Two-dimensional electromagnetic field effects in induction plasma modelling

The aim of the work is to investigate the basic phenomena of heat generation and transfer in inductively-coupled RF plasma torches working at atmospheric pressure. Many fundamental works on the subject [1,2] propose a detailed treatment of the electromagnetic, temperature and velocity fields inside the torch. In the present work, in order to highlight the effects due to the distribution of the electromagnetic and temperature fields when separated from the effect of the complex behaviour of the fluid circulation, simplified slab and cylindric geometries for the cross section of the torch have been considered. The mathematical model takes into account heat conduction and convection, using a simplified expression for the velocity field; a two-dimensional treatment of the electromagnetic field is employed. The results presented refer to torch working near the minimum plasma sustaining power and well above threshold, showing temperature and power density distributions; comparisons between results obtained using the exact two-dimensional treatment for the electromagnetic field and a simplified one-dimensional approach are presented. A simple model is also presented explaining why the transverse temperature profile tends to change its shape in order to induce an increase of the mean power along the axial coordinate when the mean plasma temperature decreases.

In this paper, a 15 KW in-wheel motor (IWM) is taken as the research object, and the coupling factors among the electromagnetic field, temperature field and flow field are analyzed, and the strong and weak coupling factors between the three fields are clarified, and by identifying the strong and weak coupling factors between the three fields, a three-field coupling analysis model for IWM with appropriate complexity is established, and the validity of the model is verified. In a certain driving condition, the electromagnetic field, temperature field and flow field characteristics of IWM are analyzed with the multi-field coupling model. The result shows that, after the IWM runs 8440 s under driving conditions, in this paper, the IWM electromagnetic torque of the rated working condition is 134.2 Nm, and IWM the electromagnetic torque of the peak working condition is 451.36 Nm, and the power requirement of the motor can be guaranteed. The highest temperature of the IWM is 150 °C, which does not exceed the insulation grade requirements of the motor (155 °C), the highest temperature of the permanent magnet (PM) is 65.6 °C, and it does not exceed the highest operating temperature of the PM, and ensures the accurate calculation of components loss and the temperature of the motor. It can be found, through research, that the electromagnetic torque difference between unidirectional coupling and bidirectional coupling is 3.2%, the maximum temperature difference is 7.98% in the three-field coupling analysis of IWM under rated working conditions. Therefore, it is necessary to consider the influence of coupling factors on the properties of motor materials when analyzing the electromagnetic field, temperature field and flow field of IWM; it also provides some reference value for the simulation analysis of IWM in the future.

Radiative energy transfer in induction plasma modelling

Numerical simulation on electromagnetic field, flow field and temperature field in semisolid slurry preparation by A-EMS

Gas metal arc welding (GMAW) process is an indispensable technology in various industrial fields. The phenomena during the welding process such as the temperature history of the base metal strongly affect to the properties and performance of the weld joint. It is very important to predict and control the phenomena in the process, however, the phenomena is very complicated and not completely understood. In this study, numerical models of the heat source and the weld pool formation in GMAW process are constructed to visualize the phenomena and predict the welding results of the GMAW process. The heat source model includes the arc plasma and metal transfer phenomena. The temperature, velocity, pressure, and electromagnetic field in the arc plasma and the molten metal are calculated. Influence of the metal vapor from the surface of high-temperature metal is also considered. Input parameters of the heat source model are the welding condition such as the current and the shielding gas used in the experiment. The properties of the heat source such as the heat input distribution, arc pressure distribution and the temperature of the droplet are calculated by the heat source model. These properties are input to the weld pool model. The weld pool model calculates the flow and temperature fields in the weld pool and can predict the penetration shape and the temperature history in the weld joint. These models are applied to pulsed-MAG welding process, the numerical result of the penetration shape shows good agreement with experimental results.

