Thermal Explosion Theory Research Articles

Self-ignition behaviour of corn cob, wheat bran and rice husk residues in ambient air from biomass gasification

The possibility of different agrowastes to self-ignite under ambient condition, due to exothermic reactions between their surface molecules and air or other oxidizing agents which are conveyed into the void volume between the particles, exists. It is imperative to investigate the self-ignition ability of these harzadous waste products causing environmental pollution after the milling process to avoid sudden fire outbreaks. In this study, the self-ignition attributes of corn cob, wheat bran and rice husk residues in ambient air from biomass gasification was investigated by evaluating their self-ignition temperatures using DIN EN 15188:2021 standard and Frank-Kamenetzkii's theory of thermal explosion at varying basket volume. The results revealed decrease in the ignition temperature of dust samples as ignition time and dust basket volume were increased. Sample C (rice husk dust residue) was considered to be the most hazardous with respect to its propensity to self-heating possessing the lowest self-ignition temperature of 173 °C at 800 mL cubic mesh. Its moisture content and activation energy of 1.41 % and 46.52 kJ/mol respectively were the lowest. Its thermal conductivity, carbon content, heating value and bulk density of 0.07 W/mK, 78.98 wt%, 26,895 kJ/kg and 255.4 kg/m3 respectively were the highest. Correlation coefficient from the Arrhenius plot showing the self-ignition behaviour of dust samples using the model of Frank-Kamenetzkii were 0.9976, 0.9910 and 0.9962 for corn cob, wheat bran and rice husk residues respectively. In conclusion, the data presented are effective in predicting the self-ignition ability of corn cob, wheat bran and rice husk residues in ambient air from biomass gasification in order to prevent sudden fire attack that may arise based on storage of their dust particles in food processing industries.

Electromagnetohydrodynamic (EMHD) convective transport of a reactive dissipative carreau fluid with thermal ignition in a non-Darcian vertical duct

A mathematical model is developed to simulate the steady, laminar exothermic reactive electromagneto-hydrodynamic combustible non-Newtonian natural convective transport in a vertical duct. Static uniform axial electrical field and transverse magnetic field are imposed. The Frank-Kamenetskii thermal explosion theory is utilized and also the Carreau fluid model, the latter due to its ability to simulate shear-thinning, Newtonian and shear-thickening behaviour. The duct contains a homogenous, isotropic porous medium and to accomodate Forchheimer inertial drag effects, a non-Darcian model is deployed. The duct walls are permeable enabling suction and injection effects to be studied. Viscous and Joule heating (Ohmic dissipation) are also featured in the model. Following a scaling transformation, the dimensionless emerging non-linear ordinary differential boundary value problem is solved with a robust numerical method (Mathematica shooting algorithm). Validation with an Adomian decomposition method (ADM) is included.

Global Existence and Uniform Blow-Up to a Nonlocal Parabolic System with Nonlinear Boundary Conditions Arising in a Thermal Explosion Theory

This paper deals with a nonlinear nonlocal parabolic system with nonlinear heat-loss boundary conditions, which arise in the thermal explosion model. Firstly, we prove a comparison principle for some kinds of parabolic systems under nonlinear boundary conditions. Using this, we improve a new theorem of the sub-and-super solution. Secondly, based on the new sub-and-super solution theorem, the sufficient conditions that the solution exists and blows up uniformly in finite time are presented. Then, we generalize some of the lemmas related to uniform blow-up solutions, which are used to introduce the uniform blow-up profiles of solutions. Finally, we give several numerical simulations to illustrate the existence and uniform blow-up of solutions.

Heuristic computing for the novel singular third order perturbed delay differential model arising in thermal explosion theory

In this study, a novel singular third order perturbed delay differential model (STO-PDDM) is designed with its two types using the traditional Lane-Emden model. The descriptions of delay/shape perturbed, and singular factors are also presented for both types of STO-PDDM. The artificial neural networks (ANNs) along with the optimization of global/local performances based on genetic algorithm (GA) and interior-point algorithm (IPA) have been used to solve the STO-PDDM. The optimization is performed using the GAIPA based on the activation function through the differential form of STO-PDDM. For solving STO-PDDM, the system's accuracy, substantiation, and authenticity have been performed by using the comparison of obtained and exact solutions. The accessible approximate solutions are used to evaluate the computational approach's robustness, stability, correctness, and convergence. The reliability of the scheme is performed through different statistical measures for solving the STO-PDDM.

