Numerical modelling of the work of a pulsed aerosol system for fire fighting at the ignitions of liquid hydrocarbon fuels

The work of a pulsed aerosol system for fire fighting is modelled, which is designed for fire fighting at oil storages and at the spills of oil products, whose vapors were modelled by gaseous methane. The system represents a device for separate installation, which consists of a charge of solid propellant (the gas generator) and a container with fine-dispersed powder of the flame-damper substance. The methane combustion was described by a one-stage gross-reaction, the influence of the concentration of vapors of the flame-damper substance on the combustion process was taken into account by reducing the pre-exponent factor in the Arrhenius law and was described by an empirical dependence. The computational experiment showed that the application of the pulsed aerosol system for fire fighting ensures an efficient transport of fine-dispersed aerosol particles of the flame-damping substance and its forming vapors to the combustion zone; the concentration of particles ensures the damping of the heat source. The work was financially supported by the President of the Russian Federation (NSh-9886.2006.9), Presidium of RAS (Project No. 4.1), and the Program of Interdisciplinary Integration Basic Research of SB RAS No. 26.     

Chemical processes in the single-electrode pulsed HF discharge plasma

It is shown that in the discharge plasma of the atomic emission spectrometer, the formation of CN molecules from CO₂ and N₂ takes place. The correctness of measuring the CO₂ concentration from the emission intensity of CN at a wavelength of 388.3 nm in respiratory processes is proved experimentally.     

Drying processes in the presence of temperature gradients--pore-scale modelling

The influence of temperature gradients on the drying of water-saturated porous networks has been studied. We have focussed on the influence of the temperature on the drying process via the equilibrium vapor density rhoe, because this is the most sensitive parameter with respect to variations of the temperature T. We have used a 2D model which accounts for both capillary and buoyancy forces. Invasion events by air or water are handled by standard rules of invasion percolation in a gradient (IPG). Vapor fluxes are calculated by solving a discretized version of the Laplace equation. In the model the temperature T varies linearly from the open side T0 to the closed side TL. The temperature gradients strongly influence the cluster evolution during the process, because they facilitate vapor transport through wet regions. When T0TL, the front movement is enhanced and the air ingress in the wet region behind the front is inhibited. The behavior of 3D systems differs from that of 2D systems, because the point where air percolates the system and the point where the water network breaks up in isolated clusters do not coincide. Before the latter fragmentation point the temperature will mainly influence the drying rates. After this point also the water distribution becomes sensitive to the temperature profile.     

Computational modelling of thermophysical processes in the light metals industry

This survey focuses on the aluminium industry, mostly on process aspects as opposed to metallurgical aspects. It covers recent work on process models involving fluid flow and heat transfer, and extends to all important categories of processes encountered in the primary aluminium industry, from raw materials and reduction to cast shop and recycling. This includes a wide variety of processes from precipitators, calciners, rotary kilns, baking furnaces, reduction cells, casting and mixing furnaces to recycling furnaces and metal filtration. A review is carried out on the modelling work, the applications, and the needs expressed not only in analysis and design but also in process control, optimization and supervision, as well as operator training. A summary is given of the problems perceived, mainly in the field of model parameters and model validation. Indications on future trends are also given. Conclusions are drawn from the survey of this fast-expanding body of knowledge that suggests tough challenges as well as unprecedented opportunities. Suggestions are made as to how some of those challenges could be met.     

Drying processes in the presence of temperature gradients --Pore-scale modelling

The European Physical Journal E - The influence of temperature gradients on the drying of water-saturated porous networks has been studied. We have focussed on the influence of the temperature on...     

Numerical modelling of the speech intelligibility in dining spaces

The objective of this paper is to study the basic characteristics of conversation intelligibility in dining spaces where the seat number and occupancy level are relatively high, and to investigate the effectiveness of strategic architectural acoustic treatments on improving the intelligibility. A radiosity-based computer model has been developed and a parametric study has been carried out using the model. Computation in a typical dining hall shows that a design merely based on the current guidelines for space use may lead to very poor conversation intelligibility. Increasing boundary absorption can typically increase the speech transmission index (STI) by 0.2-0.4. For a given amount of absorption, in a regularly-shaped dining hall the difference in intelligibility between various absorber arrangements is generally negligible, whereas in a flat or long dining hall it is important to strategically arrange the absorbers. The improvement in intelligibility by enlarging the area per diner, changing the ceiling height, and increasing the length/width ratio has also been investigated. For a given room condition, the model can give the maximum number of seats according to the requirement in intelligibility.     