Temperature and velocity fields in high-temperature lead coolant flows in a circular clearance for controlled oxygen impurity content in a flow were experimentally studied at the Nizhny Novgorod State Technical University by R.E. Alekseev (NNSTU). Temperature and velocity fields were simultaneously studied in “cold” and “hot” parts of the circuit in the following operating conditions: the lead temperature is t = 400–550 °C, the thermodynamic activity of oxygen is a = 10−5–100; the Peclet number is Pe = 500–7000, the coolant flow velocity is w = 0.1–1.5 m/s, and the average heat flux is q = 50–160 kW/m2. It has been found that the oxygen impurity content and characteristics of protective oxide coatings affect temperature and velocity fields in round and circular channels. This is due to the fact that oxygen in a coolant and oxide coatings on the surfaces limiting a liquid metal flow influence characteristics of the wall boundary region. The heat transfer process that occurs when HLMC transversely flows around heat exchange pipes is investigated now at the NNSTU. The experimental facility is a combination of two high-temperature liquid-metal stands, i.e., FT-2 with the lead coolant and FT-1 with the lead-bismuth coolant combined with an experimental section. The temperature of a heat-exchange surface is measured by thermocouples of diameter 1 mm mounted in walls of heat-exchange pipes. Velocity and temperature fields in a high-temperature HLMC flow are measured by special sensors placed in the flow cross section between rows of heat-exchange pipes. Heat transfer characteristics and temperature and velocity fields in a high-temperature lead coolant flow are studied in the following operating conditions: the lead temperature is t = 450–500 °C, the thermodynamic activity of oxygen is a = 10−5–100, and the coolant flow rate through the experimental setup is Q = 3–6 m3/h, which corresponds to coolant flow velocities of V = 0.4–0.8 m/s. Integrated experimental studies of characteristics of the heat transfer that occurs when the lead coolant transversely or obliquely flows around pipes have been carried out for the first time and the dependences Nu = f(Pe) for controlled content of thermodynamically active oxygen impurity and sediments of impurities have been obtained. It is assumed that the obtained experimental data on distribution of velocity and temperature fields in a HLMC flow will permit to study heat transfer processes and to use them for developing program codes for engineering calculations of heat exchange surfaces (steam generators) with a HLMC flow around them.

In this paper, the electromagnetic and temperature field of a 250-MW air-cooled hydro-generator in the Wuqiangxi hydropower station was calculated. The 2-D electromagnetic field model was built. Through solving the model, the additional loss and its distribution were determined. The rotor 3-D temperature field was then calculated and analyzed. Due to many gas eddies, the inner environment of a large hydro-generator is, therefore, complex. This leads to difficulty in determining the heat transfer coefficients on rotor surfaces. To accurately determine the heat transfer coefficients distributions, a method combining numerical and analytical calculations is proposed based on Fourier's theorem and Newton's heat transfer law. Using this new method, the heat transfer coefficients distributions on rotor surfaces were repeatedly calculated. The rotor temperature distribution was then computed. After comparing the measured values, the calculated temperature with determined heat transfer conditions were more accurate than that from traditional methods. This provides a theoretical basis for calculating heat transfer coefficients of outer surfaces of 1000-MW air-cooled giant hydroelectric generator.

Abstract. Loop Current rings (LCRs) are among the largest mesoscale eddies in the world ocean. They arise when bulges formed by the Loop Current in the Gulf of Mexico close off. The LCR formation process may take several weeks, and there may be several separations and reattachments before final separation occurs. It is well established that this period is characterized by a persistent saddle point in the sea surface height field, as seen in both model and satellite data. We present here a detailed study of this saddle region during the formation of Eddy Franklin in 2010, over multiple days and at several depths. Using a data-assimilating Gulf of Mexico implementation of the HYbrid Coordinate Ocean Model (HYCOM), we compare the vertical structure of the currents and temperature fields on 5 and 10 June 2010. Finite-time Lyapunov exponents (FTLE) are computed from the surface down to 200 m to estimate the location of relevant transport barriers. Several new features of the saddle region associated with LCR formation are revealed: the ridges in the FTLE fields are shown to be excellent surrogates for the manifolds delineating the material flow structures with only slight degradation at depth. The intersection of the ridges representing stable and unstable manifolds drops nearly vertically through the water column at both times; remarkably, the material boundary shapes are maintained even as they are advected. Moreover, velocity stagnation points and saddle points in the temperature field are consistently found near the intersections at all depths, and their geographic positions are also nearly constant with depth.

