We analyze the evaporation of a multisize (polydisperse) liquid fuel spray in a shear-layer betwe... more We analyze the evaporation of a multisize (polydisperse) liquid fuel spray in a shear-layer between two parallel unidirectional streams of unequal velocity. The analysis is also applicable for a shear-layer between two radially spreading streams which share the same axis of symmetry. Similarity solutions are presented for the evolution in droplet size distributions across the shear-layer, and the effects of
A shear layer formed by two unidirectional gas streams of different velocities with a multisize (... more A shear layer formed by two unidirectional gas streams of different velocities with a multisize (polydisperse) spray of evaporating droplets suspended in one of the gas streams is considered here. Similarity solutions are presented for the evolution in droplet size distributions across the shear layer and the effects of various initial droplet size distributions on the profiles of vapor concentrations
Tiny smoke particles that are typically emitted today from a variety of vehicles are of major pub... more Tiny smoke particles that are typically emitted today from a variety of vehicles are of major public concern, as they are known to cause major health and environmental problems. It is well recognized that those tiny particles are directly linked with lung cancer, and have harmful effect on the environment. As they are smaller than other types of particles (sub-micron
A new similarity solution for spray distribution in a boundary layer flow, involving an imaginary... more A new similarity solution for spray distribution in a boundary layer flow, involving an imaginary-valued variable, is presented. The flow field similarity solution has three branches, the two known solutions for accelerating flow and moderately decelerating flow ...
ABSTRACT The current work presents a mathematical analysis of aerosol particle/droplet dynamics i... more ABSTRACT The current work presents a mathematical analysis of aerosol particle/droplet dynamics in periodically changing droplet-laden flows with nonzero mean velocity. The parameters for the model are taken from experimental studies reported in the literature and include the mean flow velocity and the amplitude and frequency of oscillations. On this basis, the governing equation of droplet motion is derived and solved. The solution indicates the existence of two regimes of droplet clustering. In the first regime, each droplet moves within a fixed cluster, In the other regime, the droplets can move from one cluster to another. A mathematical study helps to reveal the separate effects of various operating parameters on the droplet behavior. The two regimes are also identified in terms of a dimensionless parameter that is comprised of the carrier fluid flow characteristics and the droplet size. The performed analysis can provide an insight into the phenomena of droplet clustering, and can be useful in analyses of droplet behavior in various aerosol flows.
A new mathematical analysis of a laminar Burke-Schumann type of spray diffusion flame in an oscil... more A new mathematical analysis of a laminar Burke-Schumann type of spray diffusion flame in an oscillating flow field is presented within a framework in which mild slip is permitted between the droplets and their host surroundings. A perturbation analysis using a small Stokes number is used for solving the liquid phase governing equations. The effect of droplet grouping in the
ABSTRACT Two unidirectional streams of different velocities are considered here. One of the strea... more ABSTRACT Two unidirectional streams of different velocities are considered here. One of the streams carries a multisize (polydisperse) spray of fuel droplets, and the other stream carries a multisize spray of droplets of a liquid oxidizer. In both streams, droplets of different sizes are assumed to travel at different longitudinal velocities, that is, drop-size-correlated velocities are assumed here. The lateral spread of the fuel vapor and the vapors produced by the droplets of the liquid, oxidizer are analyzed and their effect on the spray diffusion flame is examined. The present results indicate that not only does the fuel drop-size distribution have a profound effect on flame location and flame temperature, but the liquid oxidizer's drop-size distribution also plays an important role in determining flame properties. Specifically when the droplet distribution of the liquid oxidizer is polydisperse, a higher flame temperature can be obtained if larger amounts of smaller droplets are present in the drop-size histogram.
Two radially spreading adjacent streams, which differ in their radial velocities and thus form a ... more Two radially spreading adjacent streams, which differ in their radial velocities and thus form a radially spreading shear-layer flow, are considered here. The theory presented by the authors for sprays suspended in unidirectional [Katoshevski and Tambour, Phys. Fluids A 5, 3085 (1993)] shear layers is extended here for radiallyspreading shear layer flows. The behavior of a multisize (polydisperse) evaporating spray,
ABSTRACT Novel experimental results on the hydrodynamic forces acting on a small heated particle ... more ABSTRACT Novel experimental results on the hydrodynamic forces acting on a small heated particle at low Reynolds and Grashof numbers are presented. The temperature difference between the particle and the ambient causes free convection flow around the particle. As a result, the drag force exerted on the particle by forced flow deviates significantly from the Stokes law. This deviation is represented quantitatively for three basic directions of forced flow, namely assisting, opposing, and crossing with respect to free convection flow. Validity of the Stokes formula at mixed-convection creeping flow conditions is discussed.
