Thermal Engineering最新文献

Considerable progress has been made by now in developing mathematical models, algorithms, and available computational tools for simulating heat and mass transfer processes. Advanced approaches yield detailed information on various characteristics of mass transfer in two-phase fluids, in particular during film condensation of vapors. Models developed by various teams are implemented in CFD-codes (ANSYS Fluent, OpenFOAM, Star-CCM+, etc.). To check existing models and select the best one, cross-verification of models and algorithms implemented in various CFD codes and their verification against available and reliable experimental data are needed. In this paper, cross-verification of the VOF (Volume of Fluid) model and the algorithms implemented in the author’s ANES code was carried out against the problem of vapor condensation on a single tube. The calculations were performed using the ANES and ANSYS Fluent CFD-codes. The predictions by the ANSYS Fluent code have been demonstrated to depend on the settings of the algorithms for solving the conservation equation for the liquid volume fraction. Recommendations are presented for setting this code to obtain better agreement of the predictions with experimental data and theoretical relationships. The ANSYS Fluent code was used for two-dimensional simulation of refrigerant-21 condensation in a small tube bundle. Characteristics of the tube bundle (bank) were equal to those of the tube bundle used in the experimental setup of the Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences (tube diameter = 16 mm, transverse tube bundle pitch ({{S}_{1}}) = 26 mm, longitudinal tube bundle pitch ({{S}_{2}}) = 15 mm). Condensation of saturated vapor having a saturation temperature of ({{T}_{{sat}}}) = 333.15 K and arriving at the tube bundle at a velocity of up to 1.2 m/s was studied. The predictions demonstrate qualitative and quantitative agreement with the experimental data.

Assessment, monitoring, and prediction of the technical condition of gas turbine unit (GTU) assemblies and components are among the key matters that have to be dealt with during the operation of GTUs. In this connection, various prediction systems that use statistical, experimental, and calculated data on the change in the axial compressor (AC) characteristics resulting from the occurring erosion are becoming of great demand. The article describes an approach to the development of models of erosively worn blades on the basis of freely accessible statistical data on the failures of units as a consequence of a blade compressor’s erosion. The article also proposes a body of mathematics for specifying the blade wear degree, introducing the change in the eroded profile chord, and considering the wear nonuniformity along the blade height. The statement of the problem of numerically studying how the erosion degree and pattern affect the compressor stage performance parameters is described. The outcomes from intermediate studies on comparing different geometrical models of erosion are presented along with assessment of their applicability for flow computations in elaborating a prediction model. The results of computations of a transonic compressor stage have been obtained for different erosion wear degrees of its blading in a wide range of operation modes, and the revealed degradation pattern of the stage integral and local characteristics is analyzed. It has been found from analyzing various erosion wear degrees for the stage considered that, if there is an erosion wear, the compressor pressure ratio may drop by up to 3.31%, the ratio of temperatures by up to 1.55%, the adiabatic efficiency by up to 1.15% (abs.), and mass flowrate at the stage choke line up to 1.26%. With decreasing the rotor rotation frequency, the wear influence decreases, and the change in integral characteristics do not exceed 0.10% for the isodrome (a constant rotation frequency line) 70%. The article briefly outlines possible methods for analyzing the results for constructing the correlations between the erosion wear degree and the change in the compressor integral characteristics and also promising lines for development of studies.

