Thermal Engineering最新文献

Abstract—An analysis of the relationships for calculating the thermal properties of liquid lead (hereinafter referred to as lead) was carried out, and the method for determining its heat capacity over a wide range of temperatures, including at high values, was chosen. This is especially important for numerical studies to justify the safety of designed reactor installations with liquid metal coolants, such as BREST-OD-300 and BR-1200. Measuring the properties of lead at temperatures close to the boiling point is often difficult due to the lack of reliable methods and materials that can withstand temperatures above 2273 K. At present, theoretical approaches to calculating the properties of simple liquids based on phonon theory are being actively developed. Such approaches can be used to derive semiempirical relations for the heat capacity of liquid lead that would allow physically correct extrapolation of the data to the high-temperature region. In this regard, the aim of this work is to obtain a relationship for calculating the heat capacity of liquid lead from its melting point to its boiling point based on modern theoretical approaches. To achieve the set goal, the following tasks were solved. Firstly, an analysis of the works of various authors was carried out and empirical formulas were selected that make it possible to reliably calculate the heat capacity at a constant volume c_v (isochoric heat capacity) for a lead coolant from the melting point to 1500 K. Secondly, based on them, using phonon theory, an approximating formula was constructed, thanks to which it is possible to physically correctly extrapolate the properties of lead to the boiling point (2022 K).

An analysis is performed of the phosphate water chemistry of a high-pressure drum boiler. In Russia, water chemistries with purely phosphate alkalinity and phosphate-and-alkali water chemistry are now mainly used at power plants equipped with drum boilers. One of the main quantitative parameters determining the maintenance of phosphate water chemistries is the ratio of sodium and phosphate concentrations. Calculated dependences of the ratios of pH, the concentration of phosphate, and the sodium-to-phosphate concentration are given. A relationship is found between such ratios and the domains where acid–phosphate corrosion, the hydrogen embrittlement of metal, and alkali cracking occur. It is shown that at concentrations of phosphate below 2.5 mg/dm³, the chloride and sulfate concentrations in boiler water must be monitored to avoid the hydrogen embrittlement of metal. Dependences are presented for the pH and sodium-to-phosphate concentrations at different temperatures. Results are presented from industrial tests of purely phosphate alkalinity water chemistry during the startup and normal operation of a boiler. Analysis of the chemistry of a high-pressure drum boiler water shows that the concentration of phosphate in the pure compartment of a drum has almost no effect on the pH, but the concentration of phosphate in the drum’s salt compartment affects it strongly. Attention should therefore mainly be given to the pH prescribed by the relevant standard when managing the water chemistry in the pure compartment. It is shown that phosphate hideout is often observed when starting power units equipped with high-pressure boilers, so mono- and disodium phosphate solutions are used to maintain the pH and concentrations of phosphate. An analysis of the quality of boiler water during a startup shows there was a drop in the concentration of phosphate in the boiler water and a rise in the sodium-to-phosphate concentrations, so a hideout occurred. The possibility of identifying deviations when monitoring phosphate water chemistry is thus demonstrated, based on an analysis of sodium-to-phosphate ratios of concentrations.

Based on modern theoretical knowledge and the results of representative experimental studies, the phenomenology of reflooding of fuel assemblies is considered. The parameters (test section pressure, water subcooling, peak cladding temperature at the start of the flooding, bundle power, etc.) maintained in the experiments under consideration are close to those expected when implementing measures to manage hypothetical severe accidents at pressurized water reactors. A list of processes accompanying the reflood of fuel-rod assemblies has been formulated, and specific effects have been established that can lead to a change in the local conditions of heat exchange between the cladding of fuel-rod simulators and the steam-water mixture and affect their quenching. A comparison of the results of experimental studies showed the influence of cooling water flow rate on the spread of measured values of quench time in the upper part of the fuel assembly. The view of reflood physics allowed us to analyze the results of validation of the SOCRAT code in experiments of varying phenomenological complexity (in an intact core, with an intense steam-zirconium reaction, formation of a melt). The analysis showed that the SOCRAT code correctly predicts the temperature histories of the fuel-rod simulator claddings, the quench time, and the total mass of hydrogen released during the experiment with a tendency toward slight underestimation; the modeling results do not contradict the experimental data. During validation, it was established that the thermal hydraulics model makes the greatest contribution to the assessment of the model error in calculating the quench time and the total mass of hydrogen production when modeling experiments of varying phenomenological complexity. Good predictive capabilities of the SOCRAT code confirmed the applicability of a one-dimensional approach to modeling the reflooding of fuel assemblies.

