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Show corrected similarly. Standard float glass windows have been used; optically flat windows are not required. These results suggest that bowing of the windows from pressure and thermal distortion in high-pressure combustion systems should present no problems for the alignment system. Calibration checks with monodisperse latex spheres under quite different window access conditions show consistency in the sample volume intensity distribution. Only the absolute intensity is modified by reflection losses at each window surface. As mentioned above, any beam attenuation is accounted for by monitoring the total beam power. The alignment system has been demonstrated on the Sandia Atmospheric Combustion Exhaust Simulator (ACES) under hot flow (1100 K) conditions with purged window access. Measurements of pilot plant flyash were obtained under ambient and hot flow conditions, showing good agreement between the two measurements as expected, despite a transverse beam displacement of 50 micrometers due to thermal expansion during heatup. Without the alignment system, such a displacement would have affected the accuracy of the data in an unknown fashion. Turbulent beam steering was also studied during this same set of tests and transverse beam displacements were found to be about 40 microns in magnitude. Despite this magnitude of beam steering, the fly ash measurements were found to be consistent with size distributions obtained under ambient conditions. These results are encouraging and point to successful measurements on pressurized systems without excessive performance degradation of the instrument. For highly turbulent systems, beam steering may increase beyond the 120 micron slit width used here, with a resulting drop in the measured beam power. If such conditions exist, a larger slit can be substituted so that the beam wander falls within the slit, with a resulting compromise in the allowable maximum number density, which is inversely proportional to the slit width. Validated measurements of combustion aerosols are the conclusive test for any in situ counter. We have performed an extensive series of such validation measurements for our single particle counting instrument. In these experiments flyash and pulverized coal were injected into the Sandia ACES under ambient and hot (1100 K) oxidizing conditions. For these experiments, the test material, flyash or pulverized coal, was placed in a fluidized-bed aerosol feeder where the fluidizing velocity could be adjusted to vary the mass feedrate of the particles. The entire feeder unit was mounted on a mass scale and the time dependent mass loss or feedrate to ACES was monitored with a strip-chart recorder. The flyash was obtained from the second stage clean-up system of the Exxon fluidized-bed mini plant, while the pulverized coal is a high volatile bituminous coal (7% mineral matter content) from the Barnstone seam in Australia. Figures 4 and 5 and Table I show a representative series of measurements obtained for flyash and pulverized coal. Figure 4 gives the logarithmic number frequency distribution (dN/dlog(d )) obtained with the single particle counter for flyash and pulverized coal. The results 9 |
