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A computational model of low-melting solid fuel regression in the combustion chamber of hybrid rocket engine is presented. The numerical model is based on a system of governing equations with simple effective viscosity model accounting for turbulence the gas phase. The numerical model takes into account heating of the solid fuel by the heat flux from hot gas flow, melting of the fuel and formation of the molten layer on the grain surface. The molten layer of solid fuel considered as incompressible, high-viscosity liquid; its mechanical interaction with the gas flow leading under certain conditions to the development of instability, formation of surface waves and shedding of molten material by the flow. Equations are solved on a Cartesian mesh by the Volume Of Fluid (VOF) approach. Simulations are performed for a slab of solid fuel (wax) with subsonic flow of hot gas above it. It is shown that the molten layer loses its stability under certain condition, resulting in the formation of waves on the surface of liquid layer. The results of numerical simulations agree qualitatively with known experimental data.

Rapid phase transitions occurring with a sharp increase in a specific volume can be accompanied by explosive gas-dynamic phenomena. A model is presented for calculating shock waves generated in the atmosphere during an explosion of a liquid gas pressure reservoir, based on the assumption of a thermodynamically equilibrium state of a vapor–liquid mixture in which both vapor and liquid have equal velocities and are in a state of saturation at local pressure. The spherically symmetric expansion of a boiling liquid cloud is calculated, pressure profiles under various initial conditions are compared, and the primary shock wave parameters are validated according to the results of available experimental data. Two-dimensional calculations of shock waves during the fracture of a cylindrical tank near the underlying surface at various degrees of filling are presented.

In the present work, the effect of a noncondensable gas on the collapse of a hot bubble in cold water was studied. It is assumed that the bubble consists of a gas mixture of steam, which can condense on cold water, and a noncondensable gas. The dynamics of the bubble was modeled by the integral equations of mass and energy supplemented by the steam diffusion equation. The steam condensation rate was determined by heat fluxes on the interfacial surface from the steam and water sides. It was used a one-dimensional spherically symmetric approach. The water surrounding the bubble was considered as an incompressible fluid, the flow of which was described by the Rayleigh-Plesset. Heat transfer in water is described by a one-dimensional heat equation, which takes into account conductive and convective mechanisms of heat transfer. Calculations performed using this model showed that the presence of a noncondensable gas in a bubble does not significantly affect its collapse in cold water. This means that the noncondensable gas cannot significantly weaken the impact of water on the melt, which occurs when a bubble collapses near the interface, which leads to a stratified steam explosion.

The mechanism of stabilization of the combustion in the duct of the solid fuel grain of a solid fuel ramjet with a flame holder was analyzed for the first time. The flame holder can be either a shoulder in the inlet part of the duct, or an autonomous gas generator running on solid fuel capable of self-sustained combustion. A mathematical model for evaluating the stability of the combustion in the solid fuel ramjet grain duct was developed. It was shown that there are several parameters characterizing the solid fuel grain and the solid fuel ramjet as a whole that affect the stability of the operation of the solid fuel ramjet. The main control parameters are the temperature of the combustion products in the flame holder and the flow rate of the combustion products from the flame holder (which can be controlled by varying the sizes and shape of the flame holder), and also the degree of turbulence of the air flow in the solid fuel grain duct. The stability of the combustion in the duct of the solid fuel grain of the solid fuel ramjet was studied, and the possible modes of the operation of the solid fuel ramjet while varying the control parameters were determined.

Recent experimental results on stratified steam explosion are analyzed by the model of “non-ideal” thermal detonation based upon Hugoniot relations, with factors taking into account incomplete melt fragmentation and participation of liquid coolant. The pressure behind the shock wave and conversion ratio are obtained as functions of the mass fraction of melt undergoing fragmentation and mass fraction of coolant in the explosion zone. Calculations are performed for one of the recent experiments on stratified steam explosion carried out with simulant oxidic materials. It is confirmed that the idealized scheme for thermal detonation overestimates significantly the conversion ratio, while predicting very low pressure levels. Taking into account incomplete melt fragmentation and limited participation of coolant improved the agreement between the predictions and experiments. Ranges for the melt fragmentation fraction and mass fraction of participating coolant where the model predictions agree with experimental values are obtained.