Numerical modelling of ion transport in flames

This paper presents a modelling framework to compute the diffusivity and mobility of ions in flames. The (n, 6, 4) interaction potential is adopted to model collisions between neutral and charged species. All required parameters in the potential are related to the polarizability of the species pair via semi-empirical formulas, which are derived using the most recently published data or best estimates. The resulting framework permits computation of the transport coefficients of any ion found in a hydrocarbon flame. The accuracy of the proposed method is evaluated by comparing its predictions with experimental data on the mobility of selected ions in single-component neutral gases. Based on this analysis, the value of a model constant available in the literature is modified in order to improve the model's predictions. The newly determined ion transport coefficients are used as part of a previously developed numerical approach to compute the distribution of charged species in a freely propagating premixed lean CH₄/O₂ flame. Since a significant scatter of polarizability data exists in the literature, the effects of changes in polarizability on ion transport properties and the spatial distribution of ions in flames are explored. Our analysis shows that changes in polarizability propagate with decreasing effect from binary transport coefficients to species number densities. We conclude that the chosen polarizability value has a limited effect on the ion distribution in freely propagating flames. We expect that the modelling framework proposed here will benefit future efforts in modelling the effect of external voltages on flames. Supplemental data for this article can be accessed at http://dx.doi.org/10.1080/13647830.2015.1090018.     

Nonresonant quantum electrodynamics processes in a pulsed laser field

This review contains theoretical study of nonresonant quantum electrodynamics processes of the first and second orders in the fine-structure constant in a pulsed laser field. The approximation is examined when the pulse width is considerably greater than the characteristic time of wave oscillations. It was demonstrated that for nonrelativistic particle energy the differential cross section of a process in a pulsed light fields may considerably difference from the corresponding cross section in an absence of a laser field. Results obtained may be experimentally verified by the scientific facilities at the SLAC National Accelerator Laboratory and FAIR (Facility for Antiproton and Ion Research, Darmstadt, Germany) project.     

Numerical modelling of foam Couette flows

A numerical computation based on a tensorial visco-elasto-plastic model based on continuous mechanics is compared to experimental measurements on liquid foams for a bidimensional Couette flow between two glass plates, both in stationary and transient cases. The main features of the model are elasticity up to a plastic yield stress, and viscoelasticity above it. The effect of the friction of the plates is taken into account. The numerical modelling is based on a small set of standard material parameters that are fully characterised. Shear localisation as well as acute transient observations are reproduced and agree with experimental measurements. The plasticity appears to be the fundamental mechanism of the localisation of the flow. Finally, the present approach could be extended from liquid foams to similar materials such as emulsions, colloids or wet granular materials, that exhibit localisation.     

Numerical modelling of anisotropy in 4H－SiC MESFET‘s

A numerical model for 4H-SiC MESFET anisotropy is presented in this paper and the device performances, such as breakdown, temperature and transient characteristics, are demonstrated. The simulation results show obvious effects of the anisotropy for 4H-SiC and are in better accordance with the experimental results. The anisotropy for 4H-SiC should be involved in the device design to acquire better performances.     

Numerical analysis of TOF measurements in pulsed laser ablation

The results of numerical simulation of pulsed laser ablation both in vacuum and into a background gas are presented. The influences of different processes, such as time evolution of the surface temperature, interspecies interactions (elastic collisions, recombination-dissociation reaction), interaction with an ambient gas, and excitations-relaxation processes on time-of-flight (TOF) distributions are examined. Experimentally obtained time-of-flight distributions are further analyzed, based on the results of numerical simulation. It is found that with the aid of numerical results one can explain not only the shape of the TOF distribution, but also the distance dependency of its maximum position (mean delay time). In addition, the mechanisms leading to the appearance of bimodal time-of-flight distribution are revealed. The study presents particular interest for the analysis of experimental results obtained during pulsed laser ablation.     

