Dielectric Materials for Electrical Engineering

Chapter 17

Electrorheological Fluids 1

17.1. Introduction

The study of setting dielectric fluids (liquids, suspensions, etc.) in motion and their flow properties under electric fields and mechanical stress constitutes an important section of scientific, technological and practical investigation which has simultaneously caught the interest of researchers and manufacturers. The physical phenomena originating these laws of hydrodynamic behavior can be grouped into three categories: electrokinetic effects, electroviscous effects and electrorheological effects.

17.1.1. Electrokinetic effects

Electrokinetic effects are produced in the following situations: (i) the presence of a porous material immersed in a liquid; and (ii) when colloidal particles are placed in suspension in a liquid [HUN 81]. The electrical double layer, compact and diffuse (Stern and Gouy-Chapman layers), appearing at the solid/liquid interfaces of the initially neutral medium, reacts to the external solicitation (electric field or mechanical constraint) by implementing a reversible “electrokinetic conversion”. Thus, the application of an electric field causes a motion in the fluid (displacement of the liquid or the particles): an electrical-mechanical conversion (motor operating) or the setting in motion of the fluid polarizes the electrode, which then takes a voltage U: the mechanical-electrical conversion (generator operating). By taking the previous examples of dielectric media (i) and (ii), we obtain the following ...