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The results of experimental and computational studies of the processes accompanying the melting of metal samples heated in air using induced currents are presented. The materials used for the experimental models—spheres and cylinders with a characteristic size of 10 mm—were pure iron, nonferrous metals, and various grades of steel. An unusual physical effect observed in experiments with iron and steels and associated with the intense release of sparks from the samples was studied: small brightly glowing metal droplets. A possible thermomechanical mechanism for the emission of droplets is proposed, based on the occurrence of excess melt pressure during metal melting inside the volume of the sample, limited by the resulting solid shell consisting of iron oxides. Numerical calculations were carried out, the results of which generally confirm the hypothesis presented. [ABSTRACT FROM AUTHOR]

The characteristics of stationary, concentrated vortices of a special type are studied in a cylindrical coordinate system. A new solution for the problem of a concentrated vortex with three components of the velocity vector was constructed. It differs significantly from the previously known solution with two components of the velocity vector. The pressure distribution in a stationary concentrated vortex with and without Coriolis effect is found. The conditions under which the vortex is cyclonic are established. An analysis was conducted on ways to create a system of small vortices on the path of a tornado; with passage through these vortices, a tornado can weaken and disintegrate into a series of low-intensity vortices that are damped due to the forces of air viscosity and the friction force on the surface. Since the place and time of birth of a tornado are hard to predict and are often far from the necessary energy sources, a method for the organization of a rapid, protective obstacle system in the right place at the right time in the form of a system of concentrated vortices is discussed. It is proposed to use microwave electromagnetic radiation beams generated from airplanes or satellites as the source creating concentrated vortices on the tornado path. [ABSTRACT FROM AUTHOR]

Abstract: The results of numerical and experimental study of the effect of the Earth's magnetic field on the electric-vortex flow of liquid metal in a hemispherical container are presented. It is found that the combination of toroidal flow and azimuthal force caused by the interaction of an electric current flowing through the liquid metal with a relatively weak external magnetic field leads to an intense twist of the fluid. This effect can be observed, for example, in electrometallurgical aggregates. [ABSTRACT FROM AUTHOR]

Hypotheses about the mechanisms governing fragmentation of superheated liquid metal droplets falling into cold water are analyzed. It is shown that a physical model based on the cavitation-acoustic mechanism governing fine fragmentation of melt under steam explosion conditions is likely the most suitable one for consistently describing the fragmentation of both low-melting and refractory metals. For checking this conjecture, special experiments for studying the processes triggered when cold (20°С) water comes into contact with a heated surface and for measuring the pressure impulses (arising both in coolant and in the hot body) accompanying the coolant flashing were carried out using liquid metal (tin and steel) droplets and superheated solid steel bodies. The working substance temperatures were varied in the range from 200 to 1600°С. The results obtained from the performed experiments are not in contradiction with the melt fine fragmentation process represented by the cavitation-acoustic model. It is shown that the acoustic waves generated during explosive growth of bubbles on a hot surface propagate in the solid body and are alternating in nature. Their intensity (including that at negative pressure values) differs only slightly in the modulus from the pressure impulses measured in the coolant and is sufficient for finely fragmenting the droplets. It is experimentally found—with the use of a conductance measuring technique—that the transition from the coolant film to bubble boiling mode is preceded by a short-term (lasting a few milliseconds) process involving intense interaction of waves at the steam-liquid boundary with the heated surface. The signal from the conductance measuring transducer was subjected to a wavelet analysis for different values of the heated surface temperature. The study results testify that high-frequency (several tens of kilohertz) pulsations of electric current are generated in the preburnout region with their characteristics varying (toward increasing the amplitude and intensity) with time as the heating and heated media come closer into contact with each other. A probabilistic process development scenario is suggested. [ABSTRACT FROM AUTHOR]

