VII-5

M. Brenner, MIT

and

M. Hohman, University of Chicago

Abstract:

An electrospray forms at the tip of a capillary tube when a fluid is strongly forced by an external electric field. Sprays are caused by the instability of a thin liquid jet pulled out of the capillary tube by electrical stresses. A diverse array of instabilities can occur depending on the applied voltage, the fluid properties (viscosity, dielectric constant, conductivity) and the imposed flux. We are investigating the extent to which a ``phase diagram'' for the various behaviors of electrosprays can be constructed by understanding both the shapes and stability of electrically forced jets from a capillary tube. We have developed a long wave theory for an electrically forced jet which asymptotically reduces to the Navier Stokes equations with electrical forcing; the theory reproduces

the classic dispersion relations for instabilities about a cylinder derived by Saville as a function of parameters (conductivity, dielectric constant, viscosity, ect.) Steady solutions for thinning jets as a function of tube radius, conductivity, current, viscosity, volume flux and dielectric constant are constructed numerically, and compared with experiments of M. Shin and G. Rutledge (Chem. Eng., MIT). The stability of the various solutions is discussed, and implications for classifying the various experimentally observed behaviors is described.