Thermal Engineering最新文献

Given the growing share of nuclear power plants in the energy systems of the European part of Russia and the shortage of flexible generating capacities, there is a need to attract nuclear power plants to participate in covering the variable part of the electrical load schedule. The use of storage units, such as latent heat thermal energy storages (LHTES), capable of storing thermal energy received from nuclear power plant reactor units during off-peak hours in the power system and using it during peak load hours to generate electricity will improve the system efficiency of nuclear power plants. Based on the analysis, promising phase change materials (PCM) were identified for operation in thermal storage systems at temperatures from 200 to 300°C, which is determined by the characteristics of the steam turbine plant of a nuclear power plant, including the parameters of feed water and main steam. For the adopted process circuit of an installation with an LHTES with an increase in the temperature of the feed water after the high-pressure heaters of an indirest steam cycle nuclear power plant, the methodological basis for choosing design solutions for the storage system with lithium nitrate as a phase change material has been developed. Using the finite element method in a computer software package, modeling of unsteady heat transfer between this material and water for finned and unfinned pipes was carried out in relation to the LHTES elementary section. Based on the calculation results, graphs of the dependence of the thermal power of the section on the LHTES discharge duration were constructed. Methods are proposed for calculating the duration of LHTES discharge and the mass of the required phase change material when reducing thermal power. For a process circuit with an additional steam turbine unit with a capacity of 12 MW (for NPP power units with VVER-1200), the main characteristics of the latent heat thermal energy storage and the effectiveness of the proposed solution for different LHTES discharge durations are determined.

The article proposes an equation system that includes functions describing the properties of H₂O at the saturation line (pressure, vapor density, liquid density, saturated vapor pressure derivative, heat of vaporization, etc.). Firstly, this system satisfies the requirements of the renormalization group theory. Secondly, the system is in consistency with the Yang–Yang hypothesis in the critical point neighborhood. For describing the saturated vapor density, the Clausius–Clapeyron equation is involved. In writing the equation system, complexes characterizing the saturation line mean diameter behavior were used. The equation system includes: a) the complexes, which are selected in accordance with the recommendations suggested by Wang et al. for asymmetrical systems, b) critical indices, which are calculated on the basis of the critical point scale theory methods. Using the equation system, numerical values of the water property indicators are obtained in the range from the triple point temperature to the critical temperature. The uncertainty of the above-mentioned values are in satisfactory agreement with the uncertainties: a) of the corresponding data on the properties calculated by Wagner and Pruss in the range from the triple point temperature to the critical temperature, b) of the known experimental data. Various models of the saturation line and elasticity curve are compared with each other. It is shown that the proposed equation system conveys the available experimental information on the equilibrium water properties with a smaller uncertainty than the known models do. Data on the mean diameter are calculated on the basis of the equation system in a wide interval of relative temperatures, including the critical point neighborhood. It is discussed a behavior of this diameter within the framework of some known models.

A concept has been proposed for the creation of regional liquefied natural gas (LNG) fuel complexes on the basis of thermal power plants, ensuring the expansion and reliable functioning of the gas fuel market. The concept provides for the transfer of fuel reserve systems for electric power facilities to LNG, which is produced directly at power plants, as well as the supply of LNG from power plants to regional consumers. A description of a foreign installation for extinguishing gas consumption peaks is given: the closest analogue of a power plant with an LNG fuel backup system. A comparative technical and economic analysis of projects for the construction of a fuel oil facility and an LNG backup fuel system for CHPP-22 of PAO Mosenergo showed that, with comparable capital costs, backup using LNG can provide an economic effect of up to 654 million rubles per year at 2023 prices. If there are large volumes of LNG storage, peak fuel shipments to consumers can be ensured, and the standard reserve will be restored using a liquefaction unit. Data are provided for calculating the costs and investments required to create complexes that guarantee the maintenance of standard emergency fuel reserves in the form of LNG for the CCGT-220 power unit (1778 million rubles excluding VAT). A methodology has been proposed for allocating the costs of a complex of emergency fuels, attributable to the cost of electric power and LNG sold to third-party consumers. It is shown that the relative increase in capital costs for the construction of CCGT-220 with emergency fuel in the form of LNG in relation to similar costs for a power unit with emergency diesel fuel is 1%. The cost of in-house LNG production has been assessed. Savings during the initial formation of standard emergency reserves for the power unit amounted to 72.45 million rubles. The advantage of creating a network of LNG complexes is formulated: reserve and emergency fuel reserves at thermal power plants provide a reliable fuel supply to regional markets.