Global Existence and Blow-Up of Solutions to a Parabolic Nonlocal Equation Arising in a Theory of Thermal Explosion

Focusing on the physical context of the thermal explosion model, this paper investigates a semilinear parabolic equation u t = Δ u + a ∫ Ω u p d x , x , t ∈ Q T , n · ∇ u + g u u = 0 , x , t ∈ S T , u x , 0 = u 0 x , x ∈ Ω with nonlocal sources under nonlinear heat-loss boundary conditions, where a , p > 0 is constant, Q T = Ω × 0 , T , S T = ∂ Ω × 0 , T , and Ω is a bounded region in R N , N ≥ 1 with a smooth boundary ∂ Ω . First, we prove a comparison principle for some kinds of semilinear parabolic equations under nonlinear boundary conditions; using it, we show a new theorem of subsupersolutions. Secondly, based on the new method of subsupersolutions, the existence of global solutions and blow-up solutions is presented for different values of p . Finally, the blow-up rate for solutions is estimated also.

Neuron analysis through the swarming procedures for the singular two-point boundary value problems arising in the theory of thermal explosion

Neuron analysis through the swarming procedures for the singular two-point boundary value problems arising in the theory of thermal explosion

The determination method of the ignition modes of single coal particle with a transient coal ignition and combustion model

A transient model for the ignition and combustion of a quiescent coal particle was developed by coupling the mass, energy and species governing equations between the particle phase and the gas phase. The ignition delay times of single coal particle were calculated by using the transient ignition and combustion model with Kobayashi-Sarofim devolatilization model and Chemical Percolation Devolatilization (CPD) model, respectively. The predicted results were compared with the experimental data to further validate better performance of CPD model. The new ignition criteria of single coal particle were proposed to determine the onset of the ignition and subsequently to define the ignition modes of single coal particle by comparing the magnitude of typical ignition time scales, including the start time and the end time of devolatilization, homogeneous ignition delay time and the heterogeneous ignition delay time based on the thermal explosion theory (TET). The ignition modes map of single coal particle under various ambient oxygen molar fractions (O2 = 0–100%) and gas temperatures (Tg = 800–2000 K) was firstly depicted by using the transient ignition and combustion model with the new ignition criteria. The ignition modes of single coal particle transferred from homogeneous gas-phase ignition (GI) to homo-heterogeneous ignition (GI-HI) when the ambient oxygen molar fraction was increased from 5% to 21% under Tg = 1340 K condition, and then they transformed into hetero-homogeneous ignition (HI-GI) and heterogeneous ignition of coal (HI-coal) when the ambient oxygen molar fraction was further increased to 40% and 70%, respectively. Moreover, the simulated results showed that the critical oxygen molar fraction XO2,cr for the transition of ignition mode from homogeneous to heterogeneous ignition was 15% for the particle size of 50 μm, XO2,cr = 20% for the particle size of 100 μm, and XO2,cr = 30% for the particle size of 200 μm, respectively. The critical parameters for the transition of ignition mode of single coal particle were quantitatively determined to give a deep understanding on coal particle ignition process and to provide the guidance for improving the combustion performance of coal particles.

Optimal design of homogeneous ignition of biomass by pulse ignition technique

The volatile matters in biomass have an essential effect on their ignition stabilization. In the present work, the homogeneous ignition of seven kinds of biomass and eight kinds of coals is studied by the pulse ignition technique. At ignition, the flame brightness of biomass appears more faintly than that of coal. The flame color appears in bluish violet for biomass and yellowish red for coal. The homogeneous ignition temperature ranges from 270?C to 310?C for biomass and 390-500?C for coal, respectively, and it decreases with the decrease of the particle size. A theoretical model is established to predict the homogeneous ignition temperature by the thermal balance method and the thermal explosion theory. Based on the theoretical prediction, a quasi-linear model and a non-linear model are developed through the least square algorithm.