With the help of numerical and experimental methods it was shown that a stationary external magnetic field, which causes an azimuthal swirl of axisymmetric electric flow, leads to the generation of intensive hydrodynamic self-oscillating processes in a current- carrying liquid metal. Calculations are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Efficiency of application of electromagnetic actions for control of joint formation during electroslag welding is determined in many respects by application of external magnetic fields to welding zone and structural peculiarities of corresponding devices. The aim of present work lied in analysis of methods for generation of external magnetic fields during electroslag welding of butt joints and evaluation of their effect on weld pool melt. The main methods of generation of longitudinal and transverse magnetic fields in a welding gap are considered, and principal schemes of corresponding electromagnetic devices are given. It is shown that direction and intensity of electromagnetic force effecting the weld pool melt is determined first of all by spatial orientation of the external magnetic field in relation to object being welded, value of field magnetic induction and its frequency characteristics. Rationality of application of that or another scheme of application of magnetic field in the gap depends on welded joint parameters, and it should be considered separately for each individual case. Appropriateness of application of magnetic fields providing constant (cyclic) rearrangement of hydrodynamic structure of flows in the weld pool or creating melt vibration was indicated. In this case, usage of pulsed magnetic fields generated by discharges of capacitor batteries to electromagnet coil is perspective. Relevance of development of new schemes and devices for generation of magnetic fields and their power sources is shown. [ABSTRACT FROM AUTHOR]

Linear and non-linear stability analysis of the interface between a thin vapor film and a layer of liquid in the presence of a steady heat flux from a metal surface heated to a high temperature, to the vapor film and then from vapor to the subcooled liquid is investigated. The temperature dependence of saturation pressure is taken into account. Boundary conditions on the vapor-liquid interface that generalizes the known correlations on the free surface of liquid in the gravity field are derived. The thermal processes on the phase boundary lead to the generation of weakly decaying periodic surface waves of low amplitude and may cause small length waves (ripple), which are not capillary ones. Thermal processes on the phase interface are capable to provide the stability of a film of lights vapor under a layer of heavy liquid in the gravity field. The explosive instability may arise in the non-linear stage due to a weak variation of the film thickness or superheating of liquids. [ABSTRACT FROM AUTHOR]

Complex experimental study and numerical simulation of liquid metal flow and heat transfer in various configurations affected by longitudinal or transverse magnetic fields under conditions close to the tokamak reactor have been performed. A specific feature of the heat transfer under these conditions is the combined exposure of a strong magnetic field and thermogravitational forces, which manifests itself in previously unknown effects. Among these effects are the existence, in some modes, of MHD heat transfer areas of "degraded" heat transfer, the extremely uneven distribution of heat transfer coefficients along the perimeter of the tube and abnormally high temperature fluctuations near the wall. These phenomena including negative ones should be considered in the further designs. [ABSTRACT FROM AUTHOR]

A procedure of estimating the area of contact between cold water and a hot hemispherical surface is developed and described. Synchronous measurements of pressure pulses in liquid, the temperature of a body, and characteristics of contact between a heated body and a coolant are performed under conditions of abrupt change of boiling modes (from film to nucleate boiling). Characteristic features of the investigated processes are determined, which are largely defined by the temperature of the hemisphere, by its thermophysical properties, and by the presence of surface oxide films. It is found that the maximal value of the amplitude of pressure pulses, which may be as high as ∼1 MPa in the experiments, is observed in the region of temperatures of the hot body which are close to the temperature of limiting superheat of water. The dependences are obtained of the rate of spreading of liquid and of the time of delay of its explosive boiling from the instant of boiling on the temperature of the hemisphere. [ABSTRACT FROM AUTHOR]

Relations are derived which enable one to assess the size of fragments of a liquid-metal droplet after its fragmentation formed in the case of instantaneous contact between a hot metal surface and a coolant. The obtained experimental data demonstrate that the amplitude of pressure pulses generated during vapor film collapse (second boiling crisis) is several times lower than the values required for triggering a spontaneous vapor explosion. The assumption is validated according to which progress in studying the process of triggering a spontaneous vapor explosion is associated primarily with advances in understanding the mechanism of fragmentation of individual droplet. [ABSTRACT FROM AUTHOR]

Discusses the thermomechanical action of the fine fragmentation of liquid droplets subjected to vapor explosion. Fine fragmentation of melt into small particles with the surface of melt-liquid interaction increasing by orders of magnitude; Transition of nucleate boiling which implies that a mass of cool liquid comes in direct contact with a hot surface; Basic equations of internal pressure.

Investigates the local processes proceeding in the case of changing the boiling regime on a heated cylindrical rod with a hemispherical end immersed in water at a depth equal to the radius of the hemisphere. Vibrations of the vapor-film surface; Explosive regime of the development of instability leading to a vapor-film collapse.