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  Problemele energeticii regionale

E-Journal N3(51) 2021



1 Study of Interconnected Physical Processes in the Magnetic Fluid Sealer
Authors: Nesterov S. A. , Stradomskii Yu. I. and Belov V. S. Ivanovo State Power Engineering University, Ivanovo, Russian Federation
  Abstract: The purpose of this work is creation of an interconnected numerical model of the magnetic and hydrodynamic fields of the ferrofluid sealer to analyze the effect of centrifugal forces during shaft rotation on the retained pressure drop. The set goal was achieved by selection of the neces-sary equations, boundary conditions, assumptions and properties concerning the ferrofluids when building a numerical model of the sealer gap in the Comsol Multiphysics simulation envi-ronment. The important results of the work were the obtained and analyzed distributions of the magnetic field and pressure field in the ferrofluid, the evaluation results of the of the effect of centrifugal forces arising during the shaft rotation, on the pressure drop held by the sealer. It was shown that with a shaft radius of up to 50 mm and speed up to 3000 rpm, the change in the retained pressure drop was insignificant, and it was up to 2 % of the values with a stationary shaft. Significant manifestation of centrifugal force for the investigated shaft radii began at 6000 rpm. It was shown that the decrease in the retained pressure drop with an increase in the working gap was associated with the decrease in the magnetic field gradient. The significance of the re-sults consisted in the possibility of using the developed model for the study of the ferrofluid sealer gap processes. Comparison with the data obtained using the analytical formulas showed that the latter overestimated the retained pressure drop.
  Keywords: magnetic fluid, magnetic fluid sealer, pressure drop, numerical simulation, Comsol Multiphysics.
2 Study of Partial-Phase Steady-State Operation Modes of Phase-Shift Transformer with Hexagonal Circuit and Regulating Autotransformer
Authors: Bosneaga V., Suslov V. Institute of Power Engineering of Moldova Chisinau, Republic of Moldova
  Abstract: The scope of the work was the study of the phase failure operating for the new FACT’s type phase-shifting device, intended for the flexible connection of AC power systems. The mathamatical model has been developed for conducting this study. The device contains the main phase-shifting transformer based on hexagon circuit with additional regulating autotransformer, this creates the possibility of circular regulation of phase shift angle between connected systems. The model includes two 6-winding three-legs transformers, for which two sets of parameters can be independently set based on the data for the short circuit and no-load modes. The data for the direct sequence parameters is usually provided by the transformer manufacturers, and the data for the zero sequence parameters could be obtained upon additional request. As a result of modeling, the vectors of the voltages and currents were obtained in all windings in the investigated modes with supply source phase failure. This makes it possible to analyze the admissibility of such modes and estimate the need for taking special measures of protection against them. It is shown that the voltages on the windings of the main transformer insignificantly depend on the connection mode of the regulating autotransformer, while the pattern of currents distribution in the windings of the main and regulating transformers to a large extent is determined by said connection mode of the autotransformer. The presence of perceptible zero-sequence current flowing through the grounded neutrals of the power supply source and load is noticed. This fact is connected with the release of insignificant magnetic flux from the magnetic circuit in the surrounding space.
  Keywords: flexible connection of power systems, phase-shifting transformer, hexagon circuit diagram, regulating autotransformer, phase failure.
3 Determination of Transformer Oil Quality Parameters by its Color Coordinates
Authors: Kozlov V. K., Valiullina D. M., Kurakina O. E. and Sadykov E. M. Kazan State Power Engineering University, Kazan, Russian Federation
  Abstract: The service life of transformers and, as a consequence, of the electric power systems depends largely on the chemical composition and electrical insulating properties of the oil. In this regard, much attention is paid to the control of physical and chemical indicators and operational proper-ties of transformer oils. The aim of this work is to determine the important diagnostic parameters such as the acid number and the tangent of the dielectric loss angle of the transformer oil based on the measured coordinates of the color of the transformer oil. This goal is achieved by the study of the coordinates of the transformer oils chromaticity. For this purpose, a white light source is used, which is a LED with a pumping line of 450 nm and a maximum radiation in the region of 550--560 nm, with radiation in the range from 400 to 800 nm. Sensors 1, 2, 3 allow determining the chromaticity coordinates of the measured source R, G, B (red, green, blue), due to several receivers having spectral characteristics of sensitivity in the corresponding region of the visible spectrum. The most significant result of the work was the establishment of correla-tions between the TM chromaticity coordinates their acid number and the tangent of the dielec-tric loss angle of TM. The significance of the results obtained was that the acid number and the tangent of the dielectric loss angle of the transformer oil could be determined by the chromatici-ty coordinates, and hence, by the color of the oil.