In designing turbine blade/vane cascades, predicted or experimental distributions of flow parameters, which may differ considerably from the operating conditions of a real turbine, are often used as the boundary conditions. This difference in boundary conditions may lead to inaccuracy in the predicted performance of the entire turbine. In multistage gas turbines, the second stage operates with inlet conditions formed in the cooled and transonic first stage. Therefore, the radial distributions of flow parameters at the inlet to the next stage are considerably nonuniform. This leads to elevated total losses, including secondary losses. The effect of the degree of nonuniformity in the inlet flow parameters on the structure of secondary flows within the stator vane of a low-pressure turbine (LPT) is studied in this paper. In particular, computational and experimental studies have revealed that significant radial nonuniformity of flow parameters (especially of the total pressure) at the inlet to the vane cascade can induce pronounced radial migration of the flow near the convex (suction) surface of the vane cascade in vortex zones at the end-walls of the flow path. In these cases, the application of the standard procedure for averaging flow parameters and processing data from both numerical and experimental studies may yield zones with physically incorrect parameter values depending on the degree of inlet flow nonuniformity at the end regions, where the effect of vortex flows is most pronounced. In particular, narrow regions may appear at the circumference and at the hub where the local total pressure at the outlet exceeds the total pressure at the inlet. This procedure for processing of the calculated data technically results in “negative” values in the radial distributions of the loss coefficient in these areas (“virtual” losses). It has been demonstrated how redesigning of the cascades in the upstream high-pressure turbine (HPT) can reduce the nonuniformity of parameters and increase the efficiency of the LPT.

Structural endurance testing of rotor blades is the most important stage of perfecting newly developed blade systems for gas turbine units (GTUs). Obtaining the values of a blade’s structural endurance (fatigue) limit allows designers to evaluate the vibration reliability of a GTU’s blade system. Experimental data also provide an opportunity to verify calculated models of blades. Specialists at the Power Machines company are now working on a line of new GTUs that includes the GTE-170 gas turbine unit. The rotor blades of the GTE-170 unit’s axial compressor and gas turbine, manufactured according to original equipment design documents, are currently being studied for structural endurance on the TsKTI Research and Production Association (NPO) fatigue testing stand. Blade vibration is excited on the stand by applying a variable-frequency electromagnetic field to the area around the tip of a blade. The blade’s limit of structural endurance is determined proceeding from the readings from strain gauges glued in the zones of maximum vibration stresses. Fatigue tests of more than 300 blades used in 14 stages of axial compressors and four gas turbine stages have been run on the stand. The resulting data show that the rotor blades of the GTE-170 unit’s axial compressor and gas turbine have high vibration reliability. Based on results from comparative fatigue tests, it has been determined how replacing the grade of steel and redesigning a blade’s profile affect its vibrational strength. Stand test results have confirmed the need to perform experimental studies of the structural endurance of both newly developed and updated blades when changing their material and redesigning their profiles.

Thermal energy is one of the main sources of anthropogenic greenhouse gas emissions. To fulfill Russia’s obligations to reduce greenhouse gas emissions under the Paris Climate Agreement, it is planned to focus in the energy sector on the development and implementation of cleaner technologies for the use of energy fuels, hydrogen and hydrogen-containing mixtures, the decommissioning of obsolete equipment, and the accelerated introduction of new efficient energy plants. As part of the study, an assessment was made of the real possibilities of decarbonization of the Russian heat and power industry through the implementation of priority measures provided for in the Strategy for the Socio-Economic Development of Russia with Low Greenhouse Gas Emissions until 2050. For this purpose, a comparison was made of the carbon intensity of various technologies for generating electrical and thermal energy, taking into account the type of thermal power engineering enterprises and the efficiency of power steam turbine, gas turbine, and combined-cycle gas plants burning various types of fuel. Possibilities for reducing CO₂ emissions were assessed due to improving the quality of solid fuel, the transition from burning coal to burning natural gas, the introduction of combined-cycle gas plants, increasing the efficiency of power plants, decommissioning obsolete equipment, and the use of hydrogen-containing gases and pure hydrogen as fuel.

