Thermal Engineering最新文献

It has been shown that complex processing of hydrothermal brines from the Berikei geothermal field can be highly effective. The development of the deposit’s resources can be carried out in two stages. At the first stage, it is proposed to organize the production of chemical compounds based on self-flowing brines. After developing the technology for extracting chemical components from brine, it is recommended to move on to the second stage: implementing an integrated technology for utilizing thermal energy with the subsequent extraction of chemical components from the cooled brine. This technique allows one to use all the resources of the field. The thermal energy of the geothermal brine is recovered in a greenhouse and a geothermal steam-gas power plant (GSGP), which includes units of a binary geothermal power plant (GeoPP) and a gas turbine power plant (GTPP). In a binary GeoPP, the low-boiling working fluid is heated to a higher temperature by removing heat from the geothermal brine. Further heating of the working fluid to the evaporation temperature and its evaporation and overheating are carried out by the heat of the GTPP exhaust gases. The construction of a GSGP will allow for uninterrupted and autonomous supply of electricity to the entire complex. The development of all hydrothermal resources of the Berikei deposit will make it possible to annually obtain 2000 t of lithium carbonate and, thereby, provide a significant part of the needs of Russian industry as well as produce more than 580 000 t of table salt, which will solve the problem of import substitution of this product.

When designing new nuclear power plants, it is important to ensure cost-effective electricity production while complying with safety, reliability, and environmental protection requirements. One of the directions for solving this problem is to improve the equipment of nuclear power plants, in particular the search for the most suitable technical solutions for regenerative high- and low-pressure heaters (HPH and LPH) of steam turbine units (STU). Optimization of water subcooling to the saturation temperature of the heating steam (hereinafter referred to as subcooling) in the STU regeneration stages makes it possible to increase the power of the power unit or reduce the metal intensity of the heaters, depending on the expected economic indicators of the nuclear power plant, which leads to a reduction in the estimated cost of generated electricity. Unification of heaters will make it possible to simplify the processes of design, manufacturing, repair, and transportation of serially produced heat-transfer equipment, improve the layout of the turbine building, and reduce equipment development costs. The article presents the results of calculations of the technical and economic indicators of the heat-transfer equipment of the STU regeneration system type K-1200-6.8/50 LMZ, and draws conclusions about the possibility of finding a preferable solution based on the criterion of annual economic effect. A special feature of the methodology used is the determination of the most appropriate values of water subcooling in surface heaters of the STU regeneration system depending on operating conditions, the situation on the electricity and equipment market, as well as economic policy. The possibility of increasing the economic efficiency of the power unit by optimizing the weight and size characteristics and unifying the heat-transfer equipment of the regeneration system is shown. An additional economic effect can be obtained by using chamber-type heaters in a horizontal design, combining two heating stages in one housing. A promising layout option is that in which the entire LPH group is represented by unified surface-type devices in a horizontal design located in the condenser hood of a half-speed STU.

The article presents the results of new investigations into possible loss of cooling of spent fuel assemblies (FAs) stored in near-reactor spent fuel pools of BWR and VVER reactor plants (RPs). The experiments were carried out in 2022 on the ALADIN installation (Germany, a BWR type RP) and the “Reflooding test bench” installation (Russia, a VVER type RP). In comparing the experimental data obtained on different test benches, it was noted that the thermal-hydraulic processes that were observed during water boiling, cooling, and subsequent heat-up of fuel assemblies had similar patterns for the above-mentioned reactor types. By using the KORSAR/GP computer code, posttest calculations of experiments were carried out, the results of which were compared with the basic experimental data on the maximum fuel rod temperature and water level. Good agreement between the calculated and experimental results was obtained. Deviations of the calculated data from the experimental results were estimated with respect to the water boiling onset and fuel rod heat-up onset moments, the moment at which the fuel rod temperature reaches its maximum value, and its absolute values. The obtained results can be used for validating thermal-hydraulic codes, substantiating their applicability, and for performing safety analysis under the conditions of accidents involving loss of spent fuel pool cooling at NPPs with VVER/PWR reactor plants.

The findings in application of laser diagnostic systems for the investigation of wet steam flows in flow paths of steam turbines, specifically, in channels of various configurations, are reviewed. The experimental results accumulated over more than a decade enabled the authors to generalize and formulate the essential features of the movement of coarse erosion-hazardous droplets downstream of turbine cascades and in interblade channels. The regions with liquid phase particles are found using the data of visual analysis. The results of application of the particle image velocimetry/particle tracking velocity (PIV/PTV) methods, which implement algorithms for determining vector fields of particle velocities, are presented. The features of the distribution of kinematic characteristics of the liquid phase in various regions of turbine cascades, which affect the erosion wear rate, are discussed. Data are presented on the effect of the blade profile on the formation of trajectories of droplet flows, and methods for improving the separation ability of a blade operating in a wet stem flow are proposed. Using the experimental database on liquid phase velocity fields in turbine channels of various configurations, a semiempirical model of the flow of large erosive-dangerous droplets is formulated. It describes their movement in a cocurrent steam flow and interaction with the walls of the interblade channels. A review is presented of engineering solutions that were obtained on the basis of theoretical and experimental studies of wet steam flows using laser diagnostic systems. The concept of blade surface heating, heating steam jet injection, and optimization of the in-channel separation system is examined. The principles are formulated for the development of approaches based on laser flow diagnostic systems in the field of application of neural networks, which should considerably extend the capabilities of experimental studies since they offer the potential for increasing the amount of data obtained by implementing such experimental methods.

