Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session UF2: Chemical ModelingFocus
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Chair: Miles Turner, Doublin City University Room: 2a |
Friday, October 14, 2016 8:30AM - 9:00AM |
UF2.00001: Modeling Complex Chemical Systems: Problems and Solutions Invited Speaker: Jan van Dijk Non-equilibrium plasmas in complex gas mixtures are at the heart of numerous contemporary technologies. They typically contain dozens to hundreds of species, involved in hundreds to thousands of reactions. Chemists and physicists have always been interested in what are now called {\em chemical reduction techniques} (CRT's). The idea of such CRT's is that they reduce the number of species that need to be considered {\em explicitly} without compromising the validity of the model. This is usually achieved on the basis of an analysis of the reaction time scales of the system under study, which identifies species that are in {\em partial equilibrium} after a given time span. The first such CRT that has been widely used in plasma physics was developed in the 1960's and resulted in the concept of {\em effective} ionization and recombination rates\footnote{ D.R. Bates, A.E. Kingston and R.W.P. McWhirter, {\em Proc. R. Soc.} {\bf A267} 297 (1962) }. It was later generalized to systems in which multiple levels are effected by transport\footnote{ J. van Dijk, A. Hartgers, J. Jonkers and J.A.M. van der Mullen, {\em J. Phys. D} {\bf 33} 2798 (2000) }. In recent years there has been a renewed interest in tools for chemical reduction and reaction pathway analysis. An example of the latter is the PumpKin tool\footnote{ A.H. Markosyan, A. Luque, F. J. Gordillo-V\'azquez, U. Ebert {\em Comp. Phys. Comm.} {\bf 185} 2697--2702 (2014). The underlying algorithm is discussed in: Ralph Lehmann, {\em Journal of Atmospheric Chemistry} {\bf 47} 45--78 (2004) }. Another trend is that techniques that have previously been developed in other fields of science are adapted as to be able to handle the plasma state of matter. Examples are the Intrinsic Low Dimension Manifold (ILDM) method and its derivatives, which originate from combustion engineering, and the general-purpose Principle Component Analysis (PCA) technique\footnote{ Peerenboom, K.S.C., Parente, A., Kozak, T., Bogaerts, A. and Degrez, G. {\em Plasma Sources Science and Technology} {\bf 24}(2) 025004 (2015) }. In this contribution we will provide an overview of the most common reduction techniques, then critically assess the pros and cons of the methods that have gained most popularity in recent years. Examples will be provided for plasmas in argon and carbon dioxide. [Preview Abstract] |
Friday, October 14, 2016 9:00AM - 9:15AM |
UF2.00002: A study on ultraviolet photochemical effects on low-pressure oxygen plasmas SiJun Kim, JangJae Lee, KwangKi Kim, YoungSuk Lee, DaeWoon Kim, ShinJae You Low pressure oxygen plasmas have been applied to various industrial processing such as cleaning, ashing and oxidation. Many studies have investigated characteristics of oxygen plasma through plasma modeling and experiments. Although oxygen plasmas are electronegative discharges, photochemical effects on negative ion species and neutral radicals have not yet fully understood. In this study we use a global model (volume averaged) in capacitive reactor design to understand ultraviolet photochemical effect on low-pressure oxygen plasmas and compare with experiments. [Preview Abstract] |
Friday, October 14, 2016 9:15AM - 9:30AM |
UF2.00003: Level-lumping method for the modeling of CO$_{\mathrm{2}}$ vibrational kinetics Antonin Berthelot, Annemie Bogaerts The conversion of greenhouse gases, especially CO$_{\mathrm{2}}$, into value-added chemicals is gaining a very large interest among the scientific and industrial communities. It is known that the excitation of the asymmetric vibrational mode of CO$_{\mathrm{2}}$ is one of the most important processes to achieve high energy efficiencies, thus making the CO$_{\mathrm{2}}$ kinetics very complex. Due to this complexity, the only models that have been developed so far were zero-dimensional models, considering only the variations over time. These models require strong approximations on the geometry of the reactor. In order to reduce the calculation time and to allow the modeling of complex plasma problems in 2D or 3D geometries, we have simplified the chemistry set of CO$_{\mathrm{2}}$ and developed a lumped-levels model for the vibrational kinetics. It was found that a 3-groups model gives a good agreement with the state-to-state model at pressures of 100mbar and above, at the conditions under study. The important dissociation and recombination mechanisms of CO$_{\mathrm{2}}$ have also been investigated. This lumped-levels model is being implemented in a 2D self-consistent microwave plasma code. [Preview Abstract] |
Friday, October 14, 2016 9:30AM - 9:45AM |