The problem of taking into account a non-stationary inhomogeneous temperature field in the analysis of the stress-strain state of inductor systems for magnetic-pulse processing of materials is considered. It follows from the analysis of open information sources that the problem of analyzing a non-stationary temperature field arising from the presence of a non-uniform electromagnetic field and its effect on deformation has been sufficiently studied in relation to induction heating. At the same time, during other operations of magnetic-pulse processing of materials, heating of equipment can cause additional deformations of a significant magnitude, which, in turn, can lead to a loss of equipment performance due to destruction or irreversible deformation. A general approach to the analysis of such problems is proposed, which involves the determination of the spatial-temporal distributions of the quantitative characteristics of the electromagnetic field, temperature field and stress-strain state. The necessity of using numerical methods for carrying out such an analysis has been substantiated. The most effective numerical method is the finite element method, which makes it possible to analyze the unsteady electromagnetic field, temperature field, and stress-strain state within the same calculation scheme. In this case, within the framework of the finite element method, iterative schemes can be created that allow taking into account nonlinear effects. Here, nonlinear effects can be due to the dependence of the mechanical and electro-physical properties of the material on temperature, the plastic nature of deformation, and the need to take into account contact phenomena. The results of complex analysis for a composite single-turn inductor with a dielectric band are presented. The features of contact interaction were taken into account by introducing layers of contact finite elements. The stress-strain state of the inductor is estimated for two variants of the materials used: copper and non-magnetic steel.

In the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel subassembly is considered one of the main issues to be addressed and one of the most important and realistic accident for Lead Fast Reactors (LFR) fuel assembly. The blockage in a fast reactor Fuel Assembly (FA) may have serious effects on the safety of the plant leading to the FA damaging or melting. The external or internal blockage of the FA may impair the correct cooling of the fuel pins, be the root cause of anomalous heating of the cladding and of the wrapper and potentially impact also fuel pins not directly located above or around the blocked area. In order to model the temperature and velocity field inside a wrapped FA under unblocked and blocked conditions, detailed CFD thermal hydraulic analyses of the FA are required. ALFRED is a 300 MWth Lead-cooled fast reactor GEN.IV concept. The advanced conceptual design of the reactor was carried out within the LEADER EU project in the last years. In the SESAME EU project specific thermal-hydraulic experiments and simulations were addressed to explore the basic phenomenology of some accidental events like internal flow blockage. A CFD computational model of the ALFRED FA is built for thermal hydraulic analysis of relevant internal blockage scenarios. The whole model of the ALFRED Fuel Assembly is first presented and calculation of flow and temperature field in nominal condition is carried out. RANS simulations of idealized blockage scenarios like one sector and two-sectors blockage are performed adopting three different spacer grid location (under the active length, at half active length, above the active length). Results showed that the most likely blockage in the lower grid positioned before the active region do not perturb the temperature distribution in the fuel assembly, while the central grid ones have strong consequences and leads to a clad temperature peak behind the blockage with possible clad failure. On the other hand, the most severe case on the upper grid (2 sectors blockage) showed a manageable temperature maximum (700°C) at the end of the active region due to the lower mass flow rate in the FA. As a conclusion lower and upper grid blockages perturb only marginally the temperature field and do not lead to serious clad failure involving only creep long-term effects, while a blockage in the active region leads to serious clad damage and possible clad deformation and fusion.

