Calculation Of Thermal Processes Research Articles

A MODEL OF WELDING THERMAL PROCESSES WITH A LIMITED NUMBER OF FICTITIOUS POINT SOURCES

Analytical methods of calculation of thermal processes at welding enable to estimate operatively the influence of welding modes on parameters of a temperature field and to predict structural changes in a zone of thermal influence. In the mid-twentieth century it was suggested to calculate the heat processes in welded products with parallel boundary planes by summing up the temperature fields of the main and infinite number of fictitious point sources using thereflection method. However, due to computational difficulties, this method could not be brought to a state of wide practical application. Furthermore, since the schematization of heated bodies is conditional, the choice of the body scheme (plate, flat layer, semi-infinite body) and therefore the thermal calculation model is performed intuitively based on the accumulated experience. This uncertainty inevitably leads to discrepancy between the calculated and actual parameters of the thermal welding process. The purpose of this work is to adapt a model of thermal processes with a limited number of fictitious fast moving point sources to the calculation of thermal welding processes. The proposed model, solvable in Mathcad software, contains the equations of temperature field and temperature rate of change with account of the number
 of fictitious heat sources involved in the calculation. This model allows a reasonable limitation of the number of fictitious heat sources for providing the required accuracy of calculations, since as the fictitious heat sources move away from the product and their influence on the product heating decreases. In most cases for practical calculations 2 pairs of fictitious sources are enough for welding of 2 cm thick steel products, of 0.5 cm thick products ‒ 5 pairs, of 0.2 cm thick products ‒ 12 pairs. Comparison of the calculated values of the proposed model with actual temperature field measurements and known effects of cooling rate in the plate, plane layer and semi-infinite body within the accepted limits have confirmed its adequacy. The presented comparative results demonstrate versatility of the proposed model with a limited number of fictitious fast moving point sources, which can be applied sufficiently and successfully for analysis of the thermal welding processes of real industrial products of arbitrary thickness without discriminating into plate, plane layer and semi-infinite body models.

Проблеми аварійної динаміки теплогідравлічних процесів у перспективних реакторах із надкритичними параметрами легководного теплоносія

A complex of scientific and technical problems directly related to the priority of ensuring the operational safety and reliability of the cores of promising power nuclear reactors with supercritical thermodynamic parameters of a light-water coolant is systematized. The problems of implementation of effective heat removal from the surface of fuel elements and ensuring reliable calculation of thermal and hydrodynamic processes in turbulent flows of a supercritical coolant are considered. The main attention in the consideration of thermohydraulic processes in the near-critical region is paid to the conditionality of the physical nature of these processes by the regularities of transformation of the thermophysical properties of the coolant with changes in its temperature. It is noted that these phenomena have not been sufficiently studied and that modern designers of nuclear reactors with supercritical parameters practically do not have physically substantiated adequate ideas about the physical nature of an emergency mode of deteriorated heat transfer, which can arise unpredictably on the surface of a fuel element even if it is continuously cooled by a coolant with supercritical parameters. It is only known that the main physical sign of the occurrence of this emergency mode is a significant deterioration in heat transfer, which becomes abnormally low, but the physical reasons for such a dangerous anomaly are currently unknown. Based on the analysis of the molecular kinetics data of the near-wall coolant layer, it was proposed to consider such facts of an emergency decrease in the heat transfer intensity due to the appearance of an unknown pseudo-film boiling regime on the fuel element surface. In this context, it is shown that under the conditions under study, macromolecular assemblies in the form of pseudo-vapor formations can appear on the heat exchange surface, as a result of which the heat transfer on the fuel element surface is disturbed. Using experimental data, it is shown that there is a rather deep physical analogy between heat transfer in a supercritical thermodynamic system and the subcooled boiling process at subcritical parameters of the coolant. The dynamics of changes in the characteristics of the experimental spectra of acoustic emission of pseudo-boiling with a sequential increase in the thermal load is analyzed and it is shown that these phenomena can, in principle, be used in promising systems for diagnostic monitoring of reactors with supercritical parameters for early detection of the initial phases of pseudo-boiling and prompt prevention of the occurrence of emergency modes of deteriorated heat transfer

Application of equivalent thermal circuits for calculation of thermal processes of induction cruel furnaces with a capacity of up to 1000 kg

The article describes new approaches to calculating the thermal regimes of induction crucible furnaces, as well as methods for calculating them using converted thermal circuits. The principles of constructing thermal models of structural parts and molten metal of induction crucible furnaces based on converted ETS and their use for the development of optimal systems for automatic control of the metal melting process are considered. The methodology for the development of ETS and the compilation of heat balance equations for induction crucible furnaces with a capacity of up to 1000 kg is presented..

