Electric Arc Heaters Research Articles

Numerical simulation of keyhole behaviors and droplet transfer in laser-MIG hybrid welding of Invar alloy

PurposeThis paper aims to describe a three-dimensional mathematical and numerical model based on finite volume method to simulate the fluid dynamics in weld pool, droplet transfer and keyhole behaviors in the laser-MIG hybrid welding process of Fe36Ni Invar alloy.Design/methodology/approachDouble-ellipsoidal heat source model and adaptive Gauss rotary body heat source model were used to describe electric arc and laser beam heat source, respectively. Besides, recoil pressure, electromagnetic force, Marangoni force, buoyancy as well as liquid material flow through a porous medium and the heat, mass, momentum transfer because of droplets were taken into consideration in the computational model.FindingsThe results of computer simulation, including temperature field in welded plate and velocity field in the fusion zone were presented in this article on the basis of the solution of mass, momentum and energy conservation equations. The correctness of elaborated models was validated by experimental results and this proposed model exhibited close correspondence with the experimental results with respect to weld geometry.Originality/valueIt lays foundation for understanding the physical phenomena accompanying hybrid welding and optimizing the process parameters for laser-MIG hybrid welding of Invar alloy.

Optimal Design for a High-Power Electric Arc Heater

High-power electric arc heaters are the only viable test equipments for heating air to high temperatures (2000-10 000 K) in a few minutes for experimental ground studies of hypersonic flight vehicle thermal protection systems. With the expansion of the exploration of outer space and the rapid development of hypersonic vehicles, more powerful arc heaters are urgently required to meet the demands of the aerospace industry. However, the design of high-power arc heaters faces many technical obstacles such as the need for high structural strength, the need for high-efficiency heat-transfer for cooling, the problem of high internal temperature flow, and the electromagnetic plasma coupling problem. To address these problems, this paper has discussed an optimization scheme, in order to improve the reliability and security of a high-power arc heater in extreme conditions, and at the same time improve the thermal efficiency of the arc heater, and extend the service life of an arc heater.

Enhancing refractive index sensitivity using micro-tapered long-period fiber grating inscribed in biconical tapered fiber

Abstract A novel micro-tapered long-period fiber grating refractive index sensor is demonstrated in this study. Its transmission characteristics are investigated numerically and experimentally. The sensor is fabricated by inscribing periodical micro-tapers in a biconical single mode optical fiber (SMF-28) using a low cost electric arc heating technique. The periodical tapering in SMF enables the fundamental core mode to be coupled into the cladding modes resulting a resonant wavelength in the transmission spectrum. The resonant wavelength shifts linearly with the variation of surrounding refractive index. The refractive index sensitivity of 8188 nm/RIU has been experimentally achieved which is much higher than the previously reported refractive index sensitivity values for the sensors based on long period fiber grating. The effects of varying the number of periodical tapers, amount of grating period and waist diameter on the sensitivity have been analysed both numerically and experimentally. Our presented sensor features a low cost, a simple structure and a high sensitivity. The results presented in this study would be useful in both chemical and bio-sensing applications.

Analytical Solution for the Electric Arc Dynamics and Heat Transfer When Exposed to a Magnetic Cross-Field

The motion of the gliding DC electric arc under the effect of magnetic field is investigated. The temperature distribution in the inside and the outside of the moving arc is computed. The temperature distribution for the fixed-spot arc is also obtained. It appears that the gas relative velocity inside the arc gives rise to heat convection, which has an impact on the arc motion. A practical analytical solution is derived using magneto gas dynamic equations in order to investigate the heat transfer occurring in the arc and its vicinity, to determine its characteristics, and to estimate its velocity when it is exposed to external and electrode-induced magnetic fields. Two methods are suggested: one for the free-burning arc and the other for arc burning between close surrounding walls.

