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N. A. Lutsenko - One of the best experts on this subject based on the ideXlab platform.
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Numerical model of two-dimensional Heterogeneous Combustion in porous media under natural convection or forced filtration
Combustion Theory and Modelling, 2017Co-Authors: N. A. LutsenkoAbstract:A novel mathematical model and original numerical method for investigating the two-dimensional waves of Heterogeneous Combustion in porous media are proposed and described in detail. The mathematical model is constructed within the framework of the model of interacting interpenetrating continua and includes equations of state, continuity, momentum conservation and energy for solid and gas phases. Combustion, considered in the paper, is due to the exothermic reaction between fuel in the porous solid medium and oxidiser contained in the gas flowing through the porous object. The original numerical method is based on a combination of explicit and implicit finite-difference schemes. A distinctive feature of the proposed model is that the gas velocity at the open boundaries (inlet and outlet) of the porous object is unknown and has to be found from the solution of the problem, i.e. the flow rate of the gas regulates itself. This approach allows processes to be modelled not only under forced filtration, but als...
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Two-dimensional gas flows under Heterogeneous Combustion of solid porous media
Doklady Physics, 2017Co-Authors: V. A. Levin, N. A. LutsenkoAbstract:Two-dimensional unsteady gas flows in porous media with Heterogeneous-Combustion centers are investigated under forced filtration and free convection. With the use of numerical methods, it is shown that complex gas flows including vortex ones can arise under the Combustion of solid porous media. In the case of forced filtration, the gas tends to flow around the heated portion of an object preferring to flow along cold regions. Under natural convection, the vortex gas flows, which can exist for a reasonably long time and strongly affect the oxidizer inflow into the reaction zone, arise at the initial moment of the process in the Combustion zone and in its vicinities.
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Numerical modeling of 1D Heterogeneous Combustion in porous media under free convection taking into account dependence of permeability on porosity
Journal of Physics: Conference Series, 2016Co-Authors: N. A. LutsenkoAbstract:Using numerical experiment the one-dimensional unsteady process of Heterogeneous Combustion in porous object under free convection is considered when the dependence of permeability on porosity is taken into account. The Combustion is due to exothermic reaction between the fuel in the solid porous medium and oxidizer contained in the gas flowing through the porous object. In the present work the process is considered under natural convection, i.e. when the flow rate and velocity of the gas at the inlet to the porous objects are unknown, but the gas pressure at object boundaries is known. The influence of changing of permeability due to the changing of porosity on the solution is investigated using original numerical method, which is based on a combination of explicit and implicit finite-difference schemes. It was shown that taking into account the dependence of permeability on porosity, which is described by some known equations, can significantly change the solution in one-dimensional case. The changing of permeability due to the changing of porosity leads to the speed increasing of both cocurrent and the countercurrent Combustion waves, and to the temperature increasing in the Combustion zone of countercurrent Combustion wave.
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Effect of gravity field and pressure difference on Heterogeneous Combustion in porous media
Combustion Science and Technology, 2014Co-Authors: N. A. Lutsenko, V. A. LevinAbstract:Gravity is known to affect Heterogeneous Combustion in porous media; it is especially appreciable at very low air (oxidizer) flow rates. Effect of gravity on the Combustion of porous objects includes not only the force of gravity (gravity field inside the porous object), but also the pressure difference at boundaries of the porous object, which is caused by the action of gravity on the ambient air if the open borders of the object are located at different heights. In this work, it has been studied numerically how the gravity field inside the porous object and the above-mentioned pressure difference at the object boundaries affect the Combustion process in the object. It is revealed that the gravity field inside the porous object and the pressure difference at object boundaries lead to opposite effects: the pressure difference on object borders leads to the propagation of the Combustion wave in the same direction and the same mode as in the vertical porous object, but the gravity field leads to the spread ...
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Numerical Comparison of Heterogeneous Combustion Waves in Horizontal and Vertical Porous Objects under Free Convection
Advanced Materials Research, 2014Co-Authors: N. A. Lutsenko, Svetlana N. SorokovaAbstract:Using numerical experiment one-dimensional unsteady processes of Heterogeneous Combustion in porous object under free convection in horizontal case have been investigated and compared with vertical case. It is shown that in the case of the horizontal porous object the oxidizer supply, which is the result of natural convection, is not sufficient for the appearance of stable wave of Heterogeneous Combustion. In contrast to the vertical position of the object, there are no long-lived Combustion waves in the horizontal case, which completely burns down the solid combustible material. When the ignition zone is on the border of the object, the Combustion wave near the vicinity of the boundary burns the oxygen and becomes extinct. When the ignition zone is in the center of the porous object, two Combustion waves arise which may move very slowly, burn oxygen and become extinct.