Heat load prediction is crucial to the heat regulation of district heating systems (DHS). In heat load forecasting tasks, deep learning can frequently achieve more accurate model building. A deep learning algorithm, the temporal convolutional network (TCN), has been used for DHS heat load prediction. However, there are many hyperparameters for TCN. Manually tuning the TCN parameters cannot make the model have good performance. This study presents a hybrid method based on sand cat swarm optimization (SCSO) and TCN. The SCSO is used to optimize the hyperparameters (number of filters, filter size, dropout rate, and batch size) of TCN. To verify the effectiveness of SCSO-TCN, another two hybrid models, particle swarm optimization with TCN and the sparrow search algorithm with TCN, are established for comparison. The historical heat load data of three heat exchange stations in Tianjin is utilized for the testing experiments. The findings demonstrate that SCSO-TCN has higher predictive accuracy and better generalization ability than the PSO-TCN and SSA-TCN models.

The results of experimental studies on the creation of highly efficient designs of vibration-isolating compensators for pipelines with liquid are considered. It is noted that the only way to evaluate the effectiveness of various compensators in reducing vibration at different frequencies currently is to compare their transient vibration stiffness or transient mechanical impedance, which were measured on special stands at a given frequency. The stiffness of the compensator increases significantly with increasing frequency vibrations. Hazardous frequencies may vary between piping systems. For this reason, it is impossible to set an integral criterion for the effectiveness of a vibration-isolating compensator, similar to static stiffness. The results of measurements carried out on a special stand on the transitional vibration stiffness of a new design compensator with thin-layer rubber-metal elements (TRME) are presented. The rigidity decreased by 10 or 100 times or more in the frequency range from 50 to 800 Hz relative to the rigidity of a serial compensator based on rubber cord casing (RCC), including in the presence of water inside it. It has been experimentally shown that the vibration-isolating ability of the same compensator as part of a pipeline system, determined by the value of the dynamic force transmitted by the compensator to the pipeline from the pump, significantly depends on the presence of water in them and its flow, which is not taken into account in known methods. The results of testing compensators with RCC and TRME with a bore diameter of 80 mm as part of a stand with a ring pipeline system, a pump, systems for monitoring the flow of the working fluid, vibrations, pressure pulsations, and dynamic (vibration) forces transmitted by the compensators to the pipeline are presented. In a stand with pipelines, the efficiency of vibration-isolating compensators with TRME is still 10 and 100 times higher than compensators with RCC in the absence of water and decreases by an order of magnitude in the presence of water without its flow when the pump is vibrated by a vibrator. Efficiency decreases even further if water flows through expansion joints and pipelines while the pump is running.

A noniterative implicit method for solving the discrete conservation equations of the KORSAR/GP computer code (hereinafter referred to as KORSAR) two-fluid model is presented. The KORSAR/GP code has been developed jointly by specialists of the Federal State Unitary Enterprise Aleksandrov Research Institute of Technology (NITI) and the special design bureau OKB Gidropress. In 2009, the code was certified at the Federal Service for Environmental, Technological, and Nuclear Supervision (Rostekhnadzor) as applied to numerical safety assessment of VVER-type power reactor plants. The code uses the semi-implicit numerical scheme, which limits the integration time step by the Courant condition with respect to the velocity of a two-phase flow. To cut down the time it takes to calculate prolonged transients in reactor plants, an implicit numerical method, which does not limit the time step by the Courant condition, has been developed on the basis of the SETS (stability-enhancing two-step) method. It is based on the semi-implicit scheme. Prior to its application, discrete phase momentum conservation equations with the convective terms written in implicit form are solved at each time step. After the semi-implicit step, the specific (per unit volume) mass and energy of the phases, which are donor quantities in the convective terms of the transport equations, are calculated at the new time layer. Unlike the SETS method, the implicit method developed for the KORSAR code employs a semi-implicit scheme with linearization of unsteady terms describing the change in the specific mass and energy of a two-phase flow. This approach enables us to solve discrete equations in a noniterative manner. However, the implementation of this procedure requires that the unknown scalar variables, such as the phase specific enthalpies, the vapor volume fraction, and the pressure, be determined in the computational cells. Therefore, the semi-implicit scheme with linearization of unsteady terms with recalculated donor quantities at the end of the time step is reused. The performance and effectiveness of the developed implicit method have been confirmed by solving, using the KORSAR code, a test problem of a two-phase flow in a heated horizontal tube driven by a pressure difference.

