Thermal Engineering最新文献

This paper explores the effect of varying the number and configuration of internal cooling channels on the thermal performance of gas turbine blades. The findings demonstrate the significance of this parameter for improving blade cooling efficiency. Actually, such a study is lacking in the currently available literature. Therefore, six internal cooling configurations were designed using Autodesk Inventor employing the real turbojet airfoil RS1S. The high-pressure gas turbine rotor blades were designed with an 11° twist angle in order to predict the actual behavior of the blade cooling under operating conditions. A series of numerical tests were carried out by coupling the CAD software with COMSOL Multiphysics. A conjugate heat transfer and computational fluid dynamics model were performed. Convective heat flux (CHF), temperature, Nusselt number, air velocity, Reynolds number, and friction force were evaluated for each studied case. The findings showed that adding a second cooling channel to the trailing edge improved the convective heat flux by 63%. On the other hand, creating a new cooling channel increased the blade’s thermal inertia, leading to a cooling limitation. It was also observed that hot spots on the blade surface can develop as a result of air thermal saturation due to extended residence time in the blade channels. In fact, the blade average temperature decreased by 8% using five disconnected channels rather than five serpentine channels. The blade temperature and CHF were reduced by 16 and 22%, respectively, as a result of adding a third channel in the blade mid-zone. Overall, this paper highlighted the potential for improving blade internal cooling through the careful optimization of the number and configuration of internal channels.

Steam dumps from thermal power plants (TPPs) into the atmosphere are among the most powerful man-induced noise sources. The protection, by means of silencers, against the noise produced by high-pressure steam dumps includes, in the general case, implementation of low-noise throttling and installation of sound-absorbing components. The comparative efficiency of the silencer throttling and sound-absorbing components depends on the location and intensity of physical noise sources, which are determined by the steam dumping pipeline’s operating and geometrical parameters. The use of macroporous modules in steam dump silencers is of significant interest owing to their relative simplicity and good performance. Such modules can be used as continuously operating throttling devices; in addition, they have certain sound-absorption properties. The aerodynamic and acoustic properties of macroporous modules used as part of the silencers of noise produced by the TPP steam dumps are analyzed. The main sources causing noise from the TPP steam dumps are considered, and analytical relations for comparing their intensities are formulated. Proceeding from the performed assessments, methods for protection from the noise produced by steam dumps are suggested, which involve the use of silencers equipped with macroporous modules. In discussing matters concerned with the aerodynamics relating to continuous throttling of gaseous medium in macroporous channels of various shapes, it is shown that correct profiling of channels in coordination with the characteristic pore sizes is important for practical applications. Assessments of sound absorption in a macroporous medium are carried out. Recommendations on shaping the macroporous modules of silencers are given, and methods for calculating their efficiency in solving problems of protection from noise caused by dumping high-pressure steam into the atmosphere are presented.

The Volume of Fluid (VOF) method supplemented with heat and mass transfer models at the interphase boundary is actively employed in the investigation of film condensation and film boiling, in the calculation of evaporators, for predicting the dynamics of vapor bubble collapse in a pool of subcooled liquid, or for other purposes. The original VOF algorithm proposed by Hirt is intended for the simulation of a single-phase incompressible liquid with a free boundary at which a constant pressure is specified. The extension of the VOF-algorithm to a two-phase fluid, especially with mass transfer, is not a common problem from the standpoint of the rigor of mathematical formulation. In our previous studies, approaches have been developed to the 2D and 3D simulation of heat and mass transfer processes during vapor condensation on the surface of horizontal smooth tubes, and condensation on a smooth tube bundle was simulated in 2D formulation. This paper presents the results of 3D simulation of R-21 refrigerant condensation in a small-sized tube bundle. Characteristics of the tube bundle are the same as those of the tube bundle tested at the Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences (SB RAS) (tube diameter is 16 mm, transverse pitch is 26 mm, longitudinal pitch is 15 mm). The condensation was examined in saturated vapor flow at a temperature of ({{T}_{{sat}}}) = 333.15 K incoming onto the tube bundle at a velocity of up to 0.9 m/s. The 3D predictions agree qualitatively and quantitatively with the 2D predictions and the experimental data. The distribution of condensate in the tube bundle is presented. The spectrums of fluctuations in the average heat transfer for tubes are analyzed. It is pointed out that the thermal boundary layer development region induced by the condensate falling from the upper to lower tubes should be considered.

