Выбор рационального расположения электродов в многоэлектродной дуговой печи постоянного тока

Mathematical modelling of thermal and electrical processes during electrosurgical resection of colorectal polyps

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.

Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)

Structure optimization of tree-shaped fins for improving the thermodynamic performance in latent heat storage

Effect of a rotating cylinder on the 3D MHD mixed convection in a phase change material filled cubic enclosure

This study focuses on the determination of the optimum values of the design parameters for heat transfer and pressure drop in a tube equipped with twisted tape using Taguchi method. Design parameters affecting the heat transfer rate and pressure loss were chosen as clearance ratio (c/D = 0.0178, 0.0357, 0.0535 and 0.0714), twist ratio (y/D = 2, 2.5, 3 and 3.5), and Reynolds number (Re = 5,200, 9,600, 14,000 and 18,400). Thus, Nusselt number in terms of heat transfer and pressure drop (ΔP) basis of flow friction were considered as performance parameters. L16(43), where 16, 4, 3 indicates the number of experiments, levels and parameters, orthogonal array was selected as experimental plan. Signal to noise ratios and contribution ratios of each parameter were calculated. The purpose of this study is to obtain the highest Nusselt number and the lowest pressure drop by reducing the number of experiments, and so to provide less experimental cost and time. Consequently, the heat transfer augments with the decrease of twist ratio, clearance ratio, but the increase of Reynolds number. In addition, pressure drop decreases with the increase of twist ratio, clearance ratio, and the decrease of Reynolds number. Optimum values were found as c/D = 0.0178, y/D = 2 and Re = 18,400 for Nusselt number and c/D = 0.0714, y/D = 3.5 and Re = 5200 for pressure drop.

This paper considers processes of electric arc damping by automatic switches in the short-circuit mode. Certain conditions for facilitating a successful short-circuit arc damping are shown, such as the limitation of the short-circuit current amplitude by its active resistance, the reduction of the phase shift between current and voltage, and the amplitude loss in returning and restoring voltages. The article features oscillograms of currents and voltages in the short-circuit mode. Anode heating processes are also described within the framework of the process of arc burning (heat saturation mode) and after the change of polarity current transition through zero processes at the cathode in the temperature equalization mode. Mathematical models of processes at the cathode took into account the thermal flows of the ionic component and evaporation. The calculations were carried out with the average values of thermal coefficients for copper, as the arc base moves from contacts to contact holders, which are made of copper and its alloys. The results of the calculations proved the validity of the considered mathematical models of thermal processes at both the cathode and the anode.

One of the main directions for improving heat supply systems is the tendency to switch to low-temperature heating systems by using heat pump units is the tendency of implementation the low-temperature heating systems based on the use of heat pump units. In the work, the main attention is focused on the improvement of thermal parameters and circuit design features of elements of the heat pump system of heat supply using soil energy. For this purpose, the toolkit of mathematical modelling of processes in ground heat pumps is applied, taking into account the climatic conditions of Ukraine. The paper proves the technical possibility of creating an autonomous system of alternative heat supply for energy-saving technologies with the possibility of using ground energy, taking into account environmental requirements. It is substantiated that the use of the proposed systems is a promising direction for Ukraine, which is experiencing a shortage of its own energy resources, because it provides an opportunity to increase the share of organic fuel substitution and reduce the volume of heat emissions into the environment. A mathematical model of heat processes in the elements of the heat exchange equipment of the heat pump system based on renewable energy (soil energy) and secondary energy (wastewater) was developed, taking into account environmental requirements (preventing hypothermia of the soil during the operation of soil pipes and damage to vegetation, respectively), which allows choosing a rational mode of operation of the system under seasonal climatic changes and technological conditions. Numerical modelling of heat processes in elements of the heat exchange equipment of the heat pump system using groundwater and waste water was performed, and the energy and environmental efficiency of the system under variable climatic and technological factors was determined. Analysis and generalization of the calculation results of the heat pump heat supply systems using alternative energy based on the proposed mathematical model, taking into account environmental requirements (preventing thermal relaxation of the soil) allows to take into account the change in the temperature gradient around the soil heat exchanger and more accurately determine the heat flow from each section of the heat exchanger. It has been established that for heat pumps with soil heat exchangers, the maximum substitution ratio of the traditional fuel is 75 %, and the economically feasible quantity of soil heat exchangers is 9 units. Heat pumps using waste water can completely replace traditional heat supply systems. For individual consumers, it is possible to recommend heat pump units with soil heat exchangers, at the same time, it is necessary to provide a backup source of energy to increase the reliability of heat supply.

