Thermophysical analisis of modification of the surface of the workpiece by laser radiation

The paper presents a thermophysical analysis of modifying the surface of a workpiece by laser radiation due to the melting of a layer of a doping substance previously deposited on the surface of the base metal.The process of heating a two-layer metallic system with a laser pulse with a normal distribution of power density over the beam section is considered. Under the action of a heat source of constant power, moving in a straight line at a constant speed, the process of heat propagation tends to the limiting quasistationary state, when the temperature field does not change with time and moves along with the source.The dependences obtained allow us to estimate the effect of the laser treatment mode on the distribution of temperature fields, establish the patterns of heat propagation and relate them to phase transformations in the metal.It has been established that the technological modes of exposure to laser radiation are limited by the value of the energy per pulse from 4 to 12 J. The choice of technological modes of exposure is determined by the combination of the scanning speed of the laser beam and the radiation power.

PARTICULARITIES OF USING THEE METHODS OF MATRIX PROGRAMMING IN THE MATHEMATICAL MODELS OF HIGH VOLTAGE GLOW DISCHARGE ELECTRON SOURCES

Possibilities and particularities of using of arithmetic-logic equations in complex models of high voltage glow discharge electron sources are considered in the article. Such electron sources are find wide application in electronic industry, device production and mechanic engineering for electron beam welding, brazing, annealing of produced items, for deposition of composed ceramics films and coatings, as well as for refining of refractory materials with using of electron-beam refusing in the soft vacuum. Main problem of designing of technological high voltage glow discharge electron sources is absence of complex physical-mathematic models. This fact is caused by complicity of physical processes, taking place in the discharge gap at conditions of low and middle vacuum, and it generally holding back the elaboration and providing in industry such advanced electron sources. Complex physic-mathematic model of high voltage glow discharge electron sources, based on apply­ ing of arithmetic-logic relations and methods of matrix programming, is proposed in the article. Main physical processes, taking place in the high voltage glow discharge, as well as mathematic means for describing these processes, and main items of elect­ ron gun, are considered. Mathematic relations for proposed model are written in the form of arithmetic-logic equations. The results of simulation of distribution of elect­ ric field in the discharge gap, distribution of power density of electron beam in the fo­ cus and guiding of electron beam in the equipotential channel, are presented. Its have been shown, that using of arithmetic-logic relations is significantly simplified realiza­ tion of proposed physic-mathematic model with using the means of matrix program­ ming. Possibilities of providing parallel calculations are also analyzed.

Neutronics Design Study on Ignition Zone of Travelling Wave Reactor

Traveling wave reactor is a kind of nuclear reactor that can convert fertile material into fissile fuel as it runs using the process of nuclear transmutation. In the ignition stage of traveling wave reactor, the core performance is especially complex, since the fissile fuel and fertile material is put in different regions at the beginning. And the distribution of power density will change severely with burn-up during the reactor operation. It is an important part of the traveling wave reactor study to optimize the design of the ignition stage. In this paper, based on a two-dimensional RZ geometry model, some schemes with different sizes and compositions of the ignition zone, middle ignition zone position design and burnable neutron poison addition are simulated and analyzed. Finally, an optimized core design with multi-zone configuration and burnable neutron poison addition is shown. Some design outlines are introduced for further study.

Distribution of Power Density in the Glass Melt at Different Electrode Configurations in All-Electric Furnace

The power density in glass melts has been studied at different arrangements of electrodes in all-electric melting furnace. Bottom, top and plate electrodes have been arranged into the model furnace in form of hexahedron about the edge 1m. The results of mathematical modelling showed that there has been very narrow relationship between the distribution of power density in glass melt and the temperature field and therefore by means of suitable arrangement of electrodes it is possible to influence the intensity of convective currents of the glass melt. From evaluated dependencies of power density distribution near the tips of electrodes follows that in case of rod electrodes, the power density decreases with increasing length of the electrodes. Opposite behaviour happens at plate electrodes because the power density distribution in the centre of the basin between electrodes increases with increasing distance of the electrodes from the bottom of the furnace. By means of mathematical modelling also have been evaluated the volumes of glass melt in surroundings of electrodes where are the power densities superior to pmean (60000 W.m-3). The volumes are very small with regard on the total volume of furnace and do not exceed the value 22%. From mentioned follows that mathematical modelling of glass melting furnaces by means of CFD programme Fluent gives to acceptable computational subservience to study of power density distribution in all-electric melting furnaces.

Radiation characteristics of a coaxial waveguide with eccentric inner conductor for application in hyperthermia and microwave reflex therapy

This paper examines the radiation characteristics of a contact emitter conceived for application in hyperthermia and microwave reflex therapy. It is important to analyse the distribution of power density in the near field area, as the radiator's therapeutic sphere of activity is localized here. The contact emitter is a coaxial radiator with an eccentric course of the inner conductor. According to Huygens principle, a theoretical view of the near field radiation characteristics is made by determining the equivalent current densities in the emitter aperture. It is shown that by an eccentric shift of the inner conductor, an almost isotropic near field radiation pattern and power density can be achieved. For this, the electromagnetic field in the emitter aperture is determined by using a Bipolar coordinate system. This calculation considers only the fundamental TEM mode of the contact emitter. Besides the theoretical results near and far fields are simulated using the programme system Ansoft HFSS.