The study of the performance of an electrostatic valve used for bulk transport of particulate materials

In many mass transfer processes, it is necessary to accurately control the flow of particulate materials. Commonly used mechanical valves have serious drawbacks which can be overcome by the use of electric field, which can locally originate interparticle compressive forces throughout the bulk material as a result of the greatly enhanced electric field and charge flux densities occurring at the contact points between the particles or between the particles and the boundary. Such interparticle electroclamping forces can be established by applying an electric potential gradient between a separated pair of conductive electrode grids placed perpendicularly across the flow within the duct where the material flows. The flow control of particulate materials is, thus, achieved using no moving parts. When an electric field is applied to a packed bed of particulate solids, several types of electrical force (electrostatic attractive force, dielectrophoretic force, and electroclamping force) may be generated, depending on the bulk and surface resistivities of the particle, the geometry of the electrodes, as well as the nature of the applied field. The influence of the electrode geometry on flow control was investigated using computer modeling of the potential based on finite element techniques. Furthermore, the effect of the applied field with respect to the magnitude, frequency, pulsewidth, and pulse shape on flow controllability was experimentally investigated. The influence of the moisture content of turnip seeds on flow controllability and specific charge was investigated, and the results obtained are discussed in this paper.