Thermal Engineering最新文献

Results are presented of the experimental investigation into peculiarities of the coolant flow in a fuel-rod bundle of a fuel assembly in the RITM reactor of the retrofitted floating power unit. The purpose of this study was to experimentally determine hydrodynamic characteristics of the flow in a fuel-rod bundle of a fuel assembly. The experiments were performed in an experimental facility with air as a working fluid using a model of a fragment of a fuel-rod bundle in a fuel assembly on the basis of the hydrodynamic simulation theory. The experimental model included a bundle of fuel-rod simulators, burnable poison rod simulators, spacer grids simulators, a central displacer, and stiffening angles. Invasive methods, such as the pneumometric method and the method of tracer injection, were employed in the study. The flow features were visualized using axial and tangential velocity maps and the tracer distributions. The experiments revealed the axial flow features and the structure of transverse coolant flows. Three zones are identified in the flow structure: in the region of regular cells, at the central displacer, and at the periphery (near the fuel-assembly casing). The flow velocity in them differs by 25–30%. The arrangement of plates in the grids considerably affects the flow structure at a distance greater than L/d_h ≈ 10.0. The found flow features should be taken into account in substantiating the thermal reliability of new cassette-type cores using cellular thermohydraulic codes. The procedure of thermohydraulic calculation in cellular thermohydraulic codes should be revised to increase the number of types of calculation cells and to consider the flow maldistribution among the regions in a fuel-rod bundle and the cell types.

The problem of deep purification of industrial gases of various impurities is urgent. Two-phase turbomachines with bulk condensation of the impurity in the flow path are proposed as an alternative to the known methods (i.e., adsorption and absorption technologies). The study is devoted to numerical simulation of the process of bulk condensation in the flow path of a radial-type refrigeration turbomachine, which is controlled by changing the initial temperature of the flow. The calculations were performed for a mixture of air as an incondensable gas carrier and carbon dioxide as an impurity. It has been demonstrated that the process of bulk condensation proper and its depth (the actual range of operating conditions) can be controlled by changing the gas mixture temperature at the stage inlet. The conditions have been determined at which the process is localized predominantly in the impeller channels that is the safest regime from the standpoint of the risk of erosive wear and subsequent damage to the stage elements. For the first time, the reduction in the isentropic efficiency per percent of the degree of condensation, should it occur, was numerically estimated for refrigeration turbomachines. The obtained data are close to the values for wet steam turbines presented in the literature. A procedure for calculating the characteristic and analyzing the results has been developed. It yields the optimal regimes using a multicriteria search with the requirements for the region where the phase transition should occur, and for the radius of the particles. It is shown that increasing/decreasing the stage inlet temperature may be insufficient to meet the specified requirements for the degree of condensation and isentropic efficiency offering deep purification of gases of impurities. Therefore, assessment is required as to whether the process rate can be controlled by changing the expansion ratio and/or the impeller speed, both individually and in combination.

At the Troitsk District Power Plant (a Branch of PJSC Wholesale Generating Company No. 2), a 660 MW coal fired power unit is in operation. The power unit is equipped with a CLN660-24.2/566/566 condensing steam turbine manufactured in the People’s Republic of China. Among the power unit’s variable operation modes, the steam turbine cooling down modes play an essential role; these modes are of importance when the turbine is shut down for carrying out equipment repairs, because its casing parts cool under natural conditions to acceptable temperatures (150°С), at which thermal insulation can be dismantled from the turbine high-temperature casings, for as long as 170‒200 h. This generates the need to perform forced cooldown, which can be carried out by using steam under load, air, and combination of these two methods, with the last option regarded to be the most effective one. The article presents the result of applying the currently existing technologies for cooling down the combined high and intermediate pressure cylinder. The time taken to accomplish the turbine forced cooldown was estimated by calculation with the use of various techniques, in particular, the finite element method implemented by means of the ANSYS software system. The calculated assessment of the cooldown time was carried out with taking into account the thermally stressed state of the key “critical” components and the steam turbine low cycle fatigue strength.

