|
Abstract
Ethanol is evaporated under
controlled pressure and under microwave irradiation, in a cylindrical or in
a square cell located in a waveguide or in a resonant cavity ( , 2450 MHz). Volume (Rayleigh-Benard) and surface instabilities
(Marangoni and differential vapour recoil) occur during evaporation under microwave.
The sequence of heat transfer regimes observed (purely conductive, stationary
convective, convective driven by surface tension and finally strongly
accelerated by vapor recoil instability) as well as their localization (first
in the volume phase and then in the surface) are analysed in relation with
the absorbed field. A comparison between the results under microwave with
the evolution of the same system under law pressure only shows the
specificity of the interaction between the field and the material evaporated.
The presence of the field favours the unstationary regimes first by
increasing the thermal gradient near the surface (for the transition from
conductive to convective regime) then by an amplification of temperature
inhomogeneities through the dependance of the dielectric loss with T.
Moreover the field increases the coupling between Marangoni and vapor recoil instabilities
because of the increase of evaporation rate by the
Microwave heating.
|