Combustion of gases under filtration in porous media, or filtration combustion (FC), is character... more Combustion of gases under filtration in porous media, or filtration combustion (FC), is characterized with complex heat and mass transfer and interphase interaction and may be utilized in multiple thermo-chemical applications. The work studies filtration combustion of gases at transition from low-velocity (LV) to high-velocity (HV) regime under gas pressure growth. As shown, the transition regime of FC is characteristic for conditions of technological and experimental set-ups, at least at body pore size of d 0 >1.5 to 2 mm. When increasing working pressure by 1–2 atmospheres higher than atmospheric one, critical size of pores decreases 2–2.5 times. Theory and estimation method for velocity and temperature of stationary FC waves under the transition regime is proposed, where dimensionless complex Φ≡βPe S u 2 /Re 1/6 , (β=RT ad /E, Pe S u =S u d 0 /κ,Re=u g d 0 /ν , S u – normal laminar flame velocity, u g – gas filtration velocity) constructed on turbulent combustion to thermal re...
A method for inhomogeneous, molecular gas integrated absorption calculating is developed by using... more A method for inhomogeneous, molecular gas integrated absorption calculating is developed by using partial absorption, that depend on mean absorption coefficients Kn obtained in analytical form. These coefficients are evaluated numerically or analytically for the actual frequency dependence of the spectral absorption coefficients. A procedure for determination of mean coefficient for gas mixture is discussed.
Journal of Electromagnetic Analysis and Applications, 2020
Measurement of the electrical conductivity of electrolytes and heterogeneous materials containing... more Measurement of the electrical conductivity of electrolytes and heterogeneous materials containing them is accompanied by numerous physical and electrochemical processes, complicating measuring and interpretation of data. As a result, the measurement of the electrical conductivity of such a system is a difficult and not finally resolved problem. The new method of resistance measurement of the electrolytic systems is substantiated and tested on example of heterogeneous electrolytic system "lignin-calcium chloride water solution" in this article. The method is based on measurement of resistance of the electrolytic system at different voltages (DC) on the cell and the consequent approximation of the acquired data taking into consideration volume charges and potential barriers arising on the boarders of electrodes and electrolytic materials. Extrapolation of the resistance to the limiting small current lets one obtain a characteristic value of the active resistance of the electrolytic system. The method is technically simple, inexpensive and has several advantages compared to the methods based on AC measurements.
Journal of Electromagnetic Analysis and Applications, 2019
A consistent physical and mathematical model of the propagation of electromagnetic waves in an in... more A consistent physical and mathematical model of the propagation of electromagnetic waves in an inhomogeneous medium with strong discontinuities of the electromagnetic field at the interface of two media, which is a rough surface, was developed. Mathematical modeling of rough surfaces and their profiles was carried out using fractal geometry, which allows us to display the topology of the object as close as possible to reality. For real heterogeneous rough structures, we have developed a through-counting method that takes into account the continuity of the total current at the interfaces of adjacent media, the effect of induced surface charge and surface current. This approach lets one avoid the necessity to set surface impedances depending on the structure of the field being determined and on the material properties.
ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations, 2018
Operational control of parameters of electrolytes (first of all–of specific electric conductivity... more Operational control of parameters of electrolytes (first of all–of specific electric conductivity), is an important electrochemical technology. The methods of measurement of electric conductivity of electrolytes is a subject of permanent discussions because of complexity of physical-and-chemical processes accompanying ion transport and of electrolyte polarization near surfaces of electrodes and of electrochemical processes on the electrodes surfaces. Actual highand low-frequency conductometric methods require relatively expensive equipment and are not free of methodological flaws. In this paper a new method of electric resistance of liquid electrolytes is described and substantiated. It is based on automatic performance of a series of measurements of electrolyte resistance at DC, data processing and extrapolation of an appropriate dependence to threshold voltage at measurement cell plates. The character of functions approximating resistance-applied voltage dependence and method of r...