This work is motivated by the problem of restraining temperature escalation inside a porous heat-releasing media submerged in a pool of liquid coolant. When coolant temperature reaches saturation, boiling begins in the bulk of the porous bed, with void generation rate determined by the heating power. Amount of void determines hydrostatic pressure difference that drives natural circulation of two-phase flow through the porous material. At a certain critical value of the heat release rate, the driving head cannot overcome drag of the two phase porous media flow, which results in complete evaporation of coolant in some zone. Temperature of material in the dry zone increases significantly due to deterioration of heat exchange with single phase vapor flow in comparison with boiling flow heat transfer. The paper considers the problem of determining the critical conditions for onset of dryout in a heat-releasing porous bed of an arbitrary shape. The well-known one-dimensional problem for a flat top-flooded bed is revisited, and the functional form of the dryout boundary (expressed as the dryout heat flux, DHF) is derived using non-dimensional parameters. Asymptotic behavior of the solution is analyzed, and, by the method of asymptotic interpolation, a surrogate model is proposed consisting of three single-argument, non-dimensional functions. It is shown that such a model provides acceptable accuracy even in the cases where complete similarity of solutions is not achieved. The results obtained provide important insights into the physics of the problem, reduce the number of free parameters, and enable fast evaluation of dryout conditions without the need of numerical solution of algebraic equations involved in the exact formulation. The ultimate goal of the surrogate model development, i.e. its application to multidimensional configurations, is discussed.

Results of numerical modeling of solid fuel melting and shedding by hot gas flow are presented. The computational model is based on the Volume-of-Fluid approach, implemented on a two-dimensional Cartesian grid, with one-equation turbulence model. Simulations are presented for a slab of wax interacting with a parallel gas flow, with the properties taken to be typical of hybrid engines (nitrous oxide). Development of Kelvin-Helmholtz instability in the melt layer is demonstrated, including the wave formation and droplet shedding by the flow.

Small-scale experimental studies of melt splashing upon the impact of water are presented here, with a focus on the fluid dynamics and thermal aspects of these interactions. Gravity-accelerated droplets and forced short-duration water jets interacted with liquid Rose&rsquo, s alloy superheated to 100&ndash, 200 degrees above its melting point. A repeatability study was performed for better-control of the gravity fall of a droplet. The amount of perturbation on the melt surface was obtained from a video recording, and indicated the existence of three principal stages of interaction. The cases using the forced water jet demonstrated the occurrence of a cumulative jet of melt following the collapse of the cavity caused by the water impact. Also, it was shown that numerous small-diameter melt droplets were scattered by the primary impulse, and small-scale micro-eruptions were observed, which generated small but fast melt droplets at the later stages of interaction.

Lead-cooled fast reactors have several advantages in comparison to thermal neutron reactors and sodium-cooled fast reactors. Despite the considerable interest of international nuclear power community to this technology, safety issues associated with possible chain rupture of steam generator tubes initiated by rupture of a single tube in the tube bundle have not been completely resolved so far. Such initiating events can cause large dynamic loads on the neighboring tubes, and methods for evaluation of their consequences are to be developed. In this work, approaches are proposed for the estimation of forces acting on neighboring tubes at the initial stage of an accident initiated by tube rupture in a lead-heated steam generator. The forces considered include the shock impact caused by pressure wave propagating in liquid lead, and subsequent hydrodynamic impact caused by high-speed flow of heavy lead around the neighboring tubes. The shock impact is calculated from a model for water droplet evaporation and expansion in liquid lead based on the assumptions that two-phase water mixture is in thermodynamic and mechanical equilibrium, while liquid lead is an inviscid compressible fluid. The hydrodynamic impact is estimated using a simplified model with incompressible liquid lead and volume-averaged two-phase water-vapor mixture properties. Both models are implemented in 1D spherical coordinates. Estimates for the shock and hydrodynamic impact of tube rupture on the neighboring tubes are obtained for the conditions of BREST-OD-300 steam generator.

Experimental results on laminar propane flames propagating in a narrow gap between parallel glass plates are presented. Development and evolution of cellular flame structure is demonstrated...

