We consider a continuous optical discharge (COD), which is also known as 'laser-supported combustion wave') [1], sustained by a weakly focused CO 2 laser beam. We also introduce a cold gas flow incident in the direction of laser radiation propagation in order to stabilize the COD (Figure 1). Furthermore, the gas flow is assumed to be subsonic and laminar at atmospheric pressure. We have developed a twodimensional radiative gas-dynamic model for COD, which uses realistic quasi optics and takes into account all of important factors that are of influence, including the effect of the laser radiation refraction in the plasma, which is essentially capable of changing the light channel geometry and space distribution of the beam intensity. We determine the thermal and gasdynamic structure of COD by solving the set of equations, which includes
Microwave heating of ceramic materials in a cylindrical wave field is analyzed by numerical simulation. The issues of temperature uniformity and stability inside the sample undergoing microwave heating are addressed. The heating regimes leading to development of global and localized thermal instabilities are illustrated. The role of the temperature dependence of the material's microwave dielectric properties in the formation of instabilities is demonstrated. The tuning and matching of a cylindrical cavity containing the sample is analyzed within a simple model for the microwave and millimetre-wave frequency ranges.
A simple model is proposed and tested for simulations of ceramic processing by microwave heating. The model is based on a piecewise constant approximation of the material properties and makes it possible to separate and analyse different effects caused by the sample shape and the dependence of the material properties on temperature. Specifically, the simulation results demonstrate that microwave heating of an alumina sample can be very sensitive to a variation of its dielectric constant with temperature. For different geometries, there is a similarity in the dependences of the thermal state characteristics (temperature drop across the sample, amount of dissipated power and electric field amplitude at the sample centre) on maximal temperature. It is shown also that a temperature drop between the sample centre and surface can be strongly enhanced in the case of a spherical sample irradiated symmetrically by microwaves.
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