The Electric Field

Current vs. voltage curves (Figure 5) are commonly used in monitoring the operation of ESP. For best collection efficiency, ESP units are operated at the maximum voltage which produces a stable current. A discussion of operation monitoring of ESPs is given by DuBard and Nichols.

Much effort has been given to the task of determining the electric field within an ESP. Besides the burden of inability to solve known expressions analytically for the field in a wire-plate electrode system, this task is made difficult by uncharacterized changes in the collector electrode as the dust layer collects on it. The advent of high-speed computing has allowed satisfying solution of the field equations for a clean system.

Cristina et al. present a modern method of determining the electric field. These researchers use the following expressions for charge and electric potential:

where s is the permittivity of air (C2 N"1 m"1); Q is the ionic charge density (Cm"2); $ is the electrical potential (V).

These equations have a unique solution for DC ion flow fields. An iterative numerical procedure is used to balance the electric field and charge density of elements in an array of triangular elements superimposed on the inter-electrode space. These elements are each specified to have a constant ionic charge density. The contribution of space charge by ionized particulate matter is disregarded in this treatment. In the more dust-laden regions of an ESP, particulate matter is found to alter electric field slightly.

Equipotential field maps developed by this treatment show a fairly linear decrease in potential from the discharge to the collector electrode, with circular fields to about one-third distance across the channel (from 57.5 kV to 20 kV), then equipotential field lines parallel to the collector. Near the collector electrode, at about five-sixths the channel width, the potential has decreased to 5 kV. Electric fields of adjacent discharge electrodes interact, producing bell-shaped electric field patterns radiating from each wire to the adjacent collector plates.

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Solar Panel Basics

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