Formation Of Temperature Field Research Articles

A semi-analytical method of three-dimensional dual-phase-lagging heat conduction model

With the development of picosecond laser technology, the dual-phase-lagging (DPL) model is more suitable to describe the heat transfer problem with micro-scale effect and micro-time effect. In this paper, a three-dimensional dual-phase-lagging heat transfer model for picosecond laser processing is established. Then Fourier transform (FT) and Laplace transform (LT) are used to derive the frequency response functions (FRFs) of the problem in the frequency domain, and the inverse Laplace transform (ILT) and discrete-convolution fast Fourier transform (DC-FFT) algorithm are used to solve the temperature field. The calculation accuracy of this method is verified and the effect of phase lag constants on temperature field is studied. The results show that the semi-analytical method has a high accuracy for solving the dual-phase-lagging heat conduction model, and the phase lag of heat flux will affect the heating rate in the heating stage, and the phase lag of temperature gradient will delay the formation of temperature field. The effect of phase lag constants on temperature-time history is investigated and the related phenomena are explained by using the two-step heat transfer theory. This semi-analytical method provides a new approach to solve the problem of three-dimensional dual-phase-lagging heat transfer.

Investigation of the temperature distribution in a heterogeneous reservoir during fluid filtration, taking into account thermodynamic effects

Based on the modeling of non-isothermal fluid filtration, taking into account the Joule–Thomson effect and the adiabatic effect, the formation of temperature in a porous medium with radial-angular permeability heterogeneity is studied. It is shown that the presence of heterogeneity in the near-wellbore formation zone leads to different rates of temperature establishment in the angular distribution after the well is put into operation. Depending on the ratio of the permeability of the formation and the area of heterogeneity during fluid filtration in the angular distribution of temperature in the well, either a slow rate of temperature establishment in the region of heterogeneity is observed. The area of heterogeneity is colder than the rest of the area, or vice versa, the area of heterogeneity has an increased temperature. The results obtained complement the known data on the formation of temperature fields in reservoir conditions with non-isothermal fluid filtration, taking into account thermodynamic effects, and can be used to interpret the results of multi-sensor temperature studies in wells with formations that are heterogeneous in permeability.

ЭКСПЕРИМЕНТАЛЬНОЕ МОДЕЛИРОВАНИЕ ТЕПЛООБМЕНА В ТЕПЛОВЫДЕЛЯЮЩИХ СБОРКАХ БЫСТРЫХ РЕАКТОРОВ В АВАРИЙНЫХ РЕЖИМАХ В УСЛОВИЯХ ЕСТЕСТВЕННОЙ КОНВЕКЦИИ

The results of experimental studies of heat transfer carried out at the State Research Center RF - IPPE on models of fuel assemblies in cores and screens of fast reactors BOR-60, BN-350, BN-600, BN-800 (the relative pitch of the fuel element simulators varied in the range 1.04≤s/d≤1.24) with natural and mixed convection of liquid metal coolants, which are the basis for the development of design codes. Model fuel assemblies of fast reactors contain 37 fuel elements (fuel rod simulators) located in a triangular lattice and enclosed in a hexagonal cover. The elements were heated with nichrome heaters, which ensure a constant heat flux on the inner surface of the elements and along the length of the heat generation. The central, lateral and corner elements are rotary. On their surface, 12 chromel-alumel thermocouples each in covers made of X18H9T steel (diameter of the cover 0.8-0.5 mm, diameter of thermoelectrodes 0.2 mm) are embedded, measuring the coolant temperature in the collectors of the models, as well as in each cell at the exit from the bundles. The spacing of the elements is carried out using wire coils; variants of smooth fuel rod simulators are also used. Experimental studies on model fuel assemblies revealed regularities in the formation of temperature fields in fuel elements and coolant. Natural convection manifests itself in the region of low velocities, promotes fluid mixing between channels, leveling the uneven heating of the coolant in the cross section of the fuel assembly, and reduces the azimuthal non-uniformity of the temperature of the wall fuel elements in the fuel assembly. The results of experimental studies show that the effect of natural convection manifests itself in the range of Pe<10 (Re<2000) numbers in gratings with relative steps (s/d<1.05) and in wide bundles (s/d<1.3 to a greater extent in bundles of smooth fuel rods in comparison with bundles of ribbed fuel rods. The introduction of displacers into the peripheral channels of a fuel assembly does not fundamentally change the nature of the temperature field in a fuel assembly as compared to the version of the geometry of a fuel assembly without displacers. An attempt was made to generalize the experimental data using the Gr*Pr criterion, where Gr* is the modified Grashof number calculated from the local heat flux on the heat exchange surface and the axial coordinate measured from the beginning of heat generation. In the dependences DTwmax = f(Gr*Pr2) at Pe<100 or ribbed side elements and Pe<10 for smooth side elements, two regions of DTwmax change in the Gr*Pr2 growth function are observed - first, DTwmax ncreases to a certain “limiting” value characteristic for fixed Pe, and then - a drop in DTwmax at large values of the parameter Gr*Pr2. As the Peclet number increases, the “limiting” value of DTwmax hifts to the region of larger values of Gr*Pr2; and at Pe=370 or ribbed elements and Pe=26.5; 100 or smooth elements, the limiting value of DTwmax is not achieved in the investigated range of the Gr*Pr2 parameter variation. For smooth side elements, the limiting values of DTwmax are approximately the same for different Pe numbers and amount to DTwmax≈10.

