Contamination of optical windows by a dust-laden stream. [Laser-based diagnostic systems for in-situ characterization of entrained particles and gas-phase species

Abstract

The present work represented a laboratory study to assess optical access ports (OAP) effectiveness of three different designs. The flow conditions were controlled and OAP geometries were simple. These experiments are important for understanding the basic mechanics of OAP operation. For applications to coal conversion process streams, the design features become increasingly complex and the OAP must be operational at a specific location. Laboratory experiments addressed the rate of contamination of three OAP designs (one recessed window and two minimal-offset window designs). The rate of window contamination as measured by the relative light intensity decreased as the purge flow was increased for the recessed window design. For purge flows representing about 20 percent of the stream flow, no contamination of the windows was observed with this design. The minimal-offset, single-jet OAP did not effectively diminish window contamination. The window contamination increased as the purge flow rate was increased from zero purge. Of the three designs tested, the recessed window, porous metal insert design appears to be best suited for long-term applications (greater than 30 hours exposure time). The particulate deposition was uniform over the window surface for this design. The minimal-offset, single-jet OAP was effective for cleaning a small localized area for both the cocurrent and countercurrent jet configuration. However, a majority of laser-based diagnostic instruments relies on the collection of scattered light and the small clean area may be insufficient for instrument operation. The recessed window, porous metal insert design would be better suited for this type of instrument. 11 references, 8 figures, 1 table.