The problem of friction and heat transfer in a laminar, transition, or turbulent flow along solid permeable surfaces has been solved using a numerical simulation technique. To derive a compact mathematical description intended for engineering applications in the power industry and other thermal processes, a modern version of the Kolmogorov–Prandtl model with one differential equation (namely, the turbulent kinetic energy conservation equation) was employed. The mathematical model is represented by a system of first-order nonlinear ordinary differential equations for the distributions of flow velocity, friction stress, temperature, turbulent energy, and turbulent energy flux density across the film thickness. The problem of singularity of the mathematical description on a solid wall is discussed. The integral hydrodynamic and thermal characteristics of film flows currently receiving a lot of interest, such as the film Reynolds number and the Stanton number, were obtained. Functional correlations among dimensionless parameters that are relevant for engineering applications, including those for special regimes of film flows with recirculation and mass crossflow on permeable surfaces of structural materials, have been established. The film Reynolds and Stanton numbers are defined as functions of dimensionless parameters at which the relative values of the film thickness, acting forces, and mass crossflow are specified. The obtained correlations can be used in the design and optimization of condensation and steam-generating facilities in the power industry, for elaboration of evaporative coolers for high-stress structural elements in gas turbine and rocket equipment, simulation of hydraulic roughness, and in thin-film materials technologies.

The use of condensing heat exchangers (CHEs) in gas-fired boiler units helps cool the flue gases below the dew point. One of the issues that has to be settled in the case of CHEs installed downstream of boilers is to ensure that the flue gas removal stacks will operate without steam condensation on their inner surfaces. To protect smoke stacks against hydrate corrosion, bypassing of part of combustion products not cooled in the CHE is mainly used in practice. The article presents the results obtained from computations of the heat-transfer processes in the combustion products cooled in a CHE as they move in a reinforced concrete smoke stack fitted with clamped lining, which is protected against hydrate corrosion by bypassing. The computations are carried out for three operation modes of the 180-m high smoke stack, through which flue gases are removed from three power-generating boilers of the BKZ-420-140 NGM type installed at the Samara combined heat and power plant (CHPP), a branch of Samara PAO T Plus. The peculiarity and complexity of the computations are connected with the fact that that the flue gas’s thermophysical parameters and motion velocity in the smoke stack vary during the flue gas cooling process. The parameters’ variation pattern depends essentially on the fraction of gases directed in bypass of the CHE. A mathematical model and computer program are developed for computing the heat-transfer processes in flue gases moving in the smoke stack with CHEs installed downstream of the boilers and with the smoke stack protected against hydrate corrosion by the bypassing method. It has been determined that, for a 180-m high three-layer reinforced concrete smoke stack operating at an outdoor air temperature of –30°С and boilers operating at the nominal load, the fraction of bypassed gases makes 30–35%. With the boilers operating at partial loads equal to 75 and 60% of the nominal value, the fraction of bypassed gases makes 35–40 and 40–45%, respectively. The use of condensing heat exchangers in boiler units results in that the levels of temperature difference, free temperature deformation, and thermal stresses in the smoke stack’s structural elements are reduced by a factor of 1.33–2.80 depending on the fraction of gases passed through the CHEs, thereby enhancing the flue gas removing smoke stack performance reliability.

The active development of the Arctic and the Northern Sea Route determines the importance of the rapid development of energy-supply systems for remote regions. A key component of isolated power systems are low-power energy sources. The high cost of fossil fuels in remote regions, coupled with tightening environmental regulations, brings to the fore the challenge of implementing carbon-neutral energy generation technologies. Promising power plants, the performance of which is little dependent on weather conditions, and whose operation is not associated with the generation of greenhouse gas emissions, are low-power nuclear power plants. Currently, some countries are developing and implementing new types of reactor plants whose electrical power does not exceed 300 MW: according to the IAEA, there are more than 70 different projects. Modularity, versatility (in addition to power generation, many projects also provide for the production of thermal energy and hydrogen), increased compactness, and lower capital costs for construction compared to traditional high-power power units make it promising to create low-power reactor plants. This review presents an analysis of the current state of the problems in the design and implementation of such power plants. The technical level of domestic and foreign projects of small modular reactors (SMR) was assessed. Promising areas for the use of thermal energy from small modular installations have been identified, taking into account current trends in energy, including low-carbon and nuclear-hydrogen areas. Possible circuit solutions for the production of electricity based on advanced cycles, including the use of nontraditional working fluids, have been studied. The potential for commercialization of low-power nuclear power plant projects has been considered; the question of successful business implementation of power plants of this type remains open.