A mathematical model of complex thermal processes with combustion, radiation and flow in rotary hearth furnace (RHF) for pellet direct reduction is established with CFD commercial software Fluent. Temperature distribution, pressure field and flow field in RHF are simultaneously analyzed by numerical method. It has been found that the temperature distribution in the furnace can meet the need of thermal institution for pellet direct reduction, and great pressure field and flow field can be formed on the basis of reasonable arrangement of burner, nozzle and partition. The simulation results would be helpful for engineering design and parameter optimization of RHF.

The purpose of this study is to propose an efficient numerical method for solving the inverse nonlinear problem of the movement of the compressor rotor collar in a fluid film thrust bearing. Methods. A periodic thermoelastohydrodynamic (PTEHD) mathematical model of hydrodynamic and thermal processes in a bearing is constructed under the condition of the rotor collar motion. Within the framework of the model, an inverse nonlinear problem of determining the position of the collar under a given external load is formulated. An iterative solution method is proposed, which utilizes the solution of the direct problem. To reduce computational costs, a modified Dekker–Brent method is employed in conjunction with a modified Newton’s method. Results. Numerical experiments have been conducted, demonstrating the effectiveness of the proposed approaches. The suggested methods significantly reduce the required computational resources by minimizing the number of calls to the target function in the optimization problem. A software suite has been developed that allows for the calculation of the nonlinear system of rotor motion under various physical and geometric parameters. Conclusion. An efficient set of numerical methods for solving the inverse nonlinear problem of the motion of the rotor collar in the compressor fluid film thrust bearing is proposed. The method’s effectiveness lies in substantial savings of computational resources. The method’s efficiency has been demonstrated in numerical experiments.

This article is devoted to the methods for increasing the efficiency of the heat pump heating system using the effect based on the energy saving principles. The major aim of the study is the analysis of methods for increasing the efficiency of heat accumulation by walls of the building with the account of for climate conditions, which correspond to the requirements of the energy saving technologies. To achieve the aim the mathematical model was proposed and comparative analysis of efficiency of heat accumulation by walls of the heat pump heating system was performed for the consumers of the South regions of the Ukraine. The algorithm of calculation the energy efficiency of the heat pump heating system for heat consumers was developed taking into account the climate conditions. The estimation methods for the energy efficiency of the proposed alternative heat supply schemes were offered. The method for realization was shown using the actual example, and the effectiveness of the alternative heating for consumers was confirmed. The numerical modelling of thermal processes in the elements of building were carried out. The analysis of the results of numerical modelling of thermal processes of heat accumulation by walls for the heat pump installation of heating the of two-story building was presented. The rational ways of increasing the efficiency of the alternative heating system with heat accumulation by walls and with account of climatic conditions were grounded. Results of simulation, conclusions and decisions for the practical application of the heat pump heating system, depending on temperature of the outside air were developed. The significance of the obtained results consists in justification of conditions, which make it possible to use the heat pump heating system using the effect based on the energy saving principles. The most significant results are those recommending the increase in the efficiency of the heat pump systems for the heat supply for the consumers of the Ukraine. The analysis results can be used for designing the heating systems based on the heat pumps using the low-potential energy with heat accumulation by walls of the building. Equations are proposed that are the mathematical model of thermal processes occurring directly in the heat supply facility itself and make it possible to calculate the time-varying thermal power required to meet the needs of the heat consumer and maintain a constant level of the specified microclimate in the building using internal resources of energy consumers

Heat transfer enhancement can be done in different ways but, use of nanofluid is one of the latest approaches. A numerical investigation of turbulent forced convection through a right-angled triangular shaped corrugated tube is presented by using commercial computational fluid dynamics software, ANSYS Fluent. The length and diameter of the tube which is considered for the study are 200 mm and 8 mm respectively and uniform constant heat flux of 5,000 W/m2 is applied at the corrugated wall boundary. A 2D simulation with the axisymmetric model is considered for analyzing different parameter. The corrugation has amplitude of 1.60 mm and a wavelength of 6 mm. Realizable k-e turbulent model is employed with enhanced wall treatment for the analysis. Nanofluid is allowed to flow with uniform velocity and uniform temperature of 300 K at the inlet of the pipe with an assumption of no-slip condition. Heat transfer parameter like convective heat transfer coefficient and fluid dynamics parameters like friction factor and pumping power are calculated using Al2O3-water nanofluid of different volume fraction (1%, 2%, 3%, 4%, and 5%) for a range of Reynolds number 5000 to 25000. The result shows that the heat transfer coefficient increases with the increase in volume fraction as well as with the Reynolds number and which is 67.3% for the Reynolds number of 25000 and 5% volume fraction of Al2O3.

