Papers by Vladimir Karasev
The burning of the single Al particles (vapor phase combustion mode) and Ti particles (heterogene... more The burning of the single Al particles (vapor phase combustion mode) and Ti particles (heterogeneous combustion mode) was studied in this paper. The size range of the studied particles was 100-300 micrometers. The main task of this work was to study the specific features and the rate of generation of nano-oxide smoke as a function of the current time during the combustion of a metal microparticle freely moving in the air. The dependence of the frequency of rotation vs the diameter for Al particles is obtained. The model of rotation of Al particles during the combustion is developed.
36th AIAA Aerospace Sciences Meeting and Exhibit, 1998
In spite of the long history of metalized propellants combustion studying there is little systema... more In spite of the long history of metalized propellants combustion studying there is little systematic data on the effectof propellant formulation on the generation of condensed combustion products. The objective of this work was to study the pressure dependence of the size distribution and neat metal content of sampled combustion products of aluminized propellants with different binders and oxidizers. The formulations with AP and HMX as oxidizers and with butadiene, isoprene and energetic binders were studied. The results obtained help to provide an understanding of the role various components play in determining aluminum agglomeration at the burning surface, and metal combustion far from the surface.
International Journal of Energetic Materials and Chemical Propulsion, 2002
Novel particle collection and high speed photography techniques have been used to study the combu... more Novel particle collection and high speed photography techniques have been used to study the combustion behavior of an inert binder (IB) propellant and an energetic binder (EB) propellant. Both contained 18% aluminum and 37% coarse AP in order to provide very similar geometrical structures, and both propellants had essentially common burning rates. The aluminum combustion efficiency is higher and the characteristic agglomerate size is significantly smaller for the EB propellant than for the IB propellant (at 43 atm the agglomerate size, D43, was 190 micrometers for the EB propellant and 670 micrometers for the IB propellant). At 7.5 atm the characteristic roughness of the burning surface is about 300 micrometers for the EB propellant and about 800 micrometers for the IB propellant. X-ray photography and visual observations of quenching particles show that similar sized agglomerates can differ significantly in structure and aluminum content, and there is some indication of internal vo...
A new approach based on use of special "super heterogeneous" propellants that generate during com... more A new approach based on use of special "super heterogeneous" propellants that generate during combustion the model agglomerates with given reproducible size and structure has been elaborated for study of model agglomerate evolution. The experiments with agglomerates of 395+540 um size and initial aluminum content 42.6 °/o were carried out in pressure range 1-80 atm. The following correlation for incompleteness of aluminum combustion 7 has been found: rj =2.86-f" 02, / r°M , where rj= mu I ntu ; n\u is the mass of unbumt aluminum in sampled agglomerate and m A " is the initial mass of aluminum in agglomerate; t is the residence time for agglomerate in flame of burning sample (20<r<90 ms); P-pressure (10<P<70 atm). It was also found that the mass fraction g> of oxide accumulated on the burning agglomerate increases with completeness of aluminum combustion £ = I-17 as <p = 0.539+0.213£, and agglomerate mass also increases with 4 due to oxide accumulation on the burning agglomerate. For calculation of burning agglomerate motion law and residence time for agglomerate in flame the drag coefficient Cj was taken in the form Cj-K/Re. Here Re is the Reynolds number. A' was determined in experiments on particle trajectory visualization and found to be equal K= 45±7 at 7<Re<9. The characteristics of condensed combustion products (CCP) were measured via sampling technique at pressure 46 atm (argon or nitrogen) for 12 metalized propellant formulations manufactured using well characterized ingredients. All compositions were based on energetic binder (20%). They included totally 18 % aluminum (commercial or ultra line particles in various proportion) and contained AP or AP and HMX as oxidizer. The replacement of commercial aluminum by electrically exploded aluminum (Alex) lead to increase of burning rate, decrease of agglomerate mass and increase of metal conversion completeness. All propellant formulation exhibited very effective aluminum conversion (total unbumt aluminum content in CCP did not exceed 9%). The listed trends are mostly expressed in combustion of HMX containing propellants and even small additive of Alex (Alex/Al = 8.3/91.7) gives sizable effect. For oxide particles in the size range 0.5-100 pjn the typical three-peak structure of mass size distribution was found. The replacement of aluminum by Alex and using argon instead of nitrogen affects slightly the CCP size distribution. Thermal decomposition of different types of the binders and mixtures modeling the pocket matter was investigated at low (10 K/min) and fast (> 450 K/min) heating rate. Data obtained are not sufficient to make clear the cause of difference in agglomeration behavior for propellant formulations based on these types of hinders 14.
