456 research outputs found
Studies on electrostatic interactions of colloidal particles under two-dimensional confinement
We study the effective electrostatic interactions between a pair of charged
colloidal particles without salt ions while the system is confined in two
dimensions. In particular we use a simplified model to elucidate the effects of
rotational fluctuations in counterion distribution. The results exhibit
effective colloidal attractions under appropriate conditions. Meanwhile,
long-range repulsions persist over most of our studied cases. The repulsive
forces arise from the fact that in two dimensions the charged colloids cannot
be perfectly screened by counterions, as the residual quadrupole moments
contribute to the repulsions at longer range. And by applying multiple
expansions we find that the attractive forces observed at short range are
mainly contributed from electrostatic interactions among higher-order electric
moments. We argue that the scenario for attractive interactions discussed in
this work is applicable to systems of charged nanoparticles or colloidal
solutions with macroions.Comment: 23 pages, 11 figures, 1 tabl
Cost modelling of floating wind farms with upscaled rotors in Maltese waters
The technical viability of offshore wind projects depends upon a number of factors such as the site-specific wind resource, sea depth, seabed composition, distance to the shore and climatic conditions amongst others. The Mediterranean is characterised by deep seas relatively close to the shore and only a reasonable wind climate if compared to conditions in countries that are forerunners in the offshore wind sector. The development of floating wind turbine support structures will allow wind farms in deeper waters and will be a catalyst for the wider diffusion and larger-scale implementation of offshore wind farms on a global level. This study investigates the prospects for a hypothetical 100 MW floating offshore wind farm well to the west of the island of Malta. The study models three upscaled turbines having rotor diameters of 126, 145 and 170 m. The study shows that the rotor upscaling process can improve the economic viability of offshore wind turbines with the improved energy yield counterbalancing the higher investment costs required for such a project and thus resulting in a lower cost of energy. The levelised cost of electricity is estimated to be in the 21.0 to 23.6 €cent/kWh range which, although still well above the current market prices of electricity generated by conventional means, is expected to drop considerably over the coming years as new international players enter the offshore wind market. Increasing levels of competition, new concepts coming to fruition and wider and larger-scale diffusion of new technologies will help bring down costs of energy for the offshore wind farms of the future.Bajada New Energy, General Membrane, EcoGroup, Econetique, Energy Investment, JMV Vibro Blocks, Solar Engineering, Solar Solutionspeer-reviewe
Comparing the economic feasibility of offshore floating wind and solar photovoltaic technologies in Central Mediterranean deep waters
Malta, being a very small and densely populated island in the central Mediterranean, has little space
for large scale onshore wind turbine or photovoltaic projects. Maltese territorial waters are mostly too deep for
conventional offshore wind farms to be constructed save for a handful of near-shore reefs and shoals. The quest for
offshore wind turbine structure designs capable of being installed in deeper waters will revolutionize prospects for
offshore wind projects worldwide; but even more so in the Mediterranean region. This paper presents a preliminary
engineering analysis to develop two cost-optimized offshore floating structures to support (1) a single multi-megawatt
scale wind turbine and (2) a solar photovoltaic farm with the same energy production as that of the single wind
turbine. The primary objective of this work is to determine the most economically feasibility option for harvesting
renewable energy at sea: offshore wind or offshore solar photovoltaic energy.peer-reviewe
Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters
A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe
Analysis of a novel offshore platform with integrated energy storage operating in Central Mediterranean waters
A thermodynamic model of a novel energy storage device is described and simulated in the context of a central Mediterranean climate. The device uses a hydro-pneumatic concept to store energy as compressed air. It is designed to be integrated into an offshore floating platform. The thermodynamic model illustrates the behaviour of the compression process and the heat exchange with the surrounding environment. Different rates of compression are simulated, and it can be observed that faster compression rates lead to higher gas temperatures and pressures. The sensitivity to climatic conditions is also investigated, however this effect was seen to be minimal. A simplified Black-Box Model is also developed, with its parameters obtained through a curve-fitting process. Finally, a stochastic input is fed to both models and a comparison is made. The simplified model results in a minor over-prediction of the efficiency.peer-reviewe
Weak Long-Ranged Casimir Attraction in Colloidal Crystals
We investigate the influence of geometric confinement on the free energy of
an idealized model for charge-stabilized colloidal suspensions. The mean-field
Poisson-Boltzmann formulation for this system predicts pure repulsion among
macroionic colloidal spheres. Fluctuations in the simple ions' distribution
provide a mechanism for the macroions to attract each other at large
separations. Although this Casimir interaction is long-ranged, it is too weak
to influence colloidal crystals' dynamics.Comment: 5 pages 2 figures ReVTe
Theoretical Investigation of Local Electron Temperature in Quantum Hall Systems
In this work we solve thermo-hydrodynamical equations considering a two
dimensional electron system in the integer quantum Hall regime, to calculate
the spatial distribution of the local electron temperature. We start from the
self-consistently calculated electrostatic and electrochemical potentials in
equilibrium. Next, by imposing an external current, we investigate the
variations of the electron temperature in the linear-response regime. Here a
local relation between the electron density and conductivity tensor elements is
assumed. Following the Ohm's law we obtain local current densities and by
implementing the results of the thermo-hydrodynamical theory, calculate the
local electron temperature. We observe that the local electron temperature
strongly depends on the formation of compressible and incompressible strips.Comment: 10 pages, 4 figure
Electrolytic depletion interactions
We consider the interactions between two uncharged planar macroscopic
surfaces immersed in an electrolyte solution which are induced by interfacial
selectivity. These forces are taken into account by introducing a depletion
free-energy density functional, in addition to the usual mean-field
Poisson-Boltzmann functional. The minimization of the total free-energy
functional yields the density profiles of the microions and the electrostatic
potential. The disjoining pressure is obtained by differentiation of the total
free energy with respect to the separation of the surfaces, holding the range
and strength of the depletion forces constant. We find that the induced
interaction between the two surfaces is always repulsive for sufficiently large
separations, and becomes attractive at shorter separations. The nature of the
induced interactions changes from attractive to repulsive at a distance
corresponding to the range of the depletion forces.Comment: 17 pages, 4 Postscript figures, submitted to Physical Review
Phase behaviour of a model of colloidal particles with a fluctuating internal state
Colloidal particles are not simple rigid particles, in general an isolated
particle is a system with many degrees of freedom in its own right, e.g., the
counterions around a charged colloidal particle.The behaviour of model
colloidal particles, with a simple phenomenological model to account for these
degrees of freedom, is studied. It is found that the interaction between the
particles is not pairwise additive. It is even possible that the interaction
between a triplet of particles is attractive while the pair interaction is
repulsive. When this is so the liquid phase is either stable only in a small
region of the phase diagram or absent altogether.Comment: 12 pages including 4 figure
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