Modeling heat and mass transfer in intumescent fire-retardant coatings

The heat-and mass-transfer processes and properties of the intumescent fire-retardant compositions OVR-1, 336-11-88, and SGK-1 are studied. The mass loss and expansion ratio of the materials are determined experimentally as functions of temperature. Mechanisms of the fire-retardant effect of these materials are analyzed. A new mathematical model is proposed that permits predicting the state of protected structures under thermal loads typical of fire conditions. A comparison shows good agreement between the numerical-calculation results and data of fire tests. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 90–98, March–April, 1998.     

Macrokinetics of physicochemical condensation in two-phase systems of the gas-solid body type

The macrokinetics of the phase evolution at the microscopic level under isothermal and nonisothermal conditions is analyzed theoretically within the framework of a two-scale approach for describing physicochemical condensation processes in two-phase systems. Scenarios are established for the transformation of the condensed particles in a chemically active medium, taking into account the exothermal nature of the reaction, the finiteness of heat- and mass-transfer rates, and the phase transformations. The equilibrium constant of the heterogeneous reactions is shown to have a significant effect on the conditions of evaporation, or the increase in the incipient condensation phase. An analytical criterion is obtained for controlling the phase transformation in a reaction-capable medium, and it is supported by numerical calculations. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 37–45, May–June 1998.     

Experimental graphic-analytical prediction of internal heat- and mass-transfer processes in advanced refractory technologies

A nomogram method is suggested for representation and computation of heat- and mass-transfer processes in polycomponent systems. The nomograms are plotted with the use of mass-concentration diagrams and diagrams of target functions for thin and massive bodies, which close the temperature diagrams into a single complex, i.e., a nomogram synchronously reflecting the composite processes of energy and mass transfer in the substance with allowance for the phase and chemical transformations, cross effects, and experimentally determined processes that occur in thin bodies. The temperature, mass-concentration, and target diagrams for massive bodies characterize the development of actual technological processes. They can be used for developing programs for control over the roasting regime of refractories in advanced production processes. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 8, pp. 49 – 51, August, 2000.     

An ignition model for heterogeneous systems under nonstationary heat- and mass-exchange and its application to the composition PMMA+AP

The mathematical modeling of ignition processes for heterogeneous systems under nonstationary heat- and mass-exchange is performed with regard for the two-stage thermal degradation of oxidizer and fuel binder the heterogeneous oxidation of fuel around AP grains, the integral heat release in gas-phase reactions through the effective heights of individual flames, as well as the effect of the products of thermal decomposition on radiative and convective heat- and mass-exchange with the environment. The model is applied to a model composite system PMMA+AP. Scientific-Research Institute of Applied Mathematics and Mechanics, Tomsk 634005. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 5, pp. 18–29, September–October, 1994.     

Copper–nickel codeposition as a model for mass-transfer characterization in copper–indium–selenium thin-film production

The use of binary copper–nickel (Cu–Ni) codeposition from a complexing citrate electrolyte is proposed as a convenient model system for simple, rapid and inexpensive characterization of local mass-transfer limitations arising in the production of ternary copper-indium-selenium (CIS) thin films. Both the Cu–Ni and the CIS systems have been investigated in a small pilot cell and deposit thickness and composition distributions on a 5 × 5 cm² cathode have been compared. The experimental comparison confirms that the mass-transfer characteristics measured for copper deposition in the binary Cu–Ni codeposition system offer an excellent representation of the mass-transfer-limited deposition of copper and selenium in the ternary CIS system. The binary Cu–Ni system presents a number of advantages for process development, among which the possibility of operating at neutral pH and being much easier to handle, less expensive and less toxic than the CIS system. The results of the study presented here, although targeted to CIS production, may also be of use for the development of other electrodeposition processes in which one or more electro-active species are reduced under mass-transfer control.     

Methods of Generalized and Functional Separation of Variables in Hydrodynamic and Heat- and Mass-Transfer Equations

New direct methods are suggested for constructing exact solutions of hydrodynamic and heat- and mass-transfer equations by the generalized and functional separation of variables. These methods are based on analyzing functional and functional differential equations involving unknown functions of different variables. Specific examples are considered, and new exact solutions are obtained for the equations of a hydrodynamic boundary layer, the Navier–Stokes equations, and the nonlinear heat- and mass-transfer equations.     

