Václav Nevrlý

Dispersion of Light and Heavy Pollutants in Urban Scale Models: CO2 Laser Photoacoustic Studies

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO2 laser photoacoustic spectroscopy in the region of the atmospheric window (9–10 μm). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

First analysis of the high resolution FTIR spectrum of the ν2 band of the FCO2 radical at 970.2 cm−1

The infrared spectrum of the fluorocarboxyl radical, FCO2, was recorded at high resolution (0.0035 cm−1) in the 600–1400 cm−1 region on a Bruker IFS 120 HR Fourier transform spectrometer of the University of Wuppertal. The analysis of the A-type ν2 band of FCO2 (CF stretching mode) centred at 970.208 cm−1 was performed making use of the ground state parameters achieved by [L. Kolesniková, J. Varga, H. Beckers, M. Šimečková, Z. Zelinger, L. Nová Stříteská, P. Kania, H. Willner, and Š. Urban, J. Chem. Phys. 128, 224302/1 (2008)]. For the FCO2 radical, the ν2 transitions are, in principle, split into two spin–rotation subcomponents corresponding to J = N ±1/2. However the spin–rotation parameters in the 21 vibrational state have values similar to those of the ground state, and spin–rotation doublings are observable only for the weaker transitions involving medium Ka or Kc values in the P and R branches. The ν2 fundamental band is weakly perturbed by the 2ν5 dark overtone band at 965.4 cm−1 and the 21 and 52 energy levels of FCO2 are coupled through Fermi type resonances. The final energy level calculation was performed accounting both for the spin–rotation interaction within the 21 and 52 vibrational states, and the 21 ⇔ 52 Fermi-type resonances.

Experiments and mathematical models of methane flames and explosions in a complex geometry

The paper focuses on the application of mathematical modeling of methane turbulent combustion in a complex geometry and on the choice of parameters of one-step and two-step chemical kinetics models. Parameters of chemical kinetics have a profound influence on the correct implementation of the combustion mathematical model used in the CFD (computational fluid dynamics) simulation of the methane-air mixture explosion in a family house. Results are compared with experimental measurements.

Desorption/ablation of lithium fluoride induced by extreme ultraviolet laser radiation

Abstract The availability of reliable modeling tools and input data required for the prediction of surface removal rate from the lithium fluoride targets irradiated by the intense photon beams is essential for many practical aspects. This study is motivated by the practical implementation of soft X-ray (SXR) or extreme ultraviolet (XUV) lasers for the pulsed ablation and thin film deposition. Specifically, it is focused on quantitative description of XUV laser-induced desorption/ablation from lithium fluoride, which is a reference large band-gap dielectric material with ionic crystalline structure. Computational framework was proposed and employed here for the reconstruction of plume expansion dynamics induced by the irradiation of lithium fluoride targets. The morphology of experimentally observed desorption/ablation craters were reproduced using idealized representation (two-zone approximation) of the laser fluence profile. The calculation of desorption/ablation rate was performed using one-dimensional thermomechanic model (XUV-ABLATOR code) taking into account laser heating and surface evaporation of the lithium fluoride target occurring on a nanosecond timescale. This step was followed by the application of two-dimensional hydrodynamic solver for description of laser-produced plasma plume expansion dynamics. The calculated plume lengths determined by numerical simulations were compared with a simple adiabatic expansion (blast-wave) model.

CFD modelling for atmospheric pollutants/aerosols studies within the complex terrains of urban areas and industrial sites

Computational fluid dynamic (CFD) modelling of pollution dispersion and chemical conversion to aerosol particles in the atmospheric boundary layer (ABL) has been studied. The investigation focused on the numerical modelling above complex orographic terrains of urban areas and industrial sites including the dispersion of toxic substances in the air as a result of accidents. A finite-rate model of chemical reactions, including the turbulence chemistry for modelling the reaction between nitric acid and ammonia, has been applied. As supporting experiments, online monitoring of the spatial distribution of pollutants and aerosols has been performed above real complex areas. Minimal detectable concentrations 8 μg m–3 (SO2), 20 μg m–3 (NO2), 2 μg m–3 (O3) and minimal detectable absorptivity 5 × 10–7 cm–1 (aerosols) have been reached.