Vemuri Balakotaiah - One of the best experts on this subject based on the ideXlab platform.
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Transport effects on pattern formation and maximum temperature in homogeneous–Heterogeneous Combustion
Chemical Engineering Journal, 2016Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract We study the impact of the Lewis number, Le f (thermal diffusivity of the reaction mixture to the molecular diffusivity of the limiting reactant) and the Peclet numbers on the maximum temperature attained for coupled homogeneous–Heterogeneous Combustion process in a parallel plate reactor using one, two and three-dimensional models. For the case of 1-D models, we find that the maximum temperature never exceeds the adiabatic value for physically consistent boundary conditions. For 2-D models, we find that for Le f 1 , the hot spot temperature can exceed the adiabatic value, it is always located on the wall and its distance from the inlet and magnitude increase with increasing radial Peclet number. However, for Le f > 1 , contrary to some literature claims (Zheng and Mantzaras, 2014), the peak temperature never exceeds the adiabatic value, though the temperature can be non-monotontic across the channel. We show that 3-D solutions can bifurcate either from 1-D or 2-D solutions irrespective of the value of the Lewis number. It is also shown that an infinite number of solutions that are discontinuous in the axial coordinate can exist for the common case of large axial heat Peclet number. The implications of these observations for catalyst and process design in systems in which both homogeneous and catalytic reactions occur are discussed.
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transport effects on pattern formation and maximum temperature in homogeneous Heterogeneous Combustion
Chemical Engineering Journal, 2016Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract We study the impact of the Lewis number, Le f (thermal diffusivity of the reaction mixture to the molecular diffusivity of the limiting reactant) and the Peclet numbers on the maximum temperature attained for coupled homogeneous–Heterogeneous Combustion process in a parallel plate reactor using one, two and three-dimensional models. For the case of 1-D models, we find that the maximum temperature never exceeds the adiabatic value for physically consistent boundary conditions. For 2-D models, we find that for Le f 1 , the hot spot temperature can exceed the adiabatic value, it is always located on the wall and its distance from the inlet and magnitude increase with increasing radial Peclet number. However, for Le f > 1 , contrary to some literature claims (Zheng and Mantzaras, 2014), the peak temperature never exceeds the adiabatic value, though the temperature can be non-monotontic across the channel. We show that 3-D solutions can bifurcate either from 1-D or 2-D solutions irrespective of the value of the Lewis number. It is also shown that an infinite number of solutions that are discontinuous in the axial coordinate can exist for the common case of large axial heat Peclet number. The implications of these observations for catalyst and process design in systems in which both homogeneous and catalytic reactions occur are discussed.
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Bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion
Chemical Engineering Journal, 2015Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract Using a two-mode lumped model, we present theory and comprehensive bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion of propane and methane in short monolith, fibermat or gauze type reactors with a focus on the dependence of the ignition, extinction, hysteresis, double and boundary limit loci on the various design and operating parameters. We analyze the impact of inlet fuel mole fraction, inlet temperature, residence time and channel hydraulic radius on the relative position of the homogeneous and catalytic ignition and extinction points and identify the parameter regions in which either catalytic or homogeneous reaction dominates. We also identify the regions in which catalytic ignition leads either to an intermediate branch on which the homogeneous reaction rate is negligible or directly to a high conversion and temperature state thereby facilitating homogeneous ignition. For the case of methane oxidation, we examine both the lean and rich feeds with the operating pressure as the bifurcation variable and compare the predicted results with available experimental data and numerical simulations using detailed CFD models.
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bifurcation analysis of thermally coupled homogeneous Heterogeneous Combustion
Chemical Engineering Journal, 2015Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract Using a two-mode lumped model, we present theory and comprehensive bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion of propane and methane in short monolith, fibermat or gauze type reactors with a focus on the dependence of the ignition, extinction, hysteresis, double and boundary limit loci on the various design and operating parameters. We analyze the impact of inlet fuel mole fraction, inlet temperature, residence time and channel hydraulic radius on the relative position of the homogeneous and catalytic ignition and extinction points and identify the parameter regions in which either catalytic or homogeneous reaction dominates. We also identify the regions in which catalytic ignition leads either to an intermediate branch on which the homogeneous reaction rate is negligible or directly to a high conversion and temperature state thereby facilitating homogeneous ignition. For the case of methane oxidation, we examine both the lean and rich feeds with the operating pressure as the bifurcation variable and compare the predicted results with available experimental data and numerical simulations using detailed CFD models.
Carmen Branca - One of the best experts on this subject based on the ideXlab platform.