Combustion of gases under filtration in porous media, or filtration combustion (FC), is character... more Combustion of gases under filtration in porous media, or filtration combustion (FC), is characterized with complex heat and mass transfer and interphase interaction and may be utilized in multiple thermo-chemical applications.The work studies filtration combustion of gases at transition from low-velocity (LV) to high-velocity (HV) regime under gas pressure growth. As shown, the transition regime of FC is characteristic for
The effect of inlet window deflectors on the performance of a natural draft cooling tower subject... more The effect of inlet window deflectors on the performance of a natural draft cooling tower subjected to a crosswind was studied numerically. Three patterns of the inlet window deflectors with different setting angles (62, 72, and 82 degrees) were tested under various crosswind velocities. The assumption of heat and mass transfer equivalence was adopted for simulation. A numerical model was developed and verified by comparison with experimental data. The simulations show that the 72-degree inlet window deflectors are efficient in a wide range of crosswind velocities. The effect of the number of deflectors was also investigated and the link between the velocity profile and the critical wind velocity was clarified. It was shown that the use of deflectors in the inlet window increases the thermal efficiency of a cooling tower up to 8.6% at wind velocities greater than 2 m/s and does not exhibit any effect at the wind velocities close to critical wind velocity. The investigation may be helpful in optimal design of natural draft and “hybrid” cooling towers.
Differential approximation is derived from radiation transfer equation by averaging over the soli... more Differential approximation is derived from radiation transfer equation by averaging over the solid angle. It is one of the more effective methods for engineering calculations of radiative heat transfer in complex three-dimensional thermal power systems with selective and scattering media. The new method for improvement of accuracy of the differential approximation based on using of auto-adaptable boundary conditions is introduced in the paper. The efficiency of the named method is proved for the test 2D-systems. Self-consistent auto-adaptable boundary conditions taking into consideration the nonorthogonal component of the incident to the boundary radiation flux are formulated. It is demonstrated that taking into consideration of the non-orthogonal incident flux in multi-dimensional systems, such as furnaces, boilers, combustion chambers improves the accuracy of the radiant flux simulations and to more extend in the zones adjacent to the edges of the chamber. Test simulations utilizing the differential approximation method with traditional boundary conditions, new self-consistent boundary conditions and "precise" discrete ordinates method were performed. The mean square errors of the resulting radiative fluxes calculated along the boundary of rectangular and triangular test areas were decreased 1.5-2 times by using autoadaptable boundary conditions. Radiation flux gaps in the corner points of non-symmetric systems are revealed by using auto-adaptable boundary conditions which can not be obtained by using the conventional boundary conditions.
Journal of Engineering Physics and Thermophysics, 2014
Environmental crosswind changes the aerodynamic pattern inside a cooling tower, destroys uniform ... more Environmental crosswind changes the aerodynamic pattern inside a cooling tower, destroys uniform and axisymmetric distribution of fl ow at its inlet and outlet, and may degrade fi ll zone performance. In this paper, the effect of fl ow rotation in the over-shower zone of a natural draft cooling tower (NDCT) on the aerodynamic interaction with crosswind is studied numerically. The 3D geometry of an actual NDCT and three models of induced rotation velocity fi elds are utilized for simulation. It is demonstrated that fl ow rotation results in homogenization of the aerodynamic fi eld in the over-shower zone. The inhomogeneity of the velocity fi eld in the outlet cross section decreases linearly with rotation intensifi cation. The effect of main stream switching under strong wind conditions is found. It is shown that even moderate fl ow rotation eliminates this effect.
Journal of Engineering Physics and Thermophysics, 2013
Cooling towers (CTs) are important units in the vast majority of power plants. They have been int... more Cooling towers (CTs) are important units in the vast majority of power plants. They have been intensively investigated for the last 70 years. The abundance of works makes diffi cult to "see" the total area of investigations of CTs and to fi nd the most urgent and important results. This article contains a compact overview of contemporary publications (for the last 11 years) in the area of heat and mass transfer in CTs, especially in natural draft wet cooling towers (NDWCT), and of related phenomena. Attention is specially paid to modern numerical computational investigations.