In elaborating the design of axial flow, screw, and centrifugal pumps, there is a need to know the moment at which backflow at the impeller inlet and flow at its outlet emerge, and also the effect these flows have on the pump power performance characteristics. By using advanced modeling techniques, it is possible to estimate the integral power performance characteristics of turbine machinery; however, they are not applicable for drawing up the balance of losses in an impeller. The article presents two new techniques that can be used to draw up an energy balance in axial flow impellers: a modified S.S. Rudnev technique for the energy balance in an inducer and a procedure for processing the results of numerical computer simulation in the ANSYS CFX software with dividing the flows into active, reverse, and back flow in the inducer at the pump inlet and at its outlet. A comparison is carried out with the procedures for calculating the theoretical head proposed by other authors, and a good qualitative agreement of the calculation results obtained using them is shown. By dividing the flows into an active, reverse, and back flow, we were able to determine the change in their cross-section areas, specific energies, and theoretical heads in the inducer on the entire Q-H curve. For the inducer with a straight leading edge (without trimming) and without taking the clearance into account, the active, reverse, and back flow cross-section patterns near the leading edge are presented. It can be seen on these patterns that backflows emerge earlier than they start to affect significantly the main flow parameters. It is shown that the active flow diameters and cross-section areas vary essentially at different distances from the leading edge. The flow pattern immediately at the leading edge differs from an axially symmetrical one.

The issue of application of neural networks for analyzing the regularities of droplet motion in the interblade channel of turbomachines is examined. The droplet flow in a nozzle cascade was numerically investigated in a wide range of steam flow regimes and liquid phase conditions. The calculations were performed using an experimentally verified model of the liquid phase flow. The theoretical Mach number behind the cascade varied from 0.4 to 0.9, the relative density of the liquid phase from 1800 to 5100, the droplet diameter from 5 to 205 µm, the initial slip coefficient of the droplets from 0.1 to 0.9, and the initial angle between the velocity vectors of steam and droplets from ‒15° to +15°. The effect of various parameters on the characteristics of droplet movement through the interblade channel and droplets deposition on the blade surface was revealed. The numerical simulations yielded an array of approximately 1 million droplets, which was used to train neural networks. Based on the analysis of these data, an algorithm for using neural networks to predict the behavior of primary droplets in a turbine cascade was developed. The algorithm includes two neural networks: the first solves the problem of binary classification to determine the probability of a droplet collision with a blade, and the second predicts the features of droplet interaction with the blade surface. This algorithm was tested against a set of data that had not been engaged in the training but were in the same range of parameters. The test set consisted of three flow patterns with four different droplet diameters. The root mean square error determined for the test data set was 5.2% for the relative coordinate of the droplet deposition point and 1.5% for the dimensionless coefficient of collision energy. Estimation of the calculation time for the simulation has revealed that the algorithm using neural networks runs more than 100 times faster than its closest analogue.

The article considers the effect the gravitational enrichment in single-phase high-density media of natural and man-made origin has on the chlorine content in the coal concentrate obtained. It is pointed out that an increased content of chlorine in the applied fuel can initiate high-temperature hydrochloric acid corrosion of equipment and working surfaces, and also activate the formation of chlorine-containing organic compounds, which pose a serious threat to both the environment and human health. Studies on determining the chlorine content in the initial and enriched coal from the Kalewa field in the Republic of the Union of Myanmar were carried out. It is shown that the chlorine content after the gravitational enrichment of coal with the use of underground natural sodium chloride brines as a heavy medium increases from 0.01 to 0.20%. The chlorine content in the initial and enriched coals from the Tigyit, Kalewa, and Sintaung fields (the Republic of the Union of Myanmar), and from the Safonovo field in the Moscow brown coal basin (Russia) was studied by the method of determining the electrical conductivity of initial and enriched coal aqueous solutions. It is shown that its content in all coal samples did not exceed 0.4%. The possibility of chlorine-containing compounds to emerge and hydrochloric acid corrosion to become activated was estimated. The process of joint thermal destruction of coal and sodium chloride crystallized from the underground natural sodium chloride brine is described, based on which a conclusion has been drawn that sodium chloride does not intensify the chlorine-containing compounds and hydrogen chloride formation processes.

One of the main components of a nuclear power plant with a water-moderated water-cooled power reactor (VVER) is a horizontal steam generator (SG), whose main service is to generate the specified amount of saturated steam, which then enters the turbine. The steam wetness at the SG outlet should not exceed the maximum allowable value so that the elevated moisture content would not lead to erosive wear of the turbine blades. To maintain the required wetness, horizontal steam generators are equipped with a gravity separation system, whose essential component is a submerged perforated sheet (SPS) designed for equalizing the steam load on the evaporation surface. Elaboration of a mathematical model of the gravity separation requires theoretical and practical knowledge about the processes of water droplet formation on the evaporation surface under the dynamic impact of the steam flow. These processes depend crucially on the SPS design. This work included a study of the features of a two-phase flow near a perforated sheet, which was conducted at the Barboter experimental facility, and a numerical simulation of this process using the OpenFOAM code. The experimental facility was a water-filled vessel with transparent walls. Air was supplied into the vessel from the bottom, and an SPS with side flanges was installed in the middle of the vessel. An experiment was carried with a total air flowrate of 30 dm³/min giving a velocity of 0.94 m/s in the perforated sheet holes. Processing of photo and video records of the process yield dimensions of air bubbles moving out of the perforated sheet, the frequency of their formation, and sizes of water droplets and jets at the interface. The OpenFOAM code was used for the numerical study of air discharge through one hole of the perforated sheet with subsequent formation of water jets and droplets at the interface. The predictions demonstrate a good qualitative and quantitative agreement with the experimental values of the main parameters.