Atmospheric and Oceanic Optics, 2012
We developed a method for studying heterogeneous nucleation in a laminar flow chamber, which allo... more We developed a method for studying heterogeneous nucleation in a laminar flow chamber, which allows one to determine the relationship between the main parameters of the process, i.e., the critical size of a seed particle, supersaturation, and the temperature. The workability of this method is demonstrated for the heterogeneous nucleation of sulfur vapor on nanoparticles of tungsten oxide.
Doklady. Biochemistry and biophysics
The Journal of Physical Chemistry A, 2000
ABSTRACT Two processes of the agglomeration of aerosol particles are investigated. The first proc... more ABSTRACT Two processes of the agglomeration of aerosol particles are investigated. The first process involves silicon aerosol formation by silane pyrolysis in a flow reactor. In the second process, soot aerosol is formed during propane combustion in a Bunsen burner. The agglomerate size and morphology are analyzed by a transmission electron microscope. An imaging system is used to observe agglomerate−agglomerate coagulation and agglomerate sticking to the deposit formed on the surface (tendrils). The movement of agglomerates in the electric field is also studied using the imaging system. It is found that Coulomb interactions are significant during the sticking process and, in particular, they are responsible for the fractal dimension, inferred in the experiments to be significantly lower with respect to the values obtainable from diffusion limited cluster−cluster aggregation simulations. However, the mechanism of this interaction is different for silicon and soot agglomeration processes. It is found that the silicon agglomerates are dipoles with net charges equal to zero. By contrast, approximately half of the soot agglomerate population is estimated to be charged with a net charge equal to one elementary unit (positive or negative). The major result is that the Coulomb interactions are observed to hold considerable influence during the process of agglomerate−agglomerate sticking, in particular, encouraging the agglomerate mutual sticking at the tips of the single agglomerates.
Colloid Journal, 2014
ABSTRACT A procedure has been developed for determining the contact angle of a critical nucleus f... more ABSTRACT A procedure has been developed for determining the contact angle of a critical nucleus formed on seed particles during the heterogeneous nucleation of a vapor in a flow chamber. The procedure comprises the determination of the fraction of enlarged particles, as well as the selective separation of nanoparticles over sizes to locate the zone of intense nucleation. The concentration and size distribution of aerosol particles have been measured with a diffusion spectrometer of aerosols. Vapor concentration distributions and supersaturation fields have been determined by solving the mass-transfer problem. The calculated supersaturation fields are in good agreement with the location of the intense nucleation zone experimentally found with the help of selective separation. The fractions of enlarged particles have been determined as functions of supersaturation in the chamber. A formula has been derived for calculating the fraction and size distribution function of enlarged particles at known supersaturation and temperature fields and a preset contact angle. The contact angles are selected in a manner such that the calculated fraction of enlarged particles coincides with that measured experimentally. It has been revealed that the contact angle of critical sulfur nuclei formed on tungsten oxide seed particles with average radii aOE (c) R (p)&gt; a parts per thousand 5.8-4.4 nm is in a range of 21.2-20.5A degrees, while, in the case of sodium chloride seed particles with aOE (c) R (p)&gt; a parts per thousand 6.0-4.4 nm, the contact angle is 20.4-17.4A degrees. The size of a critical nucleus has been found to be proportional to calculated average radius of a seed particle aOE (c) R (p)&gt; in both cases.
