The effect of flux density on the formation of temperature field in alumina under conditions of heating by concentrated laser radiation

A numerical investigation is performed of the effect of the density of a flux of heating concentrated radiation of $\text{CO}_2$ laser on the formation of temperature field in the process of heating and melting of a plane layer of alumina. A mathematical model of unsteady-state radiative-conductive heat transfer is used for considering the process of heating in rigorous formulation in view of the dependence of the thermophysical properties of the solid phase on temperature and of the optical properties—on temperature and wavelength, including the generalized approach to the problem of phase transition in melting in view of formation of an extended two-phase zone. In so doing, the evaporation from the melt surface is taken into account. The presented results relate to flux densities in the range from $200$ to $3000$ W/cm$^2$. It is demonstrated that the special features of formation of temperature fields are due both to the contribution of volumetric radiation and absorption of fluxes of outer and self-radiation and to the specific nature of alumina for which the absorption coefficients of melt and of solid phase in the energetically important spectral region may differ by as much as two orders of magnitude.