair. This model is based on differential mass balance equations and accounts for transport phenomena including salt migration and diffusion as well as water osmosis and electro-osmosis. In addition, Kirchhoff’s law together with the Nernst’s law for the non-Ohmic voltage drop was used to determine the electrical behaviour of the equivalent circuit. Interestingly, the model makes also use of CFD correlations from a lower scale as input data in order to predict the effect of concentration polarization. In the higher-hierarchy model the whole stack was described, allowing the simulation of multiple cell-pairs together with the end electrode compartments. Again, CFD correlations were used to include the contribution of pumping loss in the overall energy consumption.
The model was implemented in PSE gPROMS Modelbuilder. Several simulations were carried out by changing flow arrangement (co-current, counter-current and cross-flow), operating conditions and stack features. Results showed that the model is able to reliably predict the effect of these variables on the performance of the ED unit investigated. In particular, the model was found capable of estimating the distribution of current density/voltage and concentration along the channels. In addition, stack resistance, overall and specific energy requirements were computed. Collected findings suggest that the model proposed might be a powerful tool to improve and optimise ED process
- …
