In this work, a dielectrics barriers discharge (DBD) in an Ar/O2 gas mixture excited with sinusoidal applied voltage for ozone generation has been investigated in order to draw attention to the important role of the kinetic scheme of this gas mixture in the plasma discharge. The adopted model was based on argon-oxygen plasma chemistry, the external circuit, and the Boltzmann equations. This approach predicts the optimal operating conditions and can also describes the chemical and electrical aspects of the DBD reactor. The kinetic scheme of an Ar/O2 gas mixture takes into account 15 species regrouped in 123 reactions. The time evolutions of kinetic and electric characteristics of plasma discharges, and the effect of the main discharge parameters on DBD behavior and ozone efficiency are analyzed and discussed.

Research on corona wind generation has been increasing in recent years because of its potential technological applications, particularly those related to improving heat transfer in small-scale devices. Since numerical simulations play a key role in the design of these applications, computationally efficient modeling of corona discharge is imperative. This work presents a new approach that allows rapid computation of the electrohydrodynamic (EHD) force density responsible for the generation of electric wind. Arbitrary electrode configurations can easily be dealt with in the model, since only the Laplacian electric field lines have to be determined numerically. Then, using approximated analytical approximations of the electric field intensity along the field lines, the spatial distribution of the current density and the space charge density can be easily determined. The model has been satisfactorily tested against experimental measurements of the current–voltage characteristic and the current density distribution on the cathode. Furthermore, the electric wind computed from the EHD force agrees quite satisfactorily with measurements carried out in different electrode configurations. Finally, the model has been applied to a new electrode configuration that has greater potential for heat transfer applications.

In this work, positive corona and negative corona are investigated numerically to compare their respective species productions and spatial distributions in dry air, assuming a parallel wire-to-plate electrode configuration and a stationary discharge. The electrohydrodynamic (EHD) force, which is at the origin of the EHD flow (or ionic wind), is computed by means of a simplified analytical model. This force is used in Navier-Stokes equation, which is solved along with the continuity equations for neutral species. The gain/loss rates of neutral species are determined from a plasma-chemical model that includes the most important reactions between electrons, atoms and molecules. The numerical solution of these equations allows us to compare the effect of the corona wire polarity on the 2D spatial distribution of neutral species and their corresponding number densities. The simulation results show that the effect of the EHD flow on the species distribution is greater in the case of negative corona. In the case of ozone, the spatial distribution inside the reactor is approximately similar in both coronas but, in negative corona, the concentration of ozone is around three orders of magnitude higher than that in the positive corona.

In the present work, the spatial distribution of the electric field, the space charge density and the electrohydrodynamic force (EHD) of a stationary DC positive corona discharge in air are evaluated with the aim of characterizing their effects on the electric wind generated by the electrical discharge. Two electrode configurations have been considered: (a) wire-to-plane, and (b) two wires-to-plane, with three different values of the distance between the wires (0.2 cm, 1 cm, and 2 cm). Each wire is subjected to a high positive voltage and the plane is grounded. The electric field and the space charge density have been obtained by solving numerically the continuity equation for the charged particles coupled to Poisson equation. These two physical quantities allow to calculate the EHD force and to illustrate the effect of the interaction between the two wires on the EHD force distribution.

In this work, we determine precisely the electric wind velocity, produced by a direct current (DC) corona discharge in air, using three electrode geometrical configurations: 'wire-to-plate' (a), 'two wires-to-plate' (b) and 'three wires-to-plate' (c). Each electrode wire is subjected to the same high positive voltage while the plate is grounded. The electric wind velocity is determined through a mathematical model based on the resolution of Navier-Stokes equation, in which a source term consisting in the electro-hydrodynamic (EHD) force, already established by our group in the form of a simplified analytical expression, is used. The results found allow to compare the profile of the electric wind produced by the corona discharge for the three electrode geometrical configurations ((a), (b) and (c)).

Carbon negative emission technologies (NETs) such as CO2 direct air capture (DAC) are being already considered as necessary for climate change mitigation. This paper investigates CO2 capture at room temperature and atmospheric pressure by a fluidized bed of Ca(OH)(2) powder as influenced by the relative humidity (RH) to which this sorbent was exposed during storage. Humidity is precisely controlled by means of several supersaturared salt solutions, and FTIR spectrometry is used to measure accurately the time evolution of CO2 and H2O concentrations in the effluent gas. Results show that CO2 capture is promoted by an increase of the storage RH. The observed effect is particularly important for very high storage RH (similar to 100%, near the dew point). After the capture tests, quantitative analyses of sample composition have been carried out using X-ray powder diffractometry. These analyses have revealed that the CaCO3 content after CO2 capture originates from carbonation in samples that were stored under similar to 100% RH. On the other hand, in samples stored under low to moderate RH, the presence of CaCO3 is significantly reduced, indicating that most of CO2 capture might take place through physical adsorption.

