We suggested a new approach for describing heat transfer in thermosyphons and determining the characteristic temperatures. The processes of thermogravitation convection in the coolant layer at the lower cap, phase transitions in the evaporation zone, heat transfer as a result of conduction in the lower cap are described at the problem statement. The main assumption, which was used during the problem formulation, is that the characteristic times of steam motion through the thermosyphon channel are much less than the characteristic times of thermal conductivity and free convection in the coolant layer at the lower cap of the thermosyphon. For this reason, the processes of steam motion in the thermosyphon channel, the condensate film on the upper cap and the vertical walls were not considered. The problem solution domain is a thermosyphon through which heat is removed from the energy-saturated equipment. The ranges of heat flow changes were chosen based on experimental data. The geometric parameters of thermosyphon and the fill factors were chosen the same as in the experiments (height is 161 mm, diameter is 42 mm, wall thickness is 1.5 mm, ε=4-16%) for subsequent comparison of numerical simulation results and experimental data. In the numerical analysis it was assumed that the thermophysical properties of thermosyphon and coolant caps do not depend on temperature; laminar flow regime was considered. The dimensionless equations of vortex, Poisson and energy transfer for the liquid coolant under natural convection and the equations of thermal conductivity for the lower cap wall are solved by the method of finite differences. Numerical simulation results showed the relationship between the characteristic temperatures and the heat flow supplied to the bottom cap of thermosyphon. The results of the theoretical analysis are in satisfactory agreement with the known experimental data.

The proposed method of detection the inter turn fault of transformer windings relates to the area of defectoscopy and allows detecting inter turn faults in a wide range of damaged (closed) turns. Power and instrument transformers with iron-core are widely used in power networks. As the insulation ages or is damaged, the wires between various transformer sections short circuits occur, which inevitably leads to a complete damage of the transformer. Short- circuited part of the transformer forms an additional winding, the outputs of which are short- circuited. The transition process of current increasing when DC voltage is connected to the transformer outputs occurs in diverse ways in undamaged (cut-off) winding section and in the damaged (short-circuited) section. The current growth rate in the undamaged section of the winding is determined by high magnetization inductance. The inductance of the short-circuited part of the winding is much less, so, the current growth rate in the short-circuited part is significantly greater than the current growth rate in the undamaged part of the winding. The article presents observations from computer models and real measurements of the substation auxiliary power transformer, which show the possibility of determining the presence of a turn fault in regards to the transition process parameters, the rate of current increase and decay in the transformer winding. The device aimed to find the inter turn faults in the transformer windings, working according to the proposed method will be quite simple and have a high sensitivity.

The energy efficiency of the drying section of paper machine is determined by the technology of heat flows arrangements in it. Paper drying is the most energy-consuming stage of paper production. The thermal mode of the drying section is provided by the steam condensate system which is a part of it. Analysis of exergy increments shows that almost all elements of the drying thermal process are characterized by low exergy efficiency. The main ways for increasing the degree of thermodynamic perfection of the processes occurring in the drying section of the paper machine are identified based on the exergy analysis. It is assumed that the deep internal heat recovery of the steam-air mixture for heating the source air will increase the exergy efficiency of the heat recovery plant and reduce heat removal to the environment. The effectiveness of development and implementation of a closed cycle use of steam-air mixture in the drying section was examined. Building a closed cycle provides that the air mainly has a process duty, that is, it is a transport agent for the transfer of moisture and heat along a closed circuit. The calculations show that the exergy efficiency of the processes in the recovery unit of the drying section of the paper machine of the existing production is 28.6% against 66.29% for the proposed method.

The purpose of this article is to perform a comparative study of a reversible heat engine with an ideal or real gas as a working fluid and to determine the change in its efficiency depending on the thermodynamic characteristics of the working fluid. The main research method is the method of thermodynamic potentials, based primarily on the analysis of changes in the free and internal energy of an ideal and real gas in a cyclic process. The theory of thermodynamic potentials is used to consider the Carnot quasistatic heat engine. A comparative analysis of its operation is carried out, for a cycle with both an ideal and a real gas as a working fluid. The possibility of analyzing cyclic processes occurring in heat engines using the method of thermodynamic potentials has been identified and substantiated. The study has shown that the existing formulation of the Carnot’s theorem is valid only for ideal gas as a working fluid. Based on the work carried out, the Carnot’s theorem in the general case can be formulated, for example, as follows: the efficiency of the heat engine ηr, when it operates at the reversible Carnot cycle with real gas as a working fluid, is determined by the following expression:

h_r= 1 - T_B /T_A + ε,

where T_A and T_B are the temperatures of the upper and lower isotherms of the Carnot cycle, respectively; 
ε is the correction term (positive or negative), depending on the thermodynamic properties of a real gas, which tends to zero as the properties of a real gas approach the properties of an ideal gas.

