Thermal Engineering最新文献

Based on the definition of additional boundary conditions and an additional sought function (ASF), an approximate analytical solution of the heat-conduction problem for an infinite plate subject to Newton’s symmetrical boundary conditions with a time variable heat-transfer coefficient is obtained. In accordance with the integral thermal balance method, the solution is subdivided into two stages in time. The first and the second stage include the time intervals corresponding to an irregular and a regular heat-transfer mode, respectively. At the first stage, a function characterizing the displacement with time of the temperature disturbance front along the ξ coordinate is adopted as the ASF. At the second stage, a function characterizing the change with time of the temperature at the symmetry center, in which the boundary condition of no heat transfer is specified, is considered as the ASF. Owing to the use of ASFs at both stages, it becomes possible to boil down the solution of the initial differential equation with partial derivatives to integration of an ordinary differential equation with respect to the ASF. By solving this equation at the second stage, the eigenvalues are found, which are determined in the classical methods from the Sturm–Liouville boundary value problem, in which a transcendental trigonomertic equation is solved for each particular Biot number using a numerical method. Hence, in this case, another technique for determining eigenvalues is considered, which makes it possible to obtain a formula from which eigenvalues for each particular Biot number can be found. The form in which the additional boundary conditions are given is such that their satisfaction in finding the sought solution would be equivalent for the case of solving the initial differential equation at the boundary points. It is shown that the solution of the equation at the boundary points leads to its solution also inside the domain considered; in this case, direct integration of the equation along the spatial variable is excluded and is only limited to fulfilling the thermal balance integral, i.e., the averaged initial differential equation.

The paper presents a description of the experimental facility at OKB Gidropress designed to study thermohydraulic phenomena during the core reflooding caused by a large break loss of a coolant accident in a water-moderated water-cooled (VVER) power reactor. The performed studies yielded a statistically significant amount of experimental data on the time-dependence of the temperature of the fuel-rod simulator cladding at several sections of the fuel-assembly (FA) model that is necessary for the validation of computer codes. The experiments were carried out with two fuel-assembly models with uniform and nonuniform heat release distribution along the height. Each model included 120 heated fuel-rod simulators, 13 spacer grids, six guide channel simulators, and a fuel assembly’s upper nozzle. In the experiments, five options of cooling water supply—bottom, gravity-driven bottom, top, combined, combined gravity-driven—were implemented. To confirm the reproducibility of the experiments, most of them were repeated three to five times. The fuel-assembly models, fuel-rod simulators, used instrumentation items, and experimental procedure are described. Examples are presented of the cooling dynamics of the fuel-rod simulators for different methods of cooling water supply to the reactor model, and the features of each flooding pattern are outlined. The data on the flooding time of the fuel-assembly model are generalized in the form of linear dependencies of this parameter on the relative power of the fuel-rod simulators.

A review is presented of designs of horizontal steam generators (SG) for nuclear power plants (NPP) with water-moderated water-cooled reactors (VVERs) and of experimental-and-computational studies of thermohydraulic processes running in them. Horizontal SGs are examined from the first commercial design of the PGV-440 SG and the most widely used today PGV-1000M SG to the steam generators developed for the new generation reactor units of types VVER-1200 and VVER-TOI as well as for the high-power VVER-1500 reactor. A comparative analysis was carried out of the experimental facilities developed for the investigation of thermohydraulic processes occurring in a horizontal steam generator. Each of the examined experimental facilities has limitation related to the capabilities for the simulation of a full-scale SG caused by either geometric characteristics or thermohydraulic conditions. Nevertheless, it has been demonstrated that we have at present a sufficiently large experimental database suitable for validating computational codes simulating thermohydraulic characteristics of a horizontal steam generator. A review of the available computational codes is presented. The STEG code in which the two-phase flow is described by multifluid models is examined in more detail. The validation of the STEG code against experimental data on void fraction, pressure drop, and water velocity demonstrated high accuracy of the predictions. One of the problems to be solved in designing horizontal steam generators for new generation reactor units is the improvement of the equalization ability of the submerged and steam-receiving perforated sheets due to the enhanced nonuniformity of the steam load on the evaporation surface and of the steam flow in the steam space. The results are presented of the experimental-and-computational investigation of the equalization ability of perforated sheets, which corroborate the possibility of its improvement by application of a variable perforation ratio. The areas of further experimental investigations into thermohydraulic processes in a horizontal steam generator and ideas for improving the computational codes are formulated.