This study is concerned with the computation of turbulent flow and heat transfer in U-bends of strong curvature. Following the earlier studies within the authors’ group on flows through round-ended U-bends, here attention is turned to flows through square-ended U-bends. Flows at two Reynolds numbers have been computed, one at 100,000 and the other at 36,000. In the heat transfer analysis, the Prandtl number was either 0.72 (air) or, in a further departure from our earlier studies, 5.9 (water). The turbulence modelling approaches examined, include a two-layer and a low-Re k-1 model, a two-layer and a low-Re version of the basic differential stress model (DSM) and a more recently developed, realisable version of the differential stress model that is free of wall-parameters. For the low-Re effective viscosity model (EVM) and DSMs, an alternative, recently proposed length-scale correction term, independent of wall distance has also been tested. Even the simplest model employed – two-layer EVM – reproduces the mean flow development with reasonable accuracy, suggesting that the mean flow development is mainly influenced by mean pressure rather than the turbulence field. The heat transfer parameters, on the other hand, show that only the low-Re DSMs produce reliable Nusselt number predictions for both Prandtl numbers examined. The Emerald Research Register for this journal is available at The current issue and full text archive of this journal is available at www.emeraldinsight.com/researchregister www.emeraldinsight.com/0961-5539.htm Nomenclature c1, c2, c w 1 ; c w 2 ; c1, c 0 1, c2, c 0 2 1⁄4 turbulence modelling constants ct, cm 1⁄4 coefficients f1, f2, fm, fH, fJ 1⁄4 damping functions fw1, fw2, fw3, f 0 w1, fRt, f 0 Rt, f 00 Rt, fA 1⁄4 coefficients in the Craft/NYap model k 1⁄4 turbulent kinetic energy NYap 1⁄4 new, differential, Yap correction term P 1⁄4 pressure Pij 1⁄4 production rate of the Reynolds stress Pr 1⁄4 Prandtl number T, t 1⁄4 mean, fluctuating temperature Ui, i 1⁄4 1; 2; 3 1⁄4 contravariant velocity components uiuj 1⁄4 Reynolds stress tensor uit 1⁄4 turbulent heat flux xi,i i 1⁄4 1; 2; 3 1⁄4 Cartesian coordinates Computation of flow and heat transfer

In this paper the results of a numerical investigation of the melting and solidification process of sodium nitrate, which is used as phase change material, will be presented. For the heat transfer to the sodium nitrate different finned tube designs, namely helical-, transversal- and longitudinal finned tubes, are used. The numerical results of the melting and solidification process for the different design cases will be compared. The numerical analysis of the melting process has shown that apart from the first period of the charging process natural convection is the dominant heat transfer mechanism. The numerical analysis of the melting process has also shown that for a fast melting process heat exchanger tubes should be designed in such a way that an unrestricted natural convection is guaranteed. The numerical investigation for the solidification process has shown that the dominant heat transfer mechanism is heat conduction. The investigation has also shown that the solidification front grows more uniformly from the tube surface to the outer shell compared to the melting front. Therefore no significant differences between the different tube designs are detected concerning the solidification process.

In the development of automatic control systems (ACS) for heat supply of buildings, mathematical models of their control objects play a significant role, one of the most important elements of which being the enclosing structures. The existing models of thermal processes indoors either do not take into account the dynamic effect of the enclosing structures, or are complex analytical expressions, the use of which in the engineering practice of the synthesis of ACS for the indoor thermal regime is difficult. The purpose of the study was to create a linear mathematical model of the thermal interaction of the external and internal air environment through the enclosing structures. To achieve this goal, a functional diagram of a heated room as a control object was developed, which describes the mechanism of thermal interaction of its elements. On its basis, design schemes of thermal processes for external and internal enclosing structures were developed. They were used to create systems of equations linking temperatures on the surfaces of layers of external enclosing structures and air temperatures outside and inside the premises. At the same time, the assumption was introduced that the dynamic temperature distribution over the thickness of the enclosing structure is linear. To find the temperatures at the boundaries of the layers, the average temperature value over the thickness of the structure was used. As a result of the study, equations for the dynamics of heat transfer processes were obtained, and a generalized structure of a model of multilayer external enclosing structures of a room as an element of a control object was developed. The resulting model can be used to develop a generalized mathematical model of the thermal regime of both individual rooms and the building as a whole.