Journal of Engineering Physics and Thermophysics, 2013
The infl uence of fl ow rotation in the over-shower zone of a natural draft wet cooling tower (ND... more The infl uence of fl ow rotation in the over-shower zone of a natural draft wet cooling tower (NDCT) on heat and mass transfer in this zone is investigated numerically. The 3D geometry of an actual NDCT and three models of the induced rotation velocity fi elds are utilized for calculations. Two phases (liquid and gaseous) and three components are taken into consideration. The interphase heat exchange, heat transfer to the walls, condensation-evaporation intensity fi eld, and other parameters are investigated as functions of the induced rotation intensity (the inclination of the velocity vector at the periphery). It is shown that the induced fl ow rotation intensifi es the heat and mass transfer in the over-shower zone of an NDCT. Flow rotation leads to specifi c redistribution of evaporation-condensation areas in an NDCT and stimulates water condensation near its walls.
An approximate model of IR-radiation transfer in homogeneous NO-involving systems is presented wh... more An approximate model of IR-radiation transfer in homogeneous NO-involving systems is presented which takes into account the specific features of the actual vibration-rotation spectrum. Analytical expressions are obtained for the main quantities that characterize radiative heat transfer. The model suggested is illustrated by specific examples. This paper deals with the analysis of radiative heat transfer equations, investigation of the NO vibration-rotation spectrum structure and with the discussion of experimental data on the width of spectral lines. The authors consider the problem of the force of the spectral lines and bands of NO and analytical expressions are obtained for the equivalent width of these bands. The local power of radiation sources and of radiant energy flux incident on the volume boundary are calculated for reactors of simplest geometry.
The parallels between the turbulent and the filtration combustion of a gas in an inert medium hav... more The parallels between the turbulent and the filtration combustion of a gas in an inert medium have been considered. It is suggested that in the case where the thermal interaction between the gas and the porous medium is absent, elementary processes of mixing, chemical reaction, and others, which occur in turbulent and filtration combustion, can be characterized by similar dimensionless parameters setting up a correspondence between the integral scale of turbulence and the size of the pores. The dimensionless parameters have been analyzed and the diagram of the Borghi regimes of filtration combustion has been constructed. A number of typical cases of filtration combustion have been characterized using this diagram. It is shown that the considered cases of filtration combustion concern the range of distorted flames and distributed reaction zones according to the Borghi classification. From this it was assumed that the surface of filtration combustion in the first of the considered reg...
International Journal of Heat and Mass Transfer, 2006
The results of detailed 2D numerical simulation of non-steady methane-air flame propagation in se... more The results of detailed 2D numerical simulation of non-steady methane-air flame propagation in semi-closed tubes after ignition near the closed end are presented. Flame dynamics dependence on the tubes width for adiabatic and nonadiabatic walls is obtained. It is shown that main mechanism of front acceleration is flame surface perturbation due to hydrodynamic drag near the walls, which grows due to gas thermal expansion and flow acceleration. The mechanism of vortex formation in vicinity of the front bow point is demonstrated. The vortex is generated at the flame front velocities of the order of S l $ 20 m/s and may become precursor for flow turbulization at later instants. The new theoretically possible regime of gas combustion in adiabatic conditions in narrow capillary is found. It is characterized by relatively low propagation velocity and incomplete combustion.
International Journal of Heat and Mass Transfer, 2011
ABSTRACT A new technology of water purification of organic inclusions or solutes by using a filtr... more ABSTRACT A new technology of water purification of organic inclusions or solutes by using a filtration combustion reactor with alternating flow direction is investigated numerically. An acetone aqueous solution served as a model liquid. The lean combustibility limit (LCL) was determined for a wide range of flow rates, different values of the heat exchange coefficient, length of the reactor, and for different sizes of packed bed particles. It is demonstrated that thermal insulation has the strongest effect on the LCL. A minimum concentration of acetone in water that provides self-sustaining combustion may be as low as cmin=13.5% for the reactor length L=0.4m. The nonmonotonic behavior of the LCL dependence of the flow rate for short reactors and coarse particles has been demonstrated. The physical aspects of this feature was discussed.