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devolatilization and Heterogeneous Combustion of wood fast pyrolysis oils
Industrial & Engineering Chemistry Research, 2005Co-Authors: Carmen Branca, Colomba Di Blasi, Rosario ElefanteAbstract:Weight loss curves of wood fast pyrolysis oils in air have been measured, under controlled thermal conditions, carrying out two separate sets of experiments. The first, which has a final temperature of 600 K, concerns evaporation/cracking of the oil and secondary char formation, processes associated with sample swelling and solidification. After collection and milling, in the second set of experiments, Heterogeneous Combustion of the secondary char is carried out to temperatures of 873 K. Although the details of the rate curves appear to be dependent on the commercial process (BTG, Dynamotive, Ensyn, Pyrovac) applied to produce the oil, the same qualitative features are observed in all cases. Secondary char formation and sample modification begin for temperatures of about 460−490 K. Moreover, a conceptual reaction mechanism, consisting of six main zones, can always explain the low-temperature (≤600 K) devolatilization characteristics. Similar to primary char produced from wood pyrolysis, secondary char ex...
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devolatilization in the temperature range 300 600 k of liquids derived from wood pyrolysis and gasification
Fuel, 2005Co-Authors: Carmen Branca, Colomba Di Blasi, Carmine RussoAbstract:Abstract A thermogravimetric system, previously developed for solid fuel degradation, has been modified to examine liquids obtained from conventional pyrolysis and updraft gasification of beech wood. Thermogravimetric curves in air show two main reaction stages. The first (temperatures ≤600 K) concerns evaporation, formation and release of gases and formation of secondary char (coke). Then, at higher temperatures, Heterogeneous Combustion of secondary char takes place. A reliable procedure has been developed to carry out the first stage under assigned temperature using a PID controller and the applied heat flux as the manipulated variable. It has been found that the pyrolysis temperature does not affect significantly weight loss dynamics and amount of secondary char (approximately equal to 20% of the liquid on a dry basis). The thermogravimetric curves are well predicted by a global mechanism consisting of three parallel first-order reactions (activation energies of 66, 32 and 36 kJ/mol, respectively). Due to strong physico-chemical transformations (sample swelling and solidification) associated with secondary char formation, it is not possible to avoid ignition during Heterogeneous Combustion. Therefore, this reaction stage should be investigated separately after collection and adequate re-preparation of the charred sample.
Imran Alam - One of the best experts on this subject based on the ideXlab platform.
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Transport effects on pattern formation and maximum temperature in homogeneous–Heterogeneous Combustion
Chemical Engineering Journal, 2016Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract We study the impact of the Lewis number, Le f (thermal diffusivity of the reaction mixture to the molecular diffusivity of the limiting reactant) and the Peclet numbers on the maximum temperature attained for coupled homogeneous–Heterogeneous Combustion process in a parallel plate reactor using one, two and three-dimensional models. For the case of 1-D models, we find that the maximum temperature never exceeds the adiabatic value for physically consistent boundary conditions. For 2-D models, we find that for Le f 1 , the hot spot temperature can exceed the adiabatic value, it is always located on the wall and its distance from the inlet and magnitude increase with increasing radial Peclet number. However, for Le f > 1 , contrary to some literature claims (Zheng and Mantzaras, 2014), the peak temperature never exceeds the adiabatic value, though the temperature can be non-monotontic across the channel. We show that 3-D solutions can bifurcate either from 1-D or 2-D solutions irrespective of the value of the Lewis number. It is also shown that an infinite number of solutions that are discontinuous in the axial coordinate can exist for the common case of large axial heat Peclet number. The implications of these observations for catalyst and process design in systems in which both homogeneous and catalytic reactions occur are discussed.
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transport effects on pattern formation and maximum temperature in homogeneous Heterogeneous Combustion
Chemical Engineering Journal, 2016Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract We study the impact of the Lewis number, Le f (thermal diffusivity of the reaction mixture to the molecular diffusivity of the limiting reactant) and the Peclet numbers on the maximum temperature attained for coupled homogeneous–Heterogeneous Combustion process in a parallel plate reactor using one, two and three-dimensional models. For the case of 1-D models, we find that the maximum temperature never exceeds the adiabatic value for physically consistent boundary conditions. For 2-D models, we find that for Le f 1 , the hot spot temperature can exceed the adiabatic value, it is always located on the wall and its distance from the inlet and magnitude increase with increasing radial Peclet number. However, for Le f > 1 , contrary to some literature claims (Zheng and Mantzaras, 2014), the peak temperature never exceeds the adiabatic value, though the temperature can be non-monotontic across the channel. We show that 3-D solutions can bifurcate either from 1-D or 2-D solutions irrespective of the value of the Lewis number. It is also shown that an infinite number of solutions that are discontinuous in the axial coordinate can exist for the common case of large axial heat Peclet number. The implications of these observations for catalyst and process design in systems in which both homogeneous and catalytic reactions occur are discussed.
