RELEVANCE. Epoxy foams produced by thermal expansion of polymer microspheres show promise as sandwich panel cores. During secondary heating of epoxy foams, significant shrinkage or thermal expansion may occur, depending on the foam composition. Research and prediction of these processes is necessary for the design of sandwich products with epoxy foam cores.THE PURPOSE. To study the thermal expansion and shrinkage of epoxy foams during secondary heating. To estimate the pressure created in a confined tooling space due to expansion.METHODS. Dynamic mechanical analysis was used to estimate the glass transition temperature of epoxy foams. The foaming process of microspheres was studied using thermomechanical analysis. Thermal expansion and shrinkage were assessed by measuring the linear dimensions and volume of the foam before and after heat treatment. The pressure during the thermal expansion of foam plastics was assessed using pressure sensors and recorded using the DiamonPlus dielectric composite molding process monitoring system (INASCO).RESULTS. It was shown that secondary heating of epoxy foam plastics can cause shrinkage or expansion of the material depending on the microsphere content. Thermal expansion pressure increases with increasing foam plastic density.CONCLUSIONS. The temperature conditions for secondary heat treatment were selected, and thermal expansion studies were conducted for epoxy foam plastics with different microsphere contents and initial densities. It was shown that the initial minimum foam density decreases, while the density after heat treatment increases with increasing microsphere concentration. With an increase in the initial foam plastic density at a constant microsphere concentration, the foam plastic density after heat treatment decreases. For foam plastics with a high initial density and a high microsphere content, anisotropy of expansion and contraction after heat treatment is observed.
THE PURPOSE. The purpose of this study is to conduct a comprehensive analysis of the impact of key parameters of the electric vehicle (EV) fleet and electric vehicle charging infrastructure (EVCI) on electricity consumption and peak power demand in Russia's power system in the medium and long term. In contrast to existing research, the focus is not only on forecasting the number of EVs but also on a scenario-based analysis of a wide range of influencing factors.METHODS. A mathematical model was developed to calculate the electricity consumption and maximum power demand of EVCI for all Russian cities with a population exceeding 50,000. The model accounts for the regional distribution of the EV fleet, its structure and model composition, climatic conditions, EVCI specifications, and behavioral factors. The significance of the factors was assessed using multiple linear regression.RESULTS. It was found that for an EV fleet of 1 million units, the variation in influencing factors can lead to changes in EVCI electricity consumption ranging from 0.14% to 0.62%, and in peak power demand from 0.09% to 2.26% of the 2024 levels of Russia's Unified Energy System (UES). The EVCI parameters have the greatest impact on peak power demand: the number of EVs per charging station (37.1%) and the share of fast chargers (20.8%), along with the share of plug-in hybrid electric vehicles (23.7%). Electricity consumption is most significantly influenced by the share of plug-in hybrids (32.3%), their utilization rate (26.3%), and the share of electric buses in the fleet (21.6%). The forecast up to 2050 shows that EVCI electricity consumption could reach 8.13-11.85%, and peak power demand could reach 11.54- 16.81% of the 2024 levels.
THE RELEVANCE of the study lies in ensuring high-quality electricity supply to consumers against the background of an increasing number of technological connections. One of the most important indicators of high-quality electricity supply is the voltage in electrical networks. The article considers the problems of voltage regulation in distribution networks (DN), which helps to ensure the required quality of electricity, reduce electricity losses and increase the capacity of power transmission lines.THE PURPOSE. Development of measures to ensure the quality of electricity using various methods of voltage regulation.METHODS of the study include mathematical modeling of power transmission lines (PL) taking into account the static characteristics of the load, as well as modeling of processes in distribution networks using automatic voltage regulation points (AVRP) and 10/0.4 transformers equipped with tap-changer devices for high-voltage windings without excitation (PBB) with an extended voltage regulation range of up to ±10%.RESULTS. The results of the study demonstrate the feasibility of introducing transformers with extended voltage regulation limits.CONCLUSION. The conducted study demonstrates that both of the considered methods, namely the installation of a PARN and the transition to transformers with an extended range of PBB of ±10%, make it possible to solve a key problem: maintaining the quality of electricity within the requirements at all nodes of an extended distribution network.