The use of calcium hydroxide as sorbent of CO2 in low concentration streams (1% CO2 vol.) has been experimentally investigated. For that purpose, a CO2/N2 dry gas mixture, at ambient temperature and atmospheric pressure, was flowed through a bed of Ca(OH)2, and the concentration of CO2 in the effluent gas was monitored. In order to improve the fluidizability, both hydrophilic and hydrophobic nanosilica particles were added to the sorbent, and its effect on the absorption of CO2 was investigated. The results showed that the addition of nanosilica increases the capture capacity of the sorbent (compared to the raw material), and the best results were obtained when using hydrophilic nanosilica. Additionally, to elucidate how the CO2 capture process is affected by relative humidity during the storage of Ca(OH)2, the sorbent was kept in a controlled CO2-free atmosphere with constant humidity prior to the experiments. The results showed that samples stored in an atmosphere with high relative humidity exhibit a significantly higher CO2 absorption capacity.

The objective of this work is to study the effect of changing the electrode configuration ('wire-plane' (a), 'two wires-plane' (b) and 'three wires-plane' (c)) on the spatial distribution of the neutral chemical species generated by a positive corona discharge, with a special focus on the effect of the electric wind on the distribution of these chemical species. This task is accomplished using a mathematical model that is based on the numerical resolution of Navier-Stokes equation coupled to the continuity equations of neutral species generated by the positive corona discharge. Regarding the chemical reactions, a model of plasma chemistry, which includes the most important chemical reactions occurring between electrons, atoms and molecules in the air, has been used. One of the main results is the comparison of the ozone density produced by the positive corona discharge for the three mentioned electrode configurations.

Carbon dioxide dissociation using dielectric barrier discharge has been experimentally investigated. The electrical discharge was stimulated using high voltage pulses of nanosecond duration, with a repetition rate in the range of 100–1000 Hz. The reactor consisted of two stainless steel plane circular electrodes covered with either fused silica glasses or polytetrafluoroethylene (PTFE) films. Experiments were carried in pure CO2, and the concentration of carbon monoxide and ozone in the effluent gas was determined using UV/VIS and FTIR spectrophotometry. The results have shown that using silica as dielectric layers results in a higher generation efficiency for both CO and O3.

The spatial distribution of charged particles (electrons, negative ions and positive ions) and electric field have been evaluated using a semi-analytical approach of the positive and negative corona discharge for a wire-to-plate electrode system. Thus, approximate formulas useful for the characterization and control of corona discharge devices are provided, which helps to significantly reduce computational costs. Based on the obtained results, the electro-hydrodynamic (EHD) force generated by the corona discharge has been determined, and it has been used in the Navier-Stokes equations to compute the spatial distribution of the gas velocity. As a result, the influence of the corona plasma region in the flow pattern, particularly in the vicinity of the corona electrode, has been brought to light, which helps to understand the different flow velocities observed in positive and negative coronas. Moreover, the influence of voltage, wire radius, and inter-electrode separation on the electric wind velocity has been investigated.

The electrohydrodynamic air flow generated by a positive corona discharge, and its effect on the spatial distribution of chemical species within a wire-plate corona reactor, have been numerically simulated. The computational model is based on the solutions of the Navier-Stokes equation and the continuity equation of each chemical species generated by the electrical discharge. A simplified analytical expression of the electric force density, which only requires the current density as the input parameter, has been used in the Navier-Stokes equation to obtain the velocity field. For the solution of the continuity equations, a plasma chemistry model that includes the most important reactions between electrons, atoms and molecules in air has been used. Similar to the electric force, the electron density distribution has been approximated by using a semi-analytical expression appropriate for the electrode geometry. The results of the study show that the spatial distribution of chemical species can be very different, and depends on the interplay between the electrohydrodynamic flow, the chemical kinetics of the species and its characteristic lifetime.