  Keywords: transformer oil, acid number, dielectric loss tangent, color characteristics, chromaticity coordinates
4 Accuracy Improvement for the Determination of Parameters and Voltage Drops in Busbars, Considering the Networks Power Factor
Authors: Kotsur M.I., Yarymbash D.S., Bezverkhnya Yu.S, and Kotsur I.M. Zaporizhzhia Polytechnic National University Zaporizhzhia, Ukraine
  Abstract: The power systems must satisfy the requirements both for high reliability and efficiency. The main component of the shop power supply systems is a busbar. There have been certain engineering techniques for the estimation of parameters, voltage and power losses, characterized by having a high error. Other methods have had a significant calculation efficiency, but without allowing the voltage drop to be determined as a function of the network power factor. Therefore, the aim of this work was to develop an approach that allowed an accurate estimation of the parameters and voltage drop in trolleys, depending on the network power factor. This approach was based on the decomposition of the electromagnetic processes in a trolley busbar by connecting one phase to estimate both the resistance and reactance in the absence of the external field, and two phases to estimate the resistance and reactance in the presence of the external field. The most significant results were the determination of the resistances and reactance, depending on the frequency of the current harmonics and the distance between the phases of the busbar. The dependences were proposed to estimate the resistance and reactance for the corresponding phases and current harmonic. The analytical expression of the ratio between the voltage drop in trolleys and the power factor of the network was obtained. The testing data confirmed the high accuracy of the proposed approach. The significance of the results composed a more precise determination of the parameters and voltage drops in each phase of trolleys, irregardless of their location, number, shape, as well as the phase currents’ non-symmetry, wasting no time for the field simulation.
  Keywords: busbar, electromagnetic field, model, resistance, reactance, voltage drop, current harmonics, power factor.
5 Modeling of Thermal Conductivity in a Medium with Phase Transition with a Moving Boundary of Phase Change
Authors: Mizonov V.E., Tikhonov A.I., Basova E.V., Mitrofanov A.V. Ivanovo State Power Engineering University Ivanovo, Russian Federation
  Abstract: This work is devoted to the theoretical study of the effect of the phase interface motion on thermal conductivity in a liquid-solid nonlinear medium with a phase transition. The problem under consideration deals with the Stefan problems. Its most significant feature is the jump in the phase properties at separation of their moving boundaries. The objective was achieved by solving the following tasks: the construction of the process mathematical model based on its cell representation and with the use of the Markov chain theory mathematical apparatus, performing numerical experiments with the developed model, demonstrating its operability and the possibility to achieve the set goal. The most significant scientific results were as follows. First was an algorithm for the construction of a cell mathematical model of nonlinear thermal conductivity in a phase transitions medium with a moving phase interface for domains of a canonical shape (plane wall, cylinder, ball). Second, the results of the numerical experiments, showing that the jump of properties affected greatly the kinetics of the process. The significance of the results obtained consisted in the development of a simple but informative mathematical model of the media heat treatment kinetics with phase transformations, available for a direct use in the engineering practice. The proposed algorithm for constructing the model can be effectively used in prediction the open water pipes freezing in cold regions, in modeling the heat treatment of metals, in choosing the freezing modes of food products for a long-term storage, and other thermo-physical processes.
  Keywords: nonlinear thermal conductivity, phase transition, phase interface, thermo-physical properties of phases, cell model, state vector, thermal conductivity matrix, numerical experiment.