Ignition predictions of isolated coal particles by different ignition criteria and devolatilization models

The prediction accuracy of coal ignition characteristics depends on the sub-model selections. A detailed modeling study on the influences of ignition criteria and devolatilization models on the ignition characteristics of isolated coal particles is conducted using a one-dimensional transient ignition model. The assessed ignition criteria include the thermal explosion theory (TET), the transient adiabatic criterion (TAC) and the flammability limit criterion (FLC), while the assessed the devolatilization models include the chemical percolation devolatilization (CPD) one and two competing reaction (TCR) one. Under each combination, the ignition characteristics under different oxygen concentration, particle size, and surrounding temperature are studied. The prediction results are compared with microgravity experimental data obtained from the 3.6 s drop tower in National Microgravity Laboratory Center of China (NMLC). Modeling results reveal that the particle center temperature is more reasonable to be used as the characteristic temperature in the ignition study. When devolatilization process is described by CPD model, for homogenous ignition FLC is more accurate to predict ignition temperature and time than TAC at a higher XO2 and a high Tw, while TAC is more accurate to predict ignition temperature at a large particle size. Using FLC, against TAC, the transient of ignition mode from homogenous to combined happens at a ∼ 80 K higher temperature and ∼ 50 μm larger particle size, while that from combined to heterogenous happens at 250 μm rather than 400 μm. When FLC is used as the ignition criterion, selection of devolatilization model has more notable effect on the prediction of ignition temperature and time. Furthermore, the combination of FLC and CPD is more accurate to predict ignition temperature and time at a higher XO2. Two diagrams are respectively given to guide the selection the ignition criterion and identify the ignition mode at a wide range of conditions. In addition, the mechanisms of the associated discrepancy are discussed.

Numerical estimation of thermal ignition conditions for reactive medium with Gaussian distribution of activation energy

The article investigates the solutions of the one-dimensional stationary integro-differential heat equation. The source of heat release is determined through the Gaussian distribution function of the activation energy. In such a statement, the critical conditions for the existence of a bounded solution depend on the distribution variance. With the help of numerical methods, such dependences are obtained; for their explanation, the analytical approximations of the thermal explosion theory are used.

Positive Solutions for a Singular Elliptic Equation Arising in a Theory of Thermal Explosion

In this paper, the thermal explosion model described by a nonlinear boundary value problem is studied. Firstly, we prove the comparison principle under nonlinear boundary conditions. Secondly, using the sub-super solution theorem, we prove the existence of a positive solution for the case K(x)>0, as well as the monotonicity of the maximal solution on parameter λ. Thirdly, the uniqueness of the solution for K(x)<0 is proved, as well as the monotonicity of the solutions on parameter λ. Finally, we obtain some new results for the existence of solutions, and the dependence on the λ for the case K(x) is sign-changing.

Thermal explosion characteristics of a combustible gas containing fuel droplets

This paper investigated the critical ignition conditions of combustible gas containing liquid fuel droplets. The analysis is done based on the criteria of the thermal explosion theory. It includes analytical and numerical solutions of modeling equations of fuel droplets heating and evaporation by convection and radiation from the surrounding reactive hot gas. The exothermic reaction is usually modeled as a single-step reaction obeying an Arrhenius temperature dependence. The thermal conductivity of the fuel droplet is dependent on temperature. The analytical solution produced relations between the main critical characteristic parameters in all planes of the solution. The results obtained from investigating the effect of the characteristic parameters on the explosion behavior of gas and fuel droplets and the thermal radiation proved that both of them are significant. The study proved that the criticality definitions of the thermal explosion of a single-phase system can be used effectively and efficiently to determine the critical conditions of a multi-phase system. Finally, the application of the numerical solutions of the modeling equations was used to analyze the explosion characteristics of a diesel fuel spray system.

Расчетно-аналитическое обоснование предельных значений массы аммиачной селитры при хранении на складах и терминалах

On the basis of theory of stationary thermal explosion of A.D. Frank-Kamenetsky, depending on the temperature of the critical size of the ammonium nitrate embankment, the calculations were performed, which show that it can be stored in the large volumes at the temperatures up to 30 °C. On the contrary, at the temperatures above 100 °C (for example, at 200 °C), the decomposition of nitrate occurs with acceleration and can lead to an explosion. Based on the studies performed, it is shown that the changes and additions to the fire safety requirements for ammonium nitrate storage in the buildings and structures should be determined by the requirements for fire resistance of buildings (at least II degree of fire resistance), for the purity of the product and its packaging, for the exclusion of contacts with organic substances and materials, storage conditions. Additional fire safety requirements were developed for inclusion in the normative document regarding ammonium nitrate storage. Ammonium nitrate is allowed to be stored in one-story warehouse buildings of at least II degree of fire resistance, structural fire hazard class C0. The floor area within the fire compartment should not exceed 10 500 m2. Between the fire-fighting walls of the 1st type, it is allowed to store no more than 25 000 tons of nitrite in bulk or in the special bags, as well as in the soft specialized containers for bulk products in accordance with GOST 2—2013.The conditions for placing ammonium nitrate in the stacks should be accepted in accordance with the requirements of SP 92.13330.2012. Temperature in the storage room of ammonium nitrate should not exceed 30 °C with a relative humidity of not more than 60 %. Warehouses for storing ammonium nitrate should be equipped with general exchange supply and exhaust and (or) emergency ventilation, in order to exclude the formation of a fire and explosion hazardous environment in the room during the decomposition of ammonium nitrate. Warehouses for storing ammonium nitrate in an amount of not more than 5 thousand tons may be separated from other premises, including from the warehouses for fertilizers and pesticides, by solid (without openings) type 2 fire walls.

