We analytically investigate breakup phenomena of a viscous liquid column jet closely placed in a concentric sheath on which a static electric field is imposed.Taking account of a surrounding electric field of the jet, long wave nonlinear equations of the jet radius, velocity, and electric surface charge density are derived.These equations are numerically solved for the initial-boundary condition that a semi-spherical jet initially emanates from a nozzle exit. It is shown that there exist three types of breakup modes – jetting, spraying, and spinning – depending upon the parameters Λ (electric force/fluid inertial force) and Pe (convective current/conductive current). Then, critical curves are found in the Λ-Pe parameter space, across which the mode is transferred from the jetting to the spinning through the spraying with the increase of Λ and/or the decrease of Pe. In the transition from jetting to spraying mode, the produced drop size gradually decreases with the increase of Λ for larger Pe. On the other hand, there is a range of Λ where the drop size discontinuously decreases with increasing Λ for smaller Pe, which may lead to producing a satellite drop.
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