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摘要
We show that the presence of electric charge at the interface of a capillary liquid jet plays a secondary role concerning the onset of an absolute or a convective instability in common operational conditions for cone-jet electrosprays, compared to other factors such as the convective velocity, jet diameter, surface tension gamma, density rho, or viscosity mu. Thus, in most situations, the critical convective velocity (or its related dimensionless number, the critical Weber number We(cr)) at the threshold between the dripping and the jetting regimes depends mainly on the viscosity of the fluid, scaled as a Reynolds number Re, and not so importantly on the electric forces at the interface of the jet. Accordingly, for any liquid, the classical curve of Leib and Goldstein [Phys. Fluids 29, 952 (1986)] for We(cr) versus Re is accurate enough to explore the parametrical conditions where a steady cone-jet mode is to be expected, linked to the convectively unstable nature of the issued jet. However, at the limit of low Reynolds numbers, the stability behavior becomes strongly sensitive to the electrical conductivity of the liquid. Thus, a parametrical region where a charged capillary jet becomes strongly stabilized by the viscous damping against the destabilizing surface electrical forces is described in detail in this work. The "unconditional jetting" limit previously described for a capillary jet surrounded by a coflowing liquid [A. M. Ganan-Calvo, Phys. Rev. E 78, 026304 (2008)] is here recovered in the absence of a coflowing fluid when "frozen" surface charges are present.
- 出版日期2010-6
