Dynamics Of Transient Processes Research Articles

The effect of porous coatings obtained by various methods on heat transfer and crisis phenomena during nitrogen boiling including non-stationary heating and cooling

The paper presents the main results of experimental investigation of the influence of porous coatings obtained by various methods on heat transfer and crisis phenomena during nitrogen boiling, including unsteady heating and cooling regimes. Modification of heater surfaces was carried out by the methods of directed plasma spraying, additive 3D printing and micro-arc oxidation. For all types of porous coatings, a significant intensification of heat transfer at atmospheric pressure relative to smooth heaters was obtained (maximum degree of heat transfer increase up to 6 times). The mechanisms playing a determining role in the process of heat transfer coefficients increase are suggested. The essential influence of structured capillary-porous bronze coatings on the dynamics of transient processes and development of crisis phenomena of non-stationary processes is shown, leading to degeneration of the heat transfer crisis at pulse supply of heat load and significantly reducing the time of complete cooling of the heater in the process of rewetting.

Research on the dynamics of transitional regimes in an inertial screen with two motor vibrators

Purpose. Analysis of mathematical models of vibrating screens, using the theory of oscillations and mathematical modeling to study the impact of initial start-up parameters and the dynamics of transient processes on the operation of the screen. Methodology. This research is dedicated to the analysis of mathematical models that describe the startup process and subsequent operation of a vibratory screen. Methods of oscillation theory, system dynamics, and mathematical modeling are applied to analyze the vibratory processes of screens. Special attention is given to studying the impact of initial startup parameters on the operation of the screen, including amplitude, frequency, and phase of oscillations. Within the framework of this work, detailed graphs are constructed that reflect the displacement of different points of the structure, as well as the trajectories of their movement during operation, using the Mathcad software. Results. Transitional modes of startup and steady operation are analyzed, with motion dynamics equations for both phases detailed. Displacement graphs for key screen points over time and changes in screen movement across operational modes are highlighted. Scientific novelty. The study defines a mathematical model for the motion of a screen with two motor-vibrators during startup and steady operation. It introduces a graph showing the screen points' displacement over time, from startup to steady mode, and illustrates the trajectories of these points under various operational modes. This research advances material classification techniques, enhancing process optimization and equipment efficiency. Practical significance. This research enhances vibratory material sorting by analyzing screen dynamics across operating modes, leading to optimized workflows, lower energy use, and improved sorting efficiency. It also bolsters equipment reliability and reduces the risk of failures, cutting down on maintenance and repair expenses.

DYNAMICS OF SPRINGY SYSTEMS OF PACKAGING LINES FOR FOOD PRODUCTS

The purpose of the study was to develop mathematical models and proposals for improving the technology and equipment for the supply of roll packaging materials. The analysis of features of systems for transportation of packing materials, dynamics of transient processes, research methods concerning movements of rolled materials, features of loadings in systems of cyclic action with springy elements are resulted in the article. It is shown that the modern theoretical basis of synthesis of technological machines on the basis of use of film rolled materials combines possibilities of the account of technological requirements, indicators of high productivity, neighborhood conditions, restriction of power parameters. Mathematical formalizations concerning the ratios of force factors in systems of transportation of loads of cyclic action at the levels of external force actions, generated friction forces, geometrical, kinematic and dynamic parameters were obtained. Mathematical models concerning runaway modes and estimation of stiffness of springy bonds, on the basis of film materials, methods of estimation of system parameters were offered. Synchronized combination of operations, the use of optimal laws of movement of working bodies, limitation of dynamic loads was carried to the positive directions of creating efficient technological machines and lines. It is proposed to determine the ratio of the run-out time of rolls of variable mass by the ratio of the squares of the initial and final radii. The solution of the problem of kinetic energy recovery in systems of periodic action is simultaneously connected with the restriction of the non-uniformity of the drive of machines.

Heat transfer and dynamics of transient processes at liquid film flowing on smooth and modified surfaces

The paper presents the results of an experimental study on propagation dynamics and structure of the wetting front under adiabatic conditions and on a preheated surfaces with a needle-like microstructure, as well as heat transfer and critical heat fluxes at a film flow of liquid nitrogen. The surface was structured by the method of deforming cutting (MDC). A comparison with the data obtained on a smooth plate was performed. Data of high-speed video of the processes are presented.

Studying the dynamics of nonlinear interaction between enterprise populations

The article highlights the results of a study of the dynamic evolutionary processes of trophic relations between populations of enterprises. A model based on differential equations is constructed, which describes the economic system and takes into account the dynamics of the specific income of competing populations of enterprises in relations of protocooperation, nonlinearity of growth and competition. This model can be used to analyze the dynamics of transient processes in various life cycle scenarios and predict the synergistic effect of mergers and acquisitions. A bifurcation analysis of possible scenarios of dynamic modes of merger and acquisition processes using the neural network system of pattern recognition was carried out. To this end, a Kohonen self-organizing map has been constructed, which recognizes phase portraits of bifurcation diagrams of enterprises life cycle into five separate classes in accordance with the scenarios of their development. As a result of the experimental study, characteristic modes of the evolution of economic systems were revealed, and also conclusions were made on the mechanisms of influence of the external environment and internal structure on the regime of evolution of populations of enterprises.