The plasma chemical splitting of carbon dioxide (CO2) to produce carbon monoxide (CO) in a pulsed corona discharge was investigated from both an experimental and a numerical standpoint. High voltage nanosecond pulses were applied to a stream of pure CO2 and its mixture with argon, and the gaseous products were identified using Fourier transform infrared spectroscopy. Due to the shape of pulses, the process of CO2 splitting was found to proceed in two phases. The first phase is dominated by ionization, which generates a high electron density. Then, during the second phase, direct electron impact dissociation of CO2 contributes to a large portion of CO production. Conversion and energy efficiency were calculated for the tested conditions. The conversions achieved are comparable to those obtained using other high pressure non-thermal discharges, such as dielectric barrier discharge. However, the energy efficiencies were considerably higher, which are favorable to industrial applications that require atmospheric conditions and elevated gas flow rates.

Carbon dioxide decomposition in mixtures of CO2 and O-2 has been experimentally investigated using dielectric barrier discharge, with special interest on O-3 and CO productions. Experiments have been conducted at different frequencies and operating voltages, and the concentration of O3 and CO have been measured by means of absorption spectroscopy in the UV and in the IR regions. According to the observations, the production of both species can be substantially increased by adding molecular oxygen to carbon dioxide, even in small proportions.

[PDF] [Full Text] 2007; 31 (1): 119-120. Advan in Physiol Edu Angel Agis-Torres and Elvira López-Oliva Their Critical Abilities Criticizing Models as a Strategy to Help Students Understand Hemodynamics and Develop [PDF] [Full Text] [Abstract] , December , 2010; 34 (4): 167-169. Advan in Physiol Edu Simon Brown and Susan Salter Analogies in science and science teaching [PDF] [Full Text] [Abstract] , December , 2013; 37 (4): 321-326. Advan in Physiol Edu Marina Djelic, Sanja Mazic and Dejan Zikic arterial blood flow reflection A novel laboratory approach for the demonstration of hemodynamic principles: the

The development of negative corona Trichel pulses in oxygen between a spherical cathode and a plane is investigated using a plasma chemical model of ten selected species, which includes electrons, ions and neutrals. The interaction among these species is described by a model that incorporates the most important plasma chemical processes, such as ionization, electron attachment and detachment, electron impact dissociation and excitation, and clustering. The spatio-temporal evolution of charged and neutral species and their reaction rates are evaluated along different moments during the pulses. The case of the first Trichel pulse is considered separately, since its characteristics clearly differ from the subsequent pulses. The results show that the negative space charge is constituted of different types of ions, depending on the stage of the pulse. Moreover, a spatial segregation of negative ions is observed during the post-pulse period. Regarding neutral species, ozone increases linearly with time, without being considerably affected by the occurrence of pulses.

The problem of the propagation of an electrical discharge between a spherical electrode and a plane has been solved by means of finite element methods (FEM) using a fluid approximation and assuming weak ionization and local equilibrium with the electric field. The numerical simulation of this type of problems presents the usual difficulties of convection-diffusion-reaction problems, in addition to those associated with the nonlinearities of the charged species velocities, the formation of steep gradients of the electric field and particle densities, and the coexistence of very different temporal scales. The effect of using different temporal discretizations for the numerical integration of the corresponding system of partial differential equations will be here investigated. In particular, the so-called theta-methods will be used, which allows to implement implicit, semi-explicit and fully explicit schemes in a simple way.

Ozone generation by negative DC corona discharge in N-2-O-2 mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm(3) min(-1) to 200 cm(3) min(-1)) and gas compositions (5% to 90% of O-2), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70-80%.

This work presents a study on the chemisorption of CO2 by a bed of Ca(OH)2 powder subjected to the flow of a dry CO2/N2 gas mixture (1vol.% CO2) at ambient temperature and atmospheric pressure. The amount of CO2 and vapor water in the effluent gas from the fluidized bed is analyzed by means of FTIR spectrophotometry. The results obtained indicate that, even in an almost dry atmosphere (RH⪕0.01%), CO2 capture in the fluidized bed occurs by chemisorption on Ca(OH)2, as inferred from the rise of vapor water at the end of the fast carbonation phase. The use of nanosilica as an additive increases the gas–solids contact efficiency and, therefore, enhances CO2 chemisorption on Ca(OH)2 particles. This process is initially activated by free molecular water physisorbed on the material and becomes autocatalyzed by water produced from Ca(OH)2 carbonation. Accordingly, the addition of hydrophilic nanosilica, capable of retaining higher amounts of free molecular water, yields a further enhancement of the CO2 fast sorption capacity.