6 Technology for Improving Technical, Economic and Ecological Efficiency of Boiler Plants Using Physico-Chemical Correction of the Water-Fuel Emulsions Composition
Authors: Filipshchuk A.N., Kolbasenko O.V., Shevtsov A.P., and Dymo B.V. Admiral Makarov National Shipbuilding University Мykolaiv, Ukraine
  Abstract: The aim of this work is to substantiate the possibility of increasing the technical, economic and environmental efficiency, as well as the efficiency of boilers (in terms of the intensity of corrosion processes) when burning water-fuel emulsions with the increased water and salt contents. To achieve these goals complex experimental studies were performed on the combustion of fuel oil and emulsions based on it, as well as the corrosion processes with a water content in the range from 2 to 30%, and a salt content ranging from 17 to 490 mg/dm3 hydrodynamic homogenizer. A significant result of the studies carried out is that with a water content of ~30% in the fuel gases composition, an NO2:NO ratio of 0,33 was achieved. That increased the absorption properties of gases and allowed passivation of carbon steel in sulfuric acid condensate. It also decreased the intensity of the low-temperature corrosion in the range of metal temperature of 130...70°C. All these made it possible to use condensation surfaces and to reduce the flue gases temperatures, to increase the efficiency of boilers, to ensure the economy of pure fuel, to increase the depth of utilization of the exhaust gases heat, and to reduce the concentration of toxic gases. The results obtained differed from those known. The significance of the results obtained lies in the fact that a technology was developed for the integrated use of the electrodialysis water resources, the waste and oil-containing waters, ensuring the operability of boilers, with a water content of emulsions of ~30% and a salt content of up to 450 mg/dm3.
  Keywords: emulsion, water content, salt content, cavitation, dispersion, activity, electrodialysis, diluate, catholyte, complex technology, corrosion, condensation boilers, efficiency, ecology.
7 Development of the Method for Forecasting and Calculating the Operation of Sorption Systems for Purifying the Generator Gas Based on Dolomite Use. Part I
Authors: Malko M.V.1, Vasilevich S.V.2, Mitrofanov A.V.3, Mizonov V.E.3 1Institute of Power Engineering of the National Academy of Sciences of Belarus, Minsk, Republic of Belarus, 2Belarusian State Academy of Aviation, Minsk, Republic of Belarus, 3Ivanovo State Power Engineering University, Ivanovo, Russian Federation
  Abstract: A trend towards energy diversification creates the expansion of small energy facilities that in-volve the production of solid fuel generator gas, rather than its direct combustion. The economic indicators of such facilities significantly depend on the efficiency of the generator gas purifica-tion. A promising sorbent for the purification of the generator gas is dolomite. When working as a sorbent, dolomite particles usually form a layer, through which the generator gas that is heating them is filtered. The objective of the study is to determine kinetic parameters of the thermal de-composition of dolomite, depending on the size of the sample. It was achieved using the ther-mogravimetric study of the thermal decomposition of single dolomite particles under static con-ditions at various temperatures. The most significant scientific result was that a dependence of the kinetic parameters of the gross reaction on the size of the initial particle is revealed, and a regression equation was proposed for its quantitative assessment. In addition, since the heat treatment process of the material was fairly long lasting, and the sizes of the particles allowed them to be referred to thermally thin bodies, it was inferred that the effect of a grain size on the reaction kinetics should be explained through the description of the evacuation process of gase-ous reaction products from the material. The significance of the results of the study lies in the fact that a particle size must be considered as a factor that affects the progress of the technologi-cal process, which increases the reliability of the calculation of sorption-catalytic systems based on the use of dolomite.
  Keywords: generator gas, dolomite, thermal decomposition, sorbent, thermogravimetric analysis, kinetics of decomposition, generator gas purification system.