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Bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion
Chemical Engineering Journal, 2015Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract Using a two-mode lumped model, we present theory and comprehensive bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion of propane and methane in short monolith, fibermat or gauze type reactors with a focus on the dependence of the ignition, extinction, hysteresis, double and boundary limit loci on the various design and operating parameters. We analyze the impact of inlet fuel mole fraction, inlet temperature, residence time and channel hydraulic radius on the relative position of the homogeneous and catalytic ignition and extinction points and identify the parameter regions in which either catalytic or homogeneous reaction dominates. We also identify the regions in which catalytic ignition leads either to an intermediate branch on which the homogeneous reaction rate is negligible or directly to a high conversion and temperature state thereby facilitating homogeneous ignition. For the case of methane oxidation, we examine both the lean and rich feeds with the operating pressure as the bifurcation variable and compare the predicted results with available experimental data and numerical simulations using detailed CFD models.
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bifurcation analysis of thermally coupled homogeneous Heterogeneous Combustion
Chemical Engineering Journal, 2015Co-Authors: Imran Alam, David West, Vemuri BalakotaiahAbstract:Abstract Using a two-mode lumped model, we present theory and comprehensive bifurcation analysis of thermally coupled homogeneous–Heterogeneous Combustion of propane and methane in short monolith, fibermat or gauze type reactors with a focus on the dependence of the ignition, extinction, hysteresis, double and boundary limit loci on the various design and operating parameters. We analyze the impact of inlet fuel mole fraction, inlet temperature, residence time and channel hydraulic radius on the relative position of the homogeneous and catalytic ignition and extinction points and identify the parameter regions in which either catalytic or homogeneous reaction dominates. We also identify the regions in which catalytic ignition leads either to an intermediate branch on which the homogeneous reaction rate is negligible or directly to a high conversion and temperature state thereby facilitating homogeneous ignition. For the case of methane oxidation, we examine both the lean and rich feeds with the operating pressure as the bifurcation variable and compare the predicted results with available experimental data and numerical simulations using detailed CFD models.
L. D. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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The effect of flow velocity on ignition and extinction in homogeneous-Heterogeneous Combustion
Combustion Science and Technology, 1994Co-Authors: R. J. Olsen, L. D. Schmidt, R. ArisAbstract:Abstract Ignition and extinction points are calculated for homogeneous-Heterogeneous Combustion of a premixed propane-air stream in stagnation point flow over a platinum surface as functions of inlet gas velocity and composition and power input to the catalyst surface using global rate expressions for the homogeneous and surface reactions. Curves of surface temperature and surface concentration of fuel and oxygen at the ignition and extinction points are computed at several compositions in the fuel-lean regime. [gnition and extinction of the surface reaction and autothermal behavior are found over a very broad range of velocities. Homogeneous ignition occurs only at relatively low velocities. As the velocity increases from 0.5 cm/s to 50 cm/s, autothermal behavior is supported by leaner mixtures, and the autothermal surface temperature increases substantially. Inlet compositions leaner than 1.4% propane cannot support autothermal operation at any velocity. Homogeneous ignition takes place at higher surfac...
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bifurcation behavior in homogeneous Heterogeneous Combustion i experimental results over platinum
Combustion and Flame, 1991Co-Authors: W.r. Williams, X. Song, M T Stenzel, L. D. SchmidtAbstract:Abstract Ignition, extinction, and autothermal behavior of the homogeneous and Heterogeneous oxidation reactions in air of NH3, CH4, C3H8, and an equimolar NH 3 CH 4 mixture over resistively heated polycrystalline platinum foils was studied in an atmospheric pressure flow reactor as a function of flow rate, fuel concentration, preheat temperature, and reactor geometry. Surface temperature versus power curves were experimentally determined for different compositions in these systems, which were in turn summarized in bifurcation diagrams of surface temperature or power as a function of fuel composition. Two ignitions (Heterogeneous and homogeneous), one extinction and one self-sustaining autothermal steady state, were observed for all systmes except NH 3 CH 4 oxidation. The Heterogeneous ignition occurred around 600°C for CH4 and 200°C for all other systems and was weakly dependent on the fuel composition. Long transients due to carbon formation were observed in the autothermal behavior for fuel-rich compositions in the CH4 system. A second Heterogeneous ignition occurred in NH 3 CH 4 oxidation, which ranged from 400° to 600°C. Homogeneous reaction ignited at surfaca temperatures ranging from 1050°C for C3H8 oxidation to 1500°C for CH4 and NH3 oxidation. For C3H8 and CH4 oxidation, the flame generally left the foil, but in NH3 oxidation a stable boundary layer flame was also observed under some conditions.