Thermophysical Processes Research Articles

DIRECT OBSERVATION OF HIGH-TEMPERATURE AREAS OF METAL MELT AT OXYGEN CONVERTER BLOWING WITH LOW VOLTAGE APPLICATION

Introduction. The process of oxygen conversion, despite the existing improvements, can be supplemented by physical methods of influence, including the unconventional method of applying low-voltage potential developed at the Iron and Steel Institute of the NAS of Ukraine.Problem Statement. The studies of the method of low-voltage potential application on 60, 160 and 250 ton converters have shown that the technology intensifies thermophysical and hydrodynamic processes in the gasslag-metal system and increases the converter process efficiency.Purpose. The purpose of this research is to study the features of the influence on the reaction zones of the low voltage potential application at four blowing options with the use of high-temperature physical model.Materials and Methods. A physical model that simulates the top, bottom and combined oxygen blowing under low-voltage potential application of different polarity on the lance has been used. An insert of a transparent quartz plate is made in one of the walls for visual observation and video recording. The top blowing is conductedwith two nozzle lance (nozzle diameter 1.7 mm with an angle of 30 ° to the lance). The bottom blowing is conducted with a bottom tuyere with a 1.5 mm diameter central nozzle. Combined blowing is realized by a combination ofthese options.Results. The visual observation of the reaction zones with different blowing options has shown that the highest temperature and the largest dimensions of the brightest parts of the bath correspond to the combined blowing, while the lowest ones are reported for the bottom blowing. While applying the low-voltage potential method it has been established that the reaction zone is longer at the positive polarity on the lance, during the period of silicon oxidation, and at the negative polarity on the lance, during the period of intense carbon oxidation. The video of gas bubbles flotation, probably CO, has shown that the bubbles are formed more intensively in thecase of negative polarity on the lance.Conclusions. The applied technique has allowed estimating the influence of low-voltage potential application on the geometric parameters of the reaction zone.

Modeling of Thermal Conductivity in a Medium with Phase Transition with a Moving Boundary of Phase Change

This work is devoted to the theoretical study of the effect of the phase interface motion on thermal conductivity in a liquid-solid nonlinear medium with a phase transition. The problem under consideration deals with the Stefan problems. Its most significant feature is the jump in the phase properties at separation of their moving boundaries. The objective was achieved by solving the following tasks: the construction of the process mathematical model based on its cell representation and with the use of the Markov chain theory mathematical apparatus, performing numerical experiments with the developed model, demonstrating its operability and the possibility to achieve the set goal. The most significant scientific results were as follows. First was an algorithm for the construction of a cell mathematical model of nonlinear thermal conductivity in a phase transitions medium with a moving phase interface for domains of a canonical shape (plane wall, cylinder, ball). Second, the results of the numerical experiments, showing that the jump of properties affected greatly the kinetics of the process. The significance of the results obtained consisted in the development of a simple but informative mathematical model of the media heat treatment kinetics with phase transformations, available for a direct use in the engineering practice. The proposed algorithm for constructing the model can be effectively used in prediction the open water pipes freezing in cold regions, in modeling the heat treatment of metals, in choosing the freezing modes of food products for a long-term storage, and other thermo-physical processes.

Experimental investigation on subcooling of liquid hydrogen by helium gas injection through evacuation

AbstractSubcooling is the process of bringing down the temperature of liquids lower than that of the boiling point of the corresponding vapor pressure. The performance of subcooling of cryogenic liquids mainly depends on the heat‐inleak of the system, the helium injection mass flow rate, helium injection temperature, and helium injection nozzle pattern. This paper presents an alternative method, by making use of the least heat in the leakage of the liquid hydrogen storage container, which is quite possible because containers with excellent thermal insulation are commercially available nowadays. The process involved is rapid evacuation through gas ejectors, thus reducing the effect of temperature. The advantage and the process of evacuation leading to subcooling in a unique manner are the objective of this article. The experimental results are discussed in comparison with the thermophysical process involved in the subcooling operation. A comparative study is also carried out with the theoretical heat exchange process in which helium is used as a medium for the economy of the stated process. It is stated that the current process of subcooling through evacuation is superior to the conventional heat exchange process.