Numerical modeling of the heat transfer mechanism in intumescent heat- and fire-protection materials

Characteristics of the heat-transfer mechanism in a layer of intumescent heat- and fire-protection material are considered within the framework of a model that takes into account conductive, convective, and radiative transfers. It is established that radiative heat transfer plays a dominant role in the formation of a temperature field. The coke structure (the presence of perpendicular interlayers) exerts an insignificant influence on the rate and depth of heating of the material. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 3, pp. 84–87, May–June 1998.     

Analysis of experimental data on heat and mass transfer in a boundary layer

Based on analysis of experimental heat-and mass-transfer data, the intensity of transfer processes is shown to vary discretely and multiply with the intensity in the laminar boundary layer in the transient flow region. In the cases considered, this feature is traced up to Reynolds numbers Re_x≈10⁷. It is manifested not only in the absence of chemical transformations but also in heterogenous and gas-phase combustion. The evolution of heat and mass transfer is regarded as a successive transition from one level of intensity to another. The existence of discrete levels is explained by the presence of a standing wave in the neighborhood of the laminar-turbulent transition. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 73–81, March–April, 1998.     

Heat- and mass-exchange in spinning acetate fibres

Conclusions The process of heat- and mass-transfer have been examined in the spinning of acetate fibre. A calculation of the heat- and mass-transfer coefficients and of the diffusion coefficient has been carried out.It has been found that the fibre being spun passes through four zones in the spinning tower. Zones I and II are characterized by a high rate of mass-transfer; in these zones, 70–75% of the acetone is evaporated from the fibre. In zones III and IV, the heat-exchange process is intensified; here the heat-transfer coefficient is 1.7 to 2.0 times less than in zones I and II.Translated from Khimicheskie Volokna, No. 6, pp. 23–25, November–December, 1985.     

Wildfire propagation: A two-dimensional multiphase approach

This paper describes a multiphase approach to determining the rate of propagation of a line fire through a randomly packed fuel bed of thermally thin cellulose particles and the induced hydrodynamics inside and above the litter. A set of time-dependent balance equations is solved for each phase (a gas phase andN solid phases) and the coupling between the gas phase and the solid phases is rendered through exchange terms of mass due to thermal degradation of the fuel material (heating, drying, pyrolysis, and char combustion), momentum, and energy. The radiative transfer equation for the fuel bed is deduced from the P1-approximation, and radiation from the flame to the fuel bed is accounted for using the empirical model of Markstein. The kinetics is incorporated to describe pyrolysis and combustion processes. Solution is performed numerically by a finite-volume method. The development of a line fire from the moment of initiation to quasisteady propagation is predicted and discussed. Results obtained by this multiphase model are compared to measurements made on laboratory fires using dead pine needles as fuel. The predicted rates of fire spread for some configurations, including slope effects, agree well with measured values. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 2, pp. 26–38, March–April, 1998.     

Mathematical modeling of the ignition of tree crowns

Numerical calculations of the transition of a downstream (surface) forest fire into an upstream (crown) forest fire based on a general mathematical model of forest fires are presented. It is found that the ignition of the forest canopy is a gas-phase phenomenon. Critical conditions for the transition of a downstream into an upstream forest fire are determined. The numerical calculations are compared with experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 13–22, July–August 1998.     

Interaction of a porous carbon particle with steam and carbon dioxide

As part of a diffusion-kinetic model of gasification of a porous carbon particle in steam and carbon dioxide, this paper presents a study of heat- and mass-transfer processes both inside the porous particle and in the gas phase above its surface. The radiation heat transfer between the particle and the walls of the furnace is taken into account. Heterogeneous reactions of carbon with steam and carbon dioxide and the homogeneous reaction of carbon monoxide with steam. are considered. In addition, allowance is made for pressure variation in the porous particle due to an increase in gas mass during heterogeneous reactions. Dependences of the gasification rate on the composition of the reaction mixture, pressure, furnace temperature, and particle size, and the inner surface area of the porous carbon particle.     

