High Temperature最新文献

Abstract

A model is proposed for the thermal explosion of a single particle with an exothermic chemical reaction in a turbulent temperature field of the medium. The chemical reaction rate is represented by a modified Arrhenius law, which takes into account changes in the internal structure of the particle material. Temperature fluctuations are modeled by a Gaussian random process. The study was carried out using the Lagrange and Euler approaches. In the Lagrange approach, in which a system of stochastic ordinary differential equations is solved, random temperature fluctuations of the medium and particle ensemble are calculated. Based on the results of numerical simulation of the ensemble, the dynamics of the empirical probability density function of the random particle temperature distribution is simulated. In the Euler approach, a nonstationary closed-loop equation is derived for the probability density function of random particle temperatures, which is numerically integrated using an original conservative difference scheme. The calculation results for both approaches agree satisfactorily with each other. It is shown that a random temperature field of the medium qualitatively changes the dynamics of occurrence of a thermal explosion. In a random temperature field, a thermal explosion can occur provided that in a deterministic case, the system is absolutely stable.

An Erratum to this paper has been published: https://doi.org/10.1134/S0018151X23010248

Abstract

The dynamics of thermal fields of dielectric surfaces heated as a result of initiation of a pulsed high-current surface discharge (plasma sheet) was studied. A pulsed surface discharge sliding along the surface of a dielectric was generated on the upper (flat) and lower (with a ledge) walls of the discharge chamber with quartz windows. Sequential images of optical (nanosecond range) and infrared (millisecond range) radiation were obtained near a dielectric ledge in the shape of a rectangular parallelepiped with a size of 6 × 2 × 48 mm³. The time evolution of thermal radiation from surfaces was recorded with time-lapse photography in the infrared range at pressures from 65 to 290 Torr. It is shown that the cooling time of a plasma-heated region localized near the dielectric ledge can last up to 30 ms and significantly exceeds the cooling time of a flat upper wall heated by a discharge fairly uniformly distributed over the surface of the dielectric.

Abstract

The parameters of a radio-frequency capacitive discharge confined in a closed electron drift accelerator with an extended acceleration zone have been studied for different discharge circuits, namely, with dc-closed and dc-open electrodes and with additional dc biasing of the active electrode. In the open circuit, the plasma concentration is minimal and the ion energy in the jet at the exit from the prototype is about 25 eV. The dc closing of the active electrode increases both the plasma density and the ion energy to 250 eV. A further increase or decrease in these parameters is possible by applying a positive or negative dc bias, respectively, to the active electrode.

Abstract

The paper studies the response of gas (air) bubbles in a spherical cluster to a single pulsed cosine-shaped decrease and subsequent recovery of the pressure of the surrounding liquid (water–glycerin mixture) with a pulse duration in the vicinity of the period of natural oscillations of the cluster. It is assumed that, during the response, all bubbles remain weakly nonspherical. The effect of the duration and amplitude of the excitation pulse, the position of bubbles in the cluster, the distance between bubbles, and the number of bubbles in the cluster is studied. Cubic clusters in which the centers of the bubbles are located at the nodes of a cubic grid, as well as clusters with a random arrangement of bubbles and with bubbles located at the center and vertices of a number of regular polyhedra nested in each other are considered. To estimate the effect of the interaction between bubbles, comparison with the response of a single bubble is made. One of the variants of discrete models of the dynamics of bubbles in a cluster is used, in which, along with radial oscillations, their spatial displacements and small nonspherical deformations are simulated. It has been established that, if the nonspherical deformations of the bubbles during the response are small, the maximum increase in pressure in the bubbles relative to its initial value is at most several-fold. If this assumption is ignored, significantly higher degrees of bubble compression can be obtained. The reason is that, when the condition of smallness of deformations is violated, the ranges of the parameters under consideration expand significantly.