Simulation modeling of non-stationary thermophysical processes when monitoring the reliability of main oil pipelines in the Arctic

The use of modern complexes for calculating the designed pipeline systems and for predicting their behavior for a period of more than ten years is necessary in modern conditions of the constantly developing hydrocarbon market and the development of new northern territories for greater oil production. It will allow avoiding accidents and environmental disasters that have become more frequent in recent years due to the deterioration of existing equipment. The article presents a method for monitoring the main reliability parameters of underground oil pipelines, taking into account changes in soil foundations, mainly in the Arctic zone of the Russian Federation. An oil pipeline section is considered as an object for monitoring of heat engineering processes and their influence on the reliability of the system. We describe the main results of calculations of the oil pipeline section and simulate changes in soil foundations. We used a multilayer pipe with polyurethane foam insulation and coating for the calculations to improve the reliability characteristics. This pipe has showed the best results of modeling in comparison with the design pipe.

A novel biomass gasification micro-cogeneration plant: Experimental and numerical analysis

This work presents a numerical model developed to predict the behaviour of a real micro-cogeneration biomass gasification system, based on a fixed-bed downdraft gasifier, coupled with a spark-ignition internal combustion engine. The model developed by the authors takes into account all the thermo-physical processes occurring in the whole system: gasification, cleaning, combustion and heat recovery. The numerical model is based on the Gibbs free energy minimization, applying the restricted equilibrium method. The model has been validated with the experimental data collected during an extensive experimental campaign, and a good agreement between measured data and predicted results is obtained. The present validated model has proved to be a useful tool for analyzing the performance of real micro-CHP plants. The global electrical and thermal efficiencies predicted by the model are 19.9% and 17.8%, while the measured values are 19.5% and 21.7%, respectively. Some parametric analyses have been carried out in order to assess the performance of the system as a function of the main gasifier and engine parameters, and to predict the behaviour of the system.

MATHEMATICAL MODEL OF A THERMOELECTRIC SEMICONDUCTOR SYSTEM FOR VISUALIZING THE TEMPERATURE FIELDS OF OBJECTS

Objective. The research objective is to develop a mathematical model of a thermoelectric semiconductor system to visualize the temperature fields of objects and study the thermophysical internal processes. Methods . A thermoelectric semiconductor system was developed for visualizing the temperature fields of flat objects using a liquid crystal film. Its feature is to increase the accuracy of measurements due to a more accurate coupling of the object and the device. A mathematical simulation of the system was performed based on the solution of a dynamic two- dimensional heat conduction problem with local heat sources and sinks over the area of a liquid crystal film. Results . Dependency graphs were obtained for the dependency of two-dimensional temperature distribution over the surface of the liquid crystal film in the presence of heat sources and sinks, the change in the cooling capacity, the cooling ratio, the supply voltage of the thermoelectric module on the temperature difference between the junctions for different values of the supply current. Conclusion . As a result of calculations, it was found that the color gamut of a liquid crystal film changed significantly in the presence of heat sources and sinks on its surface. During pre-calibration, the system allows visualization of the object temperature field and determines the value of its temperature at each point. Following the calculated data, it is determined that to ensure the entire operation of the thermoelectric semiconductor system, a standard thermoelectric module ICE-71 can be used with the following specifications: power range – 16 to 35 W with an average temperature difference between the junctions – 55 K, the supply current – 2  8 A with a power consumption of 40 to 90 W, the cooling ratio is from 0.38 to 0.43.