Splashes of high-temperature melt spreading over a water pool bottom can be a reason for the formation of a zone where melt, water and steam are mixed, providing conditions for powerful steam explosions. The paper considers the formation of melt splashes arising from the impact of a water jet on the surface of the melt. Numerical simulations are performed in 3D formulation, using the VOF method and an improved phase change model. The evolution of melt surface following the water jet impact is demonstrated, including the formation of a cavern, a primary melt splash known as the crown, as well as a secondary splash following the collapse of the cavern, known as the cumulative jet. Parametric study for the melt splash height dependence on the water jet geometry and velocity is carried out. The results of numerical analysis are discussed from the point of view of the similarity with respect to the momentum and kinetic energy of water jet. The significance of the results for the steam explosion problem is discussed.

The influence of bubbles of hot non-condensable gas formed at the interface between the melt and water on the formation of a mixture of melt with water capable of producing steam explosions is considered. The dynamics of such a bubble in subcooled water is analyzed numerically in a one-dimensional spherically symmetric approximation. It is shown that with significant initial superheat of the bubble relative to the water, a rapid drop in pressure in the bubble occurs due to strong heat removal into the water. This leads to the collapse of the bubble and the appearance of an accompanying flow of water. The results obtained made it possible to approximately describe the stage of collapse of the bubble as the polytropic process and to determine its index. The axisymmetric problem of the impact of the water jet on the surface of a melt during collapse of a gas bubble near the interface between the melt and water is numerically investigated. In this case, the obtained polytropic process equation is used to determine the pressure in the bubble. It is found that the resulting impact on the melt is capable of knocking out melt droplets into the water to a height of several centimeters, which leads to the formation of a layer of water mixed with the melt droplets, which is capable of producing strong steam explosions.

A collapse of the vapour film separating a hot melt droplet from the surrounding water due to sudden ambient pressure rise is considered. The pressure peak causes a direct contact between water and melt, leading to significant disturbances of the melt droplet surface. Results of numerical simulations performed by the VOF method are presented. Parametric analysis of the interaction process is performed for a molten tin droplet with initial temperature of 950 K, immersed in subcooled water having the temperature of 353 K. The interaction is initiated by sudden rise of the ambient pressure to as much as 8 MPa, imitating the arrival of a thermal detonation wave, with its gradual decrease towards the initial pressure of 0.1 MPa. Simulations reveal the collapse of the vapour film, impingement of water on the droplet surface, and subsequent expansion of vapour due to rapid water evaporation. Significant disturbances of the melt droplet surface are obtained, and implications for the steam explosion problem are discussed.

A modified two-dimensional two-phase mathematical model of forest wildfires propagation is considered. The model is based on the averaging of three-dimensional equations of two-phase medium over the height of the forest fuel (FF) layer and it includes the (k‒e)-turbulence model with additional turbulence production and dissipation terms in the forest layer and the Eddy Break-up Model for the combustion rate in the gas phase. The developed model can be used to carry out numerical simulation of the forest fire-front propagation under the conditions of a heterogeneous FF distribution, the presence of obstacles to the fire propagation, and the wind effects. This model can be used for real-time computation of the fire propagation, for expert assessments of emergency situations, and for assessments of the damage caused by forest fires.

The paper discusses the physical background of explosive phenomena caused by internal energy release in substances undergoing liquid-to-vapor phase transition. Two types of “physical” explosions are discussed: the boiling liquid expanding vapor explosion arising upon catastrophic failure of high-pressure vessels and known as one of major hazards in process industries, and the steam explosion, arising upon interaction of high-temperature melt with water or some other coolant having low enough boiling point. In both cases, the dynamics of two-phase mixture containing liquid and vapor phases of the substance is described by Euler equations with complex equation of state which is different from the equations of state for the individual phases. Numerical aspects arising in the solution of the governing equations are discussed, and results of typical numerical simulations demonstrating the development and propagation of pressure waves from the respective types of explosions are presented.

