Technical Physics最新文献

The problem of positional control of the service gates in a shipping lock as a multidimensional control object with lumped parameters is considered. A general formulation of the problem is given, including requirements for the final and intermediate states. To solve the problem, it is proposed to use a production model of the regulator in the form of a system of rules. The numerical method for solving the problem is based on presenting the control algorithm in the form of an a priori non-fixed and time-varying system of rules determined during the control process. The presented results of numerical modeling confirm the effectiveness of the proposed method for determining the positional control of objects of this type.

Cooling of a modified surface by a dispersed flow of distilled water has been investigated experimentally, and the results have been compared with cooling of an unmodified surface. The modification of the heat-exchange surface of the copper working region has been performed by processing with a high-energy electron beam; as a result, a unique microporous surface has been obtained. The macrograph of the modified surface has been obtained and profiles have been measured using a profile meter. Four series of experiments for various heat carrier parameters have been performed for the modified and unmodified surfaces. The excess pressure of the heat carrier at the sprayer input was (4–14) × 10⁵ Pa, the mass flow rate of the heat carrier (distilled water) was (2.1–4.3) × 10^–3 kg/s, and the spraying density varied in the limits (3.0–6.1) kg/(m² s). The variations of the heat flux densities for these surfaces were compared. The convective component and the component of the phase transition of the removed heat flow during cooling the surface by a dispersed flow were estimated, and the conclusion was made concerning the key contribution of the phase transition to this process was made. The amount of evaporated liquid for the considered cooling modes were compared, and the dependence of this quantity on the heat flux density was obtained. The maximal heat flux density during the cooling of the surface by a dispersed flow attained 8.5 MW/m².

Several samples of nano-oil with different concentrations of dielectric and conductive nanoparticles are prepared to describe the electrophysical characteristics of nanofluids. Permittivity and conductivity of the nanofluids are experimentally measured. The processed experimental results are compared with the calculated results obtained using the Nielsen formula. The comparative analysis shows qualitative agreement of the calculated and experimental values of permittivity and a significant difference between the experimental and calculated dependences of conductivity on the concentration of particles. Such a difference between the calculated and experimental results is due to the adsorption of ions on the surface of the particles and their subsequent sedimentation. A decrease in the conductivity can be due to a decrease in the number of mobile particles and the fact that they have significantly less mobility compared to ions in the presence of weak electric fields. Additional measurements of the conductivity of nanofluids with particles of silicon dioxide and added oleic acid reproduce the observed decrease in the conductivity.

A new efficient implicit fully coupled numerical method for calculating thermochemical nonequilibrium flows is developed. Such flows are described by partial differential equations for conservation of mass, momentum, total energy, conservation of mass for each component, transfer of turbulent characteristics, etc. The total number of equations can be very large, which greatly complicates the solution of the general finite volume vector equation by using the standard fully implicit approach. The proposed method allows one to reduce operations with block tridiagonal matrices to inversion of 5 × 5 matrices and trivial operations of matrix multiplication. The numerical method is used to calculate the afterburning of the jet and for the supersonic combustion of hydrogen in the channel. The results show that for the considered problems, the new method is about two times more efficient than the standard fully implicit method.

Vibration measurement is among the most popular and cost-effective methods for diagnostics of the overall condition of equipment and is of undeniable importance in modern technology. Thanks to this process, manufacturers and consumers can be sure of the reliability and quality of technical systems, as well as prevent possible malfunctioning and failures. Vibration measurements in various fields confirm their versatility and importance in modern technical progress. The measurement of the effects of critical temperatures on a temperature sensor is aimed at determination of possible changes in the accuracy and reliability of the sensor. This will improve the quality of temperature measurement, eliminate inaccuracies and errors in operation of equipment, and increase the efficiency of the equipment under various operating conditions. The research method in this paper is a simulation model of the sensor, which is used to test for vibration and exposure to critical temperatures. Ansys and SolidWorks Simulation software are used to create the model to avoid costly and time-consuming test cycles. The results of the simulation modeling are used to construct diagrams of mechanical stress distribution under sinusoidal vibration and diagrams of temperature distribution under critical temperatures.

An experimental setup that consists of a vacuum chamber, vacuum pump, power source, pressure gage to measure the pressure in the chamber, ballast resistor, and gas delivery system has been constructed, and the process of SiC growth in an argon arc discharge has been studied. Appropriate process conditions have been selected, and experiments on SiC synthesis have been carried out in the vacuum chamber in an argon atmosphere at a pressure of 350−500 Torr. The grown material has been examined under optical and scanning electron microscopes. It has been reliably established that the presented approach provides the synthesis of SiC nano- and microparticles with a diamond-like structure.

The influence of a three-dimensional change in the parameters of flue gases on the distributions of temperatures and radiant heat fluxes in the radiant chamber of a tubular furnace is investigated. The external heat and mass transfer in the radiant chamber of the furnace is modeled by three-dimensional differential equations of energy, radiation transfer, motion, continuity, k–ε turbulence model, and two-step model of methane combustion. To solve the equation of radiation transfer, the method of discrete ordinates is used. Areas with the highest temperature gradients are identified.

On the basis of the theory of dimensions, the relationship between the periodicity of the Debye temperatures of metals and integral hemispherical fluxes of thermal radiation is revealed. The periodicity of the Debye temperatures of metals is established in accordance with the position in the Periodic System.

The paper presents an arc discharge model as applied to the synthesis problems of semiconductor nanostructures. The model is based on a completely nonequilibrium approximation and includes charged particle density balance equations, electron energy balance and energy balance equation for the heavy component of plasma, and Poisson’s equations for describing a self-consistent electric field. As a result of a numerical study of the system of equations describing an electric arc discharge, spatial distributions of the main characteristics of an arc discharge, such as the potential and intensity of the electric field, densities of electrons and ions, and gas temperatures were obtained.

The article presents the results of studies of the process of oil displacement with supercritical CO₂ fringes and water from a low-permeable heterogeneous oil reservoir with a water content of 8% at a pressure of 8 and 12 MPa. The results show that an increase in the CO₂ injection pressure does not lead to an increase in the oil displacement coefficient within the experimental error. The mechanism of the process of displacing oil from a low-permeable heterogeneous reservoir is considered. The results of the experiment are processed in the form of a generalizing dependence.