Inclusion of nonisothermality of particles in the calculations and diagnostics of two-phase jets used for spray deposition of coatings

A method is suggested for the calculation of the temperature of large semitransparent particles of a material of low thermal conductivity during their motion in a gas jet. The temperature profile in a particle is calculated with due regard for thermal conductivity and thermal radiation. The results of calculations performed for typical parameters of a plasma jet demonstrate that the temperature at the center of an oxide particle $40$–$60\mu$m in diameter in the zone of heating may be $1500$–$2500$ K lower than the temperature at the particle surface. Here, the error of prediction of the volume-average particle temperature in isothermal approximation reaches $350$ K. The possibility of determining the volume-average temperature of particles by their thermal radiation is studied as applied to the problem of optical diagnostics of two-phase jets. It is demonstrated that the color temperature being measured may differ from the volume-average particle temperature by as much as $300$ K. The possibility is discussed of experimentally determining the temperature dependence of the index of absorption, which would enable one to considerably increase the accuracy of the obtained values of the volume-average particle temperature.