Thermal Engineering最新文献

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.

The article addresses matters concerned with the use of neural networks for predicting the gas dynamic characteristics of turbine machinery cascades. The results of elaborating the architecture of deep machine learning models for determining the profile kinetic energy loss downstream of plane nozzle vane and rotor blade (impulse type) turbine cascades are presented. A procedure for preparing the training dataset with using numerical simulation of viscous flows is described. The dataset generated is analyzed; its shortcomings, which should be removed for improving the quality of trainable neural networks are identified. Work on selecting the architecture of neural networks for rotor and nozzle vane cascades was carried out. The studies have shown that the same structure of models is efficient for both nozzle vane and rotor blade cascades. The use of prepared models yielded good agreement between the predicted results and the data available for all types of the cascades considered. It is pointed out that the neural networks yield incorrect predictions in transonic and supersonic operation conditions near the theoretical Mach number downstream of the cascade equal to unity. This stems from the lack of information on such operation conditions in the training dataset. After the models had been additionally trained under supersonic operation conditions, it became possible to “trace” the influence of the flow wave structure on the power performance characteristics downstream of the cascade. The data obtained served as a basis for stating the importance of representing curvilinear blade passages in parametric form and the necessity to prepare the training data in a wide variation range of the majority of independent parameters. The neural networks have demonstrated high-efficient performance in solving the stated problem, which made it possible to formulate a number of algorithmic concepts for applying them in solving turbine stage design problems.

We present a class of simplified approximations for modelling heat transfer in a two-dimensional furnace with inclusions. The governing equations are the well-established thermal incompressible Navier–Stokes equations subject to the Boussinesq approximation for modelling the change in density. Simplified P_N-approximations are carried out for the radiative transfer which is coupled with convection. A Taylor–Hood finite elements technique has been adopted to solve the equations using triangular meshes. The Galerkin-characteristics method is accounted for the dominant advection. Numerical results are presented under the operation of different burners and comparisons between simulations without radiation and with radiation are discussed. Results show that the temperature on the sides of the furnace is not equal. This is due to the fact that the unsteady convection-radiation heat draws the unstable heat flow towards the sides at the chosen time. The effect of higher value of Reynolds number as far as heat transfer is concerned, is that an additional mechanism of heat transfer in the azimuthal and radial directions becomes available and higher. This is commonly termed “eddy transport” and is intense, providing much better transfer of energy across the flow at a given position than in lower value of Reynolds number. Another difference worth noting is the extent of the thermal entrance region in which the transverse temperature distribution becomes fully developed. This region is relatively short in operation with 7 and 9 burners (precisely because of the intense turbulent transverse transport of energy), whereas it tends to be long under the operation of 1 and 3 burners.

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.