The article considers the feasibility of changing the structure of a distribution electrical network by transferring points of electricity transformation as close to consumers as possible. This approach is based on installation of pole-mounted transformer substations (PMTS) near consumer groups and changes the topology of the electrical network. At the same time, for groups of consumers, the configuration of sections of the low-voltage network, including service drops, changes. The efficiency of approaching transformer substations to consumers was estimated by the reduction in electrical energy losses due to the expansion of the high-voltage network. The calculation of electrical losses was carried out according to twenty-four hour consumer demand curve. To estimate the power losses in each section of the electrical network of high and low voltage, the calculated expressions were obtained. For the considered example, the electrical energy losses in the whole network with a modified topology is reduced by about two times, while in a high-voltage network with the same transmitted power, the losses are reduced to a practically insignificant level, and in installed PMTS transformers they increase mainly due to the rise in total idle losses. The payback period of additional capital investments in option with modified topology will be significantly greater if payback is assessed only by saving losses cost. Consequently, the determination of the feasibility of applying this approach should be carried out taking into account such factors as increasing the reliability of electricity supply, improving the quality of electricity, and increasing the power transmission capacity of the main part of electrical network.

The objects of the study were the Doy Chemical hollow-fiber ultrafiltration membranes which were use for preparation of make-up water for the Novocherkasskaya Regional Thermal Power Plant (RTPP).

We tried out a possibility of applying the X-ray fluorescence spectrometry to study the condition of the spent non-recoverable ultrafiltration membranes in order to identify the causes of their irreversible destruction. The ARL Quant’X X-ray fluorescence energy dispersive spectrometer of Thermo Scientific (USA) was used in the study.

Thin cuts of the Doy Chemical hollow-fiber ultrafiltration membranes were used in the experiments, which had worked for more than three years in the field conditions of the feed water of the Don River, Russia.

The analysis of the obtained samples spectra allowed us to assume that the membranes were irreversibly contaminated by iron bacteria. Basing on the conclusions made during the analysis of X-ray fluorescence spectra we developed and tested in field conditions one of the optimization variants for technological pretreatment scheme. This scheme enables a significant increase in the service life of ultrafiltration membranes, even when the feed water is heavily contaminated by bacteria. Field tests of the modernized technology were carried out at Novocherkasskaya RTPP during 2016-2018 and showed a significant increase in the service life of the membrane modules. At the same time, the quality of the filtrate, productivity and pressure drops at the cascades of ultrafiltration units fully corresponded to the normative values even in conditions of deteriorated quality of the feed river water.

It has been proved that aggressive regeneration of ultrafiltration membranes that have worked for a long time under the conditions of feed water having increased values of the total microbial number and high values of permanganate oxidation does not allow one to restore their initial state. In this case the main cause of ultrafiltration membranes contamination is iron, which is present in colloidal and bacterial forms in the pores and on the membranes surfaces. In the conditions of the Novocherkasskaya RTPP, in addition to timely flushing and chemical regeneration of ultrafiltration membranes, the necessity of organizing a preliminary treatment of the feed water with reagents having a prolonged bactericidal effect is accepted.

Electrical energy from the place of its generation is transmitted to consumers of various capacities. The distance from the source of electrical energy to the consumer can vary from several meters to several thousand kilometers. In this regard, the accurate determination of the operating parameters of the power transmission line (PTL) is a mandatory and necessary condition for the PTL normal functioning. In the current-carrying parts of the double-circuit PTL there are six incident and six reflected waves of the electromagnetic field. They determine voltages and currents. A scheme is proposed for the distribution of these waves along linear wires of a homogeneous section of a double-circuit PTL. This scheme shows that the current-carrying parts of the adjacent wires have a significant impact on voltages and currents in one wire. This scheme illustrates the distribution of the amplitude values of electromagnetic field waves, defined as the integration constant. Using the integration constants, the propagation constants of electromagnetic waves along the linear wires of the PTL and the corresponding wave impedances, one can obtain the amplitude values of the incident and reflected waves at any point of the double- circuit PTL, and hence the currents and voltages in the double-circuit PTL. The article presents a method for determining the currents and voltages in a double-circuit PTL according to the load. The proposed method will allow determining the qualitative and quantitative indicators of electrical energy (induced voltage) appearing from each wire separately and provide the possibility of their elimination, which will improve the quality of electrical energy.