Features of the formation of temperature fields during forced plasma cutting and their effect on the structure of steels

Features of the formation of temperature fields during forced plasma cutting and their effect on the structure of steels

Temperature distribution in a subduction zone

A model of the thermal and hydrodynamic structure of the subduction zone is proposed. This model includes free convection flows in the asthenospheric layer and layer C (mantle transition zone). Temperature profiles in the subducting lithospheric plate, as well as in the continental limb of the subduction zone, are presented. The heat flux due to friction at the contact between the subducting plate and the continental limb significantly affects the heat transfer and, consequently, the temperature field formation in the subduction zone. The temperature level in the crustal layer of the submerging plate implies that there is no melting in the crustal layer.

Processes of mixture formation, ignition and combustion of a diesel engine

One of the most significant concepts of deep restructuring of the economic mechanism of the Republic of Uzbekistan is the creation of an integral, effective and flexible system of economic management and the implementation on this basis of a program to improve the technical level and quality of machines. The car park of our country is more replenished with vehicles with diesel engines. The development of contemporary diesel engine building is proceeding by forcing engines: increasing the average effective pressure and speed. Therefore, high reliability and service life, fuel efficiency and environmental performance are the basic criteria for their quality. Forcing diesel engines leads to an increase in thermal and mechanical loads on the basic parts of the cylinder-piston group (CPG) (piston, liner and cylinder head), a significant increase in their temperature, as well as the temperature of piston rings and valves. Overheating of parts is accompanied by the formation of temperature fields with a pronounced uneven temperature distribution and, as a result, an increase in thermal stresses with a simultaneous deterioration of the mechanical properties of the material, the formation of cracks and, finally, the destruction of the part. In this regard, the task of protecting parts from excessive exposure to high thermal loads from the working fluid becomes urgent, or, in other words, the task of creating a diesel engine with reduced heat removal from the working fluid.

Acoustic control of the residual stresses in steel 5KhNM samples

Heat treatment (HT) is one of the main and most important stages of the technological cycle of manufacturing metal products. Residual stresses (RS) arising in metals upon their heat treatment significantly affect the service life of the products. The goal of the study is developing a technique for non-destructive acoustic testing of the residual stresses in steel samples. The method is based on the phenomenon of acoustoelasticity, i.e., the dependence of the acoustic characteristics on the parameters of the environment under study. The fields of residual stresses in rectangular samples made of die steel 5KhNM were formed using various HT modes, including cooling both in traditional media (water, oil, air) and using a water-air mixture (WAM). Control of the ratio of water-air parameters as well as the direction of the WAM flow provided the desired cooling rate and locality of the process. It is shown that the level of residual stresses decreases with the distance from the cooling plane, the microstructure and elastic characteristics of the material also change. The effect of cooling on the formation of temperature fields and the value of residual stresses was analyzed using computer simulation (CAE ANSYS program). The values of the characteristics of 5KhNM steel formed a set of input parameters in simulation. The simulation results proved the experimental data. Acoustic measurements carried out on the measuring and computing complex «ASTRON», provided determination of the velocities of elastic (longitudinal and transverse) waves and the elastic moduli of the material under study. The RS values obtained by the acoustic method were compared with the data obtained by the X-ray method. It is shown that the differences between the values measured by acoustic and X-ray methods do not exceed 10%. The results can be used in a production environment when measuring the residual stresses by the acoustic method in large-sized dies made of 5KhNM steel.