Numerical modelling of the radiation efficiency of asymmetrical structures

The radiation efficiency of a structural element is required by some models in order to predict its sound insulation. A common assumption is that the radiation on both sides of the element is the same. This is not true for asymmetrical structural elements like lightweight floors consisting of a beam-supported flat board. The radiation efficiency is larger on the beam side, because the beams act as exciters and increase the pressure level in the room. These different radiation efficiencies are calculated here for a two-dimensional cross-section by using finite elements and boundary elements. The obtained preliminary results illustrate that considering a single radiation efficiency can be a source of errors and that further investigation is required in order to improve predictions.     

On the equivalence between different methods of modelling diffusion processes

For a damped harmonic oscillator with frequency fluctuations it is shown that the phenomenological modelling of this system using the Stratonovich interpretation of stochastic differential equations leads to the same Fokker-Planck equation as the analysis of this system by means of projector techniques.     

Numerical simulation of transient processes in hydroturbines

A method for calculation of unsteady 3D turbulent flows in hydro turbines of power plants developed for simulation of the transient processes is presented herein. The method is based on joint solution to the Reynolds-averaged Navier—Stokes equations for incompressible fluid flow written for moving mesh, the equation of runner rotation and the system of 1D equations describing propagation of elastic hydraulic shock in the flow domain. The exchange in flow parameters between the penstock and hydro turbine regions is considered in this approach. Results of transient processes simulation are presented for several modes: start-up to the turbine regime, instantaneous load shedding, and output power decrease. Comparison with experimental data is performed.     

Numerical simulation on the operational characteristics of the pulsed inductive acceleration

To analyse the ionization and acceleration properties of an inductive plasma excited by a pulsed current flowing through the planar coil, the extended GLM formulations of the MHD (EGLM‐MHD) model, combined with the high‐temperature thermodynamic and transport model, is employed to simulate the characteristics of the flow. The two‐dimensional axisymmetric calculation captures the generation, growth, and acceleration of the current sheet, and the process is completed in the first half period. The sheet is mainly comprised of lower ionization level ions in the front and higher level ions at the back, and the density is one order higher than that of the residual plasma on the coil surface. As the abscissa value of the sheet is larger than the decoupling distance, a reversed flow emerges, generating a backward impulse, and the negative velocity can be more than 15 km/s at peak intensity B₀ = 0.5 T. In the second 1/4 period, the magnetic field and current density distribute non‐linearly on the surface and regularly in the sheet, caused by the reversing of the changing rate of the magnetic field and the particles' radial diffusion. The results at different intensities show that, for the same coil size, the time at which the maximum velocity V_max appears is advanced as the intensity increases, and V_max can be greater than 20 km/s above 0.5 T.     

Numerical modelling of methanol liquid pool fires

The focus of this paper is on numerical modelling of methanol liquid pool fires. A mathematical model is first developed to describe the evaporation and burning of a two-dimensional or axisymmetric pool containing pure liquid methanol. Then, the complete set of unsteady, compressible Navier-Stokes equations for reactive flows are solved in the gas phase to describe the convection of the fuel gases away from the pool surface, diffusion of the gases into the surrounding air and the oxidation of the fuel into product species. Heat transfer into the liquid pool and the metal container through conduction, convection and radiation are modelled by solving a modified form of the energy equation. Clausius–Clapeyron relationships are invoked to model the evaporation rate of a two-dimensional pool of pure liquid methanol. The governing equations along with appropriate boundary and interface conditions are solved using the flux-corrected transport algorithm. Numerical results exhibit a flame structure that compares well with experimental observations. Temperature profiles and burning rates were found to compare favourably with experimental data from single- and three-compartment laboratory burners. The model predicts a puffing frequency of approximately 12 Hz for a 1 cm diameter methanol pool in the absence of any air co-flow. It is also observed that increasing the air co-flow velocity helps in stabilizing the diffusion flame, by pushing the vortical structures away from the flame region.