Расчет характеристик дуги плазменно-дуговых печей на основе модифицированной модели дуги Меккера

The article presents a method for calculating the characteristics of heat transfer between the electric arc and gas jet in the plasma arc furnace melting space in the course of melting on the basis of modified G. Mecker’s arc column model. No engineering methods for modeling and calculating the electric and thermal characteristics of the melting plasma generator arc as a source of heating and nonlinear electric load that would be suitable for design purposes have so far been available. The concepts of the modern electric arc heating theory open the possibility to suggest — based on well-known G. Mecker’s electric arc convective model, and with attraction of the arc heat transfer model methods and the mathematical method of arc universal characteristics — a methodology for calculating the heat transfer characteristics and the related external electric and thermal characteristics of the arc produced by a plasma arc furnace melting plasma generator that is convenient for being used in design practice. The universal arc characteristics method developed for calculating the electric and thermal characteristics of Mecker’s arc column model cylindrical part enables the user to calculate the arc column characteristics at a distance away from the cathode by means of simple algebraic methods, thereby making Mecker’s mathematical model more specific. The arc model conservatism has been proven proceeding from the spatial layer with an increased volume viscosity that appears on the column surface. As a result, a boundary condition of the third kind can be applied to the arc column cylindrical part surface according to the concepts of the boundary layer theory. By using the universal arc characteristics method it is also possible to correlate the heat flux linear density boundary value on the column cylindrical part surface with the column temperature profile and, thereby, link the dependence of the plasma column electric, geometrical and thermal characteristics on the arc heat transfer conditions in the electric arc heated working space of the installation. By applying the proposed method, it is possible to identify Mecker’s heat transfer model using only the arc external volt-ampere characteristics and to calculate, by means of a simple algebraic method, the structure and values of the heat fluxes produced by the arc in the course of heat transfer to the plasma generator gas jet in the plasma arc furnace melting space. Examples of arc characteristics during operation with different gases for different stages of melting, namely, at the beginning of melting and in melting the furnace charge are given.

A new approach in producing metal bellows by local arc heating: a parametric study

Recently, dieless forming processes have been introduced to prevent the high costs of dies and tools. Local heating and axial compression process is an innovative method for producing metal bellows. In this research, producing metal bellows using simultaneous local electric arc heating and axial compression has been explained and investigated. SUS304 tubes with an outer diameter of 19 mm and a thickness of 1 mm have been employed to implement the tests. Various parameters could affect the process. Among these parameters, effects of applied displacement and device current, influencing convolution shape, thickness, and required forming force, are studied experimentally. It is found that the height, radius, and angle of the convolution and also the forming force could be controlled by alteration of these parameters. Furthermore, the result of buckling test showed that energy absorption capacity of the manufactured metal bellow has been increased in comparison to a typical tube. This method could be a suitable alternative for induction local heating and can reduce the high equipment costs.

고온 공기 가열기 개발 현황 조사 및 고찰

극초음속 공기 흡입 추진기관의 지상 시험 시 추진기관의 고속 비행 조건을 모의하기 위해 고온 공기를 공급할 수 있는 고온 공기 가열기가 필요하다. 본 논문에서는 다양한 고온 가열기들을 조사하여 유형별로 정리하고, 장단점을 비교하였다. 가열기는 크게 유동장 내 연소 가열기, 아크 가열기, 축열식 가열기, 열교환식 가열기 4종류로 분류할 수 있었으며, 각각의 장단점이 다양하므로 목적에 맞게 가열기를 선정하여야 한다. A high temperature heater is required to supply high temperature air to the hypersonic propulsion system in order to simulate high velocity flying condition during the ground test. Various high temperature heaters were reviewed, categorized, and analyzed in this paper. Heaters were categorized in 4 groups; in-stream combustion heater, electric arc heater, storage heater, and heat exchange heater. Each group has its own advantages and disadvantages, so the heater should be selected considering its purpose.

Numerical Analysis of Deformations in Sheets Made of X5CRNI18-10 Steel Welded by a Hybrid Laser-arc Heat Source

The laser-arc hybrid welding is widely used in many industries through the combination of advantages found in welding technologies used in this single process. A significant issue is the determination of the influence of heat source power distribution on welding deformations generated at the interface of joined elements and adjacent zones. Numerical estimation of welding deformations is very important and allows for the proper selection of technological parameters as well as the prediction of welded joints quality. This work concerns numerical simulation of thermomechanical phenomena in hybrid welding of sheets made of X5CRNI18-10 steel using laser beam and electric arc heat sources. Three dimensional discrete model is created in Abaqus FEA in order to estimate welding deformations generated by temperature field in the joint. Additional numerical subroutine is created in Abaqus/Standard module in which the distribution of movable hybrid heat source is implemented. The shape and size of the fusion zone is determined on the basis of numerically obtained temperature field as well as welding deformations occurring in hybrid butt-welded joints.