International Journal of Heat and Mass Transfer, 2005
The new regenerator–recuperator scheme of filtration combustion VOC oxidizing reactor is under re... more The new regenerator–recuperator scheme of filtration combustion VOC oxidizing reactor is under research. Its main characteristics, such as maximum temperature of reactor, temperature of exhaust gases, NO emission and others are calculated and compared with the same characteristics of other types of reactors (co-flow filtration combustion wave reactor, counter-flow heat exchange recuperative reactor, reverse flow regenerative reactor). It is shown
Combustion of gases under filtration in porous media, or filtration combustion (FC), is character... more Combustion of gases under filtration in porous media, or filtration combustion (FC), is characterized with complex heat and mass transfer and interphase interaction and may be utilized in multiple thermo-chemical applications. The work studies filtration combustion of gases at transition from low-velocity (LV) to high-velocity (HV) regime under gas pressure growth. As shown, the transition regime of FC is characteristic for conditions of technological and experimental set-ups, at least at body pore size of d 0 >1.5 to 2 mm. When increasing working pressure by 1–2 atmospheres higher than atmospheric one, critical size of pores decreases 2–2.5 times. Theory and estimation method for velocity and temperature of stationary FC waves under the transition regime is proposed, where dimensionless complex Φ≡βPe S u 2 /Re 1/6 , (β=RT ad /E, Pe S u =S u d 0 /κ,Re=u g d 0 /ν , S u – normal laminar flame velocity, u g – gas filtration velocity) constructed on turbulent combustion to thermal re...
A method for inhomogeneous, molecular gas integrated absorption calculating is developed by using... more A method for inhomogeneous, molecular gas integrated absorption calculating is developed by using partial absorption, that depend on mean absorption coefficients Kn obtained in analytical form. These coefficients are evaluated numerically or analytically for the actual frequency dependence of the spectral absorption coefficients. A procedure for determination of mean coefficient for gas mixture is discussed.
Journal of Electromagnetic Analysis and Applications, 2020
Measurement of the electrical conductivity of electrolytes and heterogeneous materials containing... more Measurement of the electrical conductivity of electrolytes and heterogeneous materials containing them is accompanied by numerous physical and electrochemical processes, complicating measuring and interpretation of data. As a result, the measurement of the electrical conductivity of such a system is a difficult and not finally resolved problem. The new method of resistance measurement of the electrolytic systems is substantiated and tested on example of heterogeneous electrolytic system "lignin-calcium chloride water solution" in this article. The method is based on measurement of resistance of the electrolytic system at different voltages (DC) on the cell and the consequent approximation of the acquired data taking into consideration volume charges and potential barriers arising on the boarders of electrodes and electrolytic materials. Extrapolation of the resistance to the limiting small current lets one obtain a characteristic value of the active resistance of the electrolytic system. The method is technically simple, inexpensive and has several advantages compared to the methods based on AC measurements.
Journal of Electromagnetic Analysis and Applications, 2019
A consistent physical and mathematical model of the propagation of electromagnetic waves in an in... more A consistent physical and mathematical model of the propagation of electromagnetic waves in an inhomogeneous medium with strong discontinuities of the electromagnetic field at the interface of two media, which is a rough surface, was developed. Mathematical modeling of rough surfaces and their profiles was carried out using fractal geometry, which allows us to display the topology of the object as close as possible to reality. For real heterogeneous rough structures, we have developed a through-counting method that takes into account the continuity of the total current at the interfaces of adjacent media, the effect of induced surface charge and surface current. This approach lets one avoid the necessity to set surface impedances depending on the structure of the field being determined and on the material properties.
ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations, 2018
Operational control of parameters of electrolytes (first of all–of specific electric conductivity... more Operational control of parameters of electrolytes (first of all–of specific electric conductivity), is an important electrochemical technology. The methods of measurement of electric conductivity of electrolytes is a subject of permanent discussions because of complexity of physical-and-chemical processes accompanying ion transport and of electrolyte polarization near surfaces of electrodes and of electrochemical processes on the electrodes surfaces. Actual highand low-frequency conductometric methods require relatively expensive equipment and are not free of methodological flaws. In this paper a new method of electric resistance of liquid electrolytes is described and substantiated. It is based on automatic performance of a series of measurements of electrolyte resistance at DC, data processing and extrapolation of an appropriate dependence to threshold voltage at measurement cell plates. The character of functions approximating resistance-applied voltage dependence and method of r...