ВЛИЯНИЕ РЕЖИМНЫХ И КОНСТРУКТИВНЫХ ПАРАМЕТРОВ НА НЕРАВНОМЕРНОСТЬ ТЕМПЕРАТУРНОГО ПОЛЯ НА ВЫХОДЕ ИЗ КАМЕРЫ СГОРАНИЯ ГАЗОТУРБИННОГО ДВИГАТЕЛЯ

Ensuring acceptable temperature field non-uniformity at the outlet of the combustion chamber is a very important requirement that determines the reliability and durability of the turbine. The formation of non-uniformity is determined by the nature of the interaction of the secondary air jets with the gas flow in the flame tube and depends on many factors, both structural and operational parameters. In this paper, we propose to evaluate the non-uniformity of the temperature fields at the outlet of the combustion chamber using a mixing coefficient that determines the quality of mixing jets of secondary air with a gas stream in the mixer. Based on the equation of turbulent diffusion during the flow of an annular jet into a limited space, an analytical dependence is obtained in the work that allows one to calculate the mixing process in the combustion chamber. The connection of the mixing process with the formation of temperature fields is established. Based on this, dependences are obtained for calculating the nonuniformity of temperature fields. Their satisfactory agreement with experimental data was shown. The found dependences allow one to analyze the influence of various parameters on the non-uniformity of temperature fields and accelerate the refinement of the combustion chamber by this parameter. The possibility of predicting the effect of various parameters on the unevenness of temperature fields is shown. The presence of the optimal value of the degree of opening of the mixer is confirmed, at which the minimum value of the unevenness of the temperature field at the outlet of the combustion chamber is achieved. Therefore, the analytical relationships found in the work allow optimizing the design of the mixer in the combustion chamber and the distribution of secondary air in it in order to reduce the unevenness of the temperature fields at the outlet of the combustion chamber.

Application of methods of mathematical modeling in the optimization design of technological processes of food production

Optimization of thermochemical and biological transformations occurring during the heat treatment of food products can be carried out only taking into account the dynamics of the formation of temperature fields inside the processed products. A mathematical model of the Sous-Vide processing process has been developed, which provides the determination of the dynamics of changes in the temperature field of Sous-Vide processed functional food products based on animal and vegetable raw materials. To calculate the process of Sous-Vide processing of functional products, we used the differential equation of unsteady heat conduction taking into account the Bio criterion. When solving a system of partial differential equations, the mathematical package flexPDE is used. In calculations, a spatial grid with the number of nodes 20000 was used, the accuracy of calculations was 10E-4. Experimentally determined values of thermal conductivity, specific heat capacity, density and thermal diffusivity of each of the components of the food system are used in calculations. The results of the calculated experiment in mathematical modeling of the Sous-Vide processing process show the evolution of temperature fields in different sections of the food system and on its upper surface, having the shape of an ellipsoid of rotation. The dependences of the change in the thermophysical characteristics of the longitudinal and transverse flow of the food system coolant. The results of the computational experiment show a good convergence of the mathematical model and the results obtained, which is 94%, which indicates the adequacy of the developed mathematical model of the Sous-Vide processing process. The obtained mathematical model allows, by means of a computational experiment, to analyze and optimize the Sous-Vide processing modes of a wide range of food raw materials, of various geometric shapes and sizes, with different physicochemical and thermal properties, taking into account their non-stationarity under thermal influence.

The contribution of temperature dependence of optical absorption coefficient of the sample to the formation of a thermal field in a photoacoustic cell

Expressions describing the peculiarities of the temperature field formation in the photoacoustic cell, taking into account the temperature dependence of not only the thermophysical parameters of all layers and the absorptivity, but also of the optical absorption coefficient of the sample have been obtained. A system of nonlinear algebraic equations has been derived to determine the dependence of temperatures of the illuminated layer of the sample and its reverse side on the intensity of the incident beam. As a result of numerical solution of this system, nonlinear dependences of temperatures of both sides of the sample on the beam intensity have been obtained. The sign of the thermal coefficient of the temperature dependence of the optical absorption coefficient has been found to significantly affect the nature of the dependences of the increment of the irradiated surface temperature and the rear side of the sample on the intensity. Significant effect of the substrate on the formation of the temperature field in the photoacoustic cell has been shown as well.