A numerical analysis of the experiments addressed to studies of hydrodynamic processes in a horizontal steam generator has been performed using the STEG (STEam Generator) code. The main components of the experimental model include a staggered tube bundle, a submerged perforated sheet (SPS) with baffles, and a downcomer. An air–water mixture was used as a two-phase fluid. The working fluid flow in the model was driven by natural circulation induced by air supply to the lower, middle, and upper sections of the tube bundle. The gas void fraction was measured by the γ-radiography method. In addition, pressure drops along the height of the tube bundle and water levels in the model and above SPS were also measured. Each experiment was performed at a prescribed air load on the evaporation surface and water level in the model. The STEG code was developed at the Department of Nuclear Power Plants of NRU MPEI to model thermohydraulic processes in a horizontal steam generator. The mathematical model is based on a two-fluid approach to the description of a two-phase flow using balance mass, momentum, and energy conservation equations and semiempirical closing correlations for interfacial interactions and interactions with various surrounding structures (tube bundle, walls, etc.). The STEG code was used to perform calculations for nine experimental regimes differing in the perforation ratio of the submerged perforated sheet and the supplied air flowrate. The qualitative regularities of the two-phase air–water mixture circulation in the model of a horizontal steam generator and the effect of experimental values of the main parameters on the circulation have been established. Quantitative results of comparison of the predictions with the experiment demonstrate their good agreement since the relative errors in the predicted air void fractions and pressure drops do not exceed 10%.

Conversion of solar radiation into steam is presently one of the trends in “green” energy (solar thermal energy), ecology, and clean water production. For the first time, a study of the heating and evaporation of a rotating graphene nanofluid under the influence of radiation from a solar simulator was carried out. The influence of various factors on these processes, including the direction of irradiation, graphene concentration, and liquid rotation speed, is considered. It has been shown that the evaporation rate significantly depends on the graphene concentration and the method of irradiation of the samples. When samples are irradiated from the side, as the graphene concentration increases, the average evaporation rate increases and reaches a maximum value and then decreases. When samples are irradiated from above and the liquid–air interface is in direct contact with the incident radiation, only a decrease in the evaporation rate is observed as the graphene concentration increases. In this case, heating of graphene also depends on the method of irradiating the sample. When in direct contact with radiation, graphene is heated to a high temperature, while in the bulk it is heated less efficiently than the base liquid (distilled water). It has been shown that the rate of evaporation from the surface of a rotating graphene nanofluid and the temperature of its volume significantly depend on the rotation speed. Of all the samples studied, a graphene nanofluid with a volume concentration of 0.5% is heated most efficiently. The use of thermal insulation can improve heating by approximately 5%. An analytical calculation of the profile of the interfacial surface is presented and its area is determined at different speeds of rotation of the liquid. Some effects that arise during the rotation of a graphene nanofluid and their influence on the parameters of hydrodynamics and heat and mass transfer, which is important for fundamental and applied energy problems, have been identified.

The results of an experimental study into the features of the process of coolant flow formation in the inlet section of the fuel assembly (FA) of the core of a RITM-type reactor of a small nuclear power plant (SNPP) are presented. The purpose of the work is to evaluate the influence of different design elements of the inlet section on the formation of coolant flow. To achieve this goal, a series of experiments was completed on a research aerodynamic stand with an air working environment using a large-scale experimental model, including structural elements of the FA inlet section from the throttle orifice to the fuel rod fastening unit to the diffuser, as well as a fragment of the fuel rod bundle between the absorber and spacer grids. The studies were carried out using the pneumometric method and the method of injection of a contrast admixture in several sections along the length of the model. Measurements were made over the entire cross section of the model. Features of the coolant flow are visualized by cartograms of the axial flow velocity of the working medium and the distribution of admixture in the cross section of the model. The research results were used by specialists from the design and calculation departments of OKBM Afrikantov to substantiate engineering solutions when designing new cores of RITM reactors. The results of the experiments were collected into a database and used in the validation of the LOGOS CFD computer program created by employees of the All-Russian Research Institute of Experimental Physics and the Institute for Theoretical and Mathematical Physics of Moscow State University as analogues of foreign computer programs of the same class, which include ANSYS, Star CCM, etc. Experimental data were also used when validating one-dimensional thermal-hydraulic codes used at OKBM Afrikantov in substantiating the thermal reliability of reactor cores. The thermohydraulic code CANAL is also included in this class of computer programs.

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.