A two-dimensional three-phase mathematical model of forest fires is considered. The model is based on the averaging of initial multiphase medium equations over the height of the forest fuel (FF) layer. The developed model can be used to carry out numerical simulation of the forest fire-front propagation under the conditions of a heterogeneous FF distribution, the presence of obstacles to the fire propagation, and takes into account the transfer of burning particles by wind over the FF layer and their fall-out.

A numerical model for boil-up of superheated liquid following loss of containment and expansion of two-phase mixture into the atmosphere is proposed and applied to evaluation of blast effects of Boiling Liquid Expanding Vapor Explosions (BLEVEs). The model assumes that the mixture in the two-phase cloud stays in thermodynamic equilibrium during expansion, whereas the air in the atmosphere obeys the ideal gas law with constant ratio of specific heats. The boundary between the two-phase cloud and ambient atmosphere is considered as a moving contact surface. The problem is solved numerically in the axisymmetric framework. Sample calculations of expansion of a spherical volume of superheated liquid are carried out for pressure-liquefied propane. Pressure profiles demonstrating propagation of depressurization wave into the cloud are presented together with mass fractions of vapor in the mixture. Solutions obtained for two-phase systems are compared with those for single-phase compressed gas. Scaling of overpressures in physical explosions is discussed. Validation of the model is carried out by comparison of simulations carried out in a wide range of cloud masses with experimental data. Two-dimensional simulations demonstrating BLEVE blast waves from a bursting near-surface vessel are presented.

Filtration processes which accompany the cyclic operation of the oil production well with variable bottom hole pressure are considered. The task is solved in the axis-symmetrical formulation for a layered nonuniform oil reservoir with highly and lowly permeable layers. The distributions of oil saturation are calculated for the stationary and cyclic operation of the well. It is shown that periodical variation of the bottom hole pressure of the production well upon its cyclic operation intensifies the cross-layer flows between the layers in the bottom hole zone, which could enhance oil recovery.

Nordic-type boiling water reactors employ melt fragmentation, quenching, and long term cooling of the debris bed in a deep pool of water under the reactor vessel as a severe accident (SA) mitigatio ...

The paper is devoted to numerical study of the influence of the initial shape of a vapor bubble on the surface impact of the water jet emerging due to the bubble collapse. This problem is relevant to spreading of high-temperature melt under a layer of subcooled water. The vapor bubbles formed on the melt-water interface, upon complete penetration in water, are condensing rapidly to produce high-velocity water micro-jets directed towards the melt. Impact of these jets causes upward melt splashing. Superposition of these processes forms a dynamic layer where melt is mixed with water; the presence of this premixed layer can be a pre-requisite for steam explosion. In this work, numerical modelling by the boundary element method is performed for the collapse of a bubble of an oblate spheroid. It is shown that the water jets generated in this process possess the impulse comparable to that generated by a collapsing spherical vapour bubble of the same volume. By the numerical simulations and subsequent estimates it is obtained that collapse of non-spherical bubbles near the melt-water interface produces melt splashes of the height of few centimetres, which is sufficient for the occurrence of steam explosions.

As a pre-requisite for powerful steam explosion following the spread of molten high-temperature material over the bottom of water pool, a premixed zone must be formed with certain contents of melt, water, and vapour. Experimental observations indicate that melt spreading is featured by the formation of periodic melt splashes which can be responsible for the phase premixing. The paper considers one of the key phenomena involved in this process, namely, the splash of hot melt due to impingement of a high-velocity water jet. Numerical simulations are performed in the axisymmetric formulation, revealing the whole process of water-melt interaction, as well the development of melt flow leading to its splash. Parametric study is presented for the melt splash height dependence on the water mass and velocity.

Numerical simulations are performed for a spherical bubble containing hot vapor in subcooled water. Unlike conventional cavitation problems, the initial pressure in the bubble and surrounding liquid are equal to each other. The physical mechanism for the appearance of pressure difference driving the bubble collapse is rapid cooling and condensation of vapor in the bubble. A model for the fluid dynamics and thermal processes in the bubble and in the liquid is presented. The governing equations are solved numerically in the transformed coordinates where the bubble size remains constant, with the Rayleigh-Plesset equation describing the time evolution of bubble radius. The effect of the initial superheat of vapor in the bubble with respect to the saturation temperature is studied. The bubble collapse of hot vapor is compared with an idealized case, resembling collapse of a cavitation bubble. Estimates for the kinetic energy of liquid gained in the course of bubble collapse are obtained. The results are applicable to the evaluation of the perturbations to spreading melt surface due to interaction with the unstable water-vapor interface, and to the evaluation of the premixing zone in the stratified steam explosions.