Monitoring of thermal efficiency is of utmost importance for securing efficient NPP operation. To this end, the measurement instruments should have accuracy sufficient for the possibility of determining the actual values of thermal cycle circuit parameters, thermal efficiency, and deviations of the turbine set characteristics from their standardized indicators. The error with which the reactor thermal power is determined using the reactor core thermal-physical parameters and the steam generator parameters is estimated. It is shown that the best accuracy of determining the reactor thermal power can only be achieved through improving the accuracy of determining the steam generator thermal power. An analysis has shown that the error of determining the reactor thermal power is by more than 95% due to the error of determining the feed water flowrate. If we succeed in achieving more accurate determination of the reactor thermal power, it will be possible to obtain more accurate data on the electricity generation during operation at the nominal parameters in the mode with a specified neutron power due to maintaining of the reactor plant’s actual thermal power closest to its design value; in addition, it will be possible to extend the range of power outputs available for operation during operation in the mode of maintaining the specified electric power output by increasing its maximal value. Given the specified period of NPP operation, the maximum of its energy production serves as one of the criteria for economically efficient NPP operation. By using the developed mathematical model of the turbine set used in the NPP constructed according to the AES-2006 conceptual design (with a VVER-1200 reactor), the authors have revealed the effect of the error of determining the thermal cycle circuit parameters on the power unit electric power output and the parameters that have the highest influence on the error of estimating the electric power output. The influence of the error of determining the turbine thermal parameters, moisture separation and steam reheating, high- and low-pressure regeneration, and the turbine set low-grade heat part was analyzed, and the total error of determining the electric power output has been obtained based on the analysis results. These data make it possible to formulate the requirements for the accuracy of flowrate, temperature, and pressure measurements depending on the allowable error of determining the electric power output. An analysis of the operational data of the Leningrad-2 NPP, Novovoronezh-2 NPP, and Belarussian NPP power units has shown that the potential of increasing the electric power output due to improved accuracy of determining the thermal cycle circuit parameters makes 10–15 MW.

If severe accidents occur at nuclear power plants with light water coolant, large quantities of hydrogen may be released as a result of the zirconium-steam reaction. In order to avoid explosive consequences, hydrogen passive autocatalytic recombiners (PAR) are installed in the containment to remove hydrogen flamelessly. To substantiate the hydrogen explosion safety of nuclear power plants using computer modeling, calculations of the state of the vapor-gas atmosphere inside the containment are performed, taking into account the presence of PAR. Experimental data are needed to validate computational models of recombiners. The article presents the results of a comparison of experimental and calculated data on the characteristics of the RVK-500 hydrogen recombiner. A brief description of the BM-P experimental stand is given, on which, for the first time in Russia, it was possible to study the operation of an industrial recombiner in abnormal operating modes (start modes and modes with leakage flow). To simulate abnormal operating modes of the recombiner, a CFD model is used, which describes the flow inside the recombiner in a simplified formulation (based on volumetric energy sources and the concentration of components of the vapor-gas medium). A description of the CFD model used to solve the problem of simulating the operation of the BM-P stand with the RVK-500 recombiner installed (inside the measuring chamber) is presented. For the experimental mode with leakage flow, a detailed comparison was carried out with the results of calculations performed for sensor placement points (temperature and concentration of components of the vapor-gas medium). In total, calculated and experimental data on the performance of the recombiner were compared for seven experimental modes, including the normal operation mode of the recombiner under conditions of a quiescent environment.

The scientific and technical literature presents a large number of works dedicated to the experimental study of the critical out flow of saturated and subcooled liquid through cylindrical channels. Despite this, the available sources do not provide an assessment of the extent to which certain geometric parameters and operating conditions of experiments affect the critical outflow. This article is aimed at the analysis of experimental data using statistical methods and machine learning on critical outflow obtained at Elektrogorsk Research and Development Center (EREC, Russia). The purpose of the work is to identify statistical relationships between operating and geometric parameters, as well as to quantify the influence of these parameters on the critical mass flow rate and pressure. The analysis of experimental data for channels with a filleted inlet edge showed a strong influence of the inlet edge shape both on the value of the critical mass velocity and on the final pressure in the outlet section of the channel, which is established at the critical outflow mode. A comparison of the experimental data for channels with different shapes of the inlet section with the same operating and other geometric parameters showed that for channels with a rounded inlet edge, the critical mass velocity is approximately 25% higher than for channels with a sharp inlet edge. As the nozzle throat length increases, this difference decreases asymptotically. Among the regime parameters, the main contribution to the dispersion of the critical mass velocity is made by the undersaturation (subcooling) of the medium at the inlet which comprised 51% of the total influence of the regime and geometric parameters. An increase in the undersaturation and a decrease in the length of the channel throat lead to decrease in the back pressure necessary to establish the critical outflow mode. In extreme cases, the critical pressure ratio (outlet/inlet) can be 0.1, which is significantly lower than the generally accepted value of 0.5 in engineering practice. The results obtained can be used in the future for design of experiments aimed at expanding the range of operating parameters or optimization elements whose operation is based on the phenomenon of critical outflow.

