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Papers by Leonid Dombrovsky
Fuel, 2003
Absorption spectra of several types of diesel fuel are studied experimentally. Index of refractio... more Absorption spectra of several types of diesel fuel are studied experimentally. Index of refraction of these fuels is calculated using subtractive Kramers–Krönig analysis. The ageing process of fuels is simulated by prolonged boiling. Radiative properties of diesel fuel droplets are calculated using the Mie theory and a simplified approach, based on approximations of absorption and scattering efficiency factors. It is
Volume 2: Biomedical and Biotechnology, 2012
Laser induced hyperthermia is a promising tool in a fight with human cancer especially with super... more Laser induced hyperthermia is a promising tool in a fight with human cancer especially with superficial deceases such as carcinoma or melanoma. A correct choice of the thermal treatment parameters should be based on modeling of both radiative transfer and transient heating of human tissues. An adequate computational model should allow prediction of the thermal conversions in the cells of the tissues. A computational analysis based on a general approach developed recently by the authors for indirect heating strategy showed that twodimensional effects of the radiative transfer are not so important for superficial tumors because of a very high extinction of the incident beam. This enabled us to develop a simplified transient model based on 1-D numerical solution for radiative transfer and 2-D axisymmetrical heat transfer model. tr tr J J G F 4
An identification procedure is developed for obtaining spectral radiative properties of highly sc... more An identification procedure is developed for obtaining spectral radiative properties of highly scattering dispersed materials such as porous ceramics. Traditional techniques based on measurements of the directional-hemispherical reflectance and transmittance are of limited use because of difficulties in fabricating sufficiently thin and mechanically stable samples to obtain reliable values of directional-hemispherical transmittance. However, one can use the directionalhemispherical reflectance measurements for optically thick samples to obtain the transport scattering albedo. A one-dimensional analytical solution employs the modified two-flux approximation for the identification of transport scattering albedo. An additional transmittance measurement is required to identify the transport extinction coefficient. Bi-normal narrow cone transmittance is measured for this purpose. Because the one-dimensional analytical solution is not applicable to model the bi-normal narrow cone transmittance, Monte Carlo ray-tracing technique is used to identify the transport extinction coefficient. The identification procedure is applied to obtain near-infrared radiative properties of porous ceria ceramics used in solar thermochemical reactors. The identified transport scattering coefficient is shown to be in good agreement with theoretical estimates based on the Mie theory for polydisperse pores and grains. This verifies the applicability of a model based on independent scattering and Mie theory for theoretical predictions of radiative properties of two types of ceria ceramics with porosity of 0.08 and 0.72, and for extrapolating the properties of both ceramics in a limited near-infrared range to the range of significant absorption.
International Journal of Heat and Mass Transfer, Aug 31, 2007
The visible and near-infrared radiative properties of water containing polydisperse steam bubbles... more The visible and near-infrared radiative properties of water containing polydisperse steam bubbles and core melt particles are analyzed. The alternative approximate models of radiation heat transfer in the range of water semi-transparency are considered. A new approach based on radiation balance equations for a large computational cell of size about several centimeters is suggested. This approach called large-cell model takes into account not only water heating but also radiation heat transfer between the particles of different temperatures. The latter is important for problems of fuel-coolant interaction in possible severe accident of light water nuclear reactors. The model problems considered in the paper give estimates of nonlocal effects of thermal radiation and confirm the applicability of the large-cell model at parameters typical for fuel-coolant interaction.
High Temp Engl Tr, Feb 28, 2002
An approximate description is given of the basic characteristics of absorption and scattering of ... more An approximate description is given of the basic characteristics of absorption and scattering of infrared radiation by polydisperse droplets of diesel fuel. It is demonstrated that the commonly used model of gray medium fails to give reliable values of radiation flux from the combustion products to fuel droplets. The use of the spectral band model made it possible to construct a valid efficient algorithm for the calculation of radiation heat transfer for the conditions of a diesel combustor.
Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via... more Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via short-pulsed laser irradiation. The transient effects become particularly important due to relatively strong scattering and long attenuation path of radiation in human tissues in the therapeutic window until the complete absorption. Our analysis is based on transport approximation for scattering phase function and the Monte Carlo method for radiative transfer. One-dimensional radiative transfer problem is considered, which was proved to be applicable for simulation of heat transfer and thermal destruction of tumors in superficial human tissues in the case of indirect heating strategy. A series of Monte Carlo calculations enables us to find the threshold of the steady-state approach applicability. In the biomedical problem under consideration, the steady-state solution for absorbed radiation power is sufficiently accurate at duration of laser pulse more than about 10 ps. The calculations for human tissues with embedded gold nanoshells, which are used to increase the local volumetric absorption of the radiation, showed that overheating of the nanoshells with respect to the ambient biological tissue is strongly dependent of the laser pulse duration. This effect is quantified for short pulses by solving the unsteady radiative transfer problem.
International Communications in Heat and Mass Transfer, Aug 1, 2003
Computational Thermal Sciences an International Journal, 2010
A combined two-step computational method incorporating (1) transport approximation of the scatter... more A combined two-step computational method incorporating (1) transport approximation of the scattering phase function, (2) P 1 approximation and the finite element method for computing the radiation source function at the first step, and the Monte Carlo method for computing radiative intensity at the second step is developed. The accuracy of the combined method is examined for model problems involving two multidimensional configurations of an anisotropically scattering medium. A detailed analysis is performed for a medium with scattering phase function described by a family of the Henyey-Greenstein functions. The accuracy of the two-step method is assessed by comparing the angular distribution of the radiative flux leaving the medium to that obtained by a reference-complete Monte Carlo method. This study confirms the main results of previous articles on the errors of the two-step solution method. The combined method leads to a significant reduction in computational time as compared to the reference method by at least 1 order of magnitude. Finally, possible applications of the combined method are briefly discussed.
International Journal of Heat and Mass Transfer, 2015
Transient heat transfer problems typical of recent-day cryosurgery are considered. Relatively sim... more Transient heat transfer problems typical of recent-day cryosurgery are considered. Relatively simple models are suggested to take into account different temperatures of freezing inside the biological cells and in the gaps between the cells. In the most complicated case of interpenetrating media, when there is a thermal contact between the cells and also between the gaps, the model one-dimensional problem is formulated and solved with a specific attention to the effects produced by repeated periods of freezing and thawing. It is shown that the latent heat of melting may lead to a significant difference between temperatures of the cells aggregates typical of tumors and the extracellular medium. It is important that the temperature inside the cell aggregate alternatively becomes less or greater than the ambient temperature. Such a temperature regime may lead to serious thermo-mechanical damage of the tumor cells not only due to ordinary thermal expansion during the freezing but also because of tensile stresses that arise at the surface of the frozen biological cells or their aggregates. Potential possibility of microwave monitoring of small local regions of thawing is analyzed on the basis of Mie theory calculations.
Teplofizika Vysokikh Temperatur
ABSTRACT
Teplofizika Vysokikh Temperatur
Teplofizika Vysokikh Temperatur
A two-step approximate analytical solution for the normal emittance of a plane layer of an absorb... more A two-step approximate analytical solution for the normal emittance of a plane layer of an absorbing, scattering and refracting medium is derived analytically. The analysis is based on the transport approximation and the two-step solution method for radiative transfer. The high accuracy of the approximate solution, examined by comparing its results to those obtained independently by the discrete ordinates and Monte Carlo methods, makes it suitable for application in combined experimental-analytical studies to identify selected spectral radiative properties of dispersed media in the range of semi-transparency.