FORMATION OF TEMPERATURE FIELDS AND THERMAL STRESSES ARISING DURING SOLIDIFICATION OF CYLINDRICAL CONTINUOUSLY CAST STEEL BILLETS

The article presents investigation results of the effect of inhomogeneity of boundary conditions on the intensity of metal cooling in the process of continuous casting of cylindrical billets from corrosionresistant steels. It is assumed that the boundary conditions are nonuniform along the billet perimeter. In the longitudinal direction, the cooling intensity is assumed to be constant within the cooled sector of the billet. During the research it was believed that there are flows of thermal energy between the cooling sectors. A comparative analysis of temperature gradients and resulting thermal stresses in the solidified billet at different cooling intensities realized in the secondary cooling zone was carried out The values of thermal stresses are compared with the maximum permissible for each grade of steel in order to find those cooling conditions in which the thermal stresses do not exceed the permissible values. Based on the results obtained, conclusions are drawn about the effect of cooling intensity on the occurrence of external and internal defects in the resulting cylindrical continuous cast billets. The authors have also made the conclusions about the effect of inhomogeneity of the boundary conditions on the formation of temperature fields in a solidified cylindrical continuously cast billet. The results of the conducted studies are presented in a graphic form and their detailed analysis is carried out. To calculate the temperature fields in the solidifying billet, a specially developed mathematical model was used, based on the equation of nonstationary heat conductivity. For the calculation of thermal stresses, known mathematical formulas have been used that allow calculating the values of thermal stresses arising between cooling zones in the solidifying billet during the continuous casting of steel. The obtained data are of high practical importance, since they can be used to develop rational cooling regimes, in which excess permissible thermal stresses will not be observed. This, as a consequence, will reduce the number of internal and external defects arising in the solidifying continuously cast billet.

Experimental-Calculation Estimation of the Temperature Field Distribution during the Hardening of Thin-Walled Parts by Electric Pulse Facing

The formation of temperature fields and tempering zones during electric pulse hardening of thin-walled parts is studied. A mechanism is developed to supply a filler wire for semiautomatic vibrational arc facing. The influence of the pulsed arcing parameters on the surface hardness of the part to be hardened is experimentally studied.

Formation of the Temperature Field of Dielectric Films and of a Base in the Field of a Continuous Ion Beam

The influence of the temperature dependence of the thermal conductivity and heat transfer coefficients, as well as of the emissivity of a dielectric film and of an insulating base on formation of a stationary temperature field of the dielectric–base system exposed to irradiation by a continuous ion beam in air, has been studied theoretically. Analytical expressions have been obtained for the temperature fields of a sample and base, as well as a system of interrelated nonlinear algebraic equations for characteristic temperatures. With the aid of numerical solution of a system of nonlinear algebraic equations, the dependences of the temperature of the irradiated surface of the sample–base system and of the rear side of this system on the incident ion beam parameters have been found. It has been established that these dependences are nonlinear. It has been found that heating of a sample, including its irradiated surface, decreases substantially with increase in the thermal conductivity of the base.

Компьютерное моделирование течения в микрофакельных горелочных устройствах с асимметричной подачей топлива

Выявлены основные закономерности изотермического течения топлива и окислителя в микрофакельном горелочном устройстве с односторонней подачей топлива. Получены данные компьютерного моделирования с использованием подхода DES (Detached Eddy Simulation), представляющего собой комбинацию моделей RANS (Reynolds Averaged Navier-Stokes) и LES (Large Eddy Simulation) в разных областях пространства. Установлены эффекты влияния длины закрылка, расположенного на торцевой поверхности стабилизаторов пламени, на различные характеристики течения. Показано, что наличие закрылков приводит к существенному изменению вихревой структуры в следе за стабилизаторами. Оценено влияние длины закрылков на такие параметры течения, как протяженность зоны обратных токов в закормовой области стабилизаторов пламени, уровень среднеквадратичных пульсаций скорости в данных зонах и пр. Установлено, что с увеличением длины закрылков существенно возрастает протяженность зоны обратных токов за стабилизатором. Выявлено также, что чем короче закрылки, тем больше превышает их длину протяженность зоны обратных токов. Выполнен анализ пространственного распределения пульсаций скорости в рассматриваемом горелочном устройстве при наличии и отсутствии закрылков на торцевых поверхностях стабилизаторов пламени. Показано, что наиболее высокий уровень данных пульсаций наблюдается вблизи границы зоны обратных токов, удаленной от торца стабилизатора. Установлено, что уровень среднеквадратичных пульсаций скорости является наиболее высоким в условиях отсутствия закрылка и снижается при увеличении его длины.