The effect of the distance between wood and coal particles on the characteristics of their joint ignition under conditions of high-temperature radiation-convective heating

The article presents the results of the experimental studies of the ignition processes of mixed fuels “wood + coal” under conditions corresponding to the furnace spaces of the boiler units of TPPs. It has been established that under conditions of relatively low ambient temperatures, the time characteristics of the ignition process of coal and wood particles in the composition of the mixture differ significantly from the analogous characteristics for the ignition of single particles. It is shown that woody biomass significantly accelerates the ignition of coal, compared to the ignition of homogeneous coal (the delay time is reduced by 20–30%). At the same time, it has been found that coal particles significantly slows down the process of wood ignition (on average by 30%).The analysis of the distance between particles (d) has shown that d has a significant effect on the ignition performance. It was found that there is a certain “optimal” value of d, at which the ignition delay times are minimal. It is also shown that with an increase in the ambient temperature, the effect of the distance between particles decreases significantly.Based on the results of the experimental studies, a mathematical model has been developed for the ignition of wood-coal fuel particles, which differs from the known ones by a detailed description of thermophysical and thermochemical processes occurring in the porous structure of fuels and in a small vicinity of these particles. A comparative analysis of theoretical and experimental values of ignition delay times has shown their good agreement. An asymptotic analysis of the ignition time has shown that the entire induction period can be conditionally divided into two stages: fuel heating and direct thermochemical reaction. The fuel heating time takes about 90% of the entire induction period.

Mathematical modeling of the thermochemical processes of nitrogen oxides sequestration during combustion of wood-coal mixture particles

The article presents the results of a mathematical modeling of the combustion process of the particles of biomass/coal mixtures under conditions corresponding to the combustion chambers of the boiler units of the thermal power plants. The mathematical model of the ignition process developed by the authors differs from those presented earlier by a detailed description of the complex of the thermochemical and thermophysical processes that occur both in the boundary layer of the fuel particle and in its pores.The authors have formulated a new hypothesis about the sequestration of anthropogenic nitrogen oxides (NOx) at the initial stage of fuel combustion. It is accepted that the decrease in NOx yield during the combustion of biomass/coal fuel is due to the intensification of the formation of nitric (HNO3) acid vapors and their interaction with solid products of thermal decomposition of coal.The results of a numerical modeling of the processes under study show the possibility of a theoretical analysis of the conditions for co-combustion of the coal and wood particles, which provide a significant decrease in the yield of nitrogen oxides in comparison with the combustion of homogeneous coal.

Розробка програмного комплексу раціонального проектування систем охолодження на основі термопресорних технологій

The most common way to increase power and reduce fuel consumption by modern power plants is contact cooling of a gas or air flow by water injection. A promising development of this direction is to use aerothermopressor technologies. The use of heat air, which is compressed by the power plant compressors, accelerates the flow to a speed close to the sound one and almost instantaneous evaporation of injected water (the effect of thermo-gas-dynamic compression). It is important to determine the rational parameters of the organization of thermophysical and hydrodynamic processes when developing such technologies. In this case, one should be taken into account the appropriate development of the flow path design and a special software product. It is necessary to use methods and means to determine the optimal operating parameters of the power plant heat recovery systems. This paper presents a block diagram and an algorithm of a rational methodology for designing an aerothermopressor, which makes it possible to accurately determine the efficiency of using an aerothermopressor as part of a power plant (based on a gas turbine engine) for cooling cycle air, considering the peculiarities of operating modes in the flow path, as well as under various climatic operating conditions. The algorithm of a rational methodology for designing aerothermopressor technologies allows calculating the characteristics of equipment, systems, and circuit design solutions when used as part of a power plant: an electric generator; heat-using refrigerating machines (ejector refrigerating machines, absorption refrigerating machines); turbine generator or steam generator as part of a trigeneration unit or as part of a turbo-compound unit (power plants of marine vessels); recovery boiler of one or two pressures. Modeling the aerothermopressor-cooling system operation makes it possible to reveal the effectiveness of using such a system as part of a power plant and compare it with traditional methods of cooling and humidifying cycle air.