Influence of Heating Modes of Compacted Samples from Nickel Powders with Nanosized Particles on Their Interaction with Air

In this paper, we study compact samples of pyrophoric nickel powders with the average particle size of 85 nm, obtained by the chemical-metallurgical method. For the first time, it is experimentally shown that it is possible to passivate compact samples with a diameter of 3 mm from pyrophoric nickel powders with nanosized particles in air. For a relative density of 0.4 to 0.5, the passivation time is only 3–5 s. According to the X-ray phase analysis data, only the Ni phase is observed in passivated samples. It is found that passivated samples retain their thermal stability in air upon slow (<10 deg/s) heating to ~200°C, which is an important parameter for fire safety when handling nanopowders. The electron microscopic analysis of the passivated samples did not reveal traces of sintering of nickel nanoparticles, including after checking for thermal stability. The uniform distribution of oxygen over the passivated samples according to the data of energy dispersive analysis (the standard deviation is 0.9 at %) indicates the volumetric nature of the interaction of the samples with air during passivation. For the obtained passivated samples, the critical heating conditions were determined, under which self-ignition occurs, which is in agreement with N.N. Semyonov’s classical theory of thermal explosion.

Peculiar effect of acylamino and cyan groups on thermal behavior of 2-(1-cyano-1-methylethyl)azocarboxamide

2-(1-Cyano-1-methylethyl)azocarboxamide (CABN) is a representative of new-type azo initiator in the radical polymerization industry. The peculiar water and oil soluble characters make it a versatile rising star for the industry to initiate the polymerization of monomers in either polar or nonpolar solvents based continuous phases. This paper decodes the effect of acylamino and cyan groups on thermal stability and hazards of CABN via advanced thermokinetic analysis and numerical simulation. Initially, simultaneous thermogravimetric analyzer was employed to evaluate the thermal stability of CABN and its two structurally similar azo compounds (azos), azobisisobutyronitrile (AIBN) and azodicarbonamide (AC). Followed with calorimetric experiments by differential scanning calorimetry, the effect of two functional groups on thermal behavior parameters, such as decomposition temperature, melting point, and heat of decomposition was estimated. The results indicated that the acylamino group can improve the thermal stability of CABN but with bulkier heat release. Ultimately, through the medium of thermokinetic analysis, the thermal hazard of AIBN, CABN, and AC was simulated based on auto-ignition and thermal explosion theory. The research results would provide references for the synthesis of new-type azo initiators and process safety parameters to the polymerization industry.

Условия теплового взрыва в пластине при конвективно-радиационном теплообмене

The processes of obtaining and storing energy-saturated substances are characterized by energy release in their volume. The intensity of this energy release increases with increasing temperature. The stability of the stationary temperature state of a solid with a temperature-dependent intensity of volumetric energy release is directly related to the conditions of heat transfer of this body with the environment. If the heat energy released in the volume of the body can no longer be diverted into the environment, the steady temperature state of the body becomes impossible. The paper studies the conditions for a thermal explosion in a solid in the form of a plate with a temperature-dependent coefficient of thermal conductivity and convective-radiation heat transfer on its surfaces. The statement of the nonlinear problem of steady-state thermal conductivity in the plate is represented by a system of integral relations. The limits of integration of the integrals included in these relations are the desired functions and parameters which determine the temperature state of the plate. A quantitative analysis of these relationships makes it possible to establish the influence of the parameters which determine the intensity of heat transfer and the dependence of the thermal conductivity of the plate material on the conditions for a thermal explosion with an arbitrary law of variation with temperature of the volumetric power of the energy release in the plate. The results of such an analysis are presented in the framework of a one-parameter model of the stationary theory of thermal explosion

