Features of photon diffusion in a dispersed medium

Energy transfer by thermal radiation in a dispersed medium with a variable refractive index is discussed. This transfer can be described by a surprisingly simple diffusion equation. The process is naturally to interpret as the photon diffusion. The diffusion equation is free from strict conditions of applicability of the radiation transfer equation, which are usually not satisfied in disperse media with densely packed inhomogeneities. Quantum constraints on the value of the photon diffusion coefficient are derived. These restrictions turn out to be similar to the conditions for the applicability of geometric optics. The lower limit of the thermal conductivity coefficient is obtained, which is easier to verify in the experiment. An independent derivation of this limitation is given from considerations of symmetry and dimension.

Mathematical modeling of dispersed media flows in the presence of nucleation, coagulation and phase transitions

A model of motion of a gas-dispersed medium in the presence of processes of nucleation, coagulation and phase transitions has been constructed. A homogeneous nucleation model is used to describe the nucleation process. It is believed that the process of cluster coagulation occurs due to their Brownian motion. The analysis of the solution of the coagulation equation in the particular case of monodisperse clusters in the presence of a source and sink of particles is carried out. To determine the rate of phase transitions the Hertz-KnudsenLangmuir formula is used. The calculations were carried out on the basis of a quasi-one-dimensional model within the equilibrium approximation (when the velocities and temperatures of the phases coincide). As a result of the study the main properties of the flow of a two-phase mixture in a channel in the presence of nucleation, coagulation, and phase transformations have been established. It is shown that the vapor temperature increases along the channel and reaches the saturation temperature at some distance from the channel entrance. Calculations have shown that the coagulation process has a rather strong effect on the distribution of cluster sizes along the channel.

MATHEMATICAL MODEL OF THE DYNAMICS DISPERSED MEDIA IN THE SHAPING PROCESSES BILLETS OF POWDER METALLURGY

A mathematical model has been developed for changing the dynamics of the movement of a dispersed medium in vibro-impact technological processes of shaping of powder metallurgy blanks. On the basis of the problem of two-dimensional dynamic interaction of dispersed particles of powder metal of a spacer dispersed medium, the obtained differential equation in partial derivatives under various boundary conditions. This equation describes the state of the local area of the dispersed medium. In it, the powder material of the workpiece passes from the concentrated dynamic force to the excitation phase. A partial differential equation is obtained. It describes the change in normal stress during vibrations of a dispersed medium during vibration compaction of a workpiece in powder metallurgy.

Study of thermal resistance of cold mixtures with clay addition

The article analyzes the results of heat resistance of cold-harmful mixtures with the addition of clay. The article presents the results of an experimental laboratory study of the properties of samples from CTS, obtained by various methods. The scientific novelty of the technology lies in the fact that the technology of casting in cold-rolled steel ensures high quality of the casting surface, the absence of gas defects and blockages in the casting. The selection of the composition and technological parameters for the manufacture of the mold, contributing to the production of high-quality defect-free castings, will significantly reduce their cost, which will have a positive effect on the economy of our country. The study of the change in density over time depending on the applied load was studied in a series of experiments. The density of the mixture was determined every thirty seconds during the entire time of the formation of the dispersed medium. These experiments showed that at the beginning of the formation of the shell, its density increases significantly. In works on the thermal stability of polymers, the general laws of thermal decomposition and carbonization of cyclic, spatially crosslinked hot curing polymers were investigated and it was shown that the kinetics of destruction, the composition of gaseous products, the amount of coke formed and its properties depend on the properties of the initial polymers - the degree of crosslinking of molecular chains, chemical structure, the presence of impurities of catalysts and other curing conditions, as well as the heating conditions - speed and temperature. The article summarizes some of the results of the study, which is most appropriate for thin-walled steel castings to use the following mixture composition: filler - quartz sand; binder - clay of the Kazakhstani deposit, epoxy resin, hardener.

Induced by acoustic fieldsprocesses of structure formation in high-molecular media

The paper considers the mechanisms of destruction and synthesis of macromolecules, which can be stimulated by external acoustic fields in a two-phase, oil dispersed medium containing a large number of gas bubbles. It is assumed that the dynamics of these bub-bles depends on changes in the geometry of the flow and the excitation of sound vibra-tions in the flow. Particular attention is paid to the process of changing the density of a liquid due to the effect of an internal airlift in a liquid dispersed medium. Mechanically induced kinetic changes in macromolecules (destruction and synthesis of colloidal chains) can occur when bubbles collapse. These features can be used in oil processing and well logging to assess oil saturation of reservoirs.

Modeling of the radiation induced electromagnetic field in finely-disperse media

Algorithms for supercomputer modeling of the radiation electromagnetic field in heterogeneous materials of a complex finely-dispersed structure are constructed. A geometric model of a heterogeneous medium is created using Stilinger-Lubachevsky algorithms for multimodal structures. The model includes a system of detectors for statistical evaluation of functionals on the space of solutions of the photon-electron cascade transport equations. Algorithms for the three-dimensional approximation of the results of modeling the radiation transport in a fine-dispersed medium to an electrodynamic difference grid are developed. The approximation methods based on the technology of neural networks. The method of numerical solution of the complete system of Maxwell's equations for calculating the electromagnetic field in a fine-dispersed medium is worked out. The results of demonstration calculations of the electromagnetic field are presented. The results of the calculations show that the spatial distribution of the radiation electromagnetic field has a sharply inhomogeneous structure caused by the presence of boundaries of materials with different radiation properties.

Comparison of the Results of Modeling a Dispersed Medium by Wave and Ray Methods

A large number of works on dispersed medium modeling use either pure ray optics or light transport equation in which propagation of light obeys geometric optics while scattering properties of the medium can be either calculated with wave optics or measured. In either case the distance between individual particles must be much greater than wavelength. At the same time current computer power allows to simulate paint layer with wave optics. We decided to compare paint simulation done by the scalar wave approach and by ray tracing with individual particles. One of the goals of this work is to verify the correctness of ray tracing results for various sizes of metal flakes used often in production of metallic or pearlescent paints. Ray tracing had been done in two variants. One assumes the flakes have perfectly mirror reflection, while in the other variant the reflection is slightly diffuse with the angular distribution taken from the Fraunhofer diffraction on thin disk. For not too large flakes results of these two approaches substantially differ. The second “hybrid” method is considerably closer to the wave optics results.

ELECTROPHORESIS IN THE TOTAL (CONSTANT AND ALTERNATING) ELECTRIC FIELD. II. PECULIARITIES OF THE COMBINED IMPACT OF ALTERNATING AND CONSTANT ELECTRIC FIELDS

The hydrodynamics of electrophoresis under the simultaneous impact of constant and alternating electric fields is considered. It has been shown that when the constant and alternating external fields are combined, the energy of the constant electric field is transferred into the alternating hydrodynamic field. An example is given of a dispersed medium in which a giant dispersion of the dielectric constant can arise, which in turn can contribute to an increase in the total electrophoresis rate. Analogies of the behavior of the considered dispersed medium with the action of an electroacoustic transducer based on the use of electrokinetic phenomena are given.