Analytical method of calculation of thermal fields of cast parts during crystallization

The aim of the work is to create a mathematical method that allows to calculate the distribution of thermal fields in cast parts during crystallization using a system of analytical formulas. During the calculations, a combination of known analytical formulas GF was used. Balandin, AY Weinik, S. Schwartz with their own original mathematical solutions created on the basis of the analysis of thermophysical processes in castings in the process of their crystallization. Computer simulation of thermal fields using the LVMFlow program was used to compare the results. According to the created mathematical method, examples of calculation of thermal fields for two castings made of steel 25L of hollow cylindrical shape, the wall thickness of which is 100 mm and 4 mm, respectively, are given. Calculations were performed for the conditions of crystallization of castings in a single sand form. The comparison of results of calculations by the developed method and with use of the existing software is presented. For the first time, based on our own mathematical and thermophysical developments, a comprehensive calculation method for determining the thermal field of the casting during crystallization and cooling was developed. casting. The technique is expressed in a number of analytical formulas, each of which describes a specific thermal process that occurs in the casting. This takes into account the features of the casting configuration. The created complex method of calculation of thermal fields of cast parts is a mathematical basis for determining the thermal fields of molds and rods, which allows to predict their properties and select the optimal molding materials. The created technique can also be offered as a mathematical basis for refining applied computer programs for foundry production. CASTING, TEMPERATURE, THERMAL FIELD, COOLING DYNAMICS, COOLING DURATION, MATHEMATICAL LAW, COLORING FRONT, CALCULATION

Numerical study of the boil-off gas (BOG) generation characteristics in a type C independent liquefied natural gas (LNG) tank under sloshing excitation

In this paper, a numerical model considering phase change and external heat leakage is established to study the thermodynamic and hydrodynamic of a type C LNG tank under sinusoidal sloshing excitation. The volume of fluid (VOF) method, coupled with the mesh motion treatment, is adopted to predict the movement of the vapor-liquid interface. The sinusoidal sloshing excitation is realized by a user-defined function (UDF). Compared with related fluid sloshing experiments, the feasibility of the numerical model is verified. The numerical results show that the sloshing excitation has great influences on the thermophysical process and the BOG generation of the LNG tank. The effects of different sloshing frequencies and amplitudes on the thermodynamic characteristics of the LNG tank are studied. In addition, the partial damage of the insulation system is also studied, and it is found that the sloshing has little effect on the critical superheat of the tank wall where the insulation layer is partial damaged, but it will delay the increase of the tank wall temperature. This study is significant to deeply understand the thermal behavior of the LNG sloshing and the characteristics of the BOG generation under sloshing condition during the actual marine transportation of LNG ships.

Comparative evaluation of flow-through and counter-flow indirect-evaporative air coolers and their influence on the heat balance of transformer underground substations

In order to optimize the air environment temperature of the underground engineering equipment premises, it is necessary to conduct a comparative assessment of the operation of flow-through and counter-flow indirect-evaporative air coolers. Based on the previous mathematical models that describe the thermophysical processes in the channels of indirect evaporative coolers, an analysis of the structural and standard parameters of their operation is carried out. The most rational ratios of flows through the “wet” and “dry channels” are revealed and they ensure the maximum station cooling capacity. The transformer substation of the underground illustrates the effectiveness of their use. According to a result of the studies, it has been proved that the most rational ratio of air flows through wet and dry channels for flow-through indirect-evaporative coolers is 2.1-2.2, for counter-flow heat exchangers it is 3.0. The advantage of recuperation coolers is established by such indicators as: cooling capacity - 53.5%, air cooling range - 41%.