The paper presents a brief review of experimental and computational studies of the reflooding processes occurring during large break LOCAs in the primary circuits with subsequent supply of the coolant in pressurized water-moderated water-cooled power reactors (VVER). The results of the PREMIUM project, carried out by OECD (CSNI), on the assessment of the prediction of reflooding parameters using the most well-known computer codes (RELAP5, CATHARE, ATHLET, APROS, MARS) are analyzed. The calculations were performed using data from one of the experimental regimes simulated at the FEBA test facility (Germany) for reflooding simulation. It is stated that the uncertainty of the estimate of the maximum temperature of fuel rods obtained by known system computer codes can attain 100°С as follows from the results of validation calculations. Based on a statistically significant set of experiments conducted on a unique reflooding test facility at OKB Gidropress with several cooling water supply options, the domestic KORSAR computer code was validated, including the gravity reflooding when water is supplied to the upper part of the reactor pressure plenum model. It has been demonstrated that the KORSAR code is not worse than the best international codes in terms of the accuracy of the predicted maximum temperature of fuel-rod simulators and flooding time for the test fuel assembly.

Many research teams and groups pay much attention to matters concerned with hydrodynamic impacts exerted on the equipment of nuclear power facilities (NPFs), which is reflected in numerous publications: monographs, articles, and reviews. However, despite the availability of theoretical works on this problem, matters concerned with applied investigations, i.e., immediately with direct measurements, still remain beyond the scope of scientific interests of Russian and foreign scientists. The need of studying them for practical applications is mainly stemming from the complexity of interpreting various revealed abnormalities, requirements for precise adjustment of various models, and essentially different spectral images of equipment not only within the framework of various designs of reactor plants (RPs), but in the power units of the same type within one NPP. These problems cannot be solved using solely theoretical or calculation methods, or using simulation software tools. The situation is also aggravated by the fact that the process of carrying out investigations is an exceptionally complex problem in terms of both selecting the data sources and interpreting the information obtained. In all likelihood, it is exactly these factors due to which an essentially weakened interest in experimental works on vibroacoustic topic in various RPs both in Russia and other countries can be explained. The article briefly presents some results of studying the fields of acoustic standing waves (ASWs) in the reactor coolant circuit (RCC) of a reactor plant equipped with a pressurized water reactor (VVER-1200) taking as an example power unit 1 at the Novovoronezh-2 NPP; in addition, the main ASW types are described.

A search of efficient ways for uprating the existing NPPs deserves close attention owing to significant saving of expenditures for implementing them in comparison with construction of new NPPs. In this connection, a new method for uprating an NPP with water-cooled reactors is proposed and discussed, which involves heating of feedwater in an economizer prior to supplying it to the steam generators by using the reactor coolant from the steam generator’s outlet. This results in an increased main steam output from the steam generator without changing its thermal power capacity, and a decrease in the average coolant temperature in the reactor core without changing it at the reactor outlet helps increase the core reactivity. With excess steam supplied to an additional steam turbine unit, it becomes possible to decrease the total costs for a power unit’s modernization and enhance the NPP safety through providing backup power supply for power plant auxiliaries in case of an emergency involving station blackout. A process cycle circuit of an NPP with a VVER-1200 reactor involving feedwater heating in an economizer upstream of the steam generator is developed and substantiated. The economizer main characteristics required for feedwater heating to 245 and 265°C are determined. The effect from installing the economizer on the reactor coolant pump operation and on the reactor coolant circuit as a whole is determined. It is shown that the power output of the NPP unit with a VVER-1200 reactor and with an additional turbine increases by 37.17 and 95.88 MW, respectively, with feedwater heated to 245 and 265°С.

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.