ELECTROHYDRODYNAMIC PLUMES IN POINT-PLANE GEOMETRY

We examine the flow organization induced by charge injection from a ne edle of small radius of curvature into an insulating dielectric liquid . Experimental results are presented for the electrical current as a f unction of the point-plane distance and of the applied voltage. Schlie ren visualization reveals the existence of very thin plumes which are slightly vacillating. An approximate analysis of the laminar plume is developed which takes into account the finite but very thin axial regi on where charge is confined. A classical type of asymptotic treatment results in a set of ordinary differential equations, provided the curr ent and the field distribution are known. A new expression for the ord er of magnitude of the liquid velocity is proposed which leads to esti mates of the radius a of the charge core and the typical radial scale delta of the velocity profile. For a gap spacing d, these estimates ar e of the order of 10(-3) d and 10(-2) d which confirm the thinness of such charge plumes.