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Show density in the reactor. The system has been calibrated with standard latex spheres for the submicron particle range (0.3-2.0 microns), and with monodisperse oil droplets (TSI Berglund-Liu generator) for the large particle size range (3-120 microns). These calibrations have been checked on several occasions; the results are quite consistent and agree well with the theoretical calculations and previous measurements (Holve and Davis, 1982 and Holve, 1980). A Hycam high-speed (2000 frames/s) cinephotography system has been used for photographing the slurry particles as they heat up, ignite and undergo extended oxidation. EXPERIMENTAL RESULTS AND DISCUSSION Phenomenology of Slurry Sprays Our initial measurements have focused on characterizing the size distribution of the slurry spray prior to and during combustion. The motivation for this approach is shown in the sequence of events outlined in Figure 5. Both slurry rheology and the atomizer design will influence the resulting atomization and particle size distribution. Our laminar flow reactor uses a very small scale atomizer, giving size distributions which are a factor of 2 or 3 smaller than those produced in commercial applications. Although reaction times will be significantly shorter in our small scale system, the atomizer configuration is fixed, and thus a comparative study of various fuel properties is performed. Other work has focused on studying the effect of larger scale atomizer design for a single slurry (Chigier, Meyer, 1984). The atomized slurry is the starting point for the interaction of the fuel with conventional combustion parameters. This interaction determines ignition times, char burnout, fouling-slagging properties, and finally emissions. It is clear that atomization and thus the fuel properties which affect atomization, are critical to any subsequent combustion behavior. A diverse range of events may occur in the atomization and combustion process as shown in Figure 6. For example, the atomized particles may consist of a liquid droplet containing several coal particles, or perhaps a single coal particle is surrounded by a liquid film, or there might be separate phases of liquid droplets and coal particles. In turn, the liquid itself consists of different components, including surfactants and water. Indeed, it is likely that all these phase combinations exist at some point in the spray combustion process. However, the size measurement diagnostic used here is designed to be insensitive to material properties (i.e. refractive index) so that an unambiguous particle size determination can be made. Because we do not know the phase, we will in general refer to atomized material as slurry spray or particles, even though they may be liquid droplets or liquid suspensions. Even though direct determination of the various phase combinations mentioned above cannot be obtained, we have a qualitative idea of the differences in reaction time of these phase components, so that by observing the change in size distribution with reaction time, we will be able to infer the relative significance of the different phases in the atomized spray. As an example, if agglomerates of several or more coal particles are formed in a liquid suspension, one might expect that they will break apart as they heat up and form an increased number of smaller particles. We have used the high-speed 7 |