UF2.00004: The kinetics of energetic O$^{\mathrm{-}}$ ions in oxygen discharge plasmas Alexander Ponomarev, Nikolay Aleksandrov Monte Carlo simulation was used to study the translational relaxation of energetic O$^{\mathrm{-}}$ ions formed due to dissociative electron attachment to O$_{\mathrm{2}}$ molecules in oxygen and oxygen-containing mixtures in a strong electric field. Initial O$^{\mathrm{-}}$ ions have rather high energies and are more reactive then the ions reaching equilibrium with electric field. Therefore, there is a noticeable probability that electron detachment from the energetic O$^{\mathrm{-}}$ ions or their charge transfer to form O$_{\mathrm{2}}^{\mathrm{-}}$ ions proceed prior to energy degradation of these ions. The probabilities of electron detachment and charge transfer were calculated as a function of the reduced electric field in oxygen and some oxygen-containing mixtures. Comparison with available information about the electron detachment and charge transfer rate coefficients for O$^{\mathrm{-}}$ ions shows that the effect of high reactivity of the initial energetic ions can lead to orders of magnitude increase in the effective rates of these reactions and should be considered in numerical simulation of the properties of discharge plasmas in oxygen and oxygen-containing mixtures. [Preview Abstract] |
Friday, October 14, 2016 9:45AM - 10:00AM |
UF2.00005: A validation study on CO$_2$ chemistry Peter Koelman, Stijn Heijkers, Samaneh Tadayon Musavi, Wouter Graef, Annemie Bogaerts, Jan Dijk, van The demand for renewable energy has increased the popularity of various energy sources, such as solar and wind energy. These sources are intermittent by nature, which typically does not match the demand of energy. Therefore, storage of energy is needed. Current tools for this are, however, costly, slow, and inefficient. Storing energy by the formation of valuable fuels from CO$_2$ is potentially an improvement. By plasma assisted CO$_2$ dissociation CO is produced. In subsequent steps the CO is transformed in valuable fuels. An extensive CO$_2$ microwave plasma chemistry is studied, with special attention to the vibrational modes, which provide a pathway for the dissociation. To that end we developed a global model, which is only time resolved and needs less computational time than spatially resolved models. We present the results from a verification study of the CO$_2$ chemistry. This is done by verification of input data, and by comparison of results obtained by two independent models: ZDPlaskin and PLASIMO's Global Model. We also present results from a sensitivity study of the input data. [Preview Abstract] |
Friday, October 14, 2016 10:00AM - 10:30AM |
UF2.00006: Selfconsistent vibrational and free electron kinetics for CO$_{\mathrm{2}}$ dissociation in cold plasmas Invited Speaker: Mario Capitelli The activation of CO$_{\mathrm{2}}$ by cold plasmas is receiving new theoretical interest thanks to two European groups [1-2]. The Bogaerts group developed a global model for the activation of CO$_{\mathrm{2\thinspace }}$trying to reproduce the experimental values for DBD and microwave discharges. The approach of Pietanza et al was devoted to understand the dependence of electron energy distribution function (eedf) of pure CO$_{\mathrm{2}}$ on the presence of concentrations of electronically and vibrationally excited states taken as parameter. To understand the importance of the vibrational excitation in the dissociation process Pietanza et al compared an upper limit to the dissociation process from a pure vibrational mechanism (PVM) with the corresponding electron impact dissociation rate, the prevalence of the two models depending on the reduced electric field and on the choice of the electron molecule cross section database [2]. Improvement of the Pietanza et al model is being considered [3] by coupling the time dependent Boltzmann solver with the non equilibrium vibrational kinetics of asymmetric mode and with simplified plasma chemistry kinetics describing the ionization/recombination process and the excitation-deexcitation of a metastable level at 10.5eV. A new PVM mechanism is also considered. Preliminary results [3], for both discharge and post discharge conditions, emphasize the action of superelastic collisions involving both vibrationally and electronically excited states in affecting the eedf. The new results can be used to plan a road map for future developments of numerical codes for rationalizing existing experimental values, as well as, for indicating new experimental situations. [1] T.Kozak, A.Bogaerts Plasma Sources Sci. Technol. 24, 042002 (2015); [2] L. D. Pietanza, G. Colonna, G. D'Ammando, A. Laricchiuta and M. Capitelli, Plasma Sources Sci. Technol. (Fast Track Communication) 24, 042002 (2015); J.Phys.Chem.A 120, 2614(2016); [3] L. D. Pietanza et al. Plasma Phys. Control. Fusion (2016) submitted [Preview Abstract] |
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