Measuring the Velocity and Temperature of Particles in a Low-Temperature Plasma Flow
Authors: Oksana Isaeva, Marina Boronenko, Pavel Gulyaev
Abstract: The improvement of optical methods for diagnosing fast processes in plasma deposition technologies is associated with the solution of a well-known contradiction between an increase in the speed of recording a track of a moving particle and a decrease in the signal level to a critical noise threshold. Improving the accuracy of measuring the temperature of the condensed phase of the flow, under the conditions of plasma background radiation, is possible with the transition from the brightness pyrometry of individual particles to spectral methods for determining the temperature distribution of a large group of particles by their thermal spectrum. The purpose of this study is to experimentally verify the effectiveness of using microchannel photomultipliers and nanosecond electron-optical switches to improve the accuracy and speed of time-of-flight anemometry and brightness pyrometry methods. The experimental technique for detecting tracks of self-luminous heated particles in plasma is based on the use of specialized high-speed video cameras with parallel signal reading. The technical possibilities of using high-speed video cameras for registration of particles in the technological process of plasma spraying of coatings are shown. The use of an optical shutter with a nanosecond resolution makes it possible to measure the particle velocity in the range from 10 to 350 m/s with an accuracy that ensures the calculation of the dynamic parameters of particle acceleration in the jet. The use of a microchannel photomultiplier makes it possible to measure the brightness temperature of particles even at high speeds. The set of experimental data makes it possible to determine the form of the fundamental diagram of a two-phase plasma jet by the value of the particle transfer velocity in the idle mode and the maximum load capacity of the flow. The considered experimental technique makes it possible to measure the dynamic constants of motion and heating of both individual particles in a plasma flow and the fundamental diagram of interaction during collective motion. The proposed diagnostic method is recommended to be used to study the load capacity of two-phase flows, as well as an indicator of the limiting technological state of the plasma torch and the transition to unstable spraying modes.
Keywords: optical methods, plasma technologies, particles
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