CO2 valorization by means of dielectric barrier discharge

peer reviewedAs atmospheric pollution is causing several environmental problems it is incumbent to reduce the impact of pollution on the environment. One particular problem is the production of CO2 by many transport and industrial applications. Instead of stocking CO2 and instead of being a product, it can be used as a source. The case considered is the CO2 reformation of methane producing hydrogen and CO. It is an endothermic reaction, for which the activation barrier needs to be surpassed. This can be done efficiently by the method of Dielectric Barrier Discharge. The process relies on the collision of electrons, which are accelerated under an electrical field that is created in the discharge area. This leads to the formation of reactive species, which facilitate the abovementioned reaction. This study is performed using a Matlab program with the Reaction Engineering module in COMSOL (with an incorporated kinetic mechanism) in order to model the discharge phase. Then COMSOL (continuity and Navier-Stokes equations) is used to model the flow in the post-discharge phase. The results showed that both a 2D and 3D model can be used to model the chemical-plasma process. These methods need strongly reduced kinetic mechanism, which in some cases can cause loss of precision

An extended thermodynamic model for size-dependent thermoelectric properties at nanometric scales: Application to nanofilms, nanocomposites and thin nanocomposite films

peer reviewedA new mathematical model is developed, describing size-dependent subcontinuum thermoelectric properties from an extended thermodynamic point of view. This model takes into account the non-local effects of heat transfer through phonons and electrons that are important at nanometric scales. These phenomena are extended to apply also for electric transfer as well as the Seebeck coefficient. This model includes at nanoscale size-dependent electron and phonon thermal conductivities, electric conductivity, Seebeck coefficient and carrier concentrations. We compared nanofilms to nanocomposites and assessed their thermoelectric performances in the form of a figure of merit using as an example Bismuth and BismuthTelluride materials. It appeared that the figure of merit increases considerably for nanofilms and nanocomposites with respect to bulk materials. This is caused by the scattering of phonons and electrons. Our model shows that this scattering effect is not only present at the boundary or particle-matrix interface of the nanosized material, but also within it. The effect of particle size and surface specularity has been investigated, showing that a decreasing value of the particle size and specularity increases the scattering effect and improves the thermoelectric properties. An extension towards thin films of nanocomposite has been presented. © 2015

The role of several heat transfer mechanisms on the enhancement of thermal conductivity in nanofluids

A modelling of the thermal conductivity of nanofluids based on extended irreversible thermodynamics is proposed with emphasis on the role of several coupled heat transfer mechanisms: liquid interfacial layering between nanoparticles and base fluid, particles agglomeration and Brownian motion. The relative importance of each specific mechanism on the enhancement of the effective thermal conductivity is examined. It is shown that the size of the nanoparticles and the liquid boundary layer around the particles play a determining role. For nanoparticles close to molecular range, the Brownian effect is important. At nanoparticles of the order of 1–100 nm, both agglomeration and liquid layering are influent. Agglomeration becomes the most important mechanism at nanoparticle sizes of the order of 100 nm and higher. The theoretical considerations are illustrated by three case studies: suspensions of alumina rigid spherical nanoparticles in water, ethylene glycol and a 50/50w% water/ethylene glycol mixture, respectively, good agreement with experimental data is observed. © 2016, Springer-Verlag Berlin Heidelberg

A parametric study on the emissions from an HCCI alternative combustion engine resulting from the auto-ignition of primary reference fuels

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be useful in order to gain more understanding in the emission reduction possibilities via this new combustion technology. For this purpose, the inlet temperature, the equivalence ratio and the compression ratio are changed, respectively, from 30 to 70 degrees C, 0.28 to 0.41 and 6 to 14. Also the diluting, thermal and chemical effects of exhaust gas recirculation were studied. The emission of CO, CO2, O-2 and hydrocarbons has been measured using primary reference fuels. It appears that an increase in the inlet temperature, the EGR temperature, the equivalence ratio and the compression ratio results into a decrease of the emissions of CO and the hydrocarbons of up to 75%. The emission of CO2 increased, however, by 50%. The chemical parameters showed more complicated effects, resulting into a decrease or increase of the emissions, depending on whether the overall reactivity increased or not. If the reactivity increased, generally, the emissions of CO and hydrocarbons increased, while that of CO2 increased. The increase of CO2 emissions could be compensated by altering the compression ratio and the EGR parameters, making it possible to control the emission of the HCCI engine. (c) 2008 Elsevier Ltd. All rights reserved

The effect of EGR on HCCI combustion – impact of diluting, thermal and chemical aspects: experimental and numerical approaches

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Effective thermal conductivity of nanostructures: A review

peer reviewedWe present a synthesis of recent results on thermal heat conductivity in nano-composites and nano-structures. The model is a mixt of the Effective Medium Approximation (EMA) and Extended Irreversible Thermodynamics (EXIT). The latter is particularly well adapted to the description of small scaled systems and will be used to derive the expression of the thermal conductivity of nanoparticles. The model is applied to spherical, cylindrical (nanowires) and porous nanoparticles, respectively, being embedded in host media, like polymeric matrices and semi-conductors. Good agreement is observed with other models, experimental data and Monte-Carlo simulations. © 2019 by the author(s)

Solutal Marangoni instability of binary mixtures evaporating into air: an analytical model describing highly unstable cases

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Linear stability analysis of an evaporating binary liquid layer with fully transient reference profiles

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