Ash dumps of 170 large Russian coal-fired thermal power plants (TPPs) store more than 2 billion t of ash and slag waste (ASW) at present. They occupy approximately 50 000 ha and represent main sources of environmental pollution. The amount of ASW increases by approximately 20 million t every year. Besides the recorded amount of ASW, there is also waste that is not recorded in official documents. At the same time, the latter waste is man-made sources of commercial products. Direct large-scale application of ash is limited by the instability of its properties and its noncompliance with the applicable technical requirements for the products of its processing employed in various applications in power, metallurgical, chemical, construction, and other industries. Processing of ash and slag waste and gradual removal of ash dumps are a crucial state problem whose solution requires the development of appropriate industrial processes. The review examines modern methods of large-scale processing of ash and slag waste from coal-fired TPPs with extraction of commercial materials suitable for application in various industries. The emergence of a wide range of physical, chemical, and biological processes for ash processing enables the problem of reclamation of most ash dumps to be successfully solved. The attention was focused on such technologies as flotation enrichment, magnetic separation, and thermochemical methods. The mechanism of adsorption of functional groups of various collectors on the surface of carbon ash particles is examined. A large section of the review is devoted to acid, alkaline, and thermochemical methods of extracting alumina from ash and belite sludge. Attention is also focused on works dealing with the extraction of precious and rare earth metals from ash. Some new developing areas of microbiological extraction of metals from ash are also presented.

The article considers the use of supercritical carbon dioxide (sCO₂) as working fluid in the turbine stage consisting of a vane row and a mixed-flow blade row. The operation of the existing turbine on natural gas combustion products and on supercritical carbon dioxide is analyzed by way of comparison. The numerical simulation results show that the use of supercritical carbon dioxide makes it possible to increase the turbine power output to 14.3 MW. This is more than a factor of 30 higher than the power output of the same turbine operating on natural gas combustion products. Such a significant increase of power output is achieved without changing the turbine stage design, which points to the possibility of modernizing the existing units without the need to make essential changes of the design. The turbine stage efficiency during its operation on supercritical carbon dioxide was estimated at 0.87, and that during operation on natural gas combustion products was 0.88. Despite an insignificant drop of the efficiency, the total increase of the power output results in that the use of sCO₂ is economically feasible. Based on the data obtained, a conclusion has been drawn that it is advisable to use the existing turbine stages for operation on supercritical carbon dioxide. This opens the prospects in achieving more efficient operation of power systems without the need to develop new types of turbines, decreasing capital outlays, and more rapidly introducing new technologies. The transition for using supercritical carbon dioxide as working fluid can result in obtaining a significantly higher output of turbine units while retaining high efficiency indicators and making minor changes in the equipment design.

A comparative performance analysis of a Kalina Cycle System 11 (KCS11) without and with solar energy is done based on 4E-analysis (energy, exergy, environment, and economic) for generating additional electricity from fluegas waste energy of a 660 MWe Supercritical (SupC) coal-fired power plant. The result shows that the integration of solar assisted KCS11 with main steam power plant increases the net plant energy and exergy efficiencies by about 0.04 and 0.03% points, respectively due to additional electricity generation of 647.43 kW at 40 K of superheat. Condenser and evaporator are the maximum contributor of energy and exergy losses, respectively in the proposed systems. Energetic performance of solar assisted Kalina cycle is higher than the standalone KCS11 due to decrease in turbine exhaust pressure and additional poor exergetic performance of solar heater causes less exergy efficient of solar assisted KCS11 compared to standalone KCS11. Use of solar integrated KCS11 reduces the annual ({text{C}}{{{text{O}}}_{{text{2}}}}) emission by about 1089.58 t at full load which is nearly 1.25 times higher than the standalone KCS11. The Levelized Cost of Electricity (LCoE) for producing additional electricity by solar energy at 40 K of super-heat is about 0.13 $/kW h which is 8.5% lower value compared to the solar thermal power plant.

The volume-of-fluid (VOF) method, supplemented by models of interfacial heat and mass transfer, is a universal and very effective tool for simulation and detailed analysis of intricate processes occurring in systems with phase transitions. The key feature of this method is that it can quite accurately and in detail describe the physical pattern of running processes in the presence of a sharp phase boundary and provide quantitative data on the distribution of local heat-transfer characteristics and the dynamics of the interphase boundary and associated phenomena, thereby making the VOF method advantageous in researches and engineering practice. Development and improvement of heat and mass transfer models and efficient numerical VOF algorithms, as well as preparation of recommendations for the application of these approaches, are an urgent problem. This paper proposes an approach to the prediction of interfacial heat and mass transfer rate, which is based on the analysis of phase transitions in single-component systems using the linear theory of nonequilibrium processes. The results are presented of verification calculations performed for several standard problems. The classical problems of one-dimensional boiling and condensation (the Stefan problem) are examined as are such problems as vapor condensation in tubes of different orientations, condensation from stagnant or moving vapor on the surface of smooth horizontal tubes, and film boiling on the surface of horizontal cylinders. The predictions are verified against classical solutions and available experimental data. Calculations were carried out for fluids with different thermophysical properties, including water, pentane, propane, R-113, R-21, and R-142b. The maximum ratio of the densities of liquid and vapor phases was as high as 1600 (water at atmospheric pressure). The simulation results demonstrate the versatility of the proposed approach, which allows us to recommend it for solving a variety of engineering problems.