Modelling of a temporary temperature field during arc weld surfacing of steel elements taking into account heat of the weld

Journal of Applied Mathematics and Computational Mechanics, Prace Naukowe Instytutu Matematyki i Informatyki, Politechnika Częstochowska, Scientific Research of the Institute of Mathematics and Computer Science, Czestochowa University of Technology

Kinetic Behaviors of CaC2 Production from Coke and CaO

To replace the high-temperature and energy extensive traditional calcium carbide (CaC2) production technique, characterized by electric arc heating and large granular feeds of coke and calcium oxid...

Fibrous nanocorundum products for use in a high-temperature gas flow

Results are presented from a study of the structure and kinetics of formation of a protective nano-inoculated coating on a fibrous substrate. The article examines the erosion resistance of the materials at 1600 – 1800°C in a gasdynamic unit with electric-arc heating (in an aerodynamic system with a sectional plasmotron). The gaseous medium consisted of products of the combustion of kerosene in air. Flow velocity ranged up to 100 m/sec.

Analysis of Fused Magnesia Production Process with 3000kVA Electric Arc Furnace

The present study is related to a process development for producing high purity fused magnesia. A newly designed 3000 kVA electric arc furnace is used in the field experiment. The electric resistance characteristic of fused magnesia is analyzed and the effect of electrode diameters and electrode depth buried in molten magnesia on melting electric resistance and electric arc heat conversion are discussed in detail. It shows that, for the new 3000 kVA electric arc furnace, 350~450 mm diameter electrode and ~300mm depth in molten magnesia are suitable.

Electrical Sector of Bangladesh: Problems & Prospects

Electrical is one of the most important business sectors of Bangladesh. It has been identified as a 'booster sector' in the SME Policy Strategy - 2005 and a 'thrust sector' in the National Industrial Policy - 2010 of Bangladesh. Currently this sector in producing about 15 thousand crore taka of export substitute product against local demand of 20 thousands crore taka per year. There are about 2500 electrical enterprises producing 75 types of electrical products in Bangladesh. I last few years this sector earned double digit growth and it has a very potential export market throughout the world. Bangladesh is mainly producing electrical products of HS chapter - 84, 85, 90 and 94. Global market for these products is growing with multiple digits except recent negative trend for global financial crisis in 2009. There are few natural and one man made cluster of electrical products in Bangladesh. Major products Bangladesh is producing are Electric cables, distribution board, large and medium transformer, switch gear, sub-station equipment, electric arc welding machine, enameled ware, insulator, industrial fan, heat and speed control system, magnetic contractor, Parceling bright connector, different connecting equipment, main switch, electric iron and shouldering iron, ceiling fan, table fan, adjust fan, tube light, filament bulb, light fittings, table lamp, different laps, distribution board, electric meter, switch, plug, water heater, florescent light ballast, light & fan controller, torch light, refrigerator, lift equipment, extension cord, and energy saving lamp etc. Major importers of electrical products (Bangladesh do produce) are USA, Canada, Germany, Australia, Mexico, Italy, Denmark, Hong Kong, France and Finland. Major exporters of these products are China, USA, Germany, Japan, Singapore, South Korea, Taipei, Mexico, Netherlands and Malaysia. Major problems of Bangladeshi electrical sector are under invoicing during import of finished electrical products, lack of advanced technological and technical knowledge, absence of IP protection mechanism in action, lack of infrastructure to enter into the export market with electrical goods, and quality flexibilities on imported poor quality products etc.We also recommend some actions for keeping this sector competitive and exploring export market. Government has to play active role to make it one of the fastest growing and large export earning sector of Bangladesh.

Modeling of thermal phenomena in single laser beam and laser-arc hybrid welding processes using projection method

This paper concerns mathematical and numerical modeling of thermal phenomena accompanying single laser and laser-arc hybrid butt welding of steel sheets. Coupled heat transfer and fluid flow in the fusion zone were described respectively by transient heat transfer equation and Navier–Stokes equation. Laser beam and electric arc heat sources were modeled using different heat source power distributions. Latent heat associated with the material’s state changes, buoyancy forces and liquid material flow through a porous medium were taken into account in considerations. Differential governing equations were numerically solved using projection method combined with finite volume method. Elaborated solution algorithm was implemented into computer solver used for simulation of heat transfer and fluid flow during welding. The geometry of the weld and heat affected zone as well as cooling rates were estimated on the basis of numerically obtained temperature field.

