Schlieren images observed in electrically stressed dielectric liquids

The liquid motion normally observed in electrically stressed dielectric liquids is mainly caused by two mechanisms: (a) the Coulombic force due to the interaction of the space charge with the field, and (b) the electromechanical force created by the field resulting from the spatial variation of the dielectric constant due to the variation of temperature from domain to domain and from time to time in the liquid. The direction of such a liquid motion depends on which of these two mechanisms is dominant. The schlieren images sometimes observed in liquids under applied fields show mainly the change of the already existing temperature gradients in the liquids, and this change is due to the liquid motion caused by either mechanisms (a) or (b) or both. It is concluded that the schlieren images are directly governed by the temperature distribution in the liquid and have no direct bearing on the formation and distribution of space charges.