Model of an electronic equipment cooling system based on the joint use of high-current thermoelectric semiconductor batteries and a thermal thermosipho

Objective. The objective of the study is to develop a design model of the electronic equipment cooling system based on the combined use of high-current thermoelectric semiconductor batteries of layered design and an evaporative-condensing thermal thermosyphon, as well as to study the thermophysical processes occurring during its operation.Methods. A mathematical model of the electronic equipment cooling system based on the combined use of high-current layered thermoelectric batteries and an evaporative-condensing thermal thermosyphon is presented. The design model includes a description of heat exchange processes in a layered thermoelectric element at various supply currents, determination of the amount of heat transferred through the cross-section of the channel of a thermal thermosyphon per unit of time, and the temperature values at each channel point.Result. A 2D dynamic heat conduction problem is solved for a complex system with rectangular geometry of fragments and heat sources. The temperature distribution of a thermoelement along its longitudinal axis at different values of the supply current and the change in the heat flow along its length in a thermal evaporation-condensation thermosyphon are studied.Conclusion. The results of the research have shown the effectiveness of combined use of high-current layered thermoelectric batteries and a thermal thermosyphon in electronic equipment with dense element packaging. It is shown that to increase the efficiency of electronic equipment and reduce the heat losses that occur in the heat line when the heat-generating element of radio-electronic equipment and thermoelectric semiconductor batteries are separated by a sufficiently large distance (over 0.6 m), it is advisable to use an evaporative-condensing thermal thermosyphon as a heat line.

Selection the measuring system for registering the metal parts temperature at microarc heating and its thermophysical analysis

Measuring the temperature of metal parts during thermal and thermochemical treatment is necessary for the control of the correctness of the technological process. Currently, new methods of thermochemical processing of parts under high-energy conditions, such as microarc surface alloying, are proposed. Heating is carried out by the action of microarc discharges on the surface of parts immersed in coal powder when an electric current flows. It reduces the processing time from a few hours to a few minutes, but makes it difficult to measure the temperature, because heating occurs in dynamic mode. The aim of the work was to select a measuring system for recording the metal parts’ temperature during microarc heating, and the thermophysical analysis of the heating process. The S-type sensor was selected. The measuring system also includes a digital multimeter and a personal computer. The density of the electric current on the surface of the samples was 0.53 A/cm2 The registered heating curve consists of several stages. At the first stage the heating speed was about 8 °C/s. At the second stage it increases to 16 °C/s, but then decreases to 3.5 °C/s. Then the temperature increases monotonously with an average speed of 9 °C/s. At the fourth stage the sample temperature is stabilized at 1250 °C. The thermophysical process’ model of the heating metal parts under the influence of microarc discharges was proposed. The analysis showed that the calculated data coincide with the experimental data.

ОСОБЕННОСТИ ТЕРМОМЕХАНИКИ ПУЛЬСИРУЮЩИХ ПОТОКОВ ГАЗА ВО ВПУСКНЫХ СИСТЕМАХ С КАНАВКАМИ ПРИМЕНИТЕЛЬНО К АВТОМОБИЛЬНЫМ ДВИГАТЕЛЯМ

Reciprocating internal combustion engines (RICE) are widely used as heat engines for converting the chemical energy of a fuel into mechanical work on the crankshaft. Aerodynamic and thermophysical processes in gas exchange systems significantly affect the efficiency of the RICE. This paper examines the possibility of influencing the gas dynamics and heat transfer of pulsating gas flows in the inlet system by placing a channel with grooves. It is known that the presence of grooves in the channel leads to the formation of significant secondary vortices, which radically change the physical picture of the gas flow. The studies were carried out on a laboratory bench, which was a singlecylinder model of a turbocharged RICE. A system of measurements of basic physical quantities is described, taking into account their high dynamics. Techniques for processing experimental data are presented. Primary data on instantaneous values of gas-dynamic and heatexchange characteristics of pulsating flows are presented. It was found that the presence of a channel with grooves in the inlet system leads to a decrease in the degree of turbulence to 40 % and an intensification of heat transfer in the range of 5–50 % compared to the basic inlet system. A positive effect is shown in the form of an increase in engine power by 3 % when using the modernized system.

