OCR Text |
Show the theoretical equations. The values obtained [2] were, respectively, 3 * 10-3 cm-I , and 5* 10-3 cm-I , which represents very close agreeement in the absence of detailed particle size distribution (PSD) measurements in the flame. This corresponds to 99% selfadsorption in a distance of about 10m. This is typical of pc flames. It shows that selfadsorption will not generally be a concern for a target distance of 5 cm. The primary concern, therefore, will be the question of temperature unifonnity, and possibly of particle distribution uniformity. Figure 7 illustrates the additional feature of this type of measurement, of being able to determine the relative radiating area of the particles in the field of view. This graph was obtained [2] from a set of several hundred determinations of both temperature and relative area. The temperature variations with time were found to be quite random, with graphs well fitted by Gaussian distributions. This was not the case, however, for the variation of temperature with area, as shown in Fig. 7. This behavior was observed in all the cases examined. The interpretation, that is believed to be representative of a general pattern, was based on the assumption that particles of different sizes would bum at different temperatures, with the temperature increasing with p~icle size. The temperature reported from the 2-color measurements was then an average from all the particles in the viewing volume. Since the PSD of the particles entering the flame varied randomly with time about the measurable mean distribution, the mean temperature for the group of particles then had to vary likewise, and to vary randomly. Since the mean temperatures were weighted by the particle sizes, however, the mean temperatures were then regularly dependent on the particle size or radia~g area, as shown in Fig. 7, with, notably, the temperature declining as the emitting area . (or number of small particles in the viewing volume) increased. This aspect of the flame behavior is discussed more fully in Ref. 2. 4. Conclusions. The principal conclusions of this work are that the optical probe design described is able: to obtain radiation signals from a defined volume in a particle flame; and to permit processing of the signals to give measurements of the particle temperatures and radiating areas. With a small enough defined volume, the temperature measurement 7 |