This study explores the optimization of supersonic ejector efficiency by investigating key parameters: the total length of the converging mixing chamber and constant area section (s + L), the half angle of the mixing chamber ({{varphi }_{1}}), and the length of the constant area section L. Through computational fluid dynamics (CFD) simulations, the sum of the length of the converging mixing chamber and constant area section was varied between 8D to 10D (D refers to the ejector throat diameter), revealing that exceeding this range negatively impacts both the entrainment ratio ER and pressure ratio PR. Therefore, a length of 8D was chosen for optimal performance. While Engineering Sciences Data Unit (ESDU) suggests a range of 2° to 10° for ({{varphi }_{1}}), our study shows that increasing ({{varphi }_{1}}) beyond 2° results in decreased ejector performance. Performance curves were derived and discussed for ({{varphi }_{1}}) values of 2° to 6°. Additionally, the constant area length was varied from 1D to 5D while maintaining the sum of the lengths of the converging mixing chamber and constant area section at 8D. The study found that a constant area length of 3D best satisfied design requirements, as it provided the highest entrainment ratio while maintaining a suitable pressure ratio within the designed range. These findings underscore the importance of carefully considering these parameters to achieve optimal ejector performance.

Due to its increased energy density, longer lifespan, long cycle life, and quick charging capabilities, lithium-ion batteries (LIBs) have become increasingly popular over the past few years in household appliances, electric vehicles, and in the energy sector, such as for energy storage at thermal power plants. Batteries can be used to store excess energy from solar panels and wind turbines for use during periods of low energy production (at night or on windless days). This increases the efficiency and stability of renewable energy sources. However, LIB is extremely sensitive to temperature, presenting difficulties with thermal management. This study involves the numerical analysis of a 4 × 4 arrangement of LIB cells with immersion cooling and is conducted using three different cooling fluids, including water, mineral oil, and Al₂O₃/water nanofluid. The modelling is carried out using SolidWorks, and thermal analysis is carried out in ANSYS Fluent. By varying the operational and geometrical parameters, their effects on thermal performance were studied. The results show that water and nanofluid work better than mineral oil. At higher discharge rates of 3C and 5C, water and nanofluid limit the average temperature rise of the battery module under 5°C. Varying the flow rates from 10 mLPM to 1.0 LPM showed that the average temperature decreased with an increase in flow rate. When changing the inlet temperature of the battery module from 298 to 308 K, it resulted in increased cell surface temperature and decreased heat transfer. The study shows that with a high flow rate and a low inlet temperature, the temperature rise is minimal even at a higher discharge rate of 5C.

A sampling analysis of the results from examining the metal of 25 heat recovery steam generators (HRSGs) used as part of combined cycle plants (CCPs) installed at 12 power plants in Russia is carried out. In-service examination of the HRSG metal is as a rule carried out during the equipment overhaul. The metal defects revealed during the steam generator diagnostic activities are in most frequent cases damages in weld joints, some of which were left in the steam generator manufacturing or installation stage, while the other ones emerged during the operation. Operational defects include, among others, the thinning of component walls. Factors causing various kinds of metal defects are briefly analyzed. Advanced steels developed outside of Russia are used in some heat recovery steam generators as the structural material for manufacturing the critical components. Assessing the quality of these steels and the stability of their service properties is a top-priority objective pursued in analyzing the HRSG metal state. In the course of activities carried out at the VTI on studying full-scale welded billets made of grade WB36 steel used to manufacture the drums, it has been confirmed that the main service characteristics of this steel comply with the applicable regulatory requirements, and that the steel has satisfactory properties in terms of resistance to low-cycle and brittle fracture. This made it possible to increase the fleet service life of high-pressure drums (HPDs) made of this steel. For high-chromium steels of grades P91 and Di82, the results of representative tests for long-term strength have been generalized and processed, which opens the possibility in principle to estimate the current state of metal and predict the lifetime characteristics of the critical components of heat recovery steam generators.