Processes of Development and Relaxation of Plasma Channel in the Pulse-Periodic Cesium–Mercury–Xenon Discharge

The work is devoted to the study of thermophysical and radiation processes during the formation of a plasma channel under the passage of a series of current pulses of pulsed-periodic cesium–xenon–mercury discharge. The influence of the auxiliary discharge mode, temperature, and vapor pressure of metals on the development and relaxation of the plasma channel is shown. The spectral characteristics of the passage of each of the current pulses are studied.

Оптимизация надежности теплоснабжения с учетом функций активного потребителя

The article considers the problem of analyzing and optimizing the reliability of heat supply to an active consumer (AP) of thermal energy in heat supply systems (HSS), taking into account their additional thermal power provided by their own sources of thermal energy (IT). The stated scientific and methodological problem consists in determining the optimal ratio of the values of the reliability parameters of the HSS elements (failure rates and / or restorations) and the power of the own IT AP, which ensures the required level of reliability of heat supply with minimal total costs to ensure the elemental reliability of the system and the operation of its own IT AP. The authors propose solutions based on the use of the theory of reliability, models of Markov random processes, some regularities of the theory of probability, nodal PN, models of the theory of hydraulic circuits and enlarged regularities of thermophysical processes occurring during heat supply to consumers. A computational experiment was carried out using the developed methods based on the TSS test circuit with characte­ristics close to real systems, providing the basis for conclusions and directions for further research.

Моделирование тепловых режимов в канале воздушного охлаждения аппарата восстановления титана

Numerical modeling of thermophysical processes in the air cooling channel of titanium sponge reduction apparatus is performed. The cooling channel is an area bounded by a retort filled with liquid magnesium and the apparatus wall, on which heating elements are mounted. Air flows inside the channel, cooling the retort. A mathematical model is constructed based on unsteady Navier-Stokes equations in axisymmetric formulation using a k-ω SST turbulence model. The model takes into account the radiation heat transfer between the retort and reactor walls. Four variants of thermal boundary conditions are considered. The aim of this work is to create a mathematical model of conjugate heat transfer in an air channel. Based on this model, the temperature conditions of the retort wall are calculated and the profiles of the heat transfer coefficient along the retort wall for a wide interval of air flow rates are obtained. It is shown that temperature distributions along the retort are heterogeneous and strongly depend both on external boundary conditions and on the cooling intensity. Heat transfer coefficient distributions from its outer wall for different retort heating conditions are plotted and an empirical formula for calculating the profile of this coefficient is proposed.

Influence of thermophysical processes occurring in the zone of moving contact on the mechanical properties of the surface layer of materials

Influence of thermophysical processes occurring in the zone of moving contact on the mechanical properties of the surface layer of materials

Тепловая нагрузка биметаллической оребренной трубки

This study is devoted to the problem of numerical modeling of the conjugate heat transfer in a closed-type power installation. The working elements of that are ribbed bimetallic tubes using the openFoam toolbox. The heat transfer process modeling in bimetallic tubes is associated with solving the problem of determining the value of the contact thermal resistance at the metal / metal interface. Considered design of a bimetallic tube involves crimping copper washers on the surface of an aluminum cylindrical tube. Hence, the contact surface of the tube is not isotropic in its properties. A mathematical model of conjugate heat transfer for air / bimetal / coolant medium is proposed. The features of the organization of thermophysical processes at the metal contact interface and at the metal / air and metal / coolant medium are shown. A qualitative comparison of the obtained results with the famous experimental data is carried out. Generalized temperature profiles in the rib longitudinal section are obtained by mathematical modeling. The given distributions of temperature and heat flux make it possible to estimate the contribution of each individual rib to the investigated heat removal process from the air environment. The efficiency of the considered technology of manufacturing a bimetallic finned tube is shown.