PURPOSE. Determination of quantitative characteristics of nitrogen oxide emissions during combustion of gas mixtures containing hydrogen, carbon monoxide and methane.RESULTS. Several types of gases with different chemical compositions and quantitative content of components were considered: CH4; CO; H2; 7 types of synthesis gas with different content of CH4, CO, H2, CO2, N2. These types of synthesis gas had low, medium and high values of heat of combustion. When performing numerical studies of the parameters and composition of combustion products, an approach based on the chemical equilibrium state of a multicomponent reacting mixture at a minimum value of isobaric-isothermal potential was used. The values of the main parameters of combustion products and estimates of nitrogen oxide emissions were obtained at different ratios of the initial components in the gas mixture and different values of the excess air coefficient. The values of the relative indicators of combustion product consumption correlate quite strongly with the values of the relative indicators of nitrogen oxide emissions.CONCLUSION. Numerical estimates of the relationship between the combustion heat of generator gases, the flow characteristics of the combustion products determined by the composition of the initial gas mixture, and nitrogen oxide emissions are obtained. The quantitative indicator Wps, determined by the ratio of the mass flow rates of the combustion products of the base fuel and alternative generator gas, under the condition of the same thermal power of the power plant, makes it possible to preliminary compare the expected level of NOx emissions. At Wps ≈ 1, the level of NOx emissions for the compared fuel compositions is approximately the same. Accordingly, at values of this indicator greater or less than one, the levels of nitrogen oxide emissions during combustion of the alternative generator gas are higher or lower than during combustion of the base fuel. The practical use of the Wps indicator is most effective at the stages of development and design of new power plants, including optimization of planning of computational and full-scale experiments, as well as during the transfer of operating power plants to alternative gas fuel.
RELEVANCE. Due to the significant variety of configurations of heat exchange elements and designs of heat exchangers, coefficients of the criterion equation are proposed, which allows for a more accurate comparative evaluation of the efficiency of coil heat exchangers based on springtwisted channels.THE PURPOSE. Carrying out calculations of coil heat exchangers of the "pipe in a pipe" type with a variable bending radius of a helical spiral based on spring-twisted channels and evaluating the energy efficiency of such devices in comparison with smooth-walled analogues.OBJECT of this study is a conical apparatus with coaxially mounted coil tubes. In this case, the inner tube is made in the form of a spring-twisted channel of circular cross-section, and the outer one is made of smooth pipe.METHODS. As part of the work, the engineering calculation of the conical coil apparatus has been adjusted, based on theoretical research and solving the related heat exchange problem, and includes the equations of the modified Ieshke correction factor, criterion equations for calculating heat exchange with heated (hot) and heated (cold) water, and the determination of heat transfer and heat transfer coefficients through the heat exchange surface.RESULTS. In a coil heat exchanger with spring-wound pipes, the temperature of the heated coolant is 8.88°C (60.98°C versus 52.1°C) higher than in smooth-walled pipes. The thermal efficiency of such structures is higher: the power is 25.6 kW at a drop of 20.7°C versus 23.5 kW and 20.4°C, respectively. Heat transfer coefficient of spring-twisted pipes (1543 W/(m2·K)) higher due to turbulence and secondary flows. Hydrodynamic analysis shows a reduction in the cost of pumping heat carriers based on springtwisted channels to 1,438 Watts compared with 1,590 watts for smooth-walled structures. This is due to the shorter required length of the heat exchange element. The superiority of spring-twisted channels is confirmed by a higher value of the Kirpichev criterion (17,83) compared to smoothwalled analogues (14,77), which characterizes their improved energy performance.CONCLUSION. Calculations of coil heat exchangers of the "pipe in a pipe" type with a variable bending radius of the spiral were carried out on the basis of two variants of heat exchange elements: a spring-twisted channel and a smooth pipe, the data obtained are consistent with the results of mathematical modeling. The results of the calculation confirm the technical and energy feasibility of replacing smooth tubes with spring-twisted tubes in the designs of heat exchangers. This modification makes it possible to simultaneously increase the thermal performance of the system and reduce the operational energy consumption for moving the coolant, which leads to a significant increase in the overall energy efficiency of the system. Thus, the use of spring-wound elements in heat exchangers is an innovative solution that improves the efficiency and reliability of heat exchange technology.