Increasing the energy efficiency of thermal power plants operating according to the Rankine cycle is one of the priority tasks of the Russian energy sector. Despite a significant amount of scientific research, the efficiency of installations of this type still remains low. As a technological solution to increase their efficiency, the authors consider a modernized Rankine cycle in which an aqueous solution of lithium bromide is used as a working fluid, the condensation process of exhaust steam after the turbine is replaced by the process of its absorption, and the second working fluid is an absorbent. The features of the functioning of such a cycle are outlined, and the methodology for its calculation is presented. Studies have shown that the use of lithium bromide solution can reduce the steam pressure after the turbine and increase the useful heat drop as well as the degree of cycle filling. In addition, when the heat of the solution returned from the boiler is regenerated, the average temperature of the heat supply to the cycle increases, which also increases its thermal efficiency compared to the traditional circuit. The energy efficiency of the modernized cycle was analyzed and compared with the traditional Rankine cycle on water vapor. Calculations have shown that the use of a modernized cycle allows increasing thermal efficiency by an average of 1–2% compared to the traditional solution. The indicators characteristic of both steam power and absorption cycles were studied, and graphical dependences of efficiency on the main parameters were derived. The economic effect of using the modernized scheme is to reduce fuel consumption and emissions of harmful substances into the atmosphere in proportion to the reduction in fuel consumption.

The task of energy-efficient heat supply and removal in thermal control, heating and cooling systems is very relevant for many branches of technology. The paper presents the results of the development and study of a 21 m long loop heat pipe (LHP) that is a passive heat-transfer device operating on a closed evaporation-condensation cycle and using capillary pressure to pump a working fluid. These devices can be used in systems where the heat source and the heat sink are removed from each other by a distance measured in meters and even tens of meters, without the use of additional energy sources. The device has a 24 mm diameter evaporator with a 188 mm long heating zone, a vapor line and a liquid line (external/internal diameters of 8/6 mm and 6/4 mm). A 310 mm long pipe-in-pipe heat exchanger equipped with a cooling jacket was used as a condenser. The tests were conducted with the LHP in a horizontal position. Heat was removed from the condenser by forced convection of a water-ethylene glycol mixture with temperatures of 20 and –20°C and a flow rate of 6 dm³/min. The heat load supplied to the evaporator from the electric heater increased from 200 to 1700 W in the first case and to 1300 W in the second. The vapor temperature at the outlet of the evaporator varied from 25 to 62°C and from 24 to 30°C, respectively. Its maximum temperature difference along the length of the vapor line did not exceed 4°C. Such devices can be used in energy-efficient systems for utilizing low-potential heat, heating or cooling remote objects, and for uniformly distributing heat over a large surface area of heat sinks.

The problem of a fully developed turbulent flow and developed heat transfer was solved numerically at a Reynolds number ranging from 5 × 10⁴ to 2 × 10⁵ for a spatially periodic model of a one-sided ribbed channel as a prototype of the flow path of an internal convective cooling system for a gas turbine blade. The flow and heat transfer were investigated at the Prandtl number of 0.7. The channel has a rectangular cross-section with an aspect ratio of 1.5. Square ribs with a 10% rib-to-channel height ratio are installed on one of the wide channel walls at an angle of 45° to the longitudinal axis of the channel. To quantify the effect of ribs on the flow and heat transfer, the integral parameters, such as hydraulic resistance factor and Nusselt number determined from the grid-converged solutions, are compared with the integral parameters for a fully developed flow and heat transfer in a smooth channel predicted by the same numerical method. The results of numerical simulation for the ribbed channel are also compared with published experimental data obtained under partly similar conditions. The predicted hydraulic resistance factor agrees well with the experiment. The predicted heat transfer agrees with the experiment within 11%, but the trends in heat transfer with increasing Reynolds number obtained using numerical and physical simulation are different. This difference may be caused by the fact that fully developed heat transfer could not be attained in the short experimental channel. Analytical power-law dependences on the Reynolds number are obtained for the hydraulic resistance factor and the Nusselt number pertaining to all channel walls and only to the ribbed wall. It is pointed out that the hydraulic resistance factor depends weakly on the Reynolds number, which is typical for local resistances, and the dependences for Nusselt numbers corrected for the specifics of the problem are close to the dependences for near-wall layers and flows in smooth channels.