The results obtained from experimental investigations of the dynamic characteristics of a condenser and new ejector are presented. The investigations were carried out at a thermal power plant under the turbine commercial operation conditions using an extended arrangement for measuring the ejector operation parameters and an automated data-acquisition system. The dependences of the ejector’s first stage suction pressure on the dry (atmospheric) air flowrate and the pressure in the condenser and in the ejector’s first stage receiving chamber on the steam–air mixture flowrate during their joint operation are obtained. It is proposed to determine the maximal volumetric throughput of the ejector operating on dry air with using the minimal slope factor as a function of the air flowrate. With an increase of air inleakages into the steam turbine unit vacuum chamber, the pressure difference at the initial and total air inleakages at the ejector suction varies according to a linear law and that in the condenser according to an exponential law. By using the measurement system, the condenser’s and ejector’s dynamic characteristics were determined. It has been found that the pressure growth rate at the ejector suction increases with increasing the amount of air admitted into the condenser. The time taken for the pressure to become stable remains approximately the same. However, the pressure growth rate in the condenser does not depend on the amount of air admitted, and the time taken for the pressure to become stable increases exponentially with increasing the amount of air admitted. For diagnosing the vacuum system malfunctions in controlling the steam turbine unit’s operation mode, it is recommended to provide indication of the ejector suction pressure on the turbine control board. As regards the pressure sensor, it is proposed to install it on the common pipeline supplying steam–air mixture to the ejectors. The investigation of the condenser–ejector system dynamic characteristics will make it possible to improve the turbine vacuum protection, which is one of the turbine protection system components.

The work is devoted to simulation of the bulk condensation in a supersonic flow of a vapor-gas mixture through the Laval nozzle considering the finite rate of the interphase heat transfer. Numerical methods are examined for predicting the temperature of droplets using the improved VOF (Volume of Fluid) and Eulerian multiphase models. It has been demonstrated that, compared to the Eulerian model, the VOF model more accurately predicts the known experimental data and provides the numerical solution whose stability is less susceptible to the effect of high intensity source terms. Comparison of the predictions with the experimental data of other authors has revealed that the two-temperature model more accurately describes the flow with bulk condensation than the single-temperature model does. The application of a single-temperature approximation is justified when the impurity content in the mixture does not exceed 2% (by weight) since the zone of the active condensation onset is relocated considerably compared to its relocation in the case of the two-temperature approximation. However, the single-temperature approximation is recommended only for calculating the overall heat release level that could be beneficial, for example, for quick assessment of the effect of bulk condensation on turbine stage performance. The previously obtained estimates confirmed the applicability of the single-temperature formulation at an impurity content as high as 5 wt %, but solving this problem in 3D formulation improved the accuracy of these estimates. It has been revealed that the assumption about the flow homogeneity along the channel height (as one of the assumptions employed in one-dimensional calculations) during bulk condensation in a slot-type Laval nozzle is not valid on changing-over to a three-dimensional two-temperature formulation: supersaturation persists at the phase boundary, as a result of which the droplet growth process continues at the circumference of the flow.

The thermal power plant recognized as the most pollutants emitted power plant in the world. The use of the solar systems is essential for reducing carbon emissions from thermal power plants. Such hybrid systems need a skillful energy management technology as well as incorporation of carbon conversion technology that will help to run the system expertly to maintain the power generation-demand balance and make the thermal plant more cleaner than before respectively. This work describes a fuzzy logic-based energy management system for a thermal-solar hybrid system and a carbon conversion technology to convert the captured carbon into the chemical products after calculating the environmental impact of a stand-alone thermal power plant through life cycle assessment (LCA) tool. The results of a case study demonstrate that the suggested schemes are feasible, effective and environmentally acceptable. Thermal-solar-based hybrid power plant can work environmentally harmlessly if the carbon produced from the plant is converted into the chemical product.