Electrostatic Generation in Dielectric Fluids – the Viscoelectric Effect

Simultaneous energy transfer modes have been known to interact to produce unusual “coupled” effects. This coupling now has its theoretical basis in the concept of entropy production (or dissipation or irreversibility) central to nonequilibrium irreversible thermodynamics. Over the years, many examples of coupled phenomena have been identified and studied (thermoelectricity, electrokinetics, piezoelectricity, and so forth). Electrohydrodynamics (the effect of fluid motion on electric fields and the reverse effect of electric fields on fluid motion) can be explained as a thermodynamically coupled phenomenon characterized by the viscous and electrical properties of a fluid that contain mobile charges at the molecular (e.g., ions) or macroscopic (e.g., dust) levels. This is called the “viscoelectric” effect. In the first part of this paper we apply the concepts of irreversible thermodynamics to electrohydrodynamic systems to develop the relevant relationships. The second describes experiments carried out with a new type of Couette electrostatic generator. The resulting experimental data is then discussed in light of the coupled phenomenon relations previously developed. INTRODUCTION Electrostatic generation has been known since ancient times. It is most commonly observed when certain materials are rubbed together to produce a noticeable electrostatic charge. It has also been known since the middle of the 18 century that electrostatic charging can occur in flowing dielectric fluids. Today this phenomenon is most commonly encountered as an electrical hazard with electrostatic discharges producing unwanted shock, electrical interference, and occasional disastrous explosions in the petroleum, plastics, shipping, aircraft, and agricultural industries [1]. Most researchers to date have analyzed this phenomenon via ion mobility mechanics and double layer electrohydrodynamics. However, in this proposal we propose using a unique energy-based thermodynamic analysis technique to investigate this phenomenon. Since both momentum and energy produce important conservation laws, they often give uniquely different interpretations of the same phenomenon. In the discussion below, using published correlations for the flow of dielectric fluids, we show that mass and current flows do appear to be thermodynamically coupled, and call this the thermodynamic “viscoelectric” effect (as opposed to the thermodynamics of electrohydrodynamics). In order to demonstrate the generality of this approach we are requesting funds to a) design and construct a new efficient electrostatic generator using nested annular tube geometry to measure all the relevant physical and flow properties, b) compute the resulting coupling coefficients for various dielectric liquids, c) correlate the coupling coefficients via a dimensionless number, and d) measure the reverse effect (a transverse electric field generating a mass flow or pressure) and compare it with that predicted by the thermodynamic coupled phenomenon theory. NOMENCLATURE A = Area D = Diameter f = Moody Friction Factor i = Electric Current Ji = Generalized Flow L= Length Lii = Nonequilibrium Thermodynamic Coefficients