Maximal accelerations for charged drops in an electric field

The equilibrium shapes of highly conducting, charged drops accelerating in an electric field are found. The maximum possible charge for a given field stength and surface tension is calculated. A spheroidal approximation often used for uncharged drops is generalized to include charge and is found to agree very well with the numerical solution when account is taken of the asymmetric surface stress. The charge and field values giving rise to the maximum possible acceleration of the drop are found with a view to optimizing the efficiency of certain electrospraying devices. The effects of air resistance are considered, at both low and high Reynolds numbers. In the former case, internal motion of the drop contributes to the shape, but the results are broadly similar to those for the accelerating drop. At high Reynolds number potential air flow with a constant pressure wake is assumed. It is found that the drop shape can be oblate in this case and may be stable for higher charge and field values. (C) 2002 American Institute of Physics.