Combustion of gases under filtration in porous media, or filtration combustion (FC), is character... more Combustion of gases under filtration in porous media, or filtration combustion (FC), is characterized with complex heat and mass transfer and interphase interaction and may be utilized in multiple thermo-chemical applications.The work studies filtration combustion of gases at transition from low-velocity (LV) to high-velocity (HV) regime under gas pressure growth. As shown, the transition regime of FC is characteristic for
The effect of inlet window deflectors on the performance of a natural draft cooling tower subject... more The effect of inlet window deflectors on the performance of a natural draft cooling tower subjected to a crosswind was studied numerically. Three patterns of the inlet window deflectors with different setting angles (62, 72, and 82 degrees) were tested under various crosswind velocities. The assumption of heat and mass transfer equivalence was adopted for simulation. A numerical model was developed and verified by comparison with experimental data. The simulations show that the 72-degree inlet window deflectors are efficient in a wide range of crosswind velocities. The effect of the number of deflectors was also investigated and the link between the velocity profile and the critical wind velocity was clarified. It was shown that the use of deflectors in the inlet window increases the thermal efficiency of a cooling tower up to 8.6% at wind velocities greater than 2 m/s and does not exhibit any effect at the wind velocities close to critical wind velocity. The investigation may be helpful in optimal design of natural draft and “hybrid” cooling towers.
Differential approximation is derived from radiation transfer equation by averaging over the soli... more Differential approximation is derived from radiation transfer equation by averaging over the solid angle. It is one of the more effective methods for engineering calculations of radiative heat transfer in complex three-dimensional thermal power systems with selective and scattering media. The new method for improvement of accuracy of the differential approximation based on using of auto-adaptable boundary conditions is introduced in the paper. The efficiency of the named method is proved for the test 2D-systems. Self-consistent auto-adaptable boundary conditions taking into consideration the nonorthogonal component of the incident to the boundary radiation flux are formulated. It is demonstrated that taking into consideration of the non-orthogonal incident flux in multi-dimensional systems, such as furnaces, boilers, combustion chambers improves the accuracy of the radiant flux simulations and to more extend in the zones adjacent to the edges of the chamber. Test simulations utilizing the differential approximation method with traditional boundary conditions, new self-consistent boundary conditions and "precise" discrete ordinates method were performed. The mean square errors of the resulting radiative fluxes calculated along the boundary of rectangular and triangular test areas were decreased 1.5-2 times by using autoadaptable boundary conditions. Radiation flux gaps in the corner points of non-symmetric systems are revealed by using auto-adaptable boundary conditions which can not be obtained by using the conventional boundary conditions.
Journal of Engineering Physics and Thermophysics, 2014
Environmental crosswind changes the aerodynamic pattern inside a cooling tower, destroys uniform ... more Environmental crosswind changes the aerodynamic pattern inside a cooling tower, destroys uniform and axisymmetric distribution of fl ow at its inlet and outlet, and may degrade fi ll zone performance. In this paper, the effect of fl ow rotation in the over-shower zone of a natural draft cooling tower (NDCT) on the aerodynamic interaction with crosswind is studied numerically. The 3D geometry of an actual NDCT and three models of induced rotation velocity fi elds are utilized for simulation. It is demonstrated that fl ow rotation results in homogenization of the aerodynamic fi eld in the over-shower zone. The inhomogeneity of the velocity fi eld in the outlet cross section decreases linearly with rotation intensifi cation. The effect of main stream switching under strong wind conditions is found. It is shown that even moderate fl ow rotation eliminates this effect.
Journal of Engineering Physics and Thermophysics, 2013
Cooling towers (CTs) are important units in the vast majority of power plants. They have been int... more Cooling towers (CTs) are important units in the vast majority of power plants. They have been intensively investigated for the last 70 years. The abundance of works makes diffi cult to "see" the total area of investigations of CTs and to fi nd the most urgent and important results. This article contains a compact overview of contemporary publications (for the last 11 years) in the area of heat and mass transfer in CTs, especially in natural draft wet cooling towers (NDWCT), and of related phenomena. Attention is specially paid to modern numerical computational investigations.