Aperiodic instability of the front of a crown forest fire

The stability of the three-zone structure of the front of a crown forest fire, which includes zones of vaporization, pyrolysis, and combustion gaseous products, is analyzed by the method of small perturbations. This model more accurately describes the physics of the actual process of propagation of upper forest fires. A characteristic equation is obtained and an analysis of its roots yields neutral curves for analysis of the monotonic instability of the fire front. It is shown that instability of fire-front propagation arises in a certain wavelength range. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 5, pp. 23–28, September–October 1998.     

Calculation of Filtration Throttling of Liquefied Gas with Evaporation

The throttling of a vapor–liquid mixture in porous filters of different design is mathematically described using filtration, thermodynamic, and heat- and mass-transfer equations, and an example of describing this process for carbon dioxide is presented.     

Calculation of the gasification of cokes of high-ash coals on the basis of the model of randomly porous media

A mathematical model is constructed to describe the dynamics of the pore structure of cokes of high-ash coals with allowance for the fact that the different parts of the internal volume of the structure are not equally accessible to the gaseous reactant. The model accounts for the increase in the area of the pore structure due to the removal of organic material, coalescence of pores, and opening of the interior volumes of the sample in the course of conversion. In the examination of heat- and mass-transfer processes inside the particles, attention is given to the thermal effect of the reaction along with diffusion resistance in the mineral component and the layer of reaction products — which decreases the cross section of the transport pores. The results of the calculations are compared with experimental data on the gasification of culm in gaseous carbon dioxide.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 2, pp. 58–65, March–April, 1992.     

Aeration mass-transfer related to reynolds number

A study of aeration rate data for streams and laboratory channels shows that the aeration rate can be correlated with Reynolds number and Schmidt number by a suitable dimensionless mass-transfer parameter which varies only slowly over a wide range of Reynolds number. This parameter, analogue to similar correlations in the heat- and mass-transfer fields, has two different near-constant levels, one in the low Reynolds number regime corresponding to molecular diffusivity, and another in the high Reynolds number regime corresponding to eddy diffusivity. The Schmidt number dependence has been found by comparison of gas into water data with vapour into gas data.     

Modeling of poly(amic acid) and polyimide reactors

A comprehensive kinetic model is presented which accounts for the major and side reactions present in poly(amic acid) and polyimide reactors. The mathematical framework is quite general and permits incorporation of heat- and mass-transfer aspects typically encountered in large-scale reactors. A few rate constants were curve-fitted using some (limited) experimental data available in the open literature. Using these (and the other rate constants from the literature), some interesting phenomena have been predicted at higher temperatures. Detailed experimental data are required to evaluated all the rate constants with precision. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2059–2079, 1997     

A highly effective domestic fire retardant for fireproofing fibrous textile materials

The possibility of decreasing the combustibility of textiles made of a blend of cellulose and polyester fibres (with a concentration of polyester fibre greater than 50%) by treatment with T-2 fire retardant in the presence of silicon-containing compounds was demonstrated. It was found that the effectiveness of the fireproofing effect of T-2 fire retardant for reducing the combustibility of materials when it was added to a melt of the polymer can be increased by microencapsulation in a polyvinylethoxysilane shell. The specific features of thermolysis of PETP in the presence of MIC 3G were investigated. Translated from Khimicheskie Volokna, No. 2, pp. 38–41, March–April, 1997.     

Autowaves in a heterogeneous medium with a catalytic reaction and heat and mass transfer

A mathematical model is developed to describe autowave processes in a catalytic fixed bed, which takes into account changes in coefficients of interphase heat and mass transfer and thermal conductivity of the catalytic bed, depending on the current values of system parameters. The behavior of the phase trajectories of the dynamic system is studied by methods of qualitative and numerical analysis, and an effective technique is proposed for searching for a phase trajectory corresponding to the autowave solution of the problem. Numerical studies of the mathematical model of autowave processes are performed, and the effect of system parameters on technological characteristics of the process, such as the maximum temperature and wave-propagation velocity, is considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 43–51, March–April, 2007.     

Modeling of carbon combustion in molecular and atomic oxygen

The oxidation of model carbon clusters by molecular and atomic oxygen is studied by using the ab initio electron density functional method in a generalized gradient approach and the semiempirical PM3 method. The activation energy and enthalpy for these processes are determined. The calculated energy characteristics are compared with the values obtained experimentally or theoretically by other researchers. Schemes are given for the main stages of oxidation of the model carbon clusters. The rate-determining stages are determined. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 3–10, May–June, 2006.