Gase's thermal C onductivity C alculation by low P ressures

Data on the thermal conductivity of industrial gases (vapors) are used in chemical technology, in the processing of oil and gas for analysis, calculation, and design of thermal processes and apparatus (heat exchangers, furnaces). It is believed that information requests for this property can be satisfied due to the data and recommendations for calculation available in the reference literature. Thus, it is of interest to develop a more convenient (modified) approach to the calculation of the thermal conductivity of gases at a “reference” temperature and low pressures, bypassing the aforementioned problems of the Roy – Todos method. Reliable reference materials were used as an information database of the thermal conductivity of hydrocarbons in the gas (vapor) phase. About 40 hydrocarbons representing various classes with molecular weights of 26 ... 254.5 were selected. Physico-chemical characteristics of the substances taken according to the data. The article considers the calculation of the thermal conductivity of gases at the “reference” temperature value. The proposed formulas make it possible to determine the temperature dependence of thermal conductivity at low pressures.

INFLUENCE OF GEOMETRICAL PARAMETERS OF THE INDUCTOR AND ARMATURE ON THE INDICATORS OF A LINEAR PULSE ELECTROMECHANICAL CONVERTER OF AN ELECTRODYNAMIC TYPE

Purpose. The aim of the paper is to study the influence of geometrical parameters, namely, the number of layers and the cross section of the copper tire of the inductor and the armature coils on the power and speed indicators of a linear pulse electromechanical converter (LPEC) of an electrodynamic type. Methodology. On the basis of the developed chain mathematical model, recurrent relations are obtained for the calculation of interconnected electromagnetic, mechanical and thermal processes of LPEC of an electrodynamic type. The effect of the thickness of a square copper tire and the number of its layers in the inductor and armature coils on the characteristics and characteristics of electrodynamic LPEC is investigated. It is these parameters that determine the number of turns and the axial height of the coils with limited radial dimensions. Results. The influence of the geometrical parameters of the inductor and the armature coils with limited radial dimensions on the electrical and mechanical characteristics of LPEC of an electrodynamic type is established. It has been established that with an increase in the thickness of a rectangular cross-section of copper tire from 1 to 2.5 mm, an increase in the amplitude and pulse of electrodynamic forces (EF) occurs. However, the maximum speed of the armature is the highest at LPEC wound with a 1.5 mm thick tire. The highest efficiency value is demonstrated by LPEC, in which the inductor and armature coils are wound with a 2 mm thick tire. With an increase in the number of layers of the inductor coil tire, the amplitude of the EF decreases significantly, and the magnitude of the EF pulse decreases slightly. As a result, the maximum armature speed, efficiency and temperature rise of the coils are reduced. Originality. It is established that the largest amplitude of the EF is realized in LPEC with the minimum number of layers of tires of the inductor and armature coils. The largest value of the pulse EF occurs when the maximum number of layers of the inductor and the armature. In this case, the largest values of the amplitude and pulse of the EF occur under the condition that the number of tire layers of the inductor and the armature coils are the same. Practical value. It has been established that the greatest efficiency 21.82 % is realized in LPEC, in which the number of tire layers is 2 mm thick with inductor and armature coils are 4. A catapult model for launching an unmanned aerial vehicle was made and tested on the basis of LPEC of an electrodynamic type.

Calculation of Thermal Processes in a Bonded Diamond Tool During Grinding of Glass and Other Materials

The results of calculations of thermal processes occurring in a bonded diamond tool during grinding of different materials on the surface in the contact zone with the machined material and in the interior of the diamond tool are presented. Amathematical model of the heating of the binder of the diamond tool as a result of friction in the grinding zone and cooling by a cutting liquid (CL) is described.