On Criticality for a Branched-chain Thermal Reactive-Diffusion in a Cylinder

ABSTRACT The heat distribution and branched-chain thermal criticality for a combustible exothermic reaction is examined in this study. The reactive diffusion occurs in a cylinder with pre-exponential variable factor, and the ambient heat exchange is less than the system heat exchange. With material consumption, the reaction is stimulated by initiation rate, branched-chain steps, generalized Arrhenius reaction rate, and molecular diffusion. The mathematical model of this reaction results in a highly nonlinear ordinary differential equation with boundary conditions at the cylinder surface. An approximate solution to the transformed dimensionless nonlinear equation is provided using Collocation Weighted Residual Method (CWRM) and compared with numerical method. The results for the temperature distribution and criticality for dependent parameters are presented graphically. The results from this study will assist in understanding the correlation between the thermal/ignition branched-chain and traditional theory of thermal explosion.

Characteristics of the Development of a Chain Thermal Explosion when Burning Gas Mixtures under Atmospheric Pressure

An experimental study of the features of the critical transition between two kinetic combustion regimes of gas-air mixtures reacting by a chain mechanism is carried out. The presence of two radically different combustion modes is experimentally confirmed by the example of the combustion of propane–air mixtures, both containing an inhibitor (trifluoromethane) and without it, and in complete agreement with the predictions of the theory of A chain thermal explosion (CTE). It is shown that the pattern observed in this work is characteristic not only for slow-burning but also for fast-burning gas mixtures of various compositions. The two distinct and radically different regions observed on the pressure–time variation curve during the combustion of gas mixtures are a manifestation of the general laws which combustible gas mixtures reacting by the chain mechanism follow in a wide range of pressures. It is found that fluorine-containing hydrocarbon is capable of induced oxidation in rich combustible gas mixtures. Trifluoroethane CF3H has an inhibitory effect on the chain combustion process of the propane–air mixture before it enters the CTE and promotes combustion in the CTE mode. If the transition to the CTE is not possible during the propane–air mixture combustion, the fluorinated agent has only an inhibitory effect on combustion.

Analytical and numerical solutions of sodium particle ignition based on the thermal explosion theory with different forms of reaction rates and variable thermal conductivity

Analytical and numerical solutions of sodium particle ignition under different forms of reaction rates and variable thermal conductivity were investigated. The solutions of the problem were performed by taking into consideration the convection and convection with radiation heat loss cases for spatially uniform temperature of a sodium particle. Analytical expressions for critical conditions that relates the characteristic thermophysical parameters with environmental temperature and initial particle temperature were obtained. The results showed that the much reduction in the delay time significantly depended on the adding of variable thermal conductivity and heat loss types, which is crucially important for nuclear reactor safety. It was found that, as an ambient temperature (θa) increased the ignition time drastically decreased and the temperature slightly increased for both modes of heat loss. It was significant to note that the explosion occurred in a case of the sensitized reaction rate at a time greater than that of Arrhenius and bimolecular reaction rates, which considers more safe than other reaction types. A notable increased was found in the critical temperature for sensitized reaction rate compared to other reaction rates. As γR (radiation loss parameter) increased above the critical value, the ignition time and ignition temperature decreased. The results showed that the problem could be solved analytically by properly applying the definition of criticality based on the thermal explosion theory in a more straightforward manner without using mathematical approximation solution.

Solid methane moderators: Thermodynamics and chemistry

The unique properties of solid methane enable the conversion of hot, energetic neutrons into cold neutrons, with an efficiency approximately 3.5 times that of liquid hydrogen based moderators. However, practical applications of solid methane in neutron moderators turned out to be much more challenging than initially expected. Exposure of solid methane at low temperatures to neutron radiation leads to a build-up of radiolysis products in the solid methane matrix. Accumulation of defects beyond some critical number can result in a spontaneous self-accelerated recombination process, which in combination with the expansion of hydrogen built up in bulk solid methane during irradiation, was believed to be responsible for the moderator’s breakdown. Here we present results of our thermodynamic model, based on the theory of thermal explosion. Our model agrees well with the test data obtained using methane moderators developed at the IPNS neutron source, based at Argonne National Laboratory and the data acquired during commissioning of the ISIS Target Station 2 solid methane moderator. We also discuss the products of radiolysis reactions generated by exposure of the condensed methane to neutron radiation. The succession of radiolysis reactions may lead to the production of long chain hydrocarbons, which can contaminate the moderator system and significantly reduce efficiency of the heat-exchanger. The possible solutions for cleaning moderators using targeted solvents are considered. In the conclusion we give some practical recommendations, based on our simulation results and operational experience.