Combustion Explosion and Shock Waves
The paper describes a procedure for studying the macrokinetics of combustion of agglomerates in a... more The paper describes a procedure for studying the macrokinetics of combustion of agglomerates in a solid propellant flame using special samples of a model propellant generating monodisperse agglomerates. Empirical dependences of the incompleteness of aluminum combustion in the combustion products of a propellant based on ammonium perchlorate and HMX on time and pressure were established. The mass fraction of oxide accumulated on a burning agglomerate versus the degree of aluminum conversion was determined. For fine agglomerates (310–350 m), this fraction decreases with increase in the degree of conversion. For large agglomerates (400–540 mum), it increases, and, hence, the mass of large agglomerates increases as aluminum burns out. Because of accumulation of oxide, the agglomerate size does not change markedly in the examined range of parameters.
Formation of metal oxide nanoparticles was studied during combustion of Al / Ti droplets moving i... more Formation of metal oxide nanoparticles was studied during combustion of Al / Ti droplets moving in the air at the velocity of 10 -300 m/s. A high energetic mixture was used composed by oxidizer, binder and metal particles (of size being varied between 4 and 350 μm) to ignite and eject the particles to the air as liquid burning droplets. Metal oxide nanoparticles were analyzed by a Transmission Electron Microscope. Al 2 O 3 /TiO 2 fractal aggregates were formed by the combustion of metal droplets with the size of 0.1 -10 μm which consist of primary particles with the diameter of 5 -50 nm. It was observed that in the case of Al droplet combustion oxide nanoparticles are formed in the reaction zone detached from the droplet surface. Both the ratio r/R reac (between the droplet radius and the radius of the reaction zone) and the radius of primary particles in Al 2 O 3 aggregates are functions of the droplet radius r. In the case of titanium the combustion zone was attached to the drople...
Combustion Explosion and Shock Waves - COMBUST EXPL SHOCK WAVES-ENGL, 2001
The disperse, structural, and electrophysical characteristics of fine alumina produced by combust... more The disperse, structural, and electrophysical characteristics of fine alumina produced by combustion of metal droplet agglomerates were studied experimentally. Data were obtained by transmission electron microscopy and video recording of aerosol particles moving in a homogeneous electric field. The aerosol particles are aggregates with sizes ranging from a fraction of a micrometer to a few micrometers and a fractal dimension of 1.60± 0.04 which consist of primary particles with sizes of a few to hundred nanometers. Most of the aggregates have electric charges, both positive and negative. The characteristic charge of the aggregates is equal to a few units of elementary charge. Some large aggregates rotate when the electric field polarity changes, i.e., they are dipoles.
Colloid Journal, 2013
ABSTRACT Homogeneous nucleation of ibuprofen vapor is studied in a nucleation flow chamber, a hor... more ABSTRACT Homogeneous nucleation of ibuprofen vapor is studied in a nucleation flow chamber, a horizontal quartz tube equipped with an external heater. The area of the chamber where the nucleation proceeds most efficiently is determined, and the volume of this area is estimated. The temperature and supersaturation are determined and the homogeneous nucleation rate is calculated for this area. Saturation vapor pressure over liquid ibuprofen is measured in a temperature range of 353–383 K. Using an exact formula that has recently been derived for the nucleation rate based on the works by Kusaka, Reiss, as well as the Frenkel liquid-kinetics theory, surface tension and the radius of surface of tension of a critical nucleus σ= 25.9 mN/m and R s = 1.6 nm, respectively, are calculated at 318 K. The measurement of the surface tension of an ibuprofen planar surface shows that, at 318 K, σ∞ = 24.38 mN/m; i.e., σ is higher than σ∞ by 6%. A critical nucleus is established as containing nearly 36 ibuprofen molecules.