Numerical modelling of unsteady heating and melting of the anode by electric arc. Part 2. Numerical characteristics of the anode weldpool

Numerical computations of the electric-arc heating and anode melting were carried out within the framework of the two-dimensional unsteady mathematical model. The influence of the viscous interaction “plasma-melt”, surface tension forces, electromagnetic forces, and gravitational convection on the formation of the hydrodynamics of the anode melt was considered.

Effect of Taper Angle of the Optical Fiber Microprobe in Power Collection

The objective of this experiment is to study the effect of taper angle of the optical fiber microprobe in power collection. Optical fiber microprobes with taper angle from 10° to 23° were fabricated using the automatic fusion splicer by applying one-sided pulling and electric arc heating technique. It was found that the maximum power detected by a small taper angle probe was only -34.22dBm. The highest optical power collected by the optical fiber microprobe in this study was -25.01dBm with taper angle of 22.9°. Large taper angle probe receives more light at the tip which increases the sensitivity of the probe.

New approach to modeling of temperature field in surfaced steel elements

In this work, a model of temperature field in a half-infinite body during surfacing was presented. Analytical solution was obtained by aggregating temperature increments caused by applying liquid metal and heat radiation of moving electrode. The assumptions were heat source of applied metal in parabolic shape in the cross-section of weld and Gaussian distribution of electric arc heat source. Computations of temperature field were carried out during surfacing of cuboidal steel element. The results were presented as temporary and maximum temperature distribution in element’s cross section. The accuracy of solution was verified comparing calculated fusion line to that obtained experimentally.

Effects of Arc Discharge on Wear Properties of Carbon-Carbon Composites Sliding against Cu Trolley under Electric Current

Influence of arc discharge to the contact strip of carbon-carbon composites was orthogonally studied on the HST-100 tribo-tester under electric current, which simulated working conditions of the pantograph-wire system used in electric railway. The regression equation between specific wear rate and arc discharge were obtained and analyzed through the non-linear regression and orthogonal design. The results of the experiments show that a power function between specific wear rate and arc discharge was obtained. Microstructure and phase composition were observed and analyzed by scanning electron microscope(SEM), energy dispersive X-ray spectrum(EDS) and temperature sensor. The results revealed that the arc discharge dissipation seriously affects tribological characteristics of the carboncarbon composites. The temperature of some local contact points beyond their melting point with the electric arc heat effect, and give rise to the desposite carbon and friber carbon were vaporazated, which form the lubrication film on the wear surface, and with the augmant of the arc discharge, the area of lubrication film of carbon was decrease. Therefore, the main wear form of the arc erosion of the carbon-carbon composites is evaporate erosion and material transfer.

Preparation of Nanocomposite Fluid by Electrical Arc Discharge Technique

This study proposes a new method, the electrical arc discharge system, for preparing a nanocomposite fluid with the basic ingredients of Cu, Fe and O. The proposed system has the advantages of a high-power electric arc heating system, excellent stability of the electric arc, and well-developed control technology. In the fabrication process, the positive electrode uses a copper rod and the negative electrode an iron rod, and the two electrodes are processed in the insulating processing liquid. The nanocomposite fluid generated by the synthesis system is analyzed by morphological analysis, heat transfer analysis, magnetism analysis, and rheological testing. The experiment generates satisfactory results for nanocomposite fluid with an average particle diameter of 25 nm by process conditions of vacuum pressure of 30 torr, peak current of 7 A for arc discharge, breakdown voltage of 250 V and duration time of 10 micros. The experimental results showed that the nanocomposite fluid is composed of Fe, FeO, Cu, and Cu2O. SEM images show that Fe and Cu are spherical, FeO is square, and Cu2O is ovoid. For the heat transfer experiment, the experimental temperature was set at ambient temperature of 30 degrees C, the average heat transfer coefficient is 0.708 W/m oC, which is 16.3% higher than that of deionized water. The magnetism test shows that the magnetic retentivity of the fluid is 47.27 (Oe), which makes it a soft magnetic fluid.

Use of electric-arc heating of steel in oxygen-converter production

The oxygen-converter shop of the Magnitogorsk Metallurgical Combine has introduced an additional unit for the electric-arc heating of steel. This article presents the main results that have been obtained in making converter steel with the use of electric-arc heating during out-of-furnace treatments of the steel.