A novel technique for determination of the temperature of spherical micrometre-sized particles fr... more A novel technique for determination of the temperature of spherical micrometre-sized particles from forced/free convection and photophoretic forces has been developed. The three forces were measured for suspended charged particles in an electrodynamic chamber. The forces were applied to the particle in three-dimensions, normally to each other, and measured directly in terms of the three-dimensional electric field required to maintain
ABSTRACT In rocket engines propelled by liquid fuels and liquid oxidizers, one may find regions w... more ABSTRACT In rocket engines propelled by liquid fuels and liquid oxidizers, one may find regions where two adjacent spray streams, one that carries fuel droplets and the other that carries the droplets of the liquid oxidizer, travel at different velocities and form a shear flow. A theoretical study of such unidirectional multisize (polydisperse) evaporating spray streams is presented. In each of the streams droplets of different sizes are assumed to travel at different longitudinal velocities, that is, drop-size correlated velocities are assumed for both the liquid fuel and the liquid oxidizer, The lateral evolution in drop-size distributions across the shear layer is analyzed, and its effect on the lateral spread of the fuel vapor and the vapors produced by the droplets of the liquid oxidizer is examined, It is shown that the polydisperse drop-size distributions of the liquid fuel as well as that of the liquid oxidizer control the vapor production rates and determine the shape of the vapor concentration profiles across the shear layer.
The present paper analyzes the coupling between particle temperature and drag force. The force wa... more The present paper analyzes the coupling between particle temperature and drag force. The force was measured for heated and unheated particles of about a hundred micrometers in diameter suspended in an electrodynamic chamber. Particle temperature was up to several hundred degrees above room temperature. Horizontal flow velocities were in the range of 0–0.1ms−1, providing very low particle Reynolds numbers. It was found that due to free convection, the drag force acting on a heated particle can be several times greater than the corresponding force for a non-heated one. This effect is especially significant at low flow velocities and is suppressed as the velocity increases. The influence of particle diameter, temperature difference and flow velocity is investigated, clarifying the contribution of each parameter. The drag force applied to a heated particle is found to behave according to a Stokes-like expression, modified in order to take into account the effect of free convection.
We analyze the evaporation of a multisize (polydisperse) liquid fuel spray in a shear-layer betwe... more We analyze the evaporation of a multisize (polydisperse) liquid fuel spray in a shear-layer between two parallel unidirectional streams of unequal velocity. The analysis is also applicable for a shear-layer between two radially spreading streams which share the same axis of symmetry. Similarity solutions are presented for the evolution in droplet size distributions across the shear-layer, and the effects of
A shear layer formed by two unidirectional gas streams of different velocities with a multisize (... more A shear layer formed by two unidirectional gas streams of different velocities with a multisize (polydisperse) spray of evaporating droplets suspended in one of the gas streams is considered here. Similarity solutions are presented for the evolution in droplet size distributions across the shear layer and the effects of various initial droplet size distributions on the profiles of vapor concentrations
Tiny smoke particles that are typically emitted today from a variety of vehicles are of major pub... more Tiny smoke particles that are typically emitted today from a variety of vehicles are of major public concern, as they are known to cause major health and environmental problems. It is well recognized that those tiny particles are directly linked with lung cancer, and have harmful effect on the environment. As they are smaller than other types of particles (sub-micron
A new similarity solution for spray distribution in a boundary layer flow, involving an imaginary... more A new similarity solution for spray distribution in a boundary layer flow, involving an imaginary-valued variable, is presented. The flow field similarity solution has three branches, the two known solutions for accelerating flow and moderately decelerating flow ...
ABSTRACT The current work presents a mathematical analysis of aerosol particle/droplet dynamics i... more ABSTRACT The current work presents a mathematical analysis of aerosol particle/droplet dynamics in periodically changing droplet-laden flows with nonzero mean velocity. The parameters for the model are taken from experimental studies reported in the literature and include the mean flow velocity and the amplitude and frequency of oscillations. On this basis, the governing equation of droplet motion is derived and solved. The solution indicates the existence of two regimes of droplet clustering. In the first regime, each droplet moves within a fixed cluster, In the other regime, the droplets can move from one cluster to another. A mathematical study helps to reveal the separate effects of various operating parameters on the droplet behavior. The two regimes are also identified in terms of a dimensionless parameter that is comprised of the carrier fluid flow characteristics and the droplet size. The performed analysis can provide an insight into the phenomena of droplet clustering, and can be useful in analyses of droplet behavior in various aerosol flows.