Collapse of a hot vapour bubble captured by subcooled water can produce a cumulative jet similar to that appearing in cavitating flows. In the context of stratified steam explosions following spreading of hot melt under a water layer, impact of the water jets can be a reason for melt splashes promoting the mixing of cold and hot liquids necessary for energetic interaction. In this work, the characteristics of the directional water flow caused by collapse of a bubble near a wall are obtained, and a correlation is given which relates the ultimate height of melt rise to the bubble parameters and droplet size. Estimates relevant to melt splashes caused by the cumulative water jet impact are presented which agree with the experimental observations available in the literature.

Collapse of superheated vapor bubbles in subcooled water is studied from the viewpoint of possible mechanisms of premixed zone formation in stratified vapor explosions. Numerical modeling is performed for spherically symmetric bubble collapse in subcooled water, with different initial vapor superheats. The kinetic energy of liquid flow generated due to vapor collapse is obtained. It is shown that the primary mechanism triggering vapor collapse and water flow is vapor cooling in the bubble by colder interface, lowering the vapor pressure and generating necessary pressure drop. Results are compared with an idealized case of bubble vapor maintained at the saturation conditions corresponding to water temperature. Two-dimensional simulations of bubble collapse near solid wall are performed by the boundary element method. Implications to stratified vapor explosions are discussed, and correlations for possible splashing of melt due to the impact of water jets generated by a collapsing steam bubble are obtained.

A coupled compositional and geomechanical model is presented which is applicable to simulation of thermal gas treatment of Bazhenov formation. The geomechanical module includes the criteria for rock fracturing caused by the increase in the internal pore pressure due to pyrolysis (decomposition) of solid organic material, kerogen, with formation of synthetic oil and gases, criteria for the formation of hydraulically connected system of cracks, as well as models for the permeability of fractured rock. Numerical simulations are performed for the scheme of air injection into high-permeability layers available in the impermeable kerogen-containing matrix. It is shown that straightforward technological scheme using the same permeable layer for air injection and oil production may not be viable because the cracked zone is lags behind the in-situ combustion front propagation, and synthetic oil may be burnt in the injected air, rather than reach the production well.

Bazhenov formation in West Siberia is featured by vast hydrocarbon reserves, however, its development is difficult due to the geological structure and properties of the deposit. The principal part of organic substances is contained in the impermeable rock matrix in the form of solid kerogen. The fundamental problem which must be solved for recovery of hydrocarbon reserves is to convert kerogen into fluids, and create a connected fracture system allowing flow of synthetic oil towards permeable reservoirs available. Existing technologies of enhanced oil recovery (including hydraulic fracturing and thermal gas treatment) are reviewed, and their applicability to Bazhenov formation conditions is discussed. It is shown that none of the technologies is capable of solving the problem of hydrocarbon recovery from the rock matrix where most of the kerogen reserves is concentrated. A new approach is proposed consisting in the combination of hydraulic fracturing and thermal methods, together with proper arrangement of hydrocarbon flow path in the induced crack system. Necessity for comprehensive mathematical modeling on the basis of coupled geomechanical, chemical, and filtration models is highlighted.

Termination of severe accident progression by core debris cooling in a deep pool of water under reactor vessel is considered in several designs of light water reactors. However, success of this acc ...

Flash evaporation of a superheated water droplet in heavy liquid metal coolant (lead) is considered, in application to the analysis of a lead-cooled fast reactor steam generator tube rupture accident. The model is based on thermodynamic equilibrium formulation for the expanding water-steam mixture and inviscid compressible formulation for the surrounding liquid lead, with the interface conditions determined from the solution of the Riemann problem. Numerical solution is performed in the spherically symmetric geometry using a conservative numerical scheme with a moving sharp interface. Transient pressure and velocity profiles in each phase are presented for the parameters typical of the steam generator tube rupture accidents, demonstrating the process of boiling water expansion and pressure wave formation in the coolant. The results obtained are compared with a simplified model which considers the volume-averaged parameters of boiling water droplets and considers coolant as an incompressible liquid. Good agreement between the full and simplified models is demonstrated. Impacts of coolant flow on structures caused by pressure wave propagation and subsequent coolant flow are discussed.