Dynamics of transient processes at liquid boiling-up in the conditions of free convection and forced flow in a channel under nonstationary heat release

Results on experimental investigation of the dynamics of boiling-up at stepwise heat release on a horizontally oriented cylindrical surface in a large volume of freon-21 are presented. Experimental data on the propagation velocity, structure, and other local characteristics of development of self-sustained evaporation fronts at different temperature differences of boiling-up in saturated liquid were obtained. New experimental results on the dynamics of vapor phase incipience and evolution on the surface of a vertical heat releasing tube and on the dynamics of changing the heater temperature and pressure in a flow of liquid (water, ethanol) subcooled to saturation temperature in the channel under nonstationary heat release conditions are represented. It was revealed that the dependence of the expectation time of intense bubble growth on the water motion velocity is nonmonotonic.

Parameter fluctuations in electromechanical drives with gaps in the elastic coupling

Parameter fluctuations in the power circuits and electromechanical systems of machine drives are considered. The influence of two factors—a gap in the elastic coupling; and scattering of the electric drive’s vibrational energy—on the dynamics of transient processes is studied with decrease in the active impedance of the motor.

Influence of the microstructure on the charge transport in semiconductor gas discharge electronic devices

Experimental results with nonlinear features and hysteresis characteristics in the pre-breakdown Townsend discharge regime is studied experimentally for a planar microstructure with a GaAs photocathode, an interelectrode gap thickness of 445 μ m and gas pressure in the range 28–66 Torr. An investigation of the effect of the voltage amplitude on the dynamics of transient processes in the semiconductor gas discharge microstructure was made to explain the mechanism of the current decay. A linearly increasing voltage (i.e. 3 V s − 1 and 5 V s − 1 voltage rate) was applied to the system to study current instability. The nonlinear transport mechanism of carriers through the cross-section of the discharge gap i.e. the appearance of the spatio-temporal self-organization of a nonlinear dissipative system, non-equilibrium electron motion and autocatalytic effect of carrier accumulation in the gas layer attributed to decrease of current with the increase of applied voltage. It is established that the pre-breakdown current decreases anomalously with increase of the feeding voltage and illumination intensity on the photocathode. The current density change through the cross-section of the discharge gap, i.e. the appearance of the spatio-temporal self-organization of nonlinear dissipative systems, causes these observed effects. On the other hand, the oscillatory current with non-monotonic N -shaped and hysteresis peculiarities in post-breakdown region is known to be related to a nonlinear mechanism of carrier transport in the semiconductor material caused by EL2 defect centres.

The simulation of charge transport in the nanostructure “Camel” and heterotransistors

Heterojunction bipolar GaAs transistor with AlGaAs emitter and Si-“Camel”-transistor were simulated using manyparticles method for hot electrons and stochastic dynamics method for equilibrium holes and electrons. Some transient processes were investigated at times of the order 10 −11 s. Dynamics of transient processes is affected by electron space charge and unequipotentiality of base region.

Characteristic features of an ionization system with semiconducting cathode

The characteristic features of a dc discharge generated between parallel plate electrodes and especially the discharge stabilization by the GaAs semiconducting cathode in such a system are studied. The cathode was irradiated on the back-side with IR light in a particular wavelength range that was used to control the photoconductivity of the material. The semiconductor material was found to stabilize the discharge. The current-voltage and radiation-voltage characteristics of the gas discharge cell with a semiconducting cathode were obtained experimentally. An investigation of the effect of the voltage amplitude on the dynamics of transient processes in the plane semiconductor-discharge gap structure was made for explanation of the light intensity and current decay. Expressions are obtained for the photoelectric gain.

Dynamics of Transient Processes in a Photographic System with a Semiconducting Photodetector

The physical processes determining the functioning of a dc discharge generated by parallel plate electrodes and especially the discharge stabilization by the CaAs semiconducting photodetector in a photographic system are studied. The photodetector was irradiated on the back-side with infra-red radiation in a particular wavelength range that was used to control the photoconductivity of the detector. The semiconductor photodetector was found to stabilize the radiation of the discharge. The current-voltage and radiation-voltage characteristics of the gas discharge cell with a semiconducting photodetector are obtained experimentally. An investigation of the effect of the voltage amplitude on the dynamics of transient processes in the plane photodetector-discharge gap structure was made for explanation of the liglit intensity and current decay.