When an electrostatic field is applied to a medium, an electric force arises, originated by polarization and by the possible presence of free charge. If the medium is a two-phase fluid, this force drives the vapor (of lower dielectric permittivity) towards the zone of weaker electric field, giving the opportunity of separating phases and enhancing boiling heat transfer in microgravity conditions, where buoyancy is lacking. Electric force is also responsible for bubble deformation. In this paper, after a comprehensive description of electro-hydro-dynamics (EHD) mechanisms in a two-phase fluid, some relevant literature data about EHD-induced phase separation are reported, confirming the effectiveness of the technique. The electric force on a growing and rising bubble is then evaluated numerically in some simple cases, with a fem technique. Finally, original experiments on gas bubble detachment are analyzed in the attempt to enucleate the role of different mechanisms contributing to EHD enhancement. In particular, it is stressed that the role of electric forces in altering bubble shape and increasing bubble internal pressure seems to be the most significant in promoting bubble detachment.
The Use of Electric Force as a Replacement of Buoyancy in Two-phase Flow
DI MARCO, PAOLO
2012-01-01
Abstract
When an electrostatic field is applied to a medium, an electric force arises, originated by polarization and by the possible presence of free charge. If the medium is a two-phase fluid, this force drives the vapor (of lower dielectric permittivity) towards the zone of weaker electric field, giving the opportunity of separating phases and enhancing boiling heat transfer in microgravity conditions, where buoyancy is lacking. Electric force is also responsible for bubble deformation. In this paper, after a comprehensive description of electro-hydro-dynamics (EHD) mechanisms in a two-phase fluid, some relevant literature data about EHD-induced phase separation are reported, confirming the effectiveness of the technique. The electric force on a growing and rising bubble is then evaluated numerically in some simple cases, with a fem technique. Finally, original experiments on gas bubble detachment are analyzed in the attempt to enucleate the role of different mechanisms contributing to EHD enhancement. In particular, it is stressed that the role of electric forces in altering bubble shape and increasing bubble internal pressure seems to be the most significant in promoting bubble detachment.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
