K. V. Dobrego

Flame localization inside axis-symmetric cylindrical and spherical porous media burners

It is shown analytically and by means of numerical simulation that flame front localization inside axis-symmetric cylindrical and spherical porous media burners (hereinafter PMB) is not defined only by fuel flow rate and system parameters, but also depends on combustion ignition coordinate. In a certain parameter range, combustion front does not move significantly from the place of its initial ignition. It is shown that heat losses at the outer boundary of PMB determine the specified peculiarities, with fuel flow rate, heat content of the mixture and the PMB external radius being the governing parameters.

Dynamics of filtration combustion front perturbation in the tubular porous media burner

Abstract The state-of-the-art of filtration combustion instability researches is presented. Dynamics of filtration combustion inclination instability is investigated experimentally, analytically and numerically. It is found that inclination amplitude growth velocity on the linear stage is proportional to filtration combustion wave velocity uw, system diameter D0 and inversed diameter of porous media particles d 0 : Δ X ∼u w (D 0 /d 0 ) . The tendency of thermal compensation of perturbation is confirmed by experiments and 2D numerical simulation. In the case of inclination growth stoppage, inclination maximum amplitude or amplitude of saturation can be estimated via the dimensionless wave velocity u and system geometrical parameters ΔXmax∼(u/(1−u))(D02/d0). The concept of perturbation two-staged evolution, which includes initial linear perturbation growth due to local filtration redistribution and following complex thermal and hydrodynamic reorganization of the system, is supported by experimental data and 2D simulation.

Modeling of diffusion filtration combustion radiative burner

Abstract Non-premixed filtration combustion is a new branch of the filtration combustion that combines some properties of turbulent diffusion flames and premixed filtration combustion. Two-dimensional, two-temperature and multi-component model for non-premixed filtration combustion simulation is presented. Parametric study of radiative efficiency of the burner is performed. The lower limit of total equivalence ratio ϕ for the simulated system is studied parametrically. Simulation predicts high stability of the flame at low equivalence ratios. It is shown that Burke–Schumann combustion and mixing rate well conforms to heat release rate in the non-premixed filtration combustion system.

Effect of porous media transparency on spherical and cylindrical filtrational combustion heaters performance

Abstract An influence of partial transparency of a porous media on radiative efficiency, maximum solid phase temperature and combustion localization radius of cylindrical and spherical filtration heater has been investigated by numerical modeling. It is shown that partial transmittance of radiation in amorphous quartz balls bed provides for 2–5% increase in heater radiative efficiency in comparison with opaque material of carcass. In conditions of elevated ambient temperatures (as in, e.g., thermal kilns etc.), the increase in efficiency is smaller. It is shown that the transparency of porous media may not only decrease but, unexpectedly, increase maximum solid temperatures in comparison with the opaque one, in the case of big system size and high flow rate. In the later case, superadiabatic temperature excess (50–150 K) can be obtained in a solid phase. Also, some models of porous media optical properties are discussed.

THERMAL RECOVERY OF SORBENTS BY FILTRATION COMBUSTION

Abstract We have investigated theoretically and experimentally the process of filtration combustion with hydrocarbon desorption from a porous skeleton realized, in particular, in heat cleaning of porous media out of residues of organic impurities. Two basic configurations were considered: fixed and moving beds. The problem of the combustion wave propagation in a system with three phases—gaseous, liquid, and inert solid—has been solved analytically. The specific features of this process as compared to the conventional filtration combustion of gases have been revealed. The dependences of the basic characteristics of the waves on the content of methane in the gas mixture as well as of absorbed oil and water in a porous medium have been obtained. A comparison with the experimental data has been made. Recommendations for optimizing the operation of decontamination plants on the basis of the process considered are given.

Localization of the combustion front in a disk-type filtration heater under conditions of intense external heat release

A one-temperature analytical model for determination of the localization radius of the combustion zone in a filtration heater of the “disk-sector” type is considered. The basic parametric dependences of the process on the mass flow rate, heat content of the mixture, and volume-averaged coefficient of external heat release are studied. A comparison with experimental data demonstrates that the model offers an adequate qualitative description of the basic characteristics of system operation.

Numerical analysis of electrical conduction in carbon nanostructures

Abstract. Electric conduction in structures containing fullerenes was simulated. The electric current was calculated as a function of the bias voltage using the Landauer approach, thereby connecting charge transport with the transmission of electrons. To obtain the transmission matrix components, the supplementary problem of the electron scattering by the model potential was solved. Three types of structures were considered: a single fullerene molecule, a dimer of fullerenes, and a cluster of eight fullerenes. The current-voltage characteristics of these structures may have negative-conductance regions which make it possible to use them as active components of nanoelectronic devices.

Transition from the regime of low rates of filtration combustion of gases to the regime of high rates with a pressure increase

Regularities of the transition from the regime of low rates (RLR) of filtration combustion (FC) of gases to the regime of high rates (RHR) with a pressure increase are investigated. It is shown that allowance for gas-phase transfer is important for description of FC, at least when the size of the skeleton pores d>1.5–2.0 mm and the calorific power of the fuel exceeds the limit of propagation of the flame. With an increase of 1–2 atm in the working pressure as compared to atmospheric pressure the critical pore size decreases by a factor of 2.0–2.5. A theoretical model that makes it possible to evaluate the velocities and temperatures of FC stationary waves under conditions of the transition from RLR to RHR and to establish realization limits for these regimes is proposed. It is shown that a more adequate description of the transient regime and the regime of high rates is achieved when the turbulent character of the combustion is allowed for.