Colloid Journal, 2013
Homogeneous nucleation in sulfur vapor is studied in a laminar flow chamber. Concentration and si... more Homogeneous nucleation in sulfur vapor is studied in a laminar flow chamber. Concentration and size distribution of resulting aerosol particles are measured with a diffusion spectrometer of aerosols and a PK.GTA 0,3 002 photoelectric particle counter. The crystal structure of the formed particles is studied by X ray diffraction analysis. The rate of sulfur evaporation from a boat and the profile of a deposit on the cham ber wall along the axial coordinate are determined by gravimetry. Axial and radial temperature profiles are measured using a chromel-alumel thermocouple. The vapor concentration distribution in the chamber is found and the supersaturation is calculated from the solution of the mass transfer problem. An experimental low laborious method is developed for the supersaturation cutoff. This method enables one to rapidly deter mine the position of the zone in which the nucleation proceeds at the highest rate. The position of the zone of nucleation found by this method is in good agreement with the results of calculations based on experimen tal data and theoretical calculation of the rate of nucleation by an exact formula that has been recently derived based on the works by Kusaka and Reiss, as well as the Frenkel liquid kinetics theory. The surface tension of critical sulfur nuclei resulting from the nucleation is calculated based on this formula and experimental data on the nucleation. It is established that, in a temperature range of 312-319 K, the critical nuclei have tension surface radius R s ~ 10.6 Å and surface tension σ = 72.5 ± 1.1 dyn/cm. The surface tension of critical sulfur nuclei in this temperature range is constant and approximately 5% higher than that of a planar surface.
The Journal of Chemical Physics, 2006
The critical embryo surface tension and Tolman length as a function of radius has determined from... more The critical embryo surface tension and Tolman length as a function of radius has determined from the experimental homogeneous nucleation rate as measured by this paper authors (Zn), and other researches (Hg, Mg, water, n-pentanol, n-nonane). The thermodynamic description of small-scale systems exhibits peculiar features with respect to the macroscopic systems. The basis for thermodynamics of small particles has its origin in the Gibbs theory of capillarity. Instead of this real system, the theory describes an imaginary system composed of a small droplet of the homogeneous phase β and another homogeneous phase α separated by the so called surface of tension of radius R S. The surface tension σ is attributed to this surface. The difference δ between the equimolar radius R E and the radius R S is called Tolman length. It is well known now that the surface tension is a strong function of radius for small droplets. Therefore, to describe the thermodynamics of nanoscale systems one should know both σ(R S) and the location of the surface of tension (δ). Both σ(R S) and δ can be evaluated from the experimentally measured homogeneous nucleation rate. To this aim two main shortcomings of the classical nucleation theory must be solved, that is, instead of the surface tension for the flat surface σ ∞ it should consider σ(R S); besides, replacement free energy correction factor is to be taken into account properly. The long-term discussion on the "Translation-Rotation Paradox in the Theory of Nucleation" resulted to the Reiss, Kegel, and Katz [1] (RKK) correction factor. Recently Nishioka and Kusaka [2] and Debenedetti and Reiss [3] have extended the Gibbs treatment to noncritical nucleus. This formalism results in a new expression for the reversible work W of noncritical embryo formation the extrema conditions for which give the Gibbs formula
The Journal of Chemical Physics, 2012
Journal of Aerosol Science, 2007
Particle deposition in different regions of a critical orifice assembly was studied numerically a... more Particle deposition in different regions of a critical orifice assembly was studied numerically and experimentally. The investigated orifice is an O'Keefe E-9 (O'Keefe Control Co.) orifice whose diameter is 0.231 mm and critical flow rate is 0.455 slpm. The orifice assembly has an inlet tube (inner diameter=10.4 mm, length=90 mm) and outlet tube (inner diameter=6.2 mm, length=60 mm). In the numerical study, axisymmetric, laminar flow field of the orifice assembly was obtained first by solving the Navier-Stokes equations. The diffusion loss of nanoparticles was then calculated by solving the convection-diffusion equation. Inertial impaction and interception loss of 2-10 m particles was calculated by tracing particle trajectories in the flow field. In the experimental study, monodisperse NaCl (20-800 nm in aerodynamic diameter) and fluorescein-containing oleic acid (2-10 m in aerodynamic diameter) particles were used to test particle loss in both diffusion-and inertial impaction-dominated regimes. The numerical results were compared with the experimental data and good agreement was obtained with the maximum deviation smaller than 10.4%.
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Papers by Vladimir Karasev