A new line-shape asymmetry model for wavelength modulation spectroscopy in gaseous flows

Abstract This communication reports technical notes on the development and application of an automated line-shape fitting procedure for wavelength modulation spectroscopy (WMS). Near-infrared transitions of carbon dioxide (CO2) around 1573 nm were measured in vertical cold (nonreacting) flow of CO2 at atmospheric pressure using WMS with demodulation at second harmonic frequency. Semi-empirical model based on the set of so-called Gabor functions was developed and parameters of Lorentzian line-shape profile and its asymmetry resulting from simultaneous frequency and amplitude response of the current-modulated semiconductor laser were determined. Nonlinear least-square fitting procedure employing differential evolution algorithm was successfully utilized for performing this task. Line-shape fitting procedure enabling efficient signal de-noising and background subtraction of wavelength modulation spectra was implemented into an open-source code.

Material properties of lithium fluoride for predicting XUV laser ablation rate and threshold fluence

This paper deals with prediction of extreme ultraviolet (XUV) laser ablation of lithium fluoride at nanosecond timescales. Material properties of lithium fluoride were determined based on bibliographic survey. These data are necessary for theoretical estimation of surface removal rate in relevance to XUV laser desorption/ablation process. Parameters of XUV radiation pulses generated by the Prague capillary-discharge laser (CDL) desktop system were assumed in this context. Prediction of ablation curve and threshold laser fluence for lithium fluoride was performed employing XUV-ABLATOR code. Quasi-random sampling approach was used for evaluating its predictive capabilities in the means of variance and stability of model outputs in expected range of uncertainties. These results were compared to experimental data observed previously.

Global sensitivity analysis of the XUV-ABLATOR code

Availability of numerical model providing reliable estimation of the parameters of ablation processes induced by extreme ultraviolet laser pulses in the range of nanosecond and sub-picosecond timescales is highly desirable for recent experimental research as well as for practical purposes. Performance of the one-dimensional thermodynamic code (XUV-ABLATOR) in predicting the relationship of ablation rate and laser fluence is investigated for three reference materials: (i) silicon, (ii) fused silica and (iii) polymethyl methacrylate. The effect of pulse duration and different material properties on the model predictions is studied in the frame of this contribution for the conditions typical for two compact laser systems operating at 46.9 nm. Software implementation of the XUV-ABLATOR code including graphical users interface and the set of tools for sensitivity analysis was developed. Global sensitivity analysis using high dimensional model representation in combination with quasi-random sampling was applied in order to identify the most critical input data as well as to explore the uncertainty range of model results.

CO2 laser photoacoustic spectrometry: sensitivity and drift analysis

Trace gas measurements were performed by the eddy correlation technique. The time domain stability criterion for laminar and turbulent flows measured in the street canyon model was determined. The evaluation of the instrument performance was done by the concentration measurements (CH3OH, C2H5OH). The Allan and Hadamard variance methods were used for stability analysis. The dependence of variances on different degrees of flow turbulence was evaluated. The influence of turbulence on the optimal averaging time for minimum detectable concentrations has been studied. The stability analysis of experimental set up consisting of the CO2 laser photoacoustic detection and the simulated atmosphere in a wind tunnel was performed for different sample concentrations and flows. The sensitivity and stability analysis were determined by 1000 s, 2000 s and 10 000 s measurements.

Mathematical Modeling of Methane Combustion

Mathematical Modeling of Methane Combustion The paper presents the process of the creation of the mathematical model of methane turbulent combustion using ANSYS FLUENT 13.0 software. The decommissioned mathematical model for species transfer with chemical reaction is described, where burning is based on stoichiometric equations of perfect combustion. Work also analyzes the appropriateness of models dealing with the kinetics of burning and describes their mutual comparison.