Electro-static precipitators (ESP) are very effective in the removal of fine mists and fine particles from gas streams. The concentration of atmospheric dust can also be measured by ESPs. A typical ESP is comprised of ductwork and a diffuser section. Electrostatically charged filters are located in the diffuser section. Effective performance of an ESP requires uniform flow in the diffuser section. The upstream ductwork can have a significant impact on flow entering the diffuser and hence its performance. These devices have dimensions of several meters and are difficult to prototype. Expensive experimental set-ups may be constructed to study flow fields in such devices. The other option is numerical simulation of the flow field. This is relatively inexpensive and can be completed on a smaller time scale. Computational fluid dynamics (CFD) methods are routinely employed to examine ESP performance.
In the example below CFD is applied to examine the effect of various distributor plate configurations on the uniformity of flow entering the diffuser section of an ESP. The original design employed a grid-type distributor plate (Figure 1). Flow entering the diffuser is not uniformly distributed and continues as a jet in the core of the diffuser section. This leads to a large recirculation region in the ESP.
Figure 1: Original Configuration
To introduce more uniform flow in the diffuser, the effect of a four-plate splitter was examined (Figure 2). The velocity field indicates that the recirculation region is reduced but not eliminated.
Figure 2: Intermediate Design - Results of Addition of Four-Plate Splitter
Finally, the effect of a grid employing three vertical and three horizontally placed splitter plates was examined (Figure 3). As can be seen in the velocity vector plot, uniformity of the velocity field in the ESP is significantly improved by this change.
Figure 3: Final Design - Results of Addition of Three-by-Three Splitter Plate Grid
CFD methods can be rapidly applied to examine the effect of various geometric and flow parameters on the overall flow behavior in an ESP. These techniques cannot only be applied for trouble-shooting and improving performance, but also for rapid prototyping.