A two-dimensional three-phase mathematical model of forest fires constructed by the method of averaging over the height of the forest fuel layer is considered. The gas phase in the model is described by gas dynamics equations with the k − ε turbulence model and the eddy breakup model to describe the rate of turbulent combustion and the rate of heat generation; the solid phase is described by a system of evolution equations for the change in the volume fractions of forest fuel and solid products of their pyrolysis with kinetic formulas for the rates of chemical reactions; and the disperse phase is described by the transfer equations for the mass and energy of solid burning particles in the wind field above the forest fuel layer. For the numerical implementation of the proposed model, a parallel software package is created. The results of calculations of the forest fire propagation with consideration of the basic physical-chemical processes and mechanisms typical of the real forest wildfire propagation are presented.

A multiphase model for steam explosion is considered, with assumption of mechanical equilibrium between water and vapor phases in the mixture, but with non-equilibrium drag and heat exchange with high-temperature melt droplets taken into account. Governing equations are formulated and solved numerically. Simulations of pressure waves following thermal interaction of hot melt and water-vapor mixture are presented, the structure of steam explosion wave is discussed.

Detailed comparison of numerical results obtained for IPG−4 plasmatron (base case), IPG − 3H hypothetical plasmatron and IPG − 3 real plasmatron is provided to estimate the accuracy of the similarity conditions and the applicability of that conditions for the pair of IPG − 4 and IPG − 3 plasmatrons. IPG − 3H hypothetical plasmatron is geometrically similar to IPG − 4 one and has twice larger dimensions. The operating regime of IPG − 3H is obtained from the IPG − 4 operating regime with use of the similarity conditions for the operating parameters. The operating regime of IPG − 3 real plasmatron is the same as for IPG − 3H. Vortical electric field generated by the inductor coils with high frequency current around the discharge channel is calculated with use of 2D model with far field boundary conditions. This calculation is integrated with the solver for Navier-Stokes equations for plasma flow. The comparison of IPG − 4 and IPG − 3H results shows about 4÷7% accuracy of the similarity conditions for main plasma parameters. The comparison of IPG − 4 and IPG − 3 results shows that application of the similarity conditions for this case provides a qualitative agreement but the quantitative difference in some parameters may be large, up to 35÷40%.

Stability of combustion in solid fuel scramjets is contingent upon proper geometry of fuel grain and availability of a flame holder. Flame stabilization is achieved in the recirculation zone developing due to sudden expansion behind the inlet. Previous experimental and theoretical works suggest that there exists an optimum range of length-to-diameter ratios for the flame holder. However, due to fuel burnout the channel and flame holder geometry change in the process of scramjet operation, the regression rate being variable both in time and length. The purpose of this work is to develop a computational model of a solid-fuel scramjet taking into account the geometry variation, as well as to obtain typical flow patterns at the different stages of combustion. The numerical model is based on a system of fully compressible RANS equations with k-epsilon turbulence model. Turbulent combustion is described by the Eddy Dissipation Concept (EDC) model.Stability of combustion in solid fuel scramjets is contingent upon proper geometry of fuel grain and availability of a flame holder. Flame stabilization is achieved in the recirculation zone developing due to sudden expansion behind the inlet. Previous experimental and theoretical works suggest that there exists an optimum range of length-to-diameter ratios for the flame holder. However, due to fuel burnout the channel and flame holder geometry change in the process of scramjet operation, the regression rate being variable both in time and length. The purpose of this work is to develop a computational model of a solid-fuel scramjet taking into account the geometry variation, as well as to obtain typical flow patterns at the different stages of combustion. The numerical model is based on a system of fully compressible RANS equations with k-epsilon turbulence model. Turbulent combustion is described by the Eddy Dissipation Concept (EDC) model.