Journal of Engineering Physics and Thermophysics, 2013
The infl uence of fl ow rotation in the over-shower zone of a natural draft wet cooling tower (ND... more The infl uence of fl ow rotation in the over-shower zone of a natural draft wet cooling tower (NDCT) on heat and mass transfer in this zone is investigated numerically. The 3D geometry of an actual NDCT and three models of the induced rotation velocity fi elds are utilized for calculations. Two phases (liquid and gaseous) and three components are taken into consideration. The interphase heat exchange, heat transfer to the walls, condensation-evaporation intensity fi eld, and other parameters are investigated as functions of the induced rotation intensity (the inclination of the velocity vector at the periphery). It is shown that the induced fl ow rotation intensifi es the heat and mass transfer in the over-shower zone of an NDCT. Flow rotation leads to specifi c redistribution of evaporation-condensation areas in an NDCT and stimulates water condensation near its walls.
An approximate model of IR-radiation transfer in homogeneous NO-involving systems is presented wh... more An approximate model of IR-radiation transfer in homogeneous NO-involving systems is presented which takes into account the specific features of the actual vibration-rotation spectrum. Analytical expressions are obtained for the main quantities that characterize radiative heat transfer. The model suggested is illustrated by specific examples. This paper deals with the analysis of radiative heat transfer equations, investigation of the NO vibration-rotation spectrum structure and with the discussion of experimental data on the width of spectral lines. The authors consider the problem of the force of the spectral lines and bands of NO and analytical expressions are obtained for the equivalent width of these bands. The local power of radiation sources and of radiant energy flux incident on the volume boundary are calculated for reactors of simplest geometry.
The parallels between the turbulent and the filtration combustion of a gas in an inert medium hav... more The parallels between the turbulent and the filtration combustion of a gas in an inert medium have been considered. It is suggested that in the case where the thermal interaction between the gas and the porous medium is absent, elementary processes of mixing, chemical reaction, and others, which occur in turbulent and filtration combustion, can be characterized by similar dimensionless parameters setting up a correspondence between the integral scale of turbulence and the size of the pores. The dimensionless parameters have been analyzed and the diagram of the Borghi regimes of filtration combustion has been constructed. A number of typical cases of filtration combustion have been characterized using this diagram. It is shown that the considered cases of filtration combustion concern the range of distorted flames and distributed reaction zones according to the Borghi classification. From this it was assumed that the surface of filtration combustion in the first of the considered reg...
International Journal of Heat and Mass Transfer, 2006
The results of detailed 2D numerical simulation of non-steady methane-air flame propagation in se... more The results of detailed 2D numerical simulation of non-steady methane-air flame propagation in semi-closed tubes after ignition near the closed end are presented. Flame dynamics dependence on the tubes width for adiabatic and nonadiabatic walls is obtained. It is shown that main mechanism of front acceleration is flame surface perturbation due to hydrodynamic drag near the walls, which grows due to gas thermal expansion and flow acceleration. The mechanism of vortex formation in vicinity of the front bow point is demonstrated. The vortex is generated at the flame front velocities of the order of S l $ 20 m/s and may become precursor for flow turbulization at later instants. The new theoretically possible regime of gas combustion in adiabatic conditions in narrow capillary is found. It is characterized by relatively low propagation velocity and incomplete combustion.
International Journal of Heat and Mass Transfer, 2011
ABSTRACT A new technology of water purification of organic inclusions or solutes by using a filtr... more ABSTRACT A new technology of water purification of organic inclusions or solutes by using a filtration combustion reactor with alternating flow direction is investigated numerically. An acetone aqueous solution served as a model liquid. The lean combustibility limit (LCL) was determined for a wide range of flow rates, different values of the heat exchange coefficient, length of the reactor, and for different sizes of packed bed particles. It is demonstrated that thermal insulation has the strongest effect on the LCL. A minimum concentration of acetone in water that provides self-sustaining combustion may be as low as cmin=13.5% for the reactor length L=0.4m. The nonmonotonic behavior of the LCL dependence of the flow rate for short reactors and coarse particles has been demonstrated. The physical aspects of this feature was discussed.
International Journal of Heat and Mass Transfer, 2005
The new regenerator–recuperator scheme of filtration combustion VOC oxidizing reactor is under re... more The new regenerator–recuperator scheme of filtration combustion VOC oxidizing reactor is under research. Its main characteristics, such as maximum temperature of reactor, temperature of exhaust gases, NO emission and others are calculated and compared with the same characteristics of other types of reactors (co-flow filtration combustion wave reactor, counter-flow heat exchange recuperative reactor, reverse flow regenerative reactor). It is shown
Uploads
Papers by Kirill Dobrego