RESEARCH OF NON-STATIONARY THERMAL FIELD IN RESERVOIRAND WELLBORE WITH MULTIPHASE FILTRATION

In the paper the mathematical formulation of a task of temperature filed in the wellbore and reservoir sys-tem with multiphase fluid filtration is considered. The mathematical models of two-phase non-isothermal filtration of fluid in porous media are described, which take into account non-stationary thermo hydrodynamic processes, barothermic effect, oil degassing when reservoir pressure lowers below saturation pressure. The mathematical models are developed for two-phase flow in vertical wellbore. The paper shows the results of numerical solution of formation of temperature field in reservoir and wellbore system and testing results on analytical solutions.

History of Agrophysics: Physical Modeling of Convective Heat Transfer in Greenhouses and Agricultural Fields

In 1970-1980, a new scientific direction in agrophysics was started, with efforts devoted to the physical modeling of convective heat transfer in greenhouses and agricultural fields. The base of this new branch of agrophysics was created by research efforts of Igor Uskov. Within the framework of this new branch of agrophysics several valuable scientific results have been obtained. For example, Igor Uskov developed an aerodynamic stand for use in experimental studies which allows for the formation of temperature fields within greenhouses and across agricultural fields. Using this equipment, it was shown for the first time that that heat is carried by ascending and descending air flows within a greenhouse under the influence of local sources of heat. In another example of agrophysics research, heat transfer between double walls of arched greenhouses was studied. The colored shadow method for visualization of the structure of the thermal boundary layer was developed out of this effort. Studies of heat transfer across agriculture fields has led to the heat exchange processes on the slopes being modeled.

Research on heat transfer characteristic of crude oil during the tubular heating process in the floating roof tank

By means of finite volume method, the heat transfer characteristic of crude oil under the tubular heating in the floating roof tank is investigated by numerical simulation. The evolution of temperature profile and its relationship with the flow pattern is presented in detail. A noticeable finding is that there exists the transformation of the flow pattern which affects the temperature profile apparently during the heating process. Special concern is taken on the evolution of temperature distribution on the interface between oil and the inner wall of the tank. The temperature profile on the top wall, sidewall and base wall of the tank is investigated. It is concluded that the plume induced by natural convection takes most responsibility for the formation of temperature field in the tank. The second factor is the boundary condition of the tank.

Influence of the melt thermal conductivity on temperature fields in aluminum oxide upon heating by concentrated laser radiation

The influence of the melt thermal conductivity Λm on the formation of temperature fields upon heating and melting of a plane aluminum oxide layer by CO2 laser radiation with a flux density q from 200 to 3000 W/cm2 is investigated using a rigorous model of transient combined radiative and conductive energy transfer. The maximum heating time is 100 s. Parameter Λm varies from 1.5 to 3 W/(m K). Absorption coefficient k l for the laser radiation is assumed to be 1000 cm–1. The formation of a two-phase region,which exists for a short time, has been observed in the initial melting stage at a depth less than the penetration depth of the heating laser radiation. Maxima of the heated-surface temperature and melt thickness (not coinciding in time) are found at q < 600 W/cm2. The melt thickness and its value at the maximum depend only slightly on q, while parameter Λm significantly affects the melt thickness at the maximum and during the entire heating process. It is shown that similar temperature profiles are established in the solid phase at different Λm values while approaching the quasi-steady state due to large values of the melt absorption coefficient in the wavelength range that is most energetically important for radiative transfer. The melt thermal conductivity affects only slightly the temperature of the “cold” surface that is opposite the melt.

Influence of strouhal number on the temperature fields in the locked space with the working source of the radiant heating

Is carried out a numerical study of the heat transfer process in the closed domain with the source of radiant heating. Is solved the system of differential equations in the dimensionless setting, which describes free convection in the airspace and thermal conductivities in the enclosing constructions. Examined the influence of the dimensionless parameter, which characterizes the unsteady motion of liquids or gases (Strouhal number), on the formation of temperature fields both near the heater and in the entire region. Is carried out the estimation of the average temperature, depending on the Sh.

Verification of Conjugate Heat Transfer Models in a Closed Volume with Radiative Heat Source

The results of verification of mathematical model of convective-conductive heat transfer in a closed volume with a thermally conductive enclosing structures are presented. Experiments were carried out to determine the temperature of floor premises in the working conditions of radiant heating systems. Comparison of mathematical modelling of temperature fields and experiments showed their good agreement. It is concluded that the mathematical model of conjugate heat transfers in the air cavity with a heat-conducting and heat-retaining walls correspond to the real process of formation of temperature fields in premises with gas infrared heaters system.