One-dimensional coolability problem for a flat homogeneous heat-releasing debris bed is considered, with the critical conditions for steady-state cooling characterized by the Dryout Heat Flux (DHF). DHF is determined for top-fed and bottom-fed debris beds from several two-phase models differing by the treatment of porous and interphase drag. Aleatory uncertainties due to randomness of the debris bed formation scenario and respective physical parameters (particle diameter, porosity) are quantified. The influence of ranges and distributions of input parameters on the uncertainty in the DHF are studied. Major contributors to the DHF uncertainty are identified. Influence of model uncertainty on the prediction of the lower boundary for DHF is discussed.

Coolability of heat-releasing debris bed is an important issue in the severe accident analysis and management. Traditionally, theoretical studies of top or bottom-fed debris bed coolability have be ...

On the basis of a multistep kinetic mechanism for flame inhibition by organophosphorus compounds including more than 200 reactions, a skeletal mechanism for flame inhibition by trimethylphosphate was developed. The mechanism consists of 22 irreversible elementary reactions, involving 9 phosphorus-containing species. Selection of the crucial steps was performed by analyzing P-element fluxes from species to species and by calculating net reaction rates of phosphorus-involving reactions versus the flame zone. The developed mechanism was validated by comparing the modeling results with the measured and simulated (using the starting initial mechanism) speed of H2/O2, CH4/O2, and syngas/air flames doped with trimethylphosphate. The mechanism was shown to satisfactorily predict the speed of H2/O2/N2 flames with various dilution ratios, CH4/air and syngas/air flames doped with trimethylphosphate. Besides, the developed mechanism was used in 2D CFD modeling of diffusion cup-burner methane/air flame and fairly well predicted the minimal extinguished concentration of trimethylphosphate.

Modeling of industrial accidents with liquefied toxic and flammable gases is considered. Propagation of nonreacting heavy gas clouds over complex terrains is described by a two-dimensional model with averaging over the cloud height. A numerical simulation of a toxic accident initiated by the release of chlorine in the urban environment has been performed and the number of injured people has been computed. A two-dimensional axisymmetric model based on the Favre-averaged Navier-Stokes equations is used to model the fireballs occurring upon combustion of hydrocarbon fuel-air clouds. Zones of various thermal hazards for people have been obtained.

The temperature regime of a filtering unit being cooled after an accident at a nuclear power plant is considered. A mathematical model is developed; the model is based on three-dimensional equations of thermohydrodynamics and takes into account heat-transfer mechanisms (convection, heat conduction, and radiation). For the unit variants considered, the maximum value of temperature in the sorbing module is less than 300°C, and the temperature reserve is 20–50°C.

The VAPEX computer code is used to analyze three large-scale experiments in corium/water interaction performed at the FARO Facility. Only the mixing of a corium jet with water at different values of pressure is studied in experiments L-14 and L-24; in experiment L-33, an initiating device is used to make a steam explosion after mixing. The calculations revealed the importance of taking into account the process of generation of hydrogen during the corium/melt interaction for correctly determining the pressure in the container and gas void fraction below the level. The results of VAPEX code-aided calculations and the experimental data agree qualitatively and quantitatively both at the stage of mixing and at the stage of steam explosion.

This paper reports results of experiments and numerical modeling for fires in small-and medium-scale enclosures in underventilated conditions resulting in flame exhaust to the atmosphere. Delays from ignition to the occurrence of a stable flame outside the enclosure were measured experimentally for three types of fuels (methane, propane, and propylene) with a specified fuel supply rate. Characteristic scales dependent on fuel supply rate, fuel source location, compartment geometry, and vent opening parameters are introduced and used to establish a unified nondimensional dependence of the flame exhaust time on fuel flow rate. For the smallest and largest enclosures used in the experiments, three-dimensional numerical calculations of the dynamics of fire development are performed by large eddy simulation. Calculated reaction rate isosurfaces are presented, which demonstrate the compartment fire evolution and its oscillations after exhaust into the atmosphere. It is shown that the calculation results agree qualitatively with experimental observations and that the flame exhaust times are in good agreement with the experimental correlation.