The aim of the work is the development and study of methods for reducing the cost of heat energy for heating buildings and constructions by means of usage of automated control systems based on a programmable logic controller. 

Methods: In contrast to the known methods, the proposed mathematical model of non-stationary processes in heat-intensive enclosures makes it possible, according to the adaptive control algorithm, to perform forecast and standby heating taking into account the time dependence of the outdoor air temperature. 

Results: The algorithm ensures the equality of the heating system power and the heat losses power, allows one to maintain the desired indoor air temperature in the room when the outdoor air temperature changes. The heat loss compensation mode is achieved without using the temperature chart parameters of the network water and the parameters of proportional-integral-differential control laws that are necessary to set up at common automatic heating control systems. When calculating the forecast and standby heating modes, the mathematical model allows, at given initial and final temperatures of the internal air, determining the heating system power, which provide the desired temperature at the end of a specified period of time. The adaptive control algorithm allows setting the calculated outdoor temperature and the desired internal air temperature at any time. Under the forecast control, the mathematical model allows determining the system power at which the internal air temperature will remain almost constant when the outdoor air temperature changes. 

For practical applications, the description of processes occurring during the flow of two-phase gas-liquid mixtures requires a simple physical and mathematical model that describes the behavior of a two-phase medium in the entire range of phase concentrations changes and in a wide range of pressure changes. Problems of this kind arise in various branches of industry and technology. In the space industry, one often has to deal with the movement of various gases in rocket nozzles, consider the combustion, condensation of various vapors on the nozzle walls and their further impact on the velocity sublayer at the nozzle wall. The large acoustic effect arising from the engines affects the gas-liquid mixture in the nozzles of rocket engines. In the metal industry, metal cooling occurs with the help of nozzles in which the emulsion mixture is supplied under high overpressure. But this is only a short list of applied issues in which one has to deal with a problem of this type. The paper presents the results and directions of study of the problems of two-phase dispersed gas-droplet flows in the nozzles. The main methods of investigation of two- phase heterogeneous flows are described. The main characteristics of heterogeneous two-phase flows in the nozzles, which were confirmed by experimental results, are presented. The calculation of the air-droplet flow in the Laval nozzle is given. The technique, which is based on integral energy equations for two-phase dispersed flows, is described. The main problems and questions concerning the further description and studying of two-component flows are stated.

The purpose of the article is to study the possibility and feasibility of participation of nuclear power plants (NPPs) with VVER in emergency frequency control in power systems with a high proportion of nuclear power units and, at the same time, of reducing the power consumption for the own needs of the main circulation pumps during modes with power below nominal. To solve these problems, it was proposed to increase the achievable speeds of power gain (load increase) due to the installation of frequency controlled drives of the MCP. Large system frequency variations (caused by large imbalances between generation and demand) may jeopardize electrical equipment, in terms of maintaining stable and reliable operating conditions. For NPPs, the task of preventing or localizing accidents is even more important than for TPPs, since in case of major system accidents, it is possible to completely stop external power supply of the NPPs own needs. Thus, besides the requirements for the primary control of the frequency of NPPs with VVER, today we need more stringent requirements for their emergency acceleration and mobility. The operation of NPPs with long-term non-recoverable active power shortage causes a decrease in the speed of the main circulation pumps of NPPs with VVER and a decrease in the coolant flow rate. It is shown that the installation of variable frequency drives of the MCPs at NPP with VVER is appropriate not only to save energy consumption for their drive in partial modes, but also to increase the power of NPP above the nominal (without reducing the reserve before the heat exchange crisis in the reactor core) for the elimination of system accidents, and thus to improve the safety of the NPPs included in the power system.

The methane-hydrogen fraction is a gaseous hydrocarbon by-product during oil processing for obtaining petroleum products. Until recently, the methane-hydrogen fraction was used as furnace oil in internal technological processes at a refinery. Some of the low-calorie methane-hydrogen fraction was burned in flares. Driven by the prospect of the methane-hydrogen fraction use as a fuel alternative to natural gas for burning in thermal power plants boilers, it became necessary to study the methane-hydrogen fraction combustion processes in large volumes. The conversion of ON-1000/1 and ON-1000/2 furnaces from the combustion of the methane- hydrogen fraction with combustion heat of 25.45 MJ/m³ to the combustion of the composition with combustion heat of 18.8 MJ/m³ leads to a decrease in temperature in the flame core for 100 °C as an average. The intensity of flame radiation on the radiant tubes decreases. Therefore, the operation of furnaces during combustion of methane-hydrogen fraction with a low heat of combustion at the gas oil hydro-treating unit is carried out only with a fresh catalyst, which allows lower flame temperatures in the burner.