A new mathematical analysis of a laminar Burke-Schumann type of spray diffusion flame in an oscil... more A new mathematical analysis of a laminar Burke-Schumann type of spray diffusion flame in an oscillating flow field is presented within a framework in which mild slip is permitted between the droplets and their host surroundings. A perturbation analysis using a small Stokes number is used for solving the liquid phase governing equations. The effect of droplet grouping in the
ABSTRACT Two unidirectional streams of different velocities are considered here. One of the strea... more ABSTRACT Two unidirectional streams of different velocities are considered here. One of the streams carries a multisize (polydisperse) spray of fuel droplets, and the other stream carries a multisize spray of droplets of a liquid oxidizer. In both streams, droplets of different sizes are assumed to travel at different longitudinal velocities, that is, drop-size-correlated velocities are assumed here. The lateral spread of the fuel vapor and the vapors produced by the droplets of the liquid, oxidizer are analyzed and their effect on the spray diffusion flame is examined. The present results indicate that not only does the fuel drop-size distribution have a profound effect on flame location and flame temperature, but the liquid oxidizer's drop-size distribution also plays an important role in determining flame properties. Specifically when the droplet distribution of the liquid oxidizer is polydisperse, a higher flame temperature can be obtained if larger amounts of smaller droplets are present in the drop-size histogram.
Two radially spreading adjacent streams, which differ in their radial velocities and thus form a ... more Two radially spreading adjacent streams, which differ in their radial velocities and thus form a radially spreading shear-layer flow, are considered here. The theory presented by the authors for sprays suspended in unidirectional [Katoshevski and Tambour, Phys. Fluids A 5, 3085 (1993)] shear layers is extended here for radiallyspreading shear layer flows. The behavior of a multisize (polydisperse) evaporating spray,
ABSTRACT Novel experimental results on the hydrodynamic forces acting on a small heated particle ... more ABSTRACT Novel experimental results on the hydrodynamic forces acting on a small heated particle at low Reynolds and Grashof numbers are presented. The temperature difference between the particle and the ambient causes free convection flow around the particle. As a result, the drag force exerted on the particle by forced flow deviates significantly from the Stokes law. This deviation is represented quantitatively for three basic directions of forced flow, namely assisting, opposing, and crossing with respect to free convection flow. Validity of the Stokes formula at mixed-convection creeping flow conditions is discussed.
A novel technique for determination of the temperature of spherical micrometre-sized particles fr... more A novel technique for determination of the temperature of spherical micrometre-sized particles from forced/free convection and photophoretic forces has been developed. The three forces were measured for suspended charged particles in an electrodynamic chamber. The forces were applied to the particle in three-dimensions, normally to each other, and measured directly in terms of the three-dimensional electric field required to maintain
ABSTRACT In rocket engines propelled by liquid fuels and liquid oxidizers, one may find regions w... more ABSTRACT In rocket engines propelled by liquid fuels and liquid oxidizers, one may find regions where two adjacent spray streams, one that carries fuel droplets and the other that carries the droplets of the liquid oxidizer, travel at different velocities and form a shear flow. A theoretical study of such unidirectional multisize (polydisperse) evaporating spray streams is presented. In each of the streams droplets of different sizes are assumed to travel at different longitudinal velocities, that is, drop-size correlated velocities are assumed for both the liquid fuel and the liquid oxidizer, The lateral evolution in drop-size distributions across the shear layer is analyzed, and its effect on the lateral spread of the fuel vapor and the vapors produced by the droplets of the liquid oxidizer is examined, It is shown that the polydisperse drop-size distributions of the liquid fuel as well as that of the liquid oxidizer control the vapor production rates and determine the shape of the vapor concentration profiles across the shear layer.
The present paper analyzes the coupling between particle temperature and drag force. The force wa... more The present paper analyzes the coupling between particle temperature and drag force. The force was measured for heated and unheated particles of about a hundred micrometers in diameter suspended in an electrodynamic chamber. Particle temperature was up to several hundred degrees above room temperature. Horizontal flow velocities were in the range of 0–0.1ms−1, providing very low particle Reynolds numbers. It was found that due to free convection, the drag force acting on a heated particle can be several times greater than the corresponding force for a non-heated one. This effect is especially significant at low flow velocities and is suppressed as the velocity increases. The influence of particle diameter, temperature difference and flow velocity is investigated, clarifying the contribution of each parameter. The drag force applied to a heated particle is found to behave according to a Stokes-like expression, modified in order to take into account the effect of free convection.
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Papers by David Katoshevski