The need to adapt the world’s industry and economy to constantly tightening climatic standards, as well as a constant growth of energy consumption, facilitate the development of carbon-free electricity generation technologies. Renewable energy and nuclear power plants are referred to energy sources having almost zero carbon dioxide emissions into the atmosphere. However, in view of an insufficient amount of renewable energy resources near large electricity consumers, NPPs play the most important role in the potential transition to the carbon-free economy of Russia. However, they do have certain drawbacks, such as comparatively low energy efficiency, poor maneuverability, and also high specific capital outlays. Combined use of nuclear and fossil fuel may become one of ways for partially removing these drawbacks. The article addresses a thermodynamic analysis of using fossil fuel at an NPP in an external steam superheater with subsequently expanding a part of the steam in a high-temperature turbine. A process circuit solution is proposed whose use makes it possible to obtain an expanded power unit load adjustment range. It has been shown from thermodynamic analysis results that, by subjecting a certain amount of steam from the steam generator to external superheating, it becomes possible to increase the nuclear power unit’s power output and efficiency: the maximal increase in the electric power output can total 338, 382, and 426 MW and that of net electrical efficiency of 0.73, 1.08, and 1.43% at steam superheating temperatures equal to 560, 600, and 640°С, respectively. The hybrid unit employing nuclear and hydrocarbon fuel that operates according to the proposed process cycle circuit includes a smaller amount of main equipment and features wider load adjustment ranges in comparison with standalone NPP and steam turbine thermal power plant: 102.3–132.7, 103.0–136.9, and 103.6–141.2% with respect to the reference process cycle circuit at steam superheating temperatures equal to 560, 600, and 640°С, respectively.

Cycle chemistry monitoring systems are intended for online comprehensive automatic monitoring, analysis, diagnostics, and prediction of the water chemistry in power equipment in all regimes of its operation, including startups and shutdowns, as well as for remote automatic control of one or several processes in the serviced process facility. Basic requirements for cycle chemistry monitoring systems are formulated. Mathematical models, which are based on the material balance, ionic composition of the coolant, and recurrent neural networks, have been developed and studied. They enable us to predict the concentration of impurities along the power unit’s path to prevent failures of the water chemistry. An algorithm has been developed for online quality assessment, based on dimensionless coefficients that provide fair information on the water-chemistry conditions and help to detect failures affecting the water chemistry. A simulation model with a user interface has been developed based on a set of algorithms considering the requirements for cycle chemistry monitoring systems, such as visualization, interactivity, reporting, customization, scalability, continuity, and simplicity. The model facilitates the activities performed by the operational personnel of power plants as to decision-making and prevention of failures of the water chemistry of the power unit, enables us to monitor the process parameters of the power unit in real time, analyze statistical data, predict parameters using algorithms on the basis of the material balance, ionic equilibriums, and neural networks. A user manual has been prepared to help one to understand the program interface. The manual contains a brief description of the system structure, including information and diagnostic functions, basic elements of the mnemonic diagram, and a set of control buttons.

Numerical modeling of the thermal state of the T283-1600 thyristor with various radiators, on the surface of which boiling of the 3M Novec 649 liquid dielectric occurs, was carried out. Calculations were performed in the “in-house” CFD code ANES. Heat-transfer coefficients for nucleate and transition boiling, as well as critical heat flux, were calculated using the formulas of  V.V. Yagov. The change in boiling mode from nucleate to transition was carried out with equal heat flux calculated using the corresponding formulas: approximately 110 kW/m², which is 17% lower than the critical heat flux predicted by Yagov’s formula for technically smooth surfaces. This led to slightly higher calculated temperatures of radiators on surface fragments with a transient boiling regime compared to temperatures during nucleate boiling over the entire cooling surface. The proportion of the surface area covered by the transition boiling regime did not exceed 3.2% of the total radiator area. Various forms of radiators were studied: in the form of fins from several disks and rectangular parallelepipeds with vertical slotted channels. At the same time, the geometric parameters of the fins and channels and their number and dimensions of the radiators were varied. As a result of numerical optimization, a radiator design was determined that meets the required conditions for the maximum temperature of the thyristor on the surface of contact with the radiator. To validate the results of numerical modeling, an experimental setup was created containing an assembly of thyristors with radiators immersed in a 3M Novec 649 dielectric. In normal operation, measuring the temperature of one of the radiators near the contact with the thyristor showed good agreement with the results of numerical simulation.