ДО ПИТАННЯ О РОЗРОБЦІ ПРОГРАМНО-ОБЧИСЛЮВАЛЬНОГО КОМПЛЕКСУ ТЕПЛОГІДРАВЛІЧНОГО ПРОЦЕСІВ В МАСЛОСИСТЕМІ ГТД

Currently, in connection with the creation of aircraft engines of new generations, as well as increasing requirements for the efficiency of their design and development processes, more attention is paid to the creation of a software and computing complex with respect to the thermal and hydraulic processes in the GTE oil system. In the development of modern aircraft engines, special attention is paid to increasing the resource, reducing the mass and dimensions of the engine. Conditions for the long-term operation of the gas turbine engine cause specific requirements for individual elements and their oil systems. Effective development of a new generation of gas turbine engines is largely ensured by the introduction of automated engine oil system design systems. Increasing the efficiency of gas turbine engines and the development of new technologies in propulsion engineering inevitably sets the task of oil systems improving. A promising direction is the creation of a software and computer complex with respect to the thermal and hydraulic processes in the GTE oil system. When designing the GTE oil system, it becomes necessary to calculate the exact oil consumption and pressure losses in the pipelines, calculate the heat exchange between the oil and the elements of the lubrication system, calculate the critical flow regimes in the pipelines and local resistances. The task was to create an adequate software and computer complex for the calculation of thermal hydraulic processes applied to the GTE oil system, depending on the influence of key parameters. On its basis in the future, a thermal model of the oil system will be constructed, which will allow to determine the thermal state of the oil and the support elements of the GTE rotor. In the future, the software and computing complex will be adapted for the calculation of two-phase fluid flow, namely oil and air. Studies in the presented areas require theoretical approaches to solving problems, the use of modern software packages for conducting numerical experiments and the availability of a bench base. The article shows the structure of the software and computing complex with respect to the thermal and hydraulic processes in the GTE oil system.

Creation of Model and Calculation of Thermal Processes in the Ring Graphite Electrode of the Plasmatron

This paper presents the theoretical and experimental material obtained in the study of the erosion and thermal state of the ring graphite electrode for a plasmatron. Thermal processes in graphite electrodes of plasmatrons are quite complex and multifaceted. A mathematical model of thermal processes that occur at the ring electrodes of plasmatrones has been developed. The mathematical model is based on the differential heat conduction equation for a ring electrode in cylindrical coordinates. With the use of this mathematical model, the inverse problem of heat conduction is solved: determination of the regularities of the heat exchange process by the temperatures of individual points on a solid surface. An experimental study of the temperature distribution at the end of the electrode and along the length of the electrode was carried out. Experiments have shown that the temperature on the side surfaces drops sharply towards the cold end of the electrode. When reducing the length of the electrode, the maximum temperature at the end decreases, and the temperature on the inner and outer edges of the electrode increases slightly. The most significant factors determining the temperature field at the end of the ring electrode are the power and size of the heat source. Comparison of the results of experimental studies and mathematical modeling showed a match with an acceptable degree of accuracy.

Calculation of Thermal Processes around Moving Molten Pool Using Boundary Element Method

Calculation of Thermal Processes around Moving Molten Pool Using Boundary Element Method

Thermal processes of the isolating materials in problems of nondestructive diagnostics of the main and power supply systems

Methods of calculation of thermal processes of the isolating materials are considered, in problems of nondestructive diagnostics of the main and distributive power stations. Theoretical justification of calculation of thermal processes of the multilayered isolating structure was given. On the basis

Heat Exchange in “Human body - Thermal protection - Environment” System

This article is devoted to the issues of simulation and calculation of thermal processes in the system called “Human body – Thermal protection - Environment” under low temperature conditions. It considers internal heat sources and convective heat transfer between calculated elements. Overall this is important for the Heat Transfer Theory. The article introduces complex heat transfer calculation method and local thermophysical parameters calculation method in the system called «Human body – Thermal protection – Environment», considering passive and active thermal protections, thermophysical and geometric properties of calculated elements in a wide range of environmental parameters (water, air). It also includes research on the influence that thermal resistance of modern materials, used in special protective clothes development, has on heat transfer in the system “Human body – Thermal protection – Environment”. Analysis of the obtained results allows adding of the computer research data to experiments and optimizing of individual life-support system elements, which are intended to protect human body from exposure to external factors.

Thermal Processes of the Isolating Materials in Problems of Nondestructive Diagnostics of the Main and Distributive Power Stations

Methods of calculation of thermal processes of the isolating materials are considered, in problems of nondestructive diagnostics of the main and distributive power stations. Theoretical justification of calculation of thermal processes of the multilayered isolating structure was given. On the basis of the analysis of results of operation, service life, physical processes of “ageing” and use of diagnostic parameters of the isolating structure characteristics of resistance of the equipment to refusal are offered. Time of refusal and a residual service life allow to predict using of dependences of refusal resistance.

Calculation of thermal processes in welding thick plates with moving axisymmetric heat sources

The solution of the heat conductivity problem for moving axisymmetric heat sources in a flat layer (thick plate) is described. Analytical solutions were obtained for heating with moving uniformly distributed annular and circular sources and also volume sources, distributed randomly in the thickness of the flat layer. Quasi-stationary (steady) fields of dimensionless temperature are described. The results of calculations and of experimental thermal cycles in argon-shielded welding of a steel plate are compared.