Teplofizika Vysokikh Temperatur
ABSTRACT
Teplofizika Vysokikh Temperatur
ABSTRACT
Fuel, 2003
Absorption spectra of several types of diesel fuel are studied experimentally. Index of refractio... more Absorption spectra of several types of diesel fuel are studied experimentally. Index of refraction of these fuels is calculated using subtractive Kramers–Krönig analysis. The ageing process of fuels is simulated by prolonged boiling. Radiative properties of diesel fuel droplets are calculated using the Mie theory and a simplified approach, based on approximations of absorption and scattering efficiency factors. It is
Volume 2: Biomedical and Biotechnology, 2012
Laser induced hyperthermia is a promising tool in a fight with human cancer especially with super... more Laser induced hyperthermia is a promising tool in a fight with human cancer especially with superficial deceases such as carcinoma or melanoma. A correct choice of the thermal treatment parameters should be based on modeling of both radiative transfer and transient heating of human tissues. An adequate computational model should allow prediction of the thermal conversions in the cells of the tissues. A computational analysis based on a general approach developed recently by the authors for indirect heating strategy showed that twodimensional effects of the radiative transfer are not so important for superficial tumors because of a very high extinction of the incident beam. This enabled us to develop a simplified transient model based on 1-D numerical solution for radiative transfer and 2-D axisymmetrical heat transfer model. tr tr J J G F 4
An identification procedure is developed for obtaining spectral radiative properties of highly sc... more An identification procedure is developed for obtaining spectral radiative properties of highly scattering dispersed materials such as porous ceramics. Traditional techniques based on measurements of the directional-hemispherical reflectance and transmittance are of limited use because of difficulties in fabricating sufficiently thin and mechanically stable samples to obtain reliable values of directional-hemispherical transmittance. However, one can use the directionalhemispherical reflectance measurements for optically thick samples to obtain the transport scattering albedo. A one-dimensional analytical solution employs the modified two-flux approximation for the identification of transport scattering albedo. An additional transmittance measurement is required to identify the transport extinction coefficient. Bi-normal narrow cone transmittance is measured for this purpose. Because the one-dimensional analytical solution is not applicable to model the bi-normal narrow cone transmittance, Monte Carlo ray-tracing technique is used to identify the transport extinction coefficient. The identification procedure is applied to obtain near-infrared radiative properties of porous ceria ceramics used in solar thermochemical reactors. The identified transport scattering coefficient is shown to be in good agreement with theoretical estimates based on the Mie theory for polydisperse pores and grains. This verifies the applicability of a model based on independent scattering and Mie theory for theoretical predictions of radiative properties of two types of ceria ceramics with porosity of 0.08 and 0.72, and for extrapolating the properties of both ceramics in a limited near-infrared range to the range of significant absorption.
International Journal of Heat and Mass Transfer, Aug 31, 2007
The visible and near-infrared radiative properties of water containing polydisperse steam bubbles... more The visible and near-infrared radiative properties of water containing polydisperse steam bubbles and core melt particles are analyzed. The alternative approximate models of radiation heat transfer in the range of water semi-transparency are considered. A new approach based on radiation balance equations for a large computational cell of size about several centimeters is suggested. This approach called large-cell model takes into account not only water heating but also radiation heat transfer between the particles of different temperatures. The latter is important for problems of fuel-coolant interaction in possible severe accident of light water nuclear reactors. The model problems considered in the paper give estimates of nonlocal effects of thermal radiation and confirm the applicability of the large-cell model at parameters typical for fuel-coolant interaction.
High Temp Engl Tr, Feb 28, 2002
An approximate description is given of the basic characteristics of absorption and scattering of ... more An approximate description is given of the basic characteristics of absorption and scattering of infrared radiation by polydisperse droplets of diesel fuel. It is demonstrated that the commonly used model of gray medium fails to give reliable values of radiation flux from the combustion products to fuel droplets. The use of the spectral band model made it possible to construct a valid efficient algorithm for the calculation of radiation heat transfer for the conditions of a diesel combustor.
Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via... more Transient radiative transfer effects are pertinent to thermal treatment of superficial cancer via short-pulsed laser irradiation. The transient effects become particularly important due to relatively strong scattering and long attenuation path of radiation in human tissues in the therapeutic window until the complete absorption. Our analysis is based on transport approximation for scattering phase function and the Monte Carlo method for radiative transfer. One-dimensional radiative transfer problem is considered, which was proved to be applicable for simulation of heat transfer and thermal destruction of tumors in superficial human tissues in the case of indirect heating strategy. A series of Monte Carlo calculations enables us to find the threshold of the steady-state approach applicability. In the biomedical problem under consideration, the steady-state solution for absorbed radiation power is sufficiently accurate at duration of laser pulse more than about 10 ps. The calculations for human tissues with embedded gold nanoshells, which are used to increase the local volumetric absorption of the radiation, showed that overheating of the nanoshells with respect to the ambient biological tissue is strongly dependent of the laser pulse duration. This effect is quantified for short pulses by solving the unsteady radiative transfer problem.
International Communications in Heat and Mass Transfer, Aug 1, 2003
Computational Thermal Sciences an International Journal, 2010
A combined two-step computational method incorporating (1) transport approximation of the scatter... more A combined two-step computational method incorporating (1) transport approximation of the scattering phase function, (2) P 1 approximation and the finite element method for computing the radiation source function at the first step, and the Monte Carlo method for computing radiative intensity at the second step is developed. The accuracy of the combined method is examined for model problems involving two multidimensional configurations of an anisotropically scattering medium. A detailed analysis is performed for a medium with scattering phase function described by a family of the Henyey-Greenstein functions. The accuracy of the two-step method is assessed by comparing the angular distribution of the radiative flux leaving the medium to that obtained by a reference-complete Monte Carlo method. This study confirms the main results of previous articles on the errors of the two-step solution method. The combined method leads to a significant reduction in computational time as compared to the reference method by at least 1 order of magnitude. Finally, possible applications of the combined method are briefly discussed.
International Journal of Heat and Mass Transfer, 2015
Transient heat transfer problems typical of recent-day cryosurgery are considered. Relatively sim... more Transient heat transfer problems typical of recent-day cryosurgery are considered. Relatively simple models are suggested to take into account different temperatures of freezing inside the biological cells and in the gaps between the cells. In the most complicated case of interpenetrating media, when there is a thermal contact between the cells and also between the gaps, the model one-dimensional problem is formulated and solved with a specific attention to the effects produced by repeated periods of freezing and thawing. It is shown that the latent heat of melting may lead to a significant difference between temperatures of the cells aggregates typical of tumors and the extracellular medium. It is important that the temperature inside the cell aggregate alternatively becomes less or greater than the ambient temperature. Such a temperature regime may lead to serious thermo-mechanical damage of the tumor cells not only due to ordinary thermal expansion during the freezing but also because of tensile stresses that arise at the surface of the frozen biological cells or their aggregates. Potential possibility of microwave monitoring of small local regions of thawing is analyzed on the basis of Mie theory calculations.
Teplofizika Vysokikh Temperatur
ABSTRACT
Teplofizika Vysokikh Temperatur
Teplofizika Vysokikh Temperatur
A two-step approximate analytical solution for the normal emittance of a plane layer of an absorb... more A two-step approximate analytical solution for the normal emittance of a plane layer of an absorbing, scattering and refracting medium is derived analytically. The analysis is based on the transport approximation and the two-step solution method for radiative transfer. The high accuracy of the approximate solution, examined by comparing its results to those obtained independently by the discrete ordinates and Monte Carlo methods, makes it suitable for application in combined experimental-analytical studies to identify selected spectral radiative properties of dispersed media in the range of semi-transparency.
Teplofizika Vysokikh Temperatur
ABSTRACT
Teplofizika Vysokikh Temperatur
ABSTRACT