In Gas Insulated Switchgear (GIS) the loop resistance is a key parameter which can characterize the contact condition of the conductive circuit. The current method to measure loop resistance was mostly proposed and used in routine test, commissioning test and overhaul. The monitoring of abnormal conditions of contacts in operation has not been realized yet. To early detect the hidden contact defects in conductive circuit of the operating GIS and avoid serious accidents, in this paper a novel method to predict the loop resistance of the current-carrying conductor based on the finite element method (FEM) Calculation of Temperature Field is presented. Combined with the structure, working characteristics and contact features of the GIS current-carrying conductor, a multi-physics heat transfer model was set-up coupled electromagnetic field, flow field and temperature field. Meanwhile, with the model an FEM algorithm for solving the steady and transient temperature field was designed and its availability and reliability was verified by comparing the simulation results with the experimental ones. Then different contact conditions were set and the corresponding temperature rise characteristics were obtained. The mapping relationship between the loop resistance and the temperature rise was determined. So in the last the prediction of the contact state of GIS current-carrying conductor according to the temperature factor was accomplished, which could provide a new detecting tool for GIS state maintenance.

A mathematical model describing interdependent transient temperature and electromagnetic fields in electrical contacts at three stages of pre-arcing of opening of contact (closed, initial opening, and bridging) is discussed. The dynamics of temperature change and its dependence on the contact films, and Thomson, Kohler, and Peltier effects are described. It is shown that nonuniform current density in the contact spot over the frequency range of 0-10 Hz is enhanced by current constriction rather than by the skin-effect. The relationships between the rate of appearance of the extra forces in contacts during the opening period are established. The model of thermal explosion is invoked to explain the mechanism of spontaneous separation of contact resulting from the combined action of electrodynamic and thermal forces generated by the explosive evaporation of material at high current. The model was used to describe the bridging stage of contact opening. It is established that the shape of the bridge, its temperature field, and the lifetime mechanism of rupture are determined by the dynamics of contact opening and also forces resulting from the surface tension, the pinch effect, and Joule, Thomson, and tunnel heating. >

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

A conjugate heat transfer simulation of air in a rectangular cooling channel with 45-deg ribs is presented in this paper. The test channel length is 400mm and the ratio of width to height is 1. The hydraulic diameter of the channel is 40mm and the thickness of channel wall is 3mm. The rib height is 1.9mm and the distance between nearby ribs is 19mm. The flow field and the temperature field in the solid channel are obtained by using ANSYS CFX. An energy source is added in the solid domain to simulate the Low-Voltage High-Current heating method in the experiment. The GGI method is adopted for the mesh connection between the fluid domain and solid domain. The SST turbulence model and automatic wall function in ANSYS CFX are used to simulate the flow and heat transfer in near-wall region. The numerical results show great agreement with the experimental data. The temperature distribution on the channel outer wall is shown and analyzed. The Nusselt number field on the channel wall is shown and illustrated by the flow field shown by the Vortex Core Technology. There are four secondary flow vortex cores between ribs in near wall region and a strong secondary flow can be seen in main flow region. The angled ribs leads to the unbalanced temperature and Nusselt number field on the outer wall and the inner wall of the channel respectively. The distribution law of the Nusselt number on inner wall is not similar with the one of temperature on the outer wall. But the overall distribution of outer wall temperature field is more homogeneous compared with that of the inner wall Nusselt number. Some recommendations for optimization are given based on the flow field and Nusselt number distribution.

In order to accurately analyze the temperature distribution of a high-speed magnetic suspension amorphous motor, a multi-physical coupling method, including flow field, electromagnetic field and temperature field, is proposed. The electromagnetic loss obtained by electromagnetic analysis is directly mapped to the temperature field and input to the boundary conditions of the flow field for several coupled iterations. This paper compares the thermal analysis results of two different temperature rise calculation methods, analyzes the temperature distribution of magnetic suspension amorphous motor under different working conditions, and discusses the simulation results and the measured results. The error between the multi-field coupling simulation results and the experimental results is less than 10 °C, and the error of the traditional temperature rise analysis method is 30 °C, which verifies the superiority of the proposed coupling analysis method in improving the calculation accuracy of motor temperature rise, and has important significance for the accurate prediction of motor temperature rise in the design stage.