The experiments to determine the concentration of nitrogen oxides NO_x and the burning rate w of the methane-hydrogen fraction in the ON-1000/1 furnace and natural gas in the TGM-84A boiler, depending upon the heat of combustion Q_n^r were carried out. The obtained results showed that the increase in the hydrogen content Н₂ from 10.05 % to 18.36% (by mass) results in an increase in the burning rate w by 45%. The burning rate of natural gas with methane CH₄ content of 98.89% in the TGM-84A boiler is 0.84 m/s, i.e. it is 2.5 times lower than the burning rate of the methane- hydrogen fraction with H₂ content of 10.05%. The distributions of heat flux from the flame qf over the burner height h in the TGM-84A boiler were obtained in case of natural gas burning and calculation of burning of the methane-hydrogen fraction with a hydrogen content of 10.05% and methane of 28.27%. The comparison of the obtained data shows that burning of methane- hydrogen fraction causes an increase in the incident heat flux qf at the outlet of the burner.

Modeling of the low heat conductive low-porous capillary porous coatings and metal (copper, stainless steel) surfaces (base layer) was studied. Heat and mass transfer in the porous coatings moved with excessive liquid due to the combined action of capillary and mass forces. The dynamics of vapor bubble was described along with their heat-dynamic properties, which were observed by the optic research methods. Finding solution for the thermoelasticity allowed to reveal the influence of the specific heat flow and heat tension of compression and stretching depending on time of supply and sizes of pulled particles at the time of the system limit state as to "porous coating - base layer". The theory was confirmed by the trial, which was observed by camcorder SKS-1М.

The article describes the prerequisites for development of methodology for integrated assessment of options for transition to a closed hot-water supply scheme. For analysis of promising options for transition to a closed system of hot water supply, criteria have been proposed that influence the choice of possible solutions. Block diagrams of boundary conditions and independent variables were created. A pyramid of indicators which affect the operating costs of heating system over 25 years of its operation was formulated. A method and a program for selecting the optimal transition scheme to a closed hot-water supply system with calculation of weighting factors have been developed.

Three-phase thyristor switches are designed for pulsed formation of inrush currents of electrical equipment with their subsequent shunting in steady state operation. In transformer substations, they perform a bumpless turning on of a power transformer by connecting its primary winding first to two phases of the network at the moment of zero crossing by the phase voltage of the network third phase, and then to the network third phase at the moment of zero crossing by the line voltage of the other two network phases. In this case, the starting currents of the transformer almost immediately enter the steady state without the appearance of constant components in the magnetization currents and voltage drop. To expand the functionality of thyristor switches, it is proposed, in addition to bumpless turning on of a power transformer, to disconnect it without arcing between the contacts of electrical equipment, as well as to carry out continuous voltage regulation for consumers when voltage in the network changes. The proposed method and structure for its implementation on the basis of two three-phase thyristor reactor keys and a capacitor bank make it possible while changing the network voltage to stabilize the generated reactive power at the input of the substation without creating the current distortions in the power transformer and power transmission simultaneously with stabilizing the substation output voltage. Modeling and research of the start-regulating device as part of a transformer substation was carried out in the MatLab environment. The results of numerical experiments in stationary and dynamic modes of the substation operation showed the feasibility of using the developed technical solutions for the industrial power supply system.

Structural elements of overhead power transmission lines are experiencing both horizontal and vertical loads. Wires and cables are elements of the overhead power line, on which changes in mechanical loads are observed to a greater degree. This occurs due to the change in the tension force of the wire/cable depending on the temperature and the formation of icy-rime deposits on it, as well as fluctuations in wind gusts. The article describes the most common systems and methods for determining the mechanical loads on an overhead power transmission line. A method is proposed for calculating the mechanical loads on an overhead transmission line based on mathematical models of a flexible wire, rope and a model for determining ice deposits on wires, taking into account the rotation of the wire/cable around its axis. A comparison of the improved inclinometry method with the method developed earlier for the case of formation of ice deposits on the S-50 cable has been carried out. A comparison was made on the error in determining the tension of the S-50 ground-wire protection cable using the method developed to control the mechanical parameters of overhead power lines, which takes into account the wire/cable rotation around its axis and the method for determining icy-rime deposits developed earlier. The developed method allows determining the elongation of the wire/cable in the span with one anchor support, as well as the strength of its tension with greater accuracy. However, additional clarification is required due to the influence of the wind, the formation of icy-rime deposits of various shapes, as well as the structural limitations of the wire/cable rotation when attaching it to the support.