8 Hybrid Carbon Dioxide Heat Pump for the Multifamily Residential Buildings in the Heat Supply System Based on CHP
Authors: Sit M.L., Juravliov A.A. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: The work is devoted to centralized heat supply systems based on CHP plants and the use with them heat pumps (HP) on carbon dioxide as refrigerant. Heat pumps are used in heat supply sys-tems for buildings and use the heat of the outside air and, at the same time, the heat of the return network water (WWR) as a source of low-grade heat (LHP). The aim of the study is to develop a structural diagram of such a heat pump, where the outside air is heated by a heat exchanger in-stalled in the return water line of the heating system, to develop a hydraulic circuit of a heat pump taking into account the law of regulation of the building heating system, to develop an al-gorithm for controlling the operating modes of the so-called balancing heat exchanger installed after gas cooler and internal heat exchanger of the heat pump. The most significant results were the hydraulic circuit of the heat pump, the aerodynamic circuit of the air supply path to the heat pump evaporator, the balancing heat exchanger control system, taking into account the require-ment to ensure the operation of the control valve in a single-phase flow. The significance of the results obtained consisted in obtaining the dependences between the CO temperature graph and the parameters of the thermodynamic cycle of the heat pump, which ensured the operation of the control valve of the heat pump in a single-phase environment.
  Keywords: carbon dioxide heat pump, district heating, automatic control.
9 The Role of Food Energy Technologies in Solving Global Mankind Problems
Authors: Burdo O. G. Odessa National Academy of Food Technologies, Odessa, Ukraine
  Abstract: The analysis of the Club of Rome global forecasting mode was carried out. A critical analysis of the Club of Rome activity was given. The purpose of the work is to establish the tasks of the food industry in solving the global problems of mankind. It is noted that the global crises (ener-gy, ecology and food) are most clearly manifested in the food industry. To achieve this goal, a scientific and technical idea has been proposed that to solve the global problems the innovative technologies must be involved, which were not considered at all in the Club of Rome projects. The human development paradigm was formulated, considering the modern advances in sci-ence, technology, and nanotechnology. It was substantiated that the nanotechnology use in the food industry is attractive because the food raw materials are nano-sized structures created by nature. Local energy impact on nano-sized elements of the food raw materials can shorten the process time by the orders of magnitude. Such impacts are referred to as "nanoenergy technolo-gies". The most significant result of the work was that the possibility was shown to control the development of the worst global crises by transferring the food industry onto the rails of the "nanoenergy technologies" and thus postpone the crises for another 10-40 years. The scientific significance of the obtained results was that such new effects as "barodiffusion" and "mecha-nodiffusion" were used in the work. The practical significance of the work was that a technolog-ical line for deep processing of food waste was proposed.
  Keywords: nanotechnologies, hybrid processes, electrodynamic technologies, environmental industry, food industry waste, globalistics.
10 Effectiveness of Adding Extruded Wheat Straw to Poultry Manure to Increase the Rate of Biogas Yield
Authors: Polishchuk V.М.1, Shvorov S.А.1, Zablodskiy М.M.1, Kucheruk P.P.2, Davidenko T.S.1, and Dvornyk Ye.O.1 1 National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine 2 Institute of Engineering Thermophysics of National Academy of Sciences of Ukraine, Kyiv, Ukraine
  Abstract: . The work is aimed at increasing the biogas yield rate at biogas plants by means of co-digestion poultry manure in combination with extruded wheat straw. To achieve this goal a series of batch tests were performed to study the yields of biogas and CH4 in anaerobic fermentation of mixtures of manure with extruded wheat straw. The working hypothesis of the study was that the wheat straw addition would allow optimizing carbon to nitrogen ratio reducing thus the inhibitory effect of ammonium nitrogen contained in poultry manure on the digestion process. The most important result of the study consisted in the development of a methodology for determining the efficient ratios of extruded straw to poultry manure, at which the highest rate of methane yield was ensured. The two series of the batch assays at 36°C were performed to study the effect of the straw addition to chicken manure at high and low initial volatile solids concentrations. In each series, three types of mixtures were prepared – with 100%, 65% and 35% of poultry manure by volatile solids content in the combination with wheat straw pellets. The significance of the research results was in the fact that the use of extruded straw together with chicken manure could increase the rate of methane yield by almost two times, compared to the fermentation of only poultry manure. The positive effect of wheat straw addition to poultry manure was found in mixtures with a high initial volatile solids concentration, and hence, a high concentration of nitrogen.
  Keywords: biogas, substrate, chicken droppings, straw, dry organic matter, digester, biogas plant, methane fermentation.
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