THE FEATURES MACROKINETICS THERMOLYSIS OF MULTICOMPONENT HYDROCARBONS SYSTEMS

Research objective was studying regularities for non-stationary kinetics of the thermolysis process in multicomponent hydrocarbon environments and studying regularities of compensation effect. The object of research was chosen aromatized, aromatized and waxy and waxy tars, and also tar of mix Arlansky and West Siberian oil. In the course of research was studied the nonstationary macrokinetics of the thermolysis process in multicomponent hydrocarbons systems, on the example of various nature straight-run oil residues of thermolysis. Values of effective energy of activation and effective a preexhibitor in arrhenius equation for various hydrocarbonic systems are received. At temperatures of 400-425 oС values of effective energy of activation of process is in range of 12,5 - 154,6 kJ/mol and values effective preexhibitors of ln k 0 - in the range of 0,43-25,3; at temperatures of 425-450 oС values of energy of activation is in range of 13,4-396,9 kJ/mol and values effective preexhibitors of ln k 0 – in the range from 0,64 to 64,6. Unlike the classical areniusovsky description of process, the non-stationary kinetics is described by one more constant which characterizes not stationarity of process and is connected with drift of a kinetic constant in time. The mathematical sense of a constant k is characterized by markovsky transitional probability. Values of effective constants for the studied raw materials are in range of 0,029 - 0,257 sec -1 for an interval of temperatures 400-425oС and 0,0001 – 0,7189 sec -1 for an interval of temperatures 425-450oС that corresponds to diffusive area. The kinetic compensation effect is confirmed which exists in multicomponents systems and there are included linear dependence of a logarithm preexhibitors and effective energy of activation process in an arreniusovsky constant of reaction rate. Effective kinetic parameters thermolysis process are finded can be use in the engineering calculation of thermal and thermocatalytic technological processes.

Calculation of thermal processes in heating plates with moving axisymmetric heat sources

Analytical solutions of the problem of heat conductivity in heating thin plates with moving axisymmetric heat sources with different radial distributions are presented. The solutions can be used for efficient calculations of the characteristics of the temperature field.

Calculation of thermal processes upon the laser modification of HTSC ceramics aimed at increasing the critical current

A mathematical model for the heating of a surface layer of HTSC ceramics by a CW laser beam scanned at a constant rate is considered. The calculated depths of the molten region are presented for the heating of the Bi(2223) ceramics by a CW CO2 laser. The theoretical results are in reasonable agreement with the experimental data. The calculations can be used for the optimization of laser processing of superconducting ceramics aimed at increasing the critical current density.

Contribution to the research and development of radiation chambers in steam reforming. Method for projecting primary reformer radiation chamber based on reactor modelling

A method for projecting radiation chamber representing an up-to-date method for projecting reaction furnaces based on modelling is described. The project is divided into a preliminary balance calculation, a method for projecting radiation chamber tube system and a simulation calculation of thermal chemical processes. The applicability of the model is illustrated by means of an example. Also principles for projecting radiation chambers of reforming furnaces as well as application spheres of the model to projecting practice are referred to.

Thermal processes during the interaction of optical radiation with heterogeneous layered media

We develop a method for the calculation of thermal and thermochemical processes during the interaction of optical radiation pulses of duration tp>10−6 sec with heterogeneous layered media.

Anwendung der Mischphasen‐Thermodynamik auf die Berechnung von thermischen Stofftrennverfahren

AbstractUse of multiphase thermodynamics in the calculation of thermal separation processes. The methods currently in use for calculation of the equilibrium between phases are reviewed. It is shown that such methods can be subdivided into those based on: (i) equations of state, (ii) the correspondence principle, and (iii) molecular behaviour. The latter methods have proved to be especially successful. They are based on simple and plausible representations of the interactions between atoms and molecules and can be further subdivided into methods according to the principle of local composition, in which further measurements are required, and into methods according to the principle of group increments, in which data can also be precalculated if no measurements are available. For practical purposes, however, rough methods of calculation also afford a good guide. They are often sufficiently accurate for an initial calculation and can be carried out, without the use of a computer, either with the aid of graphical methods or with a pocket calculator, so that parameter changes can be readily observed.

Calculation of thermal diffusion separation processes in a system with a traveling magnetic field

The equation of mass transfer in a